Sex differences in fighting and defense induced in rats by shock and dextro-amphetamine during morphine abstinence

Male and female rats were injected with morphine while a control group received water injections. Four days following the final morphine injection, the animals received d-amphetamine and then were tested for their reaction to a stuffed leather glove. Drugged animals, while not showing a higher incidence of attack, did show increased escape tendencies when compared to controls. Both drugged and control animals were then shocked in the presence of either a same or different sexed conspecific. Nine measures of aggressive behavior were recorded from the pairs. Factor analysis of the nine intercorrelated measures produced two orthogonal aggressive factors — one indicative of defensive-threat behavior and one relating to actual fighting. Male-male pairs under morphine abstinence plus d-amphetamine scored significantly higher than the other groups on the fighting factor while drugged male-female pairs scored significantly higher on the defensive-threat factor. Although the fighting exhibited in this study was essentially restricted to male pairs under the drugged condition, evidence is presented suggesting that the agonistic behavior observed is not the species typical intermale aggression.