The goal of this research is to better understand the cellular mechanisms by which neurons respond to physical trauma, including the recovery from sub-lethal injury and the processes leading to death after a lethal insult. A new model for such research will be developed and defined, and it will be used to investigate the efficacy of treatments that may improve the prospects of neuronal survival after injury. Molluscan neurons have great ability to recover from injury. One specific alm of the proposed research is to define the responses of cultured neurons from the snail, Helisoma trivolvis, to mechanical injury and to compare these responses to those of mammalian neurons. The model will be defined by determining the effect of axotomy on neuronal survival. The parameters of a lesion (distance from the perikaryon and lesion diameter) that will produce a predictable neuronal survival rate will be determined, and this standardized axotomy paradigm will be used to test factors that may alter neuronal recovery after injury. Since molluscs have lower body temperatures than mammals, the importance of temperature in the recovery of neurons after injury will be determined. Pathological changes in the ultrastructure of the cultured neurons after injury will also be observed and compared to those that have been reported in similarly injured mammalian neurons. Changes in ultrastructure of injured neurons will be correlated with measured levels of intracellular free calcium by using calcium sensitive fluorescent dye fluorimetry. The process by which the severed axon reseals after axotomy will be investigated by measuring the dynamics of changes in membrane electrical properties after axotomy. Agents which may alter this resealing process will be tested on the culture model,and their effects on resealing and neuronal viability will be determined.