Δ9-Tetrahydrocannabinol and the sleep-wakefulness cycle in rabbits

Abstract

The effects of 0.5 and of 1.0 mg/kg of intravenously administered Δ 9-tetrahydrocannabinol ( Δ 9-THC) on the sleep-wakefulness cylce were studied in six freely moving rabbits with chronically implanted electrodes. On three consecutive days 5-hr polygraphic recordings were made in each animal; the first record was begun immediately following administration of the drug, the second and third were made 24 and 48 hr later. At both dose levels, Δ 9-THC evoked biphasic effects on the first day; an initial phase of extremely low amplitude fast activity of the alert state was followed by a period of predominantly slow wave sleep. During the initial alert phase spike discharges appeared in the motor cortex and hippocampus and behavioral alterations characterized chiefly by loss of motor coordination were observed. A decrease in the number of REM sleep episodes was mainly responsible for a significant reduction in the total time spent in REM sleep on the first day. On the second day the percent time of REM sleep was still below the control value although the difference was statistically insignificant, but by the third day it had returned to the control level.