Stress and the development of agonistic behavior in golden hamsters.

Aggressive behavior can be studied as either offensive or defensive responses to a stimulus. The studies discussed in this review are focused on the peripubertal development of offensive aggression in male golden hamsters and its responsiveness to repeated social stress. Quantitative and qualitative changes in offensive responses were analyzed during this period. Quantitative changes in offensive responses were observed as decreased frequency of attacks. Qualitative changes were observed as changes in attack types, as animals reorient their attacks gradually from the face to the lower belly and rump. These developmental changes were altered by repeated exposure to social stress during early puberty. Daily exposure to aggressive adults during early puberty accelerated the qualitative development of offensive responses and the onset of adult-like offensive responses. In contrast, social stress had little effect on the quantitative changes associated with early puberty. However, social stress was associated with higher attack frequency during adulthood. These effects of stress during early puberty contrast with those observed with animals in late puberty. At that time, repeated exposure to aggressive adults inhibits offensive aggression. These data constitute the basis for a new theory on the development of agonistic behavior that includes the following hypotheses. First, it is hypothesized that mid-puberty is marked by a change in responsiveness to repeated social stress. As such, differences in stress responsiveness from social interactions are interpreted as a basic distinction between play fighting and adult aggression. Second, it is also hypothesized that a common neural circuitry mediates the activation of offensive responses during play fighting and adult aggressive interactions.