Lasting changes in neuronal activation patterns in select forebrain regions of aggressive, adolescent anabolic/androgenic steroid-treated hamsters

Repeated exposure to anabolic/androgenic steroids (AAS) during adolescence stimulates high levels of offensive aggression in Syrian hamsters. The current study investigated whether adolescent AAS exposure activated neurons in areas of hamster forebrain implicated in aggressive behavior by examining the expression of FOS, i.e., the protein product of the immediate early gene c-fos shown to be a reliably sensitive marker of neuronal activation. Adolescent AAS-treated hamsters and sesame oil-treated littermates were scored for offensive aggression and then sacrificed 1 day later and examined for the number of FOS immunoreactive (FOS-ir) cells in regions of the hamster forebrain important for aggression control. When compared with non-aggressive, oil-treated controls, aggressive AAS-treated hamsters showed persistent increases in the number of FOS-ir cells in select aggression regions, namely the anterior hypothalamus and lateral septum. However, no differences in FOS-ir cells were found in other areas implicated in aggression such as the ventrolateral hypothalamus, bed nucleus of the stria terminals, central and/or medial amygdala or in non-aggression areas, such as the samatosensory cortex and the suprachiasmatic nucleus. These results suggest that adolescent AAS exposure may constitutively activate neurons in select forebrain areas critical for the regulation of aggression in hamsters. A model for how persistent activation of neurons in one of these brain regions (i.e., the anterior hypothalamus) may facilitate the development of the aggressive phenotype in adolescent-AAS exposed animals is presented.