A morphological and quantitative immunohistochemical study of the interstitial cells of Cajal in the normal equine intestinal tracts.

Reasons for performing study: The interstitial cells of Cajal (ICC) play a key role in the control of intestinal motility and have been implicated in several human gastrointestinal dysmotility syndromes, in equine grass sickness and in other intestinal disorders where a significant reduction in ICC density was observed. Objectives: To investigate the density of ICC in clinically normal horses, ICC c-Kit expression was evaluated by image analysis in order to obtain numerical data. Methods: Intestinal samples from the jejunum to small colon from 5 clinically normal horses were studied. Immunohistochemical labelling of ICC was performed using an anti-c-Kit antibody. Density of ICC was calculated using image analysis software. Results: In the equine intestinal tract 2 types of ICC were observed: intramuscular ICC, i.e. ICC in the internal circular layer (IC-CM) and ICC in the external longitudinal layer (IC-LM), and myenteric ICC (IC-MY). The density of IC-MY was found to be higher throughout the small intestine. IC-MY density in the large intestine appeared to be greatest in the right ventral colon and in the small colon. IC-MY density in the ileocaecal junction showed an intermediate value compared to the small and large intestine. On the other hand, the density of IC-CM was found to be higher in the ileocaecal junction, whereas the caecum, left ventral colon and the left dorsal colon showed the lowest c-Kit immunoreactivity. The ileal tract and the ileocaecal junction showed an appreciable IC-LM density. Conclusions: Image analysis is a rapid and reproducible method to establish the density of ICC in the normal equine intestinal tract. Potential relevance: This study corroborates the findings of previous studies and provides a platform for further future pathological investigations of the equine intestine by supplying usable numerical data as comparative elements.