摘要:

The regulation of prolactin secretion by tuberoinfundibular dopamine (DA) neurons appears to be altered in the aged rat: the concentration of prolactin in the serum increases and the activity of the tuberoinfundibular DA neurons decreases. In the young female rat a brief period of stress reduces the tuberoinfundibular DA neurosecretory activity and increases the secretion of prolactin. The purpose of the present study was to determine if the responsiveness of tuberoinfundibular DA neurons to restraint stress is altered in the aged female rat. The activity of these neurons was estimated from the rate of DA synthesis in their terminals in the median eminence, as measured by the rate of accumulation of dihydroxy-phenylalanine (DOPA) after the administration of a decarboxylase inhibitor. Thirty minutes of restraint stress increased serum prolactin concentrations in both young (3 months) and aged (26 months) constant estrous rats, but reduced the rate of DOPA accumulation in the median eminence of only the young rats. Restraint also decreased the rate of DOPA accumulation in the median eminence of intermediate-aged rats (14 months) independently of whether the rats were exhibiting normal ovarian cycles (measured on the day of estrus) or were in a constant estrus. This suggests that the loss of ovarian cyclicity per se is not associated with the age-related change in the response of tuberoinfundibular DA neurons to restraint stress. To determine if the lack of response of tuberoinfundibular DA neurons to stress is related to the reduced basal activity of these neurons in the aged rat, the response of tuberoinfundibular DA neurons to 30 min of restraint was determined in rats that were pretreated with haloperidol. Haloperidol increased serum prolactin levels and consequently the tuberoinfundibular DA neuronal activity in both young and aged rats, but restraint stress reduced the rate of DOPA accumulation only in the young rats. These results reveal that the inhibition of tuberoinfundibular DA neurons by stress is impaired in the aged rat and suggest that the inhibitory neuronal mechanisms that mediate this response become disrupted as the female rat ages.

ISSN:0028-3835    

DOI:10.1159/000124755

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

In the rat, exposure to stress increases prolactin (Prl) secretion, and endogenous opioid peptides (EOP) are believed to play a role in this response. The aim of the present study was to evaluate the specific involvement of the different EOP (i.e. β-endorphin [β-END], dynorphin A [DYN-A], methionine-enkephalin [Met-ENK], and/or opiate receptors (i.e., µ/ε, ĸ, δ) in the stress-related increase in circulating Prl. Rats were subjected to inescapable intermittent footshock (60 Hz, 2.5 mA, 1 s duration, 2 h) 2 h after the intracerebroventricular (i.c.v.) injection of specific antisera raised against β-END, DYN-A or Met-ENK. In addition, selective opiate antagonists (βh-END-[6–31], a peptide β-END antagonist [5 nmol, i.c.v.], β-funaltrexamine [β-FNA], an µi receptor antagonist [4.8 nmol, i.c.v.], Mr 1,452 MS and Mr 2,266 BS, two K-receptor antagonists [10 mg/kg body weight, i.p.], ICI 154,129, a δ-receptor antagonist [100 nmol, i.c.v.]) were administered prior to footshock stress. Blood samples were collected through an indwelling jugular cannula. Exposure to footshock rapidly and significantly increased plasma Prl levels. This stress-induced release of Prl was reduced by both antisera against β-END or DYN-A, as well as by pretreatment with βh-END-(6–31), β-FNA and K-receptor antagonists. Antiserum against Met-ENK and δ-antagonist were inactive. These results suggest that the activation of the two endogenous opioid systems, β-END and DYN-A, centrally modulate the release of Prl induced

ISSN:0028-3835    

DOI:10.1159/000124756

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The present study was performed mainly to determine whether interleukin-1 (IL-1), a polypeptide produced by immunologically activated monocytes, plays a physiological role in the regulation of adrenocorticotropic hormone (ACTH) using primary monolayer cultures of rat anterior pituitary cells. Neither human IL-1α nor IL-1β stimulated the ACTH release from normal pituitary cells in concentrations ranging from 0.01 to 10 nM IL-1β caused a slight, but significant, increase in ACTH release at a concentration of 100 nM, while IL-1α did not, even at the highest dose tested. IL-1β exhibited a synergistic action with corticotropin-releasing factor (CRF) in ACTH secretion at 10 and 100 nM of CRF, but the interaction was not striking. Both of the monokines failed to cause any change in the secretions of growth hormone, prolactin, follicle-stimulating hormone and luteinizing hormone throughout concentrations ranging from 0.01 to 100 nM The effects of possible sex-related differences and prolonged preincubation of cultured pituitary cells in serum-free medium prior to assay incubation were also tested, providing no significantly different findings. These results suggest that the physiological significance of IL-1as a tissue CRF is indeed questionable and should be further clari

ISSN:0028-3835    

DOI:10.1159/000124757

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The zona incerta (ZI) is a site of dopamine nerve terminals and part of the incertohypothalamic tract (I-H). Previous findings indicate that dopamine in the ZI has a stimulatory control on the release of luteinizing hormone (LH) and occurrence of ovulation. The effect of acute administration into anaesthetised rats of selective D1 and D2 dopamine agonists and antagonists injected into the ZI on plasma luteinizing hormone (LH) and on the occurrence of ovulation has now been investigated. It was found that bilateral injections on the day of pro-oestrus of a selective D1 antagonist, Sch 23390, inhibited ovulation at 10 µg/side/rat. Unilateral injections of a selective D1 agonist, SKF 38393, at 10 µg/rat stimulated a significant rise in plasma LH concentration in ovariectomised oestrogen-primed rats, and this was partially reversed by systemic pre-treatment with Sch 23390. The selective D2 agonist, LY 171555, and D2 antagonists, sulpiride and domperidone, had no effect on plasma LH levels or ovulation. This indicates that D1 receptors (but not D2 receptors) in the ZI are involved in the control of gonadotrophin release and may have a physiological function in reproductive processe

ISSN:0028-3835    

DOI:10.1159/000124758

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Adult male Syrian (golden) hamsters, maintained under either 22 ± 2 or 32 ± 2 °C, were treated with 8 or 11 weeks of exposure to either long photoperiod (14:10), short photoperiod (8:16), or to long photoperiod with a daily afternoon melatonin injection. By 8 weeks, the animals kept at 22 °C and treated with daily afternoon melatonin injection exhibited a dramatic reduction in testicular and accessory sex organ weight, but the animals kept at 32 °C and treated in the same way exhibited only slight decreases in testicular and accessory organ weights. Short photoperiod caused a slight decrease in testicular and accessory organ weights of hamster kept at 22 °C, while it had no significant effects on reproductive organ weights of the animals maintained under 32 °C. By 11 weeks, the daily afternoon melatonin injection elicited further reduction in testicular and accessory organ weights of the animals maintained under both 22 and 32 °C. However, the reduction in animals kept at 32 °C was not as great as that in animals kept at 22 °C. Although short photoperiod caused an obvious decline in reproductive organ weights of the animals at 22 ¤C, only a slight decrease was seen in hamsters at 32 °C. As with reproductive organ weights, testosterone levels were depressed more rapidly and completely in animals maintained at 22 °C. These results indicate that elevated ambient temperature changes the rate at which the gonads of hamsters regress in response to daily afternoon melatonin injections or short photoperiod. The daily afternoon melatonin injections and short photoperiod caused pituitary regression in animals placed in both temperatures after 8 and 11 weeks of treatment. Temperature had no influence on the effects of short photoperiod and melatonin injection on pituitary weight. Finally, plasma thyroxine (T4) levels and the free T4 index (FT4I) exhibited a reduction to melatonin injection under both the lower and higher temperatures. Short photoperiod caused a decrease of plasma T4 and FT4I in animals under 22 °C, while it only led to a lesser reduction of T4 and FT4I in animals under 32 °C. Therefore, the warmer temperature appeared to have slight influence on the response of plasma T4 and the FT4I to short photoperiod. Temperature showed a strong influence on the plasma triiodothyronine (T3) and the free T3 index (FT3I). A dramatic decrease in plasma T3 levels and FT3I was observed in animals maintained at elevated ambient tempe

ISSN:0028-3835    

DOI:10.1159/000124759

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The effect of dopamine (DA) on growth hormone (GH) release was studied in perifused freshly dispersed rat anterior pituitary cells. Pulses of DA (0.01–100 nmol/l), each applied for 30 min, resulted in a prompt rise in GH release. This effect was reversible, concentration-dependent and partially antagonized by metoclopramide, a DA antagonist. The effect of DA was further tested on GH-stimulated secretion by human GH-releasing factor (hGRF). Perifusion with hGRF (6.25 pmol/l) for 2 min elicited an immediate rapid increase in GH release which lasted 20 min. Pretreatment of cells with DA (100 nmol/l) for 10 min and a subsequent hGRF challenge during continuation of DA perifusion significantly reduced the effect of hGRF pulses on GH release. The present data suggest that DA has direct opposite actions at the somatotroph level, stimulating the basal GH release and inhibiting the hGRF-induced GH secretion, and may thus be an important modulator of GH releas

ISSN:0028-3835    

DOI:10.1159/000124760

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

In an attempt to clarify the nature of histaminergic neuromodulation of the vasopressinergic system, several studies under different experimental paradigms were carried out. L-Histidine loads (8 mmol/kg, i.p.) induced a marked increase in histamine (HA) in the anterior (AHR) and posterior (PHR) hypothalamic regions, the median eminence (ME) and adenohypophysis (Ah) with no apparent effect on the concentration of HA in the neurohypophysis (Nh), as measured by high-performance liquid chromatography. These findings correlated with decreases in vasopressin (VP) levels in the AHR and ME, accompanied by increases of the neuropeptide in the PHR and Ah. Intraperitoneal injections of HA (6 µmol/kg), resulted in a significant (p < 0.005) rise in VP levels in the PHR, ME and Ah. HA induced an elevation of VP in the prefrontal cortex (PFC) from 6.23 ± 2.02 to 43 ± 4.05 µU/mg, as well as a 60% reduction in neurohypophyseal VP. These HA-induced VP responses were abolished by both mepyramine (3 µmol/kg) and famotidine (4 µmol/kg) in the PHR and PFC. Mepyramine suppressed the HA-induced VP response in the Ah and enhanced it in the Nh, while famotidine did the opposite. When alpha-fluoromethylhistidine (FMH), an irreversible inhibitor of histidine decarboxylase, was administered at doses of 100 mg/kg/day (i.p.), hypothalamic HA levels fell by 40–45% after 1 h, by 50% after 3 h, and by 65–80% after 24 h in adrenalectomized rats. In the same conditions, but after a week of treatment with FMH, the VP response to adrenalectomy was clearly impaired. These results seem to demonstrate that the physiological levels of neuronal HA are indispensable for the normal functioning of the neuroendocrine system. In this context, preliminary pharmacological evidence showed that histaminergic neuromodulation of the vasopressinergic system is mediated through H1 receptors in the Ah, H1 receptors in the ME and Nh, and both H1 and H2 receptors in the PFC and hyp

ISSN:0028-3835    

DOI:10.1159/000124761

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Grafts of normal mouse preoptic area (POA) tissue into the third ventricle of gonadotrophin-releasing hormone (GnRH)-deficient hypogonadal (hpg) mice resulted in an elevation of pituitary GnRH receptors, an increased synthesis of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) by the pituitary gland, an elevation of gonadal LH receptors and in the stimulation of steroidogenesis and spermatogenesis in the testis. In normal mice both castration or the subcutaneous implantation of testosterone capsules for 10 days reduced GnRH receptors, pituitary LH and FSH content, and the latter treatment also caused a 50% reduction in testicular LH receptors. In hpg mice bearing POA grafts testosterone implants failed to affect any of the above parameters, and castration failed to affect pituitary gonadotrophin hormone content, although there was a slight reduction in pituitary GnRH receptors after castration. These experiments suggest that neither the pituitary gonadotroph, nor the GnRH neurone represent major sites for the direct negative feedback of testosterone upon gonadotrophic hormone secretion in male mice.

ISSN:0028-3835    

DOI:10.1159/000124762

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Changes in opioid concentrations in brain and plasma as well as opioid activity have been reported to occur as a function of pregnancy and lactation in rats. The present study examines the status and steroidal regulation of the endogenous opioid, beta-endorphin, in the behaviorally and neuroendocrinologically important preoptic area (POA) and hypothalamus, and in the plasma of pregnant and nonpregnant rats. In the first study, concentrations of beta-endorphin-like immunoreactivity (β-EP-LI-Ir) in POA and hypothalamic tissues as well as in plasma were measured throughout gestation in rats. β-EP-LI-Ir concentrations in the POA were significantly higher in rats from day 6 to 18 of gestation than in nonpregnant, diestrous females. β-EP-LI-Ir concentrations in the POA declined significantly between day 18 and 22 of gestation. Changes in hypothalamic β-EP-LI-Ir concentrations were not detected either as a function of pregnancy or during pregnancy, while plasma β-EP-LI-Ir concentrations declined gradually from day 6 to 18 of pregnancy and then increased significantly prepartum (day 22 of gestation). In the second study, the effects of 2 weeks of exposure to pregnancy levels of progesterone and estradiol on brain and plasma β-EP-LI-Ir were measured. Exposure to the combination of progesterone and estradiol (administered subcutaneously via Silastic capsule implants) resulted in a significant increase in β-EP-LI-Ir concentrations in the POA, but did not affect β-EP-LI-Ir concentrations in either the hypothalamus or plasma. In the final study, the effects of estradiol exposure on β-EP-LI-Ir concentrations in brain were evaluated. Exposure to a high, but not low, dose of estradiol resulted in a significant reduction in β-EP-LI-Ir concentrations in the hypothalamus and a reduction, although nonsignificant, in the POA. These findings indicate that the increase in β-EP-LI-Ir concentrations found in the POA from day 6 to 18 of pregnancy results from exposure to high circulating levels of progesterone in the presence of estradiol, and that the prepartum decline in POA β-EP-LI-Ir concentrations may be stimulated by the prepartum shift in steroidal environment from one of progesterone dominance to one of estradiol dominance. The significance of these changes in β-EP-LI-Ir concentrations are discussed in terms of opiate regulation of maternal behavior and neuroendocrine function during the periparturit

ISSN:0028-3835    

DOI:10.1159/000124763

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The hypothalamic neurons containing substance P (SP) were examined immunohistochemically in rats with a normal estrous cycle or persistent estrus (PE), in pregnancy and in lactating state. In PE animals, the neurons increased in number 1 week after ovariectomy, but then decreased and disappeared. During pregnancy, there were many SP neurons at an early stage but later they gradually decreased in number and disappeared. Consequently, during lactation no SP neurons were evident. The external layer of the median eminence (ME) contained many immunolabeled nerve terminals. In the ME prepared by a freeze-drying technique and immunostained with gold-labeled IgG by the postembedding procedure, the immunolabeled terminals were seen to contain large cored vesicles (50–100 nm) labeled with gold and unlabeled small clear vesicles (30–50 nm). In normal cycling rats, the terminals contained large cored vesicles in diestrus, small clear vesicles in estrus, and both in proestrus. In PE rats, the terminals contained only small clear vesicles, but the cored vesicles appeared after ovariectomy. In the early stage of pregnancy, the terminals contained only small clear vesicles, but the large cored vesicles appeared in late pregnancy and during lactation. These findings present further evidence that the hypothalamic SP neurons are involved in the hypothalamic-hypophysial-gonadal axis in r

ISSN:0028-3835    

DOI:10.1159/000124764

出版商:S. Karger AG    

年代:1987

数据来源: Karger