Effects of acute and chronic treatment with trazodone, an antidepressant, on the sleep-wake activity in rats.

Rats were treated with trazodone (2.5 or 10 mg kg-1) twice a day (at light and dark onset) for 11 days, after chronic injection of physiological saline. The sleep-wake activity was recorded for 24 h on the baseline day (saline), on trazodone days 1, 5 and 11, and also on day 12, when physiological saline was injected again (withdrawal day). Trazodone administration increased non-REM sleep. The enhancement of non-REM sleep was dose-related and more pronounced during the dark cycle. The promotion of non-REM sleep was enhanced during the chronic treatment. There were no consistent changes in REM sleep. Spectral analysis of the EEG revealed an increase in slow-wave activity after administration of the high dose (10 mg kg-1) of the drug. It is concluded that trazodone, a clinically effective antidepressant, has a non-REM sleep-promoting effect. It is speculated that the promotion of sleep by trazodone may be mediated by serotonergic mechanisms.