<b>Reactive oxygen species actions on excitatory synaptic transmission in spinal substantia gelatinosa neurons </b>

Abstract

Reactive oxygen species (ROS) are a molecular species which come from O2 generated in intravital energy metabolism and the phylaxis process, and are highly-reactive. Two common examples of ROS are super-oxide (O2-) and hydrogen peroxide (H2O2). ROS are absolutely necessary to maintain life, but it is thought that surplus ROS which cannot be fully degraded by intracellular enzymes cause various disorders such as cancer or arteriosclerosis. Recent studies have suggested that ROS are involved in chronic pain such as neuropathic pain or inflammatory pain in the spinal cord. For instance, it has been reported that ROS participate in long-term potentiation in the dorsal horn of the spinal cord and is a contributing factor of secondary hyperalgesia. However, the cellular mechanism of ROS is still unclear in the dorsal horn of the spinal cord. To address this issue, we investigated the effect of ROS on glutamatergic excitatory synaptic transmission in substantia gelatinosa (SG) neurons of adult rat spinal cord slices by using the whole-cell patch-clamp technique. A ROS donor, tert-butyl hydroperoxde (t-BOOH), superfused for 5 min markedly increased the frequency and amplitude of spontaneous excitatory postsynaptic currents (sEPSCs). The t-BOOH-induced increases in sEPSC frequency were resistant to tetrodotoxin. However, in the presence of a non-NMDA receptor antagonist, CNQX, t-BOOH did not generate any sEPSC. Furthermore, the tBOOH-induced increases in sEPSC frequency were inhibited by the scavenger N-tert-butyl-α-phenyl nitrone. In the presence of a TRPA1 channel antagonist, HC-030031, t-BOOH-induced increases in sEPSC frequency were inhibited. On the other hand, in the presence of a TRPV1 channel antagonist, capsazepine, t-BOOH-induced increases in sEPSC frequency and amplitude were not affected. These results indicate that ROS enhances the spontaneous release of L-glutamate from presynaptic terminals onto the SG neurons through TRPA1 channel activation.