Distribution of calpain I, an enzyme associated with degenerative activity, in rat brain.

The calcium-activated protease calpain I was localized in rat brain by immunocytochemistry. Calpain I-like immunoreactivity (CLI) was prominent in several structures in which degeneration is an ongoing feature, e.g. spinal motoneurons, olfactory nerve. Also noteworthy was the presence of CLI in regions susceptible to age-related pathologies, e.g. cerebellar Purkinje cells, substantia nigra and subiculum. This distribution suggests that calpain I may be involved with both normal and pathological neuronal degeneration.