Accumbal dopamine and serotonin in anticipation of the next aggressive episode in rats

Autonomic and limbic neural activities are linked to aggressive behavior, and it is hypothesized that activities in the cardiovascular and monoaminergic systems play a role in preparing for an aggressive challenge. The objective was to learn about the emergence of monoamine activity in nucleus accumbens before an aggressive confrontation that was omitted at the regular time of occurrence, dissociating the motoric from the aminergic activity. Dopamine, serotonin, heart rate and behavioral activity were monitored before, during and after a single 10-min confrontation in resident male Long-Evans rats fitted with a microdialysis probe in the n. accumbens and with a telemetry sender (experiment 1). DA, but not 5-HT efflux, was confirmed to increase in n. accumbens during and after a single aggressive episode. In aggressive males that confronted an opponent daily for 10 days (experiment 2) heart rate rose 1 h before the regularly scheduled encounter relative to control rats, as measured on day 11 in the absence of any aggression. Concurrently, DA levels increased by 60-70% over baseline levels and 5-HT levels decreased by 30-35% compared to baseline levels. These changes were sustained over 1 h, and contrasted with no significant changes in DA, 5-HT, heart rate or behavioral activity in control rats. The rise in mesolimbic DA appears to be significant in anticipating the physiological and behavioral demands of an aggressive episode, and the fall in 5-HT in its termination, dissociated from the actual execution of the behavior.