Neuropathic pain memory is maintained by Rac1-regulated dendritic spine remodeling after spinal cord injury.
Localized increases in synaptic strength constitute a synaptic basis for learning and memory in the CNS and may also contribute to the maintenance of neuropathic pain after spinal cord injury (SCI) through the de novo formation or elaboration of postsynaptic dendritic structures. To determine whether SCI-induced dendritic spine remodeling contributes to neuronal hyperexcitability and neuropathic pain, we analyzed spine morphometry, localization, and functional influence in dorsal horn (DH) neurons in adult rats 1 month after sham surgery, contusion SCI, and SCI treated with a selective inhibitor of Rac1 activation, NSC23766. After SCI, DH neurons located in lamina IV-V exhibited increased spine density, redistributed spines, and mature spines compared with control neurons, which was associated with enhancement of EPSCs in computer simulations and hyperexcitable responsiveness to innocuous and noxious peripheral stimuli in unit recordings in vivo. SCI animals also exhibited symptoms of tactile allodynia and thermal hyperalgesia. Inhibition of the small GTP-binding protein Rac1 ameliorated post-SCI changes in spine morphology, attenuated injury-induced hyperexcitability of wide-dynamic range neurons, and progressively increased pain thresholds over a 3 d period. This suggests that Rac1 is an important intracellular signaling molecule involved in a spinal dendritic spine pathology associated with chronic neuropathic pain after SCI. Our report provides robust evidence for a novel conceptual bridge between learning and memory on the one hand, and neuropathic pain on the other.
Tan
Andrew M
AM
Departments of Neurology and Neurobiology and Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, Connecticut 06510, USA.
Stamboulian
Severine
S
Chang
Yu-Wen
YW
Zhao
Peng
P
Hains
Avis B
AB
Waxman
Stephen G
SG
Hains
Bryan C
BC
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D003198:Computer Simulation; D049229:Dendritic Spines / Q000378:metabolism* / Q000648:ultrastructure; D004195:Disease Models, Animal; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D006930:Hyperalgesia / Q000378:metabolism / Q000503:physiopathology; D007858:Learning / Q000502:physiology; D008297:Male; D008568:Memory / Q000502:physiology*; D009437:Neuralgia / Q000378:metabolism* / Q000503:physiopathology; D009473:Neuronal Plasticity / Q000502:physiology*; D010147:Pain Measurement; D017288:Pain Threshold / Q000502:physiology; D020671:Posterior Horn Cells / Q000378:metabolism / Q000648:ultrastructure; D051381:Rats; D017207:Rats, Sprague-Dawley; D013119:Spinal Cord Injuries / Q000378:metabolism* / Q000503:physiopathology; D009435:Synaptic Transmission / Q000502:physiology; D020830:rac1 GTP-Binding Protein / Q000037:antagonists & inhibitors / Q000378:metabolism*
D004791:Enzyme Inhibitors; C499134:Rac1 protein, rat; D020830:rac1 GTP-Binding Protein