Figure 1.

The mechanisms underlying the gestational Trp fluctuation on prenatal, perinatal, and postnatal development. The maternal circuiting Trp is affected by multiple factors, such as drug administrations and diets. The placental Trp can be synthesized to 5-HT, degraded to KYN, or transferred to the embryo. The fetus is exposed to the Trp and its metabolite, 5-HT, and KYN, which regulates the neurogenesis and neuroendocrine development as well as the gut microbiota composition and diversity in the progeny. The mother-child microbe transmissions during the 40-week pregnancy, labor, and feeding constitute the initial microbiota community in the progeny and consequentially, regulate decision making and behavioral exhibition via the MGB axis. The development and activity of the MGB axis are regulated by the maternal-fetal transfers of nutrients and microbes together with multiple environmental factors, including the disease and medicinal history, culture, eating habits, education, etc. 5-HT: serotonin; KYN: kynurenine; MGB axis: microbiota-gut-brain axis; Trp: tryptophan.