Key result
Natural stimulations and short-term peripheral inflammation induce significant spinal hemodynamic responses on functional ultrasound.
Why the study?
Spinal cord properties in chronic pain have rarely been studied at a large-scale neurovascular level due to limited spatial and temporal resolution of available techniques.
Functional ultrasound imaging reveals that spinal cord hemodynamic responses are fiber-specific, somatotopically organized, and enhanced during peripheral inflammation.
Hypothesis-generating for functional ultrasound in spinal pain imaging; leaves open human translation and clinical utility.
Despite a century of research on the physiology/pathophysiology of the spinal cord in chronic pain condition, the properties of the spinal cord were rarely studied at the large-scale level from a neurovascular point of view. This is mostly due to the limited spatial and/or temporal resolution of the available techniques. Functional ultrasound imaging (fUS) is an emerging neuroimaging approach that allows, through the measurement of cerebral blood volume, the study of brain functional connectivity or functional activations with excellent spatial (100 μm) and temporal (1 msec) resolutions and a high sensitivity. The aim of this study was to increase our understanding of the spinal cord physiology through the study of the properties of spinal hemodynamic response to the natural or electrical stimulation of afferent fibers. Using a combination of fUS and ultrasound localization microscopy, the first step of this study was the fine description of the vascular structures in the rat spinal cord. Then, using either natural or electrical stimulations of different categories of afferent fibers (Aβ, Aδ, and C fibers), we could define the characteristics of the typical hemodynamic response of the rat spinal cord experimentally. We showed that the responses are fiber-specific, located ipsilaterally in the dorsal horn, and that they follow the somatotopy of afferent fiber entries in the dorsal horn and that the C-fiber response is an N-methyl-D-aspartate receptor-dependent mechanism. Finally, fUS imaging of the mesoscopic hemodynamic response induced by natural tactile stimulations revealed a potentiated response in inflammatory condition, suggesting an enhanced response to allodynic stimulations.
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Claron et al. (2020) studied Spinal nociception and inflammation. Noxious and innocuous stimulations, peripheral inflammation (CFA) vs. Baseline, Saline was evaluated on Spinal hemodynamic response. Functional ultrasound imaging revealed that natural noxious and innocuous stimulations, as well as short-term peripheral inflammation, induce significant spinal hemodynamic responses.
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