Elsevier

Neuroscience

Volume 125, Issue 1, 2004, Pages 269-275
Neuroscience

The role of the N-methyl-d-aspartate receptor NR1 subunit in peripheral nerve injury-induced mechanical allodynia, glial activation and chemokine expression in the mouse

https://doi.org/10.1016/j.neuroscience.2004.01.024Get rights and content

Abstract

The N-methyl-d-aspartate receptor (NMDAR) has been strongly implicated in mechanisms of persistent pain states. The purpose of the present study was to determine whether the NMDAR NR-1, a key subunit in regulation of NMDAR channel complex is directly contributing to the onset and propagation of peripheral nerve injury-induced allodynia and whether N-methyl-d-aspartate (NMDA) signaling interacts with spinal chemokine (chemotactic cytokines) expression and glial activation. We used genetically engineered male mice that had their normal NR1 gene knocked out and expressed a modified NR1 gene at either normal level (NR1 +/+, wild type) or at a low level (NR1± , knock down). Each mouse underwent a peripheral nerve injury in which the lumbar 5 spinal segment (L5) nerve was transected. Mechanical allodynia was assessed using 0.008 and 0.015 g von Frey filaments on days 1, 3, 5, 7, 10, 14, 17 and 21 post-surgery. Mice were killed on day 21 and the harvested L5 spinal cord was analyzed for chemokine expression using RNAse protection assay. In a separate study, glial expression using immunohistochemistry was assessed in both groups 7 days following peripheral nerve injury. The NR1± mice displayed decreased mechanical allodynia in comparison to their wild type counterparts. However, even with dramatically impaired NMDA receptor signaling, there was still evidence of tactile hypersensitivity. Using the RPA analysis, we found decreases in mRNA chemokine expression in the NR1± mice as compared with NR1+/+ mice. There were no apparent differences in microglial or astrocytic expression between the wild type and knock down mice. These data provide important insights into the cascade of events involving the dynamic interaction between NMDAR function and spinal chemokine and glial production in neuropathic pain states. The results support the findings that chemokine signaling releases glutamate in the spinal cord.

Section snippets

NR1 knock down mice

The knockdown founder mice were generated by microinjecting NR1 constructs into C57BL/6×CBA-fertilized eggs. These mice had the normal NR1 gene knocked down and express a modified NR1 gene at a low level (NR±) (Iwasato et al., 1997, Li et al., 1994). The genotyped knockdown NR1± mice were backcrossed seven to eight times to C57BL/6. B6 were used for the initial mating with founder mice and all other breedings. The transgene is transmitted through the germ line. The generation of NR1 transgenic

Mechanical allodynia

All mice exhibited mechanical allodynia following L5 spinal nerve transection. However, the behavioral response of the NR1 knock down was significantly decreased (P<0.001) in comparison to the wild type mice. The difference in allodynic response was sustained over the postoperative period, for both the 0.008 (results not shown) and 0.015 (Fig. 1) gram von Frey filaments. A sham surgery group was not included in this study since it has been extensively shown in both mice and rats that the sham

Discussion

Using a unique genetically modified mouse model, we confirmed a vital role of NMDA signaling in the pathogenesis of tactile allodynia induced by peripheral nerve injury. The NR1± mice demonstrated a reduced behavioral hypersensitivity but the sensitivity was still present after the L5 spinal nerve transection. These data can be interpreted in two ways: 1) the NR1 deletion resulted in a 50–60% reduction of NR1 protein and thus, NMDAR can still signal glutamate transmission, albeit at a reduced

Acknowledgements

The authors would like to thank Tracy Wynkoop for editorial assistance; Dr. William F. Hickey for monoclonal antibodies and glial expertise; and the following for grant support: National Institute of Drug Abuse grant DA11276 (J.A.D.) and DA 05969 (S.M.S.); the National Institute of Arthritis and Musculoskeletal and Skin Diseases grant AR44757 (J.A.D.), Bristol-Myers Squibb/Zimmer Orthopaedic Foundation (J.A.D.).

References (38)

Cited by (31)

  • Role of Spinal Microglia in Visceral Hyperalgesia and NK1R Up-Regulation in a Rat Model of Chronic Stress

    2009, Gastroenterology
    Citation Excerpt :

    Cytokines may act at different levels in the modulation of nociception, such as modulating transcriptional pathways leading to up-regulation of receptors or channels resulting in increased sensitivity to peripheral stimuli, or they may increase the strength of synaptic neurotransmission between primary and second-order neurons. For example, several studies have described a modulatory role of cytokines on sodium channels or transient receptor potential channels35 as well as on the modulation of AMPA, NMDA, and NK1R trafficking and expression in the CNS and in isolated cell systems.36–39 We previously showed that chronic WA stress leads to increased expression of NK1R in dorsal horn neurons, and this up-regulation plays an important role in visceral hyperalgesia.13

  • Chapter 17 (-)-Linalool Attenuates Allodynia in Neuropathic Pain Induced by Spinal Nerve Ligation in C57/Bl6 Mice

    2009, International Review of Neurobiology
    Citation Excerpt :

    Continuous activation of peripheral afferent fibers by noxious stimulation induces the release of excitatory neurotransmitters into the dorsal horn, and these may elicit pain hypersensitivity or central sensitization. For instance, activation of the NMDA receptor in the spinal dorsal horn has been shown to be essential for the development of central sensitization and, thereby, mechanical allodynia (Bursztajn et al., 2004; Gao et al., 2005; Ultenius et al., 2006). Several signaling pathways and second messengers mediate central sensitization triggered by the activation of postsynaptic excitatory receptors in the dorsal horn.

View all citing articles on Scopus
View full text