Interference between histaminergic and cholinergic systems on the formalin plantar pain response in rats

The purpose of this study was to investigate the interference of histaminergic and cholinergic systems on the pain response in rats. In this study, adult male Wistar rats were selected in the weigh range of 200-250 g. Rats were kept in groups of six rats in plastic cages and in a room with ambient conditions and the optimum temperature about 23±2 °C and 12 hours of light; and the animals were fed with commercial pellet food. Stainless normal saline solution was formalin solution of 1, 2.5, and 5% which was prepared from commercial Formalin 37% with adding normal saline. Physostigmine solution of Eserine 0.01 Mg/Kg (Sigma-aldrich Co) was used as muscarinic receptors’ agonist. Thioperamide solution of Thioperamide maleate salt 2.5 Mg/Kg (Sigma-aldrich Co) was as H3 receptors’ antagonist solved with normal saline. Atropine solution of 2 Mg/Kg (Sigma-aldrich Co) was solved with normal saline as muscarinic receptor antagonist. The results showed that subcutaneous injection of atropine did not have significant effect on pain caused by plantar injection of formalin. Thioperamide intraperitoneal injection of dose 2.5 mg per kg of body weight caused a significant reduction (P<0.05) of pain in both phases of pain. Subcutaneous injection of atropine was significantly prevented from the pain of thioperamide in the second phase of the pain response as licking foot (P<0.05). Subcutaneous injection of physostigmine of 0.1 mg per kg of body weight caused a significant reduction of the pain response in both steps (P<0.05). Thioperamide intraperitoneal injection alone decreased pain response to formalin injection in both periods significantly (P<0.05). It (2.5 mg per kg of body weight) had no effect on reducing the pain of subcutaneous injection of physostigmine in both stages. It can be said that the environmental level, histaminergic and cholinergic systems have interaction in the regulation of pains originated plantar and muscarinic receptors and histamine H3 receptors are involved in the interaction between thioperamide and physostigmine.

Atropine, Thioperamide, Physostigmine, rat