Ultrasound localization microscopy and functional ultrasound reveal atypical features of the live trigeminal ganglion

Abstract

The functional imaging of the neurovascular coupling within the trigeminal ganglion (TG) is highly challenging due to its small size and its deep localization. This study combined a methodological framework able to dive into the rat trigeminal nociceptive system by jointly providing first imaging of the trigeminal ganglion blood vasculature at microscopic resolution and the measurement of its neurovascular coupling in the rat TG evoked by corneal stimulations, a robust and clinically-relevant model. Using functional ultrasound imaging (fUS), we were able to image and quantify a strong hemodynamic response in the ipsilateral TG from anesthetized rats, evoked by mechanical or chemical stimulations of corneal nociceptive fibers to intact cornea, even though TG involves less than 300 sensory neurons. The in vivo quantitative imaging of the TG’s vasculature using ultrasound localization microscopy (ULM) combined with ex-vivo (DiI) staining reveals particular features of the vascularization of the area containing the sensory neurons, that is likely the origin of this strong vaso-trigeminal response and due to the nature of this structure at the interface between the peripheral and central nervous systems. This innovative imaging approach opens the path for future studies on the mechanisms underlying changes in trigeminal local blood flow and neurovascular coupling, key mechanisms and readouts for the understanding and treatment of debilitating trigeminal pain conditions.