In assisted reproductive technology (ART) treatments, the ovarian stimulation method is important for obtaining many good quality oocytes. The first ovarian stimulation treatments used high stimulation in long and short protocols with gonadotropin releasing hormone (GnRH) agonists. It was formulated to suppress the luteinizing hormone (LH) surge while the follicles are developing. Subsequently, a moderate stimulation with an antagonist was introduced following the development of GnRH antagonists, and low stimulation that inhibits the LH surge with continuous administration of clomiphene citrate. However, cases have been reported occurred in which estrogen replacement therapy was selected to facilitate follicular development by supplementing estrogen in ovarian insufficiency. Otherwise ART cryopreservation technology has also developed. These practices are referred to as oncofertility, and have given rise to new ovarian stimulation methods in infertility treatment. Ovarian stimulation with the random start or double stimulation methods, which are not readily affected by the menstrual cycle, and progestin-primed ovarian stimulation (PPOS) that inhibits the LH surge with a progestogen have come to be performed and are showing good outcomes. As the social and medical backgrounds change, the methods of ovarian stimulation may futher improve in the future.

In mammals, the role of sperm in the process of fertilization is complex, and several well-defined steps must occur for the sperm to fertilize with the oocyte. Phospholipases (PLs), which regulate the lipid composition of the sperm by hydrolyzation of the phospholipids, are involved in the regulation of the flagellar beat, capacitation, and the acrosomal reaction, as well as in the triggering of the calcium oscillations in the oocyte that lead to oocyte activation. The emerging important role of phospholipases is also revealed by the fact that alterations of sperm lipids can lead to infertility. Phospholipases, especially PLCζ, could represent therapeutic targets to overcome male infertility.

Implantation requires a receptive endometrium, a functionally normal embryo and communication between the developing embryo and maternal tissues (cross-talk). Two-step embryo transfer (two-step ET) and stimulation of endometrium embryo transfer (SEET) are procedures for ET based on concept of embryonic modulation of endometrial receptivity. In two-step ET, a cleaved embryo is transferred on day 2, and a blastocyst is transferred on day 5. The pregnancy and implantation rates with two-step ET were found to be higher than those with cleaved ET and double blastocyst transfer. We speculated that the cleaved embryos transferred on day 2 modulate endometrial receptivity and improve the implantation rate for blastocysts transferred on day 5. In SEET, embryo culture supernatant (ECS) is injected into the uterine cavity prior to blastocyst transfer to stimulate the endometrium and provide an optimum environment for implantation of forthcoming blastocysts. The pregnancy and implantation rates with SEET were found to be higher than those with blastocyst transfer. Higher implantation and pregnancy rates with SEET could be explained by embryonic factors produced in the culture medium that modulate endometrial receptivity. Lysophosphatidic acid was detected in ECS. Two-step ET and SEET are effective options for ET based on the concept of crosstalk between embryos and maternal tissues.

The regulatory roles of the non-neuronal cholinergic system, such as its growth promoting effects on mural granulosa cells during ovarian folliculogenesis, have been reported for several mammalian species; however, its roles in the early stages of follicles are not well-understood. This study was conducted to examine the expression of transcripts involved in the non-neuronal cholinergic system, and the effects of activating acetylcholine (ACh) signaling in mouse ovaries. The transcripts encoding proteins required in processes critical for ACh metabolism and a nicotinic cholinergic receptor, CHRNA7, were detected in ovaries and isolated mural granulosa cells. Stimulation with carbachol, a cholinergic agonist, promoted proliferation of mural granulosa cells in vitro. Moreover, carbachol treatment of neonatal ovaries significantly increased the numbers of primordial follicles compared with control untreated ovaries in organ cultures. These results suggest that a functional non-neuronal cholinergic system exists in mouse ovaries, and that it promotes the proliferation of mural granulosa cells and the formation/survival of primordial follicles.