APPEARANCE AND SOME NEUROCHEMICAL FEATURES OF NITRERGIC NEURONS IN THE DEVELOPING QUAIL DIGESTIVE-TRACT

Using immunocytochemistry, NADPH-diaphorase (NADPHd) histochemistry an d electron microscopy, the appearance of nitrergic enteric neurons in different digestive tract regions of the embryonic, neonatal and adult quail was studied in whole mounts and sections. NADPHd was first expr essed by embryonic day 4-5 in two distinct locations, namely the mesen chyme of the gizzard primordium and at the caeco-colonic junction. At embryonic day 6, nitrergic neurons had already begun to form a myenter ic nerve network in the wall of the proventriculus, gizzard and proxim al part of the large intestine and by embryonic day 9, a myenteric net work was visualized along the entire digestive tract of the quail. At the level of the stomach, this network was confined to the area covere d by the intermediate muscles. By embryonic day 12-13, the NADPHd-posi tive myenteric neurons in the wall of the distal parts of the blind-en ding paired caeca also became organized into ganglia. From this develo pmental stage on, a submucous nitrergic nerve network, sandwiched betw een the lamina muscularis mucosae and the luminal side of the outer mu scle layer, became prominent in the proventriculus and intestinal wall s. In the adult quail, only a minority of the NADPHd-positive neurons stained for vasoactive intestinal polypeptide (VIP) along the intestin e. VIP-immunoreactive (IR) cell bodies were frequent in the myenteric plexus but not in the submucous plexus, whereas there were considerabl e numbers of NADPHd-positive neurons in both these plexuses. Nitrergic fibres were also observed in the outer muscle layer, but were almost absent from the lamina muscularis mucosa and lamina propria, in contra st to the dense VIP-ergic innervation encircling the bases of the inte stinal crypts.