The field of optogenetics is all about using light to stimulate cells in the body, and so far it's been used to modify pain responses in mice, reset the biological clock, and restore regular heartbeats as a gentle alternative to defibrillation. Now, researchers from Flinders University have used the technique to shine a light where the Sun don't shine, stimulating nerves in the gut to relieve chronic constipation.

Laxatives are the most common treatment for constipation, but they're not really safe for long-term use. Other drugs may be prescribed for chronic cases, but these aren't always effective and can have other side effects. More creative solutions include a capsule containing a tiny motor, which starts vibrating once it reaches the intestine to stimulate the muscles into contracting and keeping bowel movements moving along.

The Flinders research uses pulses of light to achieve a similar outcome. The gastrointestinal tract is controlled by a network of neurons known as the enteric nervous system, and past research into optogenetics has shown that neurons react particularly well to light. The idea was that light would stimulate these nerves, causing the muscles to contract and evacuate the bowel.

To let there be light in that darkest of places, the researchers implanted micro-LEDs into the gut walls of mice. When wirelessly turned on, these LEDs emitted blue light in the gut, activating the excitatory nerves and successfully emptying the bowel.

In other optogenetics studies, scientists first need to engineer animals with cells that respond more readily to light, but the Flinders team says the new study shows this treatment can work on regular cells. That said, implanting LEDs in the intestines doesn't sound like an attractive idea, but there might eventually be easier ways for a light source to get to your gut – maybe as something similar to the tiny pill-like video cameras used to image the insides of patients.

"The ability to selectively stimulate transit along the gut in live mammals using light to stimulate specific regions of the gut could avoid the use of non-specific prescription drugs which can induce a long list of unpleasant side effects," says Nick Spencer, lead investigator on the study. "The most exciting aspect is that this optogenetic technology using light has already has been shown to work in targeting cells in other organs without breeding genetically modified animals, so this signals this approach could be applied one day to humans."

The research was published in the journal Gastroenterology.