Adolescent Seizure Impacts Oligodendrocyte Development, Neuronal-Glial Circuit Formation, and Myelination
Myelin sheaths, formed by oligodendrocyte cells in the CNS, are vital for rapid conduction of electrical signals down neuronal axons. Oligodendrocyte progenitors differentiate and myelinate axons during development and following demyelinating injury. However, the mechanisms that drive the timing and specificity of developmental myelination are not well understood. It is known that oligodendrocyte progenitors receive synapses from neurons, providing a potential mechanism for neuronal-glial communication. We have previously shown that changing neuronal activity affects the proliferation of oligodendrocyte cells and neuron to OPC connections. We hypothesized that OPC proliferation and differentiation would be affected by pathological neuronal activity during adolescent development, when developmental myelination is occurring, and that this would also impact neuron to OPC connectivity and myelination. We used kainic acid to induce a seizure, then analyzed changes in the rate of OPC proliferation and differentiation five days later in the cerebral cortex, corpus callosum, and hippocampus. We found that OPC proliferation increased, the overall numbers of OPCs increased, and the number of mature oligodendrocytes decreased. We measured changes in the myelination to determine whether seizure activity directly affected myelination rate in adolescent development, and found decreased myelin in the cerebral cortex, corpus callosum, and hippocampus. We used viral monosynaptic circuit tracing to determine whether connections between neurons and OPCs were affected by seizure activity, and found a decrease in neuron to OPC connections in seizure mice compared to controls. Finally, we measured changes in the presence of kir4.1 potassium channels in OPCs, an important regulator of OPC membrane potential as well as an ion channel important for myelination, and found that there was a decrease in the number of potassium channels on OPCs after adolescent seizure. These findings provide insight into the response of the adolescent brain to seizure activity, as well as how seizures affect neuronal glial connections, OPC development and myelin formation, with the goal of understanding how these mechanisms may be important for treatment of demyelination after seizure and in epilepsy.