Administration of carbachol into the lateral ventricle and suprachiasmatic nucleus (SCN) produces dose-dependent phase shifts in the circadian rhythm of locomotor activity

The cholinergic agonist, carbachol, induces phase-dependent shifts in the timing of the circadian rhythm of locomotor activity (CRLA). The effects of carbachol injections into the lateral ventricles of hamsters were compared between circadian times that produce phase delays vs. phase advances in the CRLA. The shape of the dose-response curves and the ED₅₀ for carbachol injections were similar for the two injection times. The second experiment demonstrated the dose-dependence of phase advances produced by carbachol injections into the area of the suprachiasmatic nucleus. These results indicate that carbachol exerts similar dose-dependent actions for both phase advances and phase delays.