Interactions between delta 9-tetrahydrocannabinol and cannabidiol as evaluated by drug discrimination procedures in rats and pigeons.

Animals (rats and pigeons) were trained to discriminate between the presence and absence of delta 9-THC; the training doses were, respectively: 0.56 mg/kg (pigeons) and 3.0 mg/kg (rats). Once the drug discrimination was mastered, the pigeons were tested repeatedly after a single intramuscular (i.m.) injection of delta 9-THC (0.56 mg/kg) at the following intervals 0.5, 1.5, 4.5 and 9 hr after the injection. These results were compared with data from a separate procedure, i.e. where the various intervals after injection were examined only once per injection and both procedures yielded essentially the same outcome. Thus, less than 50% appropriate responding to THC was observed at 0.5 and 9 hr after injection, whereas greater than 90% responding to THC occurred at 1.5 and 4.5 hr. The two procedures have previously been compared in rats (Järbe, Swedberg and Mechoulam, 1981). The repeated tests procedure was then used to evaluate combinations of delta 9-THC and cannabidiol in both species. Cannabidiol prolonged the cue effects of 1 mg/kg of delta 9-THC (intraperitoneal route of administration) in rats but did not change the time-effect curve for delta 9-THC in pigeons (dose range examined: 0.10--0.56 mg/kg); the challenge doses of cannabidiol were, respectively: 30.0 mg/kg (i.p.) and 17.5 mg/kg (i.m.). The rate of responding did not differ in tests with combinations of delta 9-THC and cannabidiol as compared to delta 9-THC given alone in pigeons. Subcutaneously administered 3-PPP, a dopamine pre-synaptic blocker, did not induce responding appropriate for delta 9-THC in rats.