bluuebunny/crossref_metadata_2025_split huggingface dataset:
Melatonin Inhibits the Activation of Cyclic AMP‐Dependent Protein Kinase in Cultured Pars Tuberalis Cells from Ovine Pituitary
Authors: Hazlerigg D. G. , Morgan P. J. , Lawson W. , Hastings M. H. 
Published: September 2006

AbstractThe effect of melatonin upon the activation of the intracellular effector enzyme, cyclic AMP (cAMP)‐dependent protein kinase (PKA), was investigated in primary cultures of ovine pars tuberalis cells. Incubation of these cells with forskolin caused a rapid and dose‐dependent activation of PKA (ED50 10∼6M). When cells were incubated with forskolin and melatonin simultaneously, the activation of PKA by forskolin was dramatically inhibited. This inhibitory effect of melatonin was dose‐dependent (ED50 10−10M). Furthermore, treatment with melatonin rapidly deactivated PKA in cells prestimulated with forskolin. When pars tuberalis cell extracts were incubated with 8N3‐[32P]cAMP, an analogue of cAMP used for photoaffinity labelling of native PKA, specific binding was observed in three bands with Mr of 54, 52 and 48 kd, representing the regulatory subunits of PKA II (in phosphorylated and dephosphorylated forms) and PKA I, respectively. These results indicate that melatonin is a potent inhibitory regulator of cAMP‐mediated signal transduction in the ovine pars tuberalis, and suggest that the cellular effects of melatonin in this tissue are mediated by the dephosphorylation of specific substrate proteins.
Cortisol Exerts Site‐, Context‐ and Dose‐Dependent Effects on Agonistic Responding in Hamsters
Authors: Hayden‐Hixson Diane M. , Ferris Craig F. 
Published: September 2006

AbstractSite‐, context‐ and dose‐dependent actions of intrahypothalamic cortisol administration on the agonistic behaviors of adult male golden hamsters (n = 128 dyads) were examined. When cortisol‐treated animals were tested in paired encounters with aggressive cholesterol‐treated opponents, chronic (≥ 24 h) cortisol treatment (1 mm implants) induced significant (P < 0.05) submission in three medial hypothalamic areas (anterior hypothalamic area > medial preoptic area > ventromedial hypothalamus), but aggression in the paraventricular nucleus or third ventricle. In contrast, chronic cortisol treatment in the anterior hypothalamic area resulted in high levels of aggression during paired encounters with submissive opponents, and during territorial aggression tests with juvenile male intruders. Acute (≥ 20 min) cortisol treatment in the anterior hypothalamic area (100 nl injections) induced significant submission after 10−2 M, but significant aggression after 10−6 M microinjections in paired encounters with aggressive vehicle‐injected opponents. These findings suggest glucocorticoid‐sensitive mechanisms within the anterior hypothalamus modulate aggressive responding during intrasexual social encounters.
Immunccytochemical Localization of Angiotensinogen in Rat Brain: Dependence of Neuronal Immunoreactivity on Method of Tissue Processing
Authors: Campbell Duncan J. , Sernia Conrad , Thomas Walter G. , Oldfield Brian J. 
Published: September 2006

AbstractThere is disagreement between laboratories on the presence and location of angiotensinogen immunostaining in neuronal cells. We examined this issue by using different antisera and histological procedures to stain for angiotensinogen in brains from normal, colchicine‐treated and nephrectomized rats. Five different antisera from three laboratories were used to stain sections of paraffin‐embedded tissue, frozen sections and Vibratome sections of cerebral cortex, thalamus, hypothalamus, brainstem and cerebellum. All five antisera and all three tissue treatments were effective in showing angiotensinogen staining in glial cells, with the most intense staining being achieved in Vibratome sections. All five antisera gave identical results. Neuronal staining was also found with all antisera but mostly in paraffin‐embedded sections, with occasional light staining in frozen sections. No neuronal staining was observed in Vibratome sections. Neuronal staining was frequently perivascular, tended to have a more variable anatomical localization, and to occasionally lack bilateral symmetry in coronal sections. These results provide an explanation for the disagreement between laboratories on the presence and location of angiotensinogen immunostaining in neuronal cells. Taken together with the limited concordance between published sites of angiotensinogen and angiotensin II staining, and the recent demonstration by hybridization in situ of a specifically glial cell localization of angiotensinogen mRNA, our own results suggest a need for caution in the interpretation of neuronal staining with anti‐angiotensinogen antisera.
Effect of Hypophysectomy and Growth Hormone Replacement on Hypothalamic Growth Hormone‐Releasing Factor Messenger Ribonucleic Acid Levels
Authors: Eccleston Lynne M. , Powell John F. , Clayton Richard N. 
Published: September 2006

AbstractThe mechanisms by which the pituitary gland, and growth hormone (GH) in particular, affect growth hormone‐releasing factor (GRF) gene expression have been addressed using the technique of in situ hybridization. Anatomically matched sections through the mediobasal hypothalamus of control and hypophysectomized male rats, with or without GH hormone replacement, were analysed to obtain information on GRF mRNA levels within the arcuate nucleus and around the ventromedial hypothalamus. Hypophysectomy resulted in a 70% increase in the amount of GRF mRNA per cell (P<0.001), within neurons in the arcuate nucleus. GH replacement and T4 replacement separately partially attenuated this increase (GH replacement P< 0.001 versus hypophysectomy, T4 replacement P<0.05 versus hypophysectomy). Additionally, after hypophysectomy there was an 80% increase in the number of cells expressing the GRF gene in neurons around the ventromedial hypothalamus, when compared to shamoperated controls (P<0.01). Both GH and T4 replacement separately partially attenuated this phenomenon (P<0.01 versus hypophysectomized animals). Hypothyroidism alone did not affect GRF mRNA levels in either the arcuate nucleus or in the area surrounding the ventromedial hypothalamus. These results show that hypophysectomy increases GRF mRNA levels in two separate ways: by increasing the amount of mRNA produced per cell within the arcuate nucleus, and by increasing the number of cells expressing the gene in the area surrounding the ventromedial hypothalamus. This increase in the number of GRF mRNA‐containing cells after hypophysectomy could result from the recruitment of neurons which previously did not express the GRF gene, and may reflect the plasticity of the adult central nervous system in response to a changing endocrine environment. This could represent part of a sensor mechanism to drive the production of GRF in the arcuate nucleus in response to extreme disruption of the GRF/ GH feedback loop.
Regulation of Chromogranin A and Chromogranin B (Secretogranin I) Synthesis in Bovine Cultured Chromaffin Cells
Authors: Galindo Estelle , Bader Marie‐France , Aunis Dominique 
Published: September 2006

AbstractIn the present study we investigated the regulation of Chromogranin A (CGA) and Chromogranin B (CGB) biosynthesis in bovine chromaffin cells maintained in primary culture. Cellular proteins were labelled with [35S]methionine and the incorporated radioactivity was used as an index of the synthesis rate. The radioactivity incorporated into CGA was determined by immunoprecipitation, and that into CGB was quantified by a dot immunobinding assay using specific antibodies. Incubation of cells with carbamylcholine, nigh K+ or histamine, three potent stimulators of catecholamine secretion in chromaffin cells, increased the rate of CGA and CGB synthesis. On the other hand bradykinin, angiotensin II and prostaglandin E2, which cause little secretion, also produced an increase in both CGA and CGB synthesis. These results suggest that in chromaffin cells, the biosynthesis of chromogranins is not closely linked to the secretory activity. Inhibition of protein kinase C by sphingosine or by long‐term treatment with phorbol esters, completely abolished the synthesis of CGA and CGB induced by carbamylcholine, bradykinin and prostaglandin E2 but decreased only partially the stimulating effect of histamine. Thus, protein kinase C may not be the sole effector involved in the secretagogue‐induced modulation of Chromogranin synthesis. Forskolin, an activator of adenylate cyclase had no effect on CGA synthesis, but significantly enhanced the incorporation of radioactivity into CGB. The effect of forskolin was not modified by protein kinase C inhibitors and was additive to that induced by phorbol esters indicating that cyclic AMP did not stimulate CGB synthesis through a protein kinase C‐dependent pathway. These observations suggest that the biosynthesis of CGA and CGB in chromaffin granules is independently regulated.
Androgen‐Dependent and ‐Independent Aromatase Activity Coexists with Androgen Receptors in Male Guinea‐Pig Brain
Authors: Connolly Peter B. , Roselli Charles E. , Resko John A. 
Published: September 2006

AbstractUsing a microdissection technique we localized androgen receptors and aromatase activity (AA) in the brain of male guinea‐pigs. In addition, we evaluated the effects of castration and androgen replacement on androgen receptor dynamics and induction of AA. In the castrate animal, cytosolic androgen receptor content was highest in the basal hypothalamus, specifically in the median eminence‐arcuate nucleus (> 15 fmol mg protein 1), while lesser levels were found in the preoptic regions and amygdala. Nuclear receptor content was highest (> 150 fmol mg DNA −1) in the median eminence‐arcuate nucleus, periventricular region of the preoptic area and cortical amygdala. All regions investigated showed a significant decrease in nuclear receptors following castration and an increase with androgen replacement. However, reciprocal changes in cytosolic androgen receptors were not always evident. Aromatase activity was high in the cortical amygdala, medial amygdala, periventricular region of the preoptic area and bed nucleus of the stria terminalis. Castration and androgen replacement had significant stimulatory effects on AA in the ventral medial hypothalamus, median eminence‐arcuate nucleus, cortical amygdala and periventricular regions of the preoptic area and anterior hypothalamus. Thus, androgen receptors and AA are unevenly distributed throughout the subcortical regions of the male guinea‐pig brain and respond differently to endocrine stimuli. Our data demonstrate that AA is androgen‐dependent in some subcortical regions which contain androgen receptors. Even though nuclear receptors in all brain regions were affected by castration and dihydrotestosterone treatment, the events were not always linked to AA regulation. Due to this difference in regulation, AA may serve divergent functions in guinea‐pig brain.
Electrical Stimulation of the Basolateral Amygdala Elicits Only Growth Hormone Secretion Among Six Anterior Pituitary Hormones in the Pentobarbital‐Anesthetized Male Rat
Authors: Koibuchi Noriyuki , Kakegawa Tadao , Suzuki Mitsuo 
Published: September 2006

AbstractIn order to investigate the role of the basolateral amygdala on secretion of the adenohypophyseal hormones, the basolateral amygdala was electrically stimulated for 10 min through a chronically implanted electrode in the pentobarbital‐anesthetized adult male rat. Blood samples were withdrawn through a Silastic cannula implanted in the right atrium. Electrical stimulation of the basolateral amygdala increased plasma growth hormone, decreased plasma follicle‐stimulating hormone and suppressed the increase in plasma adrenocorticotropin. Plasma prolactin, thyroid‐stimulating hormone and luteinizing hormone were not significantly changed. These results indicate that electrical stimulation of the basolateral amygdala in the pentobarbital‐anesthetized adult male rat causes a simultaneous change in secretion of several adenohypophyseal hormones.
Neurohormonal Factors Involved in the Control of the Nocturnal Prolactin Surge that Precedes Parturition in the Rat
Authors: Grattan David R. , Averill Robert L. W. 
Published: September 2006

AbstractA nocturnal surge of prolactin (PRL) occurs in the dark period preceding parturition in the rat. The roles of oxytocin, vasoactive intestinal peptide (VIP), serotonin and the opioids in controlling the antepartum PRL surge were investigated by examining PRL secretion over the last 2 days of pregnancy in the presence of antagonists to these neurohormonal factors. Serial blood samples were collected from unanesthetized, freely moving rats via indwelling jugular cannulae, and plasma PRL was measured by radioimmunoassay. In control rats PRL levels rose in a nocturnal surge peaking at 223 ± 34 ng/ml (n = 6) at 0500 h on day 21 of pregnancy, the day of parturition. Intra‐arterial infusion of the oxytocin antagonist desGly‐NH2d(CH2)5[Tyr(Me)2, Thr4]‐OVT at a dose sufficient to completely block milk ejection (10 μg/h) had no effect on this PRL surge. Infusion of the VIP antagonist [4Cl‐D‐Phe6,Leu17]‐VIP at 2 μg/h from 2200 h on day 20 until 0500 h on day 21 significantly attenuated the antepartum PRL surge, reducing the peak to 76 ± 28 ng/ml at 0500 h on day 21 (n = 6; P<0.001). Naloxone, the opiate receptor antagonist, inhibited the antepartum PRL surge in a dose‐dependent manner. Infused at 2 mg/h naloxone partially reduced the magnitude of the PRL surge, which peaked at 128 ± 24 ng/ml at 0300 h on day 21 (n = 4; P<0.05), while at 10 mg/h naloxone totally abolished the PRL surge (n = 6; P<0.001). Injection of the serotonin synthesis inhibitor ρ‐chlorophenylalanine (250 mg/kg, sc at 1700 h on days 19 and 20 of pregnancy) increased the magnitude of the antepartum PRL surge to a peak of 327 ± 48 ng/ml at 0500 h on day 21 (n = 5), compared with 244 ± 24 ng/ml at the same time in vehicle‐injected controls (P<0.05; n = 5). The results demonstrate that the antepartum PRL surge is stimulated by an opioid mechanism, and also by VIP. Oxytocin and serotonin have no role in stimulating PRL secretion during late pregnancy.
Luteinizing Hormone Surge in Adult Female Rats After Androgen Priming
Authors: Loke D. F. M. , Ratnam S. S. , Goh H. H. 
Published: September 2006

AbstractThe effects of androgens alone and in combination with oestrogens on luteinizing hormone secretion in adult female rats were studied after 1, 2 and 4 months of priming. Each adult female rat was implanted with a Silastic capsule filled with testosterone or dihydrotestosterone alone or together with another similar capsule of oestradiol. An oestrogen challenge test was carried out in each rat after priming. Blood samples were collected before androgen priming. During the oestrogen challenge test, blood samples were collected before (0 h or day 0) and at 12, 24, 36 and 48 h after the intramuscular injection of 50 μg oestradiol vaierate for rats primed for 1 month, or daily for 5 days (days 1 to 5) for other rats. An oestrogen challenge test was also performed in two groups of untreated male and female rats which served as controls.The results indicated that long‐term androgen priming had resulted in the attenuation or total blockade of the luteinizing hormone surge which normally occurs during an oestrogen challenge test in adult female rats. This suggests that androgens may be important modulators of the luteinizing hormone surge mechanism in rats. Furthermore, the fact that the luteinizing hormone surge can be blocked by androgen priming in adult female rats suggests that the sexual dimorphic response to oestrogen feedback is not immutably imprinted in the hypothalamic‐pituitary axis as was originally proposed.
Characterization and Ontogenesis of N‐Methyl‐D‐Aspartate‐Evoked Luteinizing Hormone Secretion in Immature Female Rats
Authors: MacDonald Michael C. , Wilkinson Michael 
Published: September 2006

AbstractThe excitatory amino‐acid L‐glutamate appears to be involved in the neural regulation of puberty. We have now characterized the stimulatory effect of the glutamate agonist N‐methyl‐D‐aspartic acid (NMDA) on the secretion of luteinizing hormone (LH) in immature female rats. NMDA injections (subcutaneously) rapidly induce LH secretion (maximum at 8 min) with an ED50 of 3.25 mg/kg determined at postnatal day 30. The LH response to NMDA develops between 10 and 15 days after birth, reaches a maximum at approximately day 27 and disappears again by day 32, an age at which 80% of the rats are still prepubertal. In confirmation of work by others, we also showed that postpubertal male rats are unresponsive to NMDA. The effect of NMDA on LH release is blocked by prior injection of the glutamate antagonist MK‐801 (0.1 mg/kg). MK‐801 alone is able to reduce LH secretion in acutely ovariectomized rats but has little effect in intact, prepubertal rats. NMDA may not act exclusively on the gonadotropin‐releasing hormone neuron since inhibition of norepinephrine biosynthesis by the drug U‐14,624 largely prevents NMDA‐induced LH secretion. Interestingly, rats treated neonatally with the neurotoxin monosodium glutamate responded normally to NMDA when tested at postnatal day 25. Finally, removal of the ovaries 48 h previously reduced the LH response to NMDA. Full responsiveness was restored following estrogen priming. In summary, hypothalamic glutamate receptors of the NMDA subtype comprise a significant regulatory component of LH secretion in prepubertal female rats. LH responsiveness appears to be age‐, dose‐, estrogen‐ and norepinephrine‐dependent.
Corticotropin‐Releasing Factor Binding Sites Undergo Axonal Transport in the Rat Vagus Nerve
Authors: Mercer J. G. , Lawrence C. B. , Copeland P. A. 
Published: September 2006

AbstractCorticotropin‐releasing factor (CRF) binding sites were found to be present in the rat vagus nerve and underwent axonal transport. Binding sites accumulated on both sides of ligatures placed on the nerve and at similar rates following ligation of right or left cervical vagal trunks of either male or female rats. CRF binding sites also accumulated proximal and distal to ligatures on subdiaphragmatic vagal trunks. Binding was specific, reversible and inhibited by the CRF receptor antagonist α‐helical‐CRF(9–41). [125l]Tyr0‐ovine‐CRF binding to rat vagus nerve was not guanine nucleotide‐sensitive. CRF and cholecystokinin binding sites were transported at a similar rate in the cervical vagus, although turnover of CRF binding sites was more rapid. No differences in CRF binding site transport were observed between Zucker rats of lean or obese genotype.
Further Evidence that Most Luteinizing Hormone‐Releasing Hormone Neurons are not Directly Estrogen‐Responsive: Simultaneous Localization of Luteinizing Hormone‐Releasing Hormone and Estrogen Receptor Immunoreactivity in the Guinea‐Pig Brain
Authors: Watson Robert E. , Langub M. Chris , Landis John W. 
Published: September 2006

AbstractGonadotropin secretion from the pituitary is regulated in large part by steroid action on the brain. An important question concerns whether luteinizing hormone‐releasing hormone (LHRH) neurons themselves transduce steroid signals, or whether, alternatively, steroid‐sensitive interneuronal populations regulate their activity. A previous study in the rat employing steroid autoradiography combined with LHRH immunocytochemistry revealed that only an exceedingly small percentage of LHRH‐immunoreactive (ir) neurons was estrogen concentrating. This study has examined the relationship of estrogen receptive and LHRH‐ir cells in the male and female guinea‐pig brain with double label immunocytochemistry. Since estrogen receptor‐ir, as demonstrated with antibody H222, is known to be confined predominantly to the cell nucleus, whereas LHRH‐ir is localized mainly in the cytoplasm, single cells can be double‐labeled. Diaminobenzidine tetrahydrochloride was used for localization of LHRH‐ir while nickel‐enhanced diaminobenzidine tetrahydrochloride was used for localization of estrogen receptor‐ir. The results revealed that there were many brain nuclei that contained both LHRH and estrogen receptor‐positive cells, including the preventricular periventricular nucleus, the anterior subcompact nucleus of the medial preoptic nucleus (MPNa), the remainder of the medial preoptic nucleus, the retrochiasmatic area, and the anterior, dorsomedial, ventrolateral and arcuate nuclei. However, of a total of 2,604 LHRH‐ir cells that were examined, we observed only 5 double‐labeled cells (<0.2%). The double‐labeled cells were not restricted to a single nucleus; they were present in the MPNa, the retrochiasmatic area and the arcuate nucleus. Moreover, at the light microscopic level, LHRH cells quite frequently appeared to be apposed to estrogen receptor‐positive cells (8.8% in the female), especially in the MPNa. These results lend further support to the notion that estrogen‐mediated regulation of the LHRH system is achieved primarily through estrogen receptive interneurons. However, due to the existence of LHRH‐LHRH synaptic interactions, the possibility also exists that a small population of estrogen‐sensitive LHRH neurons could contribute to generalized activation of the LHRH system.
Differential Regulation of Luteinizing Hormone‐Releasing Hormone and Galanin Messenger Ribonucleic Acid Levels by Alpha1Adrenergic Agents in the Ovariectomized Rat
Authors: Weesner Gary D. , Bergen Hugo T. , Pfaff Donald W. 
Published: September 2006

Abstractα1‐Adrenergic control of luteinizing hormone‐releasing hormone (LHRH) and galanin mRNA levels was examined in ovariectomized rats. Each rat was ovariectomized and a permanent bilateral cannula was implanted 1 mm dorsal to the preoptic area. Eleven to 14 days later, each rat received one of three treatments: prazosin (α1 antagonist, n = 8), methoxamine (α1 agonist, n = 5) or control (no drug, n = 7). Each drug was suspended in a polyacrylamide gel matrix and delivered to the preoptic area via the bilateral cannula. After 24 h of continuous exposure to the adrenergic agents (or control), rats were anesthetized, decapitated and brains were stored in liquid nitrogen until sectioned (7 μm) on a cryostat. In situ hybridization was performed using a [32P]‐end‐labelled 59mer complementary to LHRH mRNA. Reduced silver grains, proportional to LHRH mRNA content, were quantified for number of LHRH cells per section, number of grains per labelled cell and total number of grains in labelled cells. Compared to the controls, prazosin caused a 32% decrease (P<0.05) in the number of cells expressing the LHRH gene. The LHRH cells from untreated animals had a median of 53 grains/cell with a smooth distribution above and below the median. Treatment with prazosin reduced the median number of grains/cell to 36 (P<0.05). When the number of grains in labelled cells were totalled, prazosin decreased (P<0.01) the number of grains by 47%. Surprisingly, methoxamine caused no quantitative changes in any of the parameters examined. This might be explained if LHRH transcription in control animals was proceeding at near‐maximal rates supported, in part, by an endogenous α1 ligand. Alternatively, continuous exposure to this agonist may have resulted in desensitization to its stimulatory effects. When anatomically matched brain tissue sections from these animals were examined for galanin mRNA, no differences among experimental groups were detected. In conclusion, administration of an α1‐adrenergic antagonist into the preoptic area suppressed levels of LHRH mRNA but not galanin mRNA. Therefore, the data suggest that an endogenous α1 ligand, such as norepinephrine (or epinephrine), is required to maintain a high level of LHRH gene expression in the ovariectomized rat.