Abstract
Circadian time-keeping system regulate behavior and physiological functions in most living organs. Recently, molecular links between the endogenous circadian clock and cell cycle regulation is reported. Biochemical changes, including the cancer an abnormal cell proliferation, induces dysfunction of clock in the suprachiasmatic nucleus a center of biological rhythm.Therefore, we examined an effect of carcinogenic drug on circadian-locomotor-activity rhythm. Diethylnitrosamine (DEN), which is widely used to cause hepatic carcinoma, was injected (i.p. 200 mg/kg) on rats kept under the light-dark (LD) cycle, constant dim light (DD) and constant light (LL). After the activity recording, livers of same specimens were histochemically analyzed using GST-P immunostaining, early detection marker of carcinogenicity, positive cells.After the DEN injection, decrease of activity mass on the next day was common in any of lighting conditions. Phase resetting under the LL and DD was observed without period length changes. The GST-P positive cell emerged most under the LD.It is known that locomotor activity rhythm and melatonin secretion couples well, and melatonin has a cancer chilling effect. The decrease of active mass under the LL suggested possibility to surpass restraint of melatonin secretion. [J Physiol Sci. 2007;57 Suppl:S73]
