Neuronal Activity Alters Neuron to OPC Synapses

The mechanisms that drive the timing and specificity of oligodendrocyte myelination during development, or remyelination after injury or immune attack are not well understood. Recent work has shown that oligodendrocyte progenitors receive synapses from neurons, providing a potential mechanism for neuronal-glial communication. We hypothesize that these connections are important both for correct myelination of neurons during development and for myelination during neuronal plasticity. We utilized chemogenetic tools and viral monosynaptic circuit tracing to analyze these neuroglial connections and to examine OPC proliferation, myelination, synapse formation, and neuronal-glial connectivity after increasing or decreasing neuronal activity in vivo. We found that increasing neuronal activity increased OPC activation, but not proliferation. We also found that altering neuronal activity altered neuronal-glial synaptic connections: while it did not impact the total number of neuronal inputs, or the number of inhibitory neuronal inputs, it did alter the number of excitatory neuron to OPC connections. We also found that increasing or decreasing neuronal activity impacted the ratio of excitatory and inhibitory synapses. Our data show that neuronal activity affects OPC activation, neuronal synapse formation onto OPCs, as well as the types of neuronal inputs to OPCs, indicating that neuronal activity is important for OPC circuit composition and function.