Abstract
In this report, we demonstrate the transcription, expression, and DNA-binding properties of the peroxisome proliferator-activated receptor (PPAR)-gamma subtype of the peroxisome proliferator-activated nuclear receptor family to the spinal cord with real-time PCR, Western blot, and electrophoretic mobility shift assay. To test the hypothesis that activation of spinal PPAR-gamma decreases nerve injury-induced allodynia, we intrathecally administered PPAR-gamma agonists and/or antagonists in rats after transection of the tibial and common peroneal branches of the sciatic nerve. Single injection of either a natural (15-deoxy-prostaglandin J2, 15d-PGJ2) or synthetic (rosiglitazone) PPAR-gamma agonist dose-dependently decreased mechanical and cold hypersensitivity. These effects were maximal at a dose of 100 microg and peaked at approximately 60 minutes after injection, a rapid time course suggestive of transcription-independent mechanisms of action. Concurrent administration of a PPAR-gamma antagonist (bisphenol A diglycidyl ether, BADGE) reversed the effects of 15d-PGJ2 and rosiglitazone, further indicating a receptor-mediated effect. In animals without nerve injury, rosiglitazone did not alter motor coordination, von Frey threshold, or withdrawal response to a cool stimulus. Intraperitoneal and intracerebroventricular administration of PPAR-gamma agonists (100 microg) did not decrease mechanical and cold hypersensitivity, arguing against effects subsequent to diffusion from the intrathecal space. We conclude that ligand-induced activation of spinal PPAR-gamma rapidly reverses nerve injury-induced mechanical allodynia. New or currently available drugs targeted at spinal PPAR-gamma may yield important therapeutic effects for the management of neuropathic pain. Perspective: PPAR-gamma receptor agonists such as rosiglitazone and pioglitazone are approved as insulin sensitizers by the United States Food and Drug Administration. We demonstrate PPAR-gamma expression in the spinal cord and report that activation of these receptors inhibits allodynia. BBB-permeant PPAR-gamma agonists may yield important therapeutic effects for the management of neuropathic pain.