摘要:

Using quantitative autoradiography, melatonin receptors have been studied during post‐natal and pubertal development of the rat in 2 brain and 2 pituitary structures. In the pars distalis of anterior pituitary, melatonin receptors decrease gradually in density after birth and disappear in 30 day‐old animals. In contrast melatonin binding is only expressed in the paraventricular nuclei of the thalamus at the age of 21–23 days and is always present in adult animals. In the suprachiasmatic nuclei and in the pars tuberalis of the pituitary, melatonin receptor density decreases after birth, remains stable for approximately 1 month and increases again at puberty to reach the birth values in the adult. This increase was absent in pinealectomized and in castrated animals but present in castrated animals receiving testosterone suggesting that it depends upon circulating testosterone and melatonin levels. These results show that melatonin receptors are differentially regulated during post‐natal development in each of the 4 structures studied, and that melatonin and testosterone are 2 factors which could be involved in the regulation of melatonin receptor density in the suprachiasmatic nuclei and pars tu

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1996.tb00690.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

There is increasing evidence that opiates not only have analgesic properties, but also regulate mechanisms activated during the stress response, such as the hypothalamic‐pituitary‐adrenal (HPA) axis. Indeed, opioid‐containing neurons innervate the paraventricular nucleus and the median eminence, thus modulating inputs to ACTH‐controlling neurons. In addition, dynorphin (the endogenous ligand of the kappa‐opioid receptor)‐like peptides have been found co‐localized with corticotrophin‐releasing hormone (CRH) and are believed to be co‐secreted with it in the hypophyseal portal circulation to modulate ACTH release. In this study, we evaluated the effects of the selectiveκ‐opioid receptor agonist MR‐2034 [(‐)‐N‐(2‐tetrahydrofurfuryl)‐normetazocine] on the HPA axisin vivoandin vitro. MR‐2034 was given intravenously to catheterized, freely moving, male Sprague‐Dawley rats and serial blood samples were collected for ACTH and corticosterone (B) measurements. We evaluated also the site of MR‐2034 action on the HPA axisin vivo, after the administration ofα‐helical CRH9–41, a CRH receptor antagonist, on hypothalamic CRH, pituitary ACTH, and B releasein vitro. MR‐2034 increased plasma ACTH and B levels in a dose‐related fashion and this effect was antagonized by the selectiveκ‐opioid receptor antagonist MR‐1452. In the presence ofα‐helical CRH9–41, the responses of plasma ACTH and B to MR‐2034 were blunted significantly, suggesting that this compound activates the HPA axis through a CRH‐dependent mechanism. Accordingly, MR‐2034 stimulated hypothalamic CRH releasein vitroin a concentration‐dependent fashion and this effect was antagonized dose‐dependently by MR‐1452. However, the stimulatory effect of MR‐2034 on plasma ACTH and Bin vivowas not completely abolished byα‐helical CRH9–41, suggesting that an additional, CRH‐independent, mechanism was involved. Indeed, MR‐2034 was able to stimulate basal ACTH output in a dose‐dependent manner and this effect was antagonized by MR‐1452in vitro. On the other hand, MR‐2034 did

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1996.tb00691.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

Neurotensin (NT) has been shown to be involved in neuroendocrine regulation, and the presence of both the peptide and its receptors has been demonstrated in the hypothalamus. In the present study, we show that hypothalamic neurons in primary cultures express the neurotensin receptor (NTR) and we examined a possible regulation of this receptor by glucocorticoids and activators of adenylate cyclase. In the hypothalamic cultures,125I‐NT bound to a single class of binding sites, presenting a selectivity similar to that observed for the high‐affinity NTR previously described in the adult rat brain. Radioautographic studies demonstrated that these125I‐NT binding sites were present on 3% of the neurons. A 48‐h treatment with forskolin (fsk) decreased125I‐NT binding by 30%. No effect of dexamethasone (dex) alone was found on that parameter. However, a combined treatment with both agents led to a 40% decrease in125I‐NT binding, corresponding to a reduced number of binding sites, and to a 68% decrease in the amount of NTR mRNA. In parallel, the dex plus forsk treatment increased NT release in the incubation medium. Moreover, the decreases in125I‐NT binding and NTR mRNA induced by this treatment were abolished in the presence of an anti‐NT antibody or SR 48692, a non‐peptidic antagonist of NTR, suggesting that the down‐regulation of NTR observed after dex plus fsk treatment was mediated by the release of endogenous NT. Agonist‐induced down‐regulation of the NTR in this system was confirmed by the application of an exogenous NT analogue, JMV 449. The present findings indicate that, in hypothalamic cultures, dex and fsk indirectly down‐regulate NTR expression via the

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1996.tb00692.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

In this study a possible role of 11β‐hydroxysteroid dehydrogenase (11β‐HSD) in altering the access of corticosteroids to their receptors in the hippocampus is investigated.In vitro, oxidation of corticosterone to 11‐dehydrocorticosterone (11‐DHC) was demonstrated in hippocampal homogenates. Glycyrrhetinic acid (GE) and carbenoxolone (CBX) were potent inhibitors of 11β‐HSD activity and did not display affinity for mineralocorticoid (MRs) nor glucocorticoid receptors (GRs). Intracerebroventricular injection of CBXin vivo(ED50∼30 μg) decreased oxidative activity in hippocampal homogenates, as demonstratedin vitro. In vitro, in hippocampal slices, cell nuclear retention of tritiated corticosterone, but not aldosterone, was markedly enhanced in the presence of GE, which at a concentration of 20 nM was found to inhibit 11β‐HSD activity by about 50% in the intact cell preparation. In contrast to the effect onin vitrocell nuclear uptake,in vivoautoradiography revealed that retention of corticosterone in the hippocampal cell nuclei was not affected after intracerebroventricu

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1996.tb00693.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

Gonadotropin releasing hormone (GnRH) neurons are typically simple, fusiform cells; however, over the course of prepubertal development increasing numbers take on a ‘spiny’ appearance. Following gonadectomy there is a decrease in the frequency of these spiny GnRH neurons. These observations which were made in the rat suggest that GnRH neurons are directly affected by the gonadal steroid milieu, though they do not themselves contain receptors for these steroidal hormones. In that there are important species differences in the hypothalamic‐pituitary‐gonadal axis between rats and primates, the present study was undertaken to determine whether a reduction in ovarian hormones would produce similar changes in the morphology of GnRH neurons in the monkey. A further aim was to determine whether such changes were localized to a specific brain

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1996.tb00694.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

The expression of somatostatin receptor (SSTR) subtypes and relative abundance of SSTR2 mRNA were examined in 18 pituitary adenomas using the reverse transcription‐polymerase chain reaction (RT‐PCR) method. SSTR1 and SSTR2 were expressed in all pituitary adenomas examined. Six of 9 somatotroph adenomas, 1 of 4 lactotroph adenomas and 1 of 2 thyrotroph adenomas also expressed SSTR5. SSTR3 and SSTR4 mRNAs were detected in 1 and 2 cases of somatotroph adenoma, respectively. SSTR2 mRNA expression was quantified by comparison with the PCR cycle‐dependent amplification ofβ‐actin or cyclophilin. The relative abundance of SSTR2 mRNA varied greatly among adenomas with more than a 1000‐fold difference. SSTR2 mRNAs in lactotroph adenomas were less abundant (P<0.01) than those in somatotroph adenomas. No significant correlation was found between the relative abundance of SSTR2 mRNA levels and GH sensitivity to octreotide administration. However, one of the thyrotroph adenomas exhibited marked shrinkage in tumor size after octreotide therapy, in which SSTR2 mRNA was the most abundant among the adenomas examined. GH sensitivity to octreotide was not significantly different between SSTR5 mRNA positive and negative adenomas. In conclusion, SSTR2 mRNA levels varied greatly among pituitary adenomas but were not correlated with GH sensitivity to octreotide. Further investigations of functional SSTR subtype proteins and of postreceptor signal transductions are required to clarify the molecular mechanisms of octreot

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1996.tb00695.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

We recently determined that melatonin stimulated serotonin (5‐HT) secretion from rat pineal glands by increasing 5‐HT release from the pinealocytes (μM melatonin concentrations) and by inhibiting 5‐HT uptake in the pineal sympathetic nerve endings (mM melatonin concentrations). The present study investigated whether a single melatonin injection could alter the content of indoleamines in the rat pineal gland, as well as its possible dependence on the daytime of administration. Melatonin (150 μg/kg) was i.p. injected at 8 time points (11.00 h, 14.00 h, 17.00 h, 20.00 h, 23.00 h, 02.00 h, 05.00 h and 08.00 h) to rats kept in 12:12 h light:dark cycle (lights on at 07.00 h). Melatonin injections in the afternoon (17:00 h) and late in the nighttime (02.00 h and 05.00 h) decreased pineal 5‐HT content 90 min later. The levels of 5‐hydroxyindoleacetic acid (5‐HIAA) were also decreased 90 min after the melatonin treatment at 14.00 h, 17.00 h and 02.00 h. The effect of melatonin on 5‐HT content was a long‐lasting effect (still evident after 180 min) only when injected at 02.00 h, whereas 5‐HIAA levels were found to be decreased 180 min after melatonin treatment at 14.00 h and 23.00 h. No changes in these compounds were detected 240 min after melatonin treatment. Moreover, melatonin did not change 5‐hydroxytryptophan levels at any of the daytime points studied. By contrast, 90 min after the injection of melatonin at 20.00 h, an increased content of pineal N‐acetylserotonin was observed. This effect of melatonin could be mediated through a phase alteration of the pineal N‐acetyltransferase activity rhythm by acting on the suprachiasmatic clock, althought a direct melatonin effect on the pineal rhythmic function cannot be excluded. The effects of the hormone on 5‐HT and 5‐HIAA contents agree with previous findings on the inhibitory effect of pharmacological doses of melatonin on pineal 5‐HT uptake, which presumably would result in a decreased intraneuronal content of 5‐HT and its acid metabolite. These data point to an acute regulatory action of exogenous melatonin on the pineal melatonin synthesis pathway which seems to be limited to tw

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1996.tb00696.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

To determine if prenatal androgens prevent activation of GnRH neurons in response to estradiol stimulation, Fos colocalization with GnRH was compared in the brains of normal female lambs, normal males, and androgenized females in response to a surge‐inducing dose of estradiol. Blood samples were collected every 1–2 h for 6 h before estradiol treatment up to the time of sacrifice at 17–19 h post‐treatment. Following perfusion, 60 μm coronal brain sections were immunostained for Fos (1:1000, Santa Cruz Biochemicals) and GnRH (1:40,000, LR‐1) using NiCl‐enhanced and unenhanced DAB, respectively. Although LH secretion increased in females before sacrifice, no increase was observed in males or androgenized females. Despite differences in LH secretion, the number and distribution of GnRH neurons was not sexually dimorphic. Moreover, Fos immunostaining was visible throughout steroid‐responsive limbic regions in all three groups of lambs. However, the colocalization of Fos with GnRH was highly sexually dimorphic. In females perfused after the peak of the LH surge, 65.7% of GnRH neurons in the preoptic area, anterior hypothalamus, and mediobasal hypothalamus expressed Fos, whereas only 1.7% of GnRH neurons were Fos‐positive in males and androgenized females. These findings indicate that sex differences in the activation of GnRH neurons in response to estradiol are determined prenatally through the

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1996.tb00697.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

In sheep, the surge mode of gonadotropin secretion is sexually differentiated, i.e. the LH surge is present in the female, but not in the male. The present study tested the hypothesis that sexual differentiation of the LH surge mechanism reflects a sex difference in the pattern of GnRH, and that prenatal androgens abolish the surge mode of GnRH secretion. We monitored the pattern of GnRH secretion in pituitary portal blood after acute treatment with estradiol in gonadectomized postpubertal males (n=6), females (n=6), and androgenized females (exposed prenatally to testosterone from day 30–90 in gestation, n=7). Four capsules, each containing a 30‐mm column of estradiol were implanted s.c. into each lamb to produce high physiologic concentrations of the hormone. Beginning 7 h later, portal and peripheral blood samples were collected hourly for 48 h for measurement of GnRH and LH, respectively. All females exhibited a GnRH surge beginning 13.0±0.4 h after estradiol treatment; this was accompanied by an LH surge. By contrast, only one male produced a small surge in GnRH (1.7 pg/min) with a latency of 32 h; a corresponding increase in LH occurred in this male. Likewise, among the androgenized females, only one exhibited GnRH and LH surges which began at about 22 h after estradiol treatment. Some of the androgenized females had sporadic increases in GnRH which were of lower amplitude than in the control females, and were unaccompanied by rises in LH. These findings provide the first direct evidence that the sex difference in the surge mode of LH secretion results from the sexual differentiation of the pattern of GnRH release. The study also suggests that androgens during prenatal development abolish the GnRH surge and subsequently, the generation

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1996.tb00698.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

This study used a combination of Western blotting and immunocytochemistry to test whether signalling pathways independent of cyclic AMP have the potential to induce phospho‐CREB (pCREB)‐like immunoreactivity (‐ir) in the oPT. Western blot analysis of extracts of primary cultures of oPT using an antiserum against CREB, revealed a major band of CREB‐ir at 44 KDa. The intensity of this band did not vary systematically with treatment. In extracts from untreated cells, Western blot analysis revealed a major band of pCREB‐ir at 42 KDa which was not sensitive to agonist treatment. Treatment of cells with forskolin (10−6M) increased the intensity of a number of other pCREB‐ir bands at between ca. 38 and 44 KDa. The band at 44 KDa probably represented native pCREB whilst the other bands induced by forskolin probably represented pCREB‐like proteins. Melatonin (10−6M) alone had no effect on pCREB‐ir, but it did inhibit the effect of forskolin on the ca. 38 and 44 KDa pCREB‐ir bands. Treatment with lamb serum (1%) consistently increased the intensity of the ca. 38 and 44 KDa pCREB‐ir bands relative to control cells, as assessed by Western blot. However, Western blot analysis did not reveal a consistent effect of melatonin on the pCREB‐ir response to serum. The effect of serum on pCREB‐ir in oPT cells was characterized further by immunocytochemical analysis. In contrast to experiments utilizing Western blotting, untreated cells did not possess detectable pCREB‐ir. In serum‐starved oPT and oPD cultures, treatment with serum induced exclusively nuclear pCREB‐ir. A large majority of oPT cells (≥90%) were sensitive to serum (1%), and serum caused a time‐ and dose‐dependent increase of nuclear pCREB‐ir. Melatonin attenuated the response to serum in the oPT. This inhibition of the response to serum was not apparent in the oPD, demonstrating that the effect of melatonin was specific for a tissue known to express melatonin receptors. In oPT cultures, physiological concentrations of melatonin (10−9M) partially reversed (ca. 70%) the inductive effect of 0.1% serum on nuclear pCREB‐ir. However, in contrast to studies applying forskolin, the induction of pCREB‐ir by serum occurred in the absence of measurable changes in the concentration of cyclic AMP, indicating that components of serum are able to stimulate the phosphorylation of CREB in the oPT through mechanisms independent of cyclic AMP. Both adenosine and prostaglandin E2 (PGE2) also induced nuclear pCREB‐ir in the absence of increased levels of cyclic AMP. These results demonstrate that transcriptional activities in the oPT which are under the control of CREB may be modulated by convergent cyclic AMP‐dependent and cyclic AMP‐independent pathways. Regulation of these pathways by melatonin and other factors present in serum may be an important control

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1996.tb00699.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY