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)

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.

Keywords: adaptability; argyrophilic cells; gastrointestinal tract; immunoreactive cells; plateau pika; plateau zokor.

Figure 1

Experimental animals and their habitats in this study. (A) The sampling location of experimental animals; (B) the habitat of sympatric distribution of the plateau zokor and plateau pika (the red circle indicates a mound made by the plateau zokor and the yellow circle indicates a hole made by the plateau pika); (C) plateau zokor; (D) plateau pika.

Figure 2

Distribution and morphology of argyrophilic cells in the GIT of the plateau zokor and plateau pika (400× magnification). (A–H) Plateau zokor ((A) round-shaped and cone-shaped argyrophilic cells in the corpus II of stomach; (B) cone-shaped and spindle-shaped argyrophilic cells in the duodenum; (C) oval-shaped and cone-shaped argyrophilic cells in the jejunum; (D) cone-shaped argyrophilic cells in the ileum; (E) round-shaped argyrophilic cells in the ileum; (F) cone-shaped argyrophilic cells in the colon; (G) cone-shaped and spindle-shaped argyrophilic cells in the rectum; (H) cone-shaped argyrophilic cells in the cecum); (I–T) plateau pika ((I) cone-shaped and spindle-shaped argyrophilic cells in the fundus of stomach; (J) cone-shaped and spindle-shaped argyrophilic cells in the corpus I of stomach; (K) cone-shaped and spindle-shaped argyrophilic cells in the corpus II of stomach; (L) cone-shaped argyrophilic cells in the pylorus of stomach; (M) round-shaped argyrophilic cells in the pylorus of stomach; (N) oval-shape and cone-shaped argyrophilic cells in the duodenum; (O) oval-shape and cone-shaped argyrophilic cells in the jejunum; (P) cone-shaped argyrophilic cells in the ileum; (Q) cone-shaped argyrophilic cells in the colon; (R) cone-shaped argyrophilic cells in the rectum; (S) oval-shaped argyrophilic cells in the rectum; (T) cone-shaped argyrophilic cells in the cecum). The red arrow indicates opened-type argyrophilic cells and the green arrow indicates closed-type argyrophilic cells.

Figure 3

The difference in the proportion of opened-type argyrophilic cells in the gastrointestinal organs of the plateau zokor and plateau pika. (A) The difference in the proportion of opened-type argyrophilic cells in the stomach; (B) the difference in the proportion of opened-type argyrophilic cells in the intestinal tract. * and *** indicate significant interspecific difference (p < 0.05, p < 0.001); ns indicates an insignificant interspecific difference.

Figure 4

Distribution and morphology of 5-HT-immunoreactive cells in the GIT of the plateau zokor and plateau pika (400× magnification). (A–J) Followed by the fundus of stomach, corpus I of stomach, corpus II of stomach, pylorus of stomach, duodenum, jejunum, ileum, colon, rectum, and cecum of the plateau zokor; (K–T) similarly, the plateau pika’s gastrointestinal organs. The red arrow indicates opened-type argyrophilic cells and the green arrow indicates closed-type argyrophilic cells.

Figure 5

Distribution and morphology of Gas-immunoreactive cells in the GIT of the plateau zokor and plateau pika (400× magnification). (A–J) Followed by the fundus of stomach, corpus I of stomach, corpus II of stomach, pylorus of stomach, duodenum, jejunum, ileum, colon, rectum, and cecum of the plateau zokor; (K–T) similarly, the plateau pika’s gastrointestinal organs. The red arrow indicates opened-type argyrophilic cells and the green arrow indicates closed-type argyrophilic cells.

Figure 6

Distribution and morphology of Glu-immunoreactive cells in the GIT of the plateau zokor and plateau pika (400× magnification). (A–J) Followed by the fundus of stomach, corpus I of stomach, corpus II of stomach, pylorus of stomach, duodenum, jejunum, ileum, colon, rectum, and cecum of the plateau zokor; (K–T) similarly, the plateau pika’s gastrointestinal organs. The red arrow indicates opened-type argyrophilic cells and the green arrow indicates closed-type argyrophilic cells.

Figure 7

The difference in positive expression levels for 5-HT-immunoreactive cells in the gastrointestinal organs of the plateau zokor and plateau pika. (A) In the stomach; (B) in the intestinal tract. *, **, and *** indicate significant interspecific difference (p < 0.05, p < 0.01, p < 0.001); ns indicates an insignificant interspecific difference.

Figure 8

The difference in positive expression levels for Gas-immunoreactive cells in the gastrointestinal organs of the plateau zokor and plateau pika. (A) In the stomach; (B) in the intestinal tract. ns indicates an insignificant interspecific difference.

Figure 9

The difference in positive expression levels for Glu-immunoreactive cells in the gastrointestinal organs of the plateau zokor and plateau pika. (A) In the stomach; (B) in the intestinal tract. * and ** indicate significant interspecific difference (p < 0.05, p < 0.01); ns indicates an insignificant interspecific difference.