Components and connections of the circadian timing system in mammals

Reuss, Stefan

doi:10.1007/s004410050652

Cited by 102 publications

(40 citation statements)

References 310 publications

(301 reference statements)

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“…The observations that in rats hypothalamic regions including the PVN (Mugnaini and Oertel, 1985;Meister et al, 1988;Sakaue et al, 1988) and LH (Mugnaini and Oertel, 1985;Okamura et al, 1990), RN (Nanopoulos et al, 1982;Mugnaini and Oertel, 1985;Stamp and Semba, 1995), and IGL (Takatsuji and Tohyama, 1989;Moore and Speh, 1993;Moore and Card, 1994) contain GABAergic neurons support this assumption. The IGL, RN, and PVN are regarded as important nuclei of the circadian timing system (Watts, 1991;Moore and Card, 1994;Morin, 1994;Reuss, 1996). Since the IGL is composed mostly of GABAergic neurons, GABA is believed to be the main neurotransmitter of the system (Moore and Speh, 1993).…”

Section: Discussionmentioning

confidence: 99%

Central GABAergic innervation of the mammalian pineal gland: A light and electron microscopic immunocytochemical investigation in rodent and nonrodent species

2000

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Light and electron microscopic immunocytochemical observations were made to demonstrate central pinealopetal fibers immunoreactive for gamma-aminobutyric acid (GABA) and synapses between their terminals and pinealocytes in the pineal gland of four rodent (Wistar-King rat; mouse; Syrian hamster, Mesocricetus auratus; Hartley strain guinea pig) and one nonrodent (tree shrew, Tupaia glis) species. GABA-immunoreactive myelinated and unmyelinated fibers and endings were found in the parenchyma of the pineal gland of all the animals examined. In the rodent species, GABAergic fibers were mainly found in the intermediate and proximal portions of the pineal gland and were nearly or entirely absent in the distal portion of the gland. Abundant GABAergic fibers were evenly distributed throughout the gland of the tree shrew. In all the animals, the habenular and posterior commissures contained abundant GABA-positive fibers, and some of them were followed to the pineal gland. GABA-positive endings made synaptic contact with pinealocytes, occasionally in mice and guinea pigs, and frequently in tree shrews; no synapses were observed in Syrian hamsters and rats. In the pineal gland of all the animals, GABA-immunoreactive cell bodies were not detected, and sympathetic fibers were not immunoreactive for GABA. These data indicate that GABAergic fibers are main pinealopetal projections from the brain. In view of the difference in the distribution of these fibers, central GABAergic innervation may play a more significant role in nonrodents than in rodents. The frequent occurrence of GABAergic synapses on pinealocytes in the tree shrew suggests that GABA released at these synapses directly controls activity of pinealocytes of this animal.

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Section: Discussionmentioning

confidence: 99%

Central GABAergic innervation of the mammalian pineal gland: A light and electron microscopic immunocytochemical investigation in rodent and nonrodent species

2000

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“…They are coupled to G-proteins mediating the inhibitory influences of melatonin on cyclic nucleotides [37]. Putative melatonin receptors have also been shown in other neural structures as well as in non-neural organs of various systems [38].…”

Section: Discussionmentioning

confidence: 99%

Evidence for a circadian rhythm of insulin release from perifused rat pancreatic islets

1998

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While there is strong evidence that circadian rhythms are generated in the mammalian suprachiasmatic nucleus (SCN) [1,2] and in the avian pineal gland [3,4], determinations of circadian rhythms in other isolated organs or cells are rare. Only few in vitro investigations of insect tissues or mammalian cells or organs such as intestine, adrenals [5±7], heart cell networks and liver cells [8,9] have shown the existence of circadian rhythms in culture [10,11]. In addition it has been shown that cultured mammalian retina possesses a genetically programmed circadian oscillator which regulates the synthesis of melatonin in this tissue. These observations suggest that all vertebrate photoreceptive structures synthesize melatonin under the control of circadian oscillators [12]. A circadian rhythm is an oscillation with a period duration of approximately 24 h (range 20 to 28 h). Ultradian rhythms are oscillations with periods of less than 20 h.Various investigators have postulated oscillations of insulin secretion in a range of seconds [13] or periods between 9 and 14 min under both in vivo and in vitro conditions [14] or clonal pancreatic beta cells with periods of 5 to 8 min superimposed on 15 to Diabetologia (1998) Summary This study aims to analyse a circadian rhythm of insulin secretion from isolated rat pancreatic islets in vitro and its potential modulation by melatonin, the concentrations of which change in vivo inversely to that of insulin. The circadian rhythm was evaluated in a perifusion system, adapted to the specific conditions of pancreatic islets. To determine rhythmicity of insulin secretion, 30-min fractions were collected continuously for investigative periods of 44 to 112 h. Insulin secretion in 10 experiments was analysed by using the MacAnova-program for period length (t), the c 2 -periodogram for test of significance (p < 0.001), and additionally the empirical cosine adaptation for amplitude and goodness-of-fit. Thereby a circadian pattern was observed with periods (t) between 21.8 and 26.2 h. The period duration (mean ± SEM) was 23.59 ± 0.503 h, the overall mean insulin release 1038 ± 13 pmol/l and the mean amplitude 88 ± 17 pmol/l. Adding melatonin (10 nmol/l, t = 2 h) as a hormonal Zeitgeber during analysis of circadian insulin secretion phase-response studies show phase-shifts with approximately 9 h phase advance. Thereafter the circadian period was maintained, while the amplitude was enhanced. From this it is concluded that an endogenous circadian oscillator is located within the pancreatic islets of the rat that regulates circadian insulin secretion of the insulin-producing beta cells. The pacemaker is remarkably stable, because its periodicity is not affected by factors altering insulin secretion. In agreement with inhibitory influences of melatonin (range 0.5 nmol/l to 5 mmol/l) on the insulin response in vitro, the phaseresponses support the contention that pancreatic beta cells may be targets for melatonin action. [Diabetologia (1998)

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“…This zone also receives dense inputs from the suprachiasmatic nucleus (Swanson and Cowan, 1975b;Berk and Finkelstein, 1981;Watts, 1991;Vrang et al, 1995), where a circadian rhythm generator exists (Moore, 1983;Card and Moore, 1991;Reuss, 1996), and has been considered to integrate circadian and metabolic information for regulating the hypothalamopituitary axis (Elmquist et al, 1998) and to regulate behavioral rhythms (Watts, 1991). Based on these data, we raise the possibility that the Sv may participate in the control of behavioral rhythms and associated endocrine responses.…”

Section: Functional Considerationsmentioning

confidence: 98%

Topographical organization of projections from the subiculum to the hypothalamus in the rat

et al. 2000

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Components and connections of the circadian timing system in mammals

Cited by 102 publications

References 310 publications

Central GABAergic innervation of the mammalian pineal gland: A light and electron microscopic immunocytochemical investigation in rodent and nonrodent species

Central GABAergic innervation of the mammalian pineal gland: A light and electron microscopic immunocytochemical investigation in rodent and nonrodent species

Evidence for a circadian rhythm of insulin release from perifused rat pancreatic islets

Topographical organization of projections from the subiculum to the hypothalamus in the rat

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