An immunohistochemical study of the ontogeny of the neuroendocrine system in the chicken oesophagus.

The ontogenesis and distribution of serotonin-, chromogranin A-, chromogranin B-, galanin-, neurotensin-, bombesin- and neuropeptide Y-immunoreactive elements were studied in the chicken oesophagus during pre- and post-hatching life. Unlike positive nerve elements, that were present in pre- and post-hatching life, positive endocrine cells were observed only during embryonic life in the oesophageal epithelium. The first endocrine cells, immunoreactive for serotonin and chromogranins, appeared on day 12, in the cervical and thoracic portions of the oesophagus. At the same age, but only in its distal portion, a few bombesin- and neurotensin-immunoreactive cells also appeared. The number of the endocrine cells progressively increased, reaching a maximum on day 15. They then decreased, with a cranio-caudal progression, until they disappeared a few days after hatching. Almost all the serotonin-immunoreactive cells but only a subpopulation of bombesin- and neurotensin-immunoreactive cells colocalized chromogranins. About half of this subpopulation also colocalized serotonin. All these cells reacted positively with Grimelius argyrophile stain. The mucosa of the crop never contained positive endocrine cells. Positive nervous elements appeared first in the wall of the terminal oesophagus and only one or two days later in the proximal oesophagus including the crop. Nervous elements immunoreactive for galanin first appeared from days 6 to 7, for neurotensin from days 7 to 8, for neuropeptide Y from 13 to 15 and for bombesin from 15 to 18. At day 15 galanin-immunoreactive ganglionic cells and fibres occupied both the myenteric and submucous plexus and galanin-positive nerve fibres could be seen throughout the oesophageal wall from the adventitia to a thin subepithelial network. Neurotensin- and neuropeptide Y-immunopositive ganglionic cells and fibres, by contrast, invariably occupied the muscular and submucous layers. Scattered bombesin-immunoreactive ganglionic cells were observed only in the myenteric plexus. The number of positive nerve elements progressively increased until some weeks after birth. Density and intensity were always much higher for galanin and neurotensin than for neuropeptide Y and bombesin.