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Myelin, a lipid-rich structure produced by oligodendrocytes in the central nervous system (CNS) and Schwann cells in the peripheral nervous system (PNS), insulates and protects axons, enabling the rapid transmission of action potentials. Beyond its structural role, myelin in the CNS also serves as a conduit for energy substrates, supplying axons with the necessary metabolites to sustain mitochondrial function and support fast signal propagation. This process is mediated by the activation of NMDA receptors in myelin and oligodendrocytes, triggering glucose uptake, glycolysis, and lactate transport across myelin and axonal membranes.
Lipids constitute approximately 80% of myelin’s composition. Recent findings suggest that myelin lipids may serve as an alternative energy reserve for glial cells under conditions of glucose deprivation. To investigate this, we examined the effects of marathon running on myelin content using MRI. Our findings reveal a transient reduction in white matter myelin following the marathon, with a robust recovery observed within two months. These results point to an unprecedented form of metabolic plasticity, where myelin is dynamically utilized and replenished to sustain brain function under extreme physiological demands. Whether myelin lipids play a similar role in fueling everyday brain activity remains an open question.
Funding: Supported by the Ministerio de Ciencia e Innovación, CIBERNED, and Gobierno Vasco.