High-frequency stimulation (HFS) of the sciatic nerve has been reported to produce long-term potentiation (LTP) and long-lasting
pain hypersensitivity in rats. However, the central underlying mechanism remains unclear.
Nicotinamide adenine dinucleotide phosphate (
NADPH) oxidase (NOX) belongs to a group of electron-transporting transmembrane
enzymes that produce
reactive oxygen species (ROS). Here, we found that NOX2 was upregulated in the lumbar spinal dorsal horn after HFS of the left sciatic nerve, which induced bilateral
pain and spinal LTP in both male and female rats. Blocking NOX2 with blocking
peptide or
shRNA prevented the development of bilateral
mechanical allodynia, the induction of spinal LTP, and the phosphorylation of
N-methyl-d-aspartate (
NMDA) receptor 2B (GluN2B) and
nuclear factor kappa-B (NF-κB) p65 after HFS. Moreover, NOX2
shRNA reduced the frequency and amplitude of both spontaneous excitatory postsynaptic currents and miniature excitatory postsynaptic currents in laminar II neurons. Furthermore,
8-hydroxyguanine (8-OHG), an oxidative stress marker, was increased in the spinal dorsal horn. Spinal application of ROS scavenger,
Phenyl-N-tert-butylnitrone (PBN), depressed the already established spinal LTP. Spinal application of H2O2, one ROS, induced LTP and bilateral
mechanical allodynia, increased the frequency and amplitude of spontaneous excitatory postsynaptic currents in laminar II neurons, and phosphorylated GluN2B and p65 in the dorsal horn. This study provided electrophysiological and behavioral evidence that NOX2-derived ROS in the spinal cord contributed to persistent mirror-image
pain by enhancing the synaptic transmission, which was mediated by increasing presynaptic
glutamate release and activation of
NMDA receptor and NF-κB in the spinal dorsal horn.