u-0126 and Peripheral-Nervous-System-Diseases

Focal adhesion kinase (FAK) is one of the nonreceptor protein tyrosine kinases critical for the dynamic regulation of cell adhesion structures. Recent studies have demonstrated that FAK is also localized at excitatory glutamatergic synapses and is involved in long-term modification of synaptic strength. However, whether FAK is engaged in nociceptive processing in the spinal dorsal horn remains unresolved. The current study shows that intraplantar injection of complete Freund's adjuvant (CFA) in mice significantly increases FAK autophosphorylation at Tyr397, indicating a close correlation of FAK activation with inflammatory pain. FAK activation depended on the activity of N-methyl-D-aspartate-subtype glutamate receptor (NMDAR) and metabotropic glutamate receptor (mGluR) because pharmacological inhibition of NMDAR or group I mGluR totally abolished FAK phosphorylation induced by CFA. The active FAK operated to stimulate extracellular signal-regulated kinase1/2 (ERK1/2), which boosted the protein expression of GluN2B subunit-containing NMDAR at the synaptosomal membrane fraction. Inhibition of FAK activity by spinal expression of a kinase-dead FAK(Y397F) mutant repressed ERK1/2 hyperactivity and reduced the synaptic concentration of NMDAR in CFA-injected mice. Electrophysiological recording demonstrated that intracellular loading of specific anti-FAK antibody significantly reduced the amplitudes of NMDAR-mediated excitatory postsynaptic currents on lamina II neurons from inflamed mice but not from naive mice. Behavioral tests showed that spinal expression of FAK(Y397F) generated a long-lasting alleviation of CFA-induced mechanical allodynia and thermal hyperalgesia. These data indicate that FAK might exaggerate NMDAR-mediated synaptic transmission in the spinal dorsal horn to sensitize nociceptive behaviors.

Topics: Animals; Butadienes; Disease Models, Animal; Enzyme Activation; Enzyme Inhibitors; Focal Adhesion Kinase 1; Freund's Adjuvant; Male; MAP Kinase Signaling System; Mice; Mice, Inbred Strains; Mutation; Neurons; Neurotransmitter Agents; Nitriles; Patch-Clamp Techniques; Peripheral Nervous System Diseases; Phosphorylation; Receptors, N-Methyl-D-Aspartate; Signal Transduction; Spinal Cord Dorsal Horn; Subcellular Fractions; Synaptic Potentials; Transduction, Genetic

Neuropathic pain that occurs after peripheral nerve injury is poorly controlled by current therapies. Increasing evidence shows that mitogen-activated protein kinase (MAPK) play an important role in the induction and maintenance of neuropathic pain. Here we show that activation of extracellular signal-regulated protein kinases 5 (ERK5), also known as big MAPK1, participates in pain hypersensitivity caused by nerve injury. Nerve injury increased ERK5 phosphorylation in spinal microglia and in both damaged and undamaged dorsal root ganglion (DRG) neurons. Antisense knockdown of ERK5 suppressed nerve injury-induced neuropathic pain and decreased microglial activation. Furthermore, inhibition of ERK5 blocked the induction of transient receptor potential channels and brain-derived neurotrophic factor expression in DRG neurons. Our results show that ERK5 activated in spinal microglia and DRG neurons contributes to the development of neuropathic pain. Thus, blocking ERK5 signaling in the spinal cord and primary afferents has potential for preventing pain after nerve damage.

Topics: Animals; Butadienes; Enzyme Inhibitors; Functional Laterality; Ganglia, Spinal; Hyperalgesia; Male; Microglia; Mitogen-Activated Protein Kinase 7; Nerve Tissue Proteins; Neuralgia; Neurons, Afferent; Nitriles; Oligonucleotides, Antisense; Pain Measurement; Peripheral Nervous System Diseases; Rats; Rats, Sprague-Dawley; Spinal Nerves; Time Factors; TRPV Cation Channels

Changes in the expression of many genes underlie injury-elicited plasticity in the spinal dorsal horn. Homer1 is a recently identified gene that appears to play a critical role in the expression of synaptic plasticity in several brain regions, including the hippocampus. In this study we investigated the early consequences of chronic constriction injury of the sciatic nerve on Homer1 gene expression in the spinal dorsal horn. Significant increases in Homer1a mRNA levels in the ipsilateral dorsal horn were detected at 4h post-ligation, and these levels remained elevated at 8h before returning to baseline values by 24h after the ligation. In contrast, the levels of Homer1b/c mRNA did not change at any of these selected post-ligation times. The ligation-associated induction of Homer1a was dependent on activation of NMDA receptors and the extracellular signal-regulated kinase 1 and 2 (ERK1/2) pathway. The non-competitive NMDA-receptor antagonist, MK-801, and a specific inhibitor of the ERK1/2 pathway, U0126, significantly attenuated the injury-elicited increases in Homer1a mRNA when compared to saline-treated animals. These data provide the first evidence for a potential role of Homer1a in peripheral nerve injury-elicited plasticity in the spinal dorsal horn. These data also imply that the early and transient up-regulation of Homer1a gene expression may be an important contributor to the eventual development of neuropathic pain.

Topics: Animals; Butadienes; Carrier Proteins; Constriction, Pathologic; Dizocilpine Maleate; Homer Scaffolding Proteins; Ligation; Male; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Neuronal Plasticity; Nitriles; Pain; Peripheral Nervous System Diseases; Posterior Horn Cells; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; RNA, Messenger; Sciatic Nerve; Up-Regulation