Researchers at the University of Texas at Dallas may have found a new way to help people overcome drug addiction.
Dr. Sven Kroener, assistant professor in the School of Behavioral and Brain Sciences at UT Dallas, led a study that used vagus nerve stimulation on drug-addicted rats. The report, published in the journal Learning & Memory, found that drug cravings reduced among rodents when treated using this technique.
Kroener believes VNS could effectively be used to treat humans with a substance use disorder.
“When we started the study, there was evidence that VNS facilitates the extinction of fearful memories, or fear extinction,” Kroener told DrugRehab.com. “We wanted to see if VNS can also facilitate extinction of appetitive behavior such as drug-seeking behavior and prevent reinstatement, or relapse, to drug seeking.”
VNS is a therapy that sends electric signals to the brain, and it is currently used in humans with certain conditions. This technique involves implanting a small device into the left side of a person’s chest. When activated, the machine sends low-level pulses of electric current through a wire to the vagus nerve, which extends from the abdomen to the brainstem.
The current passes through the nerve to the brainstem, which then sends signals to other areas in the brain.
Kroener and a small team of researchers spent nearly four years experimenting with VNS on rats. The results could provide groundwork for future studies on VNS and addiction in humans.
For the study, graduate student Jessica Childs applied VNS to rats in a process called extinction learning. Extinction learning refers to the gradual decrease of a previously learned behavior when the behavior is not reinforced.
Through this process, animals acquire new habits to compete with previously learned ones. The researchers aimed to determine whether the VNS can teach rats to learn new behaviors to reduce drug cravings.
Russian physiologist Ivan Pavlov famously tested the theory of extinction on dogs. He conducted an experiment in which he rang a bell and then gave food to the animals. Over time, they became conditioned to salivate at the sound of a bell.
When Pavlov repeatedly presented the bell without food, the salivation response decreased in intensity.
In the UT Dallas study, rats pressed a lever that delivered cocaine and also triggered a tone and a light. The rodents learned to self-administer the drug during daily two-hour sessions for 12 to 15 days.
“They love to press the lever because they know it will give them cocaine,” Kroener explained. “Then we give them the tone, the light comes on … [and] they start to associate that with the cocaine.”
That’s what happens with drug addiction too, he says.
“[A person with a substance use disorder] begins to associate their environment with the drug-taking experience,” he said. “It could be a bar or a neighborhood. That environment triggers their craving for the drug.”
At a certain point in the study, the rats no longer received the drug upon pressing the lever, and the light and tone disappeared. This two-hour extinction training period lasted 12 days. During this time, the animals received electric pulses every five minutes.
Researchers also conducted a second trial in which rats received a brief burst of VNS pulses only when they pressed the lever during extinction training. The lever still did not produce the drug or the tone and light.
Both sets of rats were compared against a control group that did not receive electrical stimulation.
Although the rats treated with VNS did not forget the drug-paired cues, they learned something new to compete with the old memories. Over time, these rodents pressed the lever less often but rarely stopped pressing it entirely.
Researchers eventually reinstated the light and tone but not the cocaine. While this caused the rats to crave the drug, these urges were less intense than before in animals that had received VNS during their extinction training.
Some studies have examined the effectiveness of VNS in treating certain types of epilepsy. The Food and Drug Administration has approved VNS for people who are aged 12 and older, have partial epilepsy and have seizures that aren’t well controlled with medications.
Additionally, the FDA has approved this technique for the treatment of adults who have difficult-to-treat depression and for those whose depression hasn’t been reduced through the use of medications or electroconvulsive therapy.
A 2016 study published in Proceedings of the National Academy of Sciences showed that VNS significantly reduces symptoms of rheumatoid arthritis, a chronic inflammatory disease that affects 1.3 million people in the United States.
However, VNS may cause side effects after surgery, including throat pain, cough, breathing problems and insomnia. Adjusting the electrical impulses could reduce these effects.
VNS devices that do not require surgical implantation have been approved for use in Europe to treat depression, epilepsy and pain. However, these devices have yet to be approved by the FDA for use in the United States.
Kroener began this study to find out if VNS can effectively treat psychostimulant abuse. He said he was surprised at the results.
“I was surprised at how well [the study] worked,” said Kroener.
He is currently investigating how long the beneficial effects of VNS last. Are animals that received VNS still protected against drug cravings if they remain in their cages for one month without further treatment? And could this therapy method help people overcome addiction?
He hopes to answer these questions in the future.
“If you do behavioral therapy, exposure therapy and pair this with VNS, then I would predict this is beneficial in humans,” said Kroener.
However, he says more research must be conducted to confirm this theory.
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