We assayed calpain activity in 27 human brain regions from adult (43–65 years of age) and aged (66–83 years of age) postmortem tissue samples. Calpain I (μM Ca-requiring) activity was 10 or less of the total activity; it was below detectable levels in a number of areas, and so data are are expressed as total (μM+mM Ca-dependent) calpain activity. The distribution of the enzyme was regionally heterogeneous. Highest activity was found in the spinal cord, followed by the amygdala, and levels in mesencephalic areas and in cerebellar grey matter were also high. Levels in cerebellar white matter, tegmentum, pons, and putamen were low, and activity in cortical areas was also relatively low. Although in some areas activity seemed higher with aging, the differences were not statistically significant. We previously found that the regional distribution of cathepsin D in human and in rat brain is similar, this seems to be true for calpain activity as well. The increase of protease activity with age found in rat brain is not found in human areas, as was shown previously with cathepsin D, and in the present study with ca
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