Medial accumbens lesions attenuate testosterone-dependent aggression in male rats

Male hooded rats were castrated and implanted with testosterone-filled Silastic tubes appropriate for maintaining a normal average serum testosterone concentration. They were then given lesions of the medial accumbens nucleus or sham lesions. Twenty-four hours postoperatively each male was housed with a female. Beginning 7 days following pairing and continuing once each week for 4 weeks, each lesioned or sham-lesioned male was observed for aggression toward an unfamiliar male intruder. On the day following each test of aggression toward an unfamiliar male, each lesioned and sham-lesioned male was assessed for defensiveness toward an experimenter. Rats with medial accumbens lesions displayed significantly less aggression toward an unfamiliar male intruder during each of the weekly tests than did sham-lesioned animals. The attenuation was most pronounced in animals with lesions damaging the posterior part of the medial accumbens nucleus (also designated as anterior portion of the bed nucleus of the stria terminalis) in the region of the crossover of the anterior commissure. Although medial accumbens lesions are known to make individually housed rats hyperdefensive toward an experimenter, lesion-induced hyperdefensiveness was not observed in the pair-housed animals in the present experiment. It is argued that the medial accumbens/bed nucleus of the stria terminalis area is an important region in the anterior forebrain for the modulation of hormone-dependent aggression.