New research sheds light on why methamphetamine addicts continue to crave the drug long after breaking the habit: Meth causes particularly long-lasting changes in the brain.
Nigel Bamford, assistant professor of neurology and pediatrics at the University of Washington, and colleagues report in the April 10 issue of Neuron on the effects of meth on three neurotransmitters, which carry messages between neurons in the brain.
In a normal brain, something new or interesting in the environment triggers the release of large amounts of the neurotransmitter dopamine. The elevated dopamine causes a drop in another neurotransmitter, glutamate. The result is a filtering of irrelevant information and a strong focus on a single object or event. After the novelty disappears, dopamine decreases and glutamate levels return to normal.
The researchers administered meth to mice for 10 days, equivalent to chronic use in humans. They found that meth use prompts an increase in dopamine and a decrease in glutamate, just as novel stimuli do, but the system does not reset itself after the drug is gone: Glutamate levels in the mice stayed low for 140 days. Although animal models do not necessarily translate to people, “That’s perhaps 30 years for humans,” Bamford says. “It just doesn’t go away.”
The source of the chronically lower glutamate is yet another neurotransmitter, acetylcholine. After prolonged meth use, its level in the brain stays low, effectively blocking glutamate release. Long after the last meth dose, only another dose can reverse the trend and return glutamate levels to normal.
“Now that we have some understanding of the mechanism through which meth addiction occurs, we may be able to develop other approaches to treatment,” Bamford says. The findings could have implications in other disorders that share some of the same brain circuitry, he adds.