SEQUENTIAL PATTERN OF NERVE-MUSCLE CONTACTS IN THE SMALL-INTESTINE OFDEVELOPING HUMAN FETUS - AN ULTRASTRUCTURAL AND IMMUNOHISTOCHEMICAL STUDY

The developing enteric nervous system of the human fetus has been stud ied by means of electron microscopy and neuron-specific enolase immuno cytochemistry between the 10th and 26th week of gestation, with specia l reference to the development of nerve-muscle contacts. In the 10th w eek of gestation the circular muscle layer is formed, followed by the appearance of a primitive myenteric plexus, and the longitudinal smoot h muscle layer in the 12th week of gestation. Adherens-type junctions between the smooth muscle cells and the elements of the myenteric plex us, interdigitation of nerve and muscle processes, and also contacts w ithout any morphological specialization are frequent until the 18th we ek, when the mechanical points of attachment are relocated from the ci rcular to the longitudinal muscle layer. By this time the developing m yenteric plexus becomes ensheathed by non-neuronal cells, disrupting t he direct contacts between smooth muscle cells and the primary strands of the myenteric plexus. The possible functional significance of thes e changing nerve-muscle contacts is discussed in the present paper.