The three-dimensional structure of myenteric neurons in the guinea-pig ileum

Myenteric neurons of the guinea-pig ileum were intracellularly filled with the fluorescent dye Lucifer Yellow, optically sectioned with a confocal microscope and volume reconstructed to recreate 3-D images of the cells. The resulting images provide information not evident from regular microscopy. The somata varied in cross-section from flat-oval to nearly circular, and their surface membranes were marked by invaginations and protrusions significantly increasing the surface area of the somatic membrane. The neurons could be divided into four morphological classes: Dogiel type I, Dogiel type II, filamentous, and intermediate. There was no clear correlation between cell class and the shape of the soma in cross-section. The dendritic processes of all the neurons studied extended in an orad-caudad or circumferential direction of the bowel wall. When the filled neurons were viewed edge-on, the spatial arrangement of the processes was confined to a plane that had a thickness less than the thickness of the parent soma. The broad, short dendrites of Dogiel type I neurons were oval or nearly circular in cross-section. Directly measured quantitative data were obtained for the volume and surface area of the somata and visible processes. The structural details reported herein are likely to have important implications regarding the functional properties of individual enteric ganglion neurons and circuits of enteric ganglion neurons.