Two new studies have helped explain why teens exposed to foetal alcohol are at high risk for heavy drinking and perpetuating a family cycle of alcohol addiction.
This happens because pre-natal alcohol exposure shapes sensory preference which means young people whose mothers drank when pregnant might be more likely to abuse alcohol because, in the womb, their developing senses came to prefer its taste and smell.
Researchers with the State University of New York Developmental Ethanol Research Center conducted a study on mice and 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.
Led by Steven Youngentob, PhD, the research team observed 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 foetal 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 examined after 15 days of birth, still infants, or 90 days of 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 researchers cite their finding as evidence for ethanol preference resulting from maternal use or abuse of ethanol during pregnancy.
The researchers 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 foetus becomes attuned to ethanol's chemosensory attributes. It 'likes' the taste and smell, two big factors in the flavour of alcohol.
However, Youngentob further suggested 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 odour, the prenatally exposed young rats sniffed it significantly more than control rats. To heighten ethanol's sensory impact, the odour-responsive cells in their nasal passages also became tuned. This altered odour response predicted the sniffing response of the animals. Again, these effects faded by adulthood, the rat equivalent of 30 to 40 human years.
"From a clinical perspective, an enhanced preference for ethanol odour may be an important contributor to the risk for an enhanced postnatal avidity for the drug," the researchers said.
The findings are published in the December issue of Behavioural Neuroscience.