A new study in Nature Metabolism explains a molecular process behind how the brain prepares the body before a meal. It focuses on pro-opiomelanocortin (POMC) neurons in the hypothalamus, which signal satiety and activate when food is anticipated as well as during eating. The researchers found that pockets of glycogen inside POMC neurons fuel this anticipatory activity.
To test sensory activation, mice were shown food behind a wire mesh so they could see and smell it but not eat it. Food exposure activated glycogen synthase, the enzyme that builds glycogen. Mice engineered without glycogen synthase in POMC neurons showed weaker responses: they approached food less, spent less time eating, and failed to produce insulin before feeding.
Injecting a virus to remove the enzyme in adult mice produced similar effects, so the cause was not developmental. The team also mapped connections and found that POMC neurons link with smell-processing brain regions but not visual ones. Over time, mutant mice became obese and showed indicators of prediabetes, suggesting impaired brain anticipation may contribute to obesity and diabetes.
Difficult words
- hypothalamus — brain area that controls many body functions
- neuron — nerve cell that sends signals in the brainneurons
- glycogen — stored form of sugar used by cells for energy
- glycogen synthase — enzyme that makes glycogen inside cells
- satiety — feeling of fullness after eating
- anticipatory activity — brain activity before a meal begins
- engineer — change genes or cells by scientific methodsengineered
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Discussion questions
- Why might brain anticipation of food be important for normal eating behaviour? Give one or two reasons.
- How could the finding about glycogen in POMC neurons affect ideas about obesity or diabetes?
- What differences would you expect between a mouse that can smell food but not eat it and one that can eat immediately?
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