VISUALIZATION BY [H-3] RESINIFERATOXIN AUTORADIOGRAPHY OF CAPSAICIN-SENSITIVE NEURONS IN THE RAT, PIG AND MAN

[H-3]Resiniferatoxin autoradiography revealed high densities of bindin g sites in rat dorsal root ganglia as well as in the superficial dorsa l horn of the spinal cord, known to contain the cell bodies and centra l terminals, respectively, of capsaicin-sensitive, sensory neurons. Th is binding was fully displaced by non-radioactive resiniferatoxin and was absent following administration of high, neurotoxic doses of capsa icin. The binding thus has the characteristics expected for the vanill oid (capsaicin) receptor. High density, specific resiniferatoxin bindi ng was also observed in pig spinal cord and dorsal root ganglia. Final ly, similar high density binding was detected in the dorsal horn of hu man spinal cord obtained post-mortem. We conclude that [H-3]resinifera toxin autoradiography may afford a novel neurochemical tool to identif y capsaicin-sensitive neurons in the central as well as in the periphe ral nervous system, to explore the ontogeny of these neurons, and to d etect changes in vanilloid (capsaicin) receptor expression under patho physiological conditions.