It is these cells that make you feel cold hands and feet, nausea and vomiting when you are carsick

Image source: pixabay

The brain cells that cause your motion sickness may have been discovered.

By Clare Watson

Translation | Shi Xiaozhou

Editor | Huang Yujia

Imagine driving on a winding road. If that already makes you want to puke, spare a thought for the mice used in a new study that sought to identify the brain cells that cause motion sickness.

By placing unwitting mice in a plastic tube and tying them to a spinning wheel, the researchers were able to determine which neurons were activated by the stomach-churning merry-go-round.

As a result, the mice's body temperatures dropped, they refused to eat, and they curled up in their cages, all signs that they were experiencing a reaction very similar to motion sickness in humans. Have you ever broken out in a cold sweat when you're motion sick?

The culprit for motion sickness

Based on past research, neuroscientist Pablo Machuca-Márqueza of the Autonomous University of Barcelona in Spain and his colleagues thought they should start focusing on cells in the vestibular nuclei, a group of nerve fibers in the brainstem that carry signals from the ears to the brain.

Receptors in our middle ears, as well as our limbs and eyes, send sensory information to the brain, which determines our direction when we move. This mismatch in perception is thought to cause motion sickness: We are not moving, but our eyes and inner ears tell our brain that we are.

There are many areas of the brain that process sensory input from the ears, eyes, and limbs, but we don't know which neurons actually cause motion sickness. If we can pinpoint these neurons, it may be possible to invent more effective motion sickness drugs with fewer side effects.

Mice on a running wheel (Image source: original paper)

To find out which neurons are activated specifically by motion sickness, Machuca-Márquez and his colleagues inhibited different groups of neurons in the vestibular nuclei and then tied the mice back to the spinning wheels to see if motion sickness was alleviated.

The mice spun around and around, and the results showed that by inactivating a group of vestibular neurons that express a protein called VGLUT2, the animals no longer became motion sick.

If these neurons were activated, the mice would experience motion sickness-like symptoms even when they were not on the wheel. This perceptual dissonance was like a real trip.

The researchers found that within this group of neurons expressing the VGLUT2 protein, those cells with a receptor called CCK-A on their surface were responsible for inducing most of the motion sickness behaviors in the experiments.

Image source: pixabay

The researchers located these neural circuits and found that they project centrally to the parabrachial nuclei in the brain, an area known to be involved in regulating appetite suppression, body temperature, and sleepiness.

Stimulating these projecting neural circuits caused mice to experience some of the symptoms of motion sickness. Although their body temperature dropped and they avoided sweet foods, they still ate and moved around normally. Therefore, other neural connections originating from the vestibular nuclei may trigger the physical reactions associated with motion sickness.

If a drug is used to inhibit CCK-A in mice before they are put on the running wheel, only half of the neurons in the parabrachial nucleus will remain active, and the mice's motion sickness symptoms will be alleviated.

Most motion sickness medications work in similar ways: by reducing activity in the brain's balance system or limiting signaling between the brain and the gut, thereby preventing nausea and vomiting.

Image source: pixabay

However, these drugs are only moderately effective at best. They block chemical messengers that act throughout the body to induce drowsiness, and they are effective only if taken before motion sickness sets in; if taken after motion sickness sets in, they are largely ineffective.

In 2012, NASA announced that it was developing a fast-acting nasal spray to treat motion sickness, but we're still awaiting the results of their planned clinical trials.

The good news is that if the pathway discovered in this mouse study also works in humans, researchers may have a new, clearer target to attack motion sickness.

The study was published in the Proceedings of the National Academy of Sciences (PNAS).

Original link:

https://www.sciencealert.com/the-brain-cells-that-give-you-motion-sickness-may-have-been-identified