The interaction between alcohol addiction and anxiety is not a straightforward one. People who drink large quantities of alcohol are at increased risk for stressful events like domestic abuse and car crashes, according to a new study. But the relationship also works the other way round: Significant alcohol use also appears to rewire the brain, so that it is less able to cope with and rebound from the stressors it encounters. And this could have big implications for anxiety disorders including post-traumatic stress disorder (PTSD).
Researchers gave mice alcohol over the course of a month, in doses corresponding to twice the legal driving limit for people. Then they exposed the mice to a stressful electric shock, paired with a tone (this is classic conditioning, à la Pavlov), so that the mice reacted with a stress reaction to the tone by itself. Then they "extinguished" the behavior by presenting the tone without the shock. Normal mice “unlearn” the connection and no longer react to the tone when it’s played for them.
Significant alcohol use appears to rewire the brain, so that it is less able to cope with and rebound from the stressors it encounters.
However, mice who were exposed to alcohol were not able to “unlearn” the connection – in other words, they kept reacting to the tone as if a painful shock would follow. Control mice, who were not given alcohol during the experiment, behaved as would be expected, and the stress response was “extinguished” in this group.
This finding was borne out in the brain circuitry of the mice who’d been exposed to alcohol: The cells in their prefrontal cortices had a very different shape from those of control mice, and the activity of certain receptors (the NMDA receptor) was significantly reduced.
The study could have big implications for people with anxiety disorders, and particularly those suffering from post-traumatic stress disorder, in which the memory of stressful events cannot be “turned off.” It may also be a clue as to why alcohol addiction is so difficult to treat.
As always, discovering better treatments for disorders like anxiety, PTSD, and alcoholism, which are so devastating but so common, is the real goal. "This study is exciting,” said Kash, “because it gives us a specific molecule to look at in a specific brain region, thus opening the door to discovering new methods to treat these disorders.”
The study was carried out at the University of North Carolina School of Medicine and published in Nature Neuroscience.