An ultrastructural study of the innervation of the guinea pig pancreas

The present ultrastructural study investigated the innervation of the guinea pig pancreas, with special emphasis on the pancreatic ganglia and the sympathetic and parasympathetic boutons/terminals. The pancreatic ganglion cells, ensheathed in a thin layer of connective tissue, showed typical features of autonomic neurons. Each contained a prominent eccentric round nucleus with 1 to 5 nucleoli and a copious cytoplasm with many organelles. Synapses were scattered in the ganglion and were of the axodendritic type. Axosomatic synapses were not encountered even after examination of semiserial sections in one of the tissue blocks. Desmosome-like junctions (puncta adhaerentia) were found between somata of the ganglion cells, and between their dendrites, and also between somata of the ganglion cells and satellite cells. The sympathetic nerves supplying the pancreas were demonstrated by the 5-hydroxydopamine loading method. Axon terminals loaded with the false transmitter were filled with intensely stained small dense-cored vesicles. These were present in close contact with acinar cells, islet cells as well as smooth muscle cells of arterioles. No 5-hydroxydopamine loaded axon terminals or ganglion cells were observed within the ganglia. The preganglionic parasympathetic nerve fibres supplying the pancreas traveling with the vagus nerve were studied by sectioning the left vagus nerve at mid-cervical level. Three to 7 days after left cervical vagotomy, degenerating axon terminals containing small spherical agranular vesicles, together with degenerating dendrites and neuronal somata showing electron dense cytoplasm were encountered within the pancreatic ganglion. The satellite cells were hypertrophied, showing a pale cytoplasm in which were embedded degenerating axon terminals and dendrites. In conclusion, the present study described the normal structure of pancreatic ganglia, provided ultrastructural evidence of the presence of sympathetic and parasympathetic fibres in the pancreas of the guinea pig, and reported postsynaptic changes in the dendrites after mid-cervical sectioning of the left vagus nerve.