High spatiotemporal resolution imaging of the neurovascular response to electrical stimulation of rat peripheral trigeminal nerve as revealed by in vivo temporal laser speckle contrast

Previous studies have implicated the abnormal activation of the trigeminal system to be a factor in the pathogenesis of migraine. The relationship between vascular changes and migraine, however, is under considerable debate. In this study, temporal laser speckle contrast imaging is combined with ridge tracking based vessel detection to obtain high resolution (6.7 μm × 6.7 μm), high contrast images of cerebral vascular structure. For the first time, the vasomotor and blood flow responses to electrical stimulation in rat peripheral trigeminal system were obtained simultaneously. The system is capable of picking up individual vessels with diameters down to 30 μm. The spatial spread of the blood velocity response relative to the point of stimulation was studied. Analysis of branching vessels showed a 50 ± 5% vs. 30 ± 5% change in mean peak magnitude and a 54% per second vs. 17% per second change in mean rate of increase for vessels proximal vs. distal to the stimulation site. The penetration depth of the laser used was proven to be sufficient to image dural as well as cortical vessels through a thinned skull preparation. Different responses were observed from cortical and dural vessels. While the diameter of cortical vessels did not change in response to the stimulation the blood velocity went up by 65 ± 5% per second. Dural vessels enlarged by 40 ± 8% and the blood velocity increased by 50 ± 5%. The method described here could be very useful in understanding and studying disorders in the neurovascular system.