Heterogeneous distribution of polysialylated neuronal-cell adhesion molecule during post-natal development and in the adult: an immunohistochemical study in the rat brain.

A monoclonal antibody raised against the capsular polysaccharides of meningococcus B was used for immunohistochemical studies in the rat brain, with particular focus on the substantia nigra. This antibody recognizes polysialic acid residues specifically associated with the neuronal-cell adhesion molecule, and reacts with the highly sialylated embryonic neuronal-cell adhesion molecule, but not with the weakly sialylated adult form of the molecule. Immunoreactivity to this monoclonal antibody was intense and widespread in the brain of 1-10-day-old hooded rats. Immunolabeling was associated with cell membranes and present in the intersomata space. In sections from 16- and 25-day-old rats, marked heterogeneity in the level of immunostaining appeared among individual brain nuclei. Areas devoid of labeling with the anti-meningococcus antibody still expressed immunoreactivity to a polyclonal anti-neuronal-cell adhesion molecule antibody. This suggests that the loss of immunostaining with the monoclonal antibody did not correspond to a loss of expression of neuronal-cell adhesion molecule, but to a maturation from the embryonic to the adult form of the molecule, occurring at different rates in various brain regions. In 2-month-old rats, immunolabeling with the monoclonal antibody was still present in discrete brain areas, including the substantia nigra, suggesting that the presence of highly sialylated neuronal-cell adhesion molecule outlasts post-natal development in those brain regions. It is proposed that neuronal-cell adhesion molecule associated polysialic residues may play a role in neuronal plasticity in restricted areas of the adult brain.