Prehatching development of the adrenal gland in Japanese quail (Coturnix japonica): Histological, immunohistochemical, and electron microscopic studies.

The adrenal glands play a key role in maintaining the physiological balance of birds and helping them to survive environmental changes. The objective of the present work was to give a detailed investigation of the histological, ultrastructural, and immunohistochemical findings of the adrenal gland in Japanese quail during the prehatching phase. The current study was performed on 45 healthy Japanese quail embryos at different prehatching periods. Our results showed the primordium of the quail's adrenocortical tissue appeared at 3 days of incubation as a thickening of the splanchnic mesoderm. The prospective chromaffin cells appeared at 5 days as clusters of cells migrated from the neural crest cells along the dorsal aorta toward the interrenal tissue. TH immunoreactivity was observed in the neural crest cells during their migration toward the adrenal primordium. Furthermore, these TH immunopositive cells were intermingled with the developing interrenal cell cords that developed from the coelomic epithelium. NSE immunostaining was detected within the cytoplasm of interrenal cells, chromaffin cells, and ganglion cells. Sox10 is expressed in chromaffin and ganglion cells with different staining intensities. On the 13th day of prehatching, both interrenal and chromaffin cells were β-catenin immunonegative, but on the 17th day, both cells were immunopositively. Our findings show that during prenatal life, the adrenal gland undergoes significant morphological changes. Together, the present data suggest that studying the prenatal development of the adrenal gland in birds is important for advancing our understanding of this critical organ and its functions. RESEARCH HIGHLIGHTS: The present study aimed to give a detailed study of the histological, ultrastructural, and immunohistochemical investigations of the adrenal gland in Japanese quail during the prehatching period. The interrenal primordium was observed on the third embryonic day, on the fifth ED the primordium of the chromaffin tissue appeared as row of migrating neural crest cell. At the ultrastructural level, the interrenal cells take steroid-secreting cells characters, they have varying amounts of lipid droplets and abundant mitochondria at 15th ED contained moderate number of lysosomes and mitochondria.