Differential neuropeptide expression after visceral and somatic nerve injury in the cat and rat

The expression of neuropeptides galanin, vasoactive intestinal polypeptide (VIP) and substance P was compared after injury to somatic (sciatic, pudendal) and visceral (pelvic) nerves. Studies in normal rats and the mutant rat 'mutilated foot' suggested that galanin increases in sensory but not sympathetic fibres after sciatic nerve injury, while VIP appears to increase in both sensory and sympathetic fibres, and substance P to decrease in sensory fibres. A direct comparison of neuropeptide changes after somatic and visceral nerve injury was made in the cat dorsal sacral spinal cord, where both pudenal (somatic) and pelvic (visceral) afferents terminate. Four weeks after pudendal nerve transection in the cat there was an increase of VIP and galanin but decrease of substance P in the dorsal sacral cord, similar to the changes in lumbar dorsal cord after sciatic nerve section in the rat. In contrast, 4 weeks after pelvic nerve transection in the cat, galanin was unchanged in the ipsilateral dorsal sacral spinal cord, whereas VIP is known to decrease markedly and substance P to remain unchanged. There is thus differential peptide expression before and after injury in somatic and visceral systems, which may be regulated in part by the target organ. We have proposed that the neuropeptide changes occur in neurons that regulate development, maintenance and repair after injury, processes that may differ in somatic and visceral systems.