Loss of NR1 subunit of NMDARs in primary sensory neurons leads to hyperexcitability and pain hypersensitivity: involvement of Ca(2+)-activated small conductance potassium channels.
It is well established that activation of NMDARs plays an essential role in spinal cord synaptic plasticity (i.e., central sensitization) and pain hypersensitivity after tissue injury. Despite prominent expression of NMDARs in DRG primary sensory neurons, the unique role of peripheral NMDARs in regulating intrinsic neuronal excitability and pain sensitivity is not well understood, in part due to the lack of selective molecular tools. To address this problem, we used Advillin-Cre driver to delete the NR1 subunit of NMDARs selectively in DRG neurons. In NR1 conditional knock-out (NR1-cKO) mice, NR1 expression is absent in DRG neurons but remains normal in spinal cord neurons; NMDA-induced currents are also eliminated in DRG neurons of these mice. Surprisingly, NR1-cKO mice displayed mechanical and thermal hypersensitivity compared with wild-type littermates. NR1-deficient DRG neurons show increased excitability, as indicated by increased frequency of action potentials, and enhanced excitatory synaptic transmission in spinal cord slices, as indicated by increased frequency of miniature EPSCs. This hyperexcitability can be reproduced by the NMDAR antagonist APV and by Ca(2+)-activated slow conductance K(+) (SK) channel blocker apamin. Furthermore, NR1-positive DRG neurons coexpress SK1/SK2 and apamin-sensitive afterhyperpolarization currents are elevated by NMDA and suppressed by APV in these neurons. Our findings reveal the hitherto unsuspected role of NMDARs in controlling the intrinsic excitability of primary sensory neurons possibly via Ca(2+)-activated SK channels. Our results also call attention to potential opposing effects of NMDAR antagonists as a treatment for pain and other neurological disorders.
Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27710, USA.
Promila
P
Pagadala
Chul-Kyu
CK
Park
Sangsu
S
Bang
Zheng-Zhong
ZZ
Xu
Rou-Gang
RG
Xie
Tong
T
Liu
Bao-Xia
BX
Han
W Daniel
WD
Tracey
Fan
F
Wang
Ru-Rong
RR
Ji
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D005727:Ganglia, Spinal / Q000378:metabolism; D006930:Hyperalgesia / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D010146:Pain / Q000378:metabolism; D018408:Patch-Clamp Techniques; D024681:Potassium Channels, Calcium-Activated / Q000378:metabolism*; D016194:Receptors, N-Methyl-D-Aspartate; D020133:Reverse Transcriptase Polymerase Chain Reaction; D011984:Sensory Receptor Cells / Q000378:metabolism*; D009435:Synaptic Transmission / Q000502:physiology
D002352:Carrier Proteins; C121673:Gprin1 protein, mouse; D009419:Nerve Tissue Proteins; D024681:Potassium Channels, Calcium-Activated; D016194:Receptors, N-Methyl-D-Aspartate