摘要:

This study investigated the effects of daily photoperiod length and morphine on thyrotropin-releasing hormone (TRH) and prolactin secretion in sheep. Two groups of adult ewes were kept under either 16hL:8 h D or 8 h L:16 h D photoperiods for approximately 60 days. Then the photoperiods were reversed and approximately 60 days later push-pull cannulae were implanted into the hypothalamic stalk-median eminence. After a 7-day recovery period, the ewes were subjected to hypothalamic perfusion and blood was collected at 15-min intervals from the jugular vein. Perfusates also were collected into 15-min fractions. The first 3 h of perfusion served as an equilibrium period. During the next 2 h, saline was infused into one jugular vein. This was followed by a 2-hour morphine infusion (1 mg·kg–1 • h–1). Data from 13 ewes were analyzed for effect of photoperiod and drug on TRH concentrations in the perfusates and prolactin in the serum. Prolactin was significantly (p < 0.01) higher under 16 h L:8 h D than 8 h L:16 h D and was greatly increased (p < 0.001) by morphine infusion. TRH only tended to be higher (p = 0.05) under 16 h L:8 h D than under 8 h L:16 h D, but morphine infusion induced a rapid and highly significant (p < 0.01) increase in TRH secretion. There were no photoperiod and drug interactions for either TRH or prolactin. These results suggest that increased prolactin secretion induced by long-day photoperiods is not mediated by TRH, whereas the morphine-induced increase in prolactin secretion appears to be due at least partially to increased TRH sec

ISSN:0028-3835    

DOI:10.1159/000124866

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Corticosterone was administered through various modes into several brain regions of estrogen-treated adrenalectomized-ovariectomized female rats. Daily administration of 20 µg corticosterone dissolved in propylene glycol through intracerebral cannulae effectively inhibited female sexual receptivity at each of four sites: third ventricle, ventromedial hypothalamus, preoptic area, and septum. Similar administration of lesser daily doses failed to inhibit receptivity. Implantation of pure crystalline corticosterone also had no effect on receptivity at any site. Beeswax pellets chronically releasing low doses of corticosterone significantly inhibited receptivity when implanted in the medial hypothalamus and preoptic area, with similar nonsignificant trends in the lateral septum and medial forebrain bundle, but had no effect in the dorsal hippocampus or the amygdala. The effective sites are similar to those in which estrogen activity is known to induce receptivity and those in which serotonergic activity is believed to inhibit receptivity, but do not entirely correspond to sites in the brain showing the greatest uptake of corticosterone

ISSN:0028-3835    

DOI:10.1159/000124867

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Diurnal variations of the effectivity of β-endorphin (β-End), dynorphin (DYN), Met-enkephalin (Met-Enk), D-Met2-Pro5-enkephalinamide (D-Met-Pro-Enk) and morphine to induce prolactin (PRL) and adrenocorticotropin (ACTH)&slash;corticosterone (CS) release in intact and adrenalectomized rats have been examined. The response to morphine (10 mg/kg s.c), Met-Enk (200 µg/rat i.c.v.) and D-Met-Pro-Enk (0.5 µg/rat i.c.v.) did not change with different times of the day, while that to β-End (0.5 µg/rat i.c.v.), DYN (1 µg/rat i.c.v.) and U50–488H, a selective kappa agonist (10 mg/kg s.c), showed a circadian rhythm in stimulating PRL release, with a higher increase in the afternoon (16.00–17.00 h) than in the morning (08.00–09.00 h). In adrenalectomized rats the loss of this circadian rhythm was shown. The CS release evoked by morphine, D-Met-Pro-Enk, Met-Enk and DYN was demonstrable only in the morning when the basal CS level was significantly lower than in the afternoon. The afternoon release of ACTH by morphine was higher than in the morning in adrenalectomized rats. β-End and U50–488H were equally active in the morning and in the afternoon in increasing CS secretion. The present results suggest that the diurnal rhythm in the response of CS and PRLrelease to opioids is in relation with the glucocort

ISSN:0028-3835    

DOI:10.1159/000124868

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Estradiol (E2) produces many-fold increases in the dopamine (DA) content of the anterior pituitary and also plays a role in the age-related increase in pituitary DA in female C57BL/6J mice. These studies address the following questions: (1) What are the time and dose characteristics of the E2-induced increase in pituitary DA and can other gonadal steroids – such as progesterone (P) and 5α-dihydrotestosterone – also influence pituitary DA? (2) Is the age-related increase in pituitary DA due entirely to an increase in the E2:P ratio seen in aging female mice, or can extra-ovarian factors also play a role? (3) Is the E2-induced (and therefore possibly the age-related) increase in pituitary DA secondary to an E2-induced increase in serum prolactin? In ovariectomized (OVX) mice, E2 implants increased pituitary DA in a time- and dose-dependent fashion. P implants administered to OVX mice simultaneously with E2 antagonized the E2-induced increase in pituitary DA. Daily injections of 5α-dihydrotestosterone given in conjunction with E2 implants had no effect on basal or E2-increased pituitary DA in OVX mice. Thus, E2 is the only gonadal steroid examined which increases anterior pituitary DA. In intact aging mice, P attenuates the age-related increase in pituitary DA, supporting the hypothesis that the increased ratio of E2:P secreted by the ovaries of aging female mice is responsible for the age-related increase in pituitary DA. However, at advanced ages, intact male mice also showed modest increases in anterior pituitary DA. Therefore, extra-ovarian age changes, perhaps age changes intrinsic to the pituitary, also play a minor role in the age-related increase in pituitary DA. E2 increases the secretion of prolactin, which can then feed back to increase secretion of DA from the tuberoinfundibular dopaminergic neurons, a source of pituitary DA. To determine if the E2-induced increase in pituitary DA was secondary to an E2-induced increase in serum prolactin, OVX mice were given pituitary grafts to increase serum prolactin independently of E2 treatment. The E2-induced increase of pituitary DA is not mediated, but can be enhanced by prolacti

ISSN:0028-3835    

DOI:10.1159/000124869

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Themain psychoactive component of marihuana, delta-9-tetrahydrocannabinol (THC) was injected into the 3rd cerebral ventricle. A single dose of THC (2 µl of 1(HM) decreased serum LH temporarily but did not alter serum follicle-stimulating hormone (FSH) levels. The mediobasal hypothalamic (MBH) luteinizing hormone-releasing hormone (LHRH) content was elevated by 30 min after the injection. The elevation persisted for 1 h. Then, the LHRH content returned towards the preinjection level. In contrast, the LHRH in the organum vasculosum of the lamina terminalis did not change after a single dose of THC. The results indicate that THC alters pituitary LH release by inhibiting the release of LHRH which then increases in the MBH by continued synthesis or transport from rostral areas. In addition, the data support the existence of an FSH releasing factor, the release of which is not suppressed by this dose of THC. THC did not alter the release, storage or responsiveness to LHRH of cultured anterior pituitary cells, which further supports the view that its principal site of action is on the hypothalamus

ISSN:0028-3835    

DOI:10.1159/000124870

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

We have found thyroxine 5’-deiodinase in rat posterior pituitary. The isozyme pattern was different in intermediate and neural lobes. The former contained only type I enzyme. In the neural lobe, in euthyroidism only type I was found while in hypothyroidism type II was a prominent form. Since type II 5’-deiodinase has a high affinity for thyroxine and is a more tissue-specific isozyme than type I, our results suggest there may be a previously unrecognized role of thyroid hormone in posterior pituitary physiol

ISSN:0028-3835    

DOI:10.1159/000124871

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

An increase in plasma luteinizing hormone levels which occurs in the male rat in response to the presence of a receptive female was associated with increased norepinephrine metabolism in several regions of the hypothalamus and reduced norepinephrine metabolism in preoptic area and olfactory bulbs. Hyperprolactinemia induced by grafting three anterior pituitary glands beneath the kidney capsule blocked female-induced changes in norepinephrine metabolism and attenuated the increase in luteinizing hormone release. These results suggest that endocrine and behavioral responses of male rats to the presence of a female are mediated by changes in catecholamine metabolism in several brain regions. The ability of hyperprolactinemia to induce deficits in male sexual behavior may be due to the blockade of these CNS responses to exteroceptive stimuli originating from the female.

ISSN:0028-3835    

DOI:10.1159/000124872

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The efflux of endogenous γ-aminobutyric acid (GABA) has been studied using small hypothalamic fragments containing arcuate-paraventricular nuclei and median eminence from the rat brain. The amount of GABA present in the medium and the tissue GABA content were quantified by radioreceptor assay. The endogenous GABA efflux was found to be dependent upon the Ca2+ and K+ concentrations in the incubation medium, and it required synthesis of GABA, indicating neuronal origin of the released neurotransmitter. Nipecotic acid, an inhibitor of neuronal and glial uptake, prevented reuptake of released GABA. Prolactin in concentrations of 250 and 1,000 ng/ml augmented the K+-evoked efflux of GABA. The effect of prolactin was dependent on the presence of Ca2+ and on the synthesis of GABA. In addition, prolactin seems to alter the reuptake of endogenous GABA and the uptake of [3H]-GABA. In conclusion, these results suggest that prolactin may influence its own secretion by stimulating the release of hypothalamic GABA, both through an increase of its synthesis and a modification of its reuptake

ISSN:0028-3835    

DOI:10.1159/000124873

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Testosterone is converted to estradiol in specific regions of the primate brain and accumulates as such in the nuclei of cells in hypothalamus, preoptic area, and amygdala. To locate more precisely those neurons in which nuclear estrogen receptors were occupied by estrogenic metabolites of testosterone, we injected 8 castrated male rhesus monkeys with [3H]-estradiol. Four were injected with oil for control purposes, and 4 were pretreated for 3 days with 2 mg/day testosterone propionate. This dose raised plasma testosterone levels into the high physiological range for intact males. After 60 min, brains were rapidly removed, the levels of [3H]-estradiol in nuclei were measured in the right halves of the brains by high-performance liquid chromatography, and labeled neurons were located in the left halves by autoradiography. Compared with the 4 control animals, nuclear levels of [3H]-estradiol in testosterone-treated males were reduced by 77% in the hypothalamus (p< 0.001), by 93% in the preoptic area (p< 0.001), and by 90% in the amygdala (p< 0.05). In autoradiograms from testosterone-treated males, the labeling of neurons was reduced by 72–96% in most of the regions in which the control males showed high percentages of labeled cells. However, there were only small reductions in the number of labeled neurons in lateral septum (by 31%) and arcuate nucleus (by 23%). These two regions, therefore, contained estrogen receptors that were not blocked by pretreatment with testosterone. The simplest explanation for these results is that estrogenic metabolites of testosterone prevented the uptake of [3H]-estradiol by prior occupation of estrogen receptor sites. The rather precise neuroanatomical localization of the effects pointed to the existence of two populations of estrogen target neurons in the primate brain depending on the presence or absence of local aromatase activit

ISSN:0028-3835    

DOI:10.1159/000124874

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

To test the hypothesis that the onset of maternal behavior is stimulated by estrogen, we examined the effects of medial preoptic area (MPOA) or ventromedial hypothalamus (VMH) implants of the antiestrogen 4-hydroxytamoxifen (OH-TAM) on pre- and postpartum maternal behavior and on postpartum estrus in rats. On day 20 of pregnancy, animals were implanted bilaterally with OH-TAM or cholesterol cannulae into MPOA or VMH. Unilateral cannulae of OH-TAM were also placed into MPOA. Females were tested with newborn pups for the onset of immediate retrieval, prepartum, at noon on day 21, at midnight of the day 21, and 1 day following parturition (which occurred on day 22). On the evening of parturition, implanted animals were tested with stimulus males for the occurrence of postpartum estrus. In order to examine the influence of estrogen on maternal behavior in the absence of parturitional experience, antiestrogen-implanted animals were delivered surgically (cesarean section) and were observed for the display of maternal behavior at various times after surgery. At noon of day 21, only a few animals in any group retrieved pups. However, 12 h later, females that received bilateral OH-TAM implants into MPOA remained nonresponsive, while over 80% animals in other groups retrieved and gathered pups. The antiestrogen did not disrupt the display of postpartum maternal behavior in those females that were allowed to undergo normal parturition, but it significantly reduced the number of cesarean-delivered animals showing maternal behavior. Bilaterial implants of OH-TAM into VMH, but not into MPOA, effectively blocked postpartum estrus. The MPOA implants of OH-TAM resulted in a significant reduction in cytoplasmic estrogen receptor levels and an increase in nuclear estrogen receptor concentrations. The results of these experiments lend support to the current hypothesis that estrogen acts most effectively in the MPOA to stimulate maternal behavior and in the VMH to facilitate sexual receptivity.

ISSN:0028-3835    

DOI:10.1159/000124875

出版商:S. Karger AG    

年代:1987

数据来源: Karger