Abstract

Fetal lambs were prepared for chronic intrauterine recording of behavioral states and breathing movements during the third trimester of pregnancy. Pilocarpine administered directly to the fetus produced an immediate change from quiet sleep to arousal. Neither the time spent in rapid eye movement (REM) sleep nor the latency to REM sleep was affected. Associated with this change in sleep-wake patterns, pilocarpine produced a dose-dependent increase in the incidence of fetal breathing movements. These effects of pilocarpine on behavioral states and breathing movements were blocked by atropine sulfate but not by methylatropine. We conclude that the increased incidence of breathing movements produced by pilocarpine are due, in part, to increased arousal at the expense of quiet sleep. As a result, the fetus alternates between arousal and REM sleep, and this behavioral pattern results in sustained breathing movements. In addition, pilocarpine increases the incidence of breathing movements in all three behavioral states. These effects of pilocarpine are mediated primarily via central muscarinic sites of action.