Brain cells called astrocytes help put the brakes on heroin relapse. Researchers long focused on neurons. But this mouse study found that astrocytes play a vital role in whether relapse happens. Astrocytes are glial cells once seen as mere support cells. That gives researchers a new target for preventing relapse.
Summary: Drug or opioid addiction treatment is hard, and preventing relapse is even harder. For decades, researchers focused on neurons and brain centers. They wanted to see how the brain changes with drug addiction and heroin relapse. Now they see that cells once thought of as mere support seem to play a vital role in heroin relapse. These are glial cells like astrocytes.
Substance-related disorders or drug addiction is a major problem. Among street drugs, heroin is still the biggest problem. It is an illegal opioid. Deaths from heroin overdose among young adults are not rare in the US.
SUD (substance use disorder) is not just a behavior problem. It is a brain disorder. Some people are prone to SUD because of changes in the brain. But we still know little about which changes in brain structure or chemistry cause SUD. There are many theories. Also, some people treated for heroin addiction are more likely to relapse.
In recent years, researchers have paid close attention to substance-related disorders. Most addictions share common traits. But researchers know some brain changes are unique to one substance. That is why some people are prone to alcohol addiction, others to heroin, and so on.
When researchers study addiction effects on the brain, they have mostly looked at neurons. Neurons are the main brain cells behind thinking and other mental skills. Researchers have found many changes in many parts of the brain. For example, they now better understand the role of the reward pathway in addiction. They have also found the role of brain chemicals like dopamine in addiction and relapse.
But health experts know there is still a lot to learn. For example, many drugs can change how dopamine or the reward pathway works. Yet they fail to prevent heroin relapse in many people.
Researchers think they have failed to find treatments for heroin addiction signs and many other brain disorders for one reason. They focused too much on neurons. Neurons drive our mental skills. So it is easy to conclude that broken neurons cause brain disorders.
But there are other types of brain cells too. For example, the human brain has glial cells, and they outnumber neurons. People thought they were just support cells. They hold neurons in place and play a key role in the brain’s energy use and immunity.
Now researchers see that glial cells also help run the brain. It seems they control how active neurons are. Astrocytes, a type of glial cell, make brain chemicals like glutamate to control neuron activity. They seem to act like traffic lights in the brain. So they may change how neurons work significantly. Now studies suggest that broken astrocytes have a lot to do with heroin relapse.
In a new study, researchers used mice to study heroin addiction. First, they used a standard addiction model. The mice get a dose of heroin by pressing a button. They are also given cues like a light and a sound. The next time the cues come, the mice know the heroin or substance is there.
This way, they were able to cause signs of heroin addiction, withdrawal, craving, and relapse in mice. They found significant changes in how astrocytes worked in the mice that relapsed. In these mice, astrocytes moved farther away from neurons. So they were less able to act as brakes. They were also less likely to use glutamate to stop drug-seeking. The researchers concluded that this altered astrocyte plasticity plays a central role in heroin relapse.
It is still early in this research. But it is clear that drugs that change glutamate activity are not enough. We need medicines that change how astrocytes work. If experts can find a way to tune astrocytes, they can also change how neurons work. That would strengthen this brake and help in preventing heroin relapse.
Frequently asked questions
What happens in the brain when someone relapses on heroin?
In the mouse study behind this article, relapse came with a change in astrocytes. These are the glial cells that act like traffic lights for neurons. In the mice that relapsed, astrocytes moved farther away from neurons. They used less glutamate to hold back drug-seeking. The brake weakened, and the cue of a light or a sound won. The researchers concluded that this altered astrocyte plasticity plays a central role in heroin relapse.
Why is heroin relapse so hard to prevent?
Because treatment research has aimed almost entirely at neurons. Many drugs can adjust dopamine and the reward pathway. Yet they fail to prevent heroin relapse in many people. Glial cells outnumber neurons, and astrocytes seem to control the brakes. Drugs that only change glutamate activity are not enough. The next step is a medicine that acts on astrocytes and restores that brake.
Is opioid addiction a brain disorder or a behavior problem?
It is a brain disorder. Substance use disorder is not just a behavior problem. It is a brain problem. Some people are more prone to it because of changes in the brain. Most addictions share common traits, but some brain changes are specific to one substance. That is why one person is drawn to alcohol and another to heroin. It is also why some people treated for heroin addiction are more likely to relapse.
Related reading
Blood-Brain Barrier and Neurological Disorders · Adverse Childhood Conditions and Mental Health · CBD Remedy for Opioid Addiction