Critical period for androgenic regulation of soma size of sexually dimorphic motoneurons in rat lumbar spinal cord.

In the rat spinal nucleus of the bulbocavernosus (SNB), androgens are known to act during early critical periods to regulate the number and size of motoneurons that innervate perineal muscles, and to produce sex differences in these attributes. The present study determined the end of the critical period for androgenic regulation of SNB soma size in female rats. Intact female rats received injections of testosterone propionate or oil during 1 of 4 postnatal periods, and were compared to control males and females. In adulthood, all rats were gonadectomized, treated with androgen and then sacrificed. The somatic areas of SNB motoneurons were measured. The results suggest that the soma size is increased by androgen treatment only if it is given before about day 12 after birth.