Scientists have identified a population of neurons in the brain that influences whether one drink leads to two, a finding which could ultimately lead to a cure for alcoholism.
Researchers found that alcohol consumption alters the structure and function of neurons in dorsomedial striatum, a part of brain known to be important in goal-driven behaviours.
Jun Wang, an assistant professor in the Department of Neuroscience and Experimental Therapeutics at the Texas A&M College of Medicine, and his team have used an animal model to determine that alcohol actually changes physical structure of medium spiny neurons, the main type of cell in the striatum.
These neurons can be thought of like a tree, with many branches, and many small protrusions, or spines, coming off of them. They each have one of two types of dopamine receptors, D1 or D2, and so can be thought of as either D1 or D2 neurons.
D1 neurons are informally called part of a "go" pathway in the brain, while D2 neurons are in the "no-go" pathway. In other words, when D2 neurons are activated, they discourage action.
Although it is well known that the neurotransmitter dopamine is involved in addiction, this study goes further, showing that the dopamine D1 receptor also plays an important role in addiction, researchers said.
The team found that periodic consumption of large amounts of alcohol acts on D1 neurons, making them much more excitable, which means that they activate with less stimulation.
"If these neurons are excited, you will want to drink alcohol. You'll have a craving," Wang said.
When neurons with D1 receptors are activated, they compel one to perform an action - reaching for another bottle of tequila, in this case. This then creates a cycle, where drinking causes easier activation, and activation causes more drinking, researchers said.
These changes in activation of D1 neurons might be related to the physical changes happening at the sub-cellular level in brains that have been exposed to alcohol.
They have longer branching and more of the mature, mushroom-shaped spines - the type that stores long-term memories - than their abstaining counterparts.
Conversely, the placebo group, the ones not exposed to alcohol, tended to have more of the immature versions of the mushroom-shaped spines in D1 neurons of their brains.
The total number of spines didn't change in the two groups, but the ratio between mature and immature was dramatically different between the alcohol group and the placebo group.
The alcohol-consuming animal models with the increased mature spines in D1 neurons also showed an increased preference to drink large quantities of alcohol when given the choice.
When those same animal models were given a drug to at least partially block the D1 receptor, they showed much-reduced desire to drink alcohol. However, a drug that inhibited the D2 dopamine receptors had no effect.
