The avian oesophageal motor function and its nervous control: some physiological, pharmacological and comparative aspects

Histogenesis of the Oesophagus of Guinea Fowl (Numida meleagris) at Prehatch and Posthatch

The histogenesis of the primordial oesophagus was studied to determine the period in which the tunics of the oesophagus developed and became functional in the helmeted guinea fowl (Numida meleagris). Eighteen embryos and nine keets were studied at prehatch and posthatch, respectively. Simple columnar epithelium surrounded by mesenchymal cells was obvious at the 8th day of embryonic development. By the 19th day of embryonic development, the four tunics, tunica mucosa, submucosa, tunica muscularis, and tunica adventitia/serosa, were beginning to differentiate from the mesenchymal cells and also the primordial oesophageal glands appeared as clusters of cells that invaginate from the epithelium. By the 27th day, the tunics were clearly differentiated and the primordial glands were fully developed as evident with positive reaction to Periodic Acid Schiff (PAS). The tunics of the muscularis were not well developed till at posthatch. This study therefore concludes that the primordial oesophagus is active at the late incubation due to mucin secretion by mucous glands but fully functional at posthatch since the tunica muscularis is completely developed at posthatch.

Neuro-muscular junctions of longitudinal and circular muscle fibers of the guinea-pig esophagus and their relation to myenteric plexus

The structure of the neuromuscular junctions (NMJs) and their relation to the myenteric plexus were studied by zinc iodide-osmic acid (ZIO) staining and by scanning electron microscopy in the guinea-pig esophagus. The esophageal muscle coat consisted of the inner circular and outer longitudinal striated muscle fibers. The myenteric plexus was located between the two muscle layers along its whole length and was characterized by a loose and irregular network. It was demonstrated that unmyelinated nerve fibers form NMJs with the muscle fibers of both layers. The NMJs in the longitudinal muscle can be classified as 'plate' type, whereas those of the circular muscle resemble the 'grape' type. The different NMJs in the two muscle layers probably correspond to different contractile properties. The whole-mount preparations with ZIO staining also demonstrated that some NMJs receive minute branches from the myenteric plexus. Therefore, it is likely that the myenteric plexus is involved in the control of striated muscles of the guinea-pig esophagus.

Distribution of neurotensin-immunoreactive neurons in the digestive tract of the chicken

The origin of the neurotensin-containing nerve fibers in the digestive tract of the chicken has been investigated with the use of colchicine and immunohistochemistry. Neurotensin-immunoreactive nerve fibers were found in the smooth muscle layers from the esophagus to the duodenum. Their density of distribution was very high in the esophagus and crop (maximum mean value: 1315/mm2 of sectional area in the lamina muscularis mucosae of the crop) and decreased progressively to the duodenum. Neurotensin-immunoreactive neuronal cell bodies were observed after colchicine treatment in the submucosal plexuses of the esophagus and crop and in the myenteric plexuses of the esophagus, crop, proventriculus and gizzard, and they extended varicose fibers. The number of neurotensin-immunoreactive cell bodies was high in the myenteric plexus of the gizzard (28.3 +/- 2.7/ganglion) but low in the plexuses of the esophagus, crop and proventriculus. Seven days after cutting the glossopharyngeal nerve and vagus nerve unilaterally, the number and extent of neurotensin-immunostained structures in the smooth muscle layers from the esophagus to the gizzard did not show any significant difference between operated and unoperated sides. These results indicate that in the chicken the great majority of neurotensin-immunoreactive enteric fibers originate in the intramural plexuses of the upper digestive wall and are mainly distributed to smooth muscle cells.