Melatonin and circadian control in mammals

Abstract

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.

Abnormal development of the locus coeruleus in Ear2(Nr2f6)-deficient mice impairs the functionality of the forebrain clock and affects nociception

“…Several brain areas such as the dorsomedial nucleus of the hypothalamus (Chou et al 2003), the paraventricular nucleus of the hypothalamus (Buijs et al 2003), and the pineal gland (Armstrong 1989;Cassone 1992) modulate circadian behavior and rhythm stability. Most of those structures are innervated by the LC (e.g., Shirokawa and Nakamura 1987;Cunningham and Sawchenko 1988) and may hence singly or in combination contribute to the accuracy/stability phenotype.…”

Circadian actions of melatonin at the suprachiasmatic nucleus

“…At this subjective day-night transition point, melatonin caused daily activity bouts to recur with a fixed phase relation to the time of injection. When the relation between the timing of single injections was assessed against subsequent phasing of behavioral rhythms, melatonin administration at CT 10 (roughly 22 h after activity-onset in these rats free-running in constant darkness) induced permanent phase advance of locomotor rhythms [1]. Melatonin was largely ineffective at other times tested, although report of a responder to a predawn injection [l] suggests that sensitivity of the circadian system to melatonin might reappear shortly before dawn.…”

“…phase 1,9]. Because the tissue is under constant conditions in the brain-slice chamber, this circadian rhythm of neuronal activity is generated by the SCN's biological clock.…”

Sincronização fótica de um roedor subterrâneo: um estudo cronobiológico de campo e de laboratório do tuco-tuco (Ctenomys cf. knighti)

“…As eferências que partem dos NSQs para os órgãos efetores podem ter natureza nervosa (Bartness et al, 2001) ou humoral (LeSauter & Silver, 1998). Além disso, os NSQs controlam o ritmo de secreção de melatonina pela glândula pineal e o ritmo de temperatura, ambos capazes de atingir diferentes sistemas fisiológicos (Armstrong, 1989;Buhr et al, 2010). Por fim, quase todos os órgãos podem ser considerados órgãos efetores, já que foram observados ritmos circadianos na maioria das variáveis biológicas estudadas (Szabó et.…”

“…Além do ciclo claro-escuro, a cada espécie está associado um conjunto próprio de outros ciclos ambientais (ciclos de temperatura, disponibilidade de alimento, som, etc), que agem sinergicamente no processo de sincronização dos ritmos circadianos (Stephan, 2002;Refinetti, 2010). Existem também osciladores periféricos (Yamazaki et al, 2000), e uma maior complexidade nas relações entre os componentes do sistema (Reebs & Mrosovsky, 1989;Armstrong, 1989). Não obstante, algumas propriedades emergentes do sistema podem ser entendidas utilizando-se apenas o modelo simplificado da figura 1.3 e, por essa razão, todas as discussões aqui apresentadas serão baseadas nesse modelo básico.…”