[Hippocampal adult neurogenesis and neuronal circuit formation: an analysis with special reference to polysialic acid-neural cell adhesion molecule].

It is generally thought that neurons are generated during the embryonic and early postnatal periods, but not in the adult. However, as neurogenesis continues in the dentate granule layer of the adult hippocampal formation, this would imply that new neuronal circuits are being added to the adult hippocampus by adult neurogenesis. Since these newly generated granule cells specifically express polysialic acid (PSA)-neural cell adhesion molecule (NCAM), it is possible to examine the new neuronal circuit formed by these cells using PSA immunohistochemisty. As for PSA function, it has been shown that the PSA expression of the mossy fibers is required for synaptic arrangement. Recently neurogenesis and PSA expression in the adult hippocampus are reported to be affected by neuronal activity and hormones, suggesting that they are closely associated with hippocampal plasticity.