Pineal melatonin rhythms and the timing of puberty in mammals

Summary The direction of change in daylength provides the seasonal time cue for the timing of puberty in many mammalian species. The pattern of melatonin secretion from the pineal gland transduces the environmental light-dark cycle into a signal influencing the neuroendocrine control of sexual maturation. The change in duration of nocturnal melatonin secretion is probably the key feature of the melatonin signal which conveys daylength information. This information may also be used by neuroendocrine axes controlling seasonal changes in pelage colour, growth and metabolism. The mechanism of action of melatonin on neuroendocrine pathways is unknow. Although the ability to synthesize and secrete melatonin in a pattern that reflects the duration of the night may not occur until the postnatal period, the rodent and ovine foetus has the ability to respond in utero to photoperiodic cues to which its mother is exposed in late gestation. Transplacental passage of maternal melatonin is likely to be the mechanism by which photoperiodic cues reach the foetus. Species which do not exhibit seasonal patterns of puberty, such as the human, also secrete melatonin in a pattern which reflects the environmental light-dark cycle, but they do not respond reproductively to the seasonal melatonin information.     

Zeitgeber-schedule dependent resynchronization of circadian rhythms in nocturnal mammals (Primates and Chiroptera)

Summary Changing the L: D time ratio of an entraining light-dark regime leads to characteristic alterations of the resynchronization behaviour of the circadian activity rhythms in night monkeys (Aotus trivirgatus) and African fruit bats (Rousettus aegyptiacus) after 8 h advance and delay shifts of the LD-Zeitgeber. Reduced speed of re-entrainment and occurrence of antidromic resynchronization point to a lower Zeitgeber strength of 24-h LD-cycles with a prolonged D-phase.Supported by the Deutsche Forschungsgemeinschaft (Er 59/8).     

Clinical aspects of the melatonin action: impact of development,aging, and puberty,involvement of melatonin in psychiatric disease and importance of neuroimmunoendocrine interactions

During the last decade we have learned much on physiological changes in the secretion of the pineal hormone melatonin (MLT) in man. Reportedly, there is little or no MLT secreted before age 3 months. Then MLT production commences, becmes circadian, and reaches highest nocturnal levels at the age of 1–3 years. During all of childhood nocturnal peak levles drop progressively by 80% until adult levels are reached. This alteration appears to be the consequence of increasing body size in face of constant MLT production during childhood. The biological significance of this MLT alteration is presently unknown. Because of conceptual considerations, major depressive syndrome (MDS) and seasonal affective disorder (SAD) have been in the focus of pineal research for several years. Although in these disorders alterations in MLT levels could not be substantiated, light therapy, a consequence of this research, was discovered as an effective treatment for SAD and perhaps for MDS. In addition, there is some recent evidence for low MLT levels in schizophrenia. Finally, the potential effect of MLT in neuroimmunoendocrine interactions is presently explored. Reportedly, in vitro studies and animal experiments give evidence for a modulatory role of MLT in the immune response. However, the exact way of this possible action of MLT remains to be clarified. Clinical studies are too scant for a meaningful estimation of MLT's involvement in human neuroimmunoendocrine interactions.     

Differential displacement of cells from the median eminence into the arcuate nucleus during puberty. Effects of melatonin administration

Summary A displacement of catecholaminergic-positive and catalase-containing cells from the median eminence into the arcuate nucleus at puberty has been described previously. This study reports on the displacement phenomena after postnatal administration of melatonin. Catalase-positive cells undergo a delayed displacement from the median eminence into the arcuate nucleus. However, part of this cell population lags behind within the median eminence. This differential reaction of cell displacement by catalase-positive cells is considered as a special reaction of these cells to melatonin administration.     

Differential displacement of cells from the median eminence into the arcuate nucleus during puberty. Effects of melatonin administration

A displacement of catecholaminergic-positive and catalase-containing cells from the median eminence into the arcuate nucleus at puberty has been described previously. This study reports on the displacement phenomena after postnatal administration of melatonin. Catalase-positive cells undergo a delayed displacement from the median eminence into the arcuate nucleus. However, part of this cell population lags behind within the median eminence. This differential reaction of cell displacement by catalase-positive cells is considered as a special reaction of these cells to melatonin administration.     

Pineal body and urinary sodium excretion in the rat

Zusammenfassung Ein salinischer Extrakt desCorpus pineale erzeugt bei normalen, nicht aber bei adrenalektomierten Ratten eine starke Retention von Natrium. Auf Grund der besonderen anatomischen Verhältnisse des Corpus pineale der Ratte vertreten wir die Auffassung, dass die wirksame Substanz, wahrscheinlich Adrenoglomerulotropin, in der Zirbeldrüse selbst erzeugt wird und nicht aus der Nachbarschaft dort angereichert wird.     

Bromocryptine treatment and puberty attainment in the female rat

Summary The influence of bromocryptine treatment on the timing of vaginal patency and 1st oestrus in female rats was studied. No significant influence of bromocryptine on these parameters was noted, and it is concluded that suppression of prolactin secretion has no effect on puberty attainment.Acknowledgment. We thank Professor E. Flückiger and Dr H. Friedli, Pharmaceutical Division, Sandoz Ltd, Basle, Switzerland, for the donation of bromocryptine mesylate.     

Pineal inhibition of compensatory testicular enlargement in light-deprived hamsters

Zusammenfassung Halbseitige Kastration fÜhrt bei geblendeten Goldhamstermännchen mit Atrophie der Geschlechtsorgane nur nach Pinealektomie zu kompensatorischer Hodenhypertrophie.

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Supported by grant No. HD-02937 United States Public Health Service.

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U.S.P.H.S. Career Development Awardee (No. 1 K04 HD42398).     

Pineal function cannot prevent the occurrence of castration cells in male rats

Summary The relationship between the pineal gland and the pituitary gland was investigated in male rats. The results indicate that the hypothalamo-adenohypophysial-gonadal axis is affected by the pineal gland, but the appearance of castration cells following gonal ablation may be only slightly modified by alterations in pineal gland function.     

Pineal function cannot prevent the occurrence of castration cells in male rats

The relationship between the pineal gland and the pituitary gland was investigated in male rats. The results indicate that the hypothalamo-adenohypophysial-gonadal axis is affected by the pineal gland, but the appearance of castration cells following gonad ablation may be only slightly modified by alterations in pineal gland function.     

Leptin signaling and circuits in puberty and fertility

Leptin is an adipocyte-derived hormone involved in a myriad of physiological process, including the control of energy balance and several neuroendocrine axes. Leptin-deficient mice and humans are obese, diabetic, and display a series of neuroendocrine and autonomic abnormalities. These individuals are infertile due to a lack of appropriate pubertal development and inadequate synthesis and secretion of gonadotropins and gonadal steroids. Leptin receptors are expressed in many organs and tissues, including those related to the control of reproductive physiology (e.g., the hypothalamus, pituitary gland, and gonads). In the last decade, it has become clear that leptin receptors located in the brain are major players in most leptin actions, including reproduction. Moreover, the recent development of molecular techniques for brain mapping and the use of genetically modified mouse models have generated crucial new findings for understanding leptin physiology and the metabolic influences on reproductive health. In the present review, we will highlight the new advances in the field, discuss the apparent contradictions, and underline the relevance of this complex physiological system to human health. We will focus our review on the hypothalamic circuitry and potential signaling pathways relevant to leptin’s effects in reproductive control, which have been identified with the use of cutting-edge technologies of molecular mapping and conditional knockouts.     

Comparative myogenesis in teleosts and mammals

Skeletal myogenesis has been and is currently under extensive study in both mammals and teleosts, with the latter providing a good model for skeletal myogenesis because of their flexible and conserved genome. Parallel investigations of muscle studies using both these models have strongly accelerated the advances in the field. However, when transferring the knowledge from one model to the other, it is important to take into account both their similarities and differences. The main difficulties in comparing mammals and teleosts arise from their different temporal development. Conserved aspects can be seen for muscle developmental origin and segmentation, and for the presence of multiple myogenic waves. Among the divergences, many fish have an indeterminate growth capacity throughout their entire life span, which is absent in mammals, thus implying different post-natal growth mechanisms. This review covers the current state of the art on myogenesis, with a focus on the most conserved and divergent aspects between mammals and teleosts.     

Melatonin and circadian control in mammals

Summary Although pinealectomy has little influence on the circadian locomotor rhythms of laboratory rats, administration of the pineal hormone melatonin has profound effects. Evidence for this comes from studies in which pharmacological doses of melatonin are administered under conditions of external desynchronization, internal desynchronization, steady state light-dark conditions, and phase shifts of the zeitgeber. Taken together with recent findings on melatonin receptor concentration in the rat hypothalamus, particularly at the level of the suprachiasmatic nuclei, these results suggest that melatonin is a potent synchronizer of rat circadian rhythms and has a direct action on the circadian pacemaker. It is possible, therefore, that the natural role of endogenous melatonin is to act as an internal zeitgeber for the total circadian structure of mammals at the level of cell, tissue, organ, whole organism and interaction of that organism with environmental photoperiod changes.     

Melatonin and circadian control in mammals

Although pinealectomy has little influence on the circadian locomotor rhythms of laboratory rats, administration of the pineal hormone melatonin has profound effects. Evidence for this comes from studies in which pharmacological doses of melatonin are administered under conditions of external desynchronization, internal desynchronization, steady state light-dark conditions, and phase shifts of the zeitgeber. Taken together with recent findings on melatonin receptor concentration in the rat hypothalamus, particularly at the level of the suprachiasmatic nuclei, these results suggest that melatonin is a potent synchronizer of rat circadian rhythms and has a direct action on the circadian pacemaker. It is possible, therefore, that the natural role of endogenous melatonin is to act as an internal zeitgeber for the total circadian structure of mammals at the level of cell, tissue, organ, whole organism and interaction of that organism with environmental photoperiod changes.     

Daily rhythms in the endocrine glands of drosophila larvae

Zusammenfassung Neurosekretorische Zellen, Corpus allatum, Prothoraxdrüsen- und Fettkörperzellen in Drosophilalarven zeigen tägliche, zweigipflige Schwankungen der Zellkerngrösse. Ein ähnliches Muster konnte auch in den Nucleoli der Prothoraxdrüsen beobachtet werden.