Age-related changes in calbindin-D28k, calretinin, and parvalbumin-immunoreactive neurons in the human cerebral cortex

Abstract

Calbindin-D(28k) (CB), calretinin (CRT), and parvalbumin (PV) are high-affinity cytosolic calcium (Ca(2+)) binding proteins (CBP) that have been found to regulate intracellular calcium concentrations in neurons through their buffering capacity and to protect neurons from insults that induce elevations of intracellular Ca(2+). In earlier studies we observed a substantial and neurochemically specific loss of CB from the human basal forebrain cholinergic neurons (BFCN) in the course of normal aging. In the present experiments we expanded our investigation of age-related changes in calcium binding proteins in the human brain by investigating the status of CB-, CRT-, and PV-positive neurons in 17 cortical areas. There was a trend toward a decrease in the number of CB-immunoreactive neurons in all areas studied. However, this trend reached significance in only 4 areas in which the loss of CB-positive neurons ranged between 20 and 46%. Immunoreactivity for CRT was also decreased in many areas and this difference reached significance in three regions (26-37%). Cortical neurons displaying PV immunoreactivity did not show an age-related change. Comparison with other neurochemically specific cortical neurons indicated a similar age-related loss of nonphosphorylated neurofilament and NADPH-d activity in only a few cortical areas. In contrast, neuronal acetylcholinesterase activity was increased in a few cortical areas. These observations indicate that loss of CBP-positive neurons occurs in restricted cortical regions and is not a specific change as other neurochemically specific neurons also display restricted age-related changes. Furthermore, the age-related changes in cortical CBP-positive neurons appear to be considerably smaller than similar changes in the BFCN. The age-related depletion of CBPs is likely to deprive neurons from the capacity to buffer intracellular calcium and thus to leave them vulnerable to pathological processes that can cause increased intracellular calcium and lead to their degeneration.