Repeated cocaine exposure during adolescence alters glutamic acid decarboxylase-65 (GAD65) immunoreactivity in hamster brain: correlation with offensive aggression

Male Syrian hamsters (Mesocricetus auratus) treated with low-dose (0.5 mg/kg/day) cocaine throughout adolescence (P27-P56) display highly escalated offensive aggression. The current study examined whether adolescent cocaine exposure influenced the immunohistochemical localization of glutamic acid decarboxylase-65 (GAD65), the rate-limiting enzyme in the synthesis of γ-aminobutyric acid (GABA), a fast-acting neurotransmitter implicated in the modulation of aggression in various species and models of aggression. Hamsters were administered low doses of cocaine throughout adolescence, scored for offensive aggression using the resident-intruder paradigm, and then examined for changes in GAD65 immunoreactivity in areas of the brain implicated in aggression control. When compared with saline-treated control animals, aggressive cocaine-treated hamsters showed significant differences in the area covered by GAD65 puncta in several notable aggression regions, including the anterior hypothalamus, the medial and central amygdaloid nuclei, and the lateral septum. However, no differences in GAD65 puncta were found in other aggression areas, such as the bed nucleus of the stria terminalis, the ventrolateral hypothalamus, and the corticomedial amygdala. Together, these results suggest that altered GABA synthesis and function in specific aggression areas may be involved in adolescent cocaine-facilitated offensive aggression.