Sensory stimuli associated with gestation and parturition evoke cardiac and behavioral responses in fetal rats

We examined the ability of late-gestation (Day 21) fetal rats to detect and respond to stimuli associated with gestation and parturition. Previous work in rats suggests that maternal behavior and physiology provide specific tactile, vestibular, and thermal stimuli to fetal and newborn offspring. For example, fetuses in utero are exposed to angular acceleration and vibration as the mother engages in exploratory behavior and self-grooming. Late-gestation fetuses are compressed by strong contractions of the uterus during parturition. Newly born pups are exposed to intense tactile stimulation associated with maternal licking and to prolonged extrauterine cooling during the immediate postpartum period. In the present study, we simulated five forms of biological stimuli normally associated with gestation and parturition. Using in vivo observation techniques in which fetuses were externalized from the dam’s uterus, but retained an intact umbilical circulation, we measured cardiac and behavioral responses of Day 21 rat fetuses to stimulation. Each subject received a single 5-sec presentation of (1) angular acceleration, to mimic rearing of the pregnant dam, (2) vibration, to mimic hindlimb scratching of the dam, (3) mechanical compression, to mimic labor contractions, (4) stroking, to mimic postpartum licking, or (5) cooling, to mimic the thermal effects of birth. Fetal rats responded to each form of stimulation with bradycardia and behavioral activation. These findings provide evidence that fetal offspring can detect and respond to the classes and levels of biological stimuli that are normally associated with maternal behavior and physiology during perinatal life.