The purpose of the proposed research is to determine the mechanisms which contribute to recovery of function after spinal cord injury. By developing methods which can enhance these mechanisms, we will attempt to increase the extent of recovery. We will examine two consequences of axotomy that are important to recovery: 1) cell survival after axotomy and 2) responses of the surviving cells that support axonal growth. Factors that we will study that affect cell survival are: a) the influence of the target; b) the influence of afferents; c) sprouting of undamaged neurons; and d) changes in protein synthesis. Quantitative morphological and electrophysiological methods will be used to identify characteristics of cells that survive axotomy and to characterize the responses required for regeneration. The influence of natural targets and afferents on cell survival will be tested using in vivo and in vitro methods; we will then determine whether supplying a surrogate target of fetal tissue will enhance the likelihood of neuronal survival and axonal outgrowth. Sprouting and synaptogenesis of undamaged neurons which are spared by the lesion can also mediate recovery by compensation; some of the functional consequences of sprouting will be tested. In order to investigate methods for enhancing recovery we will identify changes in axotomized cells that are correlated with the regenerative response. We will use electrophysiological methods, in situ hybridization and studies of protein synthetic changes to characterize the successful regenerative response, and we will also examine the factors that stimulate axonal outgrowth in developing neurons. We will use fetal spinal cord transplants to identify the way in which the transplanted tissue encourages metabolic activity supportive of regeneration by axotomized cells. The functional consequences of spinal cord regeneration mediated by the presence of transplanted fetal tissue will be assessed using quantitative methods developed to evaluate recovery of motor behavior. In addition to the six projects, we are proposing six core facilities, including new tissue culture, image analysis and motion analysis cores. These core facilities will make advanced technology available to all projects, and promote development of new methods for the analysis of the recovery of function after spinal cord injury. The proposed experimental program should permit identification of some of the mechanisms underlying recovery and development of ways to enhance these mechanisms in order to increase the extent of recovery following spinal cord injury.
