ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.04441.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

In the rat, vaginocervical stimulation (VCS) received during mating is required for the subsequent expression of 10–12 days of twice‐daily prolactin surges that are necessary for pregnancy or pseudopregnancy (PSP). This temporal separation of sensory stimulus and neuroendocrine response suggests that a mnemonic of the vaginocervical stimulation is created in the brain that triggers and sustains the daily prolactin surges. We investigated the possible involvement of the medial preoptic area (mPOA) and the medial amygdala (mAMYG) as potential neural sites involved in the processing of this neuroendocrine arc. Cycling female rats were bilaterally implanted with intracerebral cannulae in either the mPOA or mAMYG. On proestrus, females were manually palpated to confirm sexual receptivity and then received bilateral infusions of either the local anesthetic lidocaine, the Ca++channel blocker, verapamil, or phosphate‐buffered saline (PBS) into either brain site before or both before and after receipt of 15 intromissions from an experienced male. Unmated control females received comparable infusions of lidocaine or verapamil, and were placed in the empty test arena for 10 min. Infusions consisted of either a single bilateral infusion 15 min before mating (Expt. 1), bilateral infusions both 15 min before and after mating (Expt. 2) or eight bilateral infusions separated by 30 min intervals spanning a period beginning 45 min before and ending 2 h 45 min after mating (Expt. 3). None of the lidocaine infusions into the mPOA prevented the establishment of PSP, and neither verapamil infusions into the mAMYG nor the shorter‐term neural block (i.e. single or double lidocaine infusions) of the mAMYG prevented mating‐induced PSP. However, the longer‐term neural block (i.e. multiple lidocaine infusions) of the mAMYG significantly reduced the incidence of PSP. These data support previous findings that the mAMYG receives sensory input from VCS, and suggest that the mAMYG is a site at w

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.04432.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

The paraventricular nucleus (PVN) and A2 are novel estrogen feedback sites where estrogen may modulate the neural response to adrenergic inputs during fasting. In the present study, the effects of local estradiol (E2) perfusion through a microdialysis probe placed in the PVN or A2 on pulsatile luteinizing hormone (LH) secretion and on norepinephrine (NE) release in the PVN were examined in 48‐h fasting ovariectomized (OVX) rats to determine whether local estrogen administered in the PVN or A2 rapidly inhibits LH secretion during fasting and whether this inhibition is mediated by an increase of NE release in the PVN. Five days after ovariectomy, animals (n=5 per group) stereotaxically implanted with a guide cannula for microdialysis in the PVN (experiment 1) or both PVN and A2 (experiment 2) were deprived of food for 48 h. Blood samples and dialysates were then collected every 6 min for 3 h and every 12 min (experiment 1) or 20 min (experiment 2) for 3 h, respectively. The PVN or A2 was perfused with E2(5 ng/ml in artificial cerebrospinal fluid) through a microdialysis probe after the first hour of sampling. E2perfusion in the PVN caused a rapid and significant suppression of mean plasma LH levels and LH pulse frequency in fasting rats but no changes in unfasting animals. NE release in the PVN was not affected by the local E2perfusion of the PVN in either fasting or unfasting groups. This perfusion in A2, however, did not cause any apparent changes in plasma LH and perfusate NE levels in the PVN and A2. The present results indicate that estrogen feedback action at the PVN suppresses LH secretion rapidly during fasting and does not involve an increase of NE rel

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.04573.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

The purpose of the present study was to determine if GnRH receptor mRNA levels in the rat brain undergo changes during the estrous cycle. We focused on the arcuate and ventromedial nuclei of the hypothalamus and on the hippocampus which are sites in the rat central nervous system that have been shown to contain measurable amounts of GnRH receptor mRNA. Groups of regularly cycling female rats were decapitated at 08.00 and 17.00 h of each day of the estrous cycle, trunk blood was collected for radioimmunoassay analysis of circulating LH levels, and the brains were processed for ‘in situ’ hybridization. A cDNA probe encoding the rat pituitary GnRH receptor was transcribed ‘in vitro’ in the presence of33P‐alpha UTP and used under saturating conditions to label GnRH receptor mRNA. The results show that in the arcuate and ventromedial nuclei GnRH receptor mRNA levels are relatively high during diestrus 1, they decline slightly during diestrus 2 before they rise to the highest levels at 08.00 h of proestrus. By 17.00 h of proestrus, GnRH receptor mRNA levels had declined to the lowest levels of the estrous cycle where they remain through the morning of estrus. The GnRH receptor mRNA levels rise again sharply during the afternoon of estrus. The changes in the hippocampus follow a similar pattern in that a decline in GnRH receptor mRNA levels to its lowest levels occurs between 08.00 and 17.00 h of proestrus. However, the changes in the hippocampus did not reach statist

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.04544.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

Concentrations of the potent hypothalamic appetite stimulating peptide neuropeptide Y (NPY), and its mRNA, are increased in rats with experimental diabetes, suggesting a role in the hyperphagia of this disorder. The 2‐h feeding responses to intracerebroventricular (i.c.v.) injection of neuropeptide Y (NPY) (5, 10, and 15 μg doses) were measured in male Wistar rats treated with streptozotocin (55 mg/kg) to induce diabetes. Streptozotocin‐diabetic rats given i.c.v. NPY exhibited reduced feeding responses compared to controls (P<0.05). Dexamethasone treated rats exhibit similar changes in NPY content and mRNA in the hypothalamus to those seen in diabetes, but are not hyperphagic. Feeding repsonses were also measured in this model, to assess whether high levels of endogenous NPY might account for the reduced response in diabetes. In contrast, the feeding response to NPY in comparison to controls was unaltered in dexamethasone‐tr

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.04565.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

Fos immunocytochemistry was used in the ring dove (Streptopelia risoria) to identify areas in the forebrain and hypothalamus which might be involved in the expression of incubation behaviour and the associated changes in neuroendocrine function. In this species, both sexes participate in incubation which becomes fully established after laying the second egg in the two egg clutch. The eggs hatch after 14–15 days incubation. Observations were made in both sexes 16–18 h after laying the first egg, 3–5 h after laying the second egg, and after 12–14 days of incubation. Non‐breeding birds were used as controls. Fos‐labelled cells were observed in several forebrain areas in both sexes irrespective of reproductive status but their numbers did not change during incubation. In the hypothalamus, very few fos‐labelled cells were seen in non‐breeding birds but appeared in both sexes in thenucleus preopticus medialisafter egg laying and after 12–14 days of incubation. Fos‐labelled cells also appeared in thenucleus tuberis(≡arcuate nucleus) in both sexes after laying the first or second egg and less abundantly, after 12–14 days incubation. Additionally, in males only, fos‐labelled cells were seen after the laying of the first and second eggs in the rostral area of thenucleus tuberisclose to the walls of the third ventricle. These observations suggest that the fos‐labelled cells in thenucleus preopticus medialismay be involved in the expression of incubation behaviour while those in thenucleus tuberismay be involved in the regulation of gonad

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.04586.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

The mammalian suprachiasmatic nuclei (SCN) contain an endogenous pacemaker that generates daily rhythms in behavior and secretion of hormones. Previously we hypothesized that the SCN imposes its circadian rhythm on the rest of the brain through a rhythmic release of its transmitters in its target areas. In the present study we employed microdialysis‐mediated intracerebral administration of vasopressin (VP) and its V1‐antagonist to study the mechanisms underlying the circadian control of the release of the adrenal hormone corticosterone. Stress‐free application of the VP V1‐antagonist in the dorsomedial hypothalamus of freely moving, undisturbed animals during the middle of the light period (i.e. the trough of the corticosterone rhythm) caused an immediate increase of circulating plasma corticosterone levels. A similar administration of VP at the end of the light period completely prevented the diurnal rise in plasma corticosterone. These results indicate a pronounced inhibitory role for SCN‐derived VP at the level of the dorsomedial hypothalamus with respect to the activity of the hypothalamo‐pituitary‐adrenal axis during the day period. Thus, the daily decline in VP release sets a specific time window for the occurrence of the daily corticosterone peak. On the other hand, during the dark period corticosterone levels are decreasing together with basal VP levels. Therefore, in addition to the inhibitory VP signal from the SCN, there is also the need for an excitatory SCN signal in order to accomplish the complete circadian profile of plasma c

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.04597.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

GHRP6 is a synthetic hexapeptide which stimulates growth hormone (GH) secretion from the pituitaryin vivoandin vitro. We have previously shown that in identified somatotrophs, GHRP6 induces a biphasic increase in cytosolic Ca2+concentration ([Ca2+]i) consisting of an abrupt increase (first phase) followed by a sustained plateau of elevated [Ca2+]i (second phase). The first phase corresponds to mobilization of intracellular Ca2+pools and the second phase to influx of extracellular Ca2+ions through voltage‐sensitive Ca2+channels. In these experiments, we investigated the specific role of each of these two phases in the hormone response to GHRP6. We found that inhibition by thapsigargin of the intracellular Ca2+mobilization phase significantly inhibited the hormone response to the peptide during 30 min incubations. Inhibition of the extracellular Ca2+influx phase by nifedipine, a blocker of voltage‐sensitive Ca2+channels, resulted in a 53% reduction of the secretory response to 10−5 M GHRP6. Antagonism of PKC by phloretin, a flavonoid which prevents PKC activation, and PKC depletion induced by a 24 h treatment with 10−6 M PMA, completely inhibited the response to GHRP6. Somatostatin, which also inhibits the second phase of the Ca2+response, suppressed the secretory response to GHRP6. We conclude that, Ca2+is the main second messenger and both Ca2+mobilization and Ca2+entry play a role in the response to GHRP6. However, experiments with PKC depletion and SRIF suggest that other messengers are implicated in GHRP6 signalling

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.04608.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

The hypothalamic mechanisms which underlie the development of the fetal neuroendocrine system are unclear. However, in adult animals neuroactive amino‐acids, particularly those acting at the N‐methyl‐D‐aspartate (NMDA) receptor, have been shown to be important transmitters involved in the neuroendocrine regulation of the anterior pituitary gland. In this study we have investigated the potential role of NMDA in the neuroendocrine regulation of fetal pituitary function, by examining the ontogeny of LH and ACTH responses to NMDA during fetal development in sheep. Catheterized fetal sheep were injected with 3 intravenous doses of NMDA (1, 2 and 4 mg/kg; estimated fetal body weight) and saline vehicle on consecutive days between days 110–115, 120–125 and 135–140 gestation (term=145 days). At each gestational age fetuses also received a pituitary challenge test consisting of CRF (0.4 μg/kg), AVP (80 ng/kg) and GnRH (125 ng/kg). NMDA caused a significant dose‐related increase in ACTH at day 120–125 (P<0.02) and day 135–140 gestation (P<0.001). NMDA had no effect on ACTH secretion at day 110–115. The ACTH response to the highest does of NMDA (4 mg/kg) increased with advancing gestational age, in contrast to the ACTH response to CRF+AVP which was the same at all ages. NMDA caused a significant increase in LH secretion at all gestational ages with the greatest response observed at the latest gestational age studied (day 135–140). A similar increase in LH response to the GnRH challenge was observed late in gestation. Pretreatment of fetuses with the competitive NMDA antagonist CGP37849 (1 mg/kg) abolished the LH and ACTH responses to an intravenous injection of NMDA (4 mg/kg) given 5 min later. These data show that activation of NMDA receptors during fetal development elicits the secretion of ACTH and LH and demonstrate that NMDA receptors are functionally coupled to the neuroendocrine pathways regulating these two hormones during fetal life. The dramatic increase in ACTH repsonse to NMDA during the final days before birth occurs at a time of high adrenocortical activity and suggests an important function

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.04639.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY