Datasets:

khairi

/

pubmed-text-04

like 0

8793884

An environmentally regulated pilus-like appendage involved in Campylobacter pathogenesis.

Examination of strains of Campylobacter jejuni, Campylobacter coli, and Campylobacter fetus by electron microscopy revealed that they produced peritrichous pilus-like appendages when the bacteria were grown in the presence of bile salts. Various bile-salt supplements were used and it was found that deoxycholate and chenodeoxycholic acid caused a significant enhancement of pilus production and resulted in a highly aggregative phenotype. Morphologically, the pili were between 4 and 7 nm in width and were greater than 1 micron in length. A gene, termed pspA, which encodes a predicted protein resembling protease IV of Escherichia coli, was identified in C. jejuni strain 81-176. A site-specific insertional mutation within this gene resulted in the loss of pilus synthesis as determined by electron microscopy. Insertions upstream and downstream of the gene had no effect on pilus production. The non-piliated mutant of strain 81-176 showed no reduction in adherence to or invasion of INT 407 cells in vitro. However, this mutant, while still possessing the ability to colonize ferrets, caused significantly reduced disease symptoms in this animal model.

8793888

Gene expression of the receptor for growth-hormone-releasing hormone is physiologically regulated by glucocorticoids and estrogen.

We investigated the effects of glucocorticoids and estrogen on the gene expression of growth hormone (GH) and the receptor for growth-hormone-releasing hormone (GHRH) by measuring the mRNA levels of GH and GHRH receptor in pituitary tissues of Sprague-Dawley rats using Northern blot hybridization and specific cDNA probes. Male rats, 6 weeks of age, were either adrenalectomized (or sham-operated) or treated with varying doses of dexamethasone (40, 200, 500 or 1,000 micrograms/kg/day, i.p.) for 3 days. Female rats, 4 weeks of age, were oophorectomized or sham-operated, and treated with 17 beta-estradiol benzoate 25 micrograms/kg/day (or vehicle) s.c. for 5 days starting 10 days after oophorectomy. Adrenalectomy was associated with a reduction in weight gain and decreased GHRH receptor mRNA levels (p < 0.05 and p < 0.0001 versus sham-operated, respectively). Dexamethasone treatment, however, was associated with a dose-dependent reduction in weight gain (p < 0.0001) but dose-dependent increases in GHRH receptor mRNA and GH mRNA levels (p < 0.0001 and p < 0.05, respectively). In the female rats, weight gain was increased by oophorectomy (p < 0.005 vs. sham-operated) and decreased by estrogen treatment (p < 0.05 vs. vehicle-treated). Pituitary GHRH receptor mRNA levels were also increased by oophorectomy (p < 0.05) and decreased by estrogen (p < 0.005). GH mRNA levels were unchanged by oophorectomy but decreased after estrogen treatment (p < 0.05). In conclusion, our findings suggest that endogenous glucocorticoids and estrogen are physiological regulators of pituitary GHRH receptor gene expression. Glucocorticoids and estrogen also regulate GH secretion via effects on GH gene expression. Changes in GHRH receptor and GH mRNA levels cannot explain the growth retardation in dexamethasone-treated rats.

8793889

Somatostatin withdrawal as generator of pulsatile GH release in the dog: a possible tool to evaluate the endogenous GHRH tone?

Reportedly, somatostatin (SS) withdrawal is an effective generator of pulsatile GH release in mammals and it has been proposed that the amplitude of the GH bursts is related to the functional activity of GHRH-producing neurons. Our study was designed to test this hypothesis in the unanesthetized dog, under different conditions of endogenous GHRH function. First, we evaluated the ability of withdrawal of SS infusion to induce a GH secretory burst under basal conditions when GHRH function is thought to be enhanced, i.e. in young (2- to 3-year-old) dogs under sustained (30 days) caloric restriction (CR) or a 2-day fast. Secondly, we performed experiments in aged (11- to 17-year-old) dogs, in which hypothalamic GHRH secretion is thought to be reduced. Old dogs were evaluated under basal conditions, after a 2-day fast and after a 10-day administration of GHRH alone or followed by fasting. Both before and 14 h after the end of each experimental period, young and old dogs underwent a 3-hour (from 10.00 to 13.00 h) intravenous SS infusion (4 micrograms.kg-1.h-1). The secretory profile of GH was generated by 15-min sampling from 09.00 to 15.00 h. Under baseline conditions, SS withdrawal induced a significant burst of GH in young but not in old dogs. After CR, termination of SS infusion was followed in young dogs by a robust GH burst, significantly higher than that observed when dogs were fed ad libitum. In this instance, reduction of plasma IGF-I concentrations was unlikely to be responsible for the higher GH burst; the same pattern was present in the young dogs after a 2-day fast, when circulating IGF-I was unaltered. In old dogs, SS withdrawal did not modify baseline GH levels even after fasting, but induced a significant GH increase after GHRH priming. When GHRH priming was followed by fasting, SS withdrawal resulted in a GH burst higher than that occurring after fasting or GHRH alone. Altogether, these data support the view that the rebound rise in GH induced by withdrawal of SS is related to the endogenous GHRH tone. It is suggested that extrapolation of these findings to humans might permit probing, albeit inferentially, the endogenous GHRH tone under different physiologic or pathologic conditions.

8793890

mu-Opioid agonists stimulate growth hormone secretion in immature rats.

The purpose of the present study was to evaluate the opioid receptor subtype mediating opioid modulation of growth hormone (GH) secretion during ontogeny. The mu-agonist morphine and the kappa agonist U50,488 caused a stimulation and inhibition of GH secretion, respectively, on postnatal day 10. Studies on postnatal days 2, 5, 10, 15 and 20 showed that kappa-inhibition could be observed as early as day 2, but substantial mu-stimulation was not observed until postnatal day 10. Intracerebroventricular (i.c.v.) administration of the mu-selective peptide [D-Ala2-NMe-Phe4-Gly-ol]-enkephalin (DAMGO) elicited a marked rise in GH secretion, while administration of the delta-agonists [D-pen2D-pen5]-enkephalin (DPDPE) or deltorphin II caused only a minor and non-dose-related rise in GH secretion in neonatal rats. The relative importance of mu- and delta-receptors in stimulating GH secretion was also studied in older pups (day 20). i.c.v. administration of DAMGO stimulated GH secretion, while neither DPDPE nor deltorphin II consistently increased GH secretion. Furthermore, peripheral administration of either morphine or the highly selective mu-agonist sufentanil elicited marked GH secretion on postnatal day 20, but bined administration of the mu-antagonist beta-funaltrexamine (beta-FNA) and the delta-antagonist naltrindole substantially diminished these responses. These results suggest that both mu- and kappa-opioid receptors are involved in the regulation of GH secretion in neonatal rats. While delta-receptors do not play a prominent independent role in this response, they may act synergistically with mu-receptors in producing stimulation.

8793891

Function of the GH/IGF-1 axis in healthy middle-aged male runners.

In an attempt to examine the effect of prolonged physical activity on the function of the GH/IGF-1 axis during the aging process in man, we have evaluated basal and GHRH (GHRH-29: 1 microgram/kg i.v. as a bolus) stimulated GH secretion as well as basal plasma IGF-1 levels in a group of 25 healthy runners (50-60 years, mean age 55.5 +/- 0.6) and 24 age-matched relatively sedentary normal controls (mean age 55.8 +/- 0.7). The runners had a minimum distance in kilometers of 26 km/week for at least 15 years, peted in distances ranging from 16 km to the marathon. In runners, GHRH induced an increase of GH which was significantly higher (p < 0.001) than that observed in the age-matched controls. Baseline IGF-1 levels were significantly higher (p < 0.001) in trained runners (171 +/- 8.4 pared to the controls (91.1 +/- 5.5 micrograms/1). These data show that in middle-age prolonged physical activity increases the function of the GH/IGF-1 axis. To clarify the possible mechanisms underlying the GH/IGF-1 secretory pattern in the runners, the GH responses to both single bined administration of GHRH and arginine (ARG: 30 g infused over 30 min), a GH secretagogue likely acting via inhibition of hypothalamic somatostatin release, were investigated in 6 runners (mean age 55 +/- 1.9 years) and 6 controls (mean age 55 +/- 0.9 years). ARG clearly increased the GH response to GHRH in the controls, whereas it was unable to further potentiate the GH-releasing effect of GHRH in runners, thus suggesting that the increased GH responsiveness to GHRH might be due to an exercise-related decrease in endogenous hypothalamic somatostatinergic activity.

8793892

Regulation of chicken gonadotropin-releasing hormone-I mRNA in incubating, nest-deprived and laying bantam hens.

Secretion of luteinizing hormone is decreased when hens start to incubate their eggs and is increased after nest deprivation or hatching of the eggs. The purpose of this study was to determine whether decreased luteinizing hormone (LH) secretion during incubation in the domestic hen is associated with a decrease in hypothalamic chicken gonadotropin-releasing hormone-I (cGnRH-I) mRNA or peptide. A petitive PCR assay was developed to measure cGnRH-I mRNA. Hypothalamic mRNA was quantified as the amount of GnRH cDNA obtained by reverse transcription of cGnRH-I mRNA. The amount of hypothalamic cGnRH-I mRNA was significantly higher in laying than in incubating hens (38.7 +/- 10.3 vs. 7.7 +/- 1.6 x 10(-17) mol cDNA, p = 0.01, n = 8). The hypothalamic GnRH peptide content was not significantly different between laying and incubating hens in either the preoptic area (286.9 +/- 24.01 vs. 269.3 +/- 29.3 pg, n = 8) or the basal hypothalamus (1.67 +/- 0.19 vs. 1.54 +/- 0.21 ng, n = 8). Five days after incubating hens were deprived of their eggs, the resulting increase in LH secretion was associated with a significant increase in hypothalamic content of cGnRH-I mRNA (22.8 +/- 2.2 vs. 6.7 +/- 1.7 x 10(-17) mol cDNA, p < 0.001, n = 8). These observations suggest that a decrease in the expression of the cGnRH-I gene is a major factor in maintaining depressed LH secretion in incubating domestic chickens.

8793893

Immunological and biological activities of pituitary FSH isoforms in prepubertal male rats: effect of antiandrogens.

In male rats androgens are involved in the regulation of follicle-stimulating hormone (FSH) synthesis and secretion. Two nonsteroidal antiandrogens, flutamide and Casodex, were used to study the influence of androgens on the carbohydrate structure of FSH isoforms and the relationship with their bioactivity in prepubertal male rats. Different doses of flutamide or Casodex (vehicle, 1, 5, or 10 mg/rat/day) were administered subcutaneously for 10 days to 23-day-old rats. Immunological FSH was determined by radioimmunoassay and the bioactivity by in vitro Sertoli cell bioassay. Concanavalin A affinity chromatography was used to study the distribution of immunoactive and bioactive pituitary FSH isoforms. A significant depletion of immunological and biological pituitary FSH contents was observed even at the lowest dose of flutamide or Casodex used. The bioactive/immunoactive ratio of pituitary FSH was reduced at the highest dose of flutamide; however, no change was observed in Casodex-treated rats, suggesting a differential effect of the antiandrogens on the FSH bioactivity. Flutamide treatment provoked a significant decrease in proportion and bioactivity of FSH isoforms bearing biantennary and truncated hybrid oligosaccharide side chains and an increase in the proportion but a decrease in bioactivity of FSH isoforms bearing high-mannose oligosaccharides. Conversely, Casodex administration did not modify the proportions of FSH isoforms, although those bearing biantennary and truncated hybrid structures were less bioactive, while those bearing high-mannose oligosaccharides were more bioactive. The highest dose of flutamide decreased the bioactive/immunoactive ratio of FSH isoforms with a high degree of branching in their carbohydrate chains. Our results suggest that androgens, acting directly and indirectly at the pituitary, regulate the selective incorporation of sugar residues to the FSH molecule, thus modulating its biological activity.

8793894

Sex- and cell-specific expression of an estrogen receptor isoform in the pituitary gland.

The presence of multiple monomeric forms has been described for the estrogen receptor (ER) in the pituitary gland. We analyzed ER mRNA forms in male and female rat pituitary. A single 6.2-kb ER mRNA species was detected in the male rat pituitary, whereas the female rat pituitary exhibited two ER mRNA forms of 6.2 and 5.5 kb, respectively. The 6.2-kb mRNA was present throughout the different stages of the estrous cycle, while the 5.5-kb mRNA appeared to be restricted to proestrus, suggesting an acute regulation of ER transcription at this stage. The 5.5-kb ER mRNA could be rapidly induced either by 17 beta-estradiol replacement in ovariectomized adult female rats or by priming immature rats with pregnant-mare serum gonadotropin. Using enriched cell populations, an inverse and strong correlation was established between the presence of the 5.5-kb ER mRNA form and the number of gonadotropes. Conversely, the localization of the 5.5-kb mRNA form was demonstrated in lactotrope populations. In order to elucidate the structural modifications in the transiently expressed ER mRNA, a series of reverse-transcriptase polymerase chain reaction amplifications was carried out using several pairs of primers corresponding to the entire ER-coding region. The data showed that no alternative splicing was occurring in the ER-coding region involving a potential role of either 3'- or 5'-untranslated regions. Thus, ER presents a 17 beta-estradiol-dependent transcriptional mechanism triggered on proestrous day and specific to the female lactotropes.

8793895

Antagonism by progesterone of diethylstilbestrol-induced pituitary tumorigenesis in Fischer 344 rats: effects on sex steroid receptors and tyrosine hydroxylase mRNA.

It is known that chronic exposure of F344 rats to diethylstilbestrol (DES) induces prolactin (PRL)-secreting pituitary posed of proliferating mammotropic cells. In the present work, we studied the effects of progesterone (P4) on several parameters stimulated in the pituitary tumors (DES-T), such as nuclear estrogen receptors (NE2R), cytosolic progestin receptors (CP4R) and serum PRL. Additionally, we have measured in hypothalamus the mRNA levels for tyrosine hydroxylase (TH), the rate-limiting enzyme for synthesis of dopamine, the main PRL-inhibitory factor. We found that pellet implantation of P4 during 1 month significantly reduced weight, ligand binding to NE2R and CP4R and serum PRL in the tumorous glands. Reductions in sex steroid receptor binding were due to changes in Bmax without changes in Kd, as observed after Scatchard plot analysis. Receptor binding data, therefore, suggests a pituitary site of action of P4. TH mRNA expression was studied in tuberoinfundibular dopaminergic (TIDA) neurons by in situ hybridization techniques employing a 35S-labeled oligonucleotide probe. Mean number of grains/cell decreased significantly in DES-T, an effect partly reversed by P4 treatment. Frequency histograms were constructed by plotting the number of cells versus the number of grains/cell and examined by x2 test and analysis of residuals. We found that DES-T presented significantly more cells with less grains whereas in control glands, P4-treated rats and DES-T receiving P4, cells with a higher grain number prevailed. These results suggest that in addition to a direct pituitary effect, P4 may also antagonize DES-induced tumorigenesis acting on mRNA for TH and presumably on the activity of TIDA neurons of the hypothalamus. The use of DES-T as a model for hyperprolactinemia may allow further assessment of P4 effects in pituitary adenomas in humans.

8793896

Suckling-induced changes in neuropeptide Y and proopiomelanocortin gene expression in the arcuate nucleus of the rat: evaluation of a putative intervention of prolactin.

Hypothalamic neuropeptide Y (NPY) and proopiomelanocortin (POMC)-derived peptides located in the arcuate nucleus (ARC) have been postulated to be good candidates to play a modulatory role during lactation. In the present study, we first quantified, by in situ hybridization, lactation-induced changes in NPY and POMC gene expression throughout the ARC. In a second phase of the study, we attempted to determine whether any relationship exists between neuropeptide gene expression and the suckling stimulus itself. For this, we used experimental groups of animals submitted to suppression of the suckling stimulus by removal of pups and the subsequent restoration of the suckling stimulus by the return of the litter. Since lactation is characterized by an estrogen-deficient status [15], we attempted using ovariectomized (2 or 21 days) diestrous females to describe the changes in NPY gene expression observed during lactation. Since the suckling stimulus induces a strong prolactin (PRL) release, pleted this study by using an intravenous injection of PRL antiserum in order to discriminate the effects of PRL per se on the observed suckling-induced changes in neuropeptide gene expression. Freely nursing lactating females exhibited a large increase in NPY mRNA expression pared to diestrous females (10.10 +/- 0.50 vs. 4.51 +/- 0.35). After suppression of the suckling stimulus by removal of pups, this increase intensified during short-term suppression of 16 h (15.37 +/- 0.67) and was reversed following long-term suppression of 36 h (12.35 +/- 0.61). Ovariectomized diestrous animals showed significant changes in NPY mRNA expression pared to lactating females (5.25 +/- 0.42 vs. 10.10 +/- 0.50). Lactating females submitted to PRL immunoneutralization by PRL antiserum showed a slight increase in NPY mRNA expression pared to non-injected lactating females (13.75 +/- 0.51 vs. 12.95 +/- 0.59). Freely nursing lactating females showed a decrease in POMC mRNA expression (8.27 +/- 0.33) whereas suppression of suckling by removal of the pups (9.52 +/- 0.45) resulted in a return to diestrous POMC mRNA levels (10.77 +/- 0.36). We showed that restoration of suckling by the return of the litter induced an increase in POMC gene expression (12.55 +/- 0.66). By lowering circulating levels of PRL with PRL antiserum after restoration of suckling, we observed a decrease in POMC mRNA expression (9.81 +/- 0.46). Results of this study showed that the increase in NPY mRNA in the medial ARC during lactation did not appear to be due either to gonadal steroid-deficient status or to the suckling-induced hyperprolactinemia. If freely nursing lactating females showed a moderate decrease in POMC gene expression, restoration of the suckling stimulus by return of the pups provoked an increase in POMC gene expression which seemed to depend on high endogenous levels of PRL.

8793897

Involvement of histamine in suckling-induced release of oxytocin, prolactin and adrenocorticotropin in lactating rats.

We have previously shown that histaminergic neurons participate in mediation of the prolactin (PRL), adrenocorticotropin (ACTH) and oxytocin responses to physiological stimuli such as stress and dehydration. Since suckling is a potent stimulus for the secretion of these three hormones, we investigated the mediating role of neuronal histamine in suckling-induced release of oxytocin, PRL and ACTH in conscious lactating rats. The animals were pretreated with the histamine synthesis inhibitor alpha-fluoromethylhistidine, the H1 receptor antagonist mepyramine, the H2 receptor antagonist cimetidine or the H3 receptor agonist R (alpha) methylhistamine, which by binding to H3 autoreceptors inhibits histamine release and synthesis. After the lactating rats were separated from their pups for 240 min, the pups were returned for a suckling period of 20 min. Thereafter the mothers were sacrificed by decapitation and trunk blood was collected for determination of hormones. Lactating rats not exposed to suckling served as controls. Suckling increased oxytocin 2-fold, PRL 50-fold and ACTH 5-fold. Blockade of histamine synthesis by alpha-fluoromethylhistidine or histamine release by R(alpha)methylhistamine reduced the suckling-induced secretion of the three hormones significantly. Blockade of postsynaptic H1 receptors by mepyramine inhibited the hormone responses to suckling, while the blockade of postsynaptic H2 receptors by cimetidine decreased the suckling-induced oxytocin and PRL release but did not affect the ACTH release. None of pounds affected oxytocin, PRL or ACTH secretion in lactating mothers not exposed to suckling. In addition, suckling significantly increased the mRNA of the histamine synthesizing enzyme histidine decarboxylase in the ventrolateral tuberomammillary nucleus by 1.5-fold, indicating that the stimulus of suckling enhances the neuronal histamine synthesis. We conclude that suckling increases neuronal histamine synthesis and that histaminergic neurons by activation of postsynaptic H1 and H2 receptors are involved in the hypothalamic mediation of oxytocin, PRL and ACTH responses to suckling. These findings further substantiate a role of neuronal histamine in the neuroendocrine regulation of pituitary hormones in response to physiological stimuli.

8793898

Induction of brain prolactin receptor long-form mRNA expression and maternal behavior in pup-contacted male rats: promotion by prolactin administration and suppression by female contact.

Prolactin (PRL) is considered to induce maternal behavior toward foster young in female rats. In the present study, we studied the relationship between pup contact-induced maternal behavior and serum PRL concentrations and brain PRL receptor (PRL-R) mRNA expression in male rats. Both intact and castrated male rats exposed to foster pups gradually developed caretaking behavior such as crouching and licking, but their exhibitions of other maternal ponents, retrieval/grouping and nest building, were plete. However, in the male rats displaying crouching and licking, the itant increases in serum PRL concentration and brain mRNA expression for long-form PRL-R were observed. The expression of short-form PRL-R mRNA in the brain was not stimulated by pup contact. Administration of PRL remarkably promoted the onset of those maternal responses in male rats. On the other hand, when an intact male rat was housed in a cage where a lactating female rat and her pups were living, his scores in maternal behavior tests toward pups were lowered. And, itantly, increases in serum PRL concentration and brain expression of long-form PRL-R mRNA were reduced. In castrated male rats, however, the ratings of maternal behavior toward foster young, serum PRL concentration increase, or brain long-form PRL-R mRNA expression were not reduced at all by cohabitation with a female and her pups. These findings indicated that maternal behavior was triggered and maintained in pup-contacted male rats through elevated serum PRL levels and induced brain long-form PRL-R.

8793899

Beta-endorphin, but not oxytocin, substance P or vasoactive-intestinal polypeptide, contributes to progesterone-induced prolactin secretion in monkeys.

Progesterone (P) stimulates prolactin secretion through a neural mechanism in estrogen (E)-primed female monkeys. Several peptides, including beta-endorphin (BE), oxytocin (OT), substance P (SP) and vasoactive intestinal polypeptide (VIP) are potential prolactin stimulatory factors and could mediate the effect of P. We hypothesized that the antagonism of a pivotal peptidergic neural system would block P-induced prolactin secretion and that the function of a pivotal peptidergic system would be altered by changes in gonadal steroid concentrations. Therefore it was of interest (1) to examine the effect of infusion of antagonists to these peptides on P-induced prolactin secretion, and (2) to determine BE, OT, SP and VIP levels in the hypothalamus of monkeys of various reproductive states. For the antagonist studies, female monkeys (n = 8) were spayed, adapted to a vest and tether remote sampling system and catheterized prior to antagonist challenges. E-primed monkeys received P injections 48 h prior to antagonist administration. Prolactin increased within 36-48 h of P injection. All antagonist challenges were administered in varying doses during the P-induced prolactin elevation and blood samples were collected every 10 min for prolactin determinations. The opiate antagonist, naloxone (n = 5), reduced serum prolactin in a dose-related manner with a mean IC50 of 1.5 +/- 0.6 micrograms/kg/min. The OT (n = 4), SP (n = 4) or VIP (n = 4) antagonists did not reduce serum prolactin in a dose-related manner. We previously reported that the hypothalamic content of OT is increased by ovarian hormones. To determine whether the hypothalamic content of BE, SP or VIP was related to gonadal status, the peptide levels in 4 hypothalamic regions of monkeys in various physiological states were measured. BE (ng/mg protein) in the medial basal hypothalamus (MBH) was significantly greater in adult females (17.7 +/- 6.9; n = 6) pared to spayed females (0.6 +/- 0.2; n = 3) and juvenile females (1.8 +/- 1.1; n = 3). Hypothalamic content of SP in the preoptic area and mammillary bodies, but not the MBH, was significantly greater in gonadal intact females than spayed females. VIP content (pg/mg protein) was not significantly different between adult, spayed and juvenile females nor between adult and juvenile males in any hypothalamic area. Taken together these results support a pivotal role for BE in the neural regulation of P-induced prolactin secretion. The involvement of OT, SP, and VIP in a specific manner at the pituitary level is not indicated.

8793900

omega-Agatoxin IVA identifies a single calcium channel subtype which contributes to the potassium-induced release of acetylcholine, 5-hydroxytryptamine, dopamine, gamma-aminobutyric acid and glutamate from rat brain slices.

The voltage-dependent calcium channels (VDCCs) involved in K(+)-induced transmitter release have been studied. A maximally effective concentration of the N-type VDCC inhibitor, omega-conotoxin GVIA (GVIA) blocked the release of 5-HT (30%), DA (30%) and ACh (60%) but not that of GABA or glutamate. The O, P and Q-type VDCC inhibitor, omega-agatoxin IVA (Aga IVA, 1 microM), blocked 100% of GABA and glutamate, 70% of DA and about 50% of 5-HT and ACh release. The slopes of the inhibiton curves indicate that it acts on the same, single type of VDCC in all cases. omega-Conotoxin MVIIC pletely inhibited the release of all the transmitters. It is concluded that a single GVIA-insensitive type of VDCC is involved in the K(+)-induced release of all the transmitters and, in addition, N-type VDCCs, with a higher affinity for GVIA than MVIIC, are required for the release of 5-HT, DA and ACh. The non-N-type VDCC is not the O-type as it is not blocked by low (< 10 nM) concentrations of MVIIC. Further resolution of this VDCC into P or Q-type requires more selective antagonists.

8793901

Evaluation of anti-nociceptive effects of neuronal nicotinic acetylcholine receptor (NAChR) ligands in the rat tail-flick assay.

In the present investigation, anti-nociceptive effects of neuronal nicotinic acetylcholine receptor (NAChR) ligands, (+)- and (-)-nicotine, cytisine, methylcarbamylcholine (MCC), dimethylphenylpiperazinium iodide (DMPP), and (+/-)-epibatidine were evaluated in the rat tail-flick assay both after subcutaneous (s.c.) and intracerebroventricular (i.c.v.) administration. The pharmacology of the tail-flick response to NAChR ligands after s.c. and i.c.v. routes was similar. Epibatidine was the most potent ligand examined with a longer duration of action than any other agonist. (-)-Nicotine was more active than (+)-nicotine indicating stereospecificity. ICV administration studies indicated an apparent partial agonist activity for (+)-nicotine in the tail-flick response. Tail-flick responses to NAChR agonists are independent of opioid and muscarinic pathways and appear to be mediated both by central and peripheral NAChR recognition sites. Central administration of MCC activates both NAChR and muscarinic anti-nociceptive mechanisms. Studies employing the alpha-adrenergic receptor alkylating agent, phenoxybenzamine or the noradrenergic neurotoxin, N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4), suggested that the NAChR-noradrenergic and NAChR-serotoninergic interactions play an important role in the tail-flick response. Studies employing a selective alpha-bungarotoxin-sensitive NAChR receptor antagonist, methyllycaconitine (MLA), suggested a minimal role for these receptors in the tail-flick response. The biochemical studies also indicated that a sub-population of NAChR receptors are located pre-synaptically on noradrenergic and/or serotoninergic pathways in the hippocampus.

8793902

Effect of MK-801 at the human alpha 7 nicotinic acetylcholine receptor.

Responses of the human alpha 7 nicotinic acetylcholine receptor (alpha 7 nAChR) expressed in Xenopus laevis oocytes were quantified in the presence of barium (10 mM) to prevent secondary activation of Ca(2+)-dependent Cl- currents and atropine (2 microM) to block endogenous muscarinic receptors. Acetylcholine (ACh) elicited responses with EC50 values of 177 +/- 32 microM to 272 +/- 26 microM in different experiments. Responses to ACh (200 microM) were blocked by the nAChR antagonists alpha-bungarotoxin (IC50 = 0.54 +/- 0.04 nM), methyllycaconitine (IC50 = 0.64 +/- 0.08 nM) and mecamylamine (IC50 = 1.8 +/- 02 microM). Additionally, MK-801, a petitive blocker of N-methyl-D-aspartate (NMDA) sensitive glutamate receptor channels, inhibited the human alpha 7 nAChR. This effect was not stereoselective; the IC50 for (+)-MK-801 was 15 +/- 3 microM while that for (-)-MK-801 was 14 +/- 3 microM. The inhibition by MK-801, in contrast to methyllycaconitine, was dependent upon cell potential, consistent with a mechanism involving channel blockade. The inhibition by MK-801 reversed slowly (time constant approximately 20 pared to that by methyllycaconitine (100% recovery within 10 min). However, MK-801 did not appear to be trapped in the channel because the recovery from inhibition showed little dependence upon stimulation rate or cell potential. Thus, MK-801 acted as a non-stereoselective alpha 7 nAChR inhibitor that was only about 8-fold less potent than the nAChR antagonist mecamylamine and probably acted through channel blockade.

8793903

Inhibition by NMDA of carbachol-stimulated inositol tetrakisphosphate accumulation in rat brain cortical slices.

The present studies examined the effect of NMDA on carbachol-stimulated accumulation of inositol polyphosphates, with emphasis on the accumulation of inositol 1,3,4,5-tetrakisphosphate (Ins 1,3,4,5-P4), at short time periods in rat brain cortical slices. There was a stimulatory effect of NMDA on accumulation of labeled inositol mono-, bis- and trisphosphates but not on labeled inositol tetrakisphosphates. In the presence of carbachol Ins 1,3,4,5-P4 accumulation was preferentially inhibited by NMDA at early time periods (within 30 seconds after NMDA addition). Subsequently, total phosphoinositide breakdown was inhibited by NMDA. NMDA did not stimulate accumulation of total Ins 1,3,4,5-P4 but immediately inhibited carbachol stimulated accumulation of Ins 1,3,4,5-P4. The inhibitory effect of NMDA (1 mM) was not mimicked by increasing K+ in the medium from 10 to 30 mM. However 30 mM K+ reversed the inhibitory effect of 1 mM NMDA on carbachol-stimulated Ins 1,3,4,5-P4. Parallel experiments with veratridine (a sodium channel activator) suggest that the early inhibitory effects of NMDA on Ins 1,3,4,5-P4 accumulation are not due to decreases in ATP availability or elevations in intracellular Na+. These data indicate that NMDA increases inositol mono-, bis- and trisphosphate accumulation while blocking muscarinic cholinergic stimulated accumulation of Ins 1,3,4,5-P4.

8793904

Ibogaine block of the NMDA receptor: in vitro and in vivo studies.

Ibogaine is an hallucinogenic indole alkaloid claimed to have anti-addictive properties. Although its mechanism of action is unknown, binding studies have indicated that the drug may interact with N-methyl-D-aspartate (NMDA) receptors. We further investigated the nature of the interaction between ibogaine and NMDA receptors in voltage clamp and binding studies, and sought to confirm that the drug has NMDA receptor blocking activity in vivo. In whole-cell recordings from cultured rat hippocampal neurons, ibogaine caused a slow, concentration-dependent block of NMDA-induced currents (IC50, 3.1 microM at -60 mV). In contrast, ibogaine failed to affect either kainate- or gamma-aminobutyric acid-evoked currents. The blockade of NMDA currents was use- and voltage-dependent, and the long lasting ibogaine block could be occluded by co-application of Mg2+. Ibogaine also inhibited equilibrium [3H]dizocilpine binding to NMDA receptors in rat forebrain membranes (IC50, 3.2 microM). We conclude that ibogaine is an open channel NMDA receptor antagonist. Administration of ibogaine to mice resulted plete protection in the maximal electroshock test (ED50, 31 mg/kg, i.p.) and partial protection against NMDA-induced lethality, confirming that ibogaine can block NMDA receptors in vivo.

8793905

N-methyl-D-aspartate receptor activation by guanidinosuccinate but not by methylguanidine: behavioural and electrophysiological evidence.

Levels of methylguanidine (MG) and guanidinosuccinate (GSA) are known to be highly increased in uraemic patients. In the present work, the effects of these uraemic pounds on the excitatory amino acid system were investigated in vivo and in vitro. It was found that convulsions induced by intracerebroventricular GSA injection in mice were antagonized by N-methyl-D-aspartate (NMDA) receptor blockade, whereas those induced by MG were not significantly altered. Application of GSA (between 25 and 10,000 microM) to mouse spinal cord neurones in primary dissociated cell cultures, evoked depolarizing, inward whole-cell currents in a dose-dependent fashion and with reversal potential at 0 mV; MG did not produce such effects. GSA-induced whole-cell currents were caused by NMDA receptor activation since NMDA receptor antagonists (2-amino-5-phosphonovalerate, Mg2+ and ketamine) blocked GSA-evoked whole-cell pletely and reversibly, whereas co-application of a non-NMDA receptor antagonist (6-cyano-7-nitroquinoxaline-2,3-dione) did not affect GSA-induced current. Evoked field potentials in CA1 region of rat hippocampal slices pletely abolished by GSA, and this effect was antagonized by NMDA receptor blockade. All data were consistent with selective agonist action of GSA upon the NMDA-type glutamate receptor. In view of the results presented here, it should be examined whether NMDA receptors contribute to the plications of renal failure through GSA-induced inappropriate or excessive activation of NMDA receptors.

8793907

Subchronic intraventricular infusion of quinolinic acid produces working memory impairment--a model of progressive excitotoxicity.

It has been proposed by Yamada et al. [Neurosci. Lett. 118: 128-131 (1990); J. Pharmacobiodyn. 14: 351-355 (1991)] that subchronic i.c.v. infusion of the NMDA receptor agonist quinolinic acid may serve as a model for some aspects of neurodegenerative dementia. In the present study, quinolinic acid (9 mM) was infused i.c.v. by ALZET osmotic minipumps for 2 weeks. This treatment produced a short-term working memory deficit in the T-maze (alternation) but no change in reversal learning in the same test. The working memory deficit in the T-maze was progressive i.e. seen after 14, but not 3 days of infusion and persisted for at least for 3 weeks after the termination of the infusion. Histological examination revealed a modest decrease in the number of cells in the nucleus basalis magnocellularis but not in the striatum, entorhinal cortex, or hippocampus. However, in most of the structures studied, morphological changes such as swollen somata and irregular shape were observed indicative of alterations in neuronal function. Autoradiography in the hippocampus revealed a decrease in [3H]hemicholinium and [3H]quinuclidinyl benzilate (QNB) binding to choline uptake sites and muscarinic receptors respectively. Surprisingly no change was observed in [3H]MK-801 binding to NMDA receptor channels in the hippocampus and cortex. The subchronic infusion of quinolinic acid may serve as a model of progressive deterioration of cognitive functions.

8793906

EEG seizure activity and behavioral neurotoxicity produced by (+)-MK801, but not the glycine site antagonist L-687,414, in the rat.

The objective of the present study was pare the in vivo effects of the anticonvulsant/neuroprotective glycine-site partial agonists L-687,414 (3R-amino-1-hydroxy-4R-methylpyrrolidin-2-one) and (+)-HA966 (3-Amino-1-hydroxypyrrolidin-2-one) and the petitive N-methyl-D-aspartate (NMDA) antagonist (+)-MK801 on spontaneous cortical EEG activity and behavior in the unanesthetized rat. Comprehensive dose-response assessments demonstrated that acute i.v. injections of (+)-MK801 induced a behavioral neurotoxic prised of head-weaving, ataxia, otion and myoclonic/clonic behaviors and associated with disruptions in normal EEG rhythms including paroxysmal EEG plexes. Injections of (+)-HA966 produced behavioral sedation associated with high-amplitude, slow-wave synchronized EEG patterns; signs of ictal EEG activity were minimal (33% incidence) and only seen at the highest dose tested (100 mg/kg). Both (+)-MK801 and (+)-HA966 severely delayed the latency to slow-wave sleep (SWS). In contrast, the EEG dynamics and overt behavior associated with L687,414 were essentially indistinguishable from controls. There was no disruption in the latency to SWS and mild ataxia was evident only upon awakening. The calculated protective indices (EEG seizure ED50/anticonvulsant ED50) for (+)-MK801 and L-687,414 were 1.2 and > 4.5, respectively. The results of this study confirm that valuable pharmacological actions mediated via glycine site modulation of the NMDA receptor are possible without the clinical manifestation of unwanted neurotoxic side-effects.

8793908

Attenuation of malonate-induced degeneration of the nigrostriatal pathway by inhibitors of nitric oxide synthase.

Focal infusions of the succinate dehydrogenase inhibitor, malonate, into the substantia nigra pacta (SNc) of adult Sprague-Dawley rats resulted in a substantial depletion of ipsilateral striatal tyrosine hydroxylase (TH) activity. The percentage decrease in striatal TH activity following intranigral malonate (0.5 mumol/0.5 microliter) infusion was similar at 4 (58%) and 7 days (62%) post-infusion. To assess the role of N-methyl-D-aspartate (NMDA) receptor activation in malonate neurotoxicity, animals were pretreated with the NMDA receptor antagonist MK-801 (2 x 5 mg/kg, i.p.). Four days post-infusion of malonate (0.5 mumol/0.5 microliter) into the SNc, striatal TH activity was depleted by 58% in vehicle pretreated animals and 14% in the presence of MK-801 indicating a significant neuroprotective effect of MK-801 on malonate action. To determine the role of nitric oxide (NO) in malonate-induced nigral toxicity, the actions of malonate were evaluated in the presence of the nitric oxide synthase (NOS) inhibitors, 7-nitro indazole (7-NI) and N omega-nitro-L-arginine methyl ester (L- NAME). Systemic injections of 7-NI (20, 30, 40, 50 and 75 mg/kg, i.p.) produced a dose-related inhibition of nigral NOS activity which was maximal at a dose of 40 mg/kg. Intranigral infusion of malonate with 20 and 50 mg/kg 7-NI pretreatment produced a 46 and 31% decrease in striatal TH activity, respectively. Thus, a significant protective effect at the higher but not lower dose of 7-NI was observed. Pretreatment with a L- NAME regimen (2 x 250 mg/kg; i.p.), previously shown to inhibit brain NOS activity by greater than 86%, also produced a significant neuroprotective effect against malonate-induced neurotoxicity (30% decrease). The results of this study suggest that malonate-induced toxicity to the dopaminergic neurons of the nigrostriatal pathway is mediated, at least in part, by NMDA receptor activation and the formation of NO.

8793909

Behavioral evidence for modulation by sigma ligands of (+)MK-801-induced hyperlocomotion in monoamine-depleted mice.

The selective petitive N-methyl-D-aspartate (NMDA) antagonist (+)-5-methyl-10, 11-dihydro-5H-dibenzo(a, d)cyclohepten-5,10-imine maleate ((+)MK-801) led to a dose-dependent increase in otor activity in mice pretreated with bination of reserpine and alpha-methyl-para-tyrosine (alpha-MT). A selective and potent sigma receptor "antagonist" NE-100 (N, N-dipropyl-2- [4-methoxy-3-(2-phenylethoxy)-phenyl]-ethylamine monohydrochloride), which did not per se affect spontaneous otor activity, did not prevent the otor stimulatory effects of (+)MK-801. Sulpiride, a dopamine D2 receptor antagonist, and clozapine, a dopamine D4 receptor antagonist, which decreased spontaneous otor activity, did not prevent the otor stimulatory effects of (+)MK-801. The sigma receptor "agonists" (+)N-allynormetazocine [(+)SKF10,047], (+)pentazocine and (+)-3-(3-hydroxyphenyl)-N-(1-propyl) piperidine [(+)3-PPP], which did not per se affect spontaneous otor activity, did dose-dependently enhance the otion induced by (+)MK-801. The enhancement of (+)MK-801-induced the otion by (+)SKF10,047, (+)pentazocine and (+)3-PPP pletely blocked by NE-100. The enhancement of (+)MK-801-induced otion by (+)pentazocine was not affected by treatment with sulpiride and clozapine. As sigma ligands can markedly attenuate NMDA antagonist-induced behavior, the major physiological role of sigma receptors in vivo might be to modulate functions of the NMDA receptor ion plex.

8793910

Effects of N-methyl-D-aspartate receptor antagonists on cisplatin-induced emesis in the ferret.

Glutamate may be a key transmitter in the emetic reflex arc. The present investigation focussed on the involvement of the NMDA subtype of glutamate receptors in cisplatin-induced emesis. Ferrets were injected with cisplatin (10 mg/kg i.v.) and either of the petitive NMDA receptor antagonists dextromethorphan or memantine, or petitive receptor antagonist CGS 19755. In order to determine whether there is a synergism between NMDA blockers and 5-HT3 receptor antagonists, a submaximal dose of granisetron (0.05 mg/kg) was given alone or bination with either dextromethorphan or memantine. The latency for the onset of emesis as well as the total number of vomits and retches over 3 hr were determined. In controls, the latency for emesis was 73 +/- 6 min and the total number of vomits and retches 143 +/- 17. The corresponding figures for animals treated with dextromethorphan, 10 and 20 mg/kg, were 89 +/- 19 min (p > 0.05) and 50 +/- 17 (p = 0.008), and 113 +/- 18 min (p > 0.05) and 22 +/- 9 (p = 0.004), respectively. At 10 mg/kg, dextromethorphan failed to enhance the antiemetic effect of granisetron which by itself provided 90% inhibition. While memantine (2.5 or 5.0 mg/kg) did not have an effect per se, it tended to reduce the antiemetic effect of granisetron. CGS 19755 (10 mg/kg) provided a partial protection against cisplatin-induced emesis (latency: 111 +/- 23, number of vomits and retches 30 +/- 11). None of the NMDA receptor antagonists was free of behavioural effects (e.g. some sedation) at antiemetic doses. It is concluded that NMDA receptor antagonists may afford protection against cisplatin-induced emesis but the specificity of this effect is uncertain since it may relate to general CNS depression.

8793911

5-HT1A receptor-mediated inhibition of acetylcholine release from guinea pig myenteric plexus: potential mechanisms.

The mechanisms through which presynaptic 5-HT1A receptors cause inhibition of acetylcholine release from the guinea pig myenteric plexus were investigated. The selective 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT) and 5-hydroxytryptamine (5-HT) caused concentration-dependent inhibitions of the electrically evoked release of [3H]acetylcholine from myenteric plexus preparations that had been preincubated with [3H]choline. The inhibitory effects were not modified by the activator of adenylyl cyclase, forskolin (10 microM), the phosphodiesterase inhibitor, AH 21-132 (100 microM), or after pretreatment of the guinea pigs with pertussis toxin (60 micrograms/kg). In contrast, the protein kinase C activator 4 beta- phorbol-12,13-dibutyrate (0.1 microM) prevented the release-inhibiting effect of 8-OH-DPAT, whereas the inactive isomer 4 alpha-phorbol-12,13-dibutyrate (0.1 microM) was without effect. The results suggest that the presynaptic 5-HT1A receptor is not coupled to a pertussis toxin sensitive G protein or to adenylyl cyclase. However, protein kinase C seems to be involved in the mechanism of inhibition of acetylcholine release by presynaptic 5-HT1A receptors.

8793914

Zinc changes AMPA receptor properties: results of binding studies and patch clamp recordings.

The influence of zinc ions on alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors was investigated using binding studies with [3H]AMPA to rat cortical membranes and patch clamp recordings from cultured superior colliculus neurones. In Tris-HCl buffer, zinc (1-10 mM) significantly increased the specific binding of [3H]AMPA whereas this increase was negligible in the presence of CaCl2 (2.5 mM) and KSCN (100 mM). This effect was associated with a dramatic increase in Bmax but a decrease in both agonist and antagonist affinity. Association and dissociation experiments showed that equilibrium [3H]AMPA binding is reached with faster kinetics in the presence of zinc. At low concentrations (0.3 mM) zinc also concentration-dependently potentiated both peak and ponents of whole cell current responses to AMPA (100 microM). This effect was panied by a reduction of the degree, and slowing of the rate, of AMPA receptor desensitisation. In contrast, higher concentrations of zinc (1-3.0 mM) inhibited AMPA responses to some degree, but slowed desensitisation further. This ability of zinc to change AMPA receptor properties may be relevant to neurotoxicity associated with AMPA receptor activation.

8793912

5-HT1A receptor antagonists and lordosis behavior.

In proestrous rats, serotonin 1A (5-HT1A) receptor agonists inhibit lordosis behavior within 5-15 min following infusion into the ventromedial nucleus of the hypothalamus (VMN). In the present report, the lordosis-inhibiting effects of the 5-HT1A agonist [(+/-) 8-hydroxy-2- (di-n-propylamino) tetralin) (8-OH-DPAT] were shown to be attenuated with 5-HT1A receptor antagonists. pounds, propranolol and pindolol, that function as both beta-adrenergic and 5-HT1A receptor antagonists, and (+) WAY100135 (chiral N-t-butyl-3-(1-(4-(2-methoxy) phenyl)piperazinyl)-1-phenylpropionamide dihydrochloride, quarter hydrate), a more selective 5-HT1A receptor antagonist, were found to reduce the lordosis-inhibiting effects of 8-OH-DPAT infusion into the VMN. Proestrous rats were co-infused into the VMN with 200 ng 8-OH-DPAT plus 1000 ng or 2000 ng pindolol, 1000 ng or 2000 ng propranolol, or 2000 ng (+) WAY100135. Co-infusion with 1000 ng or 2000 ng pindolol attenuated the inhibitory effects of 8-OH-DPAT; co-infusion of 1000 ng, but not 2000 ng, propranolol, reduced the effects of 8-OH-DPAT; and co-infusion with 2000 ng (+) WAY100135 attenuated the effects of 8-OH-DPAT. Bilateral VMN infusion with 2500 ng (+) WAY100135 facilitated lordosis behavior in suboptimally, hormone-primed ovariectomized rats. These findings strengthen the argument that the inhibitory effect of 5-HT1A receptor agonists on lordosis behavior is the result of their activation of VMN 5-HT1A receptors.

8793913

Protective actions of the 5-HT2A/2C receptor agonist, DOI, on 5-HT1A receptor-mediated inhibition of lordosis behavior.

Sexually receptive proestrous rats were infused bilaterally into the ventromedial nucleus of the hypothalamus (VMN) with 200 ng of 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT), 1000 or 2000 ng of 5-methoxy-3-(di-n-propylamino) chroman (5-MEO-DPAC), or 1000 or 2000 ng of serotonin (5-HT) plus or minus the 5-HT2A/2C agonist, (2,5-dimethoxy-4-iodophenyl)-2-aminopropane HCl (DOI). DOI protected against the lordosis-inhibiting effects of 5-HT and each of the 5-HT1A agonists. These results substantiate a prior report that 2000 ng DOI could protect against the lordosis-inhibiting action of 200 ng 8-OH-DPAT and demonstrate that such protection is not unique to a single 5-HT1A agonist. Consequently, these results strengthen evidence that functionally significant interactions occur among 5-HT receptors within the VMN.

8793915

The effects of neurokinin-1 receptor agonists on spinal motoneurones of the neonatal rat.

The effects of substance P (SP) and the selective NK1 receptor agonist [Sar9Met(O2)11] substance P on neonate rat spinal motoneurones were examined using intracellular recordings. Bath-administration of SP (0.1-3 microM) or [Sar9Met(O2)11] substance P (0.01-3 microM) induced a tetrodotoxin (TTX)-insensitive (10 microM) depolarization and a tetraethylammoniumchloride (TEA)-sensitive (3 mM) decrease in membrane conductance. The duration of the slow afterhyperpolarizations (AHPs) following the action potentials were significantly reduced (p = 0.003) by both NK1 receptor agonists. The mean duration of the sAHPs (+/- SEM) in control was 67.8 +/- 6.3 ms whereas in the presence of SP and [Sar9Met(O2)11] substance P their duration was reduced to 41.7 +/- 4.6 ms. Low Ca2+ (0.2 mM)-containing artificial cerebrospinal fluid (ACSF) or addition of BaCl2 or CdCl2 (2 mM) reduced the durations of the slow AHPs by 55%. In the presence of these agents SP and [Sar9Met(O2)11] substance P practically abolished the remaining slow AHPs, suggesting that the agonists also reduce a calcium-independent current. None of the effects induced by the NK1 receptor agonists were antagonized by the NK1 receptor antagonists (+/-)-CP-96,345 (10 microM), RP 67580 (1 microM) or GR 82334 (3-5 microM). In conclusion this study demonstrates that SP and [Sar9Met(O2)11] substance P elicit their effects on NK1 receptors by modulating at least two potassium currents, namely IK and ICa(K).

8793918

Airway management for pediatric emergencies.

Several factors increase the difficulty and urgency of airway management in children in the emergency setting. Early and appropriate airway management are of prime importance in improving the e of such patients. The major decision points of airway management include one's assessment of the airway and ability to perform endotracheal intubation. If the airway is judged to be normal, oral endotracheal intubation following sedation and neuromuscular blockade is suggested. Rapid sequence intubation to prevent acid aspiration should be used. While the medications for airway management generally are administered intravenously, it should be kept in mind that intraosseous access is an acceptable alternative for the administration of several different agents, including those used for endotracheal intubation. If the airway cannot be secured following the administration of anesthetic and neuromuscular blocking agents, the ASA algorithm for the "cannot intubate/cannot ventilate" scenario should be followed (Figure). When the airway is judged to be abnormal, one of the above described awake techniques may be used. While there is ample literature concerning these techniques in adults, their use in children has been limited. Most importantly, considerable practice may be required to e and stay facile with many of these "alternative techniques" of airway management. In certain circumstances, surgical cricothyrotomy should be considered as an alternative to airway management. Regardless of the technique chosen, appropriate personnel and preparation are mandatory to ensure the safe and effective management of the airway in the pediatric trauma patient. Due to the various skills and expertise of different subspecialists, a multidisciplinary approach to such patients is mended. Such an approach may include pediatricians, emergency room physicians, surgical subspecialists, anesthesiologists, and critical care physicians.

8793920

Cardiac emergencies in children.

Pediatric cardiac emergencies require very specific treatment in the emergency room setting. Considering the possibility of a cardiac problem as the cause for the presenting symptoms is the initial step in successful management. Many patients present with what is initially considered a primary pulmonary disorder such as pneumonia, asthma, or bronchiolitis. Airway stabilization and ventilatory support, if needed, remain the first steps in stabilizing the patient. Many neonates with acutely pensating heart disease may require the patency of the ductus arteriosus for survival. Prostaglandin E given as continuous infusion is the treatment of choice. Congestive heart failure can present at any age. In older patients, it is often due to myocarditis and is characterized by low cardiac output. Supportive measures, fluid restriction, and inotropic support are the basic concepts for initial treatment. Supraventricular tachycardia is a frequent arrhythmia, especially in young children. If the patient is unstable, immediate intravenous administration of adenosine or synchronized cardioversion are the initial interventions. In stable patients, vagal maneuvers may be attempted to abort the arrhythmia.

8793919

Shock in children: the first 60 minutes.

Significant morbidity and even mortality can result if early and aggressive resuscitation is not provided for children in shock. When faced with such patients, the initial therapy must include the basics of resuscitation including airway management and assisted ventilation when indicated. Correction of metabolic abnormalities such as hypoglycemia, hypocalcemia, and acidosis may partially correct the cardiovascular dysfunction. Fluids and inotropic agents are chosen based on the underlying pathology and the associated cardiovascular parameters.

8793922

Selection by somatic signals: the advertisement of phenotypic state through costly intercellular signals.

We develop a model of intercellular signalling, to explore the possibility that the signals exchanged between cells within a body may be subject to many of the same evolutionary pressures as signals exchanged between individuals whose genetic interests conflict. Evolutionary signalling theory maintains that signals, to be reliable indicators of need, intention or quality must be more costly than would be required merely to transmit a message. Cost guarantees that poor quality individuals are less able to display the high magnitude signals produced by the higher quality individuals. Receivers have been favoured by natural selection to attend only to the costliest signals, and thereby acquire honest information from the signaller. Hence the extravagant, costly ornamentation found among males of many species, ensures that females can accurately choose among them on the basis of their qualities. However, because somatic cells are normally perfectly genetically related, and are often denied access to the germ line, there will be minimal genetic conflicts of interest. This appears to imply that reliable intercellular signals should be produced without the need for cost to ensure their reliability. Nevertheless, we show that whenever cells vary in their phenotypic qualities in ways relevant to the fitness of the body, and given that there exists a class of cell that remains "ignorant' of its phenotypic state, costly intercellular signalling will evolve as a form of quality control. Specifically, we show that given variation in the cell population, signal cost will aid the identification and removal of cells that over-represent their true phenotypic state, and which therefore could lower fitness. Cells that under-represent their state are simply peted by other cells. The cells of a body employ signals in a variety of intercellular interactions, including the development of the nervous system, the formation of neuromuscular junctions, and during the establishment of the immune repetoire. In each of these cases, cells may employ costly signals to advertise their phenotypic quality to other cells, and we review the evidence in support of this hypothesis: in effect, the cells may possess a molecular counterpart to the peacock's tail.

8793924

Birth outcomes in pregnant women taking fluoxetine.

Although fluoxetine is the most frequently prescribed antidepressant drug in the United States, its safety in pregnant women has not been established.

8793925

Esophagitis associated with the use of alendronate.

Alendronate, an aminobisphosphonate and a selective inhibitor of osteoclast-mediated bone resorption, is used to treat osteoporosis in postmenopausal women and Paget's disease of bone. Aminobiphosphonates can irritate the upper gastrointestinal mucosa.

8793926

Rotavirus infection in infants as protection against subsequent infections.

Rotavirus is the leading cause of severe diarrhea in infants. To provide a base line for assessing the efficacy of rotavirus vaccines, we evaluated the protection that is conferred by natural rotavirus infection.

8793929

The effect of legislative requirements on the use of breast-conserving surgery.

We studied the effect of state legislation requiring the disclosure of options for the treatment of breast cancer on the use of breast-conserving surgery in clinical practice.

8793988

Development of B-cell memory and effector function.

The past year has seen significant advances in our understanding of molecules that both positively and negatively regulate B- and T-cell responses. Of particular interest is the lethal phenotype of CTLA-4-deficient mice, which has illuminated the importance of downregulation of T-cell responses and the plicated role of CD40 and its ligand in directing both T- and B-cell priming.

8793989

Generation of T-cell memory.

Recent studies of T-cell memory have suggested that the persistent presence of the priming antigen is not necessary for maintenance of CD8 memory. Factors contributing to the development of memory from activated T cells remain ill defined but accumulating data suggest that cytokines play a key role in this process. There has also been recent progress in understanding turnover of naive and memory cells in the mouse.

8793990

Chemokines and lymphocyte biology.

The past few years have seen significant growth in the number of known chemokines. Along with expansion in this field e an appreciation of a role for chemokines beyond the chemotaxis of leukocytes. In particular, it appears that these molecules may represent major products of activated lymphocytes and that, in addition to chemotaxis, some of them may also regulate the growth, activation, and differentiation of lymphocytes.

8793991

Lymphocyte migration into tissue: the paradigm derived from CD4 subsets.

The appropriate recirculation and migration of naive, effector and memory T cells into inflamed tissue are precisely controlled by adhesive interactions with vascular endothelium. Analyses of CD4 lymphocytes have indicated that naive and antigen-experienced cells exhibit distinctive patterns of homing and recirculation, and that subsets of cells preferentially localize in different anatomical locations as a consequence of previous antigen exposure and differences in adhesion receptor usage.

8793992

Role of Fas-mediated cell death in the regulation of immune responses.

Interaction of the cell-surface molecule Fas (CD95 APO-1) with its specific ligand triggers apoptotic death of T and B lymphocytes. This pathway is important for eliminating self-reactive lymphocytes and thus preventing autoimmunity. Fas is also involved in controlling injurious lymphocyte reactions in immunologically 'privileged' tissues, and may provide a strategy for reducing graft rejection.

8793993

Activation of B lymphocytes: integrating signals from CD19, CD22 and Fc gamma RIIb1.

Three accessory membrane proteins, CD19, CD22 and Fc gamma RIIb1, alter signaling through membrane immunoglobulin of B cells by binding cytosolic proteins containing SH2 domains. Recent biochemical and genetic studies have shown that these receptors enable B cells to amplify responses to certain T-cell-dependent antigens (CD19), to restrict their response to T-cell zones of secondary lymphoid organs (CD22), and to dampen their response to antigens for which IgG is already available (Fc gamma RIIb1).

8793994

Mitogen-activated protein kinase cascades and regulation of gene expression.

Mitogen-activated protein kinases (MAPKs) are a group of serine/threonine specific, proline directed, protein kinases which are activated by a wide spectrum of extracellular stimuli. MAPK activation is achieved through kinase cascades, which include a MAPK kinase (MAPKK or MEK) and a MAPKK/MEK kinase (MAPKKK/MEKK). These cascades serve as information relays, connecting cell-surface receptors to specific transcription factors and other regulatory proteins, thus allowing extracellular signals to regulate the expression of specific genes. Genetic and biochemical analyses have revealed many tiers in the regulation of the activities of MAPKs, as well as different routes that lead to the activation of an individual MAPK. An emerging topic of great interest is the basis for specificity in the activation of individual MAPKs and their ability to recognize their substrates.

8793995

Type 1 and type 2: a fundamental dichotomy for all T-cell subsets.

Cytokine secretion is not confined to CD4+ T cells; rather, Type 1 and Type 2 populations of CD8+ and gamma delta T cells can also be generated in vitro and isolated from in vivo situations. These subsets and their physiological functions are significant.

8793996

Phosphatidylinositol 3-kinase related kinases.

Studies in yeast, files and mammalian cells have uncovered a novel family of signal-transducing kinases which bear an evolutionary relationship to phosphatidylinositol 3-kinase. These phosphatidylinositol 3-kinase related enzymes play critical roles in DNA repair, V(D)J bination and cell-cycle checkpoints, and their dysfunction leads to clinical manifestations ranging from immunodeficiency to cancer.

8793997

Recognition events that inhibit and activate natural killer cells.

Natural killer (NK) cells exhibit specificity for MHC class I molecules in their interactions with target cells. Instead of activating the cells, the recognition of class I molecules on target cells inhibits NK-cell lytic activity, suggesting that surveillance of normal class I expression by body cells represents a key NK-cell function. Recent advances have been made in identification of the class I specific receptors expressed by NK cells, and in the characterization of their detailed specificity and expression patterns. Other studies are beginning to unravel recognition events that activate NK cells.

8793998

Signals and susceptibility to programmed death in b cells.

Programmed death in B cells is a highly regulated process. During the past year it has e increasingly apparent that specific receptor signals influence B cell apoptosis in distinct ways as a function of developmental stage and/or apoptotic trigger. Studies making use of opposing signals for programmed death have begun to reveal molecular correlates of sensitivity and resistance to apoptosis.

8793999

Functions of TCR and pre-TCR subunits: lessons from gene ablation.

Recent gene-targeting experiments have highlighted the existence of checkpoints that ensure that alpha beta T cells do plete intrathymic differentiation if they have not attained certain landmark events. These 'proofreading' mechanisms operate by way of the pre-TCR and plexes, which are sequentially expressed during T-cell development. plexes are likely to signal via their associated CD3 subunits. By activating intracellular effectors, the CD3 subunits probably modulate gene expression profiles and drive the maturing alpha beta T cells through a precise developmental sequence.

8794000

Mechanisms of antigen uptake for presentation.

There is growing evidence that different antigen-presenting cells use specialized mechanisms for antigen uptake. Macropinocytosis and the activity of the mannose receptor have been identified as efficient mechanisms of antigen capture in dendritic cells. The mechanism of uptake determines the partment to which antigen is delivered and may determine the type of T-cell epitopes generated. New pathways for presentation of exogenous antigens on MHC class I and II molecules have been identified. These findings provide new insights into antigen presentation in vivo and will be instrumental in designing better methods of vaccination.

8794001

Regulation of antigen receptor signal transduction by protein tyrosine kinases.

The past two years have seen further clarification of the early events occurring in antigen receptor signal transduction that are mediated by the immunoreceptor tyrosine-based activation motif (ITAM). The ITAM was shown to be a specific binding site for the ZAP-70/Syk protein tyrosine kinases and the structure of plex was solved. In addition, possible mechanisms of activation and functions for these kinases were reported. Lastly, genetic studies established the critical importance of these kinases in antigen-receptor signaling and lymphocyte development.

8794002

Visualizing immune responses in vivo.

Helper T cell dependent B-cell responses develop in plex microenvironments of secondary lymphoid organs. New strategies for visualizing antigen-responsive lymphocytes offer direct insight into how differentiation proceeds in vivo.

8794004

Ataxia-telangiectasia: a multifaceted genetic disorder associated with defective signal transduction.

The gene responsible for the defect in the human genetic disorder ataxia-telangiectasia, ATM, was cloned recently. The part of the gene coding for a phosphatidylinositol 3-kinase domain showed it to be related to a family of genes involved in signal transduction, cell cycle control and the response to DNA damage. The elucidation of the role of the ATM gene product will provide valuable insight into the radiosensitivity, cancer predisposition, immunodeficiency and neuropathology that characterize this syndrome.

8794005

Immunodeficiencies caused by genetic defects in protein kinases.

The recognition that defects of ZAP-70 and, more recently, of JAK3 kinase in humans result in bined immunodeficiency, and the demonstration that targeting of these and other protein-kinase genes in mice also leads to immunodeficiency, have highlighted the crucial role that these proteins play in T-cell differentiation and activation.

8794006

Lessons from human genetic variants in the study of B-cell differentiation.

Several human B-cell immunodeficiencies result from mutations in signal transducing molecules. The past year has seen significant advances in our understanding of how these molecules are integrated into B cell signaling pathways. The phenotypes of mice deficient in several of these genes have revealed species-specific differences in the requirements for early B cell development.

8794007

Immunology of papillomavirus infection.

Studies of the immunology of papillomavirus infection e of age. Synthetic virus-like particles have been validated as vaccines for several animal papillomaviruses, and have been used to map the sero-epidemiology of human papillomavirus infection and to define papillomavirus neutralizing antibodies. Induction of cell-mediated immunity to papillomavirus early proteins is poised to e a therapeutic approach to papillomavirus infection. Studies on the immune response to papillomavirus proteins in keratinocytes are shedding light on the immunological consequences of antigen presentation by epithelial cells.

8794008

Neutralization of HIV-1 by antibody.

The humoral immune response to HIV-1 has been extensively studied over the past few years and considerable advances have been made in understanding the dynamics and specificity of the neutralizing ponent during and after seroconversion. Despite this, there is still no clear understanding of the role of neutralizing antibodies in controlling or preventing HIV-1 infection. Candidate vaccines have been based on immunogens designed to elicit a neutralizing response, but the recent vaccine trial failures force us to reconsider the role of neutralizing antibodies in HIV-1 infection and the type of vaccine preparation used.

8794009

Immunity to Lyme disease: protection, pathology and persistence.

Persistence of the Lyme disease spirochete, Borrelia burgdorferi, in the presence of an active immune response has been well documented. Evidence from the past year indicates that modulation of surface antigens by the spirochete may be a major mechanism for evading the immune response.

8794010

Invasion, control and persistence of Leishmania parasites.

Significant advances in research on the immunopathogenesis of leishmaniasis include the discovery of novel putative evasion and survival strategies of Leishmania parasites, a more detailed understanding of the function and regulation of interleukin-12, definition of molecules involved in cognate interaction between macrophages and T cells and new ideas concerning the mechanisms of host resistance and susceptibility. The use of transgenic mice for (re)probing certain immunological aspects of leishmaniasis has yielded not only predictable and confirmatory but also unexpected and pioneering results which require critical appreciation.

8794011

To kill or to cure: options in host defense against viral infection.

It is generally thought that viral clearance is mediated primarily by antigen-specific T cell responses that destroy infected cells. This assumption may not be true for all viruses. Recent studies using a transgenic mouse model of hepatitis B virus infection have shown that adoptively transferred, virus-specific cytotoxic T cells can abolish hepatitis B virus gene expression and replication in the liver without killing the hepatocytes. This effect is mediated by interferon-gamma and tumor necrosis factor-alpha, which are secreted by the cytotoxic T lymphocytes following antigen recognition. Similar noncytopathic cytokine-dependent 'curative' processes also occur in this model during an unrelated infection of the liver. Intracellular viral inactivation mechanisms such as these could greatly amplify the protective effects of the immune response. Research has also been carried out to clarify the relevance of curative versus destructive mechanisms of viral clearance in other models of viral infection.

8794013

Immune response to mouse mammary tumour virus.

Superantigens of mouse mammary tumor virus induce a strong cognate interaction between T cells and B cells. In addition to amplifying the virus-infected B-cell pool, this superantigen-driven interaction leads to the differentiation of virus-specific B cells into plasma cells. Successful interaction between T cells and B cells is required pletion of the viral life cycle.

8794014

T-cell recognition of non-peptide antigens.

Studies of two distinct human T-cell systems have provided the exciting finding that T cells are able to recognize non-peptide antigens: gammadelta T cells have been shown to recognize isopentenyl pyrophosphate and related structures and human CD1 has been shown to present microbial lipids and lipoglycans such as mycolic acids and lipoarabinomannan to T cells. T-cell responses to these non-peptide antigens should provide a strategic target for immunologic intervention in infectious disease.

8794012

Primary and secondary immune responses to Listeria monocytogenes.

Recent studies have revealed plexity of cytokine and cellular interactions required for resistance to primary Listeria monocytogenes infection and have illustrated that resistance to secondary infection may occur through multiple pathways. Analyses of Listeria epitope generation and the specificity of protective CD8(+) T cells have suggested that future research should focus on secreted protein antigens in specific resistance to infection and have increased our understanding of Listeria antigens presented by MHC class l-b molecules.

8794015

Different roles for cytotoxic T cells in the control of infections with cytopathic versus noncytopathic viruses.

The assessment of the role of T-cell-mediated cytotoxicity in immunity to viral infections has been difficult to address directly and therefore has been controversial. Recent experiments with perforin-deficient mice have shown that cytotoxicity is crucial for the resolution of infection with lymphocytic choriomeningitis virus but not for the resolution of infection with vaccinia, vesicular stomatitis, Semliki Forest or influenza virus. These findings may reflect the general pattern that T-cell-mediated cytotoxicity is crucial only for the resolution of infections with noncytopathic viruses, whereas infections with cytopathic viruses are mainly controlled by soluble mediators such as antibodies and interferons.

8794016

Virus proteins that bind cytokines, chemokines or interferons.

Some viruses express proteins to evade non-specific host defences such plement, interferons and the inflammatory response. Recent notable discoveries are the broad species specificity of orthopoxvirus interferon receptors, herpesvirus and poxvirus proteins related to chemokine receptors and proteins that bind more than one cytokine, interferon or chemokine.

8794018

Evolution and plasticity of CTL responses against HIV.

Exceptionally potent cytotoxic T lymphocyte responses are generated after HIV invasion and probably control the primary infection as well as the asymptomatic phase of HIV infection. The chronic phase appears as a quasi-equilibrium between waves of new HIV variants and variant-specific CTLs, thus sustaining continuous CTL activation which eventually fails to eradicate HIV disease progression and the reascension of viral replication. Meanwhile, both the host and the virus develop various strategies either to stop or to evade this potentially deleterious permanent CTL activity. The transient effectiveness of CTLs opens perspectives for understanding disease progression generally as well as for immune therapeutic strategies.

8794019

Macaque models for AIDS vaccine development.

Recent vaccine trials utilizing the simian immunodeficiency virus/macaque model of AIDS are beginning to yield clues regarding mechanisms of protective immunity. Although cytotoxic T lymphocyte responses to SIV may play a role in mediating protection against infection, protective immunity appears to correlate best with the development of antibodies able to neutralize primary or heterologous pathogenic viruses. Protection against disease or persistent infection may be achieved in the absence of sterilizing immunity, suggesting that new benchmarks for AIDS vaccines may be in order.

8794020

Cytotoxic T lymphocyte responses to Epstein-Barr virus.

Epstein-Barr virus induces a potent cytotoxic T lymphocyte response in man that is preferentially directed towards a particular subset of the virus latent cycle antigens; the immunodominance of these proteins, apparent in both primary and memory responses, may reflect some differential access to the HLA class I processing pathway. Effector cells recognizing these immunodominant antigens can reverse the growth of virus-induced lymphoproliferative lesions in immunosuppressed patients; however, responses to some of the subdominant latent proteins will be needed to target other virus-positive tumours.

8794021

DNA vaccines.

Preclinical DNA vaccine development has continued apace during the past year, with the investigation of several new infectious and non-infectious disease targets as well as advances in our understanding of some of the basic immunologic mechanisms, such as effector cells, responsible for conferring protection. ing year promises to be at least as exciting, as initial human clinical studies have begun.

8794024

Impact of the heart transplant waiting process on spouses.

Practitioners working with candidates for heart transplants and their families know that the heart transplant waiting process is psychologically stressful and demanding. Spouses of heart transplant candidates struggle with multiple demands. Although many have studied the impact of heart transplantation on patients, only a few investigators have studied the impact of the heart transplant waiting period on spouses.

8794026

Fatigue and fracture of pyrolytic carbon: a damage- tolerant approach to structural integrity and life prediction in "ceramic" heart valve prostheses.

The fracture and fatigue properties of Si-alloyed LTI pyrolytic carbon and pyrolytic carbon-coated graphite are described as a framework for establishing damage-tolerant analyses for maintaining structural integrity and for predicting the lifetimes of mechanical heart valve prostheses fabricated from these materials.

8794027

Effect of repetitive impact on the mechanical strength of pyrolytic carbon.

Impact loading is experienced by mechanical heart ponents when the es into contact with the housing orifice as the valve opens and closes during the cardiac cycle. Since the human heart beats approximately 40 million times per year, a large number of impact loading cycles are imposed on the carbon ponents. Contact loading can produce high mechanical stress at the contact area, leading to potential material damage and fracture. This paper describes a procedure for characterizing the effect of repetitive impact on the mechanical strength of pyrolytic carbon. The results shed light on the basic understanding of the damage formation and its strength degradation effect. In particular, fatigue crack growth was identified as the primary mechanism which causes the observed strength degradation. Design procedures based on fracture mechanics and contact mechanics are used in mechanical heart valve design to prevent structural failure associated with impact fatigue.

8794029

Infective endocarditis of the tricuspid valve in an orthotopic heart transplant recipient.

A 43-year-old orthotopic heart transplant recipient had coagulase-negative staphylococcus endocarditis 26 weeks after the operation. A diagnosis of endocarditis was confirmed and followed up by serial transoesophageal echocardiography. Treatment with intravenous gentamycin and ycin cured her endocarditis, and a 2.5 cm vegetation regressed significantly. She has been well since and, at 14 months after transplantation, was back to her normal activities. Although repeated blood culture yielded only intermittent light growths of coagulase-negative staphylococci, there were several positive samples. In a setting of infective features, light growths of coagulase-negative staphylococcus should be taken seriously if repeatedly positive in heart transplant recipients or other promised patients. Transesophageal echocardiography offers significant advantages over the transthoracic modality in suspected endocarditis.

8794030

Medical compliance and its predictors in the first year after heart transplantation.

Although poor pliance is a major risk factor for morbidity and mortality after heart transplantation, no prospective data are available on rates of pliance with ponent of the posttransplantation regimen. Little is known about the impact of health history, sociodemographic, or perioperative psychosocial variables on pliance.

8794031

Mechanical performance of pyrolytic carbon in prosthetic heart valve applications.

An experimental procedure has been developed for rigorous characterization of the fracture resistance and fatigue crack extension in pyrolytic carbon for prosthetic heart valve application. Experiments were conducted under sustained and cyclic loading in a simulated biological environment using Carbomedics Pyrolite carbon. While the material was shown to have modest fracture toughness, it exhibited excellent resistance to subcritical crack growth. The crack growth kinetics in pyrolytic carbon were formulated using a phenomenological description. A fatigue threshold was observed below which the crack growth rate diminishes. A damage tolerance concept based on fracture mechanics was used to develop an engineering design approach for mechanical heart valve prostheses. In particular, a new quantity, referred to as the safe-life index, was introduced to assess the design adequacy against subcritical crack growth in brittle materials. In addition, a weakest-link statistical description of the fracture strength is provided and used in the design ponent proof-tests. It is shown that the structural reliability of mechanical heart valves can be assured bining effective flaw detection and manufacturing quality control with adequate damage tolerance design.

8794033

Fatigue of isotropic pyrolytic carbon used in mechanical heart valves.

This study shows that the strength of silicon-alloyed pyrolytic carbon is not affected by long-life cyclic stress up to 6 x 10(8) cycles at stress levels which are two, four and eight times higher than the estimated peak service stress of a mechanical heart valve. It is demonstrated that there is clearly a threshold size for cyclic fatigue crack propagation below which the cracks do not grow at all when cycled up to 6 x 10(8) cycles at strain levels that are two and four times higher than the estimated peak service stress of the heart valve. The large sample size of the fatigue test gives a high statistical confidence in the intrinsic fatigue behavior of pyrolytic carbon, which has been demonstrated in over three million implants of the material in actual devices with an accumulated experience of over ten million patient years. Nevertheless, mechanical heart valve designers are cautioned to consider the effects of extrinsically introduced flaws.

8794034

Successful bridge to retransplantation with the wearable Novacor left ventricular assist system.

The wearable version of the Novacor left ventricular assist system has been implanted in a 44-year-old man as a bridge to retransplantation. Apart from a temporary right ventricular failure, the postoperative course was smooth and the patient underwent retransplantation after 95 days of support. plications like infection or bleeding could be avoided or minimized.

8794035

Pyrolytic carbon indentation crack morphology.

In studying fatigue and fracture behavior of brittle materials, Vickers diamond indentation cracks are often used. Many of the studies of indentation cracks use crack system models such as the radial-median crack or Palmqvist crack. These systems are also used to study small crack growth in brittle materials, and have been studied for pyrolytic carbon. However, the true morphology of these cracks in pyrolytic carbon coatings on graphite substrates have not been described. This study examined Vickers diamond and spherical ball indentation cracks in pyrolytic carbon coatings using several techniques, including serial metallographic cross sections, indentation fracture in bending, acoustic emission, and residual surface indentation scanning. The crack systems developed using these techniques were not typical of either radial median or Palmqvist systems. The morphology is unique to this material, possibly because of the coating thickness limitations. Given the difference in crack system, the application of standard indentation crack equations in studying fracture mechanics, especially for small cracks, must be questioned.

8794036

Low-dose cyclosporine treatment fails to prevent coronary luminal narrowing after heart transplantation.

Cyclosporine has been reported to induce endothelial dysfunction, arterial vasculitis, and accelerated atherosclerosis in experimental models. The purpose of the present study was to evaluate whether low-dose cyclosporine treatment started 1 year after heart transplantation reduces graft coronary artery pared with conventional cyclosporine doses.

8794040

Finite element analysis of indentation tests on pyrolytic carbon.

The stresses which cause failure at contact areas between leaflets and orifices in pyrolytic carbon heart valves are evaluated. These contact stresses have previously been studied using Hertzian crack models that apply to monolithic material. Many heart valves are not monolithic pyrolytic carbon but a pyrolytic carbon deposited on graphite. Contact loads on these layered structures cause initial cracking in the pyrolytic carbon at the interface between pyrolytic carbon and graphite rather than Hertzian surface cracks. Increasing the load on layered structures will cause a secondary cracking (of Hertzian cracks) on the surface. The contact loading was simulated with a 5.1 mm diameter ball pressing against a flat sample of graphite coated with 0.26 mm of pyrolytic carbon on each surface. Finite element analysis of this model calculated the stresses associated with a range of loads causing no cracks through initial interface cracks and secondary surface cracks plete failure. The calculated stresses are correlated with parallel laboratory experiments. A failure criterion for contact stresses is developed. The initial cracks at the graphite/pyrolytic carbon interface occur when the tensile stress in the pyrolytic carbon reaches 207 to 276 MPa and pression stress in the graphite reaches 414 to 483 MPa. These initial cracks do not propagate immediately to the surface since they run into a high pression stress field. Circular surface cracks occur at the edge of the ball/pyrolytic carbon contact area at higher loads. These cracks require a shear stress of about 241 MPa and also require a tensile ponent. The results provide a criterion for designing contact regions in pyrolytic heart valves.

8794041

The role of positive and negative signals in somite patterning.

Signals from the axial tissues, neural tube and notochord play a crucial role in patterning cell fates in adjacent somitic tissue. Work over the past four decades has indicated how signals from the axial tissues, as well as the surface ectoderm and lateral plate mesoderm, together act to pattern somitic cell fate. Furthermore, recent results have shed light on how some of these molecules control the specification and migratory behaviour of somitic cells.

8794042

Neurogenesis in the insect central nervous system.

Recent advances provide an increasingly sophisticated understanding of Drosophila CNS development. First, genes have been identified that specify unique neuroblast cell fates. Second, neuroblasts have been found to use a novel mechanism for asymmetric localization of proteins into one daughter cell at mitosis. Third, a gene controlling the choice between glial/neuronal determination has been discovered. And finally, new cell-lineage methods are being used to determine the entire lineage of identified neuroblasts, including axon projections and synaptic contacts.

8794043

Agrin, laminin beta 2 (s-laminin) and ARIA: their role in neuromuscular development.

Development of pre- and postsynaptic specializations at the vertebrate neuromuscular junction is affected by molecules concentrated in the extracellular matrix of the synaptic cleft. Agrin, laminin beta 2 and ARIA are the best characterized proteins known to be involved in particular aspects of synaptic differentiation. Recent advances in defining the domains of these molecules that are crucial for their synapse-organizing activity and their localization to synaptic basal lamina will help our understanding of the molecular mechanisms involved in synapse formation.

8794044

The role of polysialic acid and other carbohydrate polymers in neural structural plasticity.

Polysialic acid (PSA) fulfills several criteria for a molecule involved in structural plasticity, including expression in regions capable of plasticity, re-expression in structures undergoing synaptic rearrangement in the adult, downregulation following innervation, and regulation by activity. In addition, removal of PSA reduces the capacity for structural plasticity. PSA may be paradigmatic for other large polymeric carbohydrates, such as glycosaminoglycans and proteoglycans, which also are highly charged and can be extensively hydrated. These carbohydrates may affect structural plasticity by altering cell-cell and/or cell-matrix interactions by increasing intermolecular spacing through hydration.

8794045

Role of neurotrophic factors in neuronal development.

The spectrum of potential biological roles for neurotrophic factors in development and maturation of the nervous system continues to widen. Careful analysis of the phenotypes of knock-out mice has been used to test directly the 'neurotrophic hypothesis', and the role of members of the transforming growth factor beta superfamily--in particular, glial cell line derived neurotrophic factor--in regulating neuronal survival has e apparent. The effects of neurotrophin-3 on early neuronal differentiation and maturation have proved to be both multiple plex. Neurotrophic factors are also emerging as potential regulators of synapse stabilization and function.

8794046

Schwann cell development, differentiation and myelination.

Neu-differentiation factor (glial growth factor) has been established as an important regulator of early Schwann cell development, and the lineage relationship between immature Schwann cells and the neural crest has been clarified by the identification of the Schwann cell precursor. Progress has been made in identifying transcription factors that control Schwann cell development and in defining molecules that positively and negatively regulate myelin differentiation pathways. The tetraspan group has emerged as a set of proteins with prominent functions in Schwann cell biology.

8794047

Neurotrophins and activity-dependent development of the neocortex.

A number of recent results suggest that neurotrophins play an important role in early development as well as in the later, activity-dependent processes important for the final shaping of cortical connections. Many neurotrophins and their receptors are regulated in parallel with the 'critical period' in development, and their application to the neocortex can dramatically alter the functional organization of the cortex, as well as the morphological properties of neocortical neurons. In addition, recent data show that a different phenomenon of synaptic plasticity, hippocampal long-term potentiation, also critically depends on neurotrophins. Thus, neurotrophins may play a role in linking functional modifications of synapses to the morphological effects of synaptic stabilization and rearrangement, as observed in the neocortex.

8794048

Regulation of vertebrate neural cell fate by transcription factors.

Evidence that region- and cell-type-specific transcription factors regulate morphogenesis and differentiation of the vertebrate nervous es from numerous studies, including descriptions of discrete patterns of expression during neural development and analysis of mutant phenotypes. Recently published works provide insights into the roles of vertebrate transcription factors in regulating the generation of neural precursors, regionalization of the nervous system, and subsequent differentiation of specific cell types within these regions. For instance, misexpression studies in Xenopus embryos show that the newly isolated basic helix-loop-helix protein NeuroD is able to promote neurogenesis, whereas analysis of mouse embryos mutant for the homeobox gene En-1 demonstrates that this transcription factor is required for proper development of the midbrain-hindbrain region. A recent study in chick shows that binatorial expression of Islet-1, Lim-1, and two other LIM homeobox genes, Islet-2 and Lim-3, defines subclasses of motor neurons in the spinal cord, supporting a model binatorial repertoires of transcription factors may act to generate diverse cell types.

8794049

Patterning the hindbrain.

Of paramount importance for hindbrain patterning is positional information that is laid down along the rostrocaudal axis. Recent findings suggest that retinoic acid may establish rostrocaudal domains of gene expression that confer on rhombomeres their specific identities; these domains display different responses to dorsoventral signals that further refine the repertoire of cellular fates therein. After rhombomere boundaries form, a high degree of segmental autonomy is balanced by a continuing capacity for interaction along the rostrocaudal axis, exemplified by the generation of the neural crest.

8794050

Vertebrate neural progenitor cells: subtypes and regulation.

Several advances have been made recently in characterizing neural progenitor cells. In vertebrates, multipotential stem cells have been demonstrated in the developing forebrain both in vitro and in vivo, and a class of stem cells has been identified in the adult CNS. Factors that regulate the proliferation and differentiation of subtypes of neural progenitor cells have also been described. In invertebrates, progress has been made in identifying genes involved in neural progenitor cell specification, cell-fate choices and regulation.

8794052

Functions of netrins and semaphorins in axon guidance.

Neuronal growth cones respond to both contact-mediated and chemotropic guidance cues; these cues can be either attractive or repulsive. This past year has seen further characterization of two gene families implicated in long-range chemoattraction and chemorepulsion: the netrins and the semaphorins. Analysis of invertebrate members of these gene families demonstrates in vivo how netrins play multiple roles in axonal guidance in Caenorhabditis elegans, how specific domains of the netrin molecule confer attractive and repulsive guidance cues, and how semaphorins can function to generate neuromuscular specificity.

8794051

Pax proteins and eye development.

Homologous members of the Pax gene family are required for eye development in Drosophila and vertebrates. Despite superficial similarities in the phenotypes of vertebrates with mutations in pax-6 and Drosophila eyeless mutants, it remains uncertain whether the two proteins encoded by these genes parable functions. The genetic cascade triggered by eyeless leads to eye formation, whereas pax-6 is not necessary for optic vesicle formation, but is required at other stages of eye development. A second vertebrate Pax gene, pax-2, is also required during eye development and appears to play a role during closure of the choroid fissure.

8794053

Tripartite signaling of pattern: interactions between Hedgehogs, BMPs and Wnts in the control of vertebrate development.

A central issue in embryonic development is the resolution of how groups of equivalent cells are transformed into orderly and patterned arrays of distinct cell types. Recent studies suggest the involvement of the Hedgehog, Wnt and bone morphogenetic protein families in the patterning of different tissue types in vertebrate embryos. The integrated actions of members of these three families of signaling proteins appear to have been recruited in the patterning of neural tissue in addition to several different tissues. Over the past year, a clearer picture of the diverse roles of these signaling proteins in embryonic development has begun to emerge.

8794055

Neurogenic genes and vertebrate neurogenesis.

The neurogenic genes of the Delta-Notch signalling pathway mediate lateral inhibition--a mechanism that controls mitment in many tissues and serves in the developing nervous system to single out cells for a neural fate. Recent work has revealed the outlines of the signal transduction pathway from Notch to the nucleus, has clarified the mechanisms by which lateral inhibition causes adjacent cells to e different, and has shown that vertebrates use essentially the same lateral inhibition machinery as flies and worms to regulate neurogenesis.

8794054

Mechanism of synapse disassembly at the developing neuromuscular junction.

Throughout the developing nervous system of higher vertebrates, synaptic connections are concurrently being established and eliminated. The consequence of this synaptic remodeling is that axons strengthen their connections with some targets pletely disconnecting from other postsynaptic cells. The transition from multiple to single axonal innervation of skeletal muscle fibers is the most accessible example of this developmental reorganization. In muscle, the elimination of axonal input appears to be driven by a petition between different axons co-innervating the same junction, with the muscle fiber as intermediary. Asynchronous synaptic activity may be the factor that differentiates peting inputs. In some circumstances, synapses can also be lost in ways that are independent of activity. Similarities between activity-dependent and activity-independent synapse elimination provide insights into mechanisms underlying developmental synaptic reorganization.

8794056

Biochemistry of cell death.

Apoptosis is mon feature of the nervous system, occurring physiologically during development and pathologically in several diseases. In view of the latter, pathways that regulate apoptosis in neurones are of particular interest, and recent advances in this field implicate several signalling pathways in the induction of apoptosis, after withdrawal of nerve growth factor. Recent information drawn from both mammalian and invertebrate models enables us to ponents of the apoptotic pathway as either regulators or effectors.

8794058

Eph receptor tyrosine kinases and their ligands in neural development.

Receptor tyrosine kinases play important roles in many developmental phenomena, including the regulation of cell proliferation, differentiation, and survival. The largest subfamily of receptor tyrosine kinases are the Eph receptors, which are widely expressed in the nervous system. With the recent identification of several Eph ligands, it has e evident that Eph receptors and their ligands are involved in the guidance of retinal axons and in the process of hindbrain segmentation.

8794076

Diversity and function of presynaptic calcium channels in the brain.

Calcium channels in presynaptic nerve terminals are essential for neurotransmitter release, and current research has provided evidence for the involvement of a multitude of Ca2+ channel types. The diversity of Ca2+ channel structure and distribution in the brain suggests specific functional roles. Modulation by interaction with other proteins and/or by phosphorylation/dephosphorylation reactions enhances the regulatory impact of these channels on brain function.

8794077

Presynaptic potassium channels.

The past year has witnessed some significant improvements in our understanding of the molecular diversity, position, and functional properties of K+ channels in heterologous expression systems. Immunocytochemical studies have yielded important information on the localization of K+ channel proteins to synaptic terminals in mammalian brain. Although a coherent picture of native presynaptic K+ channels' function in the mammalian central nervous system is not yet available, it may emerge from improvements in patch-clamp techniques and new applications of targeted knock-out technologies.

8794078

Synaptic exocytosis and endocytosis: capacitance measurements.

Exo- and endocytosis are panied by changes in membrane capacitance. Capacitance measurements in synaptic terminals have proven recently to be a useful adjunct to other techniques in examining presynaptic mechanisms. New information has emerged from these studies about the size and dynamics of synaptic vesicle pools, about the Ca2+ dependence of the rate of exocytosis, and about the kinetics of endocytosis in synaptic terminals.