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New research sheds light on why MS symptoms get worse in hot weather

People with MS often find their symptoms get worse when it’s hot. We know the movement of sodium into nerves is partially responsible. Research published today shows an existing drug can partially block this movement into the optic nerves of rats.

Everything we do is controlled by nerves sending messages from our brains to the rest of the body. These messages are created when different chemicals move in and out of nerves.

MS symptoms arise when messages can’t travel along nerves properly, often getting worse in hot weather, or when your body heats up from exercise or even just excitement. A team of researchers from Queen Mary University London are trying to understand why.

Lead researcher Dr Mark Baker has already shown that temperature effects happen in healthy nerves partly because heat speeds up the movement of sodium into nerves. The nerve then has to work harder to get rid of it and it becomes more difficult to transmit messages.

Finding ways to block sodium

Mark, and his MS Society-funded PhD student Lavinia Austerschmidt, teamed up with other scientists and doctors to find out how to reduce this movement.

They have shown a drug called bumetanide can partially stop it happening in rats. It does this by blocking a certain transporter which helps move sodium into nerves.

“The ultimate goal of our research is to discover useful drug effects that can help people feel better” says Mark. But as bumetanide was created to work in the kidneys, when people take the drug, it can’t get from the blood into the brain.

“We need people to develop a drug that affects sodium movement but can get into the brain” Lavinia adds, “I wish I could make my own drug, but I’m not a chemist.”

Looking at the data from all angles

Lavinia says “this is a very robust result, but it’s only one part of the story. We’re doing experiments on whole nerves, so there’s lots of things happening at once. We have to look at the data from all angles”.

“This new paper shows there is at least one more pathway into the nerve for sodium” says Mark. “It is clear now that other routes, yet to be fully identified, are working in parallel. We didn’t know that before”.

Exploring myelin damage

Lavinia is relieved the easing of lockdown meant she could get back to the lab. She’s keen to now see what happens if a nerve has lost its myelin. She says “we’ve seen a big effect in healthy nerves so we’d expect to see it in demyelinated nerves too”.

In MS, inflammation around the nerve might mean there isn’t enough energy to get rid of the sodium properly, causing even more problems for the nerve. Lavinia says this shows “it’s not just demyelination causing havoc in the optic nerve. Sodium movement may be another way to explain some of what’s going on”.

Dr Emma Gray, our Assistant Director of Research says: “Many people with MS tell us their symptoms get worse in the heat. We know changes in temperature can affect the way our nerves function. The research is still at an early stage, but Mark and Lavinia’s results could be a first step to finding treatments that can help with the effects of heat sensitivity.”

You can read the paper in full on the Nature website.