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

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. The purpose of this study was to confirm the behavioural effects of a highly potent synthetic cannabinoid agonist (HU210) and the selective cannabinoid antagonist SR 141716A using conditioned place preference (CPP). HU210 (20, 60 and 100 microg kg(-1), SR141716A (0.25, 0.5, 2 and 3 mg kg(-1)), cocaine (15 mg kg(-1) and delta9-THC (1.5 mg kg(-1)) were given to male Lister hooded rats using an unbiased CPP design. SR141716A and cocaine produced place preference at all doses tested, whereas HU210 and delta9-THC produced aversion as expressed by time spent in the drug-paired compartment of the CPP apparatus. 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.