The comparative immunocytochemical distribution of 28 kDa cholecalcin (CaBP) in the hippocampus of rat, guinea pig and hedgehog.

The distribution of 28 kDa cholecalcin (calcium-binding protein, CaBP) in the hippocampal formation of the rat, guinea pig and European hedgehog was examined by immunocytochemistry. The extension of the mossy fibers (the axons of the granule cells of the dentate gyrus) was also studied using the Timm's sulfide-silver method. Cholecalcin was present in all mossy fibers. In the rat, only those pyramidal cells not reached by the labeled mossy fibers displayed cholecalcin immunoreactivity. Immunocytochemical staining of the hedgehog hippocampus showed that contacts between cholecalcin-containing mossy fibers and cholecalcin-containing pyramidal cells are possible. Consequently, the protein is probably not involved in the control of mossy fiber extension. Strikingly, no guinea pig pyramidal cells showed cholecalcin immunoreactivity. The possible involvement of cholecalcin in the differential excitability of pyramidal cells in the CA3 and CA1 areas of the hippocampus could therefore be tested in a comparative study of rat, guinea pig and hedgehog.