DEVELOPMENTAL EXPRESSION OF KG-CAM IN THE RAT NEOSTRIATUM

The present study examines the developmentally regulated expression pa ttern of an Ig superfamily member, KG-CAM, in the neostriatum of the r at. KG-CAM is a 90-kDa glycoprotein that is related to the DM-GRASP/Ne urolin family of adhesion molecules. In the embryonic and early postna tal neostriatum, the distribution of KG-CAM correlates with the distri bution of dopaminergic terminals. Early in neostriatal development, KG -CAM is found in the tyrosine hydroxylase-positive patches. In the mat uring 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 o f KG-CAM in the matrix is approximately equal to that of the patches. When the distribution of KG-CAM is examined at the ultrastructural lev el, the immunoreactivity is localized to the external surface of neuro nal and glial profiles in the neuropil. KG-CAM does not appear to be a ssociated with the guidance of dopaminergic axons from the substantian igra to the striatum, for this pathway is not immunopositive for this member of the Ig superfamily. The present study identifies an Ig super family member, KG-CAM, that appears to play a major role in the develo pment of the neostriatum. Furthermore, the high levels of KG-CAM in th e adult neostriatum suggest that this Ig superfamily member may be inv olved in maintaining the integrity of this structure in the adult rat.