Stimulating the vagus nerve of rats deters them from seeking cocaine, suggesting that this therapy could help treat drug addiction and prevent relapse in substance use disorders.
The vagus nerve is a bundle of nerve fibres connecting the brain to most internal organs. Previous research has shown that stimulating it with electrical devices called vagus nerve stimulators can treat various conditions, including depression and opioid withdrawal. at the University of Texas at Dallas and his colleagues investigated whether vagus nerve stimulation affects other aspects of addiction too, such as cravings.
To do so, they surgically implanted a cuff that wraps around the vagus nerve in 21 rats. They then placed the animals inside a cage with a lever for 2 hours daily. When the rats pulled the lever, they received cocaine. The lever also cued a sound and flashing light, which the animals learned to associate with the drug.
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After 10 days, lever pulls no longer delivered cocaine, and the sound and lights also stopped. The researchers then electrically stimulated the vagus nerve of 11 of the rats intermittently during daily 2-hour sessions for the following 10 days. All of the rats pulled the lever less and less as the days went on. Then, on day 21, the researchers triggered drug cravings in the animals by setting the lever to once again cue the sound and flashing light, but not release cocaine.
They found that in this final 2-hour session, rats that had received vagus nerve stimulation pulled the lever an average of 30 times, whereas those that didn鈥檛 pulled it almost 90 times. Driskill says this suggests that vagus nerve stimulation reduced trigger-related drug cravings in the animals. This trigger may be similar to the way driving by a bar or seeing a needle can elicit cravings in people with substance use disorders, says Driskill.
Previous research has shown that drug use can disrupt a molecule in the brain called brain-derived neurotrophic factor, or BDNF, and that vagus nerve stimulation increases the amount of BDNF in the brain. So, the researchers repeated their lever-pulling experiment, but blocked receptors for BDNF in the brains of nine rats. This time, vagus nerve stimulation didn鈥檛 significantly reduce how often the animals pulled the lever in response to cues, which suggests that BDNF may be one of the mechanisms for how this therapy treats drug cravings.
鈥淸Drug addiction] is an area where there is not a lot of therapeutic options to treat people or help people,鈥� says Driskill, who presented this data on 12 November at the Society for Neuroscience conference in Washington DC. 鈥淚 think vagus nerve stimulation is promising. But obviously, any time you work in an animal, the question is how well will this translate to humans?鈥� he says.
Vagus nerve stimulation usually requires surgery, too. 鈥淭he risk-benefit ratio would have to be explored in terms of the risks of surgery versus the benefits of perhaps reduced rates of relapse,鈥� says at the University of Colorado. 鈥淚t would also be interesting to know if similar effects could be achieved with non-invasive vagus stimulation,鈥� she says, such as those that target the nerve through skin.
