A study on mice has shown how gut-produced hunger hormones can influence decision-making and drive an animal’s behaviour. The researchers said that the findings demonstrate how the hunger hormone can cross the blood-brain barrier 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 blood-brain barrier is known to strictly restrict many substances in the blood from reaching the brain. The findings, published in the journal Neuron Researchers are the first to show how hunger hormones can directly impact the activity of the brain’s hippocampus, when an animal is considering food.
Lead author Dr. Andrew MacAskill (UCL Neuroscience, Physiology & Pharmacology) 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.”
This research put mice in an arena that had some food and looked at how the mice acted when they were hungry or full. While all the mice spent time investigating the food, only the hungry ones would begin eating, the researchers at University College London, UCL UK, found.
They also used brain imaging to study activity in the mice’s ventral hippocampus, which is a decision-making part of the brain, understood to help form and use memories to guide behaviour.
The researchers found that activity in a subset of brain cells in the ventral hippocampus increased when the mice approached the food and that this neural activity inhibited them from eating. However, when the mice were hungry, less neural activity in this brain region was observed and, therefore, they were not inhibited from eating.
The researchers also found that this corresponded to high levels of the hunger hormone ghrelin circulating in the blood. Further, by activating these ventral hippocampal neurons, the researchers were able to experimentally make mice behave as if they were full and therefore stopped eating.
Dr. MacAskill added: “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.”
First author Dr. Ryan Wee (UCL Neuroscience, Physiology & Pharmacology) 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.”