THE EQUINE ENTERIC NERVOUS-SYSTEM - NEURON CHARACTERIZATION AND DISTRIBUTION IN ADULTS AND JUVENILES

A study of myenteric and submucosal plexuses was undertaken in tile je junum and ileum of horses and ponies in which no clinical or pathologi cal evidence of intestinal abnormality was apparent. Complete transver se sections of the intestine, stained by a modified haematoxylin and e osin method, were examined using up to 20 sequential sections per anim al. Information was gathered from adult, juvenile and fetal equidae. I n adults, the longitudinal muscle layers were thinner than the circula r muscle layers and the ileum had thicker layers compared to the jejun um. In adults, the submucosal plexus had more neurons per section than the myenteric plexus by mean ratios of 1:3 in the jejunum and 1:1.9 i n the ileum. In juveniles, the ratios were respectively 1:1.8 and 1:1. 5 and in the fetus 1:2.5 and 1:1.3. The three-dimensional distribution of neurons in both plexuses varied from animal to animal and no consi stent pattern was observed. Groups of neurons contained between one an d 42 cells per section examined and their length in a cranio-caudal di rection varied from 10 to over 100 mu m. There were few statistical di fferences observed between the cranial, middle and caudal portions of either the jejunum or the ileum when neuron groups or neuron numbers p er section were examined in 10 adult animals.