INFLUENCE OF ZOLPIDEM, A NOVEL HYPNOTIC, ON THE INTERMEDIATE-STAGE AND PARADOXICAL SLEEP IN THE RAT

Paradoxical sleep (PS) in mice, rats, and cats is preceded and sometim es followed by a short-lasting stage characterized by cortical high-am plitude spindles and hippocampal low-frequency theta rhythm. This inte rmediate stage (IS) seems to correspond to a transient functional disc onnection of the forebrain from the brainstem. Pentobarbital and benzo diazepines greatly extend IS at the expense of PS, which is suppressed . Zolpidem, a new imidazopyridine hypnotic, was studied at 2.5, 5, and 7.5 mg/kg IP. At 2.5 mg/kg, which is already a true hypnotic dose, it only decreased PS during the first 2 h of recording with a rebound du ring the following 4 h of recording. At 5 mg/kg, zolpidem increased th e number and total duration of IS episodes, increased IS episodes not followed by PS, and increased PS latency of occurrence. PS amount was decreased during the first three h with a rebound in the next 3 h. At 7.5 mg/kg, the total amount of PS was also decreased. The eye movement number and theta rhythm frequency of PS were unchanged. These results show that zolpidem produces less disruption of the association betwee n IS and PS than do previous hypnotics.