Circadian rhythm of adenosine-3′,5′-monophosphate content in suprachiasmatic nucleus (SCN) and ventromedial hypothalamus (VMH) in the rat

Abstract

Twenty-four hour patterns of adenosine-3′,5′-monophosphate (cAMP) contents in the suprachiasmatic nucleus (SCN) and the ventromedial hypothalamus (VMH) were determined at 3 h intervals under various conditions in adult male rats. The cAMP levels in both the nuclei showed a circadian variation with a clear peak time, which shifted under constant conditions (blinded and constant illumination). Under both entrained and free-running conditions, a consistent phase-angle difference of 9 h in peak time was observed between cAMP rhythms in the SCN and VMH. Under the LD cycle, the peak time of cAMP rhythms in the SCN and VMH appeared at 16.00 h and 07.00 h, respectively. The cAMP rhythm in the VMH synchronized with a restricted feeding time, when the rats were subjected to restriction of access to food under constant light. On the contrary, that in SCN did not synchronize with the restricted feeding time. These results indicate that the 24-h patterns of cAMP contents in SCN and VMH are the manifestation of endogenous circadian rhythms. However, the generating mechanism of cAMP rhythm may be different between SCN and VMH, as the restricted feeding regime affected the cAMP patterns of both the nuclei in different ways.