Scopolamine-induced muscarinic supersensitivity in normal man: changes in sleep.

Scopolamine (6 microgram/kg) was administered on 3 consecutive mornings to normal human subjects. Sleep recordings obtained at night (when the central anticholinergic effect of the morning scopolamine was no longer present) indicated a significant reduction in latency to REM-sleep onset on the nights following the second and third injections. This effect is opposite to the direct pharmacological action of nighttime administration of scopolamine (i.e., prolongation of REM latency). In addition, total sleep time and sleep efficiency were reduced, and sleep latency was increased. Furthermore, scopolamine pretreatment on 2 consecutive mornings also potentiated the REM-inducing effect of arecoline, a central muscarinic agonist. These data are consistent with the development of cholinergic supersensitivity following cholinergic blockade.