Drinking too often and too much alcohol poses a risk not only to your health, but may also causes a deadly addiction. However, what happens in the brain is still unclear. Now researchers have discovered a previously unknown effect of alcohol on our brains. According to this research, even moderate but persistent alcohol consumption changes the structure of the cell spaces in the grey matter. They become more permeable and thus addictive messengers such as dopamine can spread better in the brain. According to the scientists, this effect could explain why alcohol, despite weak acute influences on our reward system, can become addictive over time.
Consumption of beer, wine or other alcoholic beverages is simply part of it for many people. After work, we often go out for a drink with colleagues or friends or relax on the sofa with a glass of wine. The only problem is that even moderate but regular alcohol consumption can lead to an addiction in the long run. “Alcohol has the ability to trigger neurological adaptations that promote the formation of strong consumption habits and addiction, and therefore often lead to alcoholism,” explains Silvia De Santis of the Spanish University Miguel Hernandez and her colleagues. However, alcohol consumption triggers a far less strong response from the reward system than other drugs. “How alcohol still develops its potent addictive effect is a previously barely understood mystery,” the researchers said.
De Santis and her team have now investigated one possible cause: changes in the grey matter that could potentially affect the concentration and spread of the brain messenger substance dopamine. Dopamine plays a crucial role in the reward system and is responsible, among other things, for the happiness and satisfaction that addicts feel when breastfeeding their addiction. Studies have shown that this neurotransmitter is not only transmitted to the synapses between neurons, but is also spread through diffusion processes in the cell spaces. “Increased diffusion in extracellular space may appear as very non-specific mechanisms of action for a drug. However, this influences a variety of communication processes in the brain,” explains co-author Wolfgang Sommer from the Central Institute for Mental Health in Mannheim. The extracellular space consists of fluid-filled cavities and canals that form between brain cells and their many extensions.
De Santis, Sommer and their colleagues have now investigated whether and how these cell gaps change due to persistent alcohol consumption in chronically alcoholic people and in rats after one month of regular alcohol consumption. Using diffusion tensor imaging, a variant of magnetic resonance tomography, they recorded how well water molecules were distributed in the extracellular space of the brains of the animal and human subjects. In addition, they used a contrast agent to determine how the structure of the cell spaces differed between the alcohol-dependent rats and healthy control animals.
The studies showed clear differences: “In both alcohol-drinking animals and alcoholic patients, our results show a far-reaching increase in diffusion in the grey matter,” De Santis and her colleagues report. “As far as we know, this is the first time that diffusion changes in the brains of alcoholics have been studied and detected.” At the same time, the structure of the extracellular space and the microglia cells affecting its shape also changed: “After chronic alcohol exposure, these immune cells of the brain react, they shrink and withdraw their dense mesh from fortians,” reports De Santis’ colleague Santiago Canals. “The removal of barriers changes the geometry of the extracellular space and creates new diffusion paths.” This means that dopamine can also spread more strongly in the brain.
According to the scientists, their findings provide an explanation for why alcohol consumption, despite rather weak acute effects on the reward system, can lead to addiction over time: the structure and shape of the cell spaces in the brain, altered by alcohol, make it easier for dopamine to spread, thus increasing its concentration and effect on different brain regions. “Increased neurotransmitter concentration over time, combined with slowing breakdown in the synapses, could help make the rather low-rewarding properties of alcohol the powerful habituation effect that leads some people into addiction,” the researchers note. If this theory is confirmed, it could also help to develop better prevention and countermeasures against alcohol addiction.