THE COMBINATION OF VIP AND ATROPINE INDUCES REM-SLEEP IN CATS RENDERED INSOMNIAC BY PCPA

Twenty-four cats were implanted with electrodes for chronic sleep reco rdings. One week after the surgery, cats were treated with two intrape ritoneal injections of parachlorophenylalanine (PCPA), an inhibitor of serotonin synthesis, to induce insomnia. Twenty-four hours after the second injection of PCPA, cats were at the peak of insomnia (strong re duction of both slow wave sleep 2 and rapid-eye movement [REM] sleep). During this period cats were divided into four groups (n = 6) and wer e injected with either atropine (0.5 mg/kg, IM [3.5 mmol/kg]), vasoact ive intestinal peptide (VIP) (200 ng, ICV [60 pmol]) or atropine plus VIP (same doses and routes of administration). The control group recei ved saline intramuscularly (IM) intracerebroventricularly and (ICV). R esults showed that VIP and atropine injected alone and in combination increased mean total time of REM sleep in PCPA-treated animals. These findings are discussed in terms of a serotonin-acetylcholine interacti on.