ISSN:0028-3835    

DOI:10.1159/000126686

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

The mouse GT1 gonadotropin-releasing hormone (GnRH) neuronal cell lines exhibit highly differentiated properties of GnRH neurons. This report investigates the direct effect of γ-aminobutyric acid (GABA) and subtype selective GABA agonists on GnRH secretion by GT1 cells in perifusion. Treatment of GT1-1 cells with GABA (10 µM) for 100 min resulted in a biphasic release of GnRH. A rapid and sharp stimulation of GnRH secretion was followed by a sustained inhibition of GnRH secretion. During the inhibitory phase, pulses of GnRH assessed by ‘cluster analysis’ were totally suppressed. The GABAA receptor agonist muscimol (10 µM) stimulated a rapid but transient release of GnRH. On the other hand, treatment of GTM cells with the GABAB receptor agonist baclofen (10 µM) resulted in the prolonged inhibition of GnRH secretion which returned to normal after the treatment stopped. These results demonstrate a direct biphasic effect of GABA upon GnRH release. The initial stimulation appears to be mediated via GABAA receptors, while the sustained inhibition of GnRH secretion appears to involve the activation of GABAB re

ISSN:0028-3835    

DOI:10.1159/000126687

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

Whether estrogen has the brain as a site of its negative feedback action was investigated by checking the acute effect of estradiol-17β (E2) on the electrical activity of the luteinizing hormone-releasing hormone (LHRH) pulse generator in ovariectomized rats fitted with chronically implanted electrode arrays in the medial basal hypothalamus. Before subcutaneous E2 implantation, the hypothalamic multiunit activity (MUA) exhibited, at an average frequency of 2.43/h, characteristic increases (volleys), each of which was associated with the initiation of an LH pulse. Within 2 h after E2 implantation, the frequency of MUA volleys was reduced significantly, probably associated with decreases in the frequency of LH pulses. The decrease in the amplitude of LH pulses occurred later than 2 h, but this effect was considered not to be mediated by the brain since the duration of MUA volleys was not changed. Since the mean serum LH concentration started to decrease within 2 h after E2 implantation, it was concluded that the acute inhibitory E2 effect on LH release is mediated by the brain. On the day after E2 implantation, intravenous infusion of naloxone (2 mg/kg/h) promptly elicited intermittent MUA volleys each of which was associated with an LH pulse. This suggests that operation of the LHRH pulse generator in the ovariectomized condition is restrained by the action of E2 with the mediation of endogenous opioid peptide neurons

ISSN:0028-3835    

DOI:10.1159/000126688

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

Exogenous administration of the neuropeptide oxytocin reliably facilitates sexual behavior in the female rat and exposure to estrogen increases oxytocin receptor (OTR) binding in the ventromedial nucleus (VMN) of the hypothalamus. We have used a novel approach to investigate the role of hypothalamic OTR in controlling behavior by infusing antisense oligodeoxy-nucleotides (oligo) to the 5’-region of the human OTR mRNA into the VMN of hormonally primed rats. Control infusions consisted of a scrambled-sequence oligo that had little or no homology to known mRNAs. OTR antisense oligo infusion significantly reduced lordosis frequency and intensity in females primed with estrogen. There was also a significantly greater number of rejection behaviors exhibited by antisense-oligo-infused estrogen-treated females versus controls and no evidence of decreased locomotion by either treatment. In contrast to the effects in estrogen-primed-females, when females were primed to be sexually receptive with estrogen plus progesterone, OTR antisense-oligo infusion had no effect on sexual behavior. The lack of effectiveness of OTR antisense oligo in females primed with progesterone may be the result of the action of this steroid on other neurotransmitter systems that also facilitate lordosis and thereby override a deficit in oxytocin binding. Alternatively, via previously described mechanisms, progesterone may enhance the effectiveness of oxytocin binding at its receptor. In vitro receptor autoradiography in estrogen-primed females indicated a 31% reduction in VMN OTR binding in the vicinity of the cannula tip in antisense-oligo-infused females compared to controls. There was no significant difference in the level of OTR binding in the central nucleus of the amygdala. In addition, OTR antisense-oligo-infused females exhibited a significant reduction in food intake as demonstrated by weight loss and a reduced appetite for sweetened milk compared to scrambled-oligo-infused controls. Since VMN damage results in increased food intake, these results indicate a lack of damage to the VMN as a result of the OTR antisense infusion

ISSN:0028-3835    

DOI:10.1159/000126689

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

Increased growth hormone-releasing factor messenger ribonucleic acid (GRF mRNA) and decreased somatostatin (SRIF) mRNA levels have been reported in the hypothalamus of hypophysectomized rats as well as of dwarf mice. In order to elucidate the effect of the growth hormone-insulin-like growth factor I (GH-IGF-I) axis on hypothalamic GRF and SRIF synthesis, we measured levels of mRNA coding for GRF and SRIF and for pituitary GH in pubertal male rats treated for 3 weeks with antirat GRF γ-globulin (GRF-ab), anti-SRIF γ-globulin (SRIF-ab) or both. Immunoneutralization of circulating endogenous GRF resulted in a marked decrease in serum IGF-I and pituitary GH mRNA levels in Northern blot analysis, whereas it caused a significant increase in GRF mRNA levels in the arcuate nucleus as assessed by both Northern blot and in situ hybridization analysis. SRIF mRNA levels in the periventricular nucleus were slightly decreased by GRF-ab treatment when analyzed by in situ hybridization, but not significantly after Northern blot analysis. Immunoneutralization of circulating endogenous SRIF failed to affect mRNA levels of hypothalamic GRF and SRIF but caused a slight reduction in pituitary GH mRNA levels. Levels of mRNA coding for hypothalamic GRF and pituitary GH were also measured by Northern blot analysis in young male rats treated with rat GRF-ab for 2 weeks and replaced with rat GH or IGF-I for the second 1 week. Replacement with either rat GH or IGF-I suppressed the increased hypothalamic GRF mRNA levels. These data indicate that endogenous GRF is essential for normal synthesis of pituitary GH and that both GH and IGF-I negatively regulate the synthesis of hypothalamic GR

ISSN:0028-3835    

DOI:10.1159/000126690

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

In situ hybridization was used to examine the effects of amygdala kindling on the expression of mRNAs for mineralocorticoid receptors (MR) and glucocorticoid receptors (GR) in the rat hippocampus. Kindling increased MR mRNA levels in the dentate gyms of the hippocampus 4 h after the last seizure, and these levels remained elevated 24 h later, but returned to baseline at 4 days. The only other hippocampal region that showed changes was the ipsilateral CA2 subfield where MR mRNA was significantly increased only at the 4-hour time point. Kindling also increased the levels of GR mRNA in the dentate gyms at 4 h; however, GR mRNA levels significantly decreased below control values at 24 h before returning to normal at 4 days. These data indicate differential transient alterations in hippocampal MR and GR receptor mRNA expression following amygdala-kindled seizures.

ISSN:0028-3835    

DOI:10.1159/000126691

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

Synaptic plasma membranes from the brain are known to have specific binding sites for several steroid hormones, but the mechanism of membrane trans-duction of steroid signals is not understood. In this study, corticosterone was found to stimulate 45Ca2+ uptake in brain synaptosomes upon depolarization of the synaptosomes by high K+ (70 mM). The stimulation of the depolarization-dependent 45Ca2+ uptake by corticosterone is concentration dependent, with the maximal effect occurring at steroid concentration of 5 – 10 × 10–7M (70–80% above control). The EC50 is estimated as 1.3 × 10–7M, which is almost identical to the Kdof the specific binding of the steroid to synaptic membranes (1.2 × 10–7M) reported previously. The stimulation of 45Ca2+ uptake in brain synaptosomes is specific to corticosterone and other glucocorticoids (cortisol, dexamethasone and triamcinolone); gonadal steroids (17β-estradiol, progesterone and testosterone) are ineffective. [3H]Nitrendipine binding was used to examine the effect of corticosterone on voltage-dependent Ca2+ channels. No effect on [3H]nitrendipine binding was found when disrupted synaptic membranes were preincubated with the steroid. However, a significant increase of membrane binding of [3H]nitrendipine was found when intact synaptosomes were first preincubated with the steroid at 37°C and then disrupted. Steroid preincubation of synaptosomes at 0°C was ineffective. Since preincubation at 37°C is required, it appears that metabolic processes modulating Ca2+ channel activity are involved in th

ISSN:0028-3835    

DOI:10.1159/000126692

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

Expression of neurotrophins and of the low-affinity neurotrophin receptor p75 was examined immunocytochemically in pituitary glands of twelve developing and adult macaques, ranging in age from fetal day 100 through age 5 years. Neurotrophins were identified by labeling with a rabbit polyclonal antiserum raised against purified mouse nerve growth factor, which recognizes brain-derived neurotropic factor and neurotrophin-3 as well. During pituitary morphogenesis, neurotrophins were present in epithelial cells distributed throughout all divisions of the anterior pituitary (pars distalis, pars intermedia, and pars tuberalis). Near term and in the adult, neurotrophin-immunoreactive cells were fewer in number and their distribution was limited to the pars distalis and pars tuberalis. A monoclonal antibody against the human neurotrophin receptor p75 heavily labeled mesenchymal boundary structures and blood vessels in the developing gland, and several populations of glial-like cells with a presumed paracrine function (folliculostellate cells in the pars distalis, and pituicytes and tanycytes in the neural lobe and infundibulum, respectively) as well as axons innervating the portal vasculature in postnatal specimens. These complementary patterns of neurotrophin and receptor expression suggest a possible inductive role for neurotrophins in pituitary morphogenesis and in the establishment of hypothalamic neural and hormonal control of pituitary function. In the adult anterior pituitary, examined using double-label immu-nocytochemistry for neurotrophins and conventional anterior-pituitary hormones, neurotrophins did not colocalize with human prolactin, human adrenocorticotropic hormone, recombinant human growth hormone, or the β sub-units of human luteinizing hormone, human follicle-stimulating hormone, or human thyrotropin. Neurotrophin-containing cells therefore appear to be a distinct population, suggesting novel paracrine or endocrine functions for this family of neuropeptides

ISSN:0028-3835    

DOI:10.1159/000126693

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

The effects of delta sleep-inducing peptide (DSIP) on pituitary cell differentiation was studied using an in vitro method and immunocytochemical techniques. Pituitary primordia were explanted from 11-day-old rat fetuses and cultured in a synthetic medium enriched with either DSIP at several concentrations, GnRH (10–9M) or TRH (10–9M). Expression of different pituitary phenotypes was quantified as the percentage of immunoreactive area per section of cultured primordia. Addition of DSIP during the first day of culture induced differentiation of LH and TSH cells only. The effect was dose-dependent. DSIP was less potent than GnRH and as potent as TRH in inducing LH and TSH differentiation. DSIP also induced lactotrope differentiation, but this effect may not be direct. DSIP had no effect on somatotrope and corticotrope differentiation. These results obtained in vitro suggest that DSIP exerts a direct action on the differentiation of several pituitary precursor ce

ISSN:0028-3835    

DOI:10.1159/000126694

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

GH is synthesized by the somatotrophs in the pituitary, where it may have paracrine actions. In order to identify the GH target cells in rat pituitary, the cellular distributions of rat GH receptor binding protein messenger ribonucleic acid (rGH-RBP mRNA) and protein were investigated at the electron-microscopic level, using in situ hybridization and immunocytology, respectively, on ultrathin frozen sections of rat pituitary. Ultrastructural distribution of 125I-bGH, 30 min after intracardiac administration was also performed in order to determine the pituitary cell types that bind the labeled hormone. In situ hybridization was performed using digoxigenin-labeled oligonucleotide probe revealed by indirect immunogold reaction. rGH-RBP mRNA was readily identified in the cytoplasmic matrix, associated with the endoplasmic reticulum and the nucleus of the somatotrophs, the lactotrophs and the gonadotrophs. No significant signal was detected in the corticotrophs or thyrotrophs. The number of gold particles in each pituitary cell type was estimated by direct counting, and was compared to the results of hybridization performed on rat liver sections as a control. The results showed that the level of rGH-RBP mRNA was higher in hepatocytes than in the pituitary cells, and was higher in the somatotrophs and lactotrophs than in the gonadotrophs. Immunocytological dectection of rGH-RBP was performed using two monoclonal antibodies (mAbs 43 and 263) directed against independent epitopes of the extracellular domain of the rGH-R. Indirect immunocytological detection showed regionalization of rGH-RBP; it was present in the cytoplasmic matrix and the nucleus of the hepatocytes and in discrete pituitary cells: somatotrophs, lactotrophs and gonadotrophs, but not in thyrotrophs or corticotrophs. Gold particle number was also higher in somatotrophs and lactotrophs than in gonadotrophs and higher in the nucleus compared to the cytoplasmic matrix. Radioiodinated GH was uptaken 30 min after injection by the same three pituitary cell types, showing evidence for the functional role of the GH receptor. In conclusion, we find that the cellular localization of rGH-RBP mRNA and protein is similar in discrete cell subpopulations of the pituitary, suggesting a direct effect of GH on somatotrophs, lactotrophs and gonadotrophs, through paracrine, autocrine or intracrine mechanisms.

ISSN:0028-3835    

DOI:10.1159/000126695

出版商:S. Karger AG    

年代:1994

数据来源: Karger