Structure and expression of differentiation antigens on functional subclasses of primary sensory neurons

Subpopulations of dorsal root ganglion neurons can be distinguished on the basis of their peripheral receptive properties, spinal terminal arbors and neuropeptide content. We have used monoclonal antibodies (MAbs) to define antigenic determinants on functional populations of DRG neurons projecting to the superficial dorsal horn of the spinal cord. Three MAbs recognize defined carbohydrate epitopes associated with lacto- and globo-series glycolipids that constitute the stage-specific embryonic antigens (SSEAs) 1, 3 and 4. SSEA-3 and SSEA-4 are present in the cytoplasm of about 10% of DRG neurons in adult rat. These neurons are distinct from those that contain substance P, somatostatin or the fluoride-resistant acid phosphatase enzyme, FRAP. SSEA-1 is present in a small percentage of DRG neurons. SSEAs are present on the surface of DRG neurons maintained in dissociated cell culture: 6% are SSEA-1+, 7% are SSEA-3+ and 10-15% are SSEA-4+. MAbs LD2, KH10, TC6 and TD10 identify epitopes expressed coincidently in 25% of small DRG neurons that project to lamina II of the dorsal horn. All somatostatin- but less than 1% of substance P-immunoreactive DRG neurons express these antigens. MAb LA4 labels a distinct population of small DRG neurons that also projects to lamina II. There is extensive overlap between LA4+ neurons and those that contain FRAP. Antigens recognized by these MAbs are expressed on the surface of 10-20% of DRG neurons in culture. Preliminary biochemical studies suggest that these antigens may be glycolipids. Molecules bearing carbohydrate differentiation antigens may be involved in the development and specification of sensory connections in the dorsal horn of the spinal cord.