PROLONGED CALPAIN-MEDIATED SPECTRIN BREAKDOWN OCCURS REGIONALLY FOLLOWING EXPERIMENTAL BRAIN INJURY IN THE RAT

Calpain, a calcium-activated neutral protease family, has been implica ted in the neuropathologic sequelae accompanying various neurological disorders. We have characterized the distribution and time course of c alpain activation following brain injury in the rat, using a monoclona l antibody that recognizes calpain-generated breakdown products (BDPs) of spectrin. Adult male Sprague-Dawley rats received lateral fluid pe rcussion brain injury of moderate severity (2.2-2.4 arm, n = 35) or se rved as controls (uninjured, n = 12). One group of animals (n = 21) we re sacrificed at either 30 minutes (min), 1 day, or 3 days post-injury , and selected brain regions were prepared for Western blot analysis. The remaining animals (n = 26) were sacrificed at 90 min, 4 hours (h), 1 day, or 7 days post-injury, and immunohistochemistry was performed. Spectrin BDPs were found predominantly in the hemisphere ipsilateral to the injury site, located primarily in cortical and hippocampal regi ons which exhibit neuronal death. Calpain-mediated spectrin breakdown was detected at 90 min in dendrites and axons, and by 4 h in neuronal perikarya. By 1 day post-injury, cortical and hippocampal regions of c alpain activation had increased in size. Delayed spectrin breakdown wa s observed in the thalamus, both at 3 days and 7 days after injury. Th ese results suggest that calpain may play an important role in the neu rodegenerative process following brain injury.