Background & Objectives : Pain is one of the preceding claims of Parkinson's disease (PD), that its mechanisms have not been fully identified. The purpose of this study was to investigate the chemical pain responses induced by subcutaneous injection of formalin in male parkinsonized rats.

  Method : In this experimental study, 40 Wistar male rats were used and PD was established by stereotaxic injection of 6-OHDA toxin into the striatum. Parkinson's disease severity determined by apomorphine-induced rotation test and then the pain response of 4 groups, the control, sham and 2 weak or full Parkinson groups, were evaluated using formalin test. Data were analyzed using ANOVA and Tukey test.

  Results : In both acute and chronic phases of the formalin test, the symptoms of pain in different groups were same, but at the interphase stage, pain intensity increased more in Parkinson 's rats, especially in full PD group compared to control (p<0.01).

  Conclusion: These results suggest that the nigrostriatal dopaminergic pathway have important modulating role on chronic pain.