bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of Chronic Treatment of Rats with Dopamine Receptor Drugs on the Post‐Translational Processing of Beta‐Endorphin in the Neurointermediate Lobe of the Pituitary Gland
Authors: Sweep C. G. J. (Fred) , Wiegant Victor M. 
Published: September 2006

AbstractTo investigate whether chronic changes in the activity of proopiomelanocortin cells in the neurointermediate lobe (NIL) of the pituitary gland are associated with changes in the enzymatic processing of β‐endorphin (βE), the effects of treatment of rats with the dopamine receptor antagonist haloperidol or the dopamine receptor agonist bromocriptine (2.5 mg.kg−1 sc, once daily for 21 days) were studied on the content of βE‐related peptides in the NIL and on the release of these peptides from NILs in an in vitro superfusion system. Treatment with haloperidol increased, and with bromocriptine decreased the tissue content and the release of Nα‐acetyl‐, β‐, γ‐ and α‐endorphin‐immunoreactivity (AcE‐, βE‐, γE, and αE‐IR). The endorphin‐IR was further characterized using reversed‐phase high‐performance liquid chromatography and specific radioimmunoassay systems, and the following peptides were identified: des‐tyrosine α‐endorphin (DTαE), αE, AcαE, γE, AcγE, βE‐(1–31), AcβE‐(1–31), AcβE‐(1–27), AcβE‐(1–26) and βE‐(1–26)/βE‐(1–27) (the latter peptides were not separated with the high‐performance liquid chromatography system used). Analysis of NIL superfusates indicated that all peptides found in the tissue were released in vitro. In addition, an as yet unidentified acetylated IR‐endorphin component was found which was not observed in extracts of NIL tissue, and therefore was probably formed during release. Following haloperidol treatment, the levels of all βE‐related peptides detected were increased in the tissues as well as superfusates, the increase in AcβE‐(1–27) being most and that in βE‐(1–26)/βE‐(1–27) least pronounced. Following bromocriptine treatment, the concentrations of all peptides in tissues and superfusates were decreased as compared to vehicle controls. The acetylated endorphins, in particular AcβE‐(1–27), were most affected and βE‐(1–26)/βE‐(1–27) least affected. The results indicate that chronic modulation of the synthesizing and secretory activity of proopiomelanocortin cells in the NIL is parallelled by changes in the enzymatic processing of βE.
The Characteristics of Medial Septal Neurons Antidromically Identified as Projecting to the Median Eminence and their Response to Gonadal Steroids
Authors: Donevan Sean D. , Ferguson Alastair V. 
Published: September 2006

AbstractWe have obtained extracellular single unit recordings from 129 neurons in the medial septum of the male rat that projected to the median eminence. These cells were identified on the basis of their antidromic responses to electrical stimulation in the median eminence. The antidromically‐evoked spike was always followed by a period of inhibition (−100 ms) which often (80%) persisted at stimulus intensities below threshold for antidromic activation. The identified neurons displayed one of three patterns of activity, the relative proportions of which were dependent upon the anesthetic. In rats anesthetized with urethane, 15% of the antidromically identified septal neurons displayed an oscillating, 25% a continuous, and 61% a low irregular pattern of spontaneous activity or no activity. In contrast, in barbiturate‐anesthetized animals only 6% exhibited an oscillating and 3% a continuous pattern of activity. The remaining neurons (91%) displayed either a low firing rate or were silent. We then assessed the responses of these identified neurons to systemic administration of gonadal steroids. Systemic administration of 17β‐estradiol elicited a rapid decrease in the firing rate of 9 of 29 neurons tested. The inhibitory response was specific to those cells displaying an oscillating (6/9) or continuous (3/6) firing pattern of which 60% were inhibited. In contrast, systemic administration of testosterone failed to elicit such changes in the activity of the identified septal neurons (n = 12) including one neuron which was subsequently shown to be inhibited by estradiol. As such identified septal neurons may contain gonadotropin‐releasing hormone, these results suggest a role for estradiol but not testosterone in the short‐term regulation of the secretion of this releasing hormone in the male rat.
Gonadotropin‐Releasing Hormone and Thyrotropin‐Releasing Hormone Regulation of G Protein Function in the Rat Anterior Pituitary Lobe
Authors: Ravindra R. , Aronstam R. S. 
Published: September 2006

AbstractIn order to evaluate the role of guanine nucleotide‐dependent transducer proteins (G proteins) in hormone‐mediated signal transduction in the anterior pituitary lobe, we examined the effect of gonadotropin‐releasing hormone (GnRH) and thyrotropin‐releasing hormone (TRH) on two parameters of G protein function, namely [35 S]GTPγS binding and low KmGTPase activity. Plasma membranes were prepared from anterior pituitary lobes of adult male rats using conventional procedures. GTP binding was determined by incubating 2 to 5 μg membrane protein with approximately 100,000 cpm [35 S]GTPγS in a buffer containing 20 mM Tris‐ HCl, 1 mM EDTA, 1 mM dithiothreitol, and 100 mM NaCI at a pH of 7.4 for 10 or 15 min at 37 °C GnRH agonist and TRH stimulated high affinity [35 S]GTPγS binding in a concentration‐dependent manner. GTP binding was maximally stimulated by GnRH agonist (1 μM) and TRH (0.1 μM) by up to 27% and 34%, respectively. A time‐course study revealed that 1 μM GnRH agonist stimulated GTP binding by 30% at 15 min; 0.1 μM TRH stimulated GTP binding by 23% at 1 min, 18% at 5 min and 25% at 10 min. A stable GTP analog, 5′‐guanylylimidodiphosphate, inhibited GnRH‐ as well as TRH‐stimulated GTP binding. GnRH antagonist did not affect GTP binding. However, in the presence of the antagonist, stimulation of GTP binding by the GnRH agonist was completely blocked.The low KmGTPase activity (EC 3.6.1.‐), another parameter of G protein function, was assayed in 2 to 5 μg membrane protein using [γ‐32 P]GTP at 37 °C in an ATP‐regenerating buffer containing 1 μM unlabeled GTP. GnRH agonist (0.1 μM) and TRH (1 μM) maximally stimulated this GTPase activity by up to 50% and 40%, respectively. GnRH agonist (1 μM) stimulated the GTPase activity by 30% at 10 min and 48% at 30 min. TRH (1 μM) stimulated the GTPase activity at all time points monitored; stimulation was 46% at 5 min, 49% at 20 min, and 41% at 30 min. Interestingly, the GnRH antagonist stimulated GTPase activity by about 20%, but inhibited GnRH agonist‐stimulated GTPase activity in a concentration‐dependent manner. These results indicate that the binding of GnRH and TRH to their receptors results in interaction of the receptor with a G protein and activation of the G protein cycle.
Pituitary Binding Sites for Gonadotrophin‐Releasing Hormone in Booroola Merino Ewes which were Non‐Carriers or Homozygotes of the Fecundity Gene F
Authors: Fleming J. S. , Lun S. , Smith P. , McNatty K. P. 
Published: September 2006

AbstractPituitary binding sites for gonadotrophin‐releasing hormone (GnRH) were examined in Booroola ewes on Days 4 and 12 of the oestrous cycle and more than 12 months after ovariectomy. No significant differences were observed in the affinity of the binding sites for [125 I]D Ala6, des Gly10 GnRH ethylamide, in non‐carriers (++) or homozygotes of the fecundity gene (FF), in intact or ovariectomized animals (overall Ka= (1.8 ± 0.1) × 109 M−1; mean ± SEM, n = 67). In ++ ewes, the number of GnRH binding sites on Day 4 of the oestrous cycle (0.199 ± 0.025 fmol/mg pituitary, n = 8) was significantly greater (P<0.05) than on Day 12 (0.107 ± 0.012 fmol/mg pituitary, n = 12). In contrast in FF ewes the number of binding sites on Days 4 and 12 were similar (Day 4: 0.119 ± 0.030, n = 8; Day 12: 0.092 ± 0.014, n = 10). On Day 4, but not Day 12, the binding site numbers were significantly higher in ++ compared with FF pituitaries (P<0.05). Likewise on Day 4, but not Day 12, the plasma concentrations of follicle‐stimulating hormone were significantly higher (P<0.005) in FF (1.60 ± 0.15 ng/ml) than ++ ewes (0.96 ± 0.10 ng/ml). After ovariectomy, no gene‐specific differences in binding site numbers were noted despite significantly higher plasma follicle‐stimulating hormone concentrations in FF animals. No gene‐specific differences in plasma luteinizing hormone concentrations were observed in these animals on Days 4 or 12, or after ovariectomy. Moreover, luteal phase plasma progesterone concentrations were also similar between ++ and FF ewes. We conclude that the gene‐specific differences in pituitary responsiveness to GnRH and in pituitary gonadotrophin output are unlikely to be due to differences in GnRH receptor binding affinities.
Estradiol Regulation of Estrogen Receptor Messenger Ribonucleic Acid in Rat Mediobasal Hypothalamus: An in situ Hybridization Study
Authors: Lauber Andrea H. , Romano Gary J. , Mobbs Charles V. , Pfaff Donald W. 
Published: September 2006

AbstractWe have used in situ hybridization to investigate estradiol regulation of estrogen receptor (ER) mRNA in regions of the mediobasal hypothalamus which contain ER and are related to specific neuroendocrine functions. Ovariectomized rats were treated with oil or 10 μg estradiol benzoate for 2, 4, 18 or 24 h. Brains were sectioned and hybridized with a [3 H]single‐stranded DNA probe prepared from the pORF cDNA of the human ER gene and exposed to autoradiographic emulsion for 4 months. Specificity of labeling was determined by counting the number of grains over cells in hypothalamic regions known to bind estradiol, compared to cells in the thalamus and cortex, and by comparing with sections pretreated with ribonuclease or hybridized with a [3 H]single‐stranded message‐sense (control) probe. Labeling for ER mRNA was distributed differently than glucocorticoid and thyroid hormone receptor mRNAs, and was regulated by estrogen differently than progestin receptor mRNA. These differences indicated specific hybridization for ER mRNA. ER‐expressing cells constituted 11.5% of the cells in the dorsomedial nucleus, 30% of the cells in the arcuate nucleus and 43% in the ventromedial nucleus, in close accordance with previous studies of ER autoradiography and binding. Quantitative analysis showed that the highest level of ER mRNA was present in the ovariectomized controls. ER mRNA levels fell 42% (ventromedial), 64% (arcuate), or remained unchanged (dorsomedial) 18 h following estradiol benzoate treatment. The pattern of decrease was similar for cells in the ventromedial nucleus and arcuate nucleus. These data show that estrogen regulation of ER mRNA in brain parallels that reported for MCF‐7 cells and rat uterus. These results also demonstrate that in situ hybridization can be used to detect and measure the relative level of a low abundance mRNA in a heterogeneous tissue in which only 12% to 40% of the cells in limited regions express the message.
Sex Differences and Steroid Control of Testosterone‐Metabolizing Enzyme Activity in the Quail Brain
Authors: Balthazart J. , Schumacher M. , Evrard L. 
Published: September 2006

AbstractThe activity of three testosterone‐metabolizing enzymes (aromatase, 5α‐reductase and 5β‐reductase) was determined in the quail brain using the Palkovits punch technique combined with a very sensitive radioenzyme assay. Sex differences and the effects of gonadectomy and testosterone treatment on the activity of the three enzymes were quantified in eight brain nuclei which are implicated in the control of various aspects of reproductive behavior and physiology. The aromatase was only present in a few brain areas in which its activity was strongly controlled by testosterone. In two brain regions (medial preoptic nucleus and preoptic area in general) the activity of the enzyme was higher in males than in females. These sex differences disappeared in gonadectomized birds and in gonadectomized birds treated with testosterone, suggesting that they might only result from different circulating steroids in both sexes. However, in the posterior part of the medial preoptic nucleus, there was a strong tendency for the induction of aromatase by testosterone to be larger in males than in females. This supports our earlier finding that in the preoptic area, the aromatase activity is sexually differentiated. This difference probably has a restricted neuroanatomical localization and could only be demonstrated by more precise anatomical methods such as immunocytochemistry. The two testosterone reductases (5α and 5β) showed a more homogeneous distribution in the brain. They were not affected by the hormonal treatments or the sex of the birds except for the 5β‐reductase which was significantly more active in three brain nuclei of the females (ventromedial nucleus of the hypothalamus, area hypothalamica lateralis and tuber) by comparison with the males. These sex differences were maintained irrespective of the hormonal status of the birds suggesting that they might be organizational in nature. The relation of these enzymes and their regulation to the control of reproduction is discussed and the usefulness of this approach combining punch technique and radioenzyme assay is evaluated.
Beta‐Adrenergic Stimulation Decreases Glial and Increases Neural Contact with the Basal Lamina in Rat Neurointermediate Lobes Incubated in vitro
Authors: Smithson K. G. , Suarez I. , Hatton G. I. 
Published: September 2006

AbstractPhysiological stimuli such as dehydration and lactation/suckling of the young have been found to induce reversible changes in the relationships of neural and glial elements with the basal lamina of the neurohypophysis. Such stimulation is associated with a decline in the extent of basal lamina occupied by glial processes and an increase in nerve terminals abutting the lamina. One possible mechanism playing a role in these changes is the activation of beta‐adrenergic receptors on the neurohypophysial glia (the pituicytes), since such cells in primary culture from adult rats undergo dramatic morphological transformation when stimulated with beta‐adrenergic agonists. We sought to determine if changes similar to those seen in vivo and predicted from the responses of cultured cells would occur with beta‐adrenergic stimulation of the isolated neurointermediate lobe in vitro. Neurointermediate lobes from adult male rats were incubated in artificial cerebrospinal fluid containing ascorbic acid alone (control) or in the same medium with either 10−8, 10−7 or 10−5 M isoproterenol for 15 min after a 30‐min period of preincubation in control medium. Quantitative ultrastructural analysis revealed significant decreases in pituicyte and, corresponding increases in neural, membrane abutting the basal lamina at the lower two drug concentrations. These results support the findings of other studies suggesting a beta‐adrenergic mediation of pituicyte morphology and a role for beta‐receptors in control of posterior pituitary function.
The Olfactory Bulbs Tonically Inhibit Serum Gonadotropin and Prolactin Levels in Male Hamsters on Long or Short Photoperiod
Authors: Pieper David R. , Lobocki Catherine A. , Thompson Melinda , Subramanian Marappa G. 
Published: September 2006

AbstractBilateral removal of the olfactory bulbs (BX) inhibits the testicular regression associated with maintenance of golden hamsters on short photoperiod (10L:14D). The present study was done to examine the reproductive endocrine changes following BX of hamsters, to test whether BX increases gonadotropin secretion by enhancing the rate of metabolism of peripheral testosterone, and to determine whether BX inhibits the response to photoperiod by blocking chemosensory signals from conspecifics.BX resulted in a marked increase in tonic serum gonadotropin levels in pre‐pubertal (23 days old) and adult hamsters maintained on long photoperiod (14L:10D). Maintenance on 10L14D inhibited gonadotropin secretion in BX hamsters, but this only reduced the previously elevated levels to those of the sham group on stimulatory photoperiod, and the testes therefore remained large.BX hamsters on 10L:14D had a higher post‐castration increase in serum luteinizing hormone than sham‐operated hamsters. Following testosterone replacement (20 mm Silastic capsules), BX animals had lower serum testosterone and higher serum follicle‐ stimulating hormone levels than the sham group. BX hamsters had a shorter mean half‐time for disappearance of testosterone from serum following removal of the capsule, but some animals in the sham group also metabolized testosterone rapidly.Isolation in cages receiving air filtered to remove pheromonal type molecules did not affect the rate or degree of testicular regression in response to short days.We conclude that the olfactory bulbs tonically inhibit gonadotropin release in golden hamsters on long or short photoperiod. The olfactory bulbs may facilitate the negative feedback of testosterone and may inhibit testosterone metabolism, but there were also steroid‐independent effects. The influence of the olfactory bulbs on the hamsters' response to short days is apparently not related to chemosensory information from other hamsters.
The Olfactory Bulbs Enhance Reproductive Hormone Secretion in Male Rats on Long or Short Photoperiod
Authors: Pieper David R. , Lobocki Catherine A. , Thompson Melinda , Subramanian Marappa G. 
Published: September 2006

AbstractUnlike seasonally breeding species such as the Syrian hamster, Sprague‐Dawley laboratory rats do not normally respond to short photoperiod (6L18D) with reproductive regression. However, removal of the olfactory bulbs (BX) unmasks a photoperiodic response in pre‐pubertal rats so that blinding or short photoperiod results in an inhibition of reproductive hormone secretion and/or a delay in pubertal development. This is apparently mediated by pineal melatonin which inhibits gonadotropin and/or prolactin secretion, but the mechanism by which BX facilitates the response to photoperiod is not clear.Experiment I was performed to determine serum levels of reproductive hormones at frequent intervals following BX and/or maintenance on short days. Twenty‐three‐day old male rats were BX or underwent sham BX (SH). They were thereafter maintained on a 14L:10D (long photoperiod) or 6L:18D photoperiod for the duration of the study. At 6 weeks following surgery, BX rats on either photoperiod had smaller testes than the SH groups. At week 8, the BX group on 6L:18D had smaller testes than the other three groups. There were transient reductions in serum luteinizing hormone and follicle‐stimulating hormone in the BX rats on short photoperiod, but there were prolonged effects of BX decreasing prolactin levels in rats on long or short photoperiod. In SH rats, testosterone was elevated for weeks 6 through 10 of the study, and BX blocked this increase.Experiment II was performed to determine whether BX alters testosterone feedback on gonadotropin secretion. Twenty‐three‐day old male rats were BX or underwent SH operation and were then returned to a room on 14L10D. Six to 8 weeks later, all animals were castrated and placed on 6L18D or returned to 14L:10D. Eight weeks following castration, the rats were implanted with Silastic capsules containing 0, 10, 20 or 40mm testosterone. The post‐castration increase in serum luteinizing hormone and follicle‐stimulating hormone was lower in the BX than SH rats. In long photoperiod, serum luteinizing hormone and follicle‐stimulating hormone were often lower in the BX rats receiving no testosterone replacement or lower doses of testosterone than in the SH group receiving similar capsules. Maintenance on short photoperiod increased the responsiveness to testosterone so that even the rats receiving low doses of testosterone had very low luteinizing hormone and follicle‐stimulating hormone levels whether they were SH or BX.In summary, BX rats on long or short photoperiod had lower serum prolactin and testosterone levels than the comparable SH group and BX inhibited the post‐castration increase in gonadotropin secretion. The data therefore suggest that the olfactory bulbs tonically enhance reproductive hormone secretion (especially around the time of pubertal development).
Autoradiographic Localization of Insulin‐Like Growth Factor I Binding Sites in the Bovine Adrenal Gland and on Cultured Bovine Adrenal Chromaffin Cells
Authors: Marley Philip D. , Haynes Kerry M. , Wertherf George A. , Perlman Robert L. 
Published: September 2006

AbstractPrevious studies have reported the presence of binding sites for insulin‐like growth factor I (IGF‐I) in membranes prepared from isolated bovine adrenal medullary cells, and IGF‐I was found to regulate the secretory function of bovine chromaffin cells. In the present study, binding sites for IGF‐I have been localized in sections of bovine adrenal gland and on cultured bovine adrenal medullary cells, using [125 l][Thr59]‐IGF‐l as the ligand in conjunction with qualitative autoradiographic techniques. Binding sites were present throughout the adrenal gland and were distributed evenly over all cortical cell layers and over both adrenaline and noradrenaline cell types in the medulla. They were also present at lower density over blood vessels and nerve bundles and over the capsule. The binding of radioligand was to a single class of sites with Kd 0.61 nM, and was completely displaced by excess unlabelled [Thr59]‐IGF‐l and by insulin (Actrapid, Kd 1.04μM). Binding sites were also identified on single cells in primary monolayer cultures of bovine adrenal medullary cells. More than 96% of the cells possessed binding sites, although only 85% of such cells were chromaffin cells, as previously determined from dopamine β‐hydroxylase immunohistochemical staining. The results suggest that IGF‐I may affect the maturation, growth or function not only of adrenal chromaffin cells but also of many others cell types in this tissue.
6‐Hydroxydopamine Lesion of Ventral Tegmental Area Dopaminergic Cell Bodies does not Impair Neuroendocrine Responses to Environmental Stimuli
Authors: Rivet Jean‐Michel , Stinus Louis , Le Moal Michel , Mormède Pierre 
Published: September 2006

AbstractTo evaluate the influence of dopamine neurons in neuroendocrine responses to environmental stimulations, rats received bilateral injections of the neurotoxin 6‐hydroxydopamine in the ventral tegmental area. Six weeks after the lesion, forebrain areas lost up to 88% of their dopamine content, and the areas innervated by the noradrenergic bundle, which passes through the ventral tegmental area, were also depleted of noradrenaline. Despite these profound changes of catecholamine content, we show that the responses of major neuroendocrine systems to environmental stimuli were not modified. Basal levels of circulating adrenocorticotropin, corticosterone, prolactin and catecholamines, as well as their increase by novel environment exposure, handling and/or electric footshock, were not modified by the lesion. These results favor the hypothesis that the effect of dopamine depletion is more on behavioral response initiation and/or performance than on the cognitive functions or emotional processes. They also question the importance of the ventral noradrenergic bundle in the activation of the hypothalamo‐pituitary‐adrenal axis by stressful stimuli.