Circadian pacemaker suprachiasmatic

Circadian clock-controlled rhythms provide most organisms with an orchestrated temporal programme that allows for appropriate timing of physiology (i.e. blood pressure, hormonal levels) and behaviour (i.e. alertness, sleep-wake cycle). The mammalian central circadian pacemaker resides in the suprachiasmatic nucleus (SCN) of the brain (Weaver 1998). At the molecular level, the core oscillator driving the mammahan clock consists of interconnected autoregulatory... 

Pittendrigh CS, Daan S 1976a A functional analysis of circadian pacemakers in nocturnal rodents. 1. The stability and lability of spontaneous frequency. J Comp Physiol A 106 223-252 Pittendrigh CS, Daan S 1976b A functional analysis of circadian pacemakers in nocturnal rodents. IV. Entrainment pacemaker as clock. J Comp Physiol [A] 106 291—331 Ralph MR, Foster RG, Davis FC, Menaker M 1990 Transplanted suprachiasmatic nucleus determines circadian period. Science 247 975-978 Redlin U, Mrosovsky N 1999 Masking by light in hamsters with SCN lesions. J Comp Physiol [A] 184 439-448... 

Jovanovska A, Prosser RA. Translational and transcriptional inhibitors block serotonergic phase advances of the suprachiasmatic nucleus circadian pacemaker in vitro. J Biol Rhythms 2002 17 137-146. 

The autonomous functions exhibit circadian rhythms which are under the control of a neuronal pacemaker, located in the suprachiasmatic nuclei (SCN) of the hypothalamus. The circadian pacemaker arises from complex dynamics of gene expression and is synchronized to the external light. In the case of mental disorders, the regular rhythms of autonomous functions are obviously disturbed which led to the formulation of the desynchronization hypotheses [8, 9], This does not necessarily contradict the transmitter hypothesis . Transmitter imbalance, of course, also interferes with the inherent system dynamics and can change the endogenous rhythmicity, eventually with the result of desynchronization. A first computational approach which simulates the rhythmicity of the HPA axis and its alterations with scaling of transmitter mediated positive and negative feedback loops is briefly summarized in the second Results section. 

Meijer, J.H. W.J. Rietveld. 1989. Neurophysiology of the suprachiasmatic circadian pacemaker in rodents. Physiol. Rev. 69 671-707. 

Yamazaki S, AlonesV, Menaker M 2002a Interaction of the retina with suprachiasmatic pacemakers in the control of circadian behavior. J Biol Rhythms 17 315-329 Yamazaki S, Straume M, Tei H, Sakaki Y, Menaker M, Block GD 2002b Effects of aging on central and peripheral mammalian clocks. Proc Natl Acad Sci USA 99 10801-10806... 

Damiola F, Le Minh N, Preitner N, Kornmann B, Fleury-Olela F, Schibler U 2000 Restricted feeding uncouples circadian oscillators in peripheral tissues from the central pacemaker in the suprachiasmatic nucleus. Genes Dev 14 2950-2961... 

The mammalian suprachiasmatic nuclei contain an endogenous pacemaker that generates daily rhythms in behaviour and secretion of hormones. They stimulate evening ACTH secretion in the rat (Cascio etal. 1987). Kalsbeek etal. (1996) used microdialysis-mediated intracerebral administration of the vasopressin V,-receptor antagonist to study the mechanisms underlying the circadian control of basic corticosterone release in the rat. By timed administration of the vasopressin antagonist divided equally over the day/night cycle, they were able to uncover the existence of an additional stimulatory input from the suprachiasmatic nucleus to the hypothalamo-pituitary-adrenal axis. 

---