Conditioned place preference after single doses or "binge" cocaine in C57BL/6J and 129/J mice.

The rewarding effect of cocaine as reflected by the development of conditioned place preference was examined in C57BL/6J and 129/J mice. Cocaine was administered in a single daily dose (2.5, 5, 10 and 20 mg/kg ip) or in a "binge" pattern (15 mg/kg ip x3, hourly). Mice remained in the conditioning compartment for 30 min immediately after each injection. Single injections of cocaine from 5 to 20 mg/kg induced conditioned place preference in each strain of mice. Only C57BL/6J mice developed conditioned place preference after "binge" cocaine administration. Both strains showed significantly greater locomotion in the conditioning compartment across the range of single doses of cocaine and after "binge" cocaine administration, but only 129/J mice showed sensitization. When mice that had received the single 10 mg/kg dose were retested 4 weeks later, the amount of time spent in the preferred side was significantly reduced compared to the initial test in the 129/J, but not in C57BL/6J mice. Thus, the persistence of conditioned place preference is strain dependent. The fact that 129/J mice did not develop conditioned place preference after "binge" cocaine administration, but did after single doses, suggests that the rewarding effects of cocaine are influenced by pattern of administration, a factor that may be relevant to the development of human cocaine addiction.