Regional serotonin and dopamine activity: Sensitivity to amphetamine and aggressive behavior in mice

Abstract

We were interested in comparing the effect of distinctive attack and defeat experience on regional monoamine turnover and on d-amphetamine (AMPH) sensitivity. Male mice were randomly assigned to groups that received zero, one, or ten defeat experiences or that attacked an intruder zero, one, or ten times. Twenty-four hours after the last attack or defeat, mice were administered one of four AMPH doses (0, 0.1, 1.0, or 10.0 mg/kg i.p.) and tested in a resident-intruder confrontation. A separate group of mice were sacrificed immediately after the last attack or defeat. Using the high-performance liquid chromatography (HPLC) technique, dihydroxyphenylacetic acid (DOPAC):dopamine (DA) and 5-hydroxyindolacetic acid (5HIAA):serotonin (5HT) were measured in micropunched sections of the corpus striatum, amygdala, and nucleus accumbens. A single defeat decreased DA turnover in the amygdala, whereas one attack experience increased DA and 5HT turnover in the n. accumbens and amygdala, respectively. AMPH sensitivity was enhanced following acute defeat. In animals that had repeated agonistic experience, acute attack or defeat did not alter DOPAC:DA or 5HIAA:5HT ratios. Mice with attack experience were more sensitive to AMPH following multiple rather than a single aggressive encounter. The distinct effects of defeat and attack experience on mesolimbic DA activity and on AMPH sensitivity suggest that monaminergic fibers terminating in the n. accumbens can be functionally dissociated from fibers terminating in the amygdala.