A Comparative Study on the Distribution Pattern of Endocrine Cells in the Gastrointestinal Tract of Two Small Alpine Mammals, Plateau Zokor (Eospalax baileyi) and Plateau Pika (Ochotona curzoniae)

SIMPLE SUMMARY: The gastrointestinal tract (GIT) is the largest and most complex endocrine organ; there are numerous endocrine cells in the mucosal layer of gastrointestinal tissue, which can secrete a variety of gastrointestinal hormones that regulate gastrointestinal digestion and absorption. The small alpine mammals, plateau zokor (Eospalax baileyi) and plateau pika (Ochotona curzoniae), live in the unique ecotope with cold, hypoxic environments and short plant-growing seasons, resulting in their differential adaptive digestive strategies for foods. In this study, we compared the distribution pattern of argyrophilic cells and the expression of 5-HT cells, Gas cells, and Glu cells in the GIT of the plateau zokor and plateau pika by using histochemical and immunohistochemical methods. Our results showed that the distribution pattern of endocrine cells in the GIT of plateau zokor and plateau pika not only have specific interspecies differences, but also exhibit parallel adaptation to the alpine environments. In addition, we conclude that the distribution pattern of endocrine cells in the GIT is consistent with the respective animals’ diets. ABSTRACT: Endocrine cells can secrete a variety of gastrointestinal hormones that regulate gastrointestinal digestion and absorption, which, in turn, play an important role in animal growth, metabolism, and acclimation. The small alpine mammals, plateau zokor (Eospalax baileyi) and plateau pika (Ochotona curzoniae), live in a unique ecotope with cold, hypoxic environments and short plant-growing seasons, resulting in differential adaptive digestive strategies for foods. Studying the distribution pattern of endocrine cells in the gastrointestinal tract (GIT) of these two animals can lead to a better understanding of the survival strategies of animals in an alpine environment. In this study, we used histochemical and immunohistochemical methods to compare the distribution pattern of argyrophilic cells and the expression of 5-HT cells, Gas cells, and Glu cells in the GIT of the plateau zokor with those of the plateau pika. The results showed that these endocrine cells we studied were widely distributed in the gastrointestinal organs of both these small mammals, and their morphology and distribution location in the GIT were almost the same. However, there were significant differences in the distribution density of argyrophilic cells between different organs in the GIT. The distribution density of argyrophilic cells in the duodenum, jejunum, ileum, and rectum of plateau zokor was significantly lower than that of plateau pika (p < 0.05) and, in the cecum of plateau zokor, was significantly higher than that of plateau pika (p < 0.001). The positive expression of 5-HT cells in the corpus I, corpus II, and pylorus of the stomach, duodenum, ileum, and rectum of plateau zokor was significantly higher than that of plateau pika (p < 0.01). In addition, the positive expression of Glu cells in the cecum was significantly higher (p < 0.01) and in the duodenum and colon was significantly lower (p < 0.05) in the plateau zokor than in the plateau pika. We conclude that the distribution pattern of endocrine cells in the GIT is consistent with the respective animals’ diets, with the plateau zokor feeding on high-fiber roots and plateau pika preferring to intake the aboveground parts of plants with lower fibers.