Regional Distribution and Mucosal Localization of Some Gastrointestinal Endocrine Cells in Quail ( Coturnix coturnix )

Abstract

The purpose of this study was to investigate the regional distribution and mucosal localization of serotonin-containing endocrine cells in the pancreas and small intestine (duodenum, jejunum, and ileum) of quails. Endocrine cells in the digestive tract were identified using the immunohistochemical peroxidase–antiperoxidase (PAP) method. Most serotonin-secreting endocrine cells were observed in the basal regions of the glands, exhibiting oval or spindle-shaped morphology. Two main types of endocrine cells were identified based on their contact with the intestinal lumen: open-type cells, which extend to the lumen and can sense luminal contents, and closed-type cells, which do not reach the lumen and are entirely embedded within the epithelium or glandular tissue. In the duodenal glands, some closed-type immunoreactive cells were detected, while open-type immunoreactive cells were mainly found in the lamina propria epithelium. Endocrine cells with luminal contact were present in the epithelial layer of the small intestine, whereas cells within the glands lacked such contact. Serotonin immunopositive reactions were most abundant in the duodenum, followed by a gradual decrease in the jejunum and ileum. In the pancreas, serotonin-positive cells were also detected, but at a lower density compared to the intestinal segments.. In the pancreas, serotonin-positive cells were more concentrated in the endocrine regions compared to the exocrine tissue.