Acute and chronic nociceptive phases observed in a rat hind paw ischemia/reperfusion model depend on different mechanisms

Complex regional pain syndrome type 1 (CRPS1) may be evoked by ischemia/reperfusion, eliciting acute and chronic pain that is difficult to treat. Despite this, the underlying mechanism of CRPS1 has not been fully elucidated. Therefore, the goal of this study is to evaluate the involvement of inflammation, oxidative stress, and the transient receptor potential ankyrin 1 (TRPA1) channel, a chemosensor of inflammation and oxidative substances, in an animal model of chronic post-ischemia pain (CPIP). Male Wistar rats were subjected to 3 h hind paw ischemia/reperfusion (CPIP model). Different parameters of nociception, inflammation, ischemia, and oxidative stress were evaluated at 1 (acute) and 14 (chronic) days after CPIP. The effect of a TRPA1 antagonist and the TRPA1 immunoreactivity were also observed after CPIP. In the CPIP acute phase, we observed mechanical and cold allodynia; increased levels of tumor necrosis factor-alpha (hind paw), ischemia-modified albumin (IMA) (serum), protein carbonyl (hind paw and spinal cord), lactate (serum), and 4-hydroxy-2-nonenal (4-HNE, hind paw and spinal cord); and higher myeloperoxidase (MPO) and N-acetyl-beta-d-glucosaminidase (NAGase) activities (hind paw). In the CPIP chronic phase, we detected mechanical and cold allodynia and increased levels of IMA (serum), protein carbonyl (hind paw and spinal cord), and 4-HNE (hind paw and spinal cord). TRPA1 antagonism reduced mechanical and cold allodynia 1 and 14 days after CPIP, but no change in TRPA1 immunoreactivity was observed. Different mechanisms underlie acute (inflammation and oxidative stress) and chronic (oxidative stress) phases of CPIP. TRPA1 activation may be relevant for CRPS1/CPIP-induced acute and chronic pain.