ATROPINE EFFECTS ON THE INTERMEDIATE STAGE AND PARADOXICAL SLEEP IN RATS

Paradoxical sleep (PS) in the rat, cat and mouse is preceded and somet imes followed by a short-lasting intermediate stage (IS) characterized by high amplitude cortical spindles and low frequency theta rhythm. T his stage, which is mimicked by an intercollicular transection, is mas sively extended at the expense of PS by low doses of barbiturates. Sin ce the pontine cholinergic cell activation of PS is suppressed by barb iturates, we studied whether atropine, an antimuscarinic compound, ext ends IS at the expense of PS. Atropine sulfate was given at 5, 10 and 20 mg/kg IP. All doses increased dose dependently the occurrence laten cy of IS and PS. The amount of IS and PS was decreased for several hou rs, principally by a decrease of the number of phases. At 20 mg/kg the phase mean duration of IS and PS was also decreased. Consequently, IS and PS are similarly supported by muscarinic processes. The theta rhy thm frequency was scored during IS and outside PS phasic motor activit ies (type 2 theta). At all doses it was significantly increased for ho urs. The theta rhythm frequency was also transiently increased during the hypersynchronization periods of PS (type 1 theta). At 20 mg/kg it was similarly the case for type 1 theta rhythm during waking.