bluuebunny/crossref_metadata_2025 huggingface dataset:
Photoperiod‐Dependent and ‐Independent Regulation of Melatonin Receptors in the Forebrain of Songbirds
Authors: Bentley G. E. , Ball G. F.
Published: March 2003

Melatonin was recently identified as playing a role in fine‐tuning the effects of gonadal steroids in the regulation of seasonal neuroplasticity within the telencephalic song control system of European starlings. The present study investigated possible seasonal regulation of melatonin receptors (MelR) within the starling song control system, in the presence or absence of gonadal steroids. Brains were sampled from photosensitive starlings exposed to short days, photostimulated starlings exposed to long days and photorefractory starlings also exposed to long days. Each condition contained a group of gonad‐intact birds and a group of castrated birds. Melatonin receptor distribution was assessed in vitro by 125–iodomelatonin (IMEL) receptor autoradiography. In general, MelR distribution was similar to that described in other songbird species. However, there was a striking downregulation of MelR in the song control nucleus Area X of intact and castrated photostimulated birds on long days compared to their photorefractory counterparts on the same long days and to the short‐day groups. Downregulation of MelR occurred independently of gonadal steroids. Nevertheless, superimposed on this general pattern of MelR downregulation during photostimulation, IMEL binding was observed in a medial subdivision of Area X when gonadal steroids were present. Downregulation of MelR in Area X during the short breeding season has implications for seasonal regulation of the song control system. Subsequent upregulation of MelR as birds become photorefractory, in the absence of any change in photoperiod, gonadal steroids or melatonin signal is the first description of photoperiod‐independent regulation of MelR in adults of any vertebrate class.
Central Nervous System Structures Labelled from the Testis Using the Transsynaptic Viral Tracing Technique
Authors: Gerendai I. , Tóth I. E. , Boldogkői Z. , Medveczky I. , Halász B.
Published: March 2003

In the present study, the transneuronal transport of neurotrophic virus technique was used to identify cell groups of the spinal cord and the brain that are transsynaptically connected with the testis. Pseudorabies virus was injected into the testis and after survival times of 3–6 days, the spinal cord and brain were processed immunocytochemically using a polyclonal antibody against the virus. Virus‐infected perikarya were detected in the preganglionic neurones of the spinal cord (T10‐L1, L5–S1) and in certain cell groups and areas of the brain stem, the hypothalamus and the telencephalon. In the brain stem, the cell goups and areas in which labelled neurones were present included, among others, the nucleus of the solitary tract, the caudal raphe nuclei, the locus coeruleus and the periaqueductal grey of the mesencephalon. In the hypothalamus, virus infected perikarya were observed in the paraventricular nucleus and in certain other cell groups. Telencephalic structures containing labelled neurones included the preoptic area, the bed nucleus of the stria terminalis, the central amygdala and the insular cortex. These data identify a multisynaptic circuit of neurones in the spinal cord and in the brain which may be involved in the control of testicular functions.
The Effect of Leptin on Luteinizing Hormone Release Is Exerted in the Zona Incerta and Mediated by Melanin‐Concentrating Hormone
Authors: Murray J. F. , Mercer J. G. , Adan R. A. H. , Datta J. , Aldairy C. , Moar K. M. , Baker B. I. , Stock M. J. , Wilson C. A.
Published: March 2003

The adipose hormone, leptin, not only restrains appetite, but also influences energy expenditure. One such influence is to promote sexual maturation and fertility. The neuromodulatory circuits that mediate this effect are not well known but the present study suggests that one mediator could be melanin‐concentrating hormone (MCH). We show that the long‐form receptor (Ob‐Rb) is expressed in the zona incerta of the rat and that administration of leptin (both 0.5 µg and 1.0 µg/side) into this area of ovariectomized, oestrogen‐primed rats stimulated the release of luteinizing hormone (LH) within 1 h, the effect enduring for a further 1 h. Injections of leptin into the arcuate nucleus induced a smaller, transient rise in LH while injections into the paraventricular and ventromedial nuclei were without effect. MCH neurones are present in the zona incerta and administration of this hormone into the medial preoptic area (mPOA) stimulates LH release, therefore we investigated the possibility that MCH might mediate this effect of leptin. An injection of MCH antiserum into mPOA prevented the rise in LH normally induced by leptin injected into the zona incerta. In addition, melanocortin receptor antagonists ([D‐Arg8]ACTH(4‐10) and [Ala6]ACTH(4‐10)), previously shown to inhibit the stimulatory effect of MCH on LH release, also inhibited the effect of leptin. We propose that one route by which leptin may promote reproductive activity is by enhancing MCH release from fibres within the mPOA. Speculative mechanisms for the action of MCH include the following possibilities: MCH may be acting on the specific MCH receptor which in turn interacts with a melanocortin or melanocortin‐like receptor; MCH may bind directly to one of the melanocortin receptors; or melanocortin antagonists may interact with the MCH receptor.
Modulation of Pituitary Dopamine D1 or D2 Receptors and Secretion of Follicle Stimulating Hormone and Luteinizing Hormone During the Annual Reproductive Cycle of Female Rainbow Trout
Authors: Vacher C. , Mañanos E. L. , Breton B. , Marmignon M.‐H. , Saligaut C.
Published: March 2003

The two gonadotrophins follicle stimulating hormone (FSH) and luteinizing hormone (LH) have distinct temporal expression and release profiles in fish, but little is known regarding their neuroendocrine control, especially for FSH. The present experiments were performed on previtellogenic, mature and preovulatory female trout. The catecholamine synthesis inhibitor, α‐methyl‐p‐tyrosine, increased plasma LH and FSH concentrations of mature fish. The dopamine agonist apomorphine decreased and the dopamine antagonist domperidone increased plasma LH concentration of preovulatory fish and delayed ovulation, but did not modify plasma FSH concentration. The dopamine D2 agonist bromocryptine inhibited LH release in cultured gonadotrophs from mature and preovulatory fish, but not from previtellogenic fish. Bromocryptine also significantly inhibited basal and salmon gonadotrophin releasing‐hormone (sGnRH)‐induced FSH release from cultured gonadotrophs of mature fish, but not of preovulatory fish, and increased FSH release from gonadotrophs of previtellogenic fish. The dopamine D1 agonist SKF 38393 had no observed effect on the release of FSH and LH, at any reproductive stage studied. The D1 agonist SKF 38393, the D2 agonist bromocriptine and sGnRH had no observed effects on cell contents of FSH and LH. Taken together, these data suggest that, at the level of the pituitary, dopamine inhibits LH release as vitellogenesis proceeds, via activation of dopamine D2 receptors. We demonstrate for the first time in fish a control of FSH release (a dopamine control), especially in mature fish which have low circulating concentrations of FSH.
Insulin and Glucose Administration Stimulates Fos Expression in Neurones of the Paraventricular Nucleus That Project to Autonomic Preganglionic Structures
Authors: Carrasco M. , Portillo F. , Larsen P. J. , Vallo J. J.
Published: March 2003

Insulin and glucose play a key role in the control of body energy homeostasis. However, the anatomical organization of the network of central insulin and glucose sensitive areas is still unclear. In the present study, we used a multiple‐labelling technique combining retrograde tracing and Fos‐like immunohistochemistry, to analyse the anatomical projections from hypothalamic neurones activated by the combined stimulus of insulin and glucose. After intraperitoneal injections of a bolus of insulin plus glucose, Fos‐like immunoreactive neurones were observed in the paraventricular nucleus (PVN), ventromedial and arcuate nuclei, as well as the lateral hypothalamic area. In addition, neurones projecting to the autonomic preganglionic levels in the brainstem and spinal cord potentially involved in the control of glucose metabolism were identified by injections of fluorochrome tracers. Thus, Fluorogold was injected into the intermediolateral cell column of the lower spinal cord and Fast Blue was injected into the dorsal motor nucleus of the vagus. Perikarya of descending neurones were detected chiefly in the dorsal, medial and lateral parvocellular subnuclei and also in the posterior magnocellular subnucleus of the PVN. In contrast, insulin‐glucose activated neurones in the PVN were observed mainly in the medial parvocellular and posterior magnocellular subnuclei. Fluorogold/Fos double‐labelled neurones were only observed in the ventral zone of the medial parvocellular subnucleus. These data indicate that, within the PVN, there could be neurones responding to insulin‐glucose administration, which are involved in the sympathetic control of the classical regulatory structures of body energy homeostasis, such as the liver and pancreas, and which could play a role in the output of the neuronal circuitry controlling food intake.
Prevention of Glucoprivic Stimulation of Corticosterone Secretion by Leptin Does Not Restore High Frequency Luteinizing Hormone Pulses in Rats
Authors: Nagatani S. , Thompson R. C. , Foster D. L.
Published: March 2003

We have previously determined that exogenous leptin prevents the inhibition of pulsatile luteinizing hormone (LH) release in the fasting rodent. The present study tested the hypothesis that the mechanism by which leptin facilitates high LH secretion is through an attenuation of the stress response produced by a deficit in energy. Because hypogonadotropism is associated with activation of the hypothalamic‐pituitary‐adrenal (HPA) axis during both metabolic stress and nonmetabolic stress, our approach included a comparison of whether exogenous leptin could prevent the rise in corticosterone produced by a nonmetabolic stress (immobilization for 2 h), as well as by a widely used metabolic stress (transient glucoprivation by 2‐deoxyglucose, 2DG; 400 mg/kg, b.w., i.v.). Each stressor was applied to well‐fed ovariectomized rats (n = 4–6 per group), 2 h after leptin (3 µg/g, b.w., i.p.) or vehicle administration. Blood samples were collected through an indwelling atrial cannula every 6 min for 1 h before and for 2 h after the stress treatment to measure LH, leptin and corticosterone. During metabolic stress (acute glucoprivation), circulating leptin decreased, corticosterone increased and LH decreased; leptin administration abolished the increase in corticosterone, but pulsatile LH secretion remained inhibited. In contrast, during nonmetabolic stress (immobilization), leptin secretion was unaffected, but circulating corticosterone increased and LH decreased; leptin treatment did not prevent either the increase in corticosterone or the decrease in LH secretion. An important overall finding is that leptin can differentially alter the HPA axis depending upon the type of stress. In addition, whether the pattern of leptin is altered depends upon the type of stress. Although a glucoprivic‐induced decrease in endogenous leptin can be a stressor responsible for the increase in corticosterone secretion, a nonmetabolic stress‐induced increase in corticosterone is not mediated by leptin. Moreover, our results reveal that the depression of LH secretion when leptin is low during reduced energy availability is not due to activation of the HPA axis. During an energy deficit, exogenous leptin could not restore high frequency LH secretion when HPA function was restored to normal. Finally, the inability of leptin to increase LH secretion in the face of 2DG supports the notion that the action of leptin is dependent upon the degree of glucose availability.
Changes in Preoptic and Hypothalamic Levels of Progesterone Receptor mRNA Across the Oestrous Cycle of the Ewe
Authors: Scott C. J. , Pereira A. M. , Tilbrook A. J. , Rawson J. A. , Clarke I. J.
Published: March 2003

We measured the levels of progesterone receptor (PR) mRNA in the hypothalamus and preoptic area (POA) of the ewe across the oestrous cycle. Perfusion‐fixed hypothalamic tissue was collected from sheep killed during the luteal and follicular phases and during behavioural oestrus. Blood samples taken at the time of tissue collection verified that the oestrous ewes were undergoing a preovulatory luteinizing hormone (LH) surge. Matched sections were taken from the POA, periventricular nucleus (PeVN), ventromedial nucleus (VMN) and arcuate nucleus of each animal. In situ hybridization was performed using a sheep specific, 35S‐labelled riboprobe for PR and semiquantitative image analysis was conducted on emulsion‐dipped slides. The number of silver grains per cell was greater in the VMN and arcuate nucleus of oestrous ewes than in luteal and follicular phase ewes; there was no cyclic variation in the level of PR mRNA expression in the cells of the POA and PeVN. The number of labelled cells per mm2 in the VMN was higher in the oestrous ewes than in luteal phase and follicular phase ewes. The number of labelled cells in the PeVN was also higher in the oestrous ewes than in follicular phase ewes, but there was no cyclic variation in the POA and arcuate nucleus. In the ewe, the onset of behavioural oestrus corresponds to the onset of the preovulatory LH surge and increased PR mRNA expression at this time is likely to be due to the high concentrations of circulating oestrogen that precede this period.
Analysis of the Post‐Translational Processing of Chromogranin A in Rat Neuroendocrine Tissue Employing an N‐Terminal Site‐Specific Antiserum
Authors: McVicar C. M. , Cunningham R. T. , Harriott P. , Johnston C. F. , Buchanan K. D. , Curry W. J.
Published: March 2003

Chromogranin A (CgA) is a complex prohormone expressed as a constituent of the regulated secretory pathway of numerous neuroendocrine cells. Recent investigations have demonstrated that CgA is selectively cleaved to generate distinct peptides in different neuroendocrine tissues. This investigation employed a site‐specific antiserum that detects residues 98–106 rat CgA to examine the amino‐terminal processing of CgA to generate β‐granin and related peptides in rat neuroendocrine tissues. Immunohistochemistry revealed moderate to intense β‐granin‐like immunostaining in cells scattered throughout the anterior pituitary, thyroid, in the islets of Langerhans and in the mucosa of the gastrointestinal tract. Variable intensities of immunostaining were observed in distinct clusters of chromaffin cells. Quantitatively, the highest concentration of β‐granin‐like immunoreactivity was detected in pituitary extracts. Significantly lower concentrations were detected in adrenal and thyroid glands, brain, ventral and dorsal pancreatic lobes and gastrointestinal tissue extracts. Chromatography resolved three distinct β‐granin‐like immunoreactants; a large CgA‐like form, an intermediate molecular form presumably corresponding to β‐granin (rat CgA1−128) and small immunoreactants that coeluted with the synthetic peptide. Two β‐granin‐like immunoreactants, 21 and 22 kDa, were detected following immunoblot analysis of pituitary extracts. This study has demonstrated that chromogranin A is subject to distinct amino‐terminal patterns of tissue‐and cell‐specific processing to generate a β‐granin‐like immunoreactant which is additionally cleaved in pancreatic, fundic and colonic tissue to generate previously unidentified peptides.
Antagonism of Central Vasopressin Receptors Blocks Hypoglycemic Stress Induced Inhibition of Luteinizing Hormone Release in Male Rhesus Macaques
Authors: Lado‐Abeal J. , Clapper J. A. , Norman R. L.
Published: March 2003

The first objective of this study was to investigate whether the inhibitory effect of insulin‐induced hypoglycemia (IIH) on luteinizing hormone (LH) secretion was the same in unrestrained adult male rhesus macaques as has been previously reported in restrained female macaques. Since IIH did inhibit pulsatile LH secretion in adult male macaques, and some previous studies have implicated arginine vasopressin (AVP) as a central mediator of this inhibition, the second objective was to investigate whether antagonism of AVP action could reverse the IIH‐induced inhibition of LH release in males. Ten adult male rhesus macaques (Macaca mulatta) were studied during 15‐h periods (07.00–22.00 h), with blood samples collected every 15‐min. There were three experimental groups; controls (n = 5), IIH (n = 6) and IIH plus vasopressin antagonist (AVPa; n = 6). During the hypoglycemia studies, the first 5 h served as a control for that occasion and an insulin bolus of 1 U/kg was administered intravenously at 12.00 h. During the IIH plus AVPa, the vasopressin antagonist was infused intravenously from 12.00 h to 17.00 h. LH and testosterone decreased progressively after the insulin bolus in the IIH group reaching a minimum value at 4 h after the infusion. However, compared to the preinfusion levels, secretion of LH and testosterone was not suppressed by hypoglycemia in the group treated with the AVP antagonist. The present study shows that in male macaques not subjected to the psychological stress of restraint, IIH suppresses LH and testosterone secretion. This inhibition of LH release can be blocked in some animals by antagonism of central vasopressin receptors, suggesting that vasopressin is involved in the suppression of gonadotropin releasing hormone/LH release induced by hypoglycemia.
Absence of Androgen Receptor in the Growth Hormone Releasing Hormone‐Containing Neurones in the Rat Mediobasal Hypothalamus
Authors: Fodor M. , Oudejans C. B. M. , Delemarre‐van de Waal H. A.
Published: March 2003

Growth hormone (GH) secretory patterns are influenced by gonadal steroids, at least in part, through modulation of hypothalamic somatostatin and GH releasing hormone (GHRH) secretion. In the adult male rat, testosterone appears to stimulate somatostatin gene expression by acting directly on androgen receptors in somatostatin neurones. The mechanism by which gonadal status influences hypothalamic GHRH gene expression is less clear. Gonadectomy reduces GHRH mRNA expression in rats, and this reduction can be prevented by the administration of testosterone or partly by a nonaromatizable androgen. While these observations suggest that androgen receptors mediate the actions of gonadal steroids on GHRH gene expression, they do not provide any information about the location of the androgen receptors involved in this process. To determine whether GHRH neurones themselves express androgen receptors, we double immunolabelled hypothalamic sections from colchicine‐pretreated male rats. Although there was an overlap in the anatomical distribution of GHRH and androgen receptor‐containing cell bodies, none of the nearly 900 GHRH immunolabelled cells we examined in each mediobasal hypothalamus appeared to contain androgen receptors. These results suggest that GHRH‐expressing neurones are not direct targets for androgens and therefore the effects of testosterone on GHRH gene expression must be produced indirectly by some other neural or endocrine intermediary process.
Crosstalk Between Oestrogen Receptors and Thyroid Hormone Receptor Isoforms Results in Differential Regulation of the Preproenkephalin Gene
Authors: Vasudevan N. , Zhu Y.‐S. , Daniel S. , Koibuchi N. , Chin W. W. , Pfaff D.
Published: March 2003

Nuclear receptors are ligand‐activated transcription factors, which have the potential to integrate internal metabolic events in an organism, with consequences for control of behaviour. Previous studies from this laboratory have shown that thyroid hormone receptor (TR) isoforms can inhibit oestrogen receptor (ER)α‐mediated induction of preproenkephalin (PPE) gene expression in the hypothalamus. Also, thyroid hormone administration inhibits lordosis, a behaviour facilitated by PPE expression. We have examined the effect of multiple ligand‐binding TR isoforms on the ER‐mediated induction of the PPE gene in transient transfection assays in CV‐1 cells. On a natural PPE gene promoter fragment containing two putative oestrogen response elements (EREs), both ERα and β isoforms mediate a four to five‐fold induction by oestrogen. Cotransfection of TRα1 along with ERα inhibited the ERα transactivation of PPE by approximately 50%. However, cotransfection with either TRβ1 or TRβ2 expression plasmids produced no effect on the ERα or ERβ mediated induction of PPE. Therefore, under these experimental conditions, interactions with a single ER isoform are specific to an individual TR isoform. Transfection with a TRα1 DNA‐binding mutant could also inhibit ERα transactivation, suggesting that competition for binding on the ERE may not be the exclusive mechanism for inhibition. Data with the coactivator, SRC‐1, suggested that coactivator squelching may participate in the inhibition. In dramatic contrast, when ERβ is cotransfected, TRα1 stimulated ERβ‐mediated transactivation of PPE by approximately eight‐fold over control levels. This is the first study revealing specific interactions among nuclear receptor isoforms on a neuroendocrine promoter. These data also suggest that the combinatorics of ER and TR isoforms allow multiple forms of flexible gene regulations in the service of neuroendocrine integration.
Centrally Regulated Blood Pressure Response to Vasoactive Peptides is Modulated by Corticosterone
Authors: Van Acker S. A. B. E. , Oitzl M. S. , Fluttert M. F. J. , De Kloet E. R.
Published: March 2003

To investigate the role of brain glucocorticoid (GR) and mineralocorticoid receptors (MR) in centrally evoked blood pressure responses, the effects of intracerebroventricular (i.c.v.) administration of angiotensin II and vasopressin were studied in adrenalectomized rats with and without corticosterone or aldosterone replacement. Five groups were examined: (i) Adrenalectomy (ADX); (ii) ADX + a subcutaneously implanted 20‐mg corticosterone pellet (low corticosterone); (iii) ADX + 100 mg corticosterone pellet (high corticosterone); (iv) ADX + 6 µg/24 h aldosterone via Alzet minipump (Aldo); and (v) Sham adrenalectomy (Sham). Pressor responses to 150 ng angiotensin II and 50 ng vasopressin i.c.v. were determined in freely moving rats using biotelemetry. The results show that, compared to sham rats, ADX rats showed significantly reduced pressor responses. This reduction of the pressor response to angiotensin II could be reversed and even further enhanced by replacement of the ADX rats with high corticosterone concentrations. In contrast, with aldostosterone, a depressor type response was observed. Corticosterone replacement could not restore the pressor response to vasopressin. We conclude that the pressor response to centrally administered vasoactive substances is substantially attenuated by removal of the adrenals and that, in the case of angiotensin II, this is due to the lack of high concentrations of circulating corticosterone occupying both MR and GR. However, predominant MR occupancy appears to play an opposite role and attenuates the angiotensin II‐induced pressor response.
Maternal Regulation of the Hypothalamic‐Pituitary‐Adrenal Axis in the 20‐Day‐Old Rat: Consequences of Laboratory Weaning
Authors: Schmidt M. , Okimoto D. K. , Dent G. W. , Gordon M. K. , Levine S.
Published: March 2003

There is a large body of evidence that the development of the hypothalamic‐pituitary‐adrenal (HPA) system in the rat is under maternal regulation. One method used to study the influence of the dam–pup interaction in neonates and weanlings is the separation of mother and litter for 24 h. Previous studies showed that, even at the time of weaning, maternal deprivation results in a dysregulation of the HPA axis at multiple levels. However, the maternal deprivation paradigm usually includes deprivation of food and water, and it was not clear to which extent the observed effects are due to either maternal cues or dehydration and fasting. The primary purpose of the present study was to determine the role of fasting and/or maternal separation on the HPA axis at the time of weaning. Pups at 20 days after parturition are capable of self‐feeding and no longer require tactile stimulation to induce eliminative functions. The results indicated that 24 h of fasting led to increased basal levels and further increases in stress induced corticosterone secretion. Fasting also appeared to contribute to the down regulation of basal glucocorticoid receptor mRNA in the hippocampus. In contrast, abrupt weaning irrespective of fasting or dehydration resulted in a suppressed adrenocorticotropin hormone response to an injection of isotonic saline. Although there was an effect of maternal separation on corticotropin‐releasing factor mRNA in the paraventricular nucleus, this effect was further exacerbated by the absence of food. Finally, all rats that were separated from their dams showed more efficient negative‐feedback. Thus, different aspects of the HPA system appear to respond differentially to either the absence of food or the absence of the mother or both.
Vasoactive Intestinal Polypeptide Contacts on Gonadotropin‐Releasing Hormone Neurones Increase Following Puberty in Female Rats
Authors: Kriegsfeld L. J. , Silver R. , Gore A. C. , Crews D.
Published: March 2003

Successful reproduction requires precise temporal coordination among various endocrine and behavioural events. The circadian system regulates daily temporal organization in behaviour and physiology, including neuroendocrine rhythms. The main circadian pacemaker in mammals is located in the suprachiasmatic nuclei (SCN) of the anterior hypothalamus. The SCN sends direct efferents to the reproductive axis via monosynaptic projections to gonadotropin‐releasing hormone (GnRH) neurones. This communication generates circadian endocrine rhythms as well as the preovulatory luteinizing hormone (LH) surge necessary for successful ovulation. One SCN peptide thought to be important for the regulation of oestrous cycles is vasoactive intestinal polypeptide (VIP). VIP neurones from the SCN contact GnRH cells, and these cells are preferentially activated during an LH surge in rats. Unlike adult rats, prepubertal females do not exhibit oestrous cycles, nor do they exhibit an LH surge in response to oestradiol positive‐feedback. The present study was undertaken to determine the extent to which the development of a ‘mature’ reproductive axis in female rats is associated with modifications in VIP contacts on GnRH neurones. The brains of diestrus adult (approximately 60 days of age) and prepubertal (21 days of age) female rats were examined using double‐label fluorescence immunohistochemistry for VIP and GnRH, with light and confocal microscopy. Although the total number of GnRH‐immunoreactive neurones did not differ between adult and prepubertal females, adults had a significant increase in the percentage of GnRH cells receiving VIP contacts compared to juveniles. These data suggest that the development of reproductive hormone rhythms and oestrous cyclicity may be, in part, due to modifications of VIP input to the GnRH system.
Plasma Agouti‐Related Protein Level: A Possible Correlation with Fasted and Fed States in Humans and Rats
Authors: Shen C.‐P. , Wu K. K. , Shearman L. P. , Camacho R. , Tota M. R. , Fong T. M. , Van der Ploeg L. H. T.
Published: March 2003

We measured plasma concentrations of agouti‐related protein (AGRP) in humans and rats and determined whether these were affected by ingestion of a meal after fasting. In 17 healthy human subjects, the mean plasma concentration of AGRP was lower in the fed state than in the fasted state. Two hours after a breakfast meal, AGRP levels dropped by 39%. By contrast, a continued fast for 2 h increased the average AGRP concentration by 73%. In rats with diet‐induced obesity, refeeding resulted in a 50% decrease in plasma AGRP concentrations following a fasting‐refeeding protocol. Our results support the notion that plasma AGRP may serve as a biomarker for the transition from a fasted to the satiated state.
Lamprey Gonadotropin Hormone‐Releasing Hormone‐III has No Selective Follicle‐Stimulating Hormone‐Releasing Effect In Rats
Authors: Kovacs M. , Seprodi J. , Koppan M. , Horvath J. E. , Vincze B. , Teplan I. , Flerko B.
Published: March 2003

Lamprey gonadotropin releasing‐hormone (LGnRH)‐III, a hypothalamic neurohormone recently isolated from sea lamprey, was reported to have a selective stimulatory effect on follicle‐stimulating hormone (FSH) release in rats and suggested to be the mammalian FSH‐releasing factor. In this study, we determined the relative luteinizing hormone (LH)‐ and FSH‐releasing potency of LGnRH‐III compared to mammalian gonadotropin‐releasing hormone (LHRH) in normal female rats, ovariectomized (OVX) and oestrogen/progesterone substituted rats and the superfused rat‐pituitary cell system. The specificity of LGnRH‐III for the mammalian LHRH receptor was investigated by blocking the receptor with an LHRH antagonist, MI‐1544. In vitro, LGnRH‐III dose‐dependently stimulated both LH and FSH secretion from rat pituitary cells at 10−7 to 10−5 M concentrations, while LHRH stimulated gonadotropin secretion at a 1000‐fold lower doses (10−10 to 10−8 M). The difference between its LH‐ and FSH‐releasing potency was similar to that of LHRH. LGnRH‐III bound to high affinity binding sites on rat pituitary cells with a Kd of 6.7 nm, Bmax=113±27 fmol/mg protein. In vivo, LGnRH‐III also stimulated both LH and FSH secretion in a dose‐dependent manner and, similar to LHRH, induced a greater rise in the serum LH than the FSH level. In normal cycling rats, it showed 180–650‐fold weaker potency than LHRH in stimulating LH secretion and 70–80‐fold weaker effect in stimulating FSH secretion. In OVX rats, LGnRH‐III demonstrated a similarly weak effect on both gonadotropins. It was found to be 40–210‐fold less potent than LHRH regarding LH release and 50–160‐fold weaker regarding FSH release. LHRH‐receptor antagonist MI‐1544 prevented both the LH‐ and the FSH‐releasing effect of LGnRH‐III both in vitro and in vivo. These results do not support the hypothesis that LGnRH‐III might be the mammalian FSH‐releasing factor but demonstrate that it is a weak agonist for the pituitary LHRH receptor and stimulates both gonadotropins in a dose‐dependent fashion.
Expression of cAMP Response Element Binding Protein‐Binding Protein in the Song Control System and Hypothalamus of Adult European Starlings (Sturnus vulgaris)
Authors: Auger C. J. , Bentley G. E. , Auger A. P. , Ramamurthy M. , Ball G. F.
Published: March 2003

In songbirds, the initiation of song behaviour and the neural substrate of this system are highly influenced by gonadal steroids. Receptors for gonadal steroid hormones, such as androgens and oestrogens, have been localized within select nuclei of the song system. An important step in steroid receptor action is the recruitment of nuclear receptor coactivators. The coactivator, cAMP response element binding protein (CREB)‐binding protein (CBP), has been implicated in both androgen and oestrogen receptor transactivation. Although the role of CBP in transcriptional mechanisms has been widely studied, little is known about CBP expression in the brain. The association between the distribution of CBP and oestrogen receptors in the hippocampus has been related to long‐term memory. However, the distribution of brain CBP has not been related to the expression of gonadal steroid receptors in a system as relevant to reproductive behaviour as the avian song system. Western immunoblotting of European starling (Sturnus vulgaris) brain tissue reveals a band at 265 kDa. Immunohistochemical localization of CBP in starling brain indicates wide, but heterogeneous expression. CBP‐immunoreactive (CBP‐ir) cells define the boundaries of song control nuclei. In HVc (sometimes called the High Vocal Center) and the robust nucleus of the archistriatum (RA), there is a higher density of CBP‐ir cells within the boundaries of these nuclei than in adjacent neostriatum or archistriatum, for HVc and RA, respectively. We also report that the distribution of CBP‐ir cells varies among different nuclei within the song control system. CBP‐ir cells within area X (also a part of the song system) and HVc are densely packed into clusters, whereas cells can be easily discriminated in RA. CBP is also highly expressed in hypothalamic areas, indicating that areas rich in steroid receptors also contain CBP. These data suggest that CBP is important for modulating transcriptional activities in the song system and other sites in the songbird brain that express gonadal steroid receptors.
The Effects of the Phytoestrogen, Coumestrol, on Gonadotropin‐Releasing Hormone (GnRH) mRNA Expression in GT1‐7 GnRH Neurones
Authors: Bowe J. , Li X. F. , Sugden D. , Katzenellenbogen J. A. , Katzenellenbogen B. S. , O'Byrne K. T.
Published: March 2003

Phytoestrogens can produce inhibitory effects on gonadotropin secretion in both animals and humans, although little is known about the mechanisms and the role of direct action on oestrogen receptors (ER) in this process. We examined the effect of coumestrol, alone and combined with ER antagonists, on gonadotropin‐releasing hormone (GnRH) mRNA expression in GT1‐7 cells. Coumestrol was found to have an inhibitory effect compared to controls, which was blocked by R,R‐THC, a selective ERβ antagonist. These results suggest that ERβ is involved in the suppression of GnRH mRNA expression by coumestrol.
Some aspects of the tensile strength of unidirectional glass fibre–polymethyl methacrylate composite used in dentures
Authors: Vallittu P. K.
Published: March 2003

The aim of this study was to determine the tensile strength and E‐modulus of unidirectional denture glass fibre–polymethyl methacrylate (GF–PMMA) composite with various fibre contents. The experimental values of tensile strength and E‐modulus were compared with values obtained by a theoretical calculation. Autopolymerized PMMA test specimens (n = 6, per group) were reinforced with unidirectional E‐glass fibres which had been wetted in a mixture of PMMA powder and monomer liquid. After storing the test specimens for 40 days in water at 37 °C, the tensile strength and E‐modulus of the test specimens were measured. The increased amount of fibres in the PMMA matrix (up to 14·8% by weight) increased the mean tensile strength of the test specimens from 40·5 MPa to 91·2 MPa (P < 0·001) and the E‐modulus from 2057 MPa to 3751 MPa (P < 0·001). The experimental tensile strength and E‐modulus values were considerably lower than those based on the theoretical calculations. This was assumed to be due to the percentage of glass fibres unimpregnated with the PMMA resin. The presence of unimpregnated glass fibres was determined using light microscopy. The results of this study suggest that a new method of incorporating the glass fibres into the PMMA resin matrix should be developed in order to obtain a well‐impregnated fibre composite reinforcement with high durability.
The relationship between occlusal support and physical exercise ability
Authors: Ishijima  , Hirai  , Koshino  , Konishi  , Yokoyama
Published: March 2003

This study was conducted to elucidate the relationship between the presence of occlusal support in edentulous subjects and their ability for physical exercise. Ten complete dentures wearers were selected and instructed to jump vertically while standing on a force plate with and without occlusal support (i.e. dentures). On the curve recorded by the force plate (1) reaction time (latency) (2) jump elevation time and (3) maximum kicking force were analysed. The reaction time, which is an index of physical quickness, was significantly prolonged when the subjects lost their occlusal support. This result suggests that reconstruction of occlusal support at a desirable mandibular position has significance not only for the restoration of masticatory function but also for the maintenance of physical exercise.
Effectiveness of two methods of denture sterilization
Authors: Webb  , Thomas  , Harty  , Willcox
Published: March 2003

Species of Candida and in particular Candida albicans may be involved in the aetiology of denture stomatitis. Studies have shown that Candida and other oral micro‐organisms including Streptococcus gordonii are associated with denture plaque; hence denture hygiene is an important factor in the prevention and treatment of the disease. The aim of this investigation was to test in vitro the efficacy of two methods of denture sterilization: (1) microwave irradiation and (2) sodium hypochlorite soak. Twenty upper acrylic dentures were prepared for microbiological assay; 10 were inoculated with C. albicans H1 and 10 with S. gordonii LGR2. Within each group, five dentures were tested in a domestic microwave oven for optimal exposure time and temperature to ensure sterilization; the five control dentures were not microwaved. Microbiological analyses showed that the inoculated dentures became sterile after six min of irradiation at medium setting (2450 MHz, 350 W). Damage to the micro‐organisms after microwave irradiation was clearly visible by scanning electron microscopy (SEM). Following the same protocol as above, experimental dentures were soaked for 8 h in either 0·02%, or 0·0125% sodium hypochlorite solution and control dentures soaked in distilled water. Microbiological analyses showed that the experimental dentures inoculated with C. albicans H1 became sterile. By contrast, those inoculated with S. gordonii LGR2 did not become sterile, and the SEM procedures confirmed these findings. The results of this study indicate that microwaving may be a more effective method of denture sterilization than denture soaking in sodium hypochlorite. However, compared with microwaving, hypochlorite reduces the levels of residual non‐viable micro‐organisms attached to the denture surface.
Masticatory muscle responses associated with unloading of biting force during food crushing
Authors: Yoshida Kazuya
Published: March 2003

The aim of this study was to evaluate masticatory muscle responses during food crushing. Electromyograms were recorded simultaneously with mandibular movement and the sound of food fracture in eight healthy adult males at the superior and inferior heads of the lateral pterygoid muscles, the anterior belly of the digastric muscle, the temporal muscle, and the masseter muscle. After fracture of the food, silent periods of the elevator muscles and excitatory responses of the depressor muscles were observed. The latency and duration of the silent periods increased significantly with increasing incisal velocity after fracture. The mean latency of the excitatory responses of the depressor muscle was stable. After the application of anaesthetic into the temporomandibular joint capsule, the excitatory response disappeared, whereas the silent period was partly maintained. These findings suggest that the excitatory response of the depressor muscle occurs via a polysynaptic reflex arc, and that several reflex arcs are involved in the development of the silent period during food crushing. An important role for the temporomandibular joint receptors is implied.
Urinary catecholamine levels and bruxism in children
Authors: Vanderas A. P. , Menenakou M. , Kouimtzis TH. , Papagiannoulis L.
Published: March 2003

This study was performed to test the hypothesis that emotionally stressful states measured by the urinary catecholamines may affect the development of bruxism. Three hundred and fourteen children, boys and girls, aged 6–8 years were included in this study. Bruxism was recorded by a clinical examination and an interview. Positive evidence of this parafunction was defined as the presence of both historical and clinical indicators. Information concerning systemic and socio‐economic factors was collected by a questionnaire. A 24‐h urine sample was collected for each subject and analysed by the high performance liquid chromatography technique to assay the catecholamine content. Of the total of 273 children who had a complete 24‐h urine sample, 167 were identified to be with and without positive evidence of bruxism. The logistic multiple‐regression analysis was carried out to test whether the presence of bruxism was affected by the variables studied; 95% probability was used. The results showed that epinephrine and dopamine had a significant and strong association with bruxism. The data therefore provide support for the concept that emotional stress is a prominent factor in the development of bruxing behaviour.
Peri‐implant tissue health in reconstructed atrophic maxillae—report of 88 patients and 470 implants
Authors: Kaptein M. L. A. , De Lange G. L. , Blijdorp P. A.
Published: March 2003

The aim of this study was to evaluate the soft‐tissue health around 470 implants placed in the upper jaw of 88 patients with severe maxillary atrophy. All patients underwent a reconstruction procedure which included a composite bone grafting from the iliac crest to the maxillary sinus. Evaluation was performed at a mean implant lifetime of 21·6±10·9 months. The following parameters were used: probing depth, plaque‐, gingival‐, bleeding index and width of the buccal keratinized mucosa. They were calculated as means for each implant and related to the type of superstructure and the thickness of the original sinus floor. (higher or lower than 5 mm). A high percentage of bleeding on probing was observed in obviously clinically healthy peri‐implant pockets. Bleeding on probing and deeper probing depth were especially observed in the group with severe maxillary atrophy (less than 5 mm initial height of the sinus floor.) There was a significant increase in mean peri‐implant probing depth and gingiva index in overdentures versus fixed bridges. No differences were observed with respect to the width of the keratinized buccal mucosa. It was concluded that implants in the reconstructed maxilla and supporting overdentures had a higher risk for bone loss, based on the worse peri‐implant tissue health observed.
Effect of three‐liquid bonding agents on bond strength to a machine milled ceramic material
Authors: Sato K. , Matsumura H. , Atsuta M.
Published: March 2003

This study determined the bond strengths of porcelain bonding systems joined to a ceramic material, with the aim of evaluating the effect of a catalyst for silane coupling as well as that of initiators for bonding agents. Two sizes of specimen were cut from ceramic blocks (Cerec 2 Vitablocs Mark II®) and then primed with either a three‐liquid self‐curing bonding agent (Clearfil Porcelain Bond®, CPB), a three‐liquid dual‐activated bonding agent (Clapearl Bonding Agent®, CBA), or their components. Unprimed specimens were also used as controls. After conditioning, the two different sized plates were bonded together with a dual‐cured luting agent (Clapearl DC®). The specimens were stored in 37 °C water for 24 h and shear bond strengths were determined. Shear testing revealed that the greatest bond strength was generated in the group consisting of ceramic material primed with CBA and exposed for 20 s prior to luting. Bond strengths of the CPB‐primed group and the CBA‐primed group without pre‐exposure were comparable, whereas the remaining groups resulted in significantly lower bond strengths than the other three groups. The priming effect was greatly enhanced when a catalyst was used with the silane coupler as compared with the application of silane alone. The results suggest that incorporation of an initiator and a catalyst for silane coupling into the bonding agent reciprocally enhances bonding between the luting agent and the ceramic material.
Location of the hinge axis and the kinematic centre in asymptomatic and clicking temporomandibular joints
Authors: Ćatić A. , Naeije M.
Published: March 2003

The study aimed to compare the locations of the hinge axis and the kinematic centre in both clicking and non‐clicking TMJs. The six degrees of freedom optoelectronic jaw movement recording system OKAS‐3D was used to record open/close movements in 10 asymptomatic subjects and 30 subjects with a clicking joint. Movement paths of the hinge axis and the kinematic axis were calculated. A t‐test was used in the analysis of the locations of the two condylar movement reference points. Variances between the values of the hinge and the kinematic axes were compared with the F‐test. Locations of the hinge axis and the kinematic centre on the average did not differ significantly for the asymptomatic subjects at the group level (P>0·05), while individually the locations differed 4·96 mm on the average. The difference between the hinge axis and the kinematic axis was significant for the group of subjects with clicking joints (P<0·01), with the average individual level difference of 9 mm. Variances differed significantly between the coordinates of the hinge and the kinematic axes between the two groups of subjects (P<0·01). The study shows the importance of the choice of a condylar movement reference point for the study of condylar movements and suggests the use of the kinematic centre in such studies.
Surface roughness evaluation of resin modified glass–ionomers polished utilizing poly(acrylic acid) gel
Authors: Geiger S. , Ravchanukayev M. , Liberman R.
Published: March 2003

The differences in polishability of modified and conventional glass–ionomers were studied following different polishing procedures. Specimens of conventional glass–ionomer (Fuji II®), resin modified glass–ionomer (Vitremer®) and compomer (Dyract®) were prepared and polished using either Soflex® or Enhance® discs with either aluminum oxide or poly(acrylic acid) gel as polishing agents. Surface roughness of the specimens was evaluated by profilometric measurements and electron microscopic examination. It was shown that Soflex® discs manifest superior polishing effect on glass–ionomers and resin modified glass–ionomers compared to the Enhance® system, although no significant differences were found for the compomer specimens. Addition of poly(acrylic acid) gel as a polishing agent reduced surface roughness of conventional glass–ionomer and resin modified glass–ionomer specimens and did not significantly affect the compomer specimens.
Evaluation of the effect of a stabilization splint on occlusal force in patients with masticatory muscle disorders
Authors: Kurita H. , Ikeda K. , Kurashina K.
Published: March 2003

The purpose of this study was to evaluate the effect of stabilization splint therapy on occlusal force in patients with masticatory muscle disorders (MD). Six female patients with myalgia or myofascial pain participated in this study. The occlusal points and load on the dental arch in maximum clenching was measured using the computerized system with Dental Prescale® before and after the use of the splint. There were no significant changes in the number of occlusal points, mean occlusal pressure, and asymmetry in occlusal balance between before and after the use of the splint. However, there were significant differences in the extent of the area of occlusion and in the integrated occlusal loads. The integrated occlusal load converged to the normal level with the use of the splint. From the results of this study, it is suggested that the use of the stabilization splint has the effect of normalizing the occlusal force.