1 1296 136 DECREASED MIR-325-5P CONTRIBUTES TO VISCERAL HYPERSENSITIVITY THROUGH POST-TRANSCRIPTIONAL UPREGULATION OF CCL2 IN RAT DORSAL ROOT GANGLIA. CHRONIC VISCERAL HYPERSENSITIVITY IS AN IMPORTANT TYPE OF CHRONIC PAIN WITH UNKNOWN ETIOLOGY AND PATHOPHYSIOLOGY. RECENT STUDIES HAVE SHOWN THAT EPIGENETIC REGULATION PLAYS AN IMPORTANT ROLE IN THE DEVELOPMENT OF CHRONIC PAIN CONDITIONS. HOWEVER, THE ROLE OF MIRNA-325-5P IN CHRONIC VISCERAL PAIN REMAINS UNKNOWN. THE PRESENT STUDY WAS DESIGNED TO DETERMINE THE ROLES AND MECHANISM OF MIRNA-325-5P IN A RAT MODEL OF CHRONIC VISCERAL PAIN. THIS MODEL WAS INDUCED BY NEONATAL COLONIC INFLAMMATION (NCI). IN ADULTHOOD, NCI LED TO A SIGNIFICANT REDUCTION IN THE EXPRESSION OF MIRNA-325-5P IN COLON-RELATED DORSAL ROOT GANGLIA (DRGS), STARTING TO DECREASE AT THE AGE OF 4 WEEKS AND BEING MAINTAINED TO 8 WEEKS. INTRATHECAL ADMINISTRATION OF MIRNA-325-5P AGOMIR SIGNIFICANTLY ENHANCED THE COLORECTAL DISTENTION (CRD) THRESHOLD IN A TIME-DEPENDENT MANNER. NCI ALSO MARKEDLY INCREASED THE EXPRESSION OF CCL2 (C-C MOTIF CHEMOKINE LIGAND 2) IN COLON-RELATED DRGS AT THE MRNA AND PROTEIN LEVELS RELATIVE TO AGE-MATCHED CONTROL RATS. THE EXPRESSION OF CXCL12, IL33, SFRS7, AND LGI1 WAS NOT SIGNIFICANTLY ALTERED IN NCI RATS. CCL2 WAS CO-EXPRESSED IN NEUN-POSITIVE DRG NEURONS BUT NOT IN GLUTAMINE SYNTHETASE-POSITIVE GLIAL CELLS. FURTHERMORE, CCL2 WAS MAINLY EXPRESSED IN ISOLECTIN B4-BINDING- AND CALCITONIN GENE-RELATED PEPTIDE-POSITIVE DRG NEURONS BUT IN FEW NF-200-POSITIVE CELLS. MORE IMPORTANTLY, CCL2 WAS EXPRESSED IN MIR-325-5P-POSITIVE DRG NEURONS. INTRATHECAL INJECTION OF MIRNA-325-5P AGOMIR REMARKABLY REDUCED THE UPREGULATION OF CCL2 IN NCI RATS. ADMINISTRATION OF BINDARIT, AN INHIBITOR OF CCL2, MARKEDLY RAISED THE CRD THRESHOLD IN NCI RATS IN A DOSE- AND TIME-DEPENDENT MANNER. THESE DATA SUGGEST THAT NCI SUPPRESSES MIRNA-325-5P EXPRESSION AND ENHANCES CCL2 EXPRESSION, THUS CONTRIBUTING TO VISCERAL HYPERSENSITIVITY IN ADULT RATS. 2019 2 6148 50 THE EXPRESSION OF TRANSCRIPTION FACTORS MECP2 AND CREB IS MODULATED IN INFLAMMATORY PELVIC PAIN. EARLY ACTIVATION OF TRANSCRIPTION FACTORS IS ONE OF THE EPIGENETIC MECHANISMS CONTRIBUTING TO THE INDUCTION AND MAINTENANCE OF CHRONIC PAIN STATES. PREVIOUS STUDIES IDENTIFIED THE CHANGES IN A NUMBER OF NOCICEPTION-RELATED GENES, SUCH AS CALCITONIN GENE-RELATED PEPTIDE (CGRP), SUBSTANCE P (SP), AND BRAIN-DERIVED NEUROTROPIC FACTOR (BDNF) IN THE PELVIC ORGANS AFTER TRANSIENT COLONIC INFLAMMATION. THE GENE AND PROTEIN EXPRESSION OF THESE NEUROPEPTIDES COULD BE MODULATED BY TRANSCRIPTION FACTORS METHYL-CPG-BINDING PROTEIN 2 (MECP2) AND CAMP RESPONSE ELEMENT-BINDING PROTEIN (CREB). IN THIS STUDY, WE AIMED TO EVALUATE TIME-DEPENDENT CHANGES IN THE EXPRESSION LEVELS OF MECP2 AND CREB IN THE LUMBOSACRAL (LS) SPINAL CORD AND SENSORY GANGLIA AFTER INFLAMMATION-INDUCED PELVIC PAIN IN RAT. ADULT SPRAGUE-DAWLEY RATS WERE TREATED WITH 2,4,6-TRINITROBENZENESULFONIC ACID (TNBS) TO INDUCE TRANSIENT COLONIC INFLAMMATION. LS (L6-S2) SPINAL CORD SEGMENTS AND RESPECTIVE DORSAL ROOT GANGLIAS (DRGS) WERE ISOLATED FROM CONTROL AND EXPERIMENTAL ANIMALS AT 1, 2, 6, 24 H AND 3 DAYS POST-TNBS TREATMENT. IMMUNOHISTOCHEMICAL (IHC) LABELING AND WESTERN BLOTTING EXPERIMENTS WERE PERFORMED TO ASSESS THE EXPRESSION OF MECP2, CREB AND THEIR PHOSPHORYLATED FORMS. TOTAL MECP2 EXPRESSION, BUT NOT PHOSPHORYLATED P-MECP2 (PS421MECP2) EXPRESSION WAS DETECTED IN THE CELLS OF THE SPINAL DORSAL HORN UNDER CONTROL CONDITIONS. COLONIC INFLAMMATION TRIGGERED A SIGNIFICANT DECREASE IN THE NUMBER OF MECP2-EXPRESSING NEURONS IN PARALLEL WITH ELEVATED NUMBERS OF PS421MECP2-EXPRESSING CELLS AT 2 H AND 6 H POST-TNBS. THE MAJORITY OF MECP2-POSITIVE CELLS (80 +/- 6%) CO-EXPRESSED CREB. TNBS TREATMENT CAUSED A TRANSIENT UP-REGULATION OF CREB-EXPRESSING CELLS AT 1 H POST-TNBS ONLY. THE NUMBER OF CELLS EXPRESSING PHOSPHORYLATED CREB (PS133CREB) DID NOT CHANGE AT 1 H AND 2 H POST-TNBS, BUT WAS DOWN-REGULATED BY THREE FOLDS AT 6 H POST-TNBS. ANALYSIS OF DRG SECTIONS REVEALED THAT THE NUMBER OF MECP2-POSITIVE NEURONS WAS UP-REGULATED BY TNBS TREATMENT, REACHING THREE-FOLD INCREASE AT 2 H POST-TNBS, AND EIGHT-FOLD INCREASE AT 6 H POST-TNBS (P