Infantile handling and sex differences in shock-elicited aggressive responding of hooded rats

Infantile handled (Days 1-20) and nonhandled, male and female Long Evans hooded rats were tested at maturity (90-100 days) over 10 daily sessions for aggressive response to footshock. Individual jump and flinch thresholds for reactivity to shock, as well as paired aggressive responding to shock, were not significantly influenced by the handling procedure, although handled females ultimately adopted higher levels of fighting than nonhandled females. Handled rats were heavier than nonhandled rats of the same sex before and after testing for social aggression. Males fought significantly more than females; the discrepancy increased with additional sessions of paired exposure to shock. Male and female fight trends over sessions were linear and positive with a greater acceleration for males. The results were interpreted as indicative of a social learning variable occurring with repeated aggressive contact and primarily affecting males.