IMMUNOHISTOCHEMICAL STUDY OF CALPAIN-MEDIATED BREAKDOWN PRODUCTS TO ALPHA-SPECTRIN FOLLOWING CONTROLLED CORTICAL IMPACT INJURY IN THE RAT

This study examined the effect of unilateral controlled cortical impac t on the appearance of calpain-mediated alpha-spectrin breakdown produ cts (BDPs) in the rat cortex and hippocampus at various times followin g injury. Coronal sections were taken from animals at 15 min, 1 h, 3 h , 6 h, and 24 h after injury and immunolabeled with an antibody that r ecognizes calpain-mediated BDPs to alpha-spectrin (Roberts-Lewis et al ., 1994). Sections from a separate group of rats were also taken at th e same times and stained with hematoxylin and eosin. Analyses of early time points (15 min, 1 h, 3 h, and 6 h following injury) revealed alp ha-spectrin BDPs in structurally intact neuronal soma and dendrites in cortex ipsilateral to site of injury that was not present in tissue f rom sham-injured control rats. By 24 h after injury labeling was not r estricted to clearly defined neuronal structures in ipsilateral cortex , although there was an increased extent of diffuse labeling. BDPs to alpha-spectrin in axons were not detected until 24 h after injury, in contrast to the more rapid accumulation of BDPs observed in neuronal s oma and dendrites. The presence of BDPs to alpha-spectrin in the corte x at the site of impact, and in the rostral and contralateral cortex, coincided with morphopathology detected by hematoxylin and eosin. alph a-Spectrin BDPs were also observed in the hippocampus ipsilateral to t he injury in the absence of overt cell death. This investigation provi des further evidence that calpain is activated after controlled cortic al impact and could contribute to necrosis at the site of injury. The appearance of calpain-mediated BDPs at sites distal to the contusion s ite and in the hippocampus also suggests that calpain activation may p recede and/or occur in the absence of extensive morphopathological cha nges.