Long latency event-related potentials in rats: response of amygdala, nucleus accumbens, dorsal hippocampus and frontal cortex to changes in reward characteristics of conditioned stimuli

Recent evidence points to a role of cytokines like tumor necrosis factor-alpha (TNF) in the generation of hyperalgesia not only in inflammatory, but also in neuropathic pain. We used the model of chronic constrictive injury (CCI) of one sciatic nerve in the mouse to investigate which of the two known TNF receptors is involved in the process that leads to hyperalgesia after nerve injury. Neutralizing antibodies to TNF, to the TNF receptor 1 (TNFR1), and to the TNF receptor 2 (TNFR2) were administered by epineurial injection once daily to mice with CCI. Testing of the animals' hind paws with thermal and innocuous mechanical stimuli revealed a reduction in thermal hyperalgesia and mechanical allodynia in mice treated with neutralizing antibodies to TNF and to TNFR1. Neutralizing antibodies to TNFR2 had no effect. We conclude that TNFR1, but not TNFR2, is mediating thermal hyperalgesia and mechanical allodynia after nerve injury.