Resection of sciatic nerve re-triggers central sprouting of A-fibre primary afferents in the rat.

We have investigated whether nerve injury or target deprivation is responsible for the injury induced central sprouting of A-fibres. Cholera toxin B subunit conjugated horseradish peroxidase was used to trace the termination of A-fibre primary afferents. Transection of the sciatic nerve induces central sprouting of sciatic myelinated A-fibre primary afferents into the spinal dorsal horn lamina II, which normally is the termination site of unmyelinated C-fibre primary afferents. The sprouting A-fibre terminals withdrew from lamina II after six to eight months. A second cut to the previously sectioned and ligated sciatic nerve re-triggered the central sprouting of A-fibre primary afferents into the spinal dorsal horn lamina II, suggesting that nerve injury per se rather than the deprivation of target tissues is the cause of central sprouting of A-fibre primary afferents.