The pattern of playful defense used during play fighting by male rats (Rattus norvegicus) castrated at birth was compared to that of sham-operated and untreated controls during the juvenile phase and after puberty. The neonatal castrates failed to exhibit the age-related changes in playful defense present in intact male rats of the same age. Following puberty, control rats, but not neonatal castrates, switched from juvenile to more adult-typical defensive tactics. That the neonatal castrations were effective was independently shown by the animals’ failure to exhibit the asymmetries in weight and play behavior indicative of dominance-subordinance relationships present in normal adult males. A previous study found that castration following weaning did not prevent the pubertal change in playful defense, but did block the formation of dominance-subordinance relationships. Therefore, it appears that the age-related shift in playful defense is a feature of the development of play fighting in males that is likely preprogrammed by gonadal hormone exposure in the perinatal period.
The postpubertal change in the playful defense of male rats depends upon neonatal exposure to gonadal hormones
