Neurovascular coupling along the optic nerve: Insights from two-photon imaging, functional ultrasound, and high-resolution BOLD fMRI

In the brain, neuronal activity triggers an increase of oxygenated blood flowvia neurovascular coupling, a process underlying BOLD fMRI and which roleis unclear for the white matter. Here, we used two-photon imaging in extremedepth, functional ultrasound imaging and high-resolution BOLD fMRI (17.2T)to investigate neurovascular coupling along the whole optic nerve, from theretina up to the first relays of vision, in sedated and awake rodents. We findthat visual stimulation increases blood flow in the optic nerve head and atthe level of the synaptic terminals, i.e. the lateral geniculate nucleus and thesuperior colliculus. However, it does not affect blood flow and oxygenation inthe intracranial part of the optic nerve. Thus, for the same axons, the needof neurovascular coupling to sustain action potential propagation and energyconsumption varies according to the local environment.