Steroid Influences on the Development and Function of a Neuromuscular System

Abstract

Publisher Summary This chapter describes the sex differences in the morphology of muscles and motoneurons, the hormone sensitivity of neurons and target in adulthood, the crucial function of this neuromuscular system in reproduction, and the ontogenetic role of steroid hormones in determining the number, size, and connectivity of these neurons. It focuses on a sexually dimorphic neuromuscular system in the rat: the spinal nucleus of the bulbocavernosus (SNB) and its target musculature. Both the development and adult function of the SNB system are controlled by steroid hormones. Perinatal secretions of androgen in male rats induce the persistence of the bulbocavernosus (BC) muscles and probably prevent the programmed cell death of the SNB motoneurons innervating them. Perinatal exposure of female rats to androgen mimics the masculine pattern of the preservation of SNB motoneurons and BC musculature. Unlike other examples of sexual differentiation in rodents, the development of the SNB system seems to be independent of the estrogenic metabolites of testosterone. At maturity, both the SNB motoneurons and BC muscles bind androgen and respond morphologically to hormonal manipulations. The morphological responsiveness of motoneurons and muscles to steroids may mediate the androgen sensitivity of the neuromuscular system as measured by spinal reflexes and fertility. Thus, SNB is a relatively simple neural system, which promises to elucidate the mechanisms by which steroid hormones direct morphology and behavioral function of the nervous system throughout ontogeny.