AGE-RELATED LOSS OF CALCIUM-BINDING PROTEINS IN RABBIT HIPPOCAMPUS

Using immunocytochemistry hippocampal levels of the calcium binding pr oteins calbindin 28K (CB) and parvalbumin (PV) was studied in young (1 month) to very old (60 month) Albino rabbits. Young (3 month) and sen escent (30 month) Wistar rats were also examined to compare the distri bution and age dependency of PV and CB in both species. The distributi on of PV-ir is similar in the rabbit and rat hippocampus. Aging in bot h species yielded a small loss of PV-ir in axon terminals. The presenc e of CB-ir interneurons throughout the hippocampus, and the heavy inve stment of the dentate gyrus (DG) granular cells with CB-ir was also si milar in both species. In rabbits, the number of CB-ir interneurons in the CA1. as well as the density of CB-ir in the DG decreased in the f irst year of life, and did not change between 12-48 months of age. A s econdary reduction in the density of CB-ir in the DG was observed at a ges beyond 48 months. A similar loss of CB-ir in the DG occurred in th e rat. In the CA1, however, the density of CB-ir was similar in young and aged rats. Another remarkable finding was the total absence of CB- ir in CAI pyramidal neurons of rabbits at any age. Thus, the distribut ion and age dependency of PV-ir in the hippocampus is similar in both species. The decline of CB-ir in the DG with advancing age is very pro minent and may be related to an altered calcium homeostasis in these c ells. However, the absence of CB-ir in the CA1 of rabbits makes a caus al role for CB in the functional decline of CAI pyramidal cells during aging unlikely.