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Effect of Melatonin on the Formalin-Induced Pain in White Male Rats
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N Ghaibi   , M Sofiabadi * 1, H Rasol pour , S Dehghan nezhad |
| 1- , Mohasofi@yahoo.com |
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Abstract: (10621 Views) |
| Introduction: Melatonin is the main prod-uct of pineal gland that has been associated with body's physiologic rhythms. New evidence suggests that melatonin plays a role in pain system. For example, the per-ipheral co-administration of melatonin and morphine produce additive analgesic effect. The purpose of this study was to evaluate the effect of central injection of melatonin on the formalin-induced pain in white male rats.
Materials & Methods: In this study, 40 NMRI white rats were divided into four equal groups (each group=10 rats) inclu-ding: control, sham (having canola without melatonin injection) and 2 melatonin group that received melatonin 0.5 and 0.1µg /kg, respectively. The canola was implemented in the right brain ventricle of the rats via sterotaxic method. After 7 days of resting and then returning to normal condition, first dose of melatonin was injected and a half hour after it 50 microliter formalin (2.5 %) was injected at the floor of right foot to evaluate the acute and chronic pain. Data acquisitions were done through counting the number of licking the injected foot and accumulation of dorsal area skin (flinching) for 1 hour. Then, the acquired data were statistically analyzed.
Findings: Administration of melatonin at the acute phase, reduced licking of the inje-cted site in both treatment groups compared to the control group (P<0.05, 0.01). In the chronic phase, the administration of 0.5 µg melatonin, significantly decreased the num-ber of the foot licking compared to the co-ntrol group, especially at 15-40 and 60 minutes of test (P<0.01). The sign of behind skin flinching significantly decreased with using of 0.5µg of melatonin compared to the control group, particularly at the acute phase and beginning time of the chronic phase (P<0.05). This behavior was increa-sed in both groups receiving melatonin at the end of chronic phase, mainly at 55 and 60 minutes of formalin test (P<0.01, 0.001).
Discussion & Conclusion: Our study sho-wed that the central injection of melato-nin has a significant analgesic effect how-ever, the analgesic pattern may vary depen-ding on time. |
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| Keywords: melatonin, formalin test, rats, br-ain ventricle |
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Full-Text [PDF 511 kb]
(2511 Downloads)
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Type of Study: Research |
Subject:
physiology
Received: 2013/10/29 | Accepted: 2013/10/29 | Published: 2013/11/11
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