Visualizing vanilloid (capsaicin) receptors in pig spinal cord by [3H]resiniferatoxin autoradiography

Autoradiographic mapping using [3H]resiniferatoxin (RTX) revealed high densities of vanilloid binding sites over areas (Rexed laminae I and II) in pig spinal cord known to be rich in central terminals of capsaicin-sensitive neurons. Also, high affinity [3H]RTX binding was detected in membranes obtained from the corresponding areas: apparent binding affinity and cooperativity but not the maximal receptor density was influenced by the assay conditions (temperature, buffer composition). No specific binding could be detected in other areas of the spinal cord by either methodology suggesting that the vanilloid receptors are present exclusively on central terminals of the capsaicin-sensitive neurons. We conclude that [3H]RTX autoradiography may afford a novel neurochemical approach to detect localized changes in vanilloid receptor expression.