DEPLETION OF BRAIN-SEROTONIN BY 5,7-DHT - EFFECTS ON THE 8-OH-DPAT-INDUCED CHANGES OF SLEEP AND WAKING IN THE RAT

The effect of 5-HT1A receptor agonist 8-OH-DPAT on sleep and wakefulne ss was studied in rats with selective serotonin depletion after ICV ad ministration of the neurotoxin 5,7-dihydroxytryptamine (5,7-DHT). Inje ction of 8-OH-DPAT to vehicle-treated animals induced biphasic effects , such that low doses (0.010 mg/kg) which act preferentially on the so matodendritic autoreceptor decreased wakefulness (W) and increased slo w wave sleep (SWS), while higher doses (0.375 mg/kg) which stimulate p ostsynaptic receptors caused opposite effects. REM sleep was suppresse d irrespective of the dosage given. Injection of the 0.010 mg/kg dose in the 5,7-DHT-treated rats did not result in significant changes in s leep or W. On the other hand, the 0.375 mg/kg dose produced changes in sleep variables which were similar to those described in the vehicle- treated animals. Our findings tend to indicate that increased SWS afte r low doses of 8-OH-DPAT depends upon the activation of inhibitory som atodendritic 5-HT1A receptors, while increased W after higher doses of the compound is related to stimulation of postsynaptic receptors.