摘要:

Abstract:This review summarizes the evidence showing that the duration of the nocturnal secretory profile of pineal melatonin (MEL) is critical for eliciting seasonally appropriate reproductive physiological and behavioral responses in mammals. We review experiments using the timed infusion paradigm (TIP) to deliver MEL either systemically or centrally to pinealectomized hamsters and sheep. In this paradigm, MEL is infused, usually once daily, for a specific number of hours and at a predetermined time of day. This experimental strategy tests most directly those features of the MEL signal that are necessary to trigger photoperiodic responses. The data suggest that the duration of the MEL stimulation is the critical feature of the MEL signal for both inhibitory and stimulatory effects of the hormone on the photoperiodic control of reproductive development in juvenile Siberian hamsters, and for the photoperiodic control of reproductive and metabolic responses in adult Siberian and Syrian hamsters and sheep. The use of the TIP reveals the importance of the frequency of the signal presentation of MEL and suggests the importance of a period of low‐to‐absent circulating concentrations of the hormone. The TIP also reveals that the characteristics of the MEL signal that regulate male sexual behavior are similar to those that are critical for reproductive and metabolic responses in Syrian hamsters. We summarize the locations of possible functional MEL target sites identified by combining the TIP with traditional brain lesion techniques. Evidence from such studies suggests that the integrity of the suprachiasmatic nucleus (SCN) region in Siberian hamsters and the anterior hypothalamus in Syrian hamsters is necessary for the response to short‐day MEL signals. The TIP has been used to deliver MEL to putative target sites for the hormone in the brain of juvenile and adult Siberian hamsters. The results of these preliminary experiments suggest that the regions of specific MEL binding in this species, especially the SCN, are effective sites where MEL may stimulate short‐day‐type responses. In contrast, results from intracranial application of MEL in sheep suggest the medial basal hypothalamus as a critical site of action. Finally, we also discuss potential applications of the TIP for identification of brain MEL target sites, understanding of other photoperiodic phenomena and responses, and resolution of the cellular/molecular basis underlying the reception and interpretation of MEL signals. It is our collective view that the TIP has played, and will continue to play, a pivotal role in elucidation of the function of MEL in the photoperiodic control of seasonal mammalian responses and that the duration of the MEL signal is the critical parameter of the nocturnal secretion profile of the hormone for the photoperiodic control of several seasonally adaptive responses in mammalian species as diverse as hamsters

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1993.tb00903.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract:Although sleep disturbance is commonly reported in pregnancy, there have been surprisingly few studies on the etiology of this condition. Since most hormones show circadian rhythmicity and maintain specific phase relationships with that of the sleep‐wake cycle, it was of interest to establish whether sleep disturbances covaried with endocrine changes. This overnight study of pregnant women compared melatonin, cortisol, and prolactin secretion rhythms in six good sleepers and six poor sleepers. The groups were compared by ratios of the areas under the various hormonal curves. Significant differences in the cortisol/melatonin ratio were found between the poor sleeper group (lower values) and the good sleeper group (higher values). Nonsignificant trends, which might be expected to become significant with larger sample sizes, were found for decreased amplitude in the cortisol rhythm and increased amplitude in the melatonin rhythm in poor sleepers. The decreased amplitude of the cortisol rhythm in poor sleepers appeared to be due to a suppression of the early morning (0500–0800) rise. Prolactin levels were high and showed no rhythmicity in both groups. These differences may reflect changes in the circadian pacemaker system of poor sleepers, with increases in melatonin release being a response to counteract poor sl

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1993.tb00904.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract:Previous studies have shown that pinealocytes of the gerbil pineal gland exhibit processes that form terminal swellings filled with abundant electron‐lucent microvesicles. The membrane of these presumptive secretory microvesicles is known to contain synaptophysin, a major integral glycoprotein of neuronal synaptic vesicles. The present study was conducted to evaluate the microtopographical relationships between the vesicle‐rich process swellings and intra‐pineal nerve terminals. For this purpose, both nerve terminals and pinealocyte process endings were visualized immunohistochemically in the same semi‐thin sections of plastic‐embedded gerbil pineals, using antibodies directed against synaptophysin. This approach consistently revealed close spatial associations of punctate immunopositive nerve endings with intensely stained bulbous process terminals of pinealocytes in or near the perivascular spaces. The light‐microscopic observations of intimate neuronal‐pinealocytic relationships were corroborated at the electron‐microscopic level. Perivascular varicosities with ultrastructural features characteristic of sympathetic nerve terminals were frequently juxtaposed to vesicle‐filled process endings of pinealocytes. Analysis of serial thin sections showed that multiple point‐to‐point contacts are encountered between noradrenergic nerve terminals and pinealocytic process swellings. Our morphological findings imply that bulbous process terminals, at least in the gerbil pineal gland, are major targets for the neuronal control of the secretory act

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1993.tb00905.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1993.tb00906.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY