Sexual dimorphism and hormone responsiveness in the spinal cord of the socially monogamous prairie vole (Microtus ochrogaster).
Prairie voles (Microtus ochrogaster) are exceptional among rodents in that many aspects of their brain and behavior are not masculinized by exogenous aromatizable androgens. However, the sexually differentiated endpoints studied to date rely on estrogenic mechanisms in other mammals. We examined whether sexual differentiation of an androgen receptor-dependent sex difference would be similarly distinct in prairie voles. Male mammals have more and larger motoneurons projecting to perineal muscles than do females. This sex difference normally arises from males' perinatal androgen exposure and can be eliminated by treating developing females with androgens. Gross dissection revealed bulbospongiosus muscles in adult male, but not female, prairie voles. Retrograde tracing from males' bulbocavernosus muscles and the external anal sphincter from both sexes revealed sexually dimorphic populations of labeled motoneurons in the ventral horn of the lumbar spinal cord. Similar to other rodents, males had twice as many motoneurons as females, although no sex difference in motoneuron size was detected. Unexpectedly, prenatal or early postnatal exposure to testosterone propionate had no effect on adult females' motoneuron number or size. In adulthood, gonadectomy alone or followed by chronic testosterone treatment also had no effect on females' motoneuron size or number, although castration reduced motoneuron size in males. Comparing gonadally intact weanlings confirmed that the sex difference in motoneuron number exists before adulthood. As with some other sexually dimorphic traits, and perhaps related to their unique social organization, sexual differentiation of the prairie vole spinal cord differs from that found in most other laboratory rodents.
Holmes
Melissa M
MM
Center for Neuroendocrine Studies, University of Massachusetts, Amherst, Massachusetts 01003, USA. holmes@cns.umass.edu
Musa
Mutaz
M
Lonstein
Joseph S
JS
Monks
D Ashley
DA
D001003:Anal Canal / Q000033:anatomy & histology / Q000294:innervation; D000818:Animals; D000831:Animals, Newborn; D003411:Arvicolinae / Q000033:anatomy & histology* / Q000378:metabolism*; D002369:Castration; D002452:Cell Count; D048429:Cell Size / Q000187:drug effects; D005260:Female; D006728:Hormones / Q000378:metabolism* / Q000494:pharmacology; D008297:Male; D009046:Motor Neurons / Q000166:cytology / Q000187:drug effects; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000294:innervation; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects; D012727:Sex Characteristics; D013116:Spinal Cord / Q000033:anatomy & histology* / Q000187:drug effects / Q000378:metabolism*; D013739:Testosterone / Q000494:pharmacology; D043343:Testosterone Propionate / Q000494:pharmacology
D006728:Hormones; D013739:Testosterone; D043343:Testosterone Propionate