Neonatal Androgen and Estrogen Treatments Masculinize the Size of Motoneurons in the Rat Spinal Nucleus of the Bulbocavernosus

: 1. Newborn female rats were injected with either a nonaromatizable androgen, dihydrotestosterone propionate (DHTP; 1 mg), or estrogen benzoate (EB; 100 micrograms), or both, or sesame oil vehicle only as a control. In the first experiment, females were injected only on the day of birth (day 1). In the second experiment, females were given daily injections on either days 1, 3, and 5 of life or on days 6, 8, and 10. At 60 days of age the animals were sacrificed and the size of the somata and nuclei of motoneurons in the spinal nucleus of the bulbocavernous (SNB) was determined. 2. As in earlier studies, neonatal EB had no effect on the adult numbers of SNB cells, and the present study demonstrated estrogen's ineffectiveness in this regard in either the absence or the presence of DHTP. Nor did neonatal estrogen influence the survival of the SNB target musculature. 3. In agreement with previous studies, early DHTP treatment resulted in more SNB cells in adulthood and both late and early neonatal treatment with DHTP also resulted in larger SNB cells in adulthood. 4. We report for the first time that neonatal EB treatment also resulted in larger adult SNB cells. EB exerted this effect after a single injection on the day of birth or after multiple injections during the early neonatal period (days 1-5) but not after late neonatal injections. 5. These data suggest that both androgens and estrogens normally act to masculinize the size of SNB motoneurons, while only androgens affect the number of SNB cells.