Cannabinoid receptors and reward in the rat: a conditioned place preference study

Rationale: We wished to investigate further the hypothesis of an endogenous cannabinoid 'aversive counter-rewarding system', as the rewarding properties of cannabinoids using standard procedures remain ambiguous. Objectives: The purpose of this study was to confirm the behavioural effects of a highly potent synthetic cannabinoid agonist (HU210) and the selective cannabinoid antagonist SR141716A using conditioned place preference (CPP). Methods: HU210 (20, 60 and 100 mu g kg(-1)) SR141716A (0.25, 0.5, 2 and 3 mg kg(-) (1)), cocaine (15 mg kg(-1)) and Delta(9)-THC (1.5 mg kg(-1)) were given to male Lister hooded rats using an unbiased CPP design. Results: SR141716A and cocaine produced place preference at all doses tested, whereas HU210 and Delta(9)-THC produced aversion as expressed by time spent in the drug-paired compartment of the CPP apparatus. Conclusions: The aversive effects of cannabinoid agonists and the rewarding effect of the cannabinoid antagonist are suggestive of a cannabinergic tone in the rat brain. Further research is needed to determine the precise relationship of that tone with the reward pathways of the brain.