When enticed by the smell of buttered popcorn, food-deprived nematodes are more willing to cross a toxic copper barrier to reach the smell of a snack compared to their well-fed counterparts
Hungry worms are more willing than satiated worms to cross a toxic barrier of copper to reach the scent of a meal.
While there is plenty of anecdotal evidence that hunger can make animals act impulsively, less is known about how hunger is signalled in the brain and how that signal shapes choices.
To better understand how hunger changes behaviour, Sreekanth Chalasani at the Salk Institute in California and his team turned to transparent roundworms called nematodes. They aimed to answer three key questions: how does hunger effect what is happening in the worm’s body, how is that change relayed to the brain and how does that ultimately shape choices?
The researchers placed around 60 nematodes (Caenorhabditis elegans) on one side of a barrier made of copper, which is toxic to them, with the smell of buttered popcorn wafting over from the other side. Half of the worms hadn’t eaten for 3 hours, while the others had eaten a recent meal.
Chalasani and his colleagues found that around 80 per cent of the hungry worms crossed the repellent copper to reach the food compared with around 20 per cent of their well-fed counterparts. When the hungry worms were fed, they reverted to the less-risky behaviour of satiated worms.
“If [the worm] is food deprived, it thinks, ‘I’m going to take that risk, because I’m getting hungrier, and so I have to make an effort to cross that barrier’,” says Chalasani.
After demonstrating that the starved worms take bold action to reach the smell of food, Chalasani wanted to find out what mechanism was triggering the hunger signal to the brain.
A genetic and imaging analysis pointed to certain proteins in the worms’ intestinal cells that may tell the brain that the gut needs food. The researchers also identified a receptor in the brain that they suspect is picking up the signal.
“The intestine then tells the brain, and the brain then changes behaviour,” says Chalasani. “That was a little bit surprising. We didn’t expect that the worm would have this level of sophistication.”
The work could help explain why some people behave irrationally when they have skipped a meal, as underlying biological patterns in nematodes often translate to humans. But Chalasani notes that being “hangry” doesn’t excuse poor behaviour. “I could be hungry and still not show it because [unlike a worm] my brain has the sophistication to suppress some of those feelings.”
Journal reference: PLOS Genetics, DOI: 10.1371/journal.pgen.1010178
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