Defensive aggression and testosterone-dependent intermale social aggression are each elicited by food competition

Castrated rats with medial hypothalamic lesions or sham lesions and castrated rats with testosterone implants or sham implants were placed on a 23-hr food deprivation schedule, adapted to a highly palatable liquid food, and then housed in pairs. The pairs were observed in competition for the highly palatable food over a 4-min period on each of six days. On the first three days, the food was dispensed in a way that allowed only one animal at a time to drink while during the second three days both animals could drink simultaneously. The pairs of animals were then separated, individually adapted to a bland liquid food, and paired with a different animal for a second series of competition tests. With highly palatable food as the incentive, rats made hyperdefensive by medical hypothalamic lesions were more successful at maintaining access to the food and more aggressive than their sham-lesioned competitors on tests when food access was restricted to a single animal but not on tests when both animals could drink simultaneously. With bland food as the incentive, lesioned animals were not consistently more successful in maintaining access to the food but were significantly more aggressive than their cagemates. With the highly palatable food, castrated males with testosterone implants were neither more successful in maintaining access to the food nor more aggressive than their cagemates with sham implants. However, when paired with an unfamiliar cagemate in preparation for competition tests with the bland food, most rats with testosterone implants attacked the new cagemate using a lateral attack and displaying piloerection.(ABSTRACT TRUNCATED AT 250 WORDS)