Esmaeal Tamaddonfard; Amir Erfanparast; Emad Khalilzadeh
Volume 3, Issue 2 , June 2012, , Pages 91-95
Abstract
In this study, the effects of subcutaneous (SC) injection of pilocarpine (a cholinomimetic agent) and atropine (a muscarinic receptors antagonist) were investigated on a tonic model of orofacial pain in rats. The contribution of the endogenous analgesic opioid system was assessed using naloxone (an opioid ...
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In this study, the effects of subcutaneous (SC) injection of pilocarpine (a cholinomimetic agent) and atropine (a muscarinic receptors antagonist) were investigated on a tonic model of orofacial pain in rats. The contribution of the endogenous analgesic opioid system was assessed using naloxone (an opioid receptors antagonist). Tonic orofacial pain was induced by SC injection of a diluted formalin solution (1%, 50 μL) in the right upper lip, and the time spent face rubbing was measured in five min blocks for 1 h. Formalin induced a biphasic (first phase: 0-5 min and second phase: 15-35 min) pain response. Pilocarpine significantly (P < 0.05) suppressed both phases of orofacial pain. Atropine did not have any effect and naloxone non-significantly increased the intensity of pain when used alone. In the pre-injection examinations, atropine prevented, but naloxone did not reverse the antinociceptive effect of pilocarpine. The results indicated that SC injection of formalin in the orofacial region induced a marked biphasic pain. Pilocarpine via muscarinic cholinergic receptors produced antinociceptive effect in the orofacial formalin-induced pain. The endogenous opioid analgesic system may not have a role in pilocarpine-induced antinociception.
Emad Khalilzadeh; Esmaeal Tamaddonfard; Amir-Abbas Farshid; Amir Erfanparast
Volume 1, Issue 3 , December 2010, , Pages 166-173
Abstract
The present study investigated the effects of intra-dentate gyrus microinjection of naloxone (an opioid antagonist) and thioperamide (an antagonist of histamine H3 receptors) in the formalin test in rats. Subcutaneous injection of formalin (50 μl, 2.5 %) in the ventral surface of right hind paw produced ...
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The present study investigated the effects of intra-dentate gyrus microinjection of naloxone (an opioid antagonist) and thioperamide (an antagonist of histamine H3 receptors) in the formalin test in rats. Subcutaneous injection of formalin (50 μl, 2.5 %) in the ventral surface of right hind paw produced a biphasic pattern (first phase: 0-5 min and second phase: 15 - 60 min) of licking/biting and shaking of the injected paw. Intra-dentate gyrus microinjections of thioperamide (2 and 4 μg) significantly (P < 0.05) suppressed the pain responses. Microinjections of naloxone (1, 2 and 4 μg) alone into the dentate gyrus non-significantly increased the intensity of pain. Pretreatment with naloxone (4 μg) significantly (P < 0.05) reversed the antinociceptive effect of thioperamide (4 μg). The results indicated that at the level of the dentate gyrus, blockade of histamine H3 receptors with thioperamide produced an analgesic effect. This thioperamide-induced antinociception may be mediated through the endogenous opioid system.
Amir Erfanparast; Esmaeal Tamaddonfard; Amir Abbas Farshid; Emad Khalilzadeh
Volume 1, Issue 2 , September 2010, , Pages 83-89
Abstract
In the present study, the effects of intra-hippocampal microinjections of morphine (an opioid agonist) and naloxone (an opioid antagonist) were investigated in the formalin-induced orofacial pain in rats. Orofacial pain was induced by subcutaneous injection of formalin (1 %, 50 μl) in the upper lip ...
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In the present study, the effects of intra-hippocampal microinjections of morphine (an opioid agonist) and naloxone (an opioid antagonist) were investigated in the formalin-induced orofacial pain in rats. Orofacial pain was induced by subcutaneous injection of formalin (1 %, 50 μl) in the upper lip region and the time spent of face rubbing was measured in 3-min blocks for 45 min. Formalin induced a biphasic (first phase: 0-3 min; second phase: 15-33 min) pain response. Intra-hippocampal microinjections of morphine at doses of 2 and 4 μg significantly (P < 0.05) attenuated the first phase, and at doses of 1, 2 and 4 μg, morphine significantly (P < 0.05) suppressed both phases of formalin-induced orofacial pain response. Intra-hippocampal microinjections of naloxone (1 and 4 μg) non-significantly increased pain when used alone, and in pretreatment microinjection, naloxone (4 μg) reversed morphine (2 μg)-induced antinociception. These results indicate that at the level of hippocampus of the brain, morphine through a naloxone-reversible mechanism produced an antinociceptive effect confronting the pain induced by formalin in the orofacial region in rats.