Administration of testosterone fails to attenuate axotomy-induced motoneuron loss but results in castration-like effect in young male rats.

It was shown previously that the severity of motoneuron loss induced by nerve transection in rats 3 or 6 weeks of age was correlated inversely with the level of testosterone in circulation [Yu, W.H.A., Exp. Neurol. 102: 230-235, 1988], and that administration of testosterone to female rats attenuated axotomy-induced neuronal cell loss in a dose-dependent manner [Yu, W.H.A., J. Neurosci. 9: 3908-3914, 1989]. The present study was undertaken to examine whether elevation of the level of plasma testosterone in gonadally intact male rats by exogenous testosterone would likewise reduce neuronal cell loss. Following unilateral transection of the hypoglossal and facial nerve at 3 or 6 weeks after birth, rats received subcutaneous injections of 0.5, 1.0, or 2.0 mg testosterone propionate (TP) dissolved in 0.1 ml sesame oil or an equal volume of vehicle alone twice weekly for the first 4 postaxotomy weeks, and once weekly thereafter for additional 6 weeks. Results indicated that males axotomized at 3 weeks of age and treated with 1.0 or 2.0 mg TP had nearly twofold greater neuronal cell loss than oil-treated controls. The resultant cell loss was similar to that of castrated males or females without TP treatment despite the fact that TP treatment significantly elevated the plasma testosterone level. Neuronal cell loss in males axotomized at 6 weeks of age, however, was unaffected by TP treatment. Although testicular atrophy was noted in all TP-treated rats, the damage appeared to be greater in the testis of the 3-week-old than that of 6-week-old rats, as manifested by the castration-like effect of neuronal cell loss in prepubertal rats.(ABSTRACT TRUNCATED AT 250 WORDS)