Testosterone propionate (TP) administration at the time of
facial nerve injury in the adult hamster augments the regenerative properties of the injured facial motoneurons (
FMN), with the
androgen receptor (AR) playing a key role in mediating the actions of TP on facial nerve regeneration. The purpose of the present study was to determine the effects of
axotomy on AR
mRNA expression in
FMN. This was accomplished using in situ hybridization in conjunction with a (35)S-labeled AR riboprobe. Gonadally intact adult male and gonadectomized (gdx) adult female hamsters were subjected to a right facial nerve
axotomy, with the left side serving as internal, unoperated control. Half the animals were subcutaneously implanted with a 10-mm TP
Silastic capsule, and the other half were
sham-implanted. An additional group of nonaxotomized, gonadally intact males was also included. Postaxotomy survival times were 1, 4, and 7 days. At 1 postoperative day 1, there were no effects of
axotomy on AR
mRNA levels. By postoperative days 4 and 7,
axotomy caused a significant decrease in AR
mRNA levels in
FMN of gonadally intact males, relative to either the contralateral control
FMN of the same animals or
FMN from the group of gonadally intact males that were not subjected to facial nerve
axotomy. There were no significant differences between AR
mRNA levels in contralateral control
FMN and
FMN from the gonadally intact group of nonaxotomized males. TP administration at the time of
axotomy had no effect on AR
mRNA levels in either the axotomized or contrala(teral control
FMN of gonadally intact males, relative to the nonaxotomized, gonadally intact male group. Corroborating our previous work, AR
mRNA levels were reduced in the contralateral control
FMN of gdx females, relative to the nonaxotomized, gonadally intact male group, with
axotomy having no additional effects. The data are discussed in a mechanistic framework suggesting how TP acts to augment facial nerve regeneration.