Ultrastructure of the perivascular nerve plexuses of the rat pancreas.

The fine structure of the arteriolar perivascular and capillary nerve plexuses of the pancreas was studied in the rat. In perfusion-fixed control specimens, occasional profiles which contained accumulations of large dense-cored vesicles and numerous profiles which contained mainly small vesicles were seen in sections of the nerves. Counts of degenerating axons in specimens from rats treated with 6-hydroxydopamine and of profiles in which the small vesicles contained dense cores in specimens fixed by immersion after incubation in buffer indicated that the arteriolar perivascular plexus contains much larger numbers of adrenergic axons than the plexus associated with the capillaries. The presence in specimens fixed by immersion after incubation in buffer containing 5-hydroxydopamine of a considerable increase in the percentage of profiles in which the small vesicles contained dense material indicated that the plexuses contain a second type of axon capable of taking up 5-hydroxydopamine. Profiles in which all of the small vesicles remained clear after incubation in 5-hydroxydopamine were regarded as sections through cholinergic axonal terminals. Such profiles were most numerous in the capillary plexus.