Research Paper: Histological and Histochemical Study of Esophagus in Pheasant (Phasianus Colchicus) Embryo

Introduction: The morphogenic and histogenetic events of an organ and their time sequencing are basic required information to study factors involved in cells differentiation and evaluating the influence of different agents during the critical period of organ formation. The birds are noted as models in experimental embryologic studies, more than other animals. The present study described the morphogenetic events of pheasant (as a native bird of Iran) esophagus, as a unique investigation.  Methods: We analyzed the pheasant embryos from fifth-24th days of incubation period. After meeting the routine methods of histology laboratory, the slides were stained with Hematoxylin-Eosin, Periodic Acid-Schiff, Alcian Blue, and Van Gieson staining methods. Then, the formation of four layers of primordial esophagus, its epithelial cell differentiation, the separation of lamina propria and submucosa, time of glands formation, their secretion activities and the shape of lumen of gland were studied by a light microscope.  Results: The data of this study indicated that the most esophageal developmental events of the pheasant occur in the first 2-thirds of the incubation period. The esophageal primordium was noted for the first time on the fifth day of incubation period. The mesenchymal boundary of the esophagus was distinguishable during seventh to eighth days of incubation period. They differentiated the lamina propria and muscular layers during the next 10 days. The epithelial layer of esophagus was gradually differentiated from pseudostratified columnar epithelium (ninth day) into the 2 layered cuboidal (9-10), simple cuboidal (10-12), and the stratified squamous (13th day onward). The esophageal glands were the only structures that began to form in the second half of the incubation period on the 15th day and completed their development on the 21th day. In the present work, the most developmental events were observed in the thoracic esophagus earlier than cervical region. Conclusion: The comparison of the obtained data with other studied birds shows a general pattern of the esophagus formation among them. However, some differences can be detected in the developmental details and in the time sequencing of the layers. Some of these variations can be related to the differences in the duration of the incubation period among different species.