Ultrastructural identification of interstitial cells of Cajal in hen oviduct

The interstitial cells of Cajal (ICC) are widely believed to be neuroeffector cells of smooth muscle activity in all tubular organs, including the oviduct. The avian oviduct involves the secretion, sheathing, and transportation of a large-sized egg, but there is no information available on ICC in this special organ. We have demonstrated the presence of ICC in different segments throughout the oviduct in the laying hen and provided details on their ultrastructure by transmission electron microscopy technique, for the first time. The observed ICC appeared bipolar and multipolar cells of different shapes, with varying nuclear morphologies, a thin rim of electron-dense cytoplasm, and an infrequent basal lamina. They showed moniliform primary processes with one or 2 secondary or terminal processes. We found ICC near smooth muscle cells, nerve fibers, and the epithelia, where they make specialized contacts in the form of close membrane associations or gap-like junctions and peg-and-socket-like junctions. Intricate labyrinthine-type networking contacts were also present in ICC processes. Moreover, we report for the first time, that ICC in avian oviduct make interdigitating contacts with the epithelium. Cytoplasmic organelles identified in ICC include numerous well-developed mitochondria, abundant rough endoplasmic reticulum, and dispersed intermediate filaments. Many caveolae and vesicles were also present. Golgi bodies and centrioles were rare. Fibroblasts, on the other hand, were distinct cells with larger cytoplasmic area, more rough endoplasmic reticulum, and less mitochondrial content. No basal lamina, intermediate filaments, or caveolae were present in fibroblasts. Their processes were shorter and showed no contacts with smooth muscle cells or nerves. We conclude that these ICC might also have a key role in the regulatory mechanisms of motility and transportation in the hen oviduct, as already proved in mammalian oviduct. Such role of ICC might also be responsible for the function of the muscular infundibulum, where the fertilization takes place, and that moves to surround the released ovum, failure of which results in the internal laying.