Successful intermale aggression and conditioned place preference in mice.

This study assessed the reinforcing properties of successful intermale agonistic encounters between OF1 male mice using the conditioned place preference paradigm. A three compartment apparatus was used and the procedure consisted of three phases: preconditioning (3 days), conditioning (8 days) and postconditioning (3 tests). Individually housed male mice were allocated to two groups. The aggression group confronted docile opponents in the preconditioning "less-preferred" compartment and were left alone in the "preferred" one. The control group was left alone in both compartments. Whereas no significant differences were found between both groups in the time spent in the less-preferred compartment, a separate analysis of animals in function of the color of the less-preferred compartment revealed a clear-cut difference. Mice developed a conditioned place preference for the aggression-paired compartment only if that experience took place in the black one. These findings suggest that the process of establishing a conditioned place preference with successful intermale aggression as reinforcer is extremely fragile and can be easily disrupted by changing the environmental cues involved.