Capsaicin is a plant neurotoxin which depolarises a subset of mammalian sensory neurons. A photoaffinity probe (4-azidophenylpropionamide) with capsaicin-like agonist activity (EC50 5 μM) has been used to covalently label rat and chick sensory neurons in culture, as well as membrane preparations from both neurons and other tissues. Dorsal root ganglion cell specific capsaicin-binding proteins, including a major band of apparent molecular mass 58 000, have been identified by means of Western blotting, using a specific anti-capsaicin antiserum characterised by radioimmunoassay with a large range of capsaicin congeners. Using the same radioimmunoassay, no endogenous capsaicin-like immunoreactive material in normal or inflamed tissue has, however, been detected.
