Effects of pharmacologic androgen treatment duration on glucocorticoid receptor α immunoreactivity of lumbosacral motor neurons in the male rat

Abstract

It has previously been suggested that anabolic-androgenic steroids may affect neuromuscular function through their potential action as glucocorticoid receptor antagonists. Alternatively, androgens may regulate the sensitivity of neuromuscular systems to glucocorticoids by modulating GR levels. The purpose of this study was to determine the effects of chronic pharmacologic testosterone treatment of gonadally intact male rats on glucocorticoid receptor α immunoreactivity (GRα-IR) of motor neurons in the lumbosacral spinal cord. Circulating testosterone levels were chronically increased by subcutaneous Silastic™ capsules containing crystalline testosterone propionate (TP) for 7, 14, and 28 days. Age-matched sham-operated gonadally intact males served as controls. Relative cytoplasmic and nuclear GRα-IR of motor neurons located in the lateral motor column of spinal cord segments L 3 and L 4 (L Lat; innervating rat hindlimb muscles) and the spinal nucleus of the bulbocavernosus (SNB; innervating the external anal sphincter, bulbocavernosus and levator ani muscles) was measured densitometrically. TP treatment duration had a significant impact on the mean GRα levels of both cellular compartments regardless of motor column (two-way ANOVA, P<0.001). The mean nuclear GRα-IR of lumbar motor neurons was significantly reduced after 7 days (OD: 0.239±0.013 S.E.M.; P<0.016) and 14 days (OD: 0.196±0.013; P<0.001) from the GRα-IR levels observed among the control group (OD: 0.296±0.012) by 20 and 40%, respectively. Interestingly, nuclear GRα-IR levels were similar to control levels after 28 days of TP treatment (OD: 0.307±0.010). Treatment-dependent changes in cytoplasmic GRα-IR paralleled the observed changes in nuclear GRα-IR. These data suggest that pharmacologic testosterone treatment effects on motor neuron gene expression may be mediated by testosterone-induced temporal fluctuations of GRα-dependent gene regulation.