1 5779 183 SPINAL MICRORNA-134-5P TARGETS GLUTAMATE RECEPTOR IONOTROPIC KAINATE 3 TO MODULATE OPIOID INDUCED HYPERALGESIA IN MICE. BACKGROUND: FENTANYL AND ITS ANALOGS ARE EXTENSIVELY USED FOR PAIN RELIEF. HOWEVER, THEIR PARADOXICALLY PRONOCICEPTIVE EFFECTS OFTEN LEAD TO INCREASED OPIOIDS CONSUMPTION AND RISK OF CHRONIC PAIN. COMPARED TO OTHER SYNTHETIC OPIOIDS, REMIFENTANIL HAS BEEN STRONGLY LINKED TO ACUTE OPIOID HYPERALGESIA AFTER EXPOSURE [REMIFENTANIL-INDUCED HYPERALGESIA (RIH)]. THE EPIGENETIC REGULATION OF MICRORNAS (MIRNAS) ON TARGETED MRNAS HAS EMERGED AS AN IMPORTANT PATHOGENESIS IN PAIN. THE CURRENT RESEARCH AIMED AT EXPLORING THE SIGNIFICANCE AND CONTRIBUTIONS OF MIR-134-5P TO THE DEVELOPMENT OF RIH. METHODS: BOTH THE ANTINOCICEPTIVE AND PRONOCICEPTIVE EFFECTS OF TWO COMMONLY USED OPIOIDS WERE ASSESSED, AND MIRNA EXPRESSION PROFILES IN THE SPINAL DORSAL HORN (SDH) OF MICE ACUTELY EXPOSED TO REMIFENTANIL AND REMIFENTANIL EQUIANALGESIC DOSE (RED) SUFENTANIL WERE SCREENED. NEXT, THE CANDIDATE MIRNA LEVEL, CELLULAR DISTRIBUTION, AND FUNCTION WERE EXAMINED BY QPCR, FLUORESCENT IN SITU HYBRIDIZATION (FISH) AND ARGONAUTE-2 IMMUNOPRECIPITATION. FURTHERMORE, BIOINFORMATICS ANALYSIS, LUCIFERASE ASSAYS, MIRNA OVEREXPRESSION, BEHAVIORAL TESTS, GOLGI STAINING, ELECTRON MICROSCOPY, WHOLE-CELL PATCH-CLAMP RECORDING, AND IMMUNOBLOTTING WERE EMPLOYED TO INVESTIGATE THE POTENTIAL TARGETS AND MECHANISMS UNDERLYING RIH. RESULTS: REMIFENTANIL INDUCED SIGNIFICANT PRONOCICEPTIVE EFFECTS AND A DISTINCT MIRNA-PROFILE FROM SUFENTANIL WHEN COMPARED TO SALINE CONTROLS. AMONG TOP 30 DIFFERENTIALLY EXPRESSED MIRNAS SPECTRUM, SPINAL MIR-134-5P WAS DRAMATICALLY DOWNREGULATED IN RIH MICE BUT REMAINED COMPARATIVE IN MICE SUBJECTED TO SUFENTANIL. MOREOVER, GLUTAMATE RECEPTOR IONOTROPIC KAINATE 3 (GRIK3) WAS A TARGET OF MIR-134-5P. THE OVEREXPRESSION OF MIR-134-5P ATTENUATED THE HYPERALGESIC PHENOTYPE, EXCESSIVE DENDRITIC SPINE REMODELING, EXCITATORY SYNAPTIC STRUCTURAL PLASTICITY, AND KAINATE RECEPTOR-MEDIATED MINIATURE EXCITATORY POSTSYNAPTIC CURRENTS (MEPSCS) IN SDH RESULTING FROM REMIFENTANIL EXPOSURE. BESIDES, INTRATHECAL INJECTION OF SELECTIVE KA-R ANTAGONIST WAS ABLE TO REVERSE THE GRIK3 MEMBRANE TRAFFICKING AND RELIEVED RIH. CONCLUSION: THE MIR-134-5P CONTRIBUTES TO REMIFENTANIL-INDUCED PRONOCICEPTIVE FEATURES VIA DIRECTLY TARGETING GRIK3 TO MODULATE DENDRITIC SPINE MORPHOLOGY AND SYNAPTIC PLASTICITY IN SPINAL NEURONS. 2023 2 6148 31 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