The Effect And Mechanism Of Neurokinin B On Puberty Onset In Rats

The onset of puberty early and late is directly related to the animal reproductive performance. The exact mechanism of the onset of puberty has not been elucidated, which is generally associated with the pulse release of GnRH. The studies show that neurokinin B (NKB) is a regulatory factor of GnRH, and it is closely related to puberty onset, and it is considered to be another important regulatory factor after Kisspeptin. Kisspeptin can promote GnRH pulse release and it is the gatekeeper of puberty onset. Recent studies have shown that the NKB receptor (NK3R) is distributed in GnRH neuron, and the exogenous NKB and its receptor agonists can amplify the effects of Kisspeptin on reproduction. So NKB directly promote the GnRH pulse release through its receptor or indirectly regulate GnRH secretion by Kisspeptin, which is unclear. Therefore, it is necessary to explore the effect pathway of NKB in the regulation of GnRH and puberty onset. In this experiment, NKB, NKB antaagonist combined with GRP-54 receptor antaagonist were used to treat in prepuberty and adult rats by the lateral ventricles, the change of day of puberty onset was observed trinal immunofluorescence techniques were detected the expression changes of NKB, GnRH and Kisspeptin in the reproductive axis of rats, followed Image-Pro Plus 6.0 and Image J software was used to analyze the mean fluorescence intensity and the positive cells in the reproductive axis of rats. The effect of NKB on puberty onset and the expression of GnRH and Kisspeptin were clarified. Real-time PCR, enzyme immunoassay, radioimmunoassay and other analysis methods were used to illustrate the effect role of NKB on the gene expression of GnRH and Kisspeptin and the level of gonadal hormones.The results showed that:(1) The day of the vulva opening in prepuberty group NKB, NKB+saline and Kp-234+NKB was significantly ahead of time (P<0.05), the weight of ovaries increased significantly (P<0.05) while the day of the vulva opening in group NKB antagonist and Kp-234+normal saline significantly delayed (P<0.05). (2) The expression of GnRH and Kiss-1 mRNA in group NKB and NKB+normal saline in hypothalamus increased (P<0.05) compared to the negative control group in prepuberty onset rats, and it suggests that NKB promote the expression of GnRH and Kisspeptin gene in hypothalamus (P<0.05). (3) The expression of the NKB, GnRH and Kisspeptin in different nuclei of the hypothalamus in rats was different. NKB and Kisspeptin mainly located in the arcuate nucleus and paraventricular nucleus, GnRH mainly distributed in the median eminence and arcuate nucleus on hypothalamus. NKB increased NKB-positive cells in the lateral ventricles of rats in the arcuate nucleus (P<0.05), the number of GnRH-positive cells in the median eminence (P<0.05) and Kisspeptin-positive cells in the arcuate nucleus and the paraventricular nucleus (P<0.05), which showed that NKB promoted the expression of GnRH and Kisspeptin in hypothalamus. (4) NKB and Kisspeptin distributed in adenohypophysis and ovarian stromal cells, granulosa cells and theca. And the expression of Kisspeptin in adenohypophysis and ovary in rats injected NKB significantly increased (P<0.05), it showed that the NKB involved in pituitary-gonadal axis regulation. (5) The average serumconcentration of NKB in group NKB antagonist and negative control was significantly lower than other groups (P<0.05). The average serum levels of E2 and P4 in group NKB and NKB+ saline were significantly higher (P<0.05) than group NKB antagonist and negative control, suggesting that NKB incerased the secretion of gonadal hormones.All in all, we can conclued:(1) NKB promote puberty onset in advnace in rats. (2) NKB up-regulate the expression of the gene of GnRH and Kisspeptin in hyphothalamus, suggesting that NKB regulate pubert onset in rats by GnRH and Kisspeptin. (3) NKB not only regulate reproduction in the central level but also in pituitary and ovarian. (4) NKB increase the secretion of gonadal hormones in the cycling blood, which further affect the puberty onset in rats.