Welcome to the next episode of the WOrM Podcast 🪱💤
Today we are looking at a single sleep-active neuron that connects far more than sleep.
In C. elegans, the RIS neuron helps regulate:
• sleep
• lipid storage
• survival
• lifespan
• memory
At the centre of the story is a conserved somatostatin-like signalling system involving the neuropeptide NLP-99 and its receptor NPR-16.
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🧠 Meet the sleep neuron
RIS is the major sleep-active neuron in C. elegans.
When RIS activates, it releases FLP-11 neuropeptides that suppress wake-promoting circuits and induce sleep.
But RIS is not working alone.
The wake-active AIY neurons release NLP-99, which signals through NPR-16 to regulate RIS.
The result is a sleep–wake circuit in which AIY promotes wakefulness and RIS promotes sleep.
The two neurons effectively behave like a biological flip-flop switch.
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💤 The effect depends on context
The same signalling pathway produces different outcomes depending on the animal’s nutritional state.
During starvation-induced L1 arrest, NLP-99 and NPR-16 suppress sleep.
In well-fed adults, the pathway instead supports RIS activation and sleep.
This apparent contradiction comes from where NPR-16 acts.
Inside RIS, NPR-16 inhibits calcium activity and limits FLP-11 release.
Outside RIS, it appears to inhibit other neurons that normally suppress RIS, producing a net activating effect.
So one receptor can both restrain and support the same sleep neuron.
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🧪 Watching a neuropeptide leave the neuron
The researchers created a fluorescent FLP-11 reporter to follow neuropeptide release from RIS.
When RIS became active and the worm entered sleep, the FLP-11 signal inside the neuron fell, consistent with release.
Deleting nlp-99 or npr-16 increased FLP-11 secretion during L1 arrest.
This helps explain why the mutants slept more despite showing weaker RIS calcium signals.
The pathway controls not only whether the neuron activates, but also how much sleep-inducing signal it releases.
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🍽️ Sleep meets metabolism
Deleting nlp-99 or npr-16 increased intestinal lipid stores during L1 arrest.
These effects depended on functional RIS.
The mutants also survived starvation longer, while adult lifespan increased by roughly one to two days.
This links a sleep circuit directly to energy storage and survival.
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🧠 Sleep and memory
RIS and FLP-11 were also required for learning and long-term olfactory memory.
The worms were trained to associate the normally attractive smell diacetyl with starvation.
Animals lacking RIS signalling, NLP-99 or NPR-16 showed impaired memory consolidation.
So this pathway does not simply decide whether a worm sleeps.
It helps determine whether an experience is retained.
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🧬 The take-home message
A conserved somatostatin-like signal acts through one sleep-active neuron to coordinate:
sleep × metabolism × survival × memory
The effect changes with nutritional state, developmental stage and the location of the receptor.
One small neural circuit can therefore organise several whole-animal functions at once.
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📄 Paper discussed
Byoungjun Park; Lama Mohsen; Inka Busack; Laura Uhlig; Lorenzo Rossi; Gill Pollmeier; Ellen Geens; Majdulin Nabil Istiban; Sajal Mandal; Reshma Dominic Savio; Isabel Beets; Attila Stetak; Henrik Bringmann. (2026)
C. elegans somatostatin/allatostatin C signaling regulates sleep, metabolism, survival, and memory via a sleep-active neuron
Science Advances, 12: eadv8387
DOI: 10.1126/sciadv.adv8387
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