Fluorescence histochemical observations on the intrinsic adrenergic innervation and monoamine-containing cells of the feline pancreas,with special reference to the terminal main pancreatic duct of wirsung

Summary Intrinsic adrenergic innervation of the pancreas of the cat was studied using two fluorescence histochemical methods. Special emphasis was focused on the monoaminergic regulation of the mechanisms responsible for dynamically active suction-pressure pumping at the choledocho-pancreatico-duodenal junction, consisting of a labyrinthine reservoir chamber surrounded by a contractile mantle of smooth muscle, described recently (Kyösola, 1976). In that junction area, a rich distribution of single varicose fluorescing nerve fibers and small nerve fascicles, both free (i.e., unrelated to the blood vessels) and forming typical perivascular nerve plexuses, as well as large ganglia of nonfluorescing nerve cells surrounded by fluorescing baskets of varicose nerves were observed in the connective, fat, and pancreatic tissues, as well as between the smooth muscle bundles of the contractile smooth muscle mantle surrounding the reservoir chamber and its minor compartments. The epithelial lining of the labyrinthine duct system contained some solitary brightly yellow fluorescing enterochromaffin cells. In addition, two other categories of fluorescing cells were observed: (1) Small rounded cells with a relatively large rounded nucleus, and exhibiting a clearly bluish, usually granular, fluorescence varying from weak to intense; (2) Larger cells exhibiting quite a weak, clearly greenish to greenish-yellow fluorescence, either gathered in homogeneous clusters or mingled with the cells of the former type into heterogeneous cells clusters. These two cell types were clearly distinguishable from each other, but intermediate cell types were also seen. Thus, a continuous scale of fluorescing cells was observed, the color of the fluorescence varying from clearly bluish to greenish-yellow, the intensity of the fluorescence varying from intense to weak (respectively, in general), and the size ranging from small to large (respectively). These cells, probably heterotopic alpha cells of the islets of Langerhans, were frequently in quite close proximity to the smooth muscle surrounding the contractile labyrinthine system or its minor compartments. On the other hand, they were frequently in close proximity to quite large thin-walled sinusoid-type blood vessels. At least some of these fluorescing cells were surrounded by fluorescing varicose nerves, suggesting the existence of a neuroendocrine link. Scattered among these fluorescing cells, and also gathered into small clusters, were nonfluorescing nerve cells interconnected with fluorescing varicose nerves. The fluorescing cells of the endocrine pancreas, similarly, could be arbitrarily classified into two main categories, although intermediate cell types were observed as well: (1) Small rounded cells with a large, ovoid to rounded, centrally placed nucleus, and exhibiting a moderate to intense granular cytoplasmic fluorescence. The color of the fluorescence varied from yellow-green to blue-green, and there were considerable differences also in the fluorescence intensity. (2) Mixed irregularly with the type (1) cells were cells with more or less the same cytologic characteristics, but slightly larger, and exhibiting a rather homogeneous weak yellow fluorescence. Sometimes the fluorescence intensity was so weak that it was hardly discernible. These cells were packed densely and irregularly with the type (1) cells within the clusters, and no clear-cut spatial organization between these two cell types was observed. In the wall of the main pancreatic duct of Wirsung, both free and perivascular fluorescing nerves were seen within the different layers, including the (distally incomplete) smooth muscle layer. The epithelial lining of the duct contained enterochromaffin cells, sometimes located so deeply in the epithelial invaginations that they were in close proximity to the smooth muscle. The distribution of fluorescing nerves in the exocrine pancreas was sparse. Typical enterochromaffin cells exhibiting a bright yellow granular cytoplasmic fluorescence were scattered either solitarily or in small groups in the epithelial lining of the acini and of the small excretory ducts. Blue-green fluorescing varicose adrenergic axons were some-times seen to connect enterochromaffin cells or groups of them located in different acini. Scattered within the parenchyme of the exocrine pancreas were clusters of nonfluorescing nerve cells surrounded by typical baskets of fluorescing varicose terminal ramifications of adrenergic axons. In the endocrine pancreas, similarly, only a relatively sparse distribution of fluorescing nerves was observed among the islet cells and surrounding clusters of them. However, groups of islet cells were observed to be interconnected by fluorescing varicose nerves coursing through or near nonfluorescing ganglia, suggesting an integrative neural connection between pancreatic islets and nonadrenergic ganglia via adrenergic nerves.