Summary: For a fruit fly, the stakes of a snack are life or death. While scientists previously believed that “sweet” and “bitter” signals traveled down completely separate neural tracks, researchers have discovered a sophisticated “decision-making hub” housed within a single pair of neurons.
The study reveals that these neurons, called SELK, act as a biological scaleโweighing competing signals of caloric reward versus potential toxicity to dictate the fly’s next move.
Key Facts
- The SELK “Umpire”: The subesophageal LK (SELK) neuron is the first identified cell that “listens” to both sweet and bitter sensors simultaneously.
- Signal Strength Imbalance: Bitter-sensing neurons send a stronger signal to SELK, while sweet-sensing neurons send a weaker one. This biological “bias” ensures the fly prioritizes avoiding toxins over finding calories.
- Dual-Messenger System: SELK doesn’t just pass a signal; it chooses a chemical response:
- Sweet Input: Triggers the release of a neurotransmitter that encourages feeding.
- Bitter Input: Triggers the secretion of a neuropeptide that halts the meal immediately.
- Evolutionary Conservation: A similar mechanism was recently found in mice, suggesting that this “one-cell decision” architecture may be preserved in humans.
- The trans-Tango Toolkit: The discovery was made possible by trans-Tango, a genetic mapping suite developed by the Barnea lab that allows scientists to see exactly which neurons are “talking” to one another.
Source: Brown University
For the fruit fly, a sense of taste is critical to whether it thrives or dies. The little winged creature has taste organs in its mouth piece as well as throughout its body, including its legs, abdomen and wing margins.ย
When a fruit fly lands on a ripe or rotting fruit, it instantly receives information about whether the fruit is bitter or sweet. Sweetness indicates a caloric payday that cues the fly to feed; bitterness prompts the fly to move on from the potentially toxic substance.
Researchers in the lab of Brown University professor Gilad Barnea have identified a pair of neurons that make this critical choice. The insights on how flies navigate this complex decision-making process, a process not previously clear to scientists, wereย publishedย online inย Nature Communications.
โIf a fly makes just one mistake about what to eat, it may die,โ said Barnea, a professor of neuroscience and director of theย Center for the Neurobiology of Cells and Circuitsย at Brownโs Carney Institute for Brain Science. โSo the decision is super important. This newly discovered mechanism illustrates the impressive level of computation that a single neuron can do.โย
Recent work has reported a similar finding in the mouse brain, Barnea said. This could indicate that the decision-making mechanism is conserved across species, including humans. Once identified, such human neurons could be attractive targets for pharmaceutical intervention.
Barnea and his research team are known forย creating theย trans-Tango toolkit, a suite of genetically encoded tools that can map neural circuitry in the fruit fly and other organisms. Lead study author Doruk Savaล, who earned his Ph.D. from Brown and is now a researcher at Harvard University, had the initial impulse to investigate taste in the fruit fly when he first joined the Barnea lab and saw, viaย trans-Tango, surprising results.
โThe mainstream understanding in the field was that sweet-sensing neural populations only โtalkโ to a certain subset of neurons, and bitter-sensing populations only talk to a different subset, and there’s really no interplay between them,โ Savaล said. โBut what I was seeing was that thereโs a neuron that is โlisteningโ to both.โ
That neuron is called subesophageal LK, or SELK. Savaล found that bitter- and sweet-sensing neural populations send messages to the SELK neurons at different strengths. The bitter-sensing population sends a stronger signal, while the sweet-sensing population sends a weaker one.
The SELK neuron interprets these signals and uses one of two different chemical messengers to tell the fly what to do next. If the substance is sweet, the SELK neuron releases a neurotransmitter that directs the fly to eat; if it is bitter, the SELK neuron secretes a neuropeptide to stop the feeding.
โWe knew there were many ways for a circuit to make a decision, but we didnโt know before this discovery that a single neuron could be the one to do it,โ said Barnea. โIf I may give Mother Nature a compliment, itโs a very elegant solution.โ
Funding: The study was supported by the National Institutes of Health (RO1DC020703, F31DC019540).
Key Questions Answered:
A: Imagine if you could taste a cake just by stepping on it! Fruit flies have taste receptors on their legs, wings, and abdomen so they can analyze their environment the moment they land. This “early warning system” sends data to the SELK neurons before the fly even commits to using its mouthpiece.
A: Evolution favors “better safe than sorry.” A missed meal (sweet) means hunger, but a single mistake with a toxin (bitter) means death. By making the bitter signal louder, the brain ensures that the “stop” command overrides the “go” command in a tie-breaker.
A: Potentially. If humans have an equivalent to the SELK neuron, it would be the ultimate “gatekeeper” for appetite. Understanding how this single cell weighs rewards against risks could lead to new pharmaceutical targets for managing overeating or chemical sensitivities.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this neuroscience research news
Author: Corrie Pikul
Source: Brown University
Contact: Corrie Pikul – Brown University
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Feeding decision-making by a single neuron via disparate neurotransmitters” by Doruk Savaล,ย Angel M. Okoro,ย Rareศ A. Moศneanu,ย Anthony M. Crown,ย Zeyu Chang,ย Rebecca Siegel,ย Altar Sorkaรง,ย Meet Zandawalaย &ย Gilad Barnea. Nature Communications
DOI:10.1038/s41467-026-69443-8
Abstract
Feeding decision-making by a single neuron via disparate neurotransmitters
Animals use gustatory information to decide whether to ingest nutritious substances or avoid toxic ones. Although certain neurons in the gustatory circuits respond to both aversive and appetitive signals, how these neurons resolve inputs with opposing valences is unknown.
Here, we examine how theย Drosophila melanogasterย neuropeptide leucokinin (LK) affects gustatory information processing to elicit the appropriate feeding behaviors.
We identify the subesophageal LK neurons (SELKs) as downstream synaptic partners of gustatory receptor neurons and show that these two groups are functionally connected. We then show that SELKs affect bitter avoidance through LK release and food intake in an acetylcholine-dependent manner.
Our study uncovers a mechanism whereby strong activation of SELKs results in LK release, leading to feeding suppression, while weak activation results in acetylcholine-dependent feeding promotion.
Thus, our results reveal that a single pair of neurons, SELKs, differentially controls opposing feeding behaviors via distinct neurotransmitters.
