Neuroscientists have found a way to alleviate pain with light.

Opiods have long been the best option for patients suffering from severe pain. The drugs interact with receptors on brain cells to tamp down the body's pain response. But now, researchers at Washington University School of Medicine in St. Louis have found a way to activate opioid receptors with light.

"It's conceivable that with much more research we could develop ways to use light to relieve pain without a patient needing to take a pain-killing drug with side effects," Edward R. Siuda, first author of the study, said in a statement.

But before that's possible, the researchers are attempting to learn the most effective ways to activate and deactivate the opioid receptor's pathways in brain cells. Bruchas, the study's principal investigator, explained that working with light rather than pain-killing drugs makes it much easier to understand how the receptors function within the complex array of cells and circuits in the brain and spinal cord.

Using a test tube, the scientists melded the light-sensing protein rhodopsin to key parts of opioid receptors to activate receptor pathways using light.

"It's been difficult to determine exactly how opioid receptors work because they have multiple functions in the body," Bruchas explained. "These receptors interact with pain-killing drugs called opiates, but they also are involved in breathing, are found in the gastrointestinal tract and play a role in the reward response."

When a person takes an opioid drug such as Vicodin or OxyContin to relieve pain, such drugs interact with receptors in the brain to blunt pain sensations. But over time, patients develop tolerance and sometimes addiction. Opioids also can dramatically slow a person's breathing, too, and typically cause constipation.

The eventual hope is to develop ways to use light to relieve pain, a line of discovery that also could lead to better pain-killing drugs with fewer side effects.

The findings are detailed in the journal Neuron.