Carbachol phase shifts circadian activity rhythms in ovariectomized rats

Ovariectomy in the rat abolishes alpha-bungarotoxin (alpha-BTX) binding within the suprachiasmatic nucleus (SCN), a putative circadian pacemaker, and markedly reduces cholinergic activation of SCN cells. Circadian rhythms of running wheel activity were monitored continuously in intact male and female and chronically ovariectomized rats before and after intraventricular carbachol injections. Carbachol produced similar phase shifts of the free-running rhythms in all groups. The results suggest that carbachol can influence the circadian system of rats by activation of cholinergic receptor sites independent of those binding alpha-BTX within the SCN.