Differences in drug-induced place conditioning between BALB/c and C57Bl/6 mice.

The influence of genotype on the rewarding effects of morphine (0, 1, 3, and 9 mg/kg), amphetamine (0, 0.5, 1, and 2 mg/kg), and cocaine (0, 2.5, 5, and 10 mg/kg) was examined in a place-conditioning paradigm. Two strains of mice, the BALB/cByJIco and the C57BL/6JIco, were used, notably because of their high difference in novelty-seeking behavior. Indeed, high novelty seeking has been associated with an increased risk for using drugs of abuse. Results clearly show that C57BL/6 mice display a conditioned place preference for stimuli paired with morphine, amphetamine, or cocaine. In contrast, BALB/c mice demonstrated place preference to morphine and place aversion to amphetamine, while cocaine was ineffective at the doses tested. No treatment induced differences in the locomotion measured in a drug-free condition. Results may be related to differences at the behavioral (difference in novelty seeking) or neurochemical level (differences in catecholaminergic or opioidergic neurotransmission).