Introduction: Pain is an experience which humans encounter it. This phenomenon is a warning about a damaged tissue, but due to the awful sense of it, scientists always attempt to decrease pain in body. Retinoic acid (RT), an active metabolite of natural vitamin A has important roles in modulation of the inflammatory responses. The aim of the present study was to analyze the pain threshold of male wistar rats which were microinjected by RT
Methods: Thirty animals divided into five groups (n=6) as follow: Control group (Acsf microinjected), the second group (DMSO as vehicle of vitamin treated), RT (1, 3, 6) µg/kg was injected intracerebroventricular (i.c.v.) into experimental animals. The tail flick test was used for the behavioral study. In acute (one-dose) and chronic (one-week) models, the drugs were microinjected 30 minutes before behavioral testing.
Results: Results demonstrated that chronic administration of RT, but not acute injection, reduced response latency withdrawals of rats (P<0.05).
Conclusion: These results showed chronic RT exposure can induce hyperalgsia effects in rat and suggest vitamin A may increase the expression of COX2 gene in brain which can raise hyperalgesia in rat.