Neuronal damage in the ischemic brain leads to rapid cell death, induced directly by the insult, and delayed secondary neurotoxicity, which depends on apoptotic cell death programs While death of neurons occurring within a short time after ischemic insults may not be a realistic target for therapy, delayed cell death might be prevented by new neuroprotective strategies Our preliminary experiments provide support for the novel hypothesis that gap junctions, intercellular channels composed of connexins that mediate electrical synchrony and metabolic cooperation between cells, participate in propagation of neuronal damage and death following global brain ischemia The goal of the proposed studies is to characterize the role of neuronal and astrocytic gap junction channels in propagating delayed neuronal death mediated by ischemic insults in field CA1 of the hippocampus. The broad hypotheses to be tested are that (1) gap junction-mediated signaling can amplify the extent of ischemic injury, and (2) gap junction blockade will reduce the extent of cell death of CA1 pyramidal neurons and astrocytes following ischemia This application proposes to address these questions using organotypic hippocampal slice cultures, from wild type and connexin-deficient mice, subjected to transient global ischemia in vitro Two complementary strategies will be used First, molecular biological and electrophysiological techniques will evaluate the extent of ischemia-induced injury in slice cultures from wild type mice Second, the extent of damage will be compared to mice in which the major neuronal (connexin36) and astrocytic (connexin43) gap junction proteins have been genetically reduced (Cx36-/+ and Cx43-/+), ablated (Cx36 and Cx43 knockouts) or differentially blocked pharmacologically As a complementary approach, we will determine the extent of ischemia mediated neurotoxicity in organotypic slice cultures of Cx43 and Cx36-knock-out mice following reexpression of HSV-Cx43 and -Cx36 (i e, """"""""gain of function"""""""" approach) These studies are expected to provide mechanistic insights into the extent of neuronal death following brain global ischemia and to have significant therapeutic application in the treatment of long-term sequelae of brain ischemia. ? ?
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