In Brief
Nicotine Addiction "Bridled"
The fact that smoking causes addiction apparently is also based on genetic predisposition. A region in the diencephalon (interbrain), called habenula (Latin for small reins) by researchers, plays a key part here, as Dr Inés Ibañez-Tallon and her colleagues at the Max Delbrück Centre for Molecular Medicine (MDC) Berlin-Buch now were able to show. They also shed light on the mechanism leading to addiction.
They researched a specific receptor for the neurotransmitter acetylcholine, which is formed by this gene cluster, in egg cells from African clawed frogs as well as in transgenic mice. Amongst other reactions, this acetylcholine receptor is activated in nicotine smokers. The gene cluster consists of three sub-groups, that is, three genes. "Although it is contained in the DNA of every cell, the receptor is developed only in very few regions of the brain. One of these is the habenula", explains Dr Ibañez-Tallon. One gene of this sub-group is called alpha5. "It is a known fact, that heavy smokers carry a punctual mutation in this gene. They run a greater risk of developing a nicotine addiction and pulmonary cancer than do people without this gene mutation", says Dr Ibañez-Tallon. A second gene in this sub-group of the receptor is called beta4.
Strong Aversion Against Nicotine
The researchers activated the beta4 gene in transgenic mice and subsequently it became apparent that these mice display a strong aversion against nicotine: They only drank water without nicotine. However, when the researchers activated the mutated variation of the alpha5 gene with the aid of a virus, these mice overcame their dislike of nicotine after two weeks only and solely drank water containing nicotine. Therefore, Dr Ibañez-Tallon and her colleagues conclude that only a balanced activity of both these genes bridles nicotine consumption.
