3-Nitrotyrosine activates excitatory interneurons by inhibiting GABA receptors in the rat spinal dorsal horn

Introduction: 3-Nitrotyrosine (3-NT) is a stable biomarker formed when reactive nitrogen species (RNS) interact with tyrosine residues. Emerging evidence suggests that RNS can amplify pain and contribute to chronic pain conditions. However, 3-NT is considered a relatively stable byproduct, and its role in pain mechanisms has not been thoroughly investigated. Objective: This study was conducted to investigate the effect of 3-NT in spinal dorsal horn neurons. Methods: We evaluated the effects of 3-NT on spontaneous excitatory postsynaptic currents (sEPSCs) and miniature inhibitory postsynaptic currents (mIPSCs) in spinal dorsal horn neurons from male Sprague-Dawley rats. Blind whole-cell patch-clamp recordings were performed on transverse slices prepared from the isolated lumbosacral spinal cord. Results: Perfusion of 3-NT increased the frequency and amplitude of sEPSCs in spinal horn neurons in a concentration-dependent manner. However, 6-cyano-7-nitroquinoxaline-2,3-dione, an AMPA/kainate receptor antagonist, blocked the enhancement of sEPSCs by 3-NT. In addition, 3-NT administration had no effect on the frequency and amplitude of miniature EPSCs (mEPSCs) in the presence of tetrodotoxin , a sodium channel blocker. Conversely, 3-NT decreased the amplitude of mIPSCs in the presence of tetrodotoxin. 3-Nitrotyrosine decreased the amplitude of mIPSCs when strychnine, a glycine receptor antagonist, was present. However, in the presence of bicuculline, a GABA A receptor antagonist, 3-NT did not alter the amplitude of mIPSCs. Conclusion: 3-Nitrotyrosine increases spontaneous glutamate release from the presynaptic terminal to spinal dorsal horn neurons by inhibiting GABA receptors on excitatory interneurons, which in turn enhances their activity.