Administration of the selective
calpain inhibitor AK295 has been shown to attenuate motor and
cognitive dysfunction after
brain trauma in rats. To explore mechanisms underlying the behavioral efficacy of posttraumatic
calpain inhibition, we investigated histologic consequences of
AK295 administration. Anesthetized Sprague-Dawley rats received lateral fluid percussion
brain injury of moderate severity (2.2 to 2.4 atm) or served as uninjured controls. At 15 minutes after injury, animals were randomly assigned to receive a 48-hour infusion of either 2 mmol/L
AK295 (120 to 140 mg/kg) or saline via the carotid artery. At 48 hours and 1 week after injury,
spectrin fragments generated specifically by
calpain were detected by Western blotting and immunohistochemistry, respectively, in saline-treated, brain-injured animals. Interestingly, equivalent
spectrin breakdown was observed in AK295-treated animals when cortical and hippocampal regions were evaluated. Similarly, administration of the
calpain inhibitor did not attenuate cortical lesion size or the numbers of apoptotic cells in the cortex, subcortical white matter, or hippocampus, as verified by
terminal deoxynucleotidyl transferase-mediated biotinylated
deoxyuridine triphosphate nick-end labeling and morphology, at 48 hours after injury. These data suggest that an overt reduction in
spectrin proteolysis, cortical lesion, or apoptotic cell death at 48 hours or 1 week is not required for behavioral improvements associated with
calpain inhibition by
AK295 after experimental
brain injury in rats.