Immunocytochemical localization of motilin-containing cells in the rabbit gastrointestinal tract

Motilin-immunopositive cells (Mo cells) are known to be present in the upper small intestine of various species, including man. However, whether Mo cells are present in the rabbit gastrointestinal tract remained to be elucidated. Therefore, this study was designed to investigate the distribution of Mo cells in the rabbit gastrointestinal tract by the avidin-biotin-peroxidase complex method using a new anti-motilin serum (CPV2) raised in chickens. The results of an enzyme-linked immunosorbent assay suggested that this antiserum recognized the C-terminal region of the motilin molecule. Motilin-immunopositive cells were found in the epithelia of the crypts and villi throughout the rabbit gastrointestinal tract from the gastric antrum to the distal colon, but no immunostaining occurred in the gastric body. Morphometric analysis revealed that Mo cells were localized preferentially in the upper small intestine, as reported for other species, and the cell densities (cells/mm 2, mean ± SE) were: gastric antrum (0.41 ± 0.16), duodenum (8.2 ± 0.8), jejunum (1.9 ± 0.5), ileum (0.62 ± 0.14), cecum (0.19 ± 0.05), proximal colon (0.13 ± 0.03), and distal colon (0.39 ± 0.18). Our results demonstrated conclusively that Mo cells exist in the rabbit gastrointestinal tract and showed for the first time their regional distribution. Furthermore, our new chicken antiserum would appear to be a useful tool for the determination of plasma motilin concentrations by radioimmunoassay and for the immunoneutralization of endogenous motilin in the rabbit.