Involvement of microglial P2X7 receptors and downstream signaling pathways in long-term potentiation of spinal nociceptive responses.
Tetanic stimulation of the sciatic nerve (TSS) produces long-term potentiation (LTP) of C-fiber-evoked field potentials in the spinal cord. This potentiation is considered to be a substrate for long-lasting sensitization in the spinal pain pathway. Because microglia have previously been shown to regulate the induction of spinal LTP, we hypothesize that P2X7 receptors (P2X7R), which are predominantly expressed in microglia and participate in the communication between microglia and neurons, may play a role in this induction. This study investigated the potential roles of P2X7Rs in spinal LTP and persistent pain induced by TSS in rats. OxATP or BBG, a P2X7R antagonist, prevented the induction of spinal LTP both in vivo and in spinal cord slices in vitro and alleviated mechanical allodynia. Down-regulation of P2X7Rs with P2X7-siRNA blocked the induction of spinal LTP and inhibited mechanical allodynia. Double immunofluorescence showed colocalization of P2X7Rs with the microglial marker OX-42, but not with the astrocytic marker GFAP or the neuronal marker NeuN. Intrathecal injection of BBG suppressed the up-regulation of microglial P2X7Rs and increased expression of Fos in the spinal superficial dorsal horn. Further, pre-administration of BBG inhibited increased expression of the microglial marker Iba-1, phosphorylated p38 (p-p38), interleukin 1β (IL-1β) and GluR1 following TSS. Pre-administration of the IL-1 receptor antagonist (IL-1ra) blocked both the induction of spinal LTP and the up-regulation of GluR1. These results suggest that microglial P2X7Rs and its downstream signaling pathways play a pivotal role in the induction of spinal LTP and persistent pain induced by TSS.
Chu
Yu-Xia
YX
Institute of Neurobiology, Institutes of Brain Science and State Key Laboratory of Medical Neurobiology, Fudan University, Shanghai, China.
Zhang
Yan
Y
Zhang
Yu-Qiu
YQ
Zhao
Zhi-Qi
ZQ
D000818:Animals; D015153:Blotting, Western; D002135:Calcium-Binding Proteins / Q000378:metabolism; D015536:Down-Regulation / Q000187:drug effects; D004594:Electrophysiology; D005455:Fluorescent Antibody Technique; D007150:Immunohistochemistry; D007278:Injections, Spinal; D053583:Interleukin-1beta / Q000378:metabolism; D017774:Long-Term Potentiation / Q000187:drug effects*; D008297:Male; D008840:Microfilament Proteins; D017628:Microglia / Q000187:drug effects / Q000378:metabolism*; D010146:Pain / Q000139:chemically induced / Q000378:metabolism / Q000503:physiopathology; D010147:Pain Measurement; D017288:Pain Threshold / Q000187:drug effects; D010766:Phosphorylation / Q000187:drug effects; D020671:Posterior Horn Cells / Q000187:drug effects / Q000378:metabolism; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D058920:Purinergic P2X Receptor Antagonists / Q000494:pharmacology; D034741:RNA, Small Interfering / Q000008:administration & dosage; D051381:Rats; D017207:Rats, Sprague-Dawley; D018091:Receptors, AMPA / Q000378:metabolism; D058486:Receptors, Purinergic P2X7 / Q000378:metabolism*; D012394:Rosaniline Dyes / Q000494:pharmacology; D012584:Sciatic Nerve / Q000187:drug effects / Q000503:physiopathology; D015398:Signal Transduction / Q000187:drug effects*; D013116:Spinal Cord / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology*; D013779:Tetrodotoxin / Q000633:toxicity; D013997:Time Factors; D015854:Up-Regulation / Q000187:drug effects
D002135:Calcium-Binding Proteins; D053583:Interleukin-1beta; D008840:Microfilament Proteins; D016760:Proto-Oncogene Proteins c-fos; D058920:Purinergic P2X Receptor Antagonists; D034741:RNA, Small Interfering; D018091:Receptors, AMPA; D058486:Receptors, Purinergic P2X7; D012394:Rosaniline Dyes; D013779:Tetrodotoxin; C100745:Aif1 protein, rat; C004692:coomassie Brilliant Blue