Effects of capsaicin applied locally to adult peripheral nerve. II. Anatomy and enzyme and peptide chemistry of peripheral nerve and spinal cord

Abstract

Capsaicin solution was applied for 15 min around a 1-cm length of sciatic nerve in the mid upper leg of adult rats. EM examination of the nerve in the treated region after 14 days shows no signs of degeneration of either myelinated or unmyelinated fibers attributable to the capsaicin. Fluoride-resistant acid phosphatase (FRAP) disappears from the central terminals of the treated nerve by 7 days. Capsaicin (1.5 mM) is sufficient to produce a complete reduction of FRAP in the spinal cord. The peptides substance P and cholecystokinin (CCK) are markedly depleted in the region of spinal cord terminations of the treated nerve at 14 days. Substance P and CCK are not affected in spinal cord regions other than in the unmyelinated afferent terminal zone. Similarly neurotensin and neurophysin which are not present in afferent fibers are not influenced by capsaicin treatment of the sciatic. Chemical changes in the spinal cord terminals of fine afferents follow local peripheral capsaicin.