Distribution and origin of aminergic neurones in dog small intestine

In dog ileum, axons containing immunoreactivity for tyrosine hydroxylase (TH) and for DOPA decarboxylase (DDC) invest the neurones of the enteric ganglia and are present around arterioles, in the deep plexus of the circular muscle and in the laminar propria of the mucosal villi. Immunoreactivity for serotonin (5-HT) was present in mucosal enterochromaffin cells and in varicose axons investing cells of the submucous plexus, but not in axons in myenteric plexus, circular muscle or mucosa. No enteric neuronal cell bodies were immunoreactive for DDC or for 5-HT. Two weeks after extrinsic denervation of the ileum, all TH staining was absent. By contrast, the pattern of DDC staining was unchanged, except around blood vessels. We conclude that motility of dog ileum is likely to be regulated by sympathetic noradrenergic inputs and by intrinsic serotonergic and 'amine-handling' neurones. Dopaminergic innervation of dog ileum appears to be restricted to a sparse vasomotor supply.