Dynorphin, won’t you myelinate my neighbor?

Accumulating evidence supports the prevalence of experience-dependent oligodendrocyte precursor cell (OPC) differentiation and myelination in learning and memory. However, the mechanisms remain unknown. In this issue of Neuron, Osso et al., (2021) report that stress causes the secretion of dynorphin by unmyelinated axons, which induces OPC differentiation and myelination of neighboring axons.