The Ca2+-activated neutral proteinase mcalpain is enriched in spinal cord and associated with myelin. Purified calpain readily degrades axonal and myelin proteins. Our findings of increased calpain activity and loss of axonal (neurofilaments, microtubules) and myelin (myelin basic and proteolipid proteins) proteins (for these are preferred substrates of calpain) from the spinal cord lesion indicated a pivotal role for calpain in the degeneration of axon and myelin. In order to elucidate the role of calpain involved in tissue destruction in spinal cord injury, it is essential to determine the level of calpain and calpastatin (its regulator) and the localization in spinal cord following injury. Thus, we plan to investigate the following: (l) calpain at the gene (mRNA) and protein (ELISA) levels and correlate with the activity in lesion at different intervals after injury; (2) determine the state of calpastatin (whether fragmented), its mRNA level and inhibitory activity; (3) examine calpain and calpastatin expression (mRNA) and activity in activated neutrophils and astrocyte culture; (4) determine immunocytochemical and immunofluorescence localization of calpain and calpastatin in the lesion after trauma; (5) examine the mechanism of membrane binding of calpastatin and its fragmentation by proteinases; (6) study the therapeutic effects of cell permeable calpain inhibitors in spinal cord injury with respect to calpain and calpastatin activity, immunolocalization, protein degradation; (7) examine the effect of high dose methylprednisolone (MP) in spinal cord injury with respect to calpain and calpastatin activity and protein degradation; (8) study the mechanism of calpain inhibition by MP and other steroid or non-steroid based anti-inflammatory drugs on purified calpain in vitro.