Sexual dimorphism in rats with respect to locomotor activity and circling behavior.

Male and female rats were tested for locomotor activity and spontaneous circling (rotation) at 4, 6, 8, 11, 13 and 15 weeks of age. Locomotor activity of females increased with age, and significant intersex differences which became apparent by 8 weeks of age were attributed to the greater persevering tendency of the females. Spontaneous rotation, on the other hand, did not change with age and significant intersex differences were not evident. Moreover, locomotor activity and rotation were not correlated at any age. In contrast to spontaneous rotation, amphetamine induced significantly more rotation in older (18 week) than in younger (5 week) females and males of both ages. Apomorphine, on the other hand, also elicited more rotation in older than in younger females, but not in males. In addition, intersex differences were not evident in younger animals tested with either drug. These data suggested that the greater persevering tendency and lateralization of females compared to males may be related to bilateral functional imbalances in nigrostriatal activity.