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Photoperiod plays an important role in the regulation of seasonal reproduction of the striped hamster,but the mechanisms involved are unknown.In other species,the KiSS-1 gene and its receptor gene GPR54,regulate the secretion of Gonadotrophin Releasing Hormone (GnRH) .In this study,16 striped hamsters were exposed to different photoperiods respectively (16L∶8D,12L∶12D and 8L∶16D) ; in addition,12 striped hamsters were injected with melatonin under 12L∶12D photoperiods along with12 striped hamsters with no injection.For all the treated groups,there were equal numbers of males and females.We analyzed the differential expression of KISS-1 and GPR54,and then correlated this expression with that of GnRH.The results showed that: (1) the melatonin concentration in the blood is consistent with the photoperiod treatment; (2) the photoperiod had significant effects on the expression of KiSS-1,but the effect on GPR54 was tissue-and sex-dependent; (3) the expression of KiSS-1 in gonads is significantly higher than that in the hypothalamus,and the expression of GPR54 is sex-dependent; (4) melatonin significantly inhibited the expression of KiSS-1 and GnRH,while activating the expression of GPR54 in the hypothalamus; (5) in the hypothalamus,a significant positive correlation existed between the expression level of KiSS-1 and that of GnRH,while a negative correlation existed between the expression level of GPR54 and that of GnRH.These results suggest that KiSS-1/GPR54 plays an important role in the seasonal reproduction of the striped hamster,and photoperiod or melatonin is the direct regulatory factor for the GPR54.