Axotomy is known to induce changes in neuropeptide expression in several types of neurons. Colchicine blocks the axonal transport and may mimic axotomy. The effects of colchicine-treatment and axotomy (local nerve crush by clamping of the gut) on enteric neurons expressing vasoactive intestinal peptide, neuropeptide Y and nitric oxide synthase were studied in rat small intestine by immunocytochemistry and in situ hybridization. Colchicine treatment significantly increased the number of submucous and myenteric neurons expressing vasoactive intestinal peptide and its mRNA. In contrast, an increase in the number of neuropeptide Y or nitric oxide synthase expressing neurons could not be detected. Axotomy markedly increased the number of myenteric vasoactive intestinal peptide-immunoreactive neurons in the segment located orally to the lesion, but not in the segment anally to the lesion, whereas that of nitric oxide synthase and neuropeptide Y expressing neurons was not affected. Double immunostaining revealed that the myenteric neurons containing nitric oxide synthase were induced by colchicine and axotomy to express vasoactive intestinal peptide. The present data indicate that colchicine and axotomy may induce marked changes in the neuropeptide expression of enteric neurons.