The depolarising action of capsaicin on rat isolated sciatic nerve

The effect of capsaicin on the isolated sciatic nerve of rat was studied by extracellular recording of membrane polarisation. Capsaicin depolarised the sciatic nerve, but desensitization occurred rapidly upon repeated administration. Several other neuroactive substances, including substance P, were inactive. The depolarisation was reduced in nerves depleted of unmyelinated fibres by neonatal capsaicin treatment, suggesting that it occurs mainly in C-fibres. This depolarising action of capsaicin could explain the irritant and acute antinociceptive properties of capsaicin.