Ultrastructural analysis of polysialylated neural cell adhesion molecule in the suprachiasmatic nuclei of the adult mouse.

The suprachiasmatic nuclei (SCN) of the anterior hypothalamus are recognized as the principal circadian clock in mammals. The adult SCN express a high level of polysialylated neural cell adhesion molecule (PSA-NCAM), a cell surface sialoglycoprotein capable of modulating cell-cell interactions. In the present study, the expression of PSA-NCAM in the mouse SCN was studied at the ultrastructural level by immunolabeling using monoclonal antibodies against the polysialic acid (PSA) moiety of PSA-NCAM. We showed that neuronal somal expression of PSA-NCAM was distributed heterogeneously in the SCN, with extensive staining of somas in the central region of the SCN, and minimal somal staining in the ventral portion of the nuclei. In contrast, immunoreactive neuropil, including unmyelinated fine axon fascicles was distributed throughout the SCN. The PSA-NCAM was also detected adjacent to synaptic junctions by both immunoperoxidase and immunogold techniques. For astrocytes, immunostaining of somas and larger processes was sparse, but staining was profuse along fine processes. Immunostained fine astrocytic processes were frequently observed between apposing neuronal somas, and in close association with synaptic junctions and small blood vessels. These findings, together with the demonstrated role of PSA-NCAM in modulating cell-cell interactions in other brain regions support a role for PSA-NCAM in regulating cell-cell interactions in the SCN. Copyright 1999 Wiley-Liss, Inc.