An electron microscope study on a neuro-endocrine complex in the proventricular mucosa of the finch, Uroloncha striata var domestica.

An endocrine complex consisting of endocrine cells, nerve endings, unmyelinated nerve fibers and Schwann cells is found near blood capillaries in the lamina propria of the proventricular mucosa of the finch.At least two types of endocrine cells (type I and II) are present mainly in the lamina propria mucosae where they form a neuro-endocrine complex, but some cells of both types are also seen in the basal part of the epithelial layer like mammalian basal-granulated cells. The type I cell has large round secretory granules of uniform ultrastructure. The type II cell contains small granules whose content is fairly diverse in density and is surrounded by either closely fitted or a vacuolated limiting membrane.The nervous elements and endocrine cells of the complex are enclosed by a common basal lamina. Unmyelinated nerve fibers are encircled by either Schwann cell or endocrine cell cytoplasm. Most nerve endings, which have small clear vesicles and large granular ones, are thought to be cholinergic. Some of these make synaptic contact with both types of endocrine cells. Probable adrenergic endings containing small cored vesicles as well as large granular ones are very few in number and come into contact with the type I endocrine cells. These findings indicate a nervous regulation of the endocrine function in the finch proventricular mucosa.The peculiar, subepithelial position and the intimate relation to nervous elements of the finch proventricular endocrine cells are discussed in comparison with the pancreatic islet cells.