Why Do Only Some People Become Addicted to Alcohol?
Theories About Addiction
The fact that not everybody who consumes a specific substance becomes addicted is an anomaly, which is actually a source of hope in scientific study. This is because if the same substance is given to two people and they both react differently, it implies that some variation in their psychological or genetic makeup is making one individual more likely to develop addiction. If this variation is identified, then it could lead to a more detailed understanding of the neurology and psychology of addiction, which could therefore help with treatment.
Although genetic factors are generally thought to play a role in the development of addiction, most researchers believe that environmental factors play a part as well. It’s estimated that between 40 percent and 60 percent of the risk of addiction comes from an individual’s biology, although this includes the effects of the environment on the “expression” of certain genes. Biological effects are evidently important because there is a widely reported genetic link, whereby somebody is more likely to become addicted to drugs if an immediate family member also was.
The other factors that can lead to drug addiction are more varied, spanning individual, family, peer and community links. This means that, for example, if a child has friends who abuse substances, that child is more likely develop a problem as well. Similarly, things like poor social skills can lead people to rely on substances to compensate in social situations. Factors such as growing up in poverty are also traditionally related to a risk of drug abuse.
The Problems and New Research
The main issues with this multi-faceted viewpoint on drug addiction are that they aren’t clearly actionable from a treatment perspective. It may well be that being a poor, aggressive teen with substance-abusing friends makes it more likely that you will develop an addiction, but there is little anybody involved with treatment can actually act on. This is the major benefit of genetic markers; they are much easier to measure objectively, which could lead to a novel treatment for drug addiction.
The new study looks into the effect of the locomotor response in mice exposed to alcohol. This response is generally related to the potential for addiction, and essentially quantifies the degree to which an individual is affected by a specific drug. The theory is that the greater the locomotor response, the greater the risk of developing a long-lasting addiction. The tests on drugs such as cocaine and amphetamine have confirmed this effect, but it’s never been specifically studied with relation to alcohol.
"We know that some people are much more vulnerable to alcoholism than others, just like some people have a vulnerability to cancer or heart disease," said Jeff Weiner, professor of physiology and pharmacology at Wake Forest Baptist Medical Center, which conducted the study. "We don't have a good understanding of what causes this vulnerability, and that's a big question. But if we can figure it out, we may be able to better identify people at risk, as well as gain important clues to help develop better drugs to treat the disease."
In order to ensure the mice were a closer model to the human population, they were bred to have a greater degree of genetic variability. There were basically two groups of mice in the study--those that received a saline (placebo) solution each day and the mice that were given alcohol.
Weiner said the study model focused on how individual animals responded to alcohol. Typically, when a drug like alcohol is given to a mouse every day, the way the animals respond increases--they become more stimulated and run around more. "In high doses, alcohol is a depressant, but in low doses, it can have a mellowing effect that results in greater activity," he said. "Those low dose effects tend to increase over time and this increase in activity in response to repeated alcohol exposure is called locomotor sensitization."
The first part of this study looked at the locomotor effect of the alcohol injection, showing that the brains of the mice that didn’t display a locomotor sensitivity to the alcohol actually responded similarly to those who received the saline solution. The researchers reported a huge degree of variation in the sensitivity to alcohol, and the effect of this was tested in the second part of the research.
In order to determine whether a mouse’s sensitivity to the effects of alcohol had an impact on whether it continued to drink, the researchers allowed the alcohol-exposed mice to choose whether to drink more alcohol. The researchers found that mice that weren’t as sensitive to alcohol drank about as much as the control group, whereas the sensitive mice drank much more. These same mice also had deficits in neuroplasticity, which is the ability of the brain to adapt its structure based on its experiences. This has also been linked to addictions to substance such as cocaine, so it could also help to explain addiction as a whole.
"We found that this loss of the ability of brain cells to change the way that they communicate with each other only occurred in the animals that showed the behavioral response to alcohol," Weiner said. "What this suggests for the first time in the alcohol addiction field is that this particular deficit may represent an important brain correlate of vulnerability to alcoholism. It's a testable hypothesis. That's why I think it's an important finding."
The new research is an important step in understanding all of the various biological factors that could lead to drug addiction. The topic is still a fertile area for research, because the more we come to understand how different substances interact with the brain, the more we’ll be able to help those suffering from addiction with targeted treatments.