Morphine conditioned place preference in the hamster.

Two experiments investigated the ability of morphine to produce a conditioned place preference in the hamster. In Experiment 1, it was found that a 15 mg/kg dose of morphine produced a conditioned place preference after eight conditioning trials. In addition, naloxone (0.4 mg/kg blocked the development of the morphine-conditioned place preference and itself produced a conditioned place aversion after four conditioning trials. In Experiment 2, the effects of four doses of morphine (0, 2.5, 5 and 15 mg/kg) on the acquisition of a conditioned place preference were studied. Only the 15 mg/kg dose produced a significant place preference. Compared to similar findings in the rat, the present results indicate that a relatively high dose of morphine is required to produce a conditioned place preference in the hamster.