Abstract
We recently developed a conditioned place preference (CPP) procedure, commonly used to study rewarding drug effects, to demonstrate that dominant sexually-experienced CD-1 male mice form CPP to contexts previously associated with defeating subordinate male C57BL/6J mice. Here we further characterized conditioned and unconditioned aggression behavior in CD-1 mice. In Exp. 1 we used CD-1 mice that displayed a variable spectrum of unconditioned aggressive behavior toward younger subordinate C57BL/6J intruder mice. We then trained the CD-1 mice in the CPP procedure where one context was intruder-paired, while a different context was not. We then tested for aggression CPP 1 day after training. In Exp. 2, we tested CD-1 mice for aggression CPP 1 day and 18 days after training. In Exp. 3-4, we trained the CD-1 mice to lever-press for palatable food and tested them for footshock punishment-induced suppression of food-reinforced responding. In Exp. 5, we characterized unconditioned aggression in hybrid CD-1 × C57BL/6J D1-Cre or D2-Cre F1 generation crosses. Persistent aggression CPP was observed in CD-1 mice that either immediately attacked C57BL/6J mice during all screening sessions or mice that gradually developed aggressive behavior during the screening phase. In contrast, CD-1 mice that did not attack the C57BL/6J mice during screening did not develop CPP to contexts previously paired with C57BL/6J mice. The aggressive phenotype did not predict resistance to punishment-induced suppression of food-reinforced responding. CD-1 × D1-Cre or D2-Cre F1 transgenic mice showed strong unconditioned aggression. Our study demonstrates that aggression experience causes persistent CPP and introduces transgenic mice for circuit studies of aggression.