اثر عصاره آبي گياه شبنم خورشيد (DROSERA SPATULATA) بر سرعت شليك نورون هاي هسته ي پاراژيگانتوسلولاريس پس از القاي درد توسط فرمالين در موش سفيد بزرگ

Effect of aqueous extract of Drosera spaiulata on firing rate of paragigantocellularis nucleus neurons after pain induction by formalin in rats

Introduction: We have previously demonstrated that i.p. injection of aqueous extract of the aerial parts of Drosera spatulata (Droseraceae) can induce remarkable analgesia in both phases of formalin test in rats. Analgesia induced in acute phase of formalin test is mainly mediated by the activation of central analgesic mechanisms. Since paragigantocellularis (PGi) nucleus activation, as a part of the brain descending pain control systems causes analgesian. Therefore, we studied the role of this nucleus in analgesic action of the extract in acute pain. This was performed by the assessment of the effects of the extract treatment on PGi neural activity that was augmented by injection of formalin to contralateral hind paw of anesthetized rats. Methods: Twenty urethane anesthetized (1.2- 1.5 g/kg, i.p.) male rats were divided into control, D. Spatulata extract (0.05 mg/kg, i.p.) and sodium salicylate (300 mg/kg, i.p.) treated groups. Firing rate of PGi neurons were recorded by extracellular single unit recording technique. Formalin (50|il, 2%, s.c.) was injected to the plantar surface of the hind paw of rats 30 min after each of the above treatments. Alterations in the response of the opposite PGi neurons were recorded. Data was analyzed by Wilcoxon ranking test. Results: In rats that received extract injections, the firing rate was increased in 66.6% of PGi neurons, while it was decreased in 16.6% of neurons (p<0.001). The extract had no effect on 16.6% of neurons in formalin injected rats. While, sodium salicylate treatment significantly decreased the firing rate in 50% of PGi neurons in formalin pretreated rats (p<0.001). Conclusion: The relation between PGi neuronal augmentation and analgesia was previously reported. Thus, the augmentation of firing rates in a high percentage of PGi neurons after the extract injection provides evidence about the role of PGi nucleus in reduction of pain in the acute phase of the formalin test. Key words: Aqueous extract of Drosera Spatulata, Formalin induced pain, Paragigantocellularis nucleus, Single unit recording, Rat ^Corresponding author e-mail: Hassanpm@yahoo.com Available online at: www.phypha.ir/ppj 281