[Brain neuronal mechanisms of circadian rhythms in mammalians]

It is now widely accepted that the suprachiasmatic nucleus (SCN) of the hypothalamus is a circadian pacemaker in the mammalians. This conclusion is based on three principal lines of the following evidence. First, ablation of the SCN results in a loss of circadian rhythms in rodents. Second, the SCN exhibits rhythms in neuronal activity and glucose metabolism both in vivo and in vitro experiments. Third, the transplantation of fetal SCN to the third ventricle of animals rendered arrhythmic++ by SCN ablation restores circadian function. In this review the anatomical, physiological and pharmacological characteristics of SCN neurons in vitro are discussed by focusing especially upon the roles of various neurotransmitters and modulators in the circadian system of mammals, in relation to the function of SCN.