Influence of zopiclone, a new generation hypnotic, on the intermediate stage and paradoxical sleep in the rat.

This study examined the influence of zopiclone, a third generation hypnotic, on the transition from slow wave sleep to paradoxical sleep (PS) which is increased at the expense of PS by barbiturates and benzodiazepines. The compound decreased sleep latency and increased the latency of the intermediate stage (IS) and PS at 2.5, 5 and 7.5 mg/kg IP. The amount of the IS was decreased because of the decrease in phase number up to 6 h at all doses. PS amount was decreased during 2 h at 2.5 mg/kg and during 4 h at 5 and 7.5 mg/kg also because of the decrease in phase number. The IS never substituted for PS. The IS spindle characteristics were not modified and the theta rhythm frequency slightly decreased at 5 mg/kg (IS) and 7.5 mg/kg (PS).