Ravenous neurones

It’s been discovered that nerve cells can sense not just how much food we’ve eaten but the nutritional balance of a meal. Since the cells’ output affects appetite and how awake the individual feels it could explain how animals are instinctively able to eat a nice balanced diet. And for humans, it could lead to the development of a nutrient formulation that curbs hunger and acts as a treatment for obesity.

It’s important for animals – including humans – to eat a balanced diet so they get the right nutrients in the right proportions to stay healthy. And, really, it’s amazing that animals can generally do this automatically, without thinking about it.

The brain is known to contain several populations of nerve cells which respond to nutrients in our food by regulating how awake and energetic we feel. It’s probably through mechanisms involving these cells that animals normally know subconsciously roughly what to eat.

Dennis Burdakov and his team at the University of Cambridge have been working on these nutrient-sensing nerve cells. They showed a few years ago that one cell type – orexin neurones – are down-regulated when they sense increased sugar levels, meaning the animal will feel less hungry. Now they’re reporting in the journal Neurone that the cells are also sensitive to another vital nutrient; amino acids, the component pieces of proteins.

Burdkov’s team measured the electric voltage across nerve cells which had been placed in different concentrations of an amino acid mixture. They found that the cells were unexpectedly and very significantly up-regulated – the complete opposite of the results they had obtained with sugars. The same was true of cells in live mice which had been fed a similar mixture.

It seems to make intuitive sense that once a neurone senses an increased sugar concentration – usually as a result of the brain’s owner having a nice snack – that the urge to eat more should be toned down. But in this case, the results seemed to show that eating protein simply makes you want to eat more protein. It was a bit odd.

Digging deeper, the scientists noticed a difference between non-essential amino acids (NEAAs) – the ones we can make in our bodies – and essential ones (EAAs) – which we have to get from our diet. When they tested individual amino acids the scientists found that, actually, EAAs on their own had little effect on the nerve cells, it was the non-essential ones which caused the increased activity.

Speaking on BBC local radio, Burdakov had an explanation. “If you eat a meal which is unbalanced and contains too many non-essential amino acids, which you can make in the body, these cells will make you keep eating until you find some essential amino acids.”

Although the cells are sending signals to say, ‘keep eating,’ their complex effects on behaviour also mean they are telling the body to wake up a bit and burn more calories. “So overall they would keep your bodyweight down,” said Burdakov.

“And that’s the exciting thing,” continued Burdakov, “possibily we can find a dietary combination of nutrients now which can tune the cells and control bodyweight as well as alertness, and that’s what we’re working on right now.”

An edited version of this article was also published at London Student.

Image credit: Wellcome images.

[1] M. M. Karnani et al., Neurone, 2011, (72), 4, 616-629.

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