Expression of gastrointestinal clock genes and associated hormones levels in hibernating and non-hibernating Daurian ground squirrels.

Extensive evidence indicates that the gut phenotypes of hibernating animals undergo periodic seasonal changes. However, the rhythmic mechanisms underlying this seasonal plasticity remain poorly understood. As an obligate hibernator, the Daurian ground squirrel (Spermophilus dauricus) displays seasonal feeding behaviors accompanied by pronounced seasonal plasticity in its gastrointestinal (GI) tract. This study compared the expression of clock genes in the stomach and small intestine of ground squirrels across different seasons (autumn, winter and spring), as well as the levels of serum arginine vasopressin (AVP) and melatonin (MT). We found that the expression of Clock, Cry1, Cry2, and Prkaa1 (encoding the AMPK α1 subunit) was elevated in the stomach during winter compared to autumn and spring, whereas Per3 expression was decreased. In the small intestine, the expression of Clock, Cry1, Cry2, Per2, and Per3 decreased in winter compared to spring or autumn, while that of Prkaa1 increased. Serum AVP levels were lowest in winter, whereas MT levels were significantly elevated in autumn compared to spring. These results indicate that seasonal changes alter clock genes expression in a tissue-specific manner, corresponding to the distinct functions and activity rhythms of the stomach and small intestine, suggesting a mechanism for regulating gastrointestinal plasticity. Furthermore, AVP and MT appear to play significant roles in regulating the hibernation-arousal cycle and rhythmic behaviors in ground squirrels. Together, these results shed light on the endogenous biological rhythms in the GI tract of ground squirrels that facilitate their adaptation to seasonal changes.