Richard J. Traub - US grants

DESCRIPTION (provided by applicant): Irritable Bowel Syndrome (IBS) is characterized by abdominal pain in the absence of pathology. Epidemiological studies further show IBS is reported most often in menstruating women compared to post-menopausal women or men suggesting gonadal hormones could be a contributing factor. It was recently hypothesized that the pain of IBS could result from sensitization of visceral afferent fibers or hyperexcitability of dorsal horn neurons. Recent data suggests a role for spinal NMDA receptors in processing noxious and innocuous visceral stimuli and NMDA receptors in the brain are modulated by estrogen. The long-term goal of this application is to examine the effects of estrogen on spinal NMDA receptor-mediated processing of noxious and innocuous colorectal stimuli. We hypothesize that estrogen increases activity at spinal NMDA receptors in the absence and presence of colonic inflammation leading to colorectal allodynia and hyperalgesia. This modulation may result from alterations in NMDA receptor subunit composition or second messenger mediated phosphorylation. Using our model of colorectal distention (CRD), we will test these hypotheses by examining the effects of estrogen replacement in ovariectomized rats on visceral sensory processing in the spinal cord in the absence and presence of colonic inflammation, in the following specific aims: 1) Determine the effects of estrogen on responses to transient innocuous, noxious and inflammatory colorectal stimuli. Behavioral, immunocytochemical and electrophysiological studies will test the hypothesis that estrogen facilitates responses to CRD in the absence and presence of colonic inflammation. 2) Characterize the effects of estrogen on subpopulations of visceroceptive projection neurons using retrograde tract tracing and immunocytochemical localization of Fos expression. This will test the hypothesis that estrogen alters the percentage and segmental distribution of supraspinal projection neurons that respond to CRD in the absence and presence of colonic inflammation. 3) Determine if NMDA receptor-mediated modulation of viscerosensory processing is affected by ovariectomy and estrogen replacement. This will test the hypothesis that the modulation of responses to CRD by estrogen is due to altering activity at NMDA receptors. 4) Determine the mechanism(s) through which estrogen modulates CRD-evoked NMDA receptor activity in the absence and presence of colonic inflammation. This will test the hypothesis that estrogen alters NMDA receptor subunit composition and/or modulates second messenger-mediated phosphorylation of tile NMDA receptor.

DESCRIPTION (provided by applicant): Functional chronic pain syndromes have no known pathophysiological basis yet affect millions of people in the United States. Many of these syndromes present as comorbid conditions. As many as 60% of patients with temporomandibular disorder (TMD) also report symptoms of abdominal pain consistent with irritable bowel syndrome (IBS), but the underlying connection between these comorbid conditions is unclear. There are some common clinical features, namely both conditions are substantially more common in women, the level of pain fluctuates during the menstrual cycle and they may be triggered or exacerbated by stress, but a mechanism that can connect these two conditions is unknown. The current application proposes a new animal model of comorbid pain conditions in which TMD and subchronic stress are combined to produce colonic hypersensitivity arising from otherwise healthy tissue. The longterm hypothesis is that persistent pain combined with stress alters the endogenous analgesia system resulting in enhanced secondary hyperalgesia in close proximity to the initial painful site, but also in hypersensitivityin distal deep tissue. The current application addresses the hypothesis that masseter muscle inflammation plus stress induces colonic hypersensitivity that is modulated by gonadal hormones. Furthermore, the visceral hypersensitivity results from central sensitization at the level of the spinal cord. This will be tested in two specific aims: Specific aim 1: Characterize a new model of comorbid pain conditions in which visceral hypersensitivity is induced by a combination of masseter muscle inflammation and subchronic stress. TMD and IBS are individually more prevalent in women and are sensitive to hormonal fluctuation during the menstrual cycle. In these individual animal models (masseter muscle inflammation, colorectal distention), females are more sensitive than males and estrogen increases sensitivity in ovariectomized rats. This aim will characterize the effects of estradiol on visceral and somatic sensitivity in the comorbidity model and test the hypothesis that the visceral hypersensitivity induced by the comorbid conditions is modulated by estradiol. Specific Aim 2: Determine if the visceral hypersensitivity in the comorbid pain model results from sensitization in the periphery or at the level of the spinal cord. As a first step in determining the underlying mechanisms that account for the increase in visceral sensitivity following injury plus stress we will determine if there are increases in neurochemical markers indicative of peripheral or central sensitization. Such changes will indicate that injury plus stress activates either a descending pathway or hormonal surge that sensitizes primary afferents and/or dorsal horn neurons. Failure to observe any neurochemical upregulation will support an alternative hypothesis that the visceral hypersensitivity results from sensitization of nociceptive processing above the level of the spinal cord. Either result will guide future studies into mechanisms underlying comorbid pain conditions.

? DESCRIPTION (provided by applicant): Chronic pain affects 100 million people in the United States at an annual cost surpassing $600 billion (2011 IOM report). Irritable bowel syndrome (IBS) and temporomandibular disorders (TMD) are functional chronic pain disorders of unknown etiology that are more prevalent in women, the pain fluctuates across the menstrual cycle, and the conditions are triggered/exacerbated by stress. The mechanisms underlying these conditions are not well understood so treatment options are poor. These conditions along with other functional pain syndromes overlap in presentation (>60% of TMD patients have IBS) further complicating pain management. A new experimental paradigm in rats models these comorbid pain conditions. Sub chronic stress induces transient visceral hypersensitivity that persists about 1 week. This new model of comorbid pain employs masseter muscle inflammation, modeling TMD, prior to the sub chronic stress to induce estrogen-dependent visceral hypersensitivity, modeling IBS. This comorbid visceral hypersensitivity persists months longer than the, transient visceral hypersensitivity induced by stress or masseter inflammation alone. Three specific aims will examine peripheral and spinal mechanisms that contribute to the acute (2 days) and chronic (1 month) phases of the comorbid visceral hypersensitivity. It is hypothesized that as the effects of the stress component of the acute/transient visceral hypersensitivity recede, there is a shift from peripheral to spinal mechanisms to maintain the chronic comorbid visceral hypersensitivity. Aim 1 will examine colonic afferent activity and the effects of peripheral CRF and mast cells in the acute and chronic phases. Aim 2 will examine changes in spinal visceroceptive neuron activity during the transition from acute to chronic pain. Aim 3 will test the hypothesis that unique gene signature sets, canonical and non-canonical signaling pathways and gene ontologies are enriched in anatomically relevant pain regions (colon, DRG, spinal cord) in the acute and chronic phases of comorbid visceral hypersensitivity. Successful completion of these specific aims will increase our understanding of mechanisms that contribute to the overlap of functional pain disorders, specifically TMD and IBS.

Chronic overlapping pain conditions (COPCs) are idiopathic pain conditions that have minimal identifiable origins in organic disease and represent a highly significant pain management challenge for physician and patient. They occur in tens of millions of Americans with annual costs exceeding $100 billion. Epidemiological data indicate many of these conditions overlap in presentation in the same patient, with odds of presenting 2 or more conditions exceeding 50%. Often spatially separate areas of the body are affected (e.g., temporomandibular disorder (TMD) and irritable bowel syndrome (IBS)), which strongly suggests the involvement of central nervous system mechanisms. Additionally, stress triggers or exacerbates many of these conditions, which occur more frequently or exclusively in women. The convergence of pain from different peripheral tissues and perceived stress most likely occurs in the brain. We propose an innovative multidisciplinary discovery-driven approach to identify novel targets for therapeutic intervention to treat these chronic pain conditions. We will use a recently reported rat model of comorbid pain hypersensitivity: masseter muscle inflammation followed by stress inducing de novo chronic visceral hypersensitivity, a defining characteristic of IBS. Combining visceral and orofacial pain measurement in awake animals, functional magnetic resonance imaging, mass spectrometry imaging of brain sections, and genetic and molecular approaches will allow identification of specific lipids and their metabolic pathways that change expression in the brain during the transition from acute to chronic overlapping pain. A longitudinal design will allow changes in brain activity in individual animals to be followed over weeks to months. In addition, areas of the brain that contribute to known sex differences in the magnitude and duration of the stress-induced and comorbid hypersensitivity should be identified. In three specific aims we will: 1) Identify changes in structure/function of brain regions in response to stress alone and pain plus stress which correlate with changes in visceral sensitivity and orofacial mechanosensitivity in male and female rats. Further, we will identify lipid moieties and the underlying metabolic pathways that change between baseline, acute and chronic pain conditions; 2) determine the effect of genetic knockdown of identified metabolic pathways in rat models of stress-induced and comorbid pain hypersensitivity. siRNA microinjected into brain regions identified in Aim 1 will be used to knockdown expression of enzymes that mediate the changes in lipid expression in the rat models. The effects of siRNA on the sensory and affective components of pain will be examined to help identify ?drugable targets? for therapeutic intervention; and 3) Use pharmacological tools to test identified targets in order to confirm the clinical utility in reversing these conditions. The proposed studies will significantly advance understanding of chronic overlapping pain conditions and identify novel treatment targets.