Reduction of Calbindin D-28k-Immunoreactive Neurons in the Dog Dentate Gyrus

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The calcium binding protein calbindin D-28k (CB) plays an important role in modulating the activity of neurons in the dentate gyrus. We observed CB immunoreactivity in the dentate gyrus of dogs of various ages (German shepherds). In the 1-year-old group, CB immunoreactivity was detected in almost all of granule cells with poor processes. In the 8-year-old group, the number of CB-immunoreactive ⁽⁺⁾ neurons in the granule cell layer was significantly reduced (73.2% vs. 1-year-old group), while CB⁺ cell bodies and fibers were well developed. In the 10-year-old group, the number of CB⁺ neurons was further reduced by 31.3% when compared to that in the 1-year-old group. This finding demonstrates that the number of CB⁺ neurons decreases in the aged dog brain and this may be associated with reduction of function in the dentate gyrus.