Identification and Distribution of the Interstitial Cells of Cajal in the Abomasum of Goats

The interstitial cells of Cajal (ICCs) are regarded as pacemakers and are involved in neurotransmission in the gastrointestinal tract (GIT) of animals. However, limited information is available about the existence of ICCs within the GIT of ruminants. In this study, we investigated the ultrastructural characteristics and distribution of ICCs in goat abomasum using transmission electron microscopy and c-kit immunohistochemistry. Two different kinds of c-kit immunoreactive cells were observed in the abomasum. The first was identified as ICCs, which appeared to be multipolar or bipolar in shape, with some processes. These c-kit immunoreactive cells were deposited in the submucosal layer, myenteric plexus between the circular and longitudinal muscle layers, and within the longitudinal and circular muscle layers of the abomasum. The second type of cell was round in shape and was identified as mast cells, which were located in the submucosal layer as well as in the lamina propria. Ultrastructurally, ICCs were also observed as stellate or spindle-shaped cells, which were consistent in shape with our c-kit immunoreactive cells. In the cytoplasm of ICCs, numerous mitochondria, rough endoplasmic reticulum, and caveolae were detected. ICCs were located in the myenteric plexus between the longitudinal and circular muscle layers (ICC-MY), with the longitudinal and circular muscle layer was replaced as "intramuscular layers" (ICC-IM), and in the submucosal layer (ICC-SM). In addition, we found ICCs surrounding nerve fibers and smooth muscle cells, where they formed heterocellular junctions in the form of close membrane associations or gap junctions and homocellular junctions among the processes of the ICCs. In the current study, we provide the first complete characterization of ICCs within the goat abomasum and propose that ICCs might have a key role in producing contractions in the ruminant stomach for proper absorption of nutrients.