title: Phosphorylation of spinal N-methyl-d-aspartate receptor NR1 subunits by extracellular signal-regulated kinase in dorsal horn neurons and microglia contributes to diabetes-induced painful neuropathy.
abstract: The N-methyl-d-aspartate receptor (NMDAR) contributes to central sensitization in the spinal cord, a phenomenon which comprises various pathophysiological mechanisms responsible for neuropathic pain-like signs in animal models. NMDAR function is modulated by post-translational modifications including phosphorylation, and this is proposed to underlie its involvement in the production of pain hypersensitivity. As in diabetic patients, streptozotocin-induced diabetic rats exhibit or not somatic mechanical hyperalgesia; these rats were named DH and DNH respectively. At three weeks of diabetes, we present evidence that somatic mechanical hyperalgesia was correlated with an enhanced phosphorylation of the NMDAR NR1 subunit (pNR1) in the rat spinal cord. This increase was not found in normal and DNH rats, suggesting that this regulation was specific to hyperalgesia. Double immunofluorescence studies revealed that the numbers of pNR1-immunoreactive neurons and microglial cells were significantly increased in all laminae (I-II and III-VI) of the dorsal horn from DH animals. Western-blots analysis showed no change in NR1 protein levels, whatever the behavioural and glycemic status of the animals. Chronic intrathecal treatment (5μg/rat/day for 7days) by U0126 and MK801, which blocked MEK (an upstream kinase of extracellular signal-regulated protein kinase: ERK) and the NMDAR respectively, simultaneously suppressed somatic mechanical hyperalgesia developed by diabetic rats and decreased pNR1. These results indicate for the first time that increased expression of pNR1 is regulated by ERK and the NMDAR via a feedforward mechanism in spinal neurons and microglia and represents one mechanism involved in central sensitization and somatic mechanical hyperalgesia after diabetes.
authors.affiliation: Clermont Université, Université d'Auvergne, Pharmacologie Fondamentale et Clinique de la Douleur, Laboratoire de Pharmacologie, Faculté de Pharmacie, Clermont-Ferrand, France. laurence.daulhac@u-clermont1.fr
authors.forename: Laurence
authors.initials: L
authors.lastname: Daulhac
authors.forename: Violette
authors.initials: V
authors.lastname: Maffre
authors.forename: Christophe
authors.initials: C
authors.lastname: Mallet
authors.forename: Monique
authors.initials: M
authors.lastname: Etienne
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Privat
authors.forename: Aline
authors.initials: A
authors.lastname: Kowalski-Chauvel
authors.forename: Catherine
authors.initials: C
authors.lastname: Seva
authors.forename: Joseph
authors.initials: J
authors.lastname: Fialip
authors.forename: Alain
authors.initials: A
authors.lastname: Eschalier
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D015153:Blotting, Western; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism / Q000503:physiopathology; D003929:Diabetic Neuropathies / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D006930:Hyperalgesia / Q000378:metabolism / Q000503:physiopathology; D007150:Immunohistochemistry; D008297:Male; D017628:Microglia / Q000187:drug effects / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects / Q000502:physiology*; D020671:Posterior Horn Cells / Q000187:drug effects / Q000378:metabolism* / Q000503:physiopathology; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013116:Spinal Cord / Q000187:drug effects / Q000378:metabolism* / Q000503:physiopathology
chemical_list: D004791:Enzyme Inhibitors; D016194:Receptors, N-Methyl-D-Aspartate; D048049:Extracellular Signal-Regulated MAP Kinases