Doctors have long recognised a link between alcoholism and anxiety disorders such
as post-traumatic stress disorder (PTSD). Those who drink heavily are
at increased risk for traumatic events like car accidents and domestic
violence, but that only partially explains the connection. New research
using mice reveals heavy alcohol use actually rewires brain circuitry, making it harder for alcoholics to recover psychologically following a traumatic experience.
"There's a whole spectrum to how people react to a traumatic event,"
said study author Thomas Kash, PhD, assistant professor of pharmacology
at the University of North Carolina School of Medicine. "It's the
recovery that we're looking at — the ability to say 'this is not
dangerous anymore.' Basically, our research shows that chronic exposure
to alcohol can cause a deficit with regard to how our cognitive brain
centers control our emotional brain centers."
How the study was done
The study, which was published online on by the journal Nature Neuroscience,
was conducted by scientists at the National Institute on Alcohol Abuse
and Alcoholism (NIAAA) and UNC's Bowles Center for Alcohol Studies.
"A history of heavy alcohol abuse could impair a critical mechanism for
recovering from a trauma, and in doing so put people at greater risk
for PTSD," said NIAAA scientist Andrew Holmes, PhD, the study's senior
author. "The next step will be to test whether our pre-clinical findings
translate to patients currently suffering from comorbid PTSD and
alcohol abuse. If it does, then this could lead to new thinking about
how we can better treat these serious medical conditions."
Over the course of a month, the researchers gave one group of mice
doses of alcohol equivalent to double the legal driving limit in humans.
A second group of mice was given no alcohol. The team then used mild
electric shocks to train all the mice to fear the sound of a brief tone.
When the tone was repeatedly played without the accompanying electric
shock, the mice with no alcohol exposure gradually stopped fearing it.
The mice with chronic alcohol exposure, on the other hand, froze in
place each time the tone was played, even long after the electric shocks
had stopped.
The pattern is similar to what is seen in patients with PTSD, who have
trouble overcoming fear even when they are no longer in a dangerous
situation.
What the findings mean
The researchers traced the effect to differences in the neural
circuitry of the alcohol-exposed mice. Comparing the brains of the mice,
researchers noticed nerve cells in the prefrontal cortex of the
alcohol-exposed mice actually had a different shape than those of the
other mice. In addition, the activity of a key receptor, NMDA, was
suppressed in the mice given heavy doses of alcohol.
Holmes said the findings are valuable because they pinpoint exactly
where alcohol causes damage that leads to problems overcoming fear.
"We're not only seeing that alcohol has detrimental effects on a
clinically important emotional process, but we're able to offer some
insight into how alcohol might do so by disrupting the functioning of
some very specific brain circuits," said Holmes.
Understanding the relationship between alcohol and anxiety at the
molecular level could offer new possibilities for developing drugs to
help patients with anxiety disorders who also have a history of heavy
alcohol use. "This study is exciting 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," said Kash."
(EurekAlert, September 2012)