Figure 2. Aggression self-administration and aggression seeking increased Fos expression in the NAc core and shell Drd1- and Drd2-expressing neurons. A, Timeline of Experiment 2. B, Number of rewarded and attack trials over 9 d (48 min session/d) of aggression self-administration under an FR1 reinforcement schedule in CD-1 mice (n = 10). Data are combined from aggression self-administration and aggression seeking experimental groups. C, Number of reward and attack responses on the final day of training for the subset of mice that were included in the self-administration group during the self-administration test (n = 5). D, Number of active and inactive lever presses during a 60 min aggression seeking test in the aggression-seeking group (n = 5). E, Representative images of the NAc shell and core stained for DAPI (top), Drd1, and Drd2 mRNA (bottom) using ISH. F, Representative images of the NAc shell or core, stained for Fos, Drd1, Drd2 mRNA, and DAPI across experimental groups (self-administration test, aggression-seeking test, and no-test control). G, Fos-labeled cells (cells/mm2) in the NAc core and shell subregions across experimental groups. H, Counts of cells colabeled with Fos + Drd1 or Fos + Drd2 in the NAc core and shell across experimental groups. Data are mean ± SEM. *Different from the no-test control group, p < 0.05. aca, Anterior commissure; LS, lateral septum.