Fig. 3

a A cartoon of oviductal transport of preimplantation embryos in mice. Ovulated eggs are fertilized in the ampulla of the oviduct. Fertilized eggs through successive cell divisions form morulae. Morulae pass through the utero-tubal junction to enter into the uterine lumen. b A schematic diagram of a cross-section of the oviduct. Ep, epithelium. c A proposed scheme of contraction–relaxation waves of oviductal muscularis at the utero-tubal region influenced by varying concentrations of AEA. In the absence of AEA, increased release of norepinephrine (NE) produces muscular contractions, resulting in narrowing of the lumen. At higher concentrations of AEA, endocannabinoid signaling through CB1 reduces the release of NE, thus relaxing the muscularis, widening the lumen. Thus, appropriate endocannabinoid signaling creates waves of contraction–relaxation, moving forward embryos from the oviduct into the uterine lumens [27]. With permission from Elsevier Inc