Sexual Dimorphism and the Influence of Neonatal Androgen in the Dorsolateral Motor Nucleus of the Rat Lumbar Spinal Cord

There is a sexually dimorphic motor nucleus, the spinal nucleus of the bulbocavernosus (SNB) in the fifth and sixth lumbar segments of the rat spinal cord. We now report a second sex difference in the dorsolateral nucleus (DLN) in the ventral horn of the rat lumbar cord, which includes motoneurons innervating the ischiocavernosus muscle, a sexually dimorphic perineal muscle. Adult females possess fewer motoneurons in the DLN, probably because of an absence of neurons innervating the ischiocavernosus muscle, which females lack. The effect of a single dose of testosterone propionate on day 2 of life was confined to a specific rostrocaudal region of the adult DLN in which it partially masculinized the female DLN. Masculinized females have more DLN neurons than control females. The direction of change induced in DLN neuron number by the neonatal hormone treatment is compatible with the hypothesis that androgens are involved with the sexually dimorphic development of the DLN. In another motor nucleus, the retrodorsolateral nucleus, a small sex difference in neuron number was found in one study, but was not replicated in a second experiment.