Differentiation of enteric plexuses and interstitial cells of Cajal in the rat gut during pre- and postnatal life.

The stomach, small and large intestine of fetuses at term, of unfed newborns, of suckling, weaning and of adult rats were studied by a combined light (LM) and electron microscope (EM) examination. Neuron-specific enolase was used as a neuronal marker under LM. Zinc-iodide-osmium (ZIO) impregnation was used for a selective staining of neurons and interstitial cells of Cajal under both LM and EM. A routine EM procedure made it possible to identify the nerve elements and ICC and to evaluate their degree of differentiation. The differentiation of enteric plexuses and ICC was poor at birth and was accomplished during the weaning period. The myenteric plexus differentiation preceded the submucous plexus differentiation; in particular, under both LM and EM myenteric neurons were already recognizable in the fetus, while the submucous neurons by day 0 under EM and by day 7 under LM. The ICC were poorly differentiated at birth and acquired the adult morphology during the suckling period. Nerve endings contacting ICC were differentiated before ICC differentiation. The ZIO uptake by both nerve elements and ICC correlated with the establishment of their differentiated features. In conclusion, the present findings confirmed that differentiation of ICC and enteric plexuses is microenvironment dependent, since their differentiative steps are interrelated and correlated with diet changes. ZIO impregnation under EM enabled a distinction to be made between a "morphological' and a "functional' differentiation, and revealed that the former is achieved during the suckling period and the latter by the weaning period. It can be suggested that during the postnatal developmental stages ICC and neuronal functions might be different from those in adulthood.