摘要:

Magnocellular hypothalamo-neurohypophysial neurones display characteristic firing patterns, related to the hormone they release. To identify the membrane currents that may underlie these firing patterns, we performed whole-cell recording of freshly dissociated magnocellular neurones from the supraoptic nucleus. After recording, cells were immunocytochemically identified by using highly selective monoclonal antibodies raised respectively against vasopressin (AVP) and oxytocin (OT) neurophysin. In 64 out of 131 neurones (48.8%), we detected the presence of a transient potassium current whose kinetic properties were characteristic of an A-current. The A-current was activated by depolarisation over –40 mV, and inactivated rapidly with a mono-exponential decay (τ = 28 ± 2.7 ms; n = 33 at 0 mV). Using conditioning prepulses of 50 ms, the voltage dependence of the inactivation was determined, and the data were adequately fit with a Boltzman equation (half-maximal inactivation: –42.5 mV). The steady-state time-dependent inactivation curve was determined using a prepulse potential at –40 mV, and data were best described with a mono-exponential equation (τ = 89.7 ms). The sensitivity to 1 mM 4-amino-pyridine (63 ± 9% inhibition, n = 6), and a reversal potential close to the theoretical Nernst equilibrium for potassium (–56.3 ± 1 mV, n = 6, vs. –58 mV) confirmed that the transient current studied was indeed an A-type potassium current. Immunocytochemical identification revealed that the A-current was selectively expressed in OT-neurophysin-posi-tive cells. As previous work in hypothalamic slice preparations suggests that the A-current is expressed by both AVP cells and OT cells, the present data suggest that whereas the A-current is expressed in the soma of OT cells, it may be expressed only on the dendritic tree of AVP cells, which is truncated in the dispersed cell preparation used here. This distribution may play a role in the specific firing characteristics of magnocel

ISSN:0028-3835    

DOI:10.1159/000127180

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

Sinoaortic baroreceptor denervation (SAD) results in increased osmotically induced secretion of vasopressin (VP) and oxytocin (OT) and increased cardiovascular responses to many centrally acting pressor agents. Studies were conducted to determine whether SAD increases the cardiovascular and endocrine responses to direct and peripheral osmotic stimulation of the supraoptic nucleus (SON). SON microdialysis was performed in urethane-anesthetized male rats with measurement of dialysate peptides, mean arterial pressure (MAP) and heart rate. Experiment 1 tested the effect of direct stimulation of the SON with hypertonic NaCl in SAD, sham-operated (control) and intake-matched (matched) rats. Osmotically induced VP release into the SON was significantly greater in SAD than in control or matched groups. VP release peaked at 36 ± 13 and 15 ± 7 pg in SAD and controls, respectively, with no increase observed in the matched group. Plasma VP was significantly elevated after SON osmotic stimulation with no differences observed among the groups. The pressor response to osmotic stimulation was greater in SAD (29 ± 4 mm Hg) than in control (20 ± 3 mm Hg) and matched animals (15 ± 3 mm Hg). Experiment 2 tested the effect of intraperitoneal injection of hypertonic NaCl on SON VP and OT release. SAD rats showed an increased central VP response to peripheral osmotic stimulation, a 64-fold increase in SAD as compared to a 4-fold one in controls. Central OT release was not significantly altered (peak of 22 ± 6 vs. 11 ± 4 pg, SAD vs. control). A direct SON osmotic challenge given 3.5 h after the intraperitoneal test confirmed an increased VP responsiveness in the SAD group. Plasma VP and OT were significantly increased after intraperitoneal hypertonic saline with no difference observed between groups. The MAP response to intraperitoneal hypertonic saline was greater in the SAD group with an elevation of 37 ± 4 versus 18 ± 3 mm Hg observed in SAD versus control subjects. These results demonstrate that baroreceptor denervation produces a state of heightened osmotic sensitivity for VP neurons, with evidence for increased central VP release to both direct and peripheral hypertonic NaCl sti

ISSN:0028-3835    

DOI:10.1159/000127181

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

The effects of different acute stressors on circulating corticosterone levels, 5-HT 1A receptors and 5-HT1A mRNA levels were measured in male Sprague-Dawley rats. Two hours restraint stress, short swim stress (15 min) and long swim stress (30 min) increased circulating corticosterone levels 10-, 13- and 18-fold, respectively, when measured immediately after termination of the stress. Each stressor produced a unique profile of changes in 5-HT1A receptors measured in coronal sections 24 h after the termination of stress with the antagonist [125I]-4-(2’-methoxyphenyl)-1-[2’-(n-2’’-pyridinyl)-p-iodobenzamido]ethylpiperazine and the agonist [3H]-8-hydroxy-2-(di-n-propylamino)tetralin. Restraint stress produced decreases in antagonist binding in the CA3 region and dentate gyms; agonist binding was decreased only in the dentate gyms. Despite the larger elevation in circulating corticosterone level measured after short swim stress, no changes in agonist or antagonist binding were detected after this stressor. In contrast, the long swim stress increased antagonist binding in the CA2 region and in layers IV–VI of the cortex; agonist binding was also increased in all regions of the hippocampus and in layers I–VI of the cortex. Thus, restraint and long swim stress produce opposite effects on 5-HT 1A receptor expression in different subregions of the hippocampus. Analysis of presynaptic 5-HT1A receptors in the raphe nuclei revealed an increase in antagonist binding in the dorsal raphe following long swim stress. No change in the level of 5-HT1A mRNA measured in adjacent sections was detected following any of the stressors. The role of corticosteroid receptors in these stress-induced alterations of 5-HT1A receptors and the potential significance of these alterations in the context of affective disorders ar

ISSN:0028-3835    

DOI:10.1159/000127182

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

Neuropeptide Y increases feeding and decreases measures of brown adipose tissue thermogenesis. In lactating rats, increased feeding, increased hypothalamic neuropeptide Y neuroactivity and decreased thermogenesis occur. Naltrexone is an opioid receptor antagonist which decreases neuropeptide Y-induced feeding and reverses neuropeptide Y-induced decreases in brown adipose tissue thermogenesis. We hypothesized that opioid receptors are involved in neuropeptide Y neuroactivity during lactation. To see if naltrexone would alter feeding, neuropeptide Y gene expression in the arcuate nucleus, neuropeptide Y levels in the paraventricular nucleus, and uncoupling protein gene expression in brown adipose tissue of lactating rats, osmotic minipumps pre-filled with either 0.9% saline or naltrexone (70 µg/h) were implanted subcutaneously in 47 female Sprague-Dawley rats weighing 309 ± 5 g. Half these rats were studied on days 10–16 of lactation, and the other half were studied 7 days after lactation. After 48 h, neuropeptide Y mRNA levels and uncoupling protein mRNA levels were determined using specific cDNA probes. Neuropeptide Y peptide levels in the paraventricular nucleus were measured by radioimmunoassay. Naltrexone decreased food intake by 26% in the post-lactating rats, but had no effect on feeding in the lactating animals. Lactation resulted in significantly increased arcuate neuropeptide Y mRNA, decreased neuropeptide Y levels in the paraventricular nucleus and decreased brown adipose tissue uncoupling protein mRNA levels. Naltrexone did not influence any of these parameters. Thus, the alterations in neuropeptide Y neuroactivity and brown fat thermogenesis which occur in lactation is not altered by generalized opioid receptor block

ISSN:0028-3835    

DOI:10.1159/000127183

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

The peptide galanin (GAL) exists in dense concentrations within the medial hypothalamus and is synthesized in a population of neurons within the paraventricular nucleus (PVN). This peptide has been linked to energy homeostasis through its behavioral, metabolic and endocrine actions, including pancreatic insulin secretion. This investigation examined whether circulating insulin, in turn, has impact on hypothalamic GAL production, GAL mRNA and peptide concentrations in the hypothalamus. Streptozotocin (STZ)-induced diabetic rats, compared to control subjects, were tested with or without insulin replacement. After STZ treatment, the rats exhibited hyperglycemia, increased food and water intake, and decreased weight gain compared to controls. These changes were reversed by daily subcutaneous injections of insulin. Measurements of GAL mRNA, via solution hybridization/nuclease protection assay, revealed a 6-fold elevation after STZ treatment compared to controls, accompanied by a similar rise in GAL peptide levels. This increase in GAL message and peptide was reversible by insulin and was detected in a mediodorsal hypothalamic (MDH) dissection which contains the PVN. It was not seen in a dissection of the mediobasal hypothalamus that includes the GAL-synthesizing neurons of the arcuate nucleus. Measurements of GAL in discrete hypothalamic nuclei of STZ diabetic rats showed a 100% increase in peptide concentrations (p < 0.05) in the PVN that was insulin responsive. Other hypothalamic areas examined failed to exhibit any change in peptide. These findings are consistent with other evidence indicating an inverse association, between circulating insulin and GAL message or peptide in the PVN, that may have physiological relevance in the control of energy balance.

ISSN:0028-3835    

DOI:10.1159/000127184

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

The effect of melatonin on the gonadotropin-releasing-hormone (GnRH)-induced oscillatory rises in intracellular calcium concentration, [Ca2+]i, was studied in cultured cells from the anterior pituitary gland of 6- to 8-day-old rats. GnRH-induced [Ca2+]i oscillations were recorded indirectly by monitoring the activity of apamin-sensitive Ca2+-activated K+ channels using the perforated patch-clamp technique and fast microperfusion system. Melatonin (1 nM) inhibited the initiation or attenuated the amplitude of oscillatory current responses induced by 10 nM GnRH in 72% of GnRH-sensitive cells. Analysis of the melatonin dose-inhibition relationship showed that melatonin inhibited the initiation of [Ca2+]i oscillations with IC50 = 0.35 nM. In partially inhibited cells, melatonin reduced the GnRH-induced current amplitude by 55% on the average, prolonged the delay in onset of response to GnRH and decreased the frequency of oscillations. Once initiated by GnRH, the amplitude and frequency of oscillatory currents was inhibited by melatonin after a latency of 10–30 s. These effects of melatonin were fully reversible. After pretreatment of neonatal gonadotropes with pertussis toxin, no inhibition by melatonin was observed. The inhibitory effect of melatonin on initiation, amplitude and frequency of GnRH-induced oscillatory current persisted in the absence of external Ca2+. Melatonin alone did not induce any transmembrane current or membrane potential changes. These observations suggest that melatonin reduces GnRH-induced calcium mobilization from intracellular store

ISSN:0028-3835    

DOI:10.1159/000127185

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

Interactions between the hypothalamic-pituitary-adrenocortical (HPA) system and melatonin secretion have been demonstrated, but only the effects of melatonin on the activity of the HPA system have been studied in man. Alterations of melatonin secretion described as low-melatonin syndrome have been demonstrated in patients suffering from a major depressive episode, and an inhibitory factor on melatonin secretion has been postulated. We investigated whether corticotropin-releasing hormone (CRH), which is thought to be involved in HPA abnormalities in depressed patients, can also suppress melatonin secretion in healthy volunteers. Ten healthy male human volunteers in a double-blind study design received randomized hourly intravenous injections from 08.00 to 18.00 h that contained 10 µg human CRH, 1 µg adrenocorticotropic hormone (ACTH), or placebo to simulate pulsatile hormone secretion. Plasma melatonin and cortisol responses during the treatment and nocturnal sleep electroencephalograms after the treatment were recorded. Administration of CRH reduced melatonin secretion significantly below values obtained after administration of placebo and ACTH. Cortisol secretion was significantly enhanced by ACTH in comparison to both placebo and CRH. Electroencephalographic sleep parameters revealed no treatment effects. Our findings suggest that CRH has an inhibitory effect on the pineal secretion of melatonin in normal man. A mechanism via a release of cortisol was not supported by our results. Secondary hormonal effects from changes in nocturnal sleep architecture were excluded. Further investigation of the action of CRH on melatonin secretion as well as the mutual feedback between the HPA system and the pineal gland may extend our knowledge of neuroendocrine alterations mediating the adaptive response to stress and the eventual involvement in the pathogenesis of depressio

ISSN:0028-3835    

DOI:10.1159/000127186

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

In animals, corticotropin-releasing hormone (CRH) has been shown to decrease gastric acid secretion after intracerebral administration. Evidence exists that in man peptides have a direct access to the brain upon intranasal administration. This study aimed at assessing brain-mediated effects of CRH on gastric pH after intranasal administration in humans. Eleven healthy men were tested on 2 occasions in a double-blind within-subject cross-over comparison during treatment with CRH (versus placebo) administered intranasally at a dose of 20 µg every 10 min. Gastric pH values were measured continuously by a gastral pH tube. After 2 h of intranasal treatment, 6 µg/kg pentagastrin was injected subcutaneously. The subject’s mood was assessed by an adjective list (EWL-N) at the end of each experimental condition. Intranasal CRH increased pH baseline values from (mean ± SE) 1.70 ± 0.31 to 2.62 ± 0.53 (corresponding to 54%), whereas during intranasal treatment with placebo pH values remained unchanged (p < 0.05). After injection of pentagastrin, pH values decreased to 0.73 ± 0.04 during placebo and to 0.93 ± 0.14 during CRH treatment (n.s.). During treatment with CRH, subjects felt less tired (p < 0.05) and deactivated (p < 0.05). Plasma cortisol and CRH levels were not affected by intranasal CRH, excluding mediation of the CRH effects via resorption into the bloodstream, and TSH levels were slightly decreased by the end of the treatment. Results confirm the notion of a pathway for CRH from the nose to the brain, initiating, via central nervous mechanisms, inhibition of gastric acid secretion and a change of mood i

ISSN:0028-3835    

DOI:10.1159/000127187

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

Retinoid X receptors (RXRs) are transcriptional factors that belong to the steroid/thyroid hormone receptor superfamily. There are 3 RXR isoforms – α, β, γ – known to bind 9-cisretinoic acid as their ligand. The expression of RXRs in human pituitary glands and pituitary adenomas has not been extensively investigated. To determine whether specific RXR isoforms may play roles in the state of differentiation of pituitary adenomas, we have investigated the immunohistochemical expression of RXRα and RXRγ in 6 nontumorous pituitaries and in 60 different pituitary adenomas using isoform-specific antibodies. In the nontumorous pituitaries, RXRα was expressed in the nuclei of almost all cells, while RXRγ was only expressed in thyrotropin (TSH) cells and in some cells positive for growth hormone (GH) and glycoprotein α-subunit (αSU) but not in luteinizing hormone (LH) β-subunit, follicle-stimulating hormone (FSH) β-subunit, prolactin (PRL) or adrenocorticotropin (ACTH) cells by double immunostaining. All 60 adenomas were RXRα positive, and 39 of 60 adenomas (65%) were positive for RXRγ. The incidence of RXRγ immunoreactivity in the different adenoma types was: 13 of 16 GH-producing adenomas (81.3%), 9 of 14 PRL-secreting adenomas (64.3%), 6 of 6 TSH-secreting adenomas (100%), 2 of 5 ACTH-secreting adenomas (40%) and 9 of 19 nonfunctioning adenomas (47.4%) including immunohistochemically gonadotropin-subunit-positive adenomas. The colocalization of RXRγ with the TSHβ subunit, GH and αSU in the same adenoma cells was frequently observed, and sometimes RXRγ was colocalized with PRL, ACTH, FSHβ or LHβ as shown by double immunostaining. We conclude that RXRα is expressed in both human pituitaries and pituitary adenomas. In contrast, RXRγ is expressed more broadly in pituitary adenomas than in normal pituitaries and thus may play a role in the differentiation-specific cell types in the human pituitary both under physiological an

ISSN:0028-3835    

DOI:10.1159/000127188

出版商:S. Karger AG    

年代:1997

数据来源: Karger