A hunger hormone produced in the gut can directly impact an area of the brain responsible for decision-making in animals, a study has found.
Researchers from University College London tested how mice acted when they were hungry or full, while imaging their brains in real time to investigate neural activity.
They focused on brain activity in the ventral hippocampus, a part of the brain focused on decision-making which helps us form memories that guide our behaviour.
The mice were first put in an arena containing food. All of the animals spent time investigating the food, but only the hungry animals would begin eating, the study found.
When mice approached the food, activity in a subset of brain cells in the ventral hippocampus increased. This stopped the animal from eating.
But if the mouse was hungry, there was less neural activity in this area, so the hippocampus no longer stopped the animal from eating. This corresponded to high levels of the hunger hormone ghrelin circulating in the blood.
Lead author Dr Andrew MacAskill, from UCL’s Neuroscience, Physiology and Pharmacology department, said: “We all know our decisions can be deeply influenced by our hunger, as food has a different meaning depending on whether we are hungry or full. Just think of how much you might buy when grocery shopping on an empty stomach.
“But what may seem like a simple concept is actually very complicated in reality; it requires the ability to use what's called ‘contextual learning’.
“We found that a part of the brain that is crucial for decision-making is surprisingly sensitive to the levels of hunger hormones produced in our gut, which we believe is helping our brains to contextualise our eating choices.”
Researchers were able to experimentally make mice behave as if they were full, by activating neurons in the ventral hippocampus. This led animals to stop eating even if they were hungry.
The scientists achieved this result again by removing the receptors for the hunger hormone ghrelin from these neurons.
Ghrelin was found to be capable of crossing the blood-brain barrier and directly impacting the brain to drive activity, controlling a circuit in the brain that is likely to be the same or similar in humans. The barrier stops most substances in the blood from reaching the brain.
First author Dr Ryan Wee, of UCL's neuroscience, physiology and pharmacology's department, said: “Being able to make decisions based on how hungry we are is very important.
“If this goes wrong it can lead to serious health problems.
“We hope that by improving our understanding of how this works in the brain, we might be able to aid in the prevention and treatment of eating disorders.”
The study is published in the Neuron journal.
