POLYSIALYLATED NEURAL CELL-ADHESION MOLECULE EXPRESSION BY NEURONS AND ASTROGLIAL PROCESSES IN THE RAT DENTATE GYRUS DECLINES DRAMATICALLY WITH INCREASING AGE

The expression of polysialylated neurons in the dentate gyrus of the h ippocampal formation of young (postnatal day 40), mature (postnatal da y 80) and aged (postnatal day 540) male Wistar rats has been investiga ted by immunohistochemical techniques employing a monoclonal antibody specific for neural cell adhesion molecule-linked alpha 2,8 polysialic acid. A strong immunoreactivity was found on the cell bodies, dendrit es and axons of granule like neuronal cells at the border between the hilar region and the granule cell layer of the young rat. In the matur e animal the number of immunoreactive neurons declined dramatically an d were virtually absent in the aged group. Using an alternative fixati on procedure, glial fibrillary acidic protein-positive and polysialyla ted astroglia processes were found in close proximity to the dendrites of the polysialylated granule-like cells. The number of astroglial pr ocesses traversing the granule cell layer showed a similar age-depende nt decline to that observed with the polysialylated neurons. Glial fib rillary acidic protein-positive and polysialylated stellate astroglia were present throughout the hippocampal formation, but did not show th e marked age-dependent decline observed with the astroglial processes in the granule cell layer. The neuronal dendrites and astroglial proce sses exhibited a strict numerical ratio in the young and mature animal and, in double immunofluorescence studies with anti-polysialic acid a nd anti-glial fibrillary acidic protein, the astroglial processes exhi bited apparent points of cell and/or dendritic contact. These findings suggest that loss of polysialylated astroglial processes precedes the decline in polysialylated dentate neurons.