Cannabinoid effects on behaviors maintained by ethanol or food: A within-subjects comparison

The cannabinoid CB1 antagonist rimonabant (SR141716A) has been proposed as a therapeutic agent for several addictive disorders, including alcoholism. Rimonabant may selectively reduce responding for an ethanol solution compared with an alternative. While this could represent a specific effect of CB1 inhibition on ethanol reinforcement, this could also result from differences in the baseline rates of behavior or experiences between comparison groups. We developed a procedure in rats that allows a within-subject comparison of ethanol and food-maintained responding and provides well matched baseline response rates. We determined the effects of acute doses of rimonabant (0.3-5.6 mg/kg, intraperitoneal) and the CB1 agonist Δ-9-tetrahydrocannabinol (1.0-5.6 mg/kg, intraperitoneal) on responding for food and ethanol under a multiple fixed-ratio schedule. To confirm that rimonabant blocked cannabinoid receptors, the ability of rimonabant to antagonize Δ-9-tetrahydrocannabinol effects in the same subjects under the same reinforcement schedule was also determined. In contrast with previous reports, rimonabant did not significantly alter responding for ethanol or food. The effects of Δ-9-tetrahydrocannabinol on responding for food were completely antagonized by rimonabant, whereas Δ-9-tetrahydrocannabinol effects on responding for ethanol were not. These results suggest that there may be neuroadaptation of the cannabinoid system following aging or chronic self-administration of ethanol.