Experience and cortical control over the pubertal transition to rougher play fighting in rats

Abstract

With the onset of puberty, play fighting in rats decreases in frequency and the tactics of attack and defense that are used are rougher. Previous studies have shown that the changes in the frequency of play and in the use of defensive tactics arise independently of social experience. Furthermore, while the former involves subcortical regulation, the latter depends on cortical mechanisms. In this study, the possible mechanisms regulating the developmental changes in the tactics of attack were examined. Two experiments were conducted using male rats. In the first study, rats reared in isolation from weaning were compared to rats reared in pairs, and were tested in the juvenile and early post-pubertal phases (30 and 60 days postnatally). In the second experiment, rats with their cortex removed shortly after birth were compared to sham-treated controls, and were tested in pairs at both the juvenile and early adult phases (30 and 90 days). Two measures of ‘roughness,’ derived from previous studies, were measured. Results showed that isolation-reared rats had the typical age-related changes in roughness of attack, whereas decorticated rats failed to show this age-related modulation, maintaining, or even exaggerating, the juvenile-typical pattern of attack. These findings suggest that social experience is not needed for this developmental change to occur, and that an intact cortex is needed to regulate this change in behavior.