Oligodendrocytes support functional development of subcortical premotor neurons and navigation

Oligodendrocytes and the myelin they produce are required for proper balance behaviors in adult vertebrates. If, when, and how they shape the functional development of vestibular (balance) circuits and associated behaviors is unclear. We first adopted a pharmacological approach to investigate the contribution of oligodendrocytes across early development of larval zebrafish ( Danio rerio ). Disruption of oligodendrogenesis reduces the number of oligodendrocytes near vestibular neurons across development, but only impacts vertical navigation — a behavior requiring vestibular function — in older larvae. Correspondingly, we found that midbrain premotor neurons in the vertical navigation circuit only decreased their responses to tilts at later ages. In contrast, we found that the vestibulo-ocular reflex was unaffected by drug treatment, and that body-tilt responses in the underlying hindbrain vestibular neurons and their target extraocular motor neurons were unchanged. Targeted photoablation of oligodendrocytes in the anterior hindbrain replicated our pharmacological findings, selectively disrupting vertical navigation in older animals. By dissociating where and when developmentally-disrupted oligodendrogenesis impacts neuronal function and behavior, our work takes a major step towards understanding how oligodendrocytes enable the maturation of sensorimotor behaviors.