The nerves of the accessory pancreatic ducts of the common starling (Sturnus vulgaris): an ultrastructural and light microscopic study.

An ultrastructural and light microscopic study was undertaken to examine the nerves of the accessory pancreatic ducts of the starling (Sturnus vulgaris), previously noted (Vinnicombe, 1982) to have a particularly dense innervation. Large numbers of nerves were found in the ducts, predominantly in the lamina propria, and all contained exclusively unmyelinated axons. Probable neuron cell bodies were observed in the smooth muscle layer, but not in the lamina propria. Schwann cells invested all the axons, and these displayed terminal swellings in a 'synapse en passage' arrangement. The nerves of the lamina propria were most numerous in the region immediately beneath the epithelium and were present in the epithelial folds. One axon was observed to have penetrated the epithelial basal lamina and to lie between two epithelial cells. Examination of the terminal profiles and their contained synaptic vesicles showed the innervation to have probable pain afferent, cholinergic, adrenergic and perhaps peptidergic components. The results of this study were compared with reports on pancreatic duct innervation in other species, mostly as parts of wider studies on pancreatic innervation.