c-fos Changes following an aggressive encounter in female California mice: a synthesis of behavior, hormone changes and neural activity.

Although there has been growing interest in the neuroanatomical and physiological mechanisms underlying aggressive behavior, little work has focused on possible mechanisms controlling natural plasticity in aggression. In the current study, we used naturally occurring changes in aggression level displayed by female Peromyscus californicus across the estrous cycle and parallel changes in c-fos expression to examine possible brain regions involved in mediating this plasticity. We found that c-fos expression was increased in females exposed to a conspecific female intruder compared with control females in numerous brain regions thought to be involved in the control of aggression. More importantly, we found that c-fos increased in the bed nucleus of the stria terminalis (BNST) and ventral lateral septum (LSv) only in the more aggressive, diestrous females, and not in the less aggressive, proestrous and estrous females. Conversely, c-fos increased in the medial amygdala (MeA) across all stages of estrus compared with controls, suggesting the MeA is not involved in mediating changes in individual levels of aggression. Moreover, we found correlations between several measures of aggression and c-fos expression in the BNST and LSv but not the MeA, again suggesting a role in mediating aggression plasticity for the former two but not the latter brain region. We further hypothesize that the BNST and the LSv may be involved more generally in mediating natural changes in aggression, such as increases often observed after individuals win aggressive interactions against conspecifics.