Fasting for chronic pain?

Hunger displaces pain in mums

Chronic pain can make everyday life hell. © Pixologic / thinkstock
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Instead of painkillers: hunger apparently works against chronic pain - at least in mice. A study shows: If they are hungry, the animals perceive less painful inflammation. Through this trick, the brain ensures that the rodents go in search of food despite the pain - and can survive, as researchers report in the journal "Cell". Should a similar circuit exist in humans, new therapies for chronic pain could result.

Hardly any sensation is more painful than pain - but the feeling can be vital. It teaches us not to put our hand on a hot plate or signal when the body needs protection. At the same time, however, pain can also be detrimental: if it becomes too prominent over a longer period of time. Then it stops us from making our everyday lives normal and may even lead us to neglect other important needs.

For animals, this also applies: With them, chronic pain could even endanger survival, for example, if they no longer go looking for food. Scientists led by Amber Alhadeff at the University of Pennsylvania wanted to know: how does the body handle this dilemma? "We were interested in how the brain processes competing needs to produce optimal behavior, " says Alhadeff's colleague Nicholas Betley.

Hunger covers pain

To find out, the researchers set mice on a 24-hour fasting cure. How would the rodents respond to acute pain or dull, chronic inflammatory pain compared to non-hungry animals, such as those that occur for a long time after an injury?

The astounding result: on acute pain stimuli, caused among other things by a hot heating plate, the hungry mice reacted just like their conspecifics. But the chronic inflammatory pain that the team caused by injecting certain active ingredients into the paws of the animals left them relatively cold. So the rodents licked their inflamed paws less often. In addition, unlike their busy cronies, they did not avoid the place where the pain had been inflicted on them. display

What is more important: pain or hunger? Sam Alhadeff

Like a painkiller

The mice behaved the same way as the rodents who had been given medication for the pain. In short, hunger seemed to have a similar effect to a potent analgesic. "We would not have expected that hunger would change our perception of pain that much, " says Alhadeff.

The question was, which circuit in the brain is behind this amazing phenomenon? The researchers already knew that so-called AgRP neurons are active during starvation. Therefore, they looked more closely at these neurons and activated them artificially. It turned out: The mice in this case showed the already known behavior although they were not really hungry at all.

Controlled by 300 neurons

In order to find out which subpopulation of the AgRP neurons is responsible for the influence of hunger on pain signals, the team switched on the different groups of neurons in the experiment in succession. They found that the stimulation of a tiny population of brain cells in the so-called parabrachial nucleus clearly suppressed the inflammatory pain.

"Only about 300 billion neurons in the brain control this specific behavior, " says Betley. Further experiments finally showed that a neurotransmitter called NPY suppresses the transmission of pain signals in these neurons. Blocked the researchers receptors for this messenger, the pain came back despite hunger.

Hierarchy ensures survival

"Our results show that there is a sort of hierarchy in the brain to prioritize behavior, " states Betley. "A competitive situation arises between different stimuli, before something like pain is perceived at all."

Nature has implemented a clever strategy in this way: It ensures that animals look for food, even if they have chronic pain and still respond meaningfully to acute pain stimuli. In other words, that they do what is most important to their survival.

New Approach to Therapies?

In the long run, these findings could also affect how people deal with human pain, scientists hope. "If there's a similar circuit here, it may open new avenues for the treatment of chronic pain, " they conclude. (Cell, 2018; doi: 10.1016 / j.cell.2018.02.057)

(Cell Press / University of Pennsylvania, 26.03.2018 - DAL)