Summary: Researchers have found that the neurotransmitter octopamine in fruit flies influences whether memories about food are stored as short-term or longer-lasting traces. This decision depends on internal energy stores such as glycogen and can shape future feeding behavior.
When glycogen reserves are high, carbohydrate-related memories become more persistent, which can drive increased food intake even after a period of fasting. Although the same mechanism has not been proven in humans, the molecular similarities suggest potential relevance for understanding overeating and obesity.
Key Facts:
- Octopamine signals in fruit flies integrate internal energy status into the formation of food-related memories.
- Elevated glycogen stores favor the formation of longer-lasting memories tied to carbohydrate rewards, promoting greater food consumption.
- These findings offer a potential framework for studying overeating and obesity, given conserved signaling pathways between flies and humans.
Source: University of Cologne
In laboratory experiments with the fruit fly Drosophila melanogaster, a team at the University of Cologne’s Institute of Zoology explored how the brain links internal energy supply to future food intake.
Similar to mammals, fruit flies use hormonal and neurotransmitter systems to regulate feeding. One key player identified in this work is octopamine, a biogenic amine closely related to noradrenaline, which modulates how rewarding food feels and how that experience is stored in memory.
The researchers show that octopamine’s signaling integrates information about the animal’s glycogen stores—stored glucose in muscle and fat—into the neural circuits that evaluate and remember the reward value of carbohydrates. That integration affects whether an experience with food is encoded as a transient short-term memory or as a more enduring memory that influences later choices.
The work was led by Professor Henrike Scholz and published in the journal eLife under the title “Octopamine integrates the status of internal energy supply into the formation of food-related memories.”
To probe this mechanism, the team manipulated the flies’ glycogen levels and subjected them to mild fasting. Glycogen serves as a reserve of glucose and is stored in adipose and muscle tissues to meet energetic demands. By altering these reserves and monitoring behavior and memory formation, the researchers could test how internal energy status shaped responses to carbohydrate rewards.
When genetically modified flies carried higher-than-normal glycogen stores, a brief fast followed by a carbohydrate reward produced a remarkably stable memory that persisted even after the flies ate again. In other words, the memory of the carbohydrate’s reward outlasted the immediate satiating effects of consumption, and this persistent memory led the flies to eat more.
High glycogen levels also reduced the immediate rewarding signal produced by carbohydrate intake. That lower immediate reward, combined with a strong, persistent memory, created a drive to continue eating. Conversely, when energy reserves were adequate and food intake was sufficient, the octopamine-mediated system suppressed formation of long-lasting memories about the food source, preventing unnecessary overeating.
These effects were specific to carbohydrates: glycogen levels did not systematically alter how the flies evaluated protein-enriched foods. The findings indicate a selective interaction between carbohydrate reward processing and internal glucose stores mediated by octopaminergic neurons.
Memories of carbohydrates—once adaptive, now potentially harmful
From an evolutionary perspective, forming durable memories of rich carbohydrate sources would be adaptive when food was scarce: remembering where energy-dense food was available would help an animal accumulate reserves. In modern or experimentally induced states of surplus, however, the same mechanism can promote excessive intake if the rewarding memory persists beyond the actual physiological need.
The authors note that although this exact mechanism has not been demonstrated in humans, many molecular players—insulin signaling and catecholamine-like transmitters—are conserved across species. Thus, similar processes might contribute to persistent food cravings and overeating in mammals, providing a possible target for future research.
Scholz and colleagues suggest that understanding how to weaken or erase these long-lasting food-related memories could become an important strategy to help reduce overeating and support weight loss.
About this neuroscience and food memory research news
Author: Eva Schissler
Source: University of Cologne
Contact: Eva Schissler – University of Cologne
Image: The image is credited to Neuroscience News
Original Research: Open access. “Octopamine integrates the status of internal energy supply into the formation of food-related memories” by Henrike Scholz et al., eLife.
Abstract
Octopamine integrates the status of internal energy supply into the formation of food-related memories
The brain adjusts feeding behavior in response to internal energy demands and food availability, but internal energy storage may also shape the type of memory formed after a feeding experience. The authors demonstrate that the duration of starvation influences whether Drosophila melanogaster forms short-term appetitive memories or more persistent intermediate memories.
Glycogen storage in muscle and adipose tissue determines how strongly sucrose-associated information is encoded. Insulin-like signaling within octopaminergic reward neurons conveys internal energy status to the memory-formation machinery, and octopamine acts to suppress long-term memory formation. Octopamine is not required for short-term memory: octopamine-deficient mutants still form appetitive short-term memories depending on internal energy status.
A combination of reduced immediate sucrose reinforcement at high glycogen levels and increased stability of food-related memories after prolonged starvation could drive higher food intake, with potential implications for understanding feeding regulation across species.