Researchers can now make real-time observations of the gut’s nervous system.

Yes, your gut has its own nervous system.

“The first time I ever heard of the enteric nervous system was two years ago, and I was like; ‘What’s that?’” says Xiling Shen, associate professor of biomedical engineering at Duke University in the US.

“Even with neurobiologists, their only exposure to it is typically something like a half-page in a textbook. But it’s actually very important.”

The enteric nervous system is a mesh-like sheath of neurons that controls the gastrointestinal tract (gut).

Because it contains five times more neurons than the spinal cord, it is often termed the “second brain”.

It regulates how food moves through the digestive system and communicates potential problems to the immune system.

While it has a direct line to both the brain and spinal cord, the enteric system has the ability to direct the organs under its control independent of either system.

But despite its importance, very little is known about the enteric nervous system, such as how it responds to medications or what can go wrong with it to cause disease.

“About one-quarter of the world’s population is affected by a functional gastrointestinal disorder,” Shen said.

“You’ve probably heard of the term functional GI disorder, which encompasses diseases like irritable bowel syndrome, constipation and incontinence.

“If you look at the physiology in these diseases, the gut looks fine. It’s the nerves that are somehow malfunctioning. And the reason the term includes so many diseases is because we really don’t have any idea what’s going on with those nerves.”

But now, Shen is changing that, by installing an observation window.

The Duke team implanted a transparent window made of tough borosilicate glass into the skin over the stomachs of mice.

With no skull or bone structures to anchor the window, a 3D-printed surgical insert was used for stabilisation.

The device holds the intestines in place while maintaining normal digestive functions, allowing researchers to look at the same spot over multiple days.

The gut is a busy, noisy environment, so the team devised a system to record both electrical and optical activity at the same time - also a first for the field.

The experiment used transgenic mice with nerves that light up green when firing.

Using a transparent graphene sensor to pick up electrical signals from the nerves gave an unobstructed view of the neural activity.

“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 behaviours,” said 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.”

The full study is accessible here.