Androgen receptor (AR) immunoreactivity in rat pudendal motoneurons: implications for accessory proteins

Pudendal motoneurons in male rats are located in two sexually dimorphic motoneuronal pools: the spinal nucleus of the bulbocavernosus (SNB) and the dorsolateral nucleus (DLN). SNB motoneurons innervate sexually dimorphic muscles bulbocavernosus (BC) and levator ani (LA) and the sexually monomorphic external anal sphincter (EAS) muscle. DLN motoneurons innervate either the sexually dimorphic ischiocavernosus (IC) muscle or the sexually monomorphic external urethral sphincter (EUS) muscle. Previous observations indicate that the size of BC, LA, and IC motoneurons in males is sensitive to adult androgen manipulations, whereas the size of EAS and EUS motoneurons is not, raising the question of whether this difference in androgen sensitivity among pudendal motoneurons reflects a difference in androgen receptor (AR) expression. AR immunocytochemistry using the PG-21 antiserum was carried out on spinal cord tissue from normal adult male rats in which specific pudendal motoneuronal subpopulations were identified with retrograde markers. Over 90% of BC, LA, and IC motoneurons displayed AR immunoreactivity in their nuclei. Among motoneurons in the SNB, significantly fewer EAS motoneurons had AR-positive nuclei, which may contribute to the reported failure of EAS motoneurons to morphologically respond to changes in androgen levels. However, within the DLN, despite the fact that IC but not EUS motoneurons are reported to respond to androgen with an increase in soma size, IC and EUS motoneurons had the same proportion of AR-positive nuclei. These results indicate that androgen receptors, while necessary, are not sufficient to confer androgen sensitivity to cells.