The Effect of the Histaminergic System on the Nociceptive Response to Plantar Injection of Formalin in Rats

The present study aims to review the effect of the histaminergic system on the plantar nociception process in rats. In this study, adult male Wistar rats in the weight range of 200 to 250 grams were used. The rats were divided into groups of six and they were put in plastic cages in a room with desirable temperature of about 23±2ºC, desirable environmental conditions and 12 hours of light. They were fed with commercial pellet food. They had 24/7 access to food and water. All of the experiments were performed in the time interval of 8 to 15 hours. 5/2 Mg/Kg thioperamide solution was used as the H3 receptor antagonist along with normal saline. There were 6 rats in the first group, i.e. control group. In this group, the nociceptive response to plantar injection of normal saline was reviewed. In the second, third and fourth group the nociceptive response was reviewed 30 minutes after the intraperitoneal injection of 1, 2.5 and 5mg thioperamide per one kilogram of body weight was reviewed. There were 6 rats in each of these groups. At first, 2 Mg/Kg of atropine was subcutaneously injected and ten minutes later, there was an intraperitoneal injection of 15Mg/Kg of thioperamide. After 20 minutes, formalin was injected to the foot plantar of rats and their nociceptive response to formalin was studied. The results showed that intraperitoneal injection of thioperamide causes a significant decrease (P<0.05) in the nociception (licking and hitting the injected foot) in the second phase. Intraperitoneal injection of 1 and 2.5 Mg/Kg thioperamide reduces the nociception as hitting the foot in the first phase and in the second phase in comparison with 1 and 5 Mg/Kg thioperamide. It can be concluded that the effect of thioperamide seen in the present study is because of inhibiting the H3 receptors.

Pain Receptors, Thioperamide, Histaminergic System, Rat