Background: Rat fetuses seem to be capable of associative learning mediated through alcohol's unconditioned properties. The newborn's suckling response immediately after birth is dependent on olfactory stimuli present in the fetal milieu and/or odorants perceived immediately after birth. The present study analyzed the impact of olfactory fetal learning supported by maternal-fetal alcohol intoxication on the newborn's first postnatal suckling response, in the presence or absence of chemosensory cues originally associated with alcohol during prenatal life.
Methods: During gestational days 17 to 20, fetuses experienced a salient novel cue (cineole) explicitly paired or not with the induction of alcohol intoxication resulting from maternal intragastric intubation of a 2 g/kg ethanol dose. A separate set of dams were intubated with only water. In experiment 1, cesarean-delivered pups were tested shortly after birth for their response to a surrogate nutritive nipple scented with cineole or with no explicit odor. In experiment 2, pups were similarly evaluated after the prenatal treatment when cineole, a novel odorant (lemon), or no explicit odor was presented either in conjunction with the nipple or before being tested with the nipple.
Results: In both experiments, fetal olfactory conditioning supported by alcohol intoxication had a significant effect on the newborn's first suckling episode, depending on the olfactory cues presented before or during suckling. Presence of cineole but not of novel odorants seemed to activate the associative memory acquired in utero. Once the memory was activated, pups that were subjected to fetal odor-alcohol pairings were found to attach significantly more to surrogate nutritive nipples than did fetal control animals.
Conclusions: Prenatal experience with alcohol intoxication can result in chemosensory associative learning mediated by the drug's postabsorptive effects. This learning determines attachment patterns of newborns when they reexperience olfactory cues that had signaled onset of the state of acute alcohol intoxication when they were fetuses. Considered in view of previous experiments, the present results generate two alternative hypotheses relative to the affective component of the memory established in utero: (1) alcohol intoxication is an appetitive reinforcer during fetal life, or (2) the calming effects of postnatal suckling behavior counteract negative hedonic components of the memory accrued in utero.