- Prenatal Alcohol Exposure/Fetal Alcohol Syndrome
Young people whose mothers drank when pregnant may be more likely to abuse alcohol because, in the womb, their developing senses came to prefer its taste and smell. Researchers have found that because the developing nervous system adapts to whatever mothers eat and drink, young rats exposed to alcohol (ethanol) in the womb drank significantly more alcohol than non-exposed rats.
The studies contribute a critical biological piece to the complex puzzle of why teens with a family history of drinking may themselves drink more. Lead author Steven Youngentob, PhD, observes that a biologically instilled preference for alcohol’s taste and smell can make young people much more likely to abuse alcohol, especially in light of social pressures, risk-taking tendencies and alcohol’s addicting qualities.
These more subtle consequences of fetal alcohol exposure come on top of the potential for Fetal Alcohol Syndrome, which leads to profound neurodevelopmental problems including mental retardation.
In one study, infantile rats exposed to alcohol (ethanol) in the womb drank significantly more of it in youth but not in adulthood. They were the offspring of dams, or mother rats, from one of three experimental groups: ethanol-exposed via the mother’s diet at levels simulating moderate to heavy drinking; pair-matched controls that ate the same amounts as ethanol exposed-dams to control for any effect of under-nutrition; and controls that ate freely.
The offspring were studied at Day 15 after birth, still infants, or Day 90 after birth, fully mature. Adult rats chose to drink ethanol or non-ethanol solutions, both from bottles. Rat pups were presented with ethanol solutions through tubes implanted in their cheeks; they could either swallow to accept, or reject it by shaking their heads, licking the chamber walls or floor, or letting it drip out.
The ethanol-exposed animals drank significantly more ethanol than both groups of control animals. The authors cite their finding as evidence for ethanol preference resulting from maternal use or abuse of ethanol during pregnancy.
The authors put forth the idea that when the developing nervous system senses ethanol in amniotic fluid, it adapts without awareness of which chemicals will help or hurt the organism. It could be alcohol; it could be carrot juice; the adaptation is the same. Given the former, the olfactory system of a developing fetus becomes attuned to ethanol’s chemosensory attributes. It “likes” the taste and smell, two big factors in the flavor of alcohol. However, Youngentob further suggests that if the nervous system has no further experience with the drug by adulthood, ethanol loses its chemosensory allure.
The related study found strong evidence of the role of the olfactory system. As in the other study, the researchers exposed the rats to ethanol by giving it to pregnant mothers. Control mothers just ate chow, and the offspring were tested either at 15 or 90 days after birth.
When exposed to ethanol odor, the prenatally exposed young rats sniffed it significantly more than control rats. To heighten ethanol’s sensory impact, the odor-responsive cells in their nasal passages also became tuned. This altered odor response predicted the sniffing response of the animals. Again, these effects faded by adulthood, the rat equivalent of 30 to 40 human years.
The authors wrote, “From a clinical perspective, an enhanced preference for ethanol odor may be an important contributor to the risk for an enhanced postnatal avidity for the drug.” That finding addresses a central goal of the research, where Youngentob and his colleagues aim to define the factors that contribute to the perpetuating cycle of abuse from fetal exposure to adult abuse and back again.
“The Effect of Gestational Ethanol Exposure on Voluntary Ethanol Intake in Early Postnatal and Adult Rats,” and “Experience-Induced Fetal Plasticity: The Effect of Gestational Ethanol Exposure on the Behavioral and Neurophysiologic Olfactory Response to Ethanol Odor in Early Postnatal and Adult Rats,” Steven L. Youngentob, PhD, SUNY Upstate Medical University and SUNY Developmental Research Center; Juan C. Molina, PhD, SUNY Upstate Medical University, Binghamton University, and SUNY Developmental Ethanol Research Center; Norman E. Spear, PhD, Binghamton University and SUNY Developmental Ethanol Research Center; and Lisa M. Youngentob, BS, SUNY Upstate Medical University and SUNY Developmental Ethanol Research Center; Behavioral Neuroscience, Vol 121, No. 6.