Effects of dihydrotestosterone and estradiol on rat facial nerve regeneration following a crush axotomy

Abstract

Previously our laboratory has demonstrated that testosterone treatment increases the regeneration rate of the rat facial nerve following a crush axotomy, and electrical stimulation (ES) reduces the initial delay in axonal sprout formation while the combination of these two treatments has an additive effect. In these studies, testosterone propionate (TP) was given to adult rat at the time of facial nerve crush axotomy at its exit from the stylomastoid foramen. Since testosterone is enzymatically metabolized to either estradiol or the nonaromatizable androgen, dihydrotestosterone (DHT), the present studies explore whether the regenerative properties of TP on the facial motoneurons are due to the effects of androgens, estrogens, or both. We also explored the effects of these metabolites in combination with the ES. Following the facial nerve axotomy and steroid implantation, adult castrated male rats were observed daily for signs of functional recovery from the facial paralysis. The average day of return of each of the four behavioral components (semi‐blink, blink reflex, full vibrissae movement, and complete recovery) was calculated for all groups. We found that although both estradiol and DHT, alone or in combination with ES treatment, reduced the variability in facial nerve recovery, their effects on facial nerve regeneration were not as potent as TP itself.