Local corticosteroid application blocks transmission in normal nociceptive C‐fibres

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Abstract
The effect of a locally applied depot form of a corticosteroid on the electrical properties of nerves was investigated in an experimental model. The segmental transmission in electrically stimulated A‐fibres and in C‐fibres of the plantar nerve in the anaesthetized rat was utilized. A drop of methylprednisolone acetate or vehicle constituent was placed on the dissected plantar nerve proximal to the stimulating electrodes after recording control responses (A‐fibre volley in the sciatic nerve and C‐fibre evoked reflex discharge in flexor motoneurons). The corticosteroid was found to suppress the transmission in thin unmyelinated C‐fibres but not in myelinated A‐beta fibres. The effect was found to be due to the corticosteroid per se. The effect was reversed when the corticosteroid was removed, which suggests a direct membrane action.