Vasoactive intestinal polypeptide (VIP) increases in the spinal cord after peripheral axotomy of the sciatic nerve originate from primary afferent neurons

Abstract

Following sciatic nerve axotomy, vasoactive intestinal polypeptide (VIP) immunoreactivity increases dramatically in the central terminal areas of the nerve whereas other primary afferent neuropeptides are depleted. The contribution of the peripheral nerve to VIP increases in the spinal cord was investigated by performing sciatic nerve section alone, dorsal rhizotomy of the lumbar roots, axotomy and rhizotomy in combination or section of other peripheral nerves terminating in the same segments as the sciatic nerve. VIP, and for comparison, substance P (SP), cholecystokinin (CCK), somatostatin (SOM), were localized in the lumbar spinal cord and corresponding sensory ganglia using unlabeled antibody immunohistochemistry. After sciatic nerve section, SP, CCK and SOM were depleted in the lumbar dorsal horn whereas VIP increased. After rhizotomy alone all neuropeptide staining including VIP was depleted; axotomy followed by rhizotomy produced the same result. Axotomy of other peripheral nerves terminating in the lumbar cord increased the area of neuropeptide depletion but correspondingly increased the area of VIP staining. A large proportion of small and medium diameter dorsal root ganglion cells were stained for VIP after nerve section or axotomy but not after rhizotomy alone. A radical change in neuropeptide metabolism of dorsal root ganglion cells occurs after peripheral axotomy, in the form of a marked increase in VIP synthesis. An intact dorsal root is necessary for increases in VIP in the spinal cord indicating the primary afferent origin of the response.