Neurons that drive mice to eat also tamp down pain caused by inflammation.

A brain circuit that affects food intake can also suppress some forms of pain in mice.

Animals must be able to prioritize competing claims for their attention, including hunger and pain. To learn how, Nicholas Betley at the University of Pennsylvania in Philadelphia and his colleagues deprived mice of food and found that the rodents spent less time licking a sore paw compared to well-fed counterparts. The team traced this effect to brain cells that express a protein called AgRP. These neurons are known to drive eating.

The researchers showed that AgRP neurons also block pain — but only the long-lasting pain of inflammation, which the researchers induced by injecting the mice with a toxic chemical. The neurons did not inhibit the acute pain of the injection itself.

Acute pain suppressed food-seeking behaviour in hungry mice, whereas inflammatory pain did not. The findings collectively show how the brain ranks opposing survival needs, the authors say.