title: GABAergic disinhibition induced pain hypersensitivity by upregulating NMDA receptor functions in spinal dorsal horn.
abstract: Intense noxious stimuli impair GABAergic inhibition in spinal dorsal horn, which has been proposed as a critical contributor to pathological pain. However, how the reduced inhibition exacerbates the transfer of nociceptive information at excitatory glutamatergic synapses is still poorly understood. The present study demonstrated that one of the striking consequences of GABAergic disinhibition was to enhance the function of N-methyl-D-aspartate subtype glutamate receptors (NMDARs), a well-characterized player in central sensitization. We found that intrathecal application of bicuculline, a GABA(A) receptor antagonist, to remove the inhibition readily elicited mechanical allodynia in naive mice, which could be dose-dependently attenuated by NMDARs antagonist D-APV. Biochemical analysis demonstrated that bicuculline did not affect the total expression levels of the obligatory NMDARs subunit NR1 and the regulatory subunit NR2A and NR2B. However, bicuculline promoted NR1 phosphorylation at Serine 897 (NR1-S897) by cAMP-dependent protein kinase (PKA). This PKA-mediated phosphorylation incorporated NR1 along with NR2B into synapses. When PKA inhibitor H-89 was intrathecally applied, it totally eliminated bicuculline-induced NMDARs phosphorylation, synaptic redistribution as well as pain sensitization. Importantly, the reduced inhibition also operated to enhance NMDARs functions after peripheral inflammation, because spinal injection of diazepam to rescue the inhibition in inflamed mice greatly depressed PKA phosphorylation of NR1-S897, reduced the synaptic concentration of NR1/NR2B and meanwhile, alleviated the inflammatory pain. These data suggested that removal of GABAergic inhibition allowed for PKA-mediated NMDARs phosphorylation and synaptic accumulation, thus exaggerating NMDARs-dependent nociceptive transmission and behavioral sensitization.
authors.affiliation: Department of Molecular Pharmacology, School of Pharmacy, Lanzhou University, Lanzhou, Donggang West Rd 199, Gansu 730000, PR China.
authors.forename: Jing
authors.initials: J
authors.lastname: Cao
authors.forename: Xian
authors.initials: X
authors.lastname: Yang
authors.forename: Yan-Ni
authors.initials: YN
authors.lastname: Liu
authors.forename: Zhan-Wei
authors.initials: ZW
authors.lastname: Suo
authors.forename: Lei
authors.initials: L
authors.lastname: Shi
authors.forename: Cheng-Rong
authors.initials: CR
authors.lastname: Zheng
authors.forename: Hong-Bin
authors.initials: HB
authors.lastname: Yang
authors.forename: Shuai
authors.initials: S
authors.lastname: Li
authors.forename: Xiao-Dong
authors.initials: XD
authors.lastname: Hu
mesh_terms: D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D000818:Animals; D001640:Bicuculline / Q000037:antagonists & inhibitors / Q000494:pharmacology; D003975:Diazepam / Q000494:pharmacology; D004347:Drug Interactions; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D058787:GABA-A Receptor Antagonists / Q000494:pharmacology; D006930:Hyperalgesia / Q000139:chemically induced / Q000378:metabolism / Q000503:physiopathology*; D007546:Isoquinolines / Q000494:pharmacology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology*; D010766:Phosphorylation / Q000187:drug effects; D020671:Posterior Horn Cells / Q000378:metabolism / Q000503:physiopathology*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011963:Receptors, GABA-A / Q000502:physiology*; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*; D013449:Sulfonamides / Q000494:pharmacology
chemical_list: D018691:Excitatory Amino Acid Antagonists; D058787:GABA-A Receptor Antagonists; D007546:Isoquinolines; D047428:Protein Kinase Inhibitors; D011963:Receptors, GABA-A; D016194:Receptors, N-Methyl-D-Aspartate; D013449:Sulfonamides; D015763:2-Amino-5-phosphonovalerate; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide; D003975:Diazepam; D001640:Bicuculline