INVOLVEMENT OF CENTRAL CANNABINOID (CB1) RECEPTORS IN THE ESTABLISHMENT OF PLACE CONDITIONING IN RATS

The involvement of cannabinoid processes in positive reinforcement was studied using an unbiased, one-compartment, conditioned place prefere nce (CPP) procedure in rats. This was achieved by examining the abilit y of the selective antagonist of the CBI cannabinoid receptor subtype, SR 141716, to counteract the CPP supported by classical reinforcers. The acquisition of CPP induced by cocaine (2 mg/kg), morphine (3 mg/kg ) and food (standard chou and sucrose pellets) was dose-dependently bl ocked by pre-pairing administration of SR 141716 (0.03-3 mg/kg). Howev er. SR 141716 (up to 10 mg/kg) did not significantly counteract the ex pression of cocaine-induced CPP. On the other hand, the synthetic CB r eceptor agonist, WIN 55212-2 (0.3-1 mg/kg), established a robust place aversion (CPA), as already described with other agonists, and CPP was never observed, even at 100-fold lower doses. The aversive effect of WIN 55212-2 was reversed by SR 141716 (0.3-1 mg/kg), suggesting that i t was accounted for by the stimulation of CBI receptors. These finding s indicate that. on their own, CB receptor agonists are unable to gene rate the processes necessary to induce a pleasurable state in animals, as assessed in place conditioning procedures. Nevertheless, a cannabi noid link may be involved in the neurobiological events, allowing the perception of the rewarding value of various kinds of reinforcers. How ever, a permanent endogenous cannabinoid tone seems unlikely to be nec essary to ensure the organism a basal hedonic level since, given alone , SR 141716 supported neither CPP nor CPA.