Today, in the US, it would be quite difficult to find someone who is not aware that smoking is hazardous to health. For many decades women have been warned not to smoke while pregnant. Yet, today, in the US, tobacco is the most commonly used drug during pregnancy.[Substance Abuse and Mental Health Services Administration (2012) available from: http://www.samhsa.gov/data/spotlight/Spot062PregnantRaceEthnicity2012.pdf].
Recognizing that pregnant women will continue to smoke, it is critical that scientists determine the consequences on the children so that adequate pharmacological or behavioral interventions can be developed.
Children born to women who smoke are more likely to use tobacco and develop dependence to nicotine as well as many other addicting substances. Understanding how this happens might lead to a therapy to prevent it. One consequence is that in utero exposure to nicotine causes the death of neurons that are responsible for allowing a normal degree of reward or pleasure to be derived from everyday experiences such as eating or drug-taking. Essentially, children born of women who smoked while pregnant are compelled to smoke excessively themselves because they derive much less pleasure from the nicotine dose in a typical cigarette and must compensate by inhaling a greater amount of nicotine. This effect extends to other substances that people abuse, such as cocaine and high fat foods.
The mechanisms in the brain that underlie addictions involve only a few neurotransmitter systems. A group of scientists at The Rockefeller University in New York recently investigated the role of two of these neurotransmitter systems that are critical in the development of addictive behaviors in response to in utero nicotine exposure. The first is a member of the endogenous opiate system and is called enkephalin, while the second is known as orexin. Enkephalin and orexin are quite powerful signals in the brain that can induce animals to self-administer nicotine and other chemicals that are rewarding, such as cocaine, alcohol, heroin and fatty foods.
What these scientists discovered was that even a very low level of nicotine exposure during in utero development is capable of re-wiring the brain so that the influence of enkephalin and orexin are greatly increased for a very long time. Indeed, the effects lasted until puberty! Essentially, if the mother smokes, even a little, during pregnancy, the developing brain alters itself in such a way that after birth the child will have a strong urge to consume highly reward chemicals, such as nicotine, alcohol and fatty foods. The brain does not seem to make a distinction between different types of rewarding chemicals.
Chemically induced abnormalities in the connections between specific parts of the brain, initiated during in utero development, may explain why some children are unable to control their reward-seeking behavior. Given the complexity of this problem it will not be easy to find an effective treatment. It is unlikely that convincing pregnant smokers to quit will be any easier.
© Gary L. Wenk, Ph.D., author of Your Brain on Food (Oxford Univ Press)