Regulation of circadian rhythms

Abstract

The human circadian system is evidently regulated by components which can be found in the retina (light input), a suprachiasmatic nucleus in the hypothalamus (clock genes) and the pineal gland (melatonin synthesis). Clock genes are interdependent through two intracellular feedback loops. The pineal gland is not the single important producer of melatonin, as immune cells can also produce this hormone. Immune cells contain active clock genes as SCN cells and we can suggest that the regulation of the circadian system is a component of the neuroimmune regulation of the organism. The endogenous character is dominant in SCN, which is modulated by darkness and which synchronizes organisms to the light/dark regime including immunity. The exogenous character seems to be dominant in the immune system which synchronizes the organism including SCN cells to other environmental stimuli. The mathematical theory of chaos shows that the circadian activity of a cell is derived from ultradian metabolic rhythms; these rhythms support the stability of living systems which can be changed by a limited repertoire of interventions. The complexity of neuroimmune interactions perhaps explains why we are far from knowing the mechanism concerning the regulation of biorhythms despite the vast number of related scientific publications.