Immunocytochemistry of the interstitial cells of Cajal in the rat intestine.

There is experimental evidence suggesting that the interstitial cells of Cajal are essential for rhythmic slow waves of the smooth muscle layers of the mammalian small intestine. Different investigators have identified them variously as modified neurons, glia, fibroblasts or modified smooth muscle cells. Since histological categorization bears on understanding their function, we have examined the immunoreactivity of the myenteric plexus of the rat small intestine, paying special attention to the cell type identified as Thuneberg's Type I-ICC. Polyclonal and monoclonal antisera directed against 4 intermediate filament proteins: neurofilament protein, glial fibrillary acidic protein, vimentin and desmin were used. In addition, antisera directed against neuron-specific enolase, substance P and vasoactive intestinal polypeptide were also tested for reactivity. Type I-ICCs were immunonegative to all the antisera directed against intermediate filament proteins and neuropeptides. However, some Type I-ICCs were immunopositive to antisera against neuron-specific enolase. On the basis of these results and the distribution of immunoreactivities to these kinds of antisera in other tissues, we suggest that Type I-ICCs are distinct from typical myenteric neurons, from glia, from fibroblasts and from smooth muscle fibers. Staining with antiserum against neuron-specific enolase suggests a relation to some type of neuron.