The Effect Of Differential Expression Of TPH2 In Rat Central Nervous System On Ejaculation Regulation

Research Background and Objective: Among the sexual dysfunctions in men,premature ejaculation（PE）is a very common type.The cause and mechanism of PE are unclear,but the current mainstream view believes that the occurrence of PE is related to the disorder of central 5-hydroxytryptamine（5-HT）transmission and/or dysfunction of 5-HT receptors.5-HT,as an important neurotransmitter in the brain center,can stimulate the ejaculation center and continue to inhibit ejaculation.Results of previous studies have indicated that the anabolism of 5-HT can also affect its level in the synapses.If the synthesis of 5-HT is disordered,it will affect the role of 5-HT in ejaculation regulation.Tryptophan hydroxylase-2 which has been proved to be a specific enzyme expressed in the central nervous system is a key enzyme in the synthesis of 5-HT in the brain center,so the expression level of tryptophan hydroxylase-2 will directly affect the content of 5-HT in synaptic space.However,few studies have reported that the level of tryptophan hydroxylase-2 in the brain is related to the regulation of ejaculation.This study aimed to investigate whether changes of TPH2 level in central brain tissue were associated with regulation of ejaculation.Materials and methods: A 6-week mating experiment was conducted between male SD rats（n=105）and female SD rats（n=105）,and the sexual behavior characteristics of each male rat in the 6-week mating experiment were recorded.Based on the ejaculation frequency,the male rats were split into three groups,“rapid”,“normal”,“sluggish” ejaculators.Then the level of 5-HT in the brain of rats in each group was determined by enzyme-linked immunosorbent assay（ELISA）.TPH2 expression was detected by Western Blot analysis and immunohistochemistry.Correlation analysis was utilized to analyze the relationship between sexual behavioral characteristics and the expression of tryptophan hydroxylase-2 in the brain.Another batch of rats with rapid ejaculation were screened out by the same method.The rats in the rapid group were randomly assigned into two groups.One group received drug intervention with dapoxetine,and the other received saline water as the blank control group.Then,male rats of the two groups received copulatory tests.The sexual behavior characteristics of each male rat in the two groups were also recorded.The level of 5-HT in the brain of the two groups was determined by ELISA.The difference of TPH2 expression in the brain center of the two groups was detected by Western Blot analysis and immunohistochemistry.Results: The results of ELISA and Western Blot showed that the concentration of 5-HT and the expression of TPH2 in rapid rats were the lowest,while those in sluggish rats were the highest.Correlation analysis also indicated the level of TPH2 was positively correlated with ejaculation latency（r=0.8633,P<0.0001）and negatively correlated with ejaculation frequency（r=-0.874,P<0.001）.The immunohistochemical results of the brains of these groups of male rats showed that TPH2 was expressed in the hippocampus,striatum,and prefrontal cortex.In addition,dapoxetine acute administration to rapid rats resulted in up-regulation of TPH2 expression and increasing the level of 5-HT in the brain.Conclusion: There was an important link between the level of TPH2 and the change of ejaculation behaviors.Decreased expression of TPH2 in relevant brain regions will lead to rapid ejaculation.Moreover,the effect of dapoxetine on prolonging ejaculation may be due to the up-regulation of TPH2 expression.