Bin Feng - US grants

Visceral pain associated with irritable bowel syndrome afflicts 13% of the US population, costing approximately $30 billion annually. Mechanical distension of hollow visceral organs evokes visceral pain. Drugs for visceral pain affect both peripheral and central nervous systems (CNS) due to similar cellular sensory pathways. Patients treated in this way suffer brain and spinal nerve related side effects, and among those, physical dependency and addiction are particularly important. Visceral pain by mechanical distension of organs initiates in the periphery, making it possible that targeting the receptors of biomechanical loading could reduce the brain and spine side effects. This project aims to understand the biomechanics of visceral nerves as relates to chronic visceral pain. This research will reveal novel therapeutic targets in the nerve ending-tissue complex specific to visceral organs, minimizing CNS side effects and improving health and quality of life for patients suffering chronic visceral pain. This project will engage students from underrepresented groups, particularly women, in middle school, high school and university through integrated outreach. Research in the PI's and Co-PI's labs will be integrated with outreach and diversity programs at the Danbury Library and UConn to engage students from underrepresented groups, particularly women, in middle school, high school and university.

The overall objective of this project is to understand the multiscale biomechanics of colorectal tissue and the micromechanical environment surrounding sensory nerve endings in both control (healthy) and TNBS-treated (in pain) colorectums. The central hypothesis posits that factors governing visceral mechanosensation and sensitization include: 1) varying mechanical properties across different layers of colorectal tissue (e.g. mucosal, muscular), 2) distinct micromechanics at couplings between nerve endings and their extracellular matrix, and 3) dynamic changes in tissue biomechanics following colorectal tissue damage and nerve ending regeneration (in TNBS-treated colorectum). This work aims to determine: 1) tissue-level biomechanics of mucosal and muscular layers of colorectum from both control (healthy) and TNBS-treated (in pain) mice, 2) micro-mechanical environments of individual colorectal sensory nerve endings from both control and TNBS-treated mice, and 3) the impact of nerve ending stress/strain on functional heterogeneity of visceral neural mechanosensation and sensitization via multiscale modeling and simulation. This project leverages novel approaches, including: a mouse IBS model of pain produced by trinitrobenzene sulfonic acid (TNBS), genetic sensory nerve labeling, optical tissue clearing, and multiscale modeling of mechanosensation together with nonlinear soft tissue biomechanics and imaging of collagen fibers. This research will introduce previously overlooked biomechanics as a critical factor in visceral nociception and pain, establish novel biomechanical tools and expand current knowledge of visceral mechanosensation and pain.

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.

Project Summary/Abstract Chronic visceral pain is the cardinal symptom of patients with irritable bowel syndrome (IBS) affecting up to 15% of the U.S. population. Efficacious and reliable therapeutic intervention is still unavailable despite the tremendous economic burden imposed by visceral pain. Drugs to treat visceral pain impact both the peripheral and central nervous systems (PNS, CNS) due to similar ion channel/modulator composition, and CNS-related side effects usually outweigh analgesic benefits. Visceral pain differs significantly from other types of pain in the `adequacy' of nociceptive stimuli, defined first by Sherrington as triggering painful and noxious reactions. Noxious cutaneous stimuli (e.g., cutting, pinching, burning) are not reliably nociceptive when applied to hollow visceral organs, whereas mechanical visceral organ distension (stretch/tension) is `adequately' nociceptive. In addition to previous studies that reveal the role of pelvic nerve (PN) afferents in encoding colorectal distension and contributing to prolonged colorectal hypersensitivity, we reveal, for the first time, a more significant participation of afferents in the lumbar splanchnic nerves (LSN) in encoding colorectal distension than previously assumed: ~40% of LSN afferents encode axial colorectal stretch, which is also produced by colorectal distension. We also found that: 1) the colorectal region with dense LSN innervation (next to the mesentery) is more compliant mechanically than the adjacent region, and 2) the colorectal submucosa has a rich network of load-bearing collagen fibers. Our new neural and mechanical data suggest an underappreciated role for LSN afferents in encoding colorectal distension, an `adequate,' noxious stimulus that evokes visceral pain in IBS patients. Accordingly, the objective of this proposal is to reveal lumbar splanchnic afferent neural encoding of colorectal distension and nociception at macro- and micro-mechanical, and molecular levels. Three specific aims are proposed. Aim 1 will quantify lumbar splanchnic afferent neural encoding of colorectal distension and colorectal nociception in prolonged colorectal hypersensitivity. Aim 2 will quantify macro- and micro-mechanics of differential mechanical neural encoding of colorectal afferent endings in the lumbar splanchnic pathway. Aim 3 will define the molecular profiles relevant to colorectal mechanosensitivity of different lumbar splanchnic afferent classes in prolonged colorectal hypersensitivity. The proposed study of the biomechanical factors in colorectal mechanosensitivity and hypersensitivity will complement existing neurophysiological approaches to synergistically advance our mechanistic understanding of colorectal afferent neural encoding and nociception, especially in the lumbar splanchnic pathway. Through this proposed research, we will establish the influence of biomechanics in colorectal mechanosensitivity and nociception in prolonged colorectal hypersensitivity. This work will provide a rationale to identify novel biomechanical and potential `drugable' targets for managing chronic IBS pain while minimizing off-target CNS effects.

Project Summary/Abstract Chronic visceral pain is the cardinal symptom of patients with irritable bowel syndrome (IBS) affecting up to 15% of the U.S. population. Efficacious and reliable therapeutic intervention is still unavailable despite the tremendous economic burden imposed by visceral pain. Pharmacological treatments of visceral pain in IBS are largely unsatisfactory with side effects outweighing therapeutic benefits. In contrast, neuromodulation (e.g., spinal cord stimulation) as an alternative to drugs has much fewer side effects. Recent advances in neuromodulation of the dorsal root ganglions (DRG) relieves certain somatic and neuropathic pain. Hence, the DRG appears to be a promising target for next-generation neuromodulatory devices to treat IBS-related visceral pain. However, knowledge is missing regarding the topological distribution and molecular profiles of functionally-characterized DRG neurons innervating the colon and rectum (colorectum), especially colorectal nociceptors. This has significantly hindered the further development of DRG neuromodulation that selectively affects a subset of DRG neurons in treating visceral pain in IBS. We aim to leverage our recent technical advances in optical electrophysiology via Ca2+ imaging and single-cell transcriptome assay of sensory neurons to characterize the topology and molecular profiles of colorectal nociceptors in the thoracolumbar and lumbosacral DRG. Three specific aims are proposed. Specific Aim 1 will quantify the topological distribution of mechano- nociceptors of the colorectum in the thoracolumbar and lumbosacral DRG in control and prolonged colorectal hypersensitivity. Specific Aim 2 will quantify the topological distribution of silent nociceptors of the colorectum in the thoracolumbar and lumbosacral DRG in control and prolonged colorectal hypersensitivity. Specific Aim 3 will define the molecular profiles of mechano- and silent nociceptors of the colorectum in the thoracolumbar and lumbosacral DRG in control and prolonged colorectal hypersensitivity. By establishing a high-throughput optical electrophysiology method, we will be able to functionally characterize a large number (>2000) of colorectal DRG neurons (including nociceptors) and reveal their topological distributions in thoracolumbar and lumbosacral DRG. The single-cell transcriptome analysis on colorectal nociceptors will reveal promising targets for chemical neuromodulation of the DRG. The outcomes of this research will guide the design of next-generation neuromodulatory devices that target DRG for effective management of chronic visceral pain while minimizing off-target side effects.