Delta-9-tetrahydrocannabinol, EEG and behavior:the importance of adaptation to the testing milieu.

Delta-9-Tetrahydrocannabinol (delta-9-THC) in doses of 0.01, 0.05, 0.1, 0.5, and 1.0 mg/kg, i.v. was administered to adult rabbits previously adapted to the testing chamber. Additionally, a group of rabbits not adapted to any part of the testing regimen was administered 1.0 mg/kg delta-9-THC. Cortical and hippocampal electroencephalographs as well as postural and activity behaviors of the unrestrained animals were recorded. In the adapted rabbits, there were dose-related increased in cortical voltage output, disruption of hippocampal theta rhythm and cortical polyspike bursts. Behaviorally, there was a dose-related tendency for standing and exploration to decrease, and at 0.5 and 1.0 mg/lh, delta-9-THC produced sprawling. In the nonadapted rabbits, administration of 1.0 mg/kh of the drug caused EEG and behavioral stimulation followed by depression of both, The results suggest that the bahavioral actions of cannabinols are largely dependent upon the animal's existing state of arousal.