Testosterone-induced acceleration of recovery from facial paralysis in male hamsters: temporal requirements of hormone exposure.

In this study, the temporal requirements of testosterone propionate (TP) exposure necessary for acceleration of recovery from facial paralysis to occur following facial nerve crush were examined. For each of two series of experiments, adult castrated male hamsters were subjected to crush axotomies of the facial nerve at its exit from the stylomastoid foramen. In the first experimental paradigm, one-half of the animals with facial nerve crush axotomies received subcutaneous TP capsules beginning on postoperative (PO) day 6 and continuing throughout the regeneration period, with the remainder of the animals sham implanted. The results indicate that, without the early exposure to TP, the accelerative effects of the hormone on facial nerve regeneration were abolished. In the second experimental paradigm, one-half of the animals with facial nerve crush axotomies received subcutaneous TP implants immediately after the crush surgeries and until PO day 7, with the remainder of the animals sham implanted. The results indicate that an early, discontinuous dose of TP immediately after crush surgeries was sufficient to produce a partial accelerative effect on the return of facial nerve function. It is hypothesized from these findings that there is a priming effect of TP that is exerted at the level of the neuron, temporally precedes behavioral recovery by a week or more and is critical to subsequent acceleration of recovery from facial paralysis.