Alterations in glial fibrillary acidic protein (GFAP) mRNA levels in the hamster facial motor nucleus: effects of axotomy and testosterone.

Testosterone propionate (TP) administered at the time of facial nerve injury in the hamster accelerates the rate of regeneration. In this study, we tested the hypothesis that the mechanism by which TP augments peripheral nerve regeneration involves regulation of glial fibrillary acidic protein (GFAP) mRNA in the facial motor nucleus. Castrated male hamsters were subjected to right facial nerve transection, with half the animals implanted subcutaneously with Silastic capsules containing exogenous TP and the remainder sham implanted. Postoperative survival times were 0.25, 1, 2, 4, 7, and 14 d. Qualitative/quantitative analyses of both film and emulsion autoradiograms were accomplished. Axotomy, with or without TP, resulted in a dramatic increase in GFAP mRNA levels by 1 d post-operative on the axotomized side, relative to controls. GFAP mRNA levels remained elevated throughout all postoperative times in both the nonhormone- and TP-treated animals. Qualitative examination of the film autoradiograms indicated a generalized decrease in the amount of GFAP mRNA in the control and axotomized nuclei of TP-treated animals when compared to the control and axotomized nuclei, respectively, of nonhormone-treated animals. Statistical comparison of the values obtained for both the film and emulsion autoradiograms confirmed this impression. Thus, while the injury-induced increases in GFAP mRNA expression were not blocked by TP, the overall extent of the increase was significantly tempered by steroid treatment. These data suggest that hormonal modulation of the astrocytic response to peripheral nerve injury may be a contributing factor in the ability of steroids to enhance the regenerative capacities of injured motor neurons.