ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1994.tb00609.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

A transgene consisting of the rat vasopressin structural gene containing a reporter in exon III, flanked by 5 kb of upstream and 3 kb of downstream sequences, is expressed in vasopressinergic, but not oxytocinergic, magnocellular neurons of rats. Functionally appropriate physiological stimuli increase transgene expression in magnocellular neurons in an exaggerated fashion; the magnitude of the transgene response to osmotic challenge exceeds that of the endogenous gene by 10–15 fold. Magnocellular vasopressinergic neurons in the rat are now accessible to rational and precise genetic perturbation of function and regulatio

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1994.tb00610.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe glucocorticoid, corticosterone (CORT), is believed to have an important function in modulating nutrient ingestion and metabolism. Recent evidence described in this review suggests that the effects of this adrenal hormone are mediated through two steroid receptor subtypes, the type I mineralocorticoid receptor and the type II glucocorticoid receptor. These receptors, which have different affinities for CORT, respond to different levels of circulating hormone. They mediate distinct effects of the steroid, which can be distinguished by the specific nutrient ingested and by the particular period of the circadian cycle.Under normal physiological conditions, the type I receptor is tonically activated, either by low basal levels of circulating CORT (0.5–2 μg%) normally available across the circadian cycle or possibly by the mineralocorticoid aldosterone. This type I activation is required for the maintenance of fat ingestion and fat deposition that occurs during most meals of the feeding cycle. In contrast, the type II receptor is phasically activated by moderate levels of CORT (2–10 μg%) normally reached during the circadian peak. Activation of this receptor is required for the natural surge in carbohydrate ingestion and metabolism that is essential at the onset of the active feeding cycle when the body's glycogen stores are at their nadir, and gluconeogenesis is needed to maintain blood glucose levels. This receptor is also activated during periods of increased energy requirements, such as, after exercise and food restriction, when CORT levels rise further (>10 μg%) and when its catabolic effects on fat and protein stores predominate to provide additional substrates for glucose homeostasis. These functions of CORT on fat and carbohydrate balance are mediated, in part, by type I and type II receptors located within the hypothalamic paraventricular nucleus, which is known to have key functions in controlling nutrient intake and metabolism, as well as circulating CORT levels. Moreover, the type II receptors within this nucleus, in addition to the arcuate nucleus, may interact positively with the peptide, neuropeptide Y, and the catecholamine, norepinephrine, both of which act to enhance natural carbohydrate feeding and CORT release at the onset of the natural feeding cycle.Thus, under normal conditions, endogenous CORT has a primary function in controlling nutrient ingestion and metabolism over the natural circadian cycle, through the coordinated action of the type I and type II steroid receptor systems. Through this action, CORT has impact on total caloric intake and body weight gain over the long term. Moreover, under conditions of obesity, diabetes and food restriction, steroid receptor function is greatly disturbed in association with chronic high circulating levels of CORT and abnormal glucose homeostasis. These disturbances in steroid action, along with dysfunction in brain neurochemical processes, very possibly contribute to the maintenance of hyperphagia and body weight gain in obese and diabetic

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1994.tb00611.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe localization of pituitary adenylate cyclase‐activating polypeptide (PACAP) in the hypothalamus‐pituitary system in rats was examined in light and electron microscopic immunocytochemistry using a specific antiserum to synthetic PACAP 1–38 (R0831). In light microscopic study, intensely PACAP‐immunostained perikarya were observed in the supraoptic and paraventricular magnocellular nucleus in the hypothalamus. In the median eminence, many immunoreactive nerve fibers were observed in the internal layer, but a few immunoreactive terminals were noticed in the external layer. In the pituitary gland, numerous immunoreactive nerve fibers were observed in the posterior lobe. In the intermediate lobe, moderately immunostained cells were observed, but in the anterior lobe no immunostained cells were noticed. In electron microscopic study, PACAP‐immunoreactivity was examined by avidin‐biotin peroxidase complex method. In the perikarya of the supraoptic and paraventricular magnocellular nucleus, DAB‐reaction products were distributed diffusely in the cytoplasmic matrix, frequently attaching to the rough‐surfaced endoplasmic reticulum. In the nerve terminals of the posterior lobe, reaction products were observed among the secretory granules, but sometimes upon them. In the cells of the intermediate lobe, reaction products were also distributed in the cyt

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1994.tb00612.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe daily production of melatonin from the pineal gland influences circadian and seasonal behaviour and physiology. To further understand how melatonin may function, it is important to characterize the receptor and signal transduction systems. Using the detergent digitonin, we were able to solubilize the receptor from the ovine pars tuberalis (PT) membrane. The receptor was isolated as a complex associated with its heterotrimeric G‐protein. In the solubilized state, pre‐bound125l‐2‐iodomelatonin was stable at 4°C, but was displaceable by GTPγS. The receptor‐G‐protein complex could be separated by molecular mass using native polyacrylamide gel electrophoresis. We demonstrate that the receptor‐complex has a molecular mass of 525 kDa and differs from solubilized receptor‐complexes isolated from either the lizard brain, chicken brain or the ovine hippocampus. Furthermore the receptor complex isolated from the hippocampus had the lowest molecular mass of these tissues (365 kDa) and was found not to be sensitive to GTPγS. This may indicate the existence of a distinct non‐G‐protein couple

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1994.tb00613.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractIn the rat hippocampus, neuronal morphology and survival are profoundly affected by adrenal steroids, and synaptic plasticity can be modulated by the ovarian sex steroids estrogen and progesterone, β‐amyloid peptides, which accumulate in neuritic plaques and are derived from the amyloid precursor protein (APR), have been shown to be both trophic and toxic for hippocampal neurons. Of the various APR isoforms, APP695 is the predominant form found in rat brain and the APP695 mRNA is abundantly expressed in the hippocampus. In order to investigate the hypothesis that APR may serve as a mediator of the steroid effects, we have monitored the hippocampal expression of APP695 mRNA byin situhybridization, with aging and with steroid manipulation. In aged female rats we observed a decrease in the level of APP695 mRNA relative to young female rats, while no such age difference was evident in male rats. Physiological, surgical and pharmacological manipulation of glucocorticoids appeared to have no effect on APP695 mRNA levels in the hippocampus. Treatment of young, ovariectomized female rats with estrogen and progesterone, resulted in an increase in hippocampal APP695 expression compared to untreated, ovariectomized contro

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1994.tb00614.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThis study investigated whether melatonin could modulate the phosphorylation of the calcium/cyclic AMP response‐element binding‐protein (CREB) within primary cell cultures of ovine pars tuberalis (oPT) and pars distalis (oPD). Gel shift assays confirmed the presence of nuclear factors able to alter the electrophoretic mobility of a32P‐labelled CRE oligonucleotide. Two shifted bands were observed probably due to monomer and dimer binding to the CRE. Each band was supershifted by antisera directed against both CREB and the phosphorylated form of CREB (P‐CREB), consistent with a specific role of CREB proteins in transcriptional regulation. To study the physiological role of CREB, the nuclear immunoreactivity for P‐CREB was followed in primary cultures of oPT given different pharmacological treatments. Cells stimulated with forskolin responded with a robust time‐ and dose‐dependent increase in nuclear phospho‐CREB immunoreactivity (P‐CREB‐ir), confirming that activation of this transcription factor occurred through the cyclic AMP‐PKA pathway. Maximal stimulation was achieved within 15 min and persisted for up to 1 h. Treatment with melatonin alone did not alter basal P‐CREB‐ir levels, yet melatonin inhibited the forskolin‐induced increase in P‐CREB‐ir in a dose‐dependent manner (IC50 of between 10−10M and 10−8M melatonin when tested against 1 μM forskolin). In contrast, in primary cultures of oPD, melatonin failed to block forskolin‐stimulated increases in either the content of cyclic AMP or the intensity of nuclear P‐CREB‐ir, confirming that the action of melatonin upon P‐CREB‐ir is tissue specific. These results demonstrate that, consistent with its inhibitory effect on the activation of PKA within oPT, melatonin prevents or reverses the phosphorylation of CREB induced by activation of the cyclic AMP signal transduction pathway. Therefore melatonin has the potential to regulate gene expression in the oPT by acting upon the CREB transcription factor. However, this paper also shows that 12‐0‐tetradecanoylphorbol‐13‐acetate (TPA) which activates PKC also leads to the phosphorylation of CREB in oPT cells, suggesting the potential involvement of other signal transduction p

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1994.tb00615.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractNeuroactive steroid modulation of GABAAreceptors was investigated in the peptidergic nerve terminals of the posterior pituitary using patch clamp techniques. In common with GABAAreceptors in cell bodies, the nerve terminal GABAAreceptor was potentiated by the synthetic steroid alphaxalone and by physiological concentrations of the progesterone metabolite allopregnanolone. Both of these agents enhanced Cl−currents elicited by GABA. Estradiol‐17β had a weak inhibitory effect on GABA responses of nerve terminals, but only at high concentrations. The potentiating action was manifest as an increase in the probability of channel opening, with no effect on the rate of desensitization of the GABAAreceptor. Neuroactive steroids enhanced GABA‐gated Cl∼ channel activity in cell‐free membrane patches, thus demonstrating a membrane delimited response. These results indicated that with regard to allosteric modulation by neuroactive steroids, the nerve terminal GABAAreceptor is similar to the GABAAreceptors of nerve cell bodies and endocrine cells. Neuroactive steroids are thus capable of altering the chemosensitivity of nerve terminal membranes by enhancing GABA inhibition at this location. The neuroactive steroid sensitivity of nerve terminal GABAAreceptors provides a pathway by which gonadal steroid derivatives could regulate peptide secretion from neurosecretory neurons. Such a pathway could participate in the coordination of neuropeptide secretion during complex neuroendocrine functions. With specific regard to the neurohypophysis, neuroactive steroid‐induced changes in the sensitivity of nerve terminal GABAAreceptors could play a role in the initiation of oxytocin secretion during the transition between pregnancy and

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1994.tb00616.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractAcute studies of GH removal by hypophysectomy or GH replacement in adult rats have shown that GH has a positive influence on its hypothalamic inhibitory hormone somatostatin (SRIH). The present study was undertaken to assess the effect of lifelong exposure to elevated GH on the development and differentiation of SRIH‐producing hypothalamic neurons, including comparison of differing GH levels and heterologous species of GH. Expression of somatostatin peptide and mRNA was evaluated using respective immunocytochemistry andin situhybridization in brains of transgenic mice bearing constructs of either human (hGH) or bovine (bGH) linked to metallothionein (MT) promoter or bGH linked to phosphoenolpyruvate carboxykinase (PEPCK) promoter. Nontransgenic littermates served as controls. All transgenic constructs resulted in high levels of circulating heterologous GH and significantly elevated body weights. Both bGH levels and body weights were higher in PEPCK‐bGH than in MT‐bGH mice; mean weights were not different between MT‐bGH and MT‐hGH mice. Numbers of SRIH‐immunoreactive neurons in the hypophysiotropic periventricular nucleus (PeN) of transgenic mice showed a two‐fold increase (P<0.01) relative to control animals; the number of SRIH‐positive cells in the medial basal hypothalamus (MBH) was comparable for transgenic and control mice. Total SRIH mRNAin situhybridization intensity also showed a two‐fold increase (P<0.05) in the PeN of all transgenic mice compared with controls, and was not elevated in the MBH. The higher levels of GH produced in PEPCK‐bGH transgenic mice led to greater weight gain, but not to greater SRIH expression than in other GH‐transgenic mice, suggesting that the increased SRIH cell number and mRNA in the PeN of MT‐GH‐transgenic mice may represent a plateau of maximal feedback stimulation. The results indicate that lifelong elevated heterologous GH in mice stimulates hypothalamic SRIH expression markedly. It is not known whether this mechanism is direct or indirectviaa mediator of GH such as IGF, but the heterologous GH appears to be specific to these

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1994.tb00617.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThis study was undertaken to investigate the roles of PACAP and VIP in the control of pituitary hormone secretion in the ewe. The first experiment was designed to identify any direct effects at the level of the pituitary and was conducted during the luteal phase of a prostaglandin‐synchronized oestrous cycle. PACAP (0.008, 0.04, 0.2 and 1.0 nmol/min) or VIP (0.06, 0.2, 0.6 and 1.8 nmol/min) was infused into the carotid artery over a 10 min period. Blood samples were taken before and after the infusions so that plasma PRL, LH and GH concentrations could be measured. Blood pressure was also monitored to determine if the doses used were biologically active. In no case was an effect on hormone secretion observed. In contrast, the highest dose of each peptide induced an increase in heart rate to almost three‐fold the resting value. Although both peptides are activein vivo, this result suggests that neither peptide has a direct effect on hormone release from the pituitary of prostaglandin‐synchronized ewes. In a second experiment, we investigated whether the peptides had central effects on hormone secretion. Intracerebroventricular (ICV) injection of PACAP or VIP at the dose 10nmol was tested in ovariectomized ewes. After injection, PACAP suppressed PRL and GH secretion so that plasma hormone concentrations from 1–3 h after injection were significantly different from the control (P<0.05 for PRL, P<0.01 for GH). In addition, PACAP significantly reduced mean LH concentration (P<0.05) and LH pulse frequency (P<0.01). A similar suppressive effect on LH secretion was also observed after ICV injection of VIP (P<0.05 for both parameters), although PRL and GH release were not affected. These results suggest a possible role for PACAP in the neuroendocrine control of PRL, GH and LH secretion in sheep. In addition, VIP may be involved in the control of LH secretion. In contrast, there is no evidence to suggest that either peptide is a hypophysiotropic factor for PRL, LH or GH in prostaglandin‐synchron

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1994.tb00618.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY