Cobalt uptake enables identification of capsaicin- and bradykinin-sensitive subpopulations of rat dorsal root ganglion cells in vitro.

A novel modification of the stimulated cobalt uptake technique has been used to identify rat dorsal root ganglion cells expressing capsaicin and bradykinin receptors. The technique involves incubating intact dorsal root ganglia in vitro in a modified Krebs solution in which cobalt chloride has been substituted for calcium. Activation of dorsal root ganglion cells by capsaicin or bradykinin in the presence of the cobalt ions results in cobalt influx into the excited cells. Histochemical methods were then used to visualize the intracellular accumulation of cobalt, and labelled cells were counted and characterized. Capsaicin (2 microM) or bradykinin (500 nM) applied for 20 min induced cobalt uptake in 13.8 +/- 0.6 and 9.6 +/- 0.5% of neuronal profiles in dorsal root ganglia (L4), respectively, a significantly larger number than stained in control ganglia (in the absence of agonists: 1.8 +/- 0.7%). The longest diameter of the soma of stained dorsal root ganglion cells following capsaicin and bradykinin perfusion were significantly different from each other and from the non-labelled population (17.5 +/- 0.7 and 24.5 +/- 0.2 microns for capsaicin; 23.2 +/- 0.9 and 25.5 +/- 0.4 microns for bradykinin; labelled and non-labelled cells, respectively). The distribution of cell diameters revealed that while capsaicin-sensitive cells were exclusively small-sized, bradykinin-sensitive cells were predominantly small and medium sized. The selective bradykinin-2 receptor antagonist HOE-140 (5.0 microM) blocked the bradykinin-induced staining (2.16 +/- 0.02%) but not that of capsaicin. The bradykinin-1 agonist [des-Arg9]-bradykinin did not induce any significant increase in stained cells over the control number (2.2 +/- 0.7%).(ABSTRACT TRUNCATED AT 250 WORDS)