Distribution of NADPH-diaphorase activity in the embryonic chicken gut.

The appearance and distribution of NADPH-diaphorase activity in neuronal cells and fibres in different regions of the embryonic chicken gut was studied histochemically using whole mount preparations and cryostat sections. NADPH-diaphorase activity was detected in neuronal cell bodies as early as embryonic day 5.5 (E5.5 - the earliest age examined), mainly in the foregut, although some positive cells were also seen in the hindgut at this stage. NADPH-diaphorase-positive fibres were first detected in the developing nerve tracts which connect the ganglia at E5.5. The complexity of the network was maximal in the proventriculus-gizzard junction. By E9.5, NADPH-diaphorase-positive fibres were found in the circular muscle layer. NADPH-diaphorase-positive submucosal neurons were first detected at E11.5. The density of innervation was maximal at E15.5 and declined later development. The expression of neuronal NADPH-diaphorase activity progressed in a craniocaudal direction and followed a developmental pattern similar to that previously described for several neuropeptides in the avian gut.