Cutaneous induction of breathing in perinatal rats

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We tested the hypothesis that cutaneous stimulation present during perinatal life induces and maintains breathing in fetal and neonatal rats. Late-gestation (Day 21) rat fetuses with intact umbilical connections were externalized from the uterus of a spinally transected dam. In the first experiment, fetuses were externalized into air heated to intrauterine temperature (37.5°C) and were either stroked with a brush for 2 min to mimic the dam’s postpartum licking or not stroked. The single episode of stimulation more than doubled fetal breathing rates for the duration of a 1-h test, demonstrating facultative effects of cutaneous stimulation on perinatal respiratory behavior. In the second experiment, we investigated the effects of simulated maternal licking on pups’ postpartum breathing rates. Fetuses were exposed to a regime mimicking birth in which the amniotic sac was removed, the fetus was exposed to postpartum nest temperature (26°C), and its umbilical cord was occluded. Subjects were then exposed to (1) brush stroking, to mimic maternal licking at birth; (2) body compression, to simulate effects of uterine contractions during labor; (3) body compression followed by stroking; or (4) neither compression nor stroking. Compressed and/or stroked pups showed similar, rapid respiratory rates. Most of the noncompressed, nonstroked controls did not; only 25% of the nonstimulated pups were respiring at the end of the test. The third experiment addressed potential confounds which might arise from the fetuses’ exposure to anesthesia prior to respiratory measurements. Fetuses delivered by cesarean section without anesthesia were either stroked or remained undisturbed. Pups in a vaginal delivery control group were removed from the nest after 2 min of postpartum licking by the dam. All of the stroked and vaginally delivered pups were respiring after 1 h, in contrast to 25% of the nonstroked controls. Together, these results suggest that cutaneous stimulation, delivered in amounts that approximate biological values, provides a powerful stimulus to perinatal respiratory behavior. In conjunction with previous work, these findings support the view that fetal sensory experience plays an important role in mediating the cascade of adaptive adjustments required for the transition from fetus to newborn.