EXPRESSION OF POLYSIALYLATED NEURAL CELL-ADHESION MOLECULE BY PROLIFERATING CELLS IN THE SUBEPENDYMAL LAYER OF THE ADULT-RAT, IN ITS ROSTRAL EXTENSION AND IN THE OLFACTORY-BULB

The highly sialylated isoform of the neural cell adhesion molecule is thought to be expressed predominantly in the developing nervous system , where it is implicated in a variety of dynamic events linked to neur al morphogenesis. It has become increasingly evident, however, that th is ''embryonic'' neural cell adhesion molecule isoform continues to be expressed in certain adult neuronal systems, and in particular, in th ose that can undergo structural plasticity. In the present study, we p erformed light microscopic immunocytochemistry with an antibody specif ic for polysialylated neural cell adhesion molecule and confirmed our earlier observations [Bonfanti L. et al. (1992) Neuroscience 49, 419-3 6] showing polysialylated neural cell adhesion molecule-immunoreactive cells in the subependymal layer of the lateral ventricle of the adult rat, a region where cell proliferation continues into the postnatal p eriod. In addition, we used an antibody raised against the proliferati ng cell nuclear antigen and found that proliferating cells continue to be visible in this area, even in the adult. Double immunolabeling sho wed that many of these newly generated cells displayed high polysialyl ated neural cell adhesion molecule immunoreactivity. Cells from a port ion of the subependymal layer migrate to the olfactory bulb and contri bute to the continual replacement of its granule neurons [Luskin M. B. (1993) Neuron 11, 173-189]. We found polysialylated neural cell adhes ion molecule-immunoreactive cells all along the pathway purported to b e followed by the newly generated cells to their final destination and in neurons corresponding to granular and periglomerular cells in the olfactory bulb. Our present observations thus support the contention t hat polysialylation is a feature of neurons capable of dynamic change and may contribute to the molecular mechanisms permitting cell prolife ration and migration not only during development but also in the adult .