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 sungorus) to investigate whether a circadian rhythm is present in the content of the second messenger cyclic adenosine 3',5'-monophosphate (cAMP) in the suprachiasmatic nucleus (SCN), the endogenous clock in mammals. In animals held under light/dark conditions (LD), we observed high levels at the end of the light phase and low levels during the night in frozen SCN punches. In animals held in continuous dark, a similar rhythm was seen although a second peak was present in the subjective day. In senile hamsters under LD, the decrease of cAMP levels at the light transition was not seen. These data, obtained for the first time from hamsters, support the view that cAMP is involved in time-keeping mechanisms within the SCN.