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.