SUMMARY: Drosophila uses the neurotransmitter octopamine to decide whether to store food memories for the long-term or short-term, a process influenced by energy stores that influences future feeding behavior.
High glycogen levels stabilize food memories and increase food intake even after fasting, and research suggests that a similar mechanism may also influence overeating in humans.
Key Facts:
“Octopamine in Drosophila determines the storage of food-related memories based on energy stores. Higher glycogen levels lead to longer-lasting food memories and increased food intake. This study provides potential insight into overeating and obesity in humans.”
Source: University of Cologne
A research team from the Institute of Zoology at the University of Cologne used behavioral experiments with fruit flies (Drosophila melanogaster) to study the brain’s control of food intake.
Like humans, food intake in fruit flies is controlled by insulin-like molecules, which, among other things, are influenced by neurotransmitter systems that mediate decision-making.
This system uses the neurotransmitter octopamine, a molecule related to norepinephrine, which determines whether the memory of carbohydrate ingestion is stored in long-term or short-term memory.
The results may therefore explain why it is so hard to lose weight. If the memory of the rewarding effects of food lasts longer than the rewarding and satiating effects of actual food intake, this could lead to increased food intake. Credit: Neuroscience News
This decision is made according to the body’s energy reserves, which has a decisive influence on future eating behavior.
The study, led by Professor Henrike Scholz, has been published in eLife under the title “Octopamine integrates the state of the body’s energy supply into the formation of food-associated memories”.
The researchers investigated how mild fasting and reduced glycogen concentrations in fat and muscle tissues affected carbohydrate perception in fruit flies. Glycogen, a storage form of glucose, is stored in fat tissue and is primarily used as an energy source for muscles.
Information about the energy reserves of these tissues is integrated into the decision-making system by octopamine and influences brain biomechanics.
Previous studies have shown that overeating can lead to increased glycogen levels in animals and humans, and in this study, researchers genetically altered fruit flies to increase their glycogen levels.
Because energy stores increase during fasting, a very stable memory is formed that does not disappear even if you eat again, even if the nutritional value of the next meal is sufficient to compensate for the nutritional deficit caused by the fast. This memory triggers an increase in food intake.
When glycogen levels were very high, consuming carbohydrates in experiments had a less rewarding effect in the brain, and this reduced effect stimulated the desire to keep eating.
When food intake is sufficient or the animal has enough energy, the decision-making system inhibits the formation of such long-term memories about food sources.
This was independent of the carbohydrate content of the food or whether it was enriched with protein. In general, glycogen levels did not affect how fruit flies evaluated protein-enriched foods.
Carbohydrate memories – once useful, now harmful
Depending on your energy levels, octopamine determines what memories are formed in response to food intake. Foods that normally provide sufficient nutritional value may no longer be perceived as satisfying enough. As a result, you may overeat, regardless of the nutritional value or type of food.
“In ancient times, when food was a limited or scarce resource, this mechanism may have helped to store energy when food was available. In times of food surplus, the long-term memory of carbohydrate sources could drive excessive food intake and lead to the development of obesity,” said lead author Henrike Scholz.
Although there are no studies proving a similar mechanism in humans, the molecules involved are very similar in fruit flies and humans, which led the researchers to suggest that the mechanism works in a similar way.
These results may therefore explain why it is difficult to lose weight: if the memory of the rewarding effects of food lasts longer than the rewarding and satiating effects of actual food intake, it may lead to increased food intake.
“In the future, it may be important to find ways to erase this long-lasting memory and make weight loss easier,” Scholz concluded.
More about this neuroscience and food memory research news
Author: Eva Sisler
Source: University of Cologne
Contact: Eva Schissler – University of Cologne
Image: This image is provided by Neuroscience News
Original research: Open Access.
“Octopamine integrates the state of the body’s energy supply into the formation of food-associated memories” Henrike Scholz et al. eLife
Abstract
Octopamine integrates the state of the body’s energy supply into the formation of food-related memories
The brain regulates food intake according to the body’s energy needs and food availability, but do the body’s energy stores affect the type of memory formed?
We show that the duration of starvation determines whether Drosophila melanogaster forms appetitive short-term memories or longer-lasting intermediate memories.
Internal glycogen stores in muscle and adipose tissue influence how intensively sucrose-related information is stored. Insulin-like signaling in octopaminergic reward neurons integrates internal energy stores into memory formation. Octopamine, in turn, inhibits long-term memory formation.
Octopamine is not required for short-term memory, as octopamine-deficient mutants can form short-term appetitive memories for sucrose and other nutrients depending on the body’s energy status.
The reduced positive reinforcing effect of sucrose in the presence of high body glycogen levels, combined with the increased stability of food-associated memories due to prolonged fasting, may lead to increased food intake.
