Studies of vasoactive intestinal polypeptide expression in injured peripheral neurons using capsaicin, sympathectomy...

The increased expression of vasoactive intestinal polypeptide (VIP) in injured peripheral neurons was studied. In contrast to substance P, there was a marked increase, and maintained fast axonal transport, of VIP in rat sciatic nerve after peripheral axotomy. Local capsaicin application to the nerve trunk failed to inhibit the injury-induced VIP increase, and capsaicin even increased VIP levels when applied locally to uninjured nerves. Pharmacological sympathectomy showed that some of the peripheral VIP increase may occur in post-ganglionic sympathetic fibres. The VIP increase after injury appeared unaffected in the mf mutant rat, in spite of its loss of lumbar dorsal root ganglion cells. VIP-staining fibres in the epi- and peri-neurium and perivascular plexuses of sciatic nerve showed an increase in number in parallel with the changes of the nerve VIP content. These findings suggest that sensory and sympathetic nerve fibres expressing VIP after injury play a role in the regulation of blood flow to nerves, and in the pathophysiological processes in nerve and dorsal spinal cord which follow peripheral nerve injury.