RESUMO
OBJECTIVE: The objective of the current study is to define whether intra-articular nerve growth factor (NGF), an inflammatory mediator that contributes to osteoarthritic pain, is necessary and sufficient for the development or maintenance of injury-induced facet joint pain and its concomitant spinal neuronal hyperexcitability. METHOD: Male Holtzman rats underwent painful cervical facet joint distraction (FJD) or sham procedures. Mechanical hyperalgesia was assessed in the forepaws, and NGF expression was quantified in the C6/C7 facet joint. An anti-NGF antibody was administered intra-articularly in additional rats immediately or 1 day following facet distraction or sham procedures to block intra-articular NGF and test its contribution to initiation and/or maintenance of facet joint pain and spinal neuronal hyperexcitability. NGF was injected into the bilateral C6/C7 facet joints in separate rats to determine if NGF alone is sufficient to induce these behavioral and neuronal responses. RESULTS: NGF expression increases in the cervical facet joint in association with behavioral sensitivity after that joint's mechanical injury. Intra-articular application of anti-NGF immediately after a joint distraction prevents the development of both injury-induced pain and hyperexcitability of spinal neurons. Yet, intra-articular anti-NGF applied after pain has developed does not attenuate either behavioral or neuronal hyperexcitability. Intra-articular NGF administered to the facet in naïve rats also induces behavioral hypersensitivity and spinal neuronal hyperexcitability. CONCLUSION: Findings demonstrate that NGF in the facet joint contributes to the development of injury-induced joint pain. Localized blocking of NGF signaling in the joint may provide potential treatment for joint pain.
