London, Nov 19 A hunger hormone produced in the gut can have a direct impact on a decision-making part of the brain, driving an animal's behaviour, a new study has found.
The study, published in the journal Neuron, is the first to show how hunger hormones can directly impact the activity of the brain’s hippocampus when an animal is considering food.
"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," said lead author Dr Andrew MacAskill (University College London (UCL) Neuroscience, Physiology & Pharmacology).
To conduct the study, the researchers placed mice in an arena with food and observed how the mice behaved when hungry or full while imaging their brains in real time to investigate neural activity.
The researchers focused on brain activity in the ventral hippocampus (the underside of the hippocampus), a decision-making part of the brain which is understood to help us form and use memories to guide our behaviour.
They found that activity in a subset of brain cells in the ventral hippocampus increased when animals approached food, and this activity inhibited the animal from eating.
However, when the mouse was hungry, there was less neural activity in this area, and the hippocampus no longer prevented the animal from eating.
The researchers discovered that this corresponded to high levels of the hunger hormone ghrelin in the blood.
This discovery has shown that the hunger hormone can cross the blood-brain barrier (which prevents many substances in the blood from reaching the brain) and directly impact the brain to drive activity, controlling a circuit in the brain that is likely to be the same or similar in humans, the study mentioned.
"It appears that the hippocampus puts the brakes on an animal’s instinct to eat when it encounters food, to ensure that the animal does not overeat -- but if the animal is indeed hungry, hormones will direct the brain to switch off the brakes, so the animal goes ahead and begins eating," MacAskill said.
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