Developmental expression of KG-CAM in the rat neostriatum

The present study examines the developmentally regulated expression pattern of an Ig superfamily member, KG-CAM, in the neostriatum of the rat. KG-CAM is a 90-kDa glycoprotein that is related to the DM-GRASP/Neurolin family of adhesion molecules. In the embryonic and early postnatal neostriatum, the distribution of KG-CAM correlates with the distribution of dopaminergic terminals. Early in neostriatal development, KG-CAM is found in the tyrosine hydroxylase-positive patches. In the maturing neostriatum, the levels of KG-CAM remain high within the patches, and KG-CAM upregulates in the matrix compartment. As the neostriatum is reaching its adult morphology, 5 weeks postnatal, the expression of KG-CAM in the matrix is approximately equal to that of the patches. When the distribution of KG-CAM is examined at the ultrastructural level, the immunoreactivity is localized to the external surface of neuronal and glial profiles in the neuropil. KG-CAM does not appear to be associated with the guidance of dopaminergic axons from the substantia nigra to the striatum, for this pathway is not immunopositive for this member of the Ig superfamily. The present study identifies an Ig superfamily member, KG-CAM, that appears to play a major role in the development of the neostriatum. Furthermore, the high levels of KG-CAM in the adult neostriatum suggest that this Ig superfamily member may be involved in maintaining the integrity of this structure in the adult rat.