VISUALIZING VANILLOID (CAPSAICIN) RECEPTORS IN PIG SPINAL-CORD BY [H-3] RESINIFERATOXIN AUTORADIOGRAPHY

Autoradiographic mapping using [H-3]resiniferatoxin (RTX) revealed hig h densities of vanilloid binding sites over areas (Rexed laminae I and II) in pig spinal cord known to be rich in central terminals of capsa icin-sensitive neurons. Also, high affinity [H-3]RTX binding was detec ted in membranes obtained from the corresponding areas: apparent bindi ng 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 co rd by either methodology suggesting that the vanilloid receptors are p resent exclusively on central terminals of the capsaicin-sensitive neu rons. We conclude that [H-3]RTX autoradiography may afford a novel neu rochemical approach to detect localized changes in vanilloid receptor expression.