摘要:

Daily administration of melatonin (MT) markedly delays sexual maturation in the male Wistar rat. In this study, we have evaluated pituitary responsiveness to GnRH and the level of tonic inhibition by endogenous opioids in normal juvenile male rats and in rats with delayed sexual development induced by daily afternoon MT injection (100 µg, s.c.) starting at 20 days of life. Plasma LH responses to repetitive intravenous GnRH administration (100 ng/100 g body weight), or to different doses of GnRH administered subcutaneously (5–100 ng/100 g body weight) were normal in MT-treated rats both at 30 and 40 days of life despite significantly lower number of pituitary GnRH receptors and decreased pituitary gonadotropin content. One naloxone (NAL) injection (2.5–5.0 mg/kg, s.c.) produced a significant increase of plasma LH in normal 40- and 55-day-old rats, which was not seen in MT-treated rats of the same age. In contrast, no increase of plasma LH was seen in 30-day-old control rats nor in MT-treated rats at this age. Pretreatment with morphine sulfate (10 mg/kg, s.c), or with the potent Met-enkephalin analog FK 33–824 (1.0 mg/kg, s.c.) prevented the NAL-induced rise of plasma LH in control rats at day 40 of life. In all instances, plasma PRL levels were decreased after NAL both in untreated and in MT-treated rats. The lack of response to the NAL stimulation test in intact, sexually retarded MT-treated animals at 40 and 55 days of life further demonstrates that chronic administration of MT delays the maturation of neuroendocrine pathways that control the LH (GnRH) secretion during sexual maturation. Furthermore, the presence of normal pituitary responsiveness to GnRH in these rats confirms that MT administration does not impair pituitary response to this secret

ISSN:0028-3835    

DOI:10.1159/000124992

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

This study tested the hypothesis that estradiol can enhance LH pulse frequency in the ewe by an action which does not depend on other ovarian hormones. Long-term ovariectomized ewes were treated with a small subcutaneous estradiol implant at a time equivalent to the early breeding season (October), and frequent blood samples (6-min intervals) were obtained during sequential 3-hour periods over the next 84 h. All ewes responded with an increase in frequency of LH pulses, a response evident by 60 h and maintained at 84 h after initiation of the estradiol stimulus. Mean (± SE) pretreatment frequency was one pulse every 41 ± 2 min; that at the height of the response was one pulse every 34 ± 2 min(p < 0.01). This increased rate was equivalent to the annual mid-winter maximum observed in ovariectomized ewes not treated with estradiol. These findings are consistent with the hypothesis that estradiol can enhance LH pulse frequency by an action which does not depend on other ovarian steroids. It is suggested that this action contributes to the heightened pace of LH pulses during the follicular phase of the estrous cyc

ISSN:0028-3835    

DOI:10.1159/000124993

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

Because arginine vasotocin (AVT) activates male sexual behaviors in the rough-skinned newt (Taricha granulosa), quantitative autoradiography with radiolabelled arginine vasopressin (3H-AVP) was used to characterize putative AVT receptors in the telencephalon of this amphibian. Analyses were restricted to specific binding sites in the medial pallium, although dense binding also was observed in the dorsal pallium and amygdala pars lateralis. Binding of 3H-AVP to these sites was saturable, specific, reversible, of high affinity (Kd= 1 nM) and low capacity (57 fmol/mg protein). The rank order of potency of related peptides in inhibiting 3 d(CH2)5[Tyr(Me)2 AVP, oxytocin, and [dPen1Tyr(Me)2 mesotocin ≫ desGly(NH2)AVP, AVP fragment 4–9 and pressinoic acid. Thus, these binding sites appear to represent authentic central nervous system receptors for AVT. Furthermore, ligand specificity for the binding sites in this amphibian differ from that reported for AVP binding sites in rat brains. The AVT receptors in the medial pallium, dorsal pallium, and amygdala pars lateralis may represent site(s) of action where AVT elicits sexual behaviors in male T. granulosa.

ISSN:0028-3835    

DOI:10.1159/000124994

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

The present study was concerned with the effect of suckling on the hypothalamic release of thyrotropin-releasing hormone (TRH), dopamine and adrenaline in lactating rats as estimated by push-pull perfusion of the median eminence-arcuate nucleus area. The push-pull cannula was implanted on day 15 of pregnancy. This surgery did not interfere with pregnancy, time of delivery or lactation. Push-pull perfusion was performed on day 8 or 14 of lactation and 30 out of 42 perfusions were successful. On the day of perfusion mothers and young were separated. Six hours later push-pull perfusion was begun and 6 samples at 15-min intervals were collected. In control animals, not allowed to nurse pups during perfusion, the release of TRH, dopamine and adrenaline did not change during the 90-min period. In experimental animals, reunited with their litter after 30 min of perfusion, the hypothalamic release of adrenaline did not change. However, both on day 8 and 14 suckling induced a 50% decrease in the release of dopamine (p < 0.025) which lasted for 15–30 min. Suckling on day 14 did not affect the concentration of TRH in the perfusate, but on day 8 the TRH output gradually decreased for 45 min after the onset of sucklin

ISSN:0028-3835    

DOI:10.1159/000124995

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

The effects of sustained delivery of morphine and/or testosterone (T) on male rat copulatory behavior, penile reflexes and dopaminergic metabolism in selected brain regions were examined. Castration was followed by (1) a decrease in the number of male rats exhibiting intromissive and ejaculatory behavior in mating tests, (2) decreased erections in ex copula tests, and (3) increases in dopamine and dihydroxyphenylacetic acid (DOPAC) concentrations in the mediobasal hypothalamus (MBH) and the preoptic area-anterior hypothalamus (POA-AH). The decreased incidence of copulatory behavior and penile reflexes seen after castration was effectively prevented by a 4-day treatment with 5-mm T-containing Silastic capsules. Chronic morphine implants, conversely, accentuated the castration-induced decrements in copulatory behavior and prevented the 5-mm-T-induced facilitation, but did not alter the number of animals displaying erection (although the number of erections displayed by testosterone-treated rats was reduced) in ex copula tests. Treatment of castrated rats with 5 mm T, but not morphine alone, nor the combination of 5 mm T plus morphine, significantly reduced dopamine and DOPAC levels in the MBH. In the POA-AH, 5 mm T was without effect, whereas morphine, alone or in combination with 5 mm T, reduced the levels of dopamine and DOPAC. These data suggest that (1) the decline in sexual behavior induced by chronic morphine is primarily due to a failure of sexual arousal, and not of erectile ability, and (2) although the decline in sexual activity seen after castration is associated with alterations in dopaminergic metabolism, the effects of morphine and testosterone on sexual activity are opposite and dissociated from alterations in dopaminergic metabolism.

ISSN:0028-3835    

DOI:10.1159/000124996

出版商:S. Karger AG    

年代:1988

数据来源: Karger