An immunohistochemical and quantitative examination of dorsal root ganglion neuronal subpopulations

Sensory neurons of adult rat lumbar dorsal root ganglia were labeled in cryostat sections with antisera against tyrosine hydroxylase (TH), substance P (SP), and somatostatin (SOM), and with a monoclonal antibody (RT97) that labels the 145- and 200-kilodalton (kd) subunits of neurofilaments. These neurons were also histochemically stained for fluoride-resistant acid phosphatase (FRAP), and the size and distribution of each population were determined. In addition, the double-label immunoperoxidase technique of Sternberger and Joseph (Sternberger, L.A., and S.A. Joseph (1979) J. Histochem. Cytochem. 27: 1424-1429) was employed to determine whether these antibodies labeled distinct or overlapping populations of neurons. The results indicate that the dopaminergic (TH+) cells constitute a separate population from the SP+ and SOM+ neurons and that the size distributions of the SP+, SOM+, TH+, and FRAP+ cells are all different despite the fact that all of these subpopulations are part of the "small dark" subpopulation as indicated by their size and by the fact that they are RT97-. RT97 is a putative marker for the "large light" population (Anderton, B., H.B. Coakham, J. A. Garson, A.A. Harper, and S.N. Lawson (1982) J. Physiol. (Lond.) 334: 97-98P). Furthermore, the distribution data indicate that all of the "small dark" cell subpopulations are not evenly distributed within the ganglion, and the staining with RT97 and with another antibody which recognizes the 68-kd neurofilament subunit indicates heterogeneity among the "large light" population. These results are discussed in terms of the significance of the "small dark"-"large light" classification.