Circadian pacemaker nucleus

Lesions of serotonergic neurons in laboratory animals have been reported by some, but not all, investigators to disrupt locomotor rhythms or to result in the loss of the daily rhythm of corticosterone. There is evidence that, in the hamster, the median raphe nucleus projects to the SCN whereas the dorsal raphe nucleus innervates the IGL furthermore, the serotonergic innervation to the SCN and not the IGL is necessary for the photic entrainment of locomotor activity [22]. It appears then, that the SCN circadian pacemaker or clock is modulated by stimulation of serotonergic receptors in the SCN and that serotonergic projections to the SCN may modulate the phase of the SCN in intact animals. 

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. 

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. 

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