Cholecalcin (28-kDa calcium-binding protein) in the rat hippocampus: development in normal animals and in altered thyroid states. An immunocytochemical study.

An immunocytochemical study of cholecalcin (28-kDa calcium-binding protein, CaBP, calbindin) was carried out during the development of the rat hippocampus. In normal animals, the protein appeared from Postnatal Day 3 in the granule cells of the dentate gyrus and from Day 5 in the CA1-CA2 pyramidal cells of Ammon's horn. The cells of both regions thus showed positive cholecalcin labeling about 1 week after their formation. The sequence of labeling of the granule cells was a reflection of the major sequences of neurogenesis. Cholecalcin could not be detected in hippocampal cells until dendritic arborization and axon growth had occurred. There was a good correlation between the appearance of cholecalcin and the onset of synaptogenesis. In animals with an experimentally altered thyroid state, in which hippocampal development is retarded or accelerated due to abnormal cell maturation, cholecalcin appearance was similarly retarded or accelerated. Cholecalcin seems to be synthesized at the same time as the hippocampal cells become functional.