Association between chemosensory stimuli and cesarean delivery in rat fetuses: neonatal presentation of similar stimuli increases motor activity.

Recent studies conducted in this laboratory indicated that prenatal chemosensory stimulation followed by cesarean delivery strongly affected postnatal responsiveness to odors derived from the administered substances. The present experiments were performed in order to examine if an associative process was responsible for such effects. In Experiment 1 rat fetuses during Gestational Day 21 were exposed to a tenuous alcohol solution or to a lemon-containing solution either 40 or 10 min prior to cesarean delivery. All subjects were subsequently tested in terms of changes in neonatal motor activity when confronted with the odor of alcohol or lemon. Rats experiencing prenatal cues 10 min prior to delivery exhibited higher and differential responsiveness to the smell of these cues when compared to those experiencing similar solutions 40 min prior to delivery. In Experiment 2 each fetus sequentially experienced both cues. Subsequent tests confirmed that the delay between prenatal sensory experience and birth induction was critical in terms of significantly affecting olfactory-mediated motor responses. The results suggest that consequences related with cesarean delivery act as an unconditioned stimulus capable of being associated with orosensory cues present in the amniotic fluid.