Health UK (Commonwealth Union) – A recent study conducted by UCL researchers reveals that a hunger hormone originating in the gut has the capacity to directly influence a crucial decision-making region of the brain, steering an animal’s behavior. Published in Neuron and based on experiments with mice, this groundbreaking research sheds light on the direct impact of hunger hormones on the hippocampus, specifically when an animal is contemplating food-related choices.
Dr. Andrew MacAskill, the lead author from UCL Neuroscience, Physiology & Pharmacology, emphasized the profound influence of hunger on decision-making. He indicated that we all recognize that our decisions can be significantly swayed by hunger, as the significance of food varies depending on whether we are hungry or satiated. Consider the impulse to purchase more items when grocery shopping on an empty stomach. However, what appears to be a straightforward concept is, in reality, intricately complex, requiring the utilization of what is known as ‘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.”
In the experiment, mice were placed in an arena containing food, and their behavior was observed in both hungry and satiated states. The researchers utilized real-time brain imaging to examine neural activity. Although all mice explored the food, only those in a hungry state proceeded to eat.
The study focused on the ventral hippocampus, situated on the underside of the hippocampus, a brain region associated with decision-making and memory formation guiding behavior.
The researchers observed that a specific subset of brain cells in the ventral hippocampus became more active as animals approached food, inhibiting eating behavior. However, when the mice were hungry, neural activity in this region decreased, indicating that the hippocampus no longer suppressed the urge to eat. This was correlated with elevated levels of the hunger hormone ghrelin in the bloodstream.
To further elucidate these findings, UCL researchers conducted experiments to induce a sense of fullness in mice by activating ventral hippocampal neurons. This manipulation caused hungry mice to refrain from eating. Similarly, removing ghrelin receptors from these neurons produced the same outcome.
Previous research indicated the presence of ghrelin receptors in the hippocampus of animals, including non-human primates, but understanding how these receptors functioned was limited.
This discovery highlights the role of ghrelin receptors in the brain, demonstrating that the hunger hormone can traverse the blood-brain barrier, impacting the brain directly. This influence regulates a brain circuit likely to be analogous in humans.
Dr MacAskill said “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.”
The researchers are extending their investigations to explore whether hunger influences learning or memory. They are examining whether mice exhibit variations in performance on non-food-specific tasks based on their level of hunger. Additionally, the scientists anticipate that further research may unveil comparable mechanisms in play for stress or thirst.
The team is optimistic that their discoveries might offer insights into the mechanisms underlying eating disorders. They are particularly interested in determining if ghrelin receptors in the hippocampus play a role in such disorders. Furthermore, the researchers aim to explore connections between dietary factors and various health outcomes, such as the potential correlation with the risk of mental illnesses.
First author Dr Ryan Wee of the UCL Neuroscience, Physiology & Pharmacology says “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.”
