L. Buéno Unité de Neurogastroentérologie INRA Toulouse, France

Symposium Mayoly sur le Syndrome de l'Intestin Irritable. Organisateur: Pr. Boucekkine VOIE DE SIGNALISATION ET D'INTEGRATION DE LA DOULEUR VISCERALE L. Buéno Unité de Neurogastroentérologie INRA Toulouse, France Alger, 25 Avril 2010

Processing of Sensory Signals in Spinal Cord, Brain Stem, and Brain Gracilis and Cuneatus Brain Stem Dorsal column nociceptive pathway Lat. spinothalamic tract Spinal Cord Spinoreticular tract Dorsal Root Abdominal Viscus

Ascending Pain Pathways IBS - Ascending Visceral Pain Pathway

Descending Pain Modulation ACC Thalamus PAG Locus coeruleus Caudal raphe nucleus Amygdala Noradrenergic Rostral ventral medulla Serotonergic Test balloon Opioid Spinal cord Spinal afferent Rectosigmoid

Brain Activation with Noxious Visceral Stimulation Prefrontal Cortex Cing Cx included MCC pACC Thalamus Pf, Re, Cl, Li Locus coeruleus Subnucleus reticularis dorsalis Spinal cord Lamina 1 IBS

Convergence of Somatic and Visceral Afferents in the Spinal Cord Brain Dorsal root ganglion Somatic afferent Spinothalamic tract Visceral afferent Gallbladder

Divergence of Somatic and Visceral Afferents in the Spinal Cord (Wolf et al. 1965)

Colonic Referred Pain (mechanosensitivity) Increased pain intensity

Mechanoreceptors of the Digestive tract - localisation Vascular (8/10 high threshold) Serosal (1/3 low threshold) Tonic & Phasic distensions Tonic Distension (act in series) Mucosal (8/10 low threshold) Phasic Distension (act in parallel)

- + - + + + Possible sites of alterations in gut sensitivity 1 Afferent nerve terminals 2 Brain Dorsal horn Raphe 3 Brain integrative nuclei Cortex Limbic system Nuclei 4 Diffuse noxious inhibitory system 5-HT 5-HT Thalamus 4 Gut Wall Dorsal root Ganglia 3 Nociceptive stimulus SP --- SPINAL EAA - CORD - DH PN + 2 1

Spinal Gating for Three Classes of Visceral Nociceptors (Low, High and Silent) Account for Normal Regulatory Functions, Acute and Chronic Pain Synaptic terminal, second order, active neuron Synaptic terminal, spinal and inactive neuron Threshold Threshold Threshold Low High Silent Low High Silent Low High Silent Normal sensation (No pain) Inflammation (Chronic pain) High intensity (Acute pain)

Postsynaptic receptors at dorsal horn level: - NMDA, AMPA - NK1, NK2, NK3 - CGRP1, SST3 - 5-HT1, 5-HT3 - opioid (µ,d,k) - a2 adrenergic - GABAA Presynaptic receptors at dorsal horn level: - CCK - GABAA - 5-HT3 - µ,d,k - a2 adrenergic Mediators contained in visceral primary afferents : - glutamate, aspartate - SP, NKA, NKB - CGRP - somatostatin - VIP, galanin (Bueno et al. 1996)

Receptors at nerve terminals of nociceptive fibers as putative targets to reduce inflammation-induced hyperalgesia Other putative targets (spinal cord level) TRPV1….5 mGluR1,5 CB1, CB2 Sub.P 2 opioid NK1,2,3 Nociceptive terminal CCK1 and….. others Hist. Tryp. PGE2 5-HT H+ ATP NGF IL-1ß Pressure Heat Bradykinin Other putative targets (periphery) Tissue damage Mast cell LIF IL6 TNFa NGF Proteases CRF PAR1, PAR2 CRF-R1, CRF-R2 TrkA, p75

Role of Mast cell in mucosal inflammation-induced visceral hyperalgesia Stress Mast cell CRF Degranulation minutes Histamine Leukotrienes Cytokines* proteases NGF Allergy IgE, SP,5-HT PAF, ATP Inflammation hours GM-CSF, IL-1 Secretion Infection NGF, NPY Cytokines* Chemokines Sympathetic activation Cytokines: TNFa, IL-3, IL-5, IL-4, IL-13, IL-10, GM-CSF * (adapted from Shakoory et al,2004, Penicci et al.2003)

BIDIRECTIONAL REGULATION OF MAST-CELL-EOSINOPHIL FUNCTION SP SCF Endothelium/ Epithelium IL-4 PAR2 tryptase PAR2 Mast cell Cytokines chymase Eotaxin PAR2 SCF Cytokines GM-CSF Chemokines IL-1 / TNF-a CCR3 Eosinophil/ neutrophils Adapted from Shakoory et al. 2004

ROLE OF MAST CELLS IN VISCERAL PAIN: (degranulation in response to mechanical stimuli) Sensitization Density Normal barosensitivity Normal barosensitivity P P Post-stress Post-infection Pain Pain P P MC degranulation MC degranulation

Role of mast cell in favorising increase in colonic gut permeability and subsequent increase in visceral sensitivity to distension STRESS CRF Mastcell activation 5-HT, tryptase NGF activation Visceral hyperalgesia Cytokines Chemokines Inflammatory mediators sensory nerve terminal sensitization T-lymphocyte Neutrophils TJ OPENING IFN  MLC MLCK MLCP (Ait-Belgnaoui et al. Pain 2005)

Repetitive Stimulation Sensitizes the Spinal Cord Dorsal root ganglion Wind-up Sensitized spinal circuits Mechanosensitive afferent Repeated balloon distention

MODULATION OF NEURONAL NOCICEPTIVE TRANSMISSION AT SPINAL CORD LEVEL BY GLIAL CELLS (from Svensson et al. 2010)

GLIAL CELL NEUROMEDIATORS INVOLVED IN NOCICEPTIVE TRANSMISSION AT SPINAL CORD LEVEL ? ? (from Svensson et al. 2010)

SPINAL MICROGLIA ACTIVATION IN STRESS -INDUCED VISCERAL HYPERALGESIA Bradesi et al. 2009

SPINAL MICROGLIA ACTIVATION IN “NARCOTIC BOWEL SYNDROME” Agostini et al. 2010 (in press)

CONCLUSIONS La douleur d'origine digestive est le plus souvent associée à une sensibilisation des mécano-récepteurs pariétaux principalement par les produits de dégranulation des mastocytes. La présence d'une micro-inflammation associée à une redistribution des terminaisons est un facteur majeur de l'hypersensibilité viscérale observée dans le SII. La douleur viscérale chronique est déclenchée par à une hypersensibilité locale mais facilité et entretenue par une facilitation et amplification spinale des messages nociceptifs Outre les facteurs locaux, les cellules gliales et en particulier la microglie participent à la facilitation spinale de cette transmission nociceptive

L. Buéno Unité de Neurogastroentérologie INRA Toulouse, France