Visualization by [3H]resiniferatoxin autoradiography of capsaicin-sensitive neurons in the rat, pig and man.

[3H]Resiniferatoxin autoradiography revealed high densities of binding sites in rat dorsal root ganglia as well as in the superficial dorsal horn of the spinal cord, known to contain the cell bodies and central terminals, respectively, of capsaicin-sensitive, sensory neurons. This binding was fully displaced by non-radioactive resiniferatoxin and was absent following administration of high, neurotoxic doses of capsaicin. The binding thus has the characteristics expected for the vanilloid (capsaicin) receptor. High density, specific resiniferatoxin binding was also observed in pig spinal cord and dorsal root ganglia. Finally, similar high density binding was detected in the dorsal horn of human spinal cord obtained post-mortem. We conclude that [3H]resiniferatoxin autoradiography may afford a novel neurochemical tool to identify capsaicin-sensitive neurons in the central as well as in the peripheral nervous system, to explore the ontogeny of these neurons, and to detect changes in vanilloid (capsaicin) receptor expression under pathophysiological conditions.