Implantation of PNS graft inhibits the induction of neuronal nitric oxide synthase and enhances the survival of spinal motoneurons following root avulsion.

In a spinal root injury model, our previous studies have shown that induction of nitric oxide synthase (NOS) appears only in spinal motoneurons of the root-avulsed segment in which significant motoneuron loss occurs but not in those of the distal root-axotomized segment (root axotomy 5-10 mm from the spinal cord) in which most motoneurons survive the injury. One hypothesis for the different response of motoneurons to root avulsion and distal root axotomy is that neurotrophic factors produced by the remaining peripheral nervous system (PNS) component are available for the distally axotomized motoneurons but are not available following avulsion. This hypothesis is tested in the present study by implantation of a PNS graft following the root avulsion. Results of the present study show that implantation of a PNS graft significantly enhances the survival of motoneurons following avulsion. Expression of NOS due to avulsion injury is completely inhibited in all motoneurons that regrow into the PNS graft. These results indicate that induction of NOS in avulsed motoneurons may result from the deprivation of neurotrophic factors produced by the PNS component, and the survival promoting effects of neurotrophic factors may be achieved by modifying certain cellular molecules such as NOS.