Evidence now indicates a critical role for increased intracellular calcium levels in cellular damage and neuronal death after traumatic brain injury (TBI). A major source of increased intracellular calcium is calcium influx through voltage sensitive calcium channels (VSCC). Six major subtypes of VSCC's have been identified, including L, N, P, Q, R and T. Each of these channels has been demonstrated in the mammalian nervous system, and each could contribute importantly to the movement of calcium after TBI. The relative contributions of each calcium channel subtype to calcium-induced neuronal pathology are currently unknown. Such information is vital because the identification of a specific channel or channels that mediate the majority of calcium flux could lead to the development of targeted channel blocking drugs with substantial neuroprotective activity. The proposed experiments will examine the contribution of each VSCC subtype to the histopathological and neurobehavioral consequences of TBI. Specific VSCC blockers will be administered after TBI produced using the lateral fluid percussion injury procedure in rats. The ability of each VSCC to provide histological and neurobehavioral (i.e., cognitive and motor) protection will be compared and evaluated. In addition, the relative roles of each channel subtype in mediating calcium flux from the extracellular compartment will be examined directly by measuring changes in extracellular calcium levels after TBI using the techniques of in vivo microdialysis and calcium sensitive microelectrodes. Calcium-dependent phosphorylation of calcium calmodulin-dependent kinase II (CaMKII) will be examined qualitatively and quantitatively as an index of increased intracellular calcium levels after TBI using immunohistochemistry. Specifically, the ability of VSCC blockers to reduce or prevent increases in intracellular levels of phosphorylated CaMKII after TBI will be evaluated. This research will provide important insights into the mechanisms of brain injury, and specifically the role of disruption of calcium homeostasis. New information about the relative contributions of specific VSCC's to the pathophysiology of TBI will be obtained, and the neuroprotective potential of novel neuronal VSCC blockers will be assessed using histological, biochemical and behavioral techniques. Calcium channel blockers are already in development for various forms of brain injury. This research will therefore provide clinically relevant information concerning the feasibility of their application for the treatment of brain injury in humans, and may indicate new directions for their continued therapeutic development.
