Conditioned place preference to morphine in cannabinoid CB1 receptor knockout mice

Recent reports have suggested an involvement of the brain cannabinoid system in the morphine-reward pathway. To address this question we evaluated whether CB I receptor knockout mice would show a conditioned place preference to morphine. CB I receptor knockout mice developed a strong place preference to 4 and 8 mg/kg morphine, similar to that in wild-type Swiss-Webster mice. This data thus does not support a contribution of the brain cannabinoid system to morphine reward. (C) 2002 Elsevier Science BY All rights reserved.