KNDy Neurons Mediate Photoperiod Regulation Of Reproductive Activity In Black-lined Hamsters

Seasonal reproduction is a reproductive strategy that animals choose to reproduce under the best conditions in order to adapt to changes in the external environment.Among them,the photoperiod is the most important environmental signal to synchronize animal physiological behavior with seasonal changes.Light signal regulates the complex reproductive activities of animals through the hypothalamic-pituitary-gonadal axis(HPGA),but the specific mechanism of action is still unclear.Three neuropeptides,kisspeptin,neurokinin B(NKB)and dynorphin(DYN),were co-expressed by KNDy neurons in the arcuate nucleus of hypothalamus.It is involved in the regulation of reproductive endocrine in animals and plays an important role in the pulse secretion of gonadotropin-releasing hormone(GnRH)/luteinizing hormone(LH).As an intermediate mediator,KNDy neurons can not only regulate the release of GnRH,but also mediate the negative feedback effect of sex hormones on GnRH.It is the central node in the feedback regulation loop of the animal reproductive system.Cricetulus barabensis is a rodent pest in farmland and grasslands in northern China,and it has a wide distribution range and strong reproductive ability.The peak of reproduction usually occurs in spring and autumn.It has the characteristics of light-sensitive seasonal reproduction,and the reproduction is closely related to the illumination time and seasonal changes.At the same time,reproduction is regulated by complex neuroendocrine system.The fluctuation of the hamster population is obviously affected by seasonal changes,and it is an ideal experimental material for studying the mechanism of photoperiod regulation of the seasonal reproduction of rodents.However,the molecular mechanism that light regulates the seasonal reproduction of Cricetulus barabensis through KNDy neurons has not been reported yet.Combining the ecological characteristics of the hamster,this study takes female Cricetulus barabensis as the research object,and KNDy neurons as the center.30 adult female hamsters were divided into 3groups equally,which were treated with short light group(L:D=8:16,SD),medium light group(L:D=12:12,MD)and long light group(L:D=16:8,LD)for 10 weeks,to study the anxiety behavior,the differences in body weight and feed intake,the content of estradiol(E2)and cortisol in feces and the serum follicle stimulating hormone(FSH),luteinizing hormone(LH),kisspeptin,neurokinin B(NKB)and dynorphin(DYN)concentration difference of Cricetulus barabensis under different light conditions,and the differential expression of genes related to KNDy neurons at mRNA and protein levels.In order to explore the molecular mechanism of different photoperiods regulating the reproductive activity of the Cricetulus barabensis hypothalamus through KNDy neurons,and the regulatory effects of various factors on the striped hamster's reproductive activities,the specific results were analyzed as follows:1.The results of anxiety behavior analysis of Cricetulus barabensis showed that different photoperiods have significant difference in the number of times the Cricetulus barabensis entered the open arm and the residence time.Compared with MD group,the number and residence time of individuals in SD and LD group were increased,and the number of entering the open arm and residence time of the SD group was significantly higher than that of the MD group(P<0.05),which can reduce its anxiety.2.Analysis results of body weight and food intake of Cricetulus barabensis showed that there was no significant difference in body weight under different photoperiod(P>0.05).However,the body weight of LD group showed an increasing trend,while the body weight of SD group showed a decreasing trend.In addition,the food intake of SD group was higher than that of MD and LD group,and the food intake of SD group at the 4th and 6th weeks was significantly higher than that of MD group(P<0.05),indicating that light,as an important environmental factor,affected the physiological activities of Cricetulus barabensis.3.The results of the analysis of hormone concentration in feces showed that the content of E2 increased with the increase of light duration,but it did not reach the significant level.Cortisol levels were relatively low in SD group and relatively high in MD group,but did not reach a significant level.The results of serum hormone concentration analysis showed that FSH and LH in serum increased with the extension of illumination time,and the concentratio n of FSH in LD group was extremely significantly higher than that in SD group(P<0.01),and MD group was significantly higher than that in SD group(P<0.05).KNDy neurons showed different response patterns under different light conditions,the concentration of Kisspeptin also showed an increasing trend with the extension of light time,and LD group was significantly higher than SD group(P<0.05),while NKB and DYN tended to be stable under different light conditions.4.By analyzing the differential expression of KISS1 R,GnRH,TAC3,TACR3,PDYN and KOR genes in the hypothalamus,the analysis results showed that the expression of TAC3,TACR3 and PDYN increased with the increase of light duration,and the expression of TAC3 and TACR3 in SD group were significantly lower than that in LD group(P<0.05),and PDYN in SD group was extremely significantly lower than that in MD and LD groups(P<0.01).The expression of KISS1 R,GnRH and KOR were relatively low in MD group,while SD and LD could increase the expression of KISS1 R and KOR.The expression level of KISS1 R in SD group was significantly higher than that in MD group(P<0.05),and the expression level of GnRH in LD group was significantly higher than that in MD group(P<0.05),and the expression level of KOR in SD group was significantly higher than that in LD group(P<0.05)and extremely significantly higher than that in MD group(P<0.01).5.By analyzing the differential expression of KISS1 R,GnRH,NKB,NK3 R,DYN and KOR proteins in the hypothalamus,the analysis results showed that the protein expression pattern was similar to the gene expression pattern.The protein expressions of GnRH,NKB,NK3 R and DYN increased with the increase of light duration,while the protein expression s of KISS1 R and KOR decreased with the increase of light duration.The protein expressions of GnRH,NKB and DYN in SD group were significantly lower than those in LD group(P<0.05).The protein expression levels of KOR and KISS1 R were the highest in SD group,and the protein expression level of KOR in SD group was significantly higher than that in LD group(P<0.05),and the protein expression level of KISS1 R in SD group was significantly higher than that in MD group(P<0.05).Therefore,we hypothesized that photoperiod was an important environmental factor affecting the expression of KNDy neurons in Cricetulus barabensis,and KNDy neurons regulate the reproductive activities of Cricetulus barabensis mainly by regulating the concentrations of GnRH and FSH in serum.However,the activity of KNDy neurons in Cricetulus barabensis was affected by many factors,and the specific regulatory mechanism needs further study.In summary,we have studied the different photoperiod conditions of Cricetulus barabensis KNDy neurons in the hypothalamus differentially expressed genes,discussed the striped hamsters KNDy neurons mediated photoperied regulation the molecular mechanism of seasonal reproduction.This study provides an important theoretical basis for controlling the occurrence of rodent infestation,the law of population dynamic fluctuation and the mechanism of seasonal fluctuation of population.