Calcium-binding proteins are concentrated in the CA2 field of the monkey hippocampus: a possible key to this region's resistance to epileptic damage.

Previous immunocytochemical studies have shown a heterogeneous distribution of parvalbumin (PA) and calbindin (CB) in the rat hippocampal formation. The results of the present study showed a heterogeneous distribution of PA and CB in primate Ammon's horn. The density and intensity of immunoreactivity for both of these calcium-binding proteins was greatest in CA2 as compared to CA1 and CA3. CB-immunoreactivity was localized to the cell bodies, dendrites, and axon initial segments of pyramidal cells whereas PA-immunostaining was found in the axon terminals, dendrites and cell bodies of interneurons that have features similar to GABAergic inhibitory neurons. Based on previous studies that have shown a protective role of calcium-binding proteins in neurons exposed to hyperstimulation, these results suggest that the resistance of CA2 pyramidal cells in temporal lobe epilepsy is due to the high concentration of CB and PA in this region of Ammon's horn.