title: Pioglitazone rapidly reduces neuropathic pain through astrocyte and nongenomic PPARγ mechanisms.
abstract: Repeated administration of peroxisome proliferator-activated receptor gamma (PPARγ) agonists reduces neuropathic pain-like behavior and associated changes in glial activation in the spinal cord dorsal horn. As PPARγ is a nuclear receptor, sustained changes in gene expression are widely believed to be the mechanism of pain reduction. However, we recently reported that a single intrathecal (i.t.) injection of pioglitazone, a PPARγ agonist, reduced hyperalgesia within 30 minutes, a time frame that is typically less than that required for genomic mechanisms. To determine the very rapid antihyperalgesic actions of PPARγ activation, we administered pioglitazone to rats with spared nerve injury and evaluated hyperalgesia. Pioglitazone inhibited hyperalgesia within 5 minutes of injection, consistent with a nongenomic mechanism. Systemic or i.t. administration of GW9662, a PPARγ antagonist, inhibited the antihyperalgesic actions of intraperitoneal or i.t. pioglitazone, suggesting a spinal PPARγ-dependent mechanism. To further address the contribution of nongenomic mechanisms, we blocked new protein synthesis in the spinal cord with anisomycin. When coadministered intrathecally, anisomycin did not change pioglitazone antihyperalgesia at an early 7.5-minute time point, further supporting a rapid nongenomic mechanism. At later time points, anisomycin reduced pioglitazone antihyperalgesia, suggesting delayed recruitment of genomic mechanisms. Pioglitazone reduction of spared nerve injury-induced increases in GFAP expression occurred more rapidly than expected, within 60 minutes. We are the first to show that activation of spinal PPARγ rapidly reduces neuropathic pain independent of canonical genomic activity. We conclude that acute pioglitazone inhibits neuropathic pain in part by reducing astrocyte activation and through both genomic and nongenomic PPARγ mechanisms.
authors.affiliation: Department of Physiology, School of Medicine, University of Kentucky Medical Center, Lexington, KY, USA School of Science and Engineering, Neuroscience Graduate Program, Tulane University Health Sciences Center, New Orleans, LA, USA Department of Psychology and Neuroscience, Center for Neuroscience, University of Colorado, Boulder, CO, USA.
authors.forename: Ryan B
authors.initials: RB
authors.lastname: Griggs
authors.forename: Renee R
authors.initials: RR
authors.lastname: Donahue
authors.forename: Jenny
authors.initials: J
authors.lastname: Morgenweck
authors.forename: Peter M
authors.initials: PM
authors.lastname: Grace
authors.forename: Amanda
authors.initials: A
authors.lastname: Sutton
authors.forename: Linda R
authors.initials: LR
authors.lastname: Watkins
authors.forename: Bradley K
authors.initials: BK
authors.lastname: Taylor
mesh_terms: D000704:Analysis of Variance; D000820:Animal Diseases; D000818:Animals; D019540:Area Under Curve; D001253:Astrocytes / Q000187:drug effects* / Q000378:metabolism; D002211:Capsaicin / Q000494:pharmacology; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D006930:Hyperalgesia / Q000188:drug therapy / Q000209:etiology; D007004:Hypoglycemic Agents / Q000627:therapeutic use*; D007276:Injections, Intraventricular; D008297:Male; D009437:Neuralgia / Q000150:complications / Q000188:drug therapy* / Q000473:pathology; D059225:Nociception / Q000187:drug effects; D016761:Oncogene Proteins v-fos / Q000378:metabolism; D047495:PPAR gamma / Q000378:metabolism*; D017288:Pain Threshold / Q000187:drug effects; D000077205:Pioglitazone; D011597:Psychomotor Performance / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D066148:Spinal Cord Dorsal Horn / Q000378:metabolism / Q000473:pathology; D045162:Thiazolidinediones / Q000627:therapeutic use*
chemical_list: D005904:Glial Fibrillary Acidic Protein; D007004:Hypoglycemic Agents; D016761:Oncogene Proteins v-fos; D047495:PPAR gamma; D045162:Thiazolidinediones; D002211:Capsaicin; D000077205:Pioglitazone