Identification of enteric motor neurones which innervate the circular muscle of the guinea pig small intestine.

Retrograde transport of the carbocyanine dye DiI from the deep muscular plexus of guinea pig small intestine was carried out in organotypic culture to identify circular muscle motor neurones. Seventy-four % of DiI labelled neurones were located within 4 rows of myenteric ganglia oral or anal to the application site. Some motor neurones had axons extending up to 37 rows of myenteric ganglia in the anal direction, or long axons travelling up to 18 rows of ganglia in the oral direction. Ninety four percent of the filled cells had Dogiel type I soma morphology; of these, neurones oral to the application site consistently had lamellar dendrites and were readily distinguishable from those located anally which had short filamentous dendrites. The methods described in this study make it possible to distinguish circular muscle motor neurones from other cell types in the myenteric plexus for the first time.