Mechanisms of DRG Stimulation to Modulate Visceral Afferent Function

University Of Connecticut Storrs, Storrs-Mansfield CT

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Abstract

Project Summary/Abstract Chronic visceral pain affects up to 15% of the U.S. population affected by irritable bowel syndrome (IBS). Despite the tremendous economic burden imposed by visceral pain (IBS has an annual health care cost of ~$30Bn), efficacious and reliable therapeutic intervention is still unavailable. Current neuromodulatory strategies (e.g., spinal cord stimulation) have limited or no success in treating visceral pain from the lower abdomen and pelvis. Dorsal root ganglia (DRG) have emerged as a promising neuromodulatory target to manage certain types of chronic pain according to a recent pilot clinical study. But it remains unknown whether and in what mechanisms visceral pain could be effectively attenuated by DRG stimulation. Since sensitization of visceral afferents is necessary for the persistence of visceral pain, we focus here on elucidating the underlying mechanisms to attenuate or reverse visceral afferent sensitization (and thus treat visceral pain) via DRG stimulation. To achieve that, we propose the development of a multi-wire microelectrode array and its application in a novel ex vivo preparation that includes distal colon/rectum (colorectum), DRG and nerve roots in continuity for simultaneous single-unit recordings of visceral afferents. Three specific aims are proposed. Specific Aim 1 will develop and perfect our ex vivo preparation for simultaneous single-unit recordings from colorectal afferents at L6 nerve roots in response to colorectal stretch. Specific Aim 2 will determine protocols of electrical stimulation around L6 DRG (e.g., pulse frequency, width, location and magnitude) to achieve attenuation of afferent drive from the distal colon/rectum. Specific Aim 3 will determine the effect of DRG stimulation via in vivo behavioral assays of visceral motor responses to colorectal distention. With colorectum, DRG and nerve roots in continuity, the ex vivo preparation affords easy access to L6 DRG for electrical stimulation while using the newly developed electrode array to record single-unit responses from multiple visceral afferents to mechanical colorectal stretch, a physiologically relevant stimulus. This unique approach will provide concrete experimental evidence to address whether DRG stimulation could effectively modulate visceral afferent drive without off-target stimulation of motor efferents, the answer to which could have profound impact on the application of DRG stimulation to treat visceral pain. The effect of DRG stimulation will be further validated by an in vivo mouse behavioral assay of electromyographic responses to graded colorectal distension. The outcomes of this research will guide the design of next-generation neuromodulatory devices that target DRGs for effective management of chronic visceral pain.