There areseveral neurotransmittersat feel the pain and processing nervoussystem, and until now cholinergic system has not been well studied in this field. The purpose of this research is investigating effects of atropine and physostigmine on the response of formalin pain test. We divided 50 male wistar head rats into 5 groups , first group ( saline normal injection 5 μ ) , second group ( 1% formalin injection into 50 μ ) , third group ( physostigmine injection 0/1 mg / kg ) , fourth group (atropine injection 2 mg / kg ) , fifth group ( atropine injection 2 mg / kg and physostigmine 0/1 mg/kg ) , after formalin injection , the animals were placed inside mirror pain machine and it was recorded pain response at the time ranges 0-5 and 15-45 . Results investigated with spss software and ANOVA and Duncan’s test. Formalin injection causes pain response in both time ranges. Atropine injection alone had no effect on pain response. Physostigmine effect alone, with a significant reduction (p< 0/05) in the number of foot motions in both stage and duration causesof licking and biting in the 15-45 minutes stage . Atropine and physostigmine injections in fifth group cause significant reduction in the number of foot motions and duration of licking and biting in the time range of 15-45 minutes.Perhaps there is a close relationship between cholinergic system and peripheral pain that can be taken through the action of muscarinic receptors.
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