Neuron-class specific responses govern adaptive remodeling of myelination in the neocortex

Abstract

Myelination plasticity plays a critical role in neurological function, including learning and memory. However, it is unknown whether this plasticity is enacted through uniform changes across all neuronal subtypes, or whether myelin dynamics vary between neuronal classes to enable fine-tuning of adaptive circuit responses. We performed in vivo two-photon imaging to investigate the dynamics of myelin sheaths along single axons of both excitatory callosal projection neurons and inhibitory parvalbumin+ interneurons in layer 2/3 of adult mouse visual cortex. We find that both neuron types show dynamic, homeostatic myelin remodeling under normal vision. However, monocular deprivation results in experience-dependent adaptive myelin remodeling only in parvalbumin+ interneurons, but not in callosal projection neurons. Monocular deprivation induces an initial increase in elongation events in myelin segments of parvalbumin+ interneurons, followed by a contraction phase affecting a separate cohort of segments. Sensory experience does not alter the generation rate of new myelinating oligodendrocytes, but can recruit pre-existing oligodendrocytes to generate new myelin sheaths. Parvalbumin+ interneurons also show a concomitant increase in axonal branch tip dynamics independent from myelination events. These findings suggest that adaptive myelination is part of a coordinated suite of circuit reconfiguration processes, and demonstrate that distinct classes of neocortical neurons individualize adaptive remodeling of their myelination profiles to diversify circuit tuning in response to sensory experience.