Sara Salimi; Esmaeal Tamaddonfard; Farhad Soltanalinejad-Taghiabad
Volume 12, Issue 4 , December 2021, , Pages 429-436
Abstract
The aim of the present study was to investigate the effects of intra-ventrolateral periaqueductal gray (vlPAG) microinjection of histamine and thioperamide (a histamine H3 receptor antagonist/inverse agonist) on neuropathic pain. To explore the possible mechanism, naloxone was microinjected alone or ...
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The aim of the present study was to investigate the effects of intra-ventrolateral periaqueductal gray (vlPAG) microinjection of histamine and thioperamide (a histamine H3 receptor antagonist/inverse agonist) on neuropathic pain. To explore the possible mechanism, naloxone was microinjected alone or in combination with histamine and thioperamide. Neuropathic pain was induced by the left sciatic nerve chronic constriction injury. Both the right and left sides of vlPAG of the brain were surgically cannulated. Cold allodynia and mechanical hyperalgesia were recorded by acetone evaporation and von Frey filament tests. Areas under curve of allodynia and hyperalgesia were calculated. Histamine (0.50 and 2.00 µg per site), thioperamide (4.00 µg per site) and thioperamide (4.00 µg per site) before histamine (2.00 µg per site) suppressed cold allodynia and mechanical hyperalgesia after microinjection into the vlPAG. Microinjection of naloxone (0.25 and 1.00 µg per site) into the vlPAG had no effect on cold allodynia and mechanical hyperalgesia. The anti-allodynic and anti-hyperalgesic effects induced by microinjection of histamine (2.00 µg per site) and thioperamide (4.00 µg per site) into the vlPAG were inhibited by prior microinjection of naloxone (1.00 µg per site) into the same site. The above-mentioned agents did not alter locomotor activity. Based on our present results, it was concluded that exogenous (by histamine microinjection) and endogenous (by thioperamide microinjection) histamine of the vlPAG might contribute to the descending pain control mechanisms through a naloxone-sensitive mechanism.
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.