It’s safe to say that substance abuse disorders, including alcoholism and binge drinking, are complex issues that are rarely caused by a single factor. Nonetheless, a team of researchers from the Medical University of South Carolina may have discovered a brain receptor in a single region of the brain that controls the initiation of binge drinking – at least in mice.
Their new study, which appears in the journal Neuropharmacology, focuses on a type of opioid receptor known as the kappa opioid receptor (KOR). Unlike most other receptors in this category, KOR does not produce pleasurable, relaxing or pain-killing effects, but instead generates discomfort, stress and anxiety.
Previous research has shown KOR to be implicated in alcohol abuse disorders, which led the study authors to hypothesize that it may play a role in binge drinking. However, because these receptors perform different functions in different regions of the brain, the researchers were keen to discover which particular KOR are most closely associated with this type of behavior.
They therefore decided to investigate a series of structures within the brain known as the extended amygdala, which are involved in emotional processing. In particular, they looked at the KOR within the bed nucleus of the stria terminals (BNST) in a group of mice that had been “trained” to drink excessive amounts of alcohol over a four-hour period each evening.
When the researchers injected a chemical that blocks KOR directly into this part of the rodents’ brains, it caused them to moderate their drinking, consuming only a small amount of alcohol but not enough to become intoxicated during the usual four-hour period.
"Blocking these kappa receptors in the extended amygdala didn't completely abolish drinking," explained study author Harold Haun in a statement. "It brought it down to a more moderate level, the equivalent being a glass of wine at dinner opposed to a bottle."
Conversely, when another chemical that activates KOR was injected into the BNST, the mice increased their drinking – all of which points to a central role for the kappa opioid receptor in controlling binge drinking.
Why a brain receptor that causes stress and anxiety should have such an influence over this type of behavior isn’t entirely clear, although Haun says that “what we do know is that kappa opioid receptors play an important role in the negative emotional state that drives drinking when it becomes compulsive in alcohol use disorder.”
It’s unlikely that doctors will be injecting anything directly into the brains of human binge drinkers any time soon, although study co-author Howard Becker believes this finding could help researchers understand “how new therapeutics may have some value in helping to quell the desire and motivation to drink excessively in those who have developed an alcohol use disorder or are on the threshold of doing so.”