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The involvement of the transient receptor potential A1 (TRPA1) in the maintenance of mechanical and cold hyperalgesia in persistent inflammation.

Diogo Santos M da Costa, Flavia Carla Meotti, Edinéia Lemos Andrade, Paulo César Leal, Emerson Marcelo Motta, João B Calixto

Pain, 2010 Mar , 148, 431-7

This study investigated the role of TRPA1 in the development and maintenance of mechanical and cold hyperalgesia in persistent inflammation induced by Complete Freund's Adjuvant (CFA) in mice. The intraplantar ( injection of CFA induced a long lasting (28 days) hyperalgesia for both mechanical and thermal (cold) stimuli. The intraperitoneal (i.p., 30-300 mg/kg), intraplantar (, 100 microg/site) or intrathecal (i.t., 10 microg/site) injection of the TRPA1 selective antagonist HC-030031 significantly reduced the mechanical hyperalgesia evaluated by the von Frey hair test. The effect of HC-030031 was evidenced on the day after CFA injection and was kept throughout the test. However, the intracerebroventricular (i.c.v., 10 microg/site) injection of HC-030031 did not interfere with CFA-induced hyperalgesia. Treatment with HC-030031 (300 mg/kg, i.p.) completely inhibited the noxious cold hyperalgesia induced by tetrafluoroethane in mice that received CFA. The pre-treatment with the TRPA1 oligonucleotide antisense (AS-ODN, i.t.) consistently prevented both mechanical and cold hyperalgesia. Interestingly, both TRPA1 protein expression and mRNA were over-expressed in spinal cord and dorsal root ganglia (DRG) of mice treated with CFA, an effect that was fully prevented by the pre-treatment with the TRPA1 antagonist HC-030031. Collectively, the present results showed that TRPA1 present at either peripheral or spinal sites play a relevant role in the development and maintenance of both mechanical and cold hyperalgesia during CFA-induced inflammation. Thus, TRPA1 selective antagonists represent promising candidates to treat hyperalgesia in persistent inflammatory states.