Mussel Brains Reveal How Nervous Systems Survive Oxygen Starvation and Rebound

When the tide recedes from a rocky Mediterranean shore, the mussels clinging to the stones simply close their shells and wait. Inside those shells, oxygen levels plummet, carbon dioxide accumulates, and the entire body shifts into a biochemical holding pattern that would kill most animals within minutes. When the water returns, oxygen floods back in, triggering a surge of reactive molecules that can ravage cells. Yet the Mediterranean mussel, Mytilus galloprovincialis, endures this cycle twice a day, every day, without apparent injury. A new study published in BMC Biology has now peered inside the nervous system of these remarkable animals to ask how a tissue as oxygen-hungry as the brain copes with such dramatic swings, and the answers reveal an elegant, multi-layered program of neural resilience that could inform everything from stroke research to the study of climate-driven hypoxia in the oceans.

The research, led by scientists at the Stazione Zoologica Anton Dohrn in Naples, Italy, set out to address a glaring gap in comparative physiology. Intertidal bivalves are famous for their tolerance of hypoxia and reoxygenation, but the cellular and molecular mechanisms behind that tolerance remain largely unexplored, particularly in the nervous system. This is a critical blind spot, because neural tissue is among the most metabolically active in any animal, demanding a continuous supply of oxygen to sustain ion gradients, neurotransmitter cycling, and the electrical signaling that underpins behavior. In humans, even brief interruptions of cerebral oxygen flow cause devastating damage, which makes the mussel’s nonchalance all the more intriguing.

To build a foundation, the team first performed a detailed histochemical characterization of each ganglion of the mussel’s nervous system, mapping out the architecture of the cerebro-pleural ganglia, pedal ganglia, and visceral ganglia, along with the commissures and connectives that link them. Using molecular markers, they charted the distribution of catecholaminergic, peptidergic, and serotonergic neurons, identifying populations of cells that produce dopamine-like catecholamines, the neuropeptide FMRFamide, and serotonin. This anatomical atlas provided the necessary roadmap for asking which parts of the mussel brain respond when oxygen disappears and returns.

The pedunculate pedal ganglia emerged as a focal point of the response. Histochemical analysis showed that catecholaminergic, peptidergic, and serotonergic neurons distributed within the pedal ganglia contribute to the homeostatic response to hypoxia and the subsequent reoxygenation phase. In practical terms, this means that the mussel’s nervous system does not simply shut down and ride out the stress passively; instead, specific neurochemical signaling systems modulate their activity in a coordinated way as conditions change. Neuroplasticity of this kind, the authors conclude, represents one important component of a broader, integrated set of strategies that the animal deploys to adapt to fluctuating oxygen.

But neurochemical remodeling is only part of the story. To probe deeper, the researchers turned to transcriptomics, sequencing the messenger RNA landscape of the pedal ganglia under normoxic, hypoxic, and reoxygenation conditions. This unbiased approach generated a catalog of candidate adaptive genes whose expression shifts in response to oxygen stress, spanning multiple biological processes. Among the most prominent functional categories were the regulation of cellular homeostasis, the control of programmed cell death, the regulation of cell proliferation, and, perhaps unsurprisingly, mitochondrial biology. Mitochondria are the cellular power plants where oxygen is consumed, and they are also the primary source of the reactive oxygen species that spike dangerously when oxygen suddenly returns after a period of scarcity.

Several of the genes flagged by the analysis belong to pathways that will be familiar to anyone who studies hypoxia biology. The hypoxia-inducible factor pathway, centered on the transcription factor HIF-1α and its regulators, including prolyl hydroxylase domain-containing protein 2 and the von Hippel–Lindau tumor suppressor, is the canonical oxygen-sensing machinery of animal cells. The transcriptomic data also pointed to genes involved in antioxidant defense, mitochondrial electron transport, and even an alternative oxidase, a mitochondrial enzyme that allows some invertebrates to keep electrons flowing through their respiratory chains in ways that sidestep the reactive oxygen bursts typical of standard respiration. Genes connected to apoptosis regulation, including components of tumor necrosis factor receptor signaling, suggest that the mussel brain actively manages the decision between cell survival and cell death during stress.

Markers of cell proliferation, such as proliferating cell nuclear antigen, added another dimension. Their presence hints that the mussel nervous system may maintain or even replenish its cellular components in response to stress, a form of structural plasticity that complements the neurochemical changes. Taken together, the transcriptomic results paint a picture of a nervous system that engages a coordinated transcriptional program, adjusting everything from energy metabolism to life-and-death decisions at the single-cell level, in order to preserve function through cycles of oxygen withdrawal and restoration.

The team then asked whether microRNAs, the small regulatory RNAs that fine-tune gene expression after transcription, might orchestrate these responses. MicroRNAs are powerful post-transcriptional regulators in virtually every animal lineage, and they have been implicated in hypoxic responses in mammals. Using small RNA sequencing, the researchers identified a suite of mature microRNAs expressed in the pedal ganglia, including microRNAs that appear to be entirely novel to science. However, when they compared the miRNA profiles across hypoxia and reoxygenation conditions, they found no significant changes. This negative result is itself informative: it suggests that post-transcriptional regulation mediated by microRNAs plays, at most, a secondary role in how the mussel nervous system copes with fluctuating oxygen, leaving transcriptional regulation and neurochemical plasticity as the primary levers of adaptation.

The study represents the first comprehensive look at the molecular and cellular regulatory mechanisms that allow the nervous system of M. galloprovincialis to adapt to natural oxygen fluctuations. Its significance extends well beyond molluscan curiosity. As climate change warms the oceans and coastal waters experience increasingly frequent and severe hypoxic events, understanding how resilient species maintain neural function under oxygen stress becomes a matter of ecological urgency. Mussels are ecosystem engineers, forming reefs that shelter entire communities, and their capacity to withstand deoxygenation shapes the fate of these habitats. Moreover, the conserved pathways uncovered in this work, from HIF signaling to mitochondrial alternative oxidases, offer comparative insights that may one day illuminate how mammalian brains, including our own, could be better protected against ischemia and reperfusion injury.

There is also a humbling evolutionary lesson embedded in the data. The molecular tools the mussel deploys, including oxygen sensors, mitochondrial safeguards, apoptotic gatekeepers, and modulatory neurotransmitters, are not exotic inventions. They are variations on themes shared across the animal kingdom, tuned by natural selection in an environment where oxygen comes and goes with the tides. What the Naples team has shown is that resilience is not a single trait but an orchestra: neurochemical flexibility in defined ganglia, a shifting transcriptomic program governing homeostasis, death, proliferation, and mitochondria, and a microRNA layer that, in this context, appears to hold steady while the rest of the system adapts. As hypoxic waters spread across the world’s coastlines, the lowly Mediterranean mussel may prove to be one of the best teachers we have about how nervous systems endure the thin line between suffocation and recovery.

Subject of Research: Neural and molecular adaptations of the Mediterranean mussel Mytilus galloprovincialis to hypoxia and reoxygenation stress.

Article Title: Effect of hypoxia and reoxygenation on the nervous system of the Mediterranean mussel Mytilus galloprovincialis

Article References: van Gelderen, T. A., D’Aniello, E., Macina, A., D’Aniello, S., Gallo, A., Carrella, S., & Mirra, S. (2026). Effect of hypoxia and reoxygenation on the nervous system of the Mediterranean mussel Mytilus galloprovincialis. BMC Biology. https://doi.org/10.1186/s12915-026-02731-3

Image Credits: AI Generated

DOI: 10.1186/s12915-026-02731-3

Keywords: hypoxia, reoxygenation, Mytilus galloprovincialis, nervous system, neuroplasticity, pedal ganglia, transcriptomics, microRNAs, mitochondria, HIF-1alpha, intertidal bivalves, marine biology