The Effort Of Estrogen Receptor α (ERα) Expression In Hypothalamic Arcuate Nucleus On Seasonal Breeding Of Tan Sheep

The reproduction of seasonal breeding is on the control of hypothalamic-pituitary-gonadal axis (HPGA) system. The changes of ERα expression levels in thenucleus of hypothalamus may affect the expression of Kiss1gene through the feedbackeffects of estrogen, which in turn cause changes in GnRH secretion. Then it may affectovulation and other reproductive activities by regulating the secretion of LH/FSH orother related hormones and taking effects on the gonads. The mechanism of seasonalbreeding regulation in sheep is poorly understood at present. The ERα expression levelin the hypothalamus of sheep in each estrus period and its relationship with seasonalbreeding has not been studied in detail. Revealing the molecular regulating mechanismof non-seasonal estrus will help us to break the restriction of seasonal breeding throughthe artificial regulation in sheep. It is meaningful of improving reproductiveperformance including litter size in sheep. In this study, blood samples were collectedfrom jugular venous and their serums were separated to measure hormone levels duringdifferent periods of estrus in Tan Sheep. By immunofluorescence techniques, ERαexpression levels and the number of kisspeptin cells were counted at differentreproductive status in different parts of the hypothalamic arcuate nucleus (rostral ARC,middle ARC, caudal ARC) in40healthy adult female Tan Sheep. The main results wereas follows:①Levels of estrogen, progesterone, follicle-stimulating hormone and luteinizinghormone were measured in Tan Sheep. The results showed that the secretion of E2hadno significant changes around the four periods of estrus. However, it was higher duringproestrus than the other three periods (P>0.05). The secretion of P4in diestrus wassignificantly higher than the others (P<0.05), and it was significantly higher in anestrusthan in proestrus and estrus period (P<0.05). There was no significant differencebetween the proestrus and the estrus period (P>0.05). The secretions of FSH and LHwere higher in anestrus than the others. Difference in LH was significant (P<0.05), butin FSH it was not significant (P>0.05). The LH secretion was significantly higher indiestrus than in estrus (P<0.05).②The expression level of ERα in the rostral and the caudal ARC of hypothalamicin Tan Sheep was highest during the proestrus period and lowest during the anestrusperiod. The expression level in the estrus was significantly higher than the diestrus period. Both of them were significantly lower than the proestrus period (P<0.05) andsignificantly higher than the anestrus period (P<0.05). It presented the same trend in themiddle ARC of hypothalamic in Tan Sheep. But the difference was not significant(P>0.05). The ERα expression level in the caudal ARC of hypothalamic in Tan Sheepwas significantly higher than the rostral and the middle ARC at different reproductivestatus (P<0.05) except in the anestrus period (P>0.05). It was significantly higher in themiddle ARC of hypothalamic than the caudal ARC during the anestrus period (P<0.05).③The number of kisspeptin cells in the rostral and the caudal ARC ofhypothalamic in Tan Sheep reached the top during the estrus period and hit the bottomduring the anestrus period. Its number in the proestrus was significantly higher than thediestrus period. Both of them were significantly lower than the estrus period (P<0.05)and significantly higher than the anestrus period (P<0.05). It presented the same trend inthe middle ARC of hypothalamic in Tan Sheep. But the differences between diestrusand anestrus, proestrus and estrus were not significant (P>0.05). The number ofkisspeptin cells in the caudal ARC of hypothalamic in Tan Sheep was significantlyhigher than the rostral and the middle ARC at different reproductive status(P<0.05).However, there was no significant difference between the caudal ARC and themiddle ARC of hypothalamic (P>0.05).The ERα expression level and the number of kisspeptin cells at differentreproductive status in different parts of the hypothalamic arcuate nucleus aresignificantly different in Tan Sheep, which indicates that both of them play importantroles in the seasonal breeding. Meanwhile, the results verify that the rostral and thecaudal arcuate nucleus of hypothalamic in Tan Sheep may play "secretion central" rolesand the caudal ARC is the main part. However, whether the middle arcuate nucleusplays an "inhibit central" role is unclear.