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 recordings. One week after the surgery, cats were treated with two intraperitoneal 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 reduction of both slow wave sleep 2 and rapid-eye movement [REM] sleep). During this period cats were divided into four groups (n = 6) and were injected with either atropine (0.5 mg/kg, IM [3.5 mmol/kg]), vasoactive intestinal peptide (VIP) (200 ng, ICV [60 pmol]) or atropine plus VIP (same doses and routes of administration). The control group received saline intramuscularly (IM) intracerebroventricularly and (ICV). Results 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 interaction.