Peripheral inflammation increased the synaptic expression of NMDA receptors in spinal dorsal horn.
Considerable evidence has indicated that the aberrant, sustained enhancement of spinal NMDA receptors (NMDARs) function is closely associated with behavioral sensitization during inflammatory pain. However, the molecular mechanisms underlying inflammation-induced NMDARs hyperfunction remain poorly understood. The present study performed immunoblotting analysis to evaluate the possible changes in the protein expression of spinal NMDARs after injection of complete Freund's adjuvant (CFA) in mice. We found that CFA did not affect the total protein level of NMDARs subunit NR1 in spinal dorsal horn. However, NR1 immunoreactivity at synapses significantly increased after CFA injection, which was correlated in the time course with the development of mechanical allodynia. Inhibition of spinal NMDARs with D-APV completely eliminated the CFA-induced increase in NR1 immunoreactive density at synapses, and direct application of NMDA onto the spinal cord of naïve mice mimicked the effects of CFA, suggesting the importance of NMDARs activity in regulating the synaptic content of NR1 during inflammatory pain. Moreover, cAMP-dependent protein kinase (PKA) downstream to NMDARs was also required for NR1 synaptic expression because inhibition of PKA activity abolished the enhancement of synaptic NR1 immunoreactivity evoked by either CFA or NMDA. Thus, our data suggested that NMDARs- and PKA-dependent increase in NR1 synaptic expression represented an important mechanism for the hyperfunction of spinal NMDARs following peripheral inflammation.
Department of Molecular Pharmacology, School of Pharmacy, Lanzhou University, Lanzhou, Gansu 730 000, PR China.
Xian
X
Yang
Hong-Bin
HB
Yang
Qin-Jian
QJ
Xie
Xiao-Hua
XH
Liu
Xiao-Dong
XD
Hu
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D000818:Animals; D001522:Behavior, Animal; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005620:Freund's Adjuvant / Q000009:adverse effects; D007839:Functional Laterality; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology*; D007249:Inflammation / Q000139:chemically induced / Q000473:pathology*; D007546:Isoquinolines / Q000494:pharmacology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D016202:N-Methylaspartate / Q000494:pharmacology; D010147:Pain Measurement; D020671:Posterior Horn Cells / Q000473:pathology*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D016194:Receptors, N-Methyl-D-Aspartate / Q000235:genetics / Q000378:metabolism*; D012694:Serine / Q000378:metabolism; D013116:Spinal Cord / Q000473:pathology*; D013347:Subcellular Fractions / Q000378:metabolism / Q000473:pathology; D013449:Sulfonamides / Q000494:pharmacology; D013569:Synapses / Q000378:metabolism* / Q000648:ultrastructure
D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; D007546:Isoquinolines; C409466:NR1 NMDA receptor; D047428:Protein Kinase Inhibitors; D016194:Receptors, N-Methyl-D-Aspartate; D013449:Sulfonamides; D012694:Serine; D016202:N-Methylaspartate; D015763:2-Amino-5-phosphonovalerate; D005620:Freund's Adjuvant; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide