THE MORPHOLOGY AND PROJECTIONS OF RETROGRADELY LABELED MYENTERIC NEURONS IN THE HUMAN INTESTINE

Background & Aims: Myenteric ganglia in the human gastrointestinal tra ct contain a mixture of many different types of nerve cells that canno t be distinguished by their location. The aim of this study was to cha racterize different functional types of cells by using retrograde labe ling in vitro to identify neurons according to their targets. Methods: The retrograde label 1,1'-didodecyl 3,3,3',3'-indocarbocyanine perchl orate (Dil) was applied to different target layers of human small or l arge intestine. After 3-5 days in organotypic culture, myenteric neuro ns projecting to the Dil application site were visualized and mapped u sing fluorescence microscopy. Results: Myenteric motor neurons project ing to the external muscle layer were typically unipolar cells with la mellar dendrites (Dogiel type I) and had short projections up to 16 mm long. In contrast, presumed interneurons with Dogiel type I morpholog y were shown to project up to 68 mm aborally or up to 38 mm orally. Mu ltipolar Dogiel type II neurons with smooth cell bodies were labeled m ost frequently from the submucous plexus. No myenteric neurons were la beled by Dil applied to the mucosa. Conclusions: Myenteric neurons lab eled from each target had characteristic size, morphology, polarity, a nd length of projections, indicating that there is a high degree of or ganization in the human enteric nervous system.