Effects of testosterone on pelvic autonomic pathways: progress and pitfalls

Testosterone has potent effects on reproductive behavior, many of which are due to actions on brain nuclei and spinal motoneurons controlling perineal muscles. The autonomic circuits involved in penile erection, ejaculation and emission, have been less commonly considered as targets for circulating androgens. This review demonstrates that many components of pelvic autonomic reflex pathways, including preganglionic neurons, autonomic ganglion cells and primary afferent neurons, are likely to be influenced by testosterone. The steroid appears to play an important role in maintaining neuronal morphology, transmitter synthesis and receptor expression throughout adulthood. Surprisingly, the effects of testosterone are not limited to neurons involved in reproductive reflexes. The challenge is now to determine the range of neuronal features influenced by androgens, and the mechanisms by which these occur. Studies of androgen receptor location indicate that in many autonomic neurons gene expression may be directly influenced by androgens, but a mismatch between receptor distribution and androgen action shows that in some cells other mechanisms must exist. It is also possible that androgens are metabolised to estrogens by some peripheral neurons. Irrespective of the mechanism, it is time to acknowledge that testosterone is an important "maintenance factor" for autonomic neurons.