Simple Summary Ambient temperature has affected the physiological activities of wild animals, such as reproduction. Pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptor (PAC1R) regulate reproduction in mammals via influencing follicle development under ambient temperature variations. However, the effect of PACAP/PAC1R on the reproduction of Phodopus sungorus remains unclear. In this study, we explored the relationship between PACAP/PAC1R and follicle-stimulating hormone (FSH), involved in follicle development, at different ambient temperatures, which will ultimately influence the reproduction of Phodopus sungorus. The development of growing follicles and antral follicles were inhibited at low (8 degrees C, 14 degrees C) and high (29 degrees C) temperatures as well as PACAP/PAC1R expression and FSH serum concentration. The PKA/PKG and PKC phosphorylation sites of PACAP/PAC1R may be involved in the pathway of FSH synthesis through cAMP-PKA and its downstream signal pathway. Moreover, there was a significant positive correlation between the expression levels of PACAP/PAC1R and the number of the growing and antral follicles, as well as the serum FSH concentration and the number of antral follicles. In conclusion: (1) PACAP/PAC1R is evolutionarily conservative and exerts functions through major functional elements; (2) the temperature-dependent follicle development is correlated with the expression of PACAP/PAC1R and the serum FSH concentration. Therefore, PACAP/PAC1R and FSH are involved in the follicle development at different temperatures. These results not only provide a working basis for the study of Phodopus sungorus reproduction, but also provide a theoretical basis for the regulation of population dynamic equilibrium. In Phodopus sungorus, the relationship between pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptor (PAC1R), follicle-stimulating hormone (FSH), and follicle development remains unclear. In this study, we found that the development of growing follicles and antral follicles were inhibited at low (8 degrees C, 14 degrees C) and high (29 degrees C) temperatures. Meanwhile, PACAP/PAC1R expression and follicle-stimulating hormone (FSH) serum concentration significantly decreased during ambient temperatures of 8 degrees C, 14 degrees C and 29 degrees C compared to 21 degrees C. Thus, ambient temperature may influence the expression of PACAP/PAC1R and the synthesis of FSH for involvement in follicle development. Moreover, PACAP/PAC1R had major functional elements including PKA/PKG and PKC phosphorylation sites, which may involve in the pathway of FSH synthesis through cAMP-PKA and its downstream signal pathway. Moreover, there was a significant positive correlation between the expression levels of PACAP/PAC1R and the number of the growing and antral follicles, as well as the serum FSH concentration and the number of antral follicles. However, there was no significant correlation between the expression levels of PACAP/PAC1R and the serum FSH concentration, indicating a complicated pathway between PACAP/PAC1R and FSH. In conclusion, ambient temperature affects the expression of PACAP/PAC1R and the serum FSH concentration. The expression of PACAP/PAC1R and the serum FSH concentration are correlated with follicle development, which implies that they are involved in follicle development, which will ultimately influence the reproduction of Phodopus sungorus. This study can lay the foundation for future investigation on the regulation mechanism of reproduction in Phodopus sungorus.
