摘要:

Exposure of adult male hamsters to short days (<12.5 light/day) leads to suppression of gonadal function which is secondary to reductions in gonadotropin and prolactin (PRL) secretion. PRL secretion is decreased in short days despite a reduction of dopaminergic (DA) input from the hypothalamus, suggesting that the pituitary may become more sensitive to the inhibitory effects of DA. Although hypothalamic DA metabolism is altered by short-day exposure, it is not known whether the DA system can respond to PRL feedback or whether these changes in DA or PRL levels are responsible for the observed changes in gonadotropin secretion. To address these questions, the effects of PRL-secreting ectopic pituitary grafts on hypothalamic catecholamine metabolism and the effects of experimental manipulations of catecholamine metabolism on PRL and gonadotropin secretion were evaluated in adult male hamsters exposed to a 14 h light: 10 h dark (l4L:lOD) or a 5L:19D photoperiod. Short-photoperiod exposure led to expected reductions in testes weight, plasma PRL levels, and in vitro PRL secretion, but circulating levels of luteinizing hormone or follicle-stimulating hormone were not affected. Norepinephrine and DA turnover in the median eminence and in the medial basal hypothalamus was also reduced in the 5L:19D as compared to the l4L:lOD animals. Pituitary grafts elevated PRL levels and hypothalamic DA turnover in animals from either photoperiod, but in vitro PRL secretion was reduced only from the pituitaries of 14L:10D hamsters. Short-photoperiod exposure increased the ability of DA to suppress PRL secretion, and this effect could be reversed by the presence of an ectopic pituitary graft. The manipulation of photoperiod and plasma PRL levels also affected circulating gonadotropin levels, possibly by altering catecholamine metabolism in the medial basal hypothalamus and in the medial preoptic area. From these data, we conclude that short-photoperiod exposure causes complex changes in hypothalamic catecholamine metabolism and responsiveness that may partially explain photoperiod-mediated changes in hormonal feedback control systems.

ISSN:0028-3835    

DOI:10.1159/000124159

出版商:S. Karger AG    

年代:1985

数据来源: Karger

摘要:

In the present experiment we examined spontaneous endogenous in vitro dopamine release from the corpus striatum of female rats during the morning (09.00–09.30 h) and afternoon (15.00–15.30 h) photoperiod on each day of the estrous cycle. In the morning, the spontaneous dopamine release rates of D-1, D-2 and proestrous female rats were characterized by initial low values which gradually increased (approximately 3-fold) over the 2.5-hour in vitro perifusion. In the afternoon, spontaneous release rates of D-1, D-2 and estrous females gradually declined (approximately 2.5-fold) over the perifusion period. This rhythmic diurnal fluctuation was disrupted in the afternoon of proestrus and morning of estrus when release rate profiles remained stable over the entire perifusion period. These results suggest that changes in spontaneous in vitro dopamine release of corpus striata derived from rats in different phases of the estrous cycle may reflect novel in vivo interactions of both photoperiodic and hormonal c

ISSN:0028-3835    

DOI:10.1159/000124160

出版商:S. Karger AG    

年代:1985

数据来源: Karger

摘要:

The effect of bradykinin (BK) on the release of β-endorphin-like immunoreactivity (β-EpLI) in rats was studied in vivo and in vitro. Intraperitoneal injection of BK at 5 µg/100g body weight resulted in significant increase in the plasma β-EpLI level after 15 min. BK at concentrations of 10–12–10–7M also caused dose-dependent stimulation of β-EpLI release from dispersed cells of rat anterior pituitary. On gel chromatography, the β-EpLI released by incubation of the cells with 10–7M BK separated into two components, eluted in the same positions as human β-lipotropin and human β-endorphin, respectively. BK did not stimulate β-EpLI release in Ca++-free medium. Addition of 10–3 M verapamil or 10–6M dexamethasone to the incubation medium inhibited BK-induced β-EpLI release from the cells. Quabain (10–5M) also stimulated β-EpLI release, but its effect was not additive with that of BK. These results indicate that BK stimulates β-EpLI release and that calcium ion is involved in the

ISSN:0028-3835    

DOI:10.1159/000124161

出版商:S. Karger AG    

年代:1985

数据来源: Karger

摘要:

Sex differences have been observed in the perinatal sexual differentiation of the neural substrate which regulates territorial marking behavior in the Mongolian gerbil. The present study examines the relative contribution of prenatal and postnatal steroid environment to sexual differentiation in the male and androgenized female using territorial marking behavior as an endpoint. Selective suppression of steroid effects in the pre- and postnatal period was accomplished with the antiandrogen flutamide or the antiestrogen MER-25. Treatment was given (1) prenatally (for 5 days before expected parturition), on the day of birth, and postnatally (to day 10) or (2) prenatally and on the day of birth only. Animals without postnatal antisteroid treatment were intact or were gonadectomized on day 2 and given testosterone propionate (TP) treatment on day 7. (It has previously been shown that day 7 is beyond the period of maximum steroid responsiveness in the male but not in the androgenized female.) MER-25, flutamide, or day-2 ovariectomy had no effect on adult marking behavior responsiveness in females given TP on day 7. All groups marked at normal male frequencies. The presence of flutamide prenatally and on the day of birth in day-2 castrates given TP on day 7 yielded adults with marking responsiveness equivalent to day-7 TP-treated females. In contrast, males given day-7 TP without prenatal and birthday flutamide showed significantly lower marking frequencies, suggesting that the presence of androgen prenatally and on the day of birth rendered day-2 castrates less responsive to TP given on day 7. The present study demonstrates that male-female differences in the neonatal period of maximum steroid responsiveness of the neural substrate which regulates marking behavior are not due to perinatal effects of ovarian steroids and can be attenuated or eliminated by inhibition of androgen effects in the male between day 5 prepartum and day 2 postpartum.

ISSN:0028-3835    

DOI:10.1159/000124162

出版商:S. Karger AG    

年代:1985

数据来源: Karger

摘要:

An adenosine-sensitive adenylate cyclase has been demonstrated in anterior pituitary cultured cells in the present studies. N-ethylcarboxamideadenosine (NECA), L-N6 MECA. Adenosine showed a biphasic effect on adenylate cyclase: stimulation at lower and inhibition at higher concentrations, whereas 2’-deoxyadenosine only inhibited adenylate cyclase in a concentration-dependent manner. The stimulatory effect of NECA on adenylate cyclase was dependent on metal ion concentrations and was blocked by 3-isobutyl-1-methylxanthine and 8-phenyltheophylline. Various agonists such as isoproterenol, prostaglandins (PGE1), vasoactive intestinal peptide, corticotropin-releasing factor, NaF, and forskolin, all stimulated adenylate cyclase to various degrees. The stimulatory effect of vasoactive intestinal peptide and corticotropin-releasing factor on adenylate cyclase was found to be almost additive with the stimulation exerted by NECA. These data indicate the presence of adenosine stimulatory receptors (‘Ra’) in anterior pituitary which are coupled to adenylate cyclase. It is possible that adenosine may act as one of the important regulators to regulate and/or modulate the effects of agents/factors in the release of pituitary h

ISSN:0028-3835    

DOI:10.1159/000124163

出版商:S. Karger AG    

年代:1985

数据来源: Karger

摘要:

The rise in the concentration of LH in the serum that takes place in ovariectomized, estrogen-primed rats exposed to the odors from a cage with bedding soiled by a male rat was completely prevented by bilateral lesions destroying the ventral premammillary (PMv) nuclei. These results suggest that the pheromonal stimuli generate stimuli that course through a pathway which involves the PMv nuclei before they reach the hypothalamus. In addition, the chemosensory information is apparently transmitted centrally by an uncrossed pathway in view of the fact that removal of one vomeronasal organ combined with lesions of the contralateral PMv nucleus, but not of the ipsilateral nucleus, suppressed the release of LH in rats exposed to male odors. Since pheromonal stimuli are known to activate the accessory olfactory system, of which the medial (Me) amygdaloid nucleus and the bed nucleus of the stria terminalis (BNST) are parts, the effect of stimulating these nuclei in rats bearing lesions of the PMv nucleus was also investigated. Unilateral lesions of the PMv nucleus prevented the release of LH in ovariectomized, estrogen-primed rats and the advancement of LH surge in proestrous rats induced by electrochemical stimulation (anodic d.c. 100 µA/30 s) of the ipsilateral Me amygdaloid nucleus but not those induced by stimulation of the contralateral Me amygdaloid nucleus. Similar results were obtained stimulating the medial part of the BNST in proestrous rats. It is concluded that the impulses evoked by pheromonal stimuli inducing LH release in the rat are conveyed by an uncrossed pathway and relay in the PMv nucleus before they reach the medial basal hypothalamus

ISSN:0028-3835    

DOI:10.1159/000124164

出版商:S. Karger AG    

年代:1985

数据来源: Karger

摘要:

The temporal correlation of the secretion of corticosterone (CS) and grotwh hormone (GH) with the sleep-wakefulness cycle in adult male rats was studied by serial blood sampling at 10-min intervals over a 11-hour period from 11.00 to 22.00 h. Cortical EEGs recorded continuously during the blood sampling were scored into wakefulness and sleep, and the amounts of sleep for every 10 min was plotted against the CS and GH values. All 11-hour time series of CS, GH and amount of sleep were found to have three major ultradian rhythms with periodicities of 1.5 h and its multiples. For CS, there was a significantly negative cross-correlation between the amounts of sleep. Although the most prominent CS rhythm was the 1.5-hour period, CS secretion occurring with a 3.0-hour period had such a phase relationship with the 3.0-hour period sleep rhythm that the secretion began in the late stage of the sleep cycle and reached its peak around the time of wakefulness between sleep cycles. In contrast, a GH secretory burst occurred in the early stage of the sleep cycle occurring with a 3.0-hour period, with a definite time lag after the onset of the sleep cycle. The present study demonstrates that three different functions, CS, GH secretions and sleep-wakefulness, have common ultradian rhythms with similar periods, and manifest their rhythms based on their own pacemakers. It is assumed further that each pacemaker is fixed in specific phase relations with others.

ISSN:0028-3835    

DOI:10.1159/000124165

出版商:S. Karger AG    

年代:1985

数据来源: Karger

摘要:

The natural estrogen, estradiol-17β, and a synthetic agonist, diethyl stilbestrol (DES), accumulated selectively in cell nuclei of the male dove preoptic area and posterior hypothalamus following intramuscular injection of the corresponding 3H-labelled tracers. Nuclear incorporation of radioactivity was saturable and specific, as shown by the effect of competition doses of unlabelled estrogens. The non-aromatizable androgen, 5α-dihydrotestosterone (DHT), did not compete with estrogens for nuclear binding sites, indicating that cross-reaction with androgen receptors is unlikely. Estradiol uptake was higher in the preoptic area than in the posterior hypothalamus, whereas DES uptake did not differ significantly between these areas. Although both brain areas are likely to contain specific estrogen receptors, only the preoptic area is known to be directly involved in the control of male precopulatory courtship behavior in the dove. Aromatase activity responsible for the local conversion of testosterone to biologically active estradiol-17β, measured in vitro, was also much higher in the preoptic and posterior hypothalamic areas than in adjacent areas of the basal forebrain and hypothalamus. The similarity in localization of aromatase activity and intranuclear uptake of estradiol indicates that the formation of estrogen may occur only within discrete brain areas containing specific estrogen receptors. Intranuclear uptake of DES in the preoptic area, which is half that of estradiol, is correlated with lower effectiveness both in inducing aromatase activity in the preoptic area and in eliciting an estrogen-dependent behavior in castrated males. The effectiveness of estrogens on behavior in the male dove is likely to depend upon characteristics of estrogen receptors in the preoptic ar

ISSN:0028-3835    

DOI:10.1159/000124166

出版商:S. Karger AG    

年代:1985

数据来源: Karger

摘要:

To evaluate whether ovarian steroids modify the prolactin (PRL) response to opioid receptor blockade, the effects of naloxone infusion (1.6 mg/h for 4 h) on PRL secretion were studied in 5 postmenopausal women. Naloxone infusion was performed in basal conditions and after chronic oral treatment with conjugated estrogens (CE) (1.25 mg/day, for 20 days) or CE plus medroxyprogesterone acetate (MPA) (10 mg/day, for 20 days). Under basal conditions, 17β-estradiol, estrone, gonadotropin, and PRL plasma levels were in the normal range for postmenopausal women, and naloxone failed to affect PRL secretion. Naloxone induced a significant PRL increase after CE treatment alone (p < 0.001) or in combination with MPA (p < 0.001). The increase was significantly higher (p < 0.05) after CE + MPA treatment than after CE treatment alone. These data suggest that steroids modulate the stimulatory effect of naloxone on PRL secretion in postmenopausal women

ISSN:0028-3835    

DOI:10.1159/000124167

出版商:S. Karger AG    

年代:1985

数据来源: Karger

摘要:

The rat neurohypophysis contains both opioid receptors and substantial amounts of endogenous opioid peptides. Inhibitory influences of opioids on the secretion of both oxytocin and vasopressin have been described. We have examined the effects of a range of opioid agonists and antagonists with differing relative selectivities towards opioid receptor subclasses on the secretion of oxytocin and vasopressin from the isolated neurohypophysis. Oxytocin and vasopressin release evoked by brief periods of electrical stimulation in control experiments was compared to evoked release in the presence of test compounds. Oxytocin release was depressed approximately 25% by the δ-agonist (D-Ala2, D-Leu5)-enkephalin but not affected by putative K-agonists or by β-endorphin. The use of opioid antagonists revealed a strong inhibition of oxytocin secretion by endogenous opioids released during electrical stimulation. Naloxone, relatively µ-selective, enhanced oxytocin secretion by up to 90% with a half-maximal effect at approximately 10^6M. MR2266, a relatively K-selective antagonist also enhanced oxytocin secretion but displayed agonist-like activity at high concentrations. ICI 154129, a δ-selective antagonist, was without effect on oxytocin secretion. Vasopressin release was unaffected by any of the agonists tested and not potentiated by antagonists at a range of stimulation frequencies. The data do not support the suggestion of an inhibitory endogenous opioid influence over vasopressin secretion within the neurohypophysis but indicate that an endogenous opioid peptide, possibly acting via µ- or ĸ- rather than δ-receptors, strongly suppresses the secretion of ox

ISSN:0028-3835    

DOI:10.1159/000124168

出版商:S. Karger AG    

年代:1985

数据来源: Karger