Morphology of horseradish peroxidase (HRP)-injected glial cells in the myenteric plexus of the guinea-pig.

Glial cells of the myenteric plexus from guinea pig small intestine were intracellularly filled with horseradish peroxidase (HRP), and histochemically stained. Camera lucida-like drawings of twenty cells were morphologically and morphometrically analyzed. The cells have very small ellipsoid somata (8.5 +/- 0.7 microns equivalent diameter, i.e., about 330 micron3 volume), and send up to 20 thin and short processes (less than 26 to about 110 microns in length). The morphology of the cells appears to depend on their location within the plexus. Glial cells located within the ganglia are similar to CNS protoplasmic astrocytes; they are star-shaped, and their very short processes are irregularly branched. In contrast, glial cells within the interganglionic fiber tracts resemble CNS fibrous astrocytes. They extend longer processes that are parallel to the fiber tracts, and show less tendency to branch. We propose that the morphology of enteric glia is determined by the structure of the microenvironment. Both cell types form several flat endfeet at a basal lamina either surrounding blood vessels or at the ganglionic border. Furthermore, the occurrence of "holes" in the glial cell processes suggests that particular neuronal cell processes may be enwrapped in a specific manner. Fractal analysis of camera lucida-like drawings of the cells showed that the cells have a highly complex surface structure, comparable to that of protoplasmic astrocytes in the brain. These tiny cells may possess a membrane surface area of approximately 2000 micron2, almost 90% of which are contributed by the cell processes.(ABSTRACT TRUNCATED AT 250 WORDS)