title: Altered expression and uptake activity of spinal glutamate transporters after nerve injury contribute to the pathogenesis of neuropathic pain in rats.
abstract: The central glutamatergic system has been implicated in the pathogenesis of neuropathic pain, and a highly active central glutamate transporter (GT) system regulates the uptake of endogenous glutamate. Here we demonstrate that both the expression and uptake activity of spinal GTs changed after chronic constriction nerve injury (CCI) and contributed to neuropathic pain behaviors in rats. CCI induced an initial GT upregulation up to at least postoperative day 5 primarily within the ipsilateral spinal cord dorsal horn, which was followed by a GT downregulation when examined on postoperative days 7 and 14 by Western blot and immunohistochemistry. Intrathecal administration of the tyrosine kinase receptor inhibitor K252a and the mitogen-activated protein kinase inhibitor PD98059 for postoperative days 1-4 reduced and nearly abolished the initial GT upregulation in CCI rats, respectively. Prevention of the CCI-induced GT upregulation by PD98059 resulted in exacerbated thermal hyperalgesia and mechanical allodynia reversible by the noncompetitive NMDA receptor antagonist MK-801, indicating that the initial GT upregulation hampered the development of neuropathic pain behaviors. Moreover, CCI significantly reduced glutamate uptake activity of spinal GTs when examined on postoperative day 5, which was prevented by riluzole (a positive GT activity regulator) given intrathecally twice a day for postoperative days 1-4. Consistently, riluzole attenuated and gradually reversed neuropathic pain behaviors when the 4 d riluzole treatment was given for postoperative days 1-4 and 5-8, respectively. These results indicate that changes in the expression and glutamate uptake activity of spinal GTs may play a critical role in both the induction and maintenance of neuropathic pain after nerve injury via the regulation of regional glutamate homeostasis, a new mechanism relevant to the pathogenesis of neuropathic pain.
authors.affiliation: Massachusetts General Hospital Pain Center, Department of Anesthesia and Critical Care, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA.
authors.forename: Backil
authors.initials: B
authors.lastname: Sung
authors.forename: Grewo
authors.initials: G
authors.lastname: Lim
authors.forename: Jianren
authors.initials: J
authors.lastname: Mao
mesh_terms: D027322:Amino Acid Transport System X-AG / Q000032:analysis / Q000378:metabolism*; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D001692:Biological Transport; D002227:Carbazoles / Q000494:pharmacology; D003250:Constriction; D016291:Dizocilpine Maleate / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D027342:Excitatory Amino Acid Transporter 2 / Q000378:metabolism; D005419:Flavonoids / Q000494:pharmacology; D050491:Glutamate Plasma Membrane Transport Proteins; D018698:Glutamic Acid / Q000378:metabolism; D006930:Hyperalgesia / Q000209:etiology; D026121:Indole Alkaloids; D007700:Kinetics; D008297:Male; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors; D009437:Neuralgia / Q000209:etiology*; D010525:Peripheral Nerves / Q000378:metabolism / Q000601:surgery; D051381:Rats; D017207:Rats, Sprague-Dawley; D020794:Receptor Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D019782:Riluzole / Q000494:pharmacology; D013116:Spinal Cord / Q000737:chemistry / Q000378:metabolism*; D027981:Symporters / Q000378:metabolism; D015854:Up-Regulation
chemical_list: D027322:Amino Acid Transport System X-AG; D002227:Carbazoles; D004791:Enzyme Inhibitors; D027342:Excitatory Amino Acid Transporter 2; D005419:Flavonoids; D050491:Glutamate Plasma Membrane Transport Proteins; D026121:Indole Alkaloids; D027981:Symporters; D018698:Glutamic Acid; D016291:Dizocilpine Maleate; D019782:Riluzole; C049985:staurosporine aglycone; D020794:Receptor Protein-Tyrosine Kinases; D020928:Mitogen-Activated Protein Kinases; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one