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Repeated methamphetamine use causes long-term adaptations in brains of mice, researchers find
April 10, 2008Repeatedly stimulating the mouse brain with methamphetamine depresses important areas of the brain, and those changes can only be undone by re-introducing the drug, according to research at the University of Washington and other institutions. The study, which appears in the April 10 issue of the journal Neuron, provides one of the most in-depth views of the mechanisms of methamphetamine addiction, and suggests that withdrawal from the drug may not undo the changes the stimulant can cause in the brain.
The researchers set out to determine what sort of changes happen in the brain because of repeated use of the stimulant methamphetamine, and to better understand addiction-related behaviors like drug craving and relapse. Methamphetamine, also known as simply meth, is one of the most popular illegal drugs in the United States, and abuse of the drug can cause severe addiction.
Scientists have believed that abuse of drugs like meth can cause changes to the neurons in the brain and the synapses and terminals that control transmission of information in the brain. In this project, researchers focused on the mouse brain, and how it was affected by methamphetamine over 10 days, which is the mouse equivalent of chronic use in humans.
They found that the long administration and withdrawal of the drug depressed the neural terminals controlling the flow of signals between two areas of the brain, the cortex and striatum. Even a long period of withdrawal -- the equivalent of years in humans -- did not return the terminals to normal activity level. Re-introducing the drug, however, reversed the changes in the brain.
The areas affected by the drug are called pre-synaptic terminals, and are related to the flow of information from the cortex to the striatum. When a person sees something new in their environment, the scientists explained, she focuses attention on that item. At the neuron level, that process stimulates the release of dopamine, a chemical involved in transmitting signals in the brain. As the person sees the new item over and over again, the dopamine response drops, and synapses in the brain adapt to the no-longer-new item.
What happens with methamphetamine use is that the drug makes the nervous system release dopamine, which helps a user focus a lot of attention on a particular goal. Scientists believe that meth allows dopamine in the striatum to filter information coming from the cortex through the pre-synaptic terminals. The filtering of some of the terminals would help someone ignore other things and focus on that one goal or task.
After chronic use of methamphetamine, the filtering process eventually becomes a permanent depression in the activity of those terminals in the brain, the scientists found. And the only thing that can help the pre-synaptic terminals recover in mice, they found, was re-administering the drug.
"What we found is that the repeated use of methamphetamine causes adaptations in the brain, and that only re-introducing the drug can reverse that," said Dr. Nigel Bamford, UW assistant professor of neurology and pediatrics and a physician at Seattle Children's Hospital. "We think these changes in the brain may account for at least some of the physiological components of meth addiction."
If the mechanism turns out to be similar in people, Bamford said, this could have big effects on the treatment and management of methamphetamine addiction. One treatment for drug addiction is to give people smaller and smaller amounts of the drug to wean them from it and reduce the effects of withdrawal. Unfortunately, that method would not affect the adaptation of the neural terminals in the brain.
"Now that we have some understanding of the mechanism through which meth addiction occurs, we may be able to develop other approaches to treating addiction," explained Bamford. "We might be able to target some of the chemical receptors in the brain to reset the system and get rid of this depressed state in the pre-synaptic terminals."
Though scientists believe that other stimulants, like methylphenidate, may have similar effects on the brain, they caution against applying these findings to other situations. These synaptic changes may not occur in patients with underlying conditions that require treatment with stimulants, the scientists said.
University of Washington
They found that the long administration and withdrawal of the drug depressed the neural terminals controlling the flow of signals between two areas of the brain, the cortex and striatum. Even a long period of withdrawal -- the equivalent of years in humans -- did not return the terminals to normal activity level. Re-introducing the drug, however, reversed the changes in the brain.
The areas affected by the drug are called pre-synaptic terminals, and are related to the flow of information from the cortex to the striatum. When a person sees something new in their environment, the scientists explained, she focuses attention on that item. At the neuron level, that process stimulates the release of dopamine, a chemical involved in transmitting signals in the brain. As the person sees the new item over and over again, the dopamine response drops, and synapses in the brain adapt to the no-longer-new item.
What happens with methamphetamine use is that the drug makes the nervous system release dopamine, which helps a user focus a lot of attention on a particular goal. Scientists believe that meth allows dopamine in the striatum to filter information coming from the cortex through the pre-synaptic terminals. The filtering of some of the terminals would help someone ignore other things and focus on that one goal or task.
After chronic use of methamphetamine, the filtering process eventually becomes a permanent depression in the activity of those terminals in the brain, the scientists found. And the only thing that can help the pre-synaptic terminals recover in mice, they found, was re-administering the drug.
"What we found is that the repeated use of methamphetamine causes adaptations in the brain, and that only re-introducing the drug can reverse that," said Dr. Nigel Bamford, UW assistant professor of neurology and pediatrics and a physician at Seattle Children's Hospital. "We think these changes in the brain may account for at least some of the physiological components of meth addiction."
If the mechanism turns out to be similar in people, Bamford said, this could have big effects on the treatment and management of methamphetamine addiction. One treatment for drug addiction is to give people smaller and smaller amounts of the drug to wean them from it and reduce the effects of withdrawal. Unfortunately, that method would not affect the adaptation of the neural terminals in the brain.
"Now that we have some understanding of the mechanism through which meth addiction occurs, we may be able to develop other approaches to treating addiction," explained Bamford. "We might be able to target some of the chemical receptors in the brain to reset the system and get rid of this depressed state in the pre-synaptic terminals."
Though scientists believe that other stimulants, like methylphenidate, may have similar effects on the brain, they caution against applying these findings to other situations. These synaptic changes may not occur in patients with underlying conditions that require treatment with stimulants, the scientists said.
University of Washington
Methamphetamine Current Events and Methamphetamine News RSSLocal health investigation sheds light on gastroschisis birth defect
Results of an investigation conducted by University of Nevada, Reno researchers, public health officials and area physicians published this week in the Archives of Pediatrics & Adolescent Medicine, indicate that Washoe County experienced a cluster of a particular birth defect, gastroschisis, during the period April 2007 - April 2008.
Wastewater used to map illicit drug use
A team of researchers has mapped patterns of illicit drug use across the state of Oregon using a method of sampling municipal wastewater before it is treated.
Risky sexual behavior among male clients of Tijuana sex workers heightens risk of HIV transmission
A study by a bi-national team of global health researchers at the University of California, San Diego School of Medicine, examining HIV infection among male clients of female sex workers in Tijuana, has found that over half of male clients had recently had unprotected sex.
Brain protein central to both Parkinson's, drug addiction identified
Scientists have identified a protein that appears not only to be central to the process that causes Parkinson's disease but could also play a role in muting the high from methamphetamine and other addictive drugs.
Brain protein central to both Parkinson's, drug addiction identified
Scientists have identified a protein that appears not only to be central to the process that causes Parkinson's disease but could also play a role in muting the high from methamphetamine and other addictive drugs.
Prenatal meth exposure linked to abnormal brain development
A first of its kind study examining the effects of methamphetamine use during pregnancy has found the drug appears to cause abnormal brain development in children.
Methamphetamine use cost the US about $23 billion in 2005, RAND study estimates
The economic cost of methamphetamine use in the United States reached $23.4 billion in 2005, including the burden of addiction, premature death, drug treatment and many other aspects of the drug, according to a new RAND Corporation study.
Success of anti-meth ads questioned by study
An independent review investigating the effectiveness of a publicly funded graphic anti-methamphetamine advertising campaign has found that the campaign has been associated with many negative outcomes.
Methamphetamine abuse linked to underage sex, smoking and drinking
Teens who have never done drugs, but engage in other risky behaviours such as drinking, smoking and being sexually active, are more likely to use crystal meth, medical researchers at the University of Alberta have concluded.
Hope for treating relapse to methamphetamine abuse
A new study at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory suggests that vigabatrin (a.k.a. gamma vinyl-GABA, or GVG) blocks drug-seeking behavior in animals previously trained to associate methamphetamine with a particular environment.
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