Myelin-associated glycoprotein is not detectable in perikaryal myelin of spiral ganglion neurons of adult mice.

Abstract

The expression of the adhesion molecules N-CAM (neural cell adhesion molecule), L1, myelin-associated glycoprotein (MAG), and P0 has been investigated by postembedding-immunoelectron microscopy in spiral ganglia of adult mice in which both axons and neuronal cell bodies are myelinated. L1 was absent from both axonal and perikaryal myelin of spiral ganglion neurons but was expressed on unmyelinated nerve fibers. P0 was expressed in compacted parts of both types of myelin but was absent from non-compacted myelin. MAG was not detectable in perikaryal myelin but was strongly expressed in axonal myelin both periaxonally and in non-compacted regions. Conversely, N-CAM was detectable at the interface between myelin and neuronal perikarya and in non-compacted regions of perikaryal myelin, whereas it was hardly detectable in axonal myelin. This inverse expression of MAG and N-CAM in perikaryal and axonal myelin points to the possibility that N-CAM may functionally replace MAG in perikaryal myelin of spiral ganglion neurons.