CIRCADIAN-RHYTHM AND EFFECTS OF LIGHT ON CAMP CONTENT OF THE DWARF HAMSTER SUPRACHIASMATIC NUCLEUS

The present study was conducted in the dwarf hamster (Phodopus sungoru s) to investigate whether a circadian rhythm is present in the content of the second messenger cyclic adenosine 3',5'-monophosphate (cAMP) i n the suprachiasmatic nucleus (SCN), the endogenous clock in mammals. In animals held under light/dark conditions (LD), we observed high lev els at the end of the light phase and low levels during the night in f rozen SCN punches. In animals held in continuous dark, a similar rhyth m was seen although a second peak was present in the subjective day. I n senile hamsters under LD, the decrease of cAMP levels at the light t ransition was not seen. These data, obtained for the first time from h amsters, support the view that cAMP is involved in time-keeping mechan isms within the SCN. (C) 1998 Elsevier Science Ireland Ltd.