Abstract
For application to spinal cord dysfunction, several approaches may be envisioned: the use of neural implants as axonal bridges for repair of damaged spinal circuitry, provision of cells for replacement of lost or damaged neuronal or glial elements, and provision of neurotransmitters and/or neurotrophic factors by implanted cellular minipumps. This chapter discusses these approaches. The primary goal of implantation of cellular bridges into the spinal cord is to provide a permissive substrate for axonal growth across the injury site to enable repair of cord circuitry and restoration of function following traumatic injury. In addition to providing a supportive growth environment, homotypic grafts of fetal spinal cord could potentially provide for the replacement of lost neuronal populations and restore spinal circuitry via reciprocal host-graft connections. Several laboratories have utilized serotonergic or noradrenergic cells as graft sources in spinal injured or denervated animals. Serotonergic cells have typically been obtained from embryonic mesencephalic or medullary raphe regions. In spinal cords of adult rats denervated of serotonergic input by 5,7-dihydroxytryptamine, serotonergic cell suspensions implanted 7 days after the lesion were found to survive for up to 12 months after grafting, with dense fiber outgrowth rostral and caudal to the grafts.