Effects of 5-hydroxytryptamine on spermatozoal hyperactivation and in vitro fertilization in mice

In this study, we examined the effects of 5-hydroxytryptamine (5-HT) on the motility and hyperactivation of mouse spermatozoa. In addition, we examined whether 5-HT increases the success of in vitro fertilization (IVF) in mice. Interestingly, 5-HT and agonists of the 5-HT₂, 5-HT₃, 5-HT₄, and 5-HT₇ receptors significantly increased the percentage of hyperactivated spermatozoa but did not affect the percentage of motile spermatozoa. Moreover, agonists of the 5-HT₂, 5-HT₃, and 5-HT₄ receptors significantly affected the velocities, linearity, straightness, wobbler coefficient, amplitude and/or frequency of spermatozoa. In particular, the improvement of hyperactivation by 5-HT was strongly inhibited by antagonists of the receptors 5-HT₄ and 5-HT₇ and was completely inhibited by a mixture of the four 5-HT-receptor antagonists. The increase in hyperactivation by the agonists was significantly inhibited by the corresponding 5-HT-receptor antagonist. Moreover, 5-HT significantly increased the percentage of two-cell embryos. The increase in the IVF success rate by 5-HT was significantly inhibited by a 5-HT₄-receptor antagonist. These results suggest that 5-HT increased hyperactivation through the 5-HT receptors and increased the success of IVF in mice.