You've no doubt been urged to "go with your gut" when facing a tricky decision that you just can't seem to think your way through. It turns out, the gut can indeed act as something of a second brain, as it contains five times more neurons than the spinal cord. Despite this cache of neurological activity, the gut's nervous system has not been extensively observed. To fix that, a Duke University researcher did the logical thing – inserted a window in a mouse's abdomen so he could watch.

The window was made from a strong borosilicate glass – the same material that made Pyrex glass a favorite in the kitchen. To secure the window into place, associate professor of biomedical engineering at Duke University, Xiling Shen, first inserted a 3D-printed holder into the mouse's abdomen that allowed the digestive system to work normally while keeping the intestines from moving too much so that they didn't interfere with observations. The insert was sutured to the abdominal wall and the window was placed over it and secured in place with instant adhesive.

The mice used in the experiment were no ordinary rodents. They were transgenic mice that had been engineered to have nerves that light up green when firing. So with the window in place, Shen was able to watch as the gut's nervous system – known as the enteric nervous system – was activated by watching for flashes of green. What's more, he created a transparent graphene sensor that was able to read the electrical signals of the nerves and indicate their response to things like neurotransmitters, drugs and stimulation from light in real time.

With these two monitoring systems in place, Shen believes we can gain greater insight than ever before into the workings of the gut and hopefully help treat functional GI disorders – conditions where the nerves in our digestive system cause problems, such as irritable bowel syndrome, incontinence and constipation.

"So much is known about the brain and spinal cord because we can open them up, look at them, record the neural activities and map their behaviors," says Shen. "Now we can start doing the same for the gut. We can see how it reacts to different drugs, neurotransmitters or diseases. We have even artificially activated individual neurons in the gut with light, which nobody has ever done before. This innovation will help us understand this 'dark' nervous system that we currently have completely no idea about."

Shen's work was published in the journal Nature Communications on June 7. This video shows a portion of the observations he made.

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