Developmental and hormonal factors in the sexually dimorphic, asymmetrical response to focal cortical lesions

The developmental and hormonal determinants of the lateralized response to focal cortical suction lesions were examined in a series of experiments. In an initial study, Sprague-Dawley male rats 25, 30, 55 or 90 days of age, received right unilateral focal frontocortical suction lesions. Only 90-day-old rats developed hyperactivity, suggesting a specific role for maturational factors in the production of this response. Prepubertally castrated adult male rats receiving right frontocortical suction lesions at 90 days also failed to develop hyperactivity, suggesting that sexual maturational factors and/or the presence of testosterone are necessary for the expression of this response. Testosterone implants, producing physiological relevant levels of circulating testosterone reinstated the hyperactivity response to adult cortical lesions in prepubertally castrated male rats. Similar lesions in the left hemisphere, however, did not produce hyperactivity in castrated male rats with testosterone replacement. Finally, in ovariectomized adult female rats, testosterone did not allow the expression of a hyperactivity response to right frontocortical suction lesions. Together, these results demonstrate both an organizational and permissive role for sex steroids in the sexually dimorphic asymmetrical response to cortical injury.