Prenatal Stress Modulates Placental and Fetal Serotonin Levels and Determines Behavior Patterns in Offspring of Mice

Available evidence from animal studies suggests that placental serotonin plays an important role in proper fetal development and programming by altering brain circuit formation, which later translates into altered abnormal adult behaviors. Several environmental stimuli, including stress and maternal inflammation, affect placental and, hence, fetal serotonin levels and thus may disturb fetal brain development. We investigated the effect of prenatal stress of varying intensities on the formation of adaptive behaviors in mouse offspring and the role of placental serotonin in these processes. Mild prenatal stress increased placental serotonin synthesis, whereas exposure to moderate stress decreased it. Prenatal stress of varying intensities also resulted in multidirectional changes in animal behavior in progeny, consistent with changes in serotonin levels in the placenta and fetal tissues. Mice exposed to mild prenatal stress showed higher sociality and exploratory activity, whereas, after moderate stress, in contrast, they avoided contact with other individuals of their species and had reduced exploratory activity, with no effect on locomotor activity. Thus, in mice, stressors of varying intensities during the critical period of intrauterine development can affect the synthesis of serotonin by the placenta and lead to multidirectional changes in animal behavior in postnatal life.