Ultrastructure of the developing myenteric plexus of chicken small intestine.

The present ultrastructural study established the main morphological events that occur during the myenteric plexus formation in the chicken duodenum from the 7th day of incubation (E7) up to hatching, with special attention to the appearance of different axon profiles and synaptic contacts. Transmission electron microscopy revealed that the compartmentalization of the enteric mesenchyma into outer and inner zones precedes the sequential morphological maturation of the crest derived cells during myenteric plexus formation. On E7, a slender neuropil was present in the migrating cell clusters, but all the crest derived cells were uniform. In the following stages, the neuronal and enteroglial cells were distinguishable. The first significant sign of neuronal maturation was the morphological heterogeneity in the vesicle population on E11. Progressive changes in the synaptogenesis were identified, and the axosomatic synapses were characteristic around hatching. On E18, a transient direct muscle-ganglion contact with the circular muscle layer was observed, in addition to the permanent ganglionar contact to the longitudinal layer of the muscularis externa.