MORPHOLOGIC AND QUANTITATIVE-EVALUATION OF THE MYENTERIC PLEXUSES ANDNEURONS IN THE LARGE COLON OF HORSES

Objective-To determine the number of myenteric piexuses and neurons in the large colon of clinically normal horses and whether the number wa s decreased in the large colon of horses with colon disease. Design-Pr ospective study. Sample Population-Colon samples from 15 clinically no rmal horses and 31 horses with colon disease. Procedure-Samples were o btained, fixed, and stained with H&E. The number of myenteric plexuses and neurons and longitudinal muscle thickness were determined in each segment of colon for clinically normal horses. Counts for segments we re compared with each other and with counts in the same segment from h orses with colon disease. Results-Myenteric plexus and neuron densitie s and longitudinal muscle thickness in clinically normal horses were s ignificantly greater in the pelvic flexure and left dorsal and transve rse colons. Horses with chronic obstruction (> 24 hours' duration) or with previous obstruction had significantly lower neuron density in th e pelvic flexure. Myenteric plexus density in horses with strangulatin g large colon torsion/volvulus was significantly less in the right ven tral, right dorsal, and transverse colons, and neuron density in these horses was significantly less in all segments of colon, except the le ft ventral colon. Horses with colon strangulation that survived had si gnificantly greater neuron density than horses with colon strangulatio n that died. Enteroglial cell numbers were increased in myenteric plex uses of horses with acute and chronic obstruction. Clinical Implicatio ns-Myenteric plexus and neuron densities can be estimated by evaluatin g linear counts of H&E-stained colon samples. Enteroglial cells may in crease in number in response to myenteric plexus inflammation, which m ay affect bowel function.