Smoking has a lasting impact on the brain
With around five million deaths per year, smoking is one of the most common causes of death worldwide. In particular, the damage to the respiratory tract and the cardiovascular system from tobacco use has been known for a long time. But Swiss researchers have now found that smoking also leaves traces in the brain in the long term.
Respiratory complaints such as smoking cough (chronic obstructive pulmonary disease, COPD) or lung cancer are typical side effects of tobacco consumption. According to the results of the Swiss researchers, however, there is also something like a smoking brain. Because tobacco consumption has a lasting impact on the glutamate system in the brain, the scientists headed by Gregor Hasler from the University Clinic and Polyclinic for Psychiatry at the University of Bern report in the journal "Proceedings of the National Academy of Sciences" (PNAS). The glutamate receptor mGluR5 is significantly less common in the brains of smokers and ex-smokers, which has a significant impact on signal transmission in the brain. The researchers also suspect that these impairments of the glutamate system are related to the high relapse rate in the attempt to remove smoke. Drugs that intervene directly in the glutamate system could possibly help smokers with their weaning, Gregor Hasler and colleagues continue.
Sustainable changes in the brains of smokers In their joint study in the brains of 14 smokers, ex-smokers and non-smokers, scientists from the University of Bern, the ETH Zurich and the University of Zurich have the concentration of the metabotropic glutamate receptor 5 using positron emission tomography 5 (mGluR5) measured. The glutamate receptor plays an important role in signaling in the brain. Here, the researchers suspect a connection with the difficulties that around 90 percent of smokers have with smoking cessation. So far it is unclear why so many of the roughly 75 percent of smokers who try to withdraw are unable to keep up. Hasler and colleagues assume that nicotine addiction develops as a kind of learning process in which the glutamate system plays a central role. From previous studies on mice, it is known that glutamate has a significant influence on the development of addictions, such as nicotine and cocaine addiction. The current results of the scientists seem to support this thesis and also provide a possible explanation for the high relapse rate in smoking cessation.
Smokers with significantly reduced concentration of the glutamate receptor mGluR5 The investigation with the new positron emission tomography method showed that smokers and ex-smokers had a greatly reduced concentration of the glutamate receptor (mGluR5). "We found a significant global reduction in the mGluR5 distribution" by an average of more than 20 percent in the volume ratio of the so-called gray matter in the 14 smokers, the researchers report in the journal "PNAS". The most significant reductions in mGluR5 concentration compared to non-smokers were to be found in the area of the bilateral medial orbitofrontal cortex. Here the smokers showed a 30 percent lower concentration of the glutamate receptor. According to the researchers, reduced mGluR5 values were also observed among ex-smokers. Although they had not smoked on average for 25 weeks, they showed a 10 to 20 percent reduction in the glutamate receptor. The scientists emphasize that this shows the lasting effect that smoking has on the brain. Overall, the "change in the glutamate system among smokers was far greater in scale and in local expansion than previously thought," continued Hasler and colleagues.
Impairment of the glutamate system Cause of the high relapse rate According to the researchers, the reason for the reduction in the glutamate receptor is the continued nicotine intake. The reduction in mGluR5 values among ex-smokers suggests that their receptors have not yet fully recovered. Apparently, the recovery of the glutamate system takes an extremely long time. "It is likely that this very slow normalization contributes to the very high relapse rate among ex-smokers", Hasler and colleagues write. So far, it has not been clear what lasting effects smoking has on signal transmission in the brain. The tolerance formation in the glutamate system with repeated nicotine consumption probably also contributes to the fact that the abstinence from nicotine can go hand in hand with withdrawal symptoms, like inner restlessness, irritability, fear or also physical symptoms, such as headache.
Medicines to regulate the glutamate receptor to help you quit smoking? In the current "development of drugs that act on the mGluR5 protein", it should be taken into account that the effects on smokers and ex-smokers can differ significantly from those on non-smokers. However, corresponding medications may also have the potential "to reduce the risk of relapse, the withdrawal symptoms and other psychological consequences of nicotine consumption", Hasler and colleagues write. Two of the researchers involved work for the pharmaceutical company Novartis, which is currently testing various drugs that target the mGlu5 receptor. (fp)
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