Gonadal steroid enhancement of facial nerve regeneration: Role of heat shock protein 70

Over the past decade, our laboratory has been investigating the now well-established neurotrophic capabilities of gonadal steroids in the context of peripheral nerve injury and repair. The focus of our work has been on the hamster facial motoneuron (FMN) system (Kujawa & Jones, 1995), although we have recently begun to explore two additional motoneuron injury paradigms, the rat sciatic and hamster rubrospinal systems (Kujawa et al., 1993). In this brief review, we will discuss the effects of androgens and estrogens on the regenerative properties and the molecular programming of injured hamster FMN. This will be followed by a discussion of the effects of androgens on the glial response to injury in the facial nucleus. Finally, a working model of the mechanism by which gonadal steroids enhance neuronal reparative processes will be advanced. Our proposed mechanism involves a neuroprotective role for gonadal steroids, in that we hypothesize that exposure to these agents at the time of injury reduces the need for the injured neuron to mount a classical “stress response” involving the production of heat shock protein 70. Finally, a series of future directions for our work will be presented.