Circadian rhythm of the rat suprachiasmatic brain slice is rapidly reset by daytime application of cAMP analogs.

Cellular mechanisms underlying the primary circadian pacemaker in mammals were investigated by isolating rat suprachiasmatic nuclei in brain slices and maintaining them in vitro for up to 3 days. The circadian rhythm of neuronal firing rate was used to assess the phase of the pacemaker. This rhythm was rapidly reset by bath application of cAMP analogs. Moreover, the pacemaker demonstrated circadian sensitivity to analog treatment: the rhythm was advanced by application during the donor's day, but not during the donor's night. These results suggest that cAMP-mediated events may stimulate pacemaker afferents within the SCN or may directly influence the pacemaker mechanism.