Neuroendocrine complexes in the gut of the snail Helix aspersa

To our knowledge, this paper presents the first description of neuroendocrine complexes in invertebrates. Neuroendocrine complexes have been identified in the lamina propria of the snail gut by light microscopy using Giemsa‐stained, deplasticized sections and by electron microscopy. Silver impregnations and immunocytochemical tests for 15 different peptide hormones yielded negative results. The ultrastructure of the snail neuroendocrine complexes is basically similar to that of neuroendocrine complexes in vertebrates. They are composed of endocrine cells and associated unmyelinated nerve processes, both being surrounded by a discontinuous glial sheath and a basement membrane. The endocrine cells contain small (139 nm), round, dense‐cored granules. The presence of complex multivesicular bodies and autophagic vesicles in the endocrine cells suggests that excess granules may be eliminated by a process of crinophagy. Some of the neuroendocrine complexes were seen to form connections with the epithelium by means of an endocrine cell cytoplasmic process, a fact that strongly suggests a functional integration between the intestinal epithelium and the enteric nervous system.