title: The role of nicotinic acetylcholine and opioid systems of the ventral orbital cortex in modulation of formalin-induced orofacial pain in rats.
abstract: Nicotinic acetylcholine and opioid receptors are involved in modulation of pain. In the present study, we investigated the effects of microinjection of nicotinic acetylcholine and opioid compounds into the ventral orbital cortex (VOC) on the formalin-induced orofacial pain in rats. For this purpose, two guide cannulas were placed into the left and right sides of the VOC of the brain. Orofacial pain was induced by subcutaneous injection of a diluted formalin solution (50μl, 1.5%) into the right vibrissa pad and face rubbing durations were recorded at 3-min blocks for 45min. Formalin produced a marked biphasic pain response (first phase: 0-3min and second phase: 15-33min). Epibatidine (a nicotinic receptor agonist) at doses of 0.05, 0.1 and 0.2μg/site, morphine (an opioid receptor agonist) at doses of 0.5, 1 and 2μg/site and their sub-analgesic doses (0.025μg/site epibatidine with 0.25μg/site morphine) combination treatment suppressed the second phase of pain. The antinociceptive effect induced by 0.2μg/site of epibatidine, but not morphine (2μg/site), was prevented by 2μg/site of mecamylamine (a nicotinic receptor antagonist). Naloxone (an opioid receptor antagonist) at a dose of 2μg/site prevented the antinociceptive effects induced by 2μg/site of morphine and 0.2μg/site of epibatidine. No above-mentioned chemical compounds affected locomotor activity. These results showed that at the VOC level, epibatidine and morphine produced antinociception. In addition, opioid receptor might be involved in epibatidine-induced antinociception, but the antinociception induced by morphine was not mediated through nicotinic acetylcholine receptor.
authors: Division of Physiology, Department of Basic sciences, Faculty of Veterinary Medicine, Urmia University, Urmia, Iran.
authors: Shahnaz
authors: S
authors: Yousofizadeh
authors: Division of Physiology, Department of Basic sciences, Faculty of Veterinary Medicine, Urmia University, Urmia, Iran. Electronic address: etamaddonfard@yahoo.com.
authors: Esmaeal
authors: E
authors: Tamaddonfard
authors: Division of Pathology, Department of Pathobiology, Faculty of Veterinary Medicine, Urmia University, Urmia, Iran.
authors: Amir Abbas
authors: AA
authors: Farshid
mesh_terms: D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000627:therapeutic use; D000818:Animals; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000008:administration & dosage / Q000037:antagonists & inhibitors / Q000627:therapeutic use*; D004359:Drug Therapy, Combination; D005157:Facial Pain / Q000139:chemically induced / Q000188:drug therapy*; D005557:Formaldehyde; D008124:Locomotion / Q000187:drug effects; D008297:Male; D008464:Mecamylamine / Q000008:administration & dosage / Q000494:pharmacology*; D008845:Microinjections; D009020:Morphine / Q000008:administration & dosage / Q000037:antagonists & inhibitors / Q000627:therapeutic use*; D009270:Naloxone / Q000008:administration & dosage / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000008:administration & dosage / Q000494:pharmacology; D018722:Nicotinic Agonists / Q000008:administration & dosage / Q000627:therapeutic use; D018733:Nicotinic Antagonists / Q000008:administration & dosage / Q000494:pharmacology; D010147:Pain Measurement / Q000187:drug effects; D017397:Prefrontal Cortex / Q000187:drug effects* / Q000378:metabolism; D011725:Pyridines / Q000008:administration & dosage / Q000037:antagonists & inhibitors / Q000627:therapeutic use*; D051381:Rats
chemical_list: D000701:Analgesics, Opioid; D019086:Bridged Bicyclo Compounds, Heterocyclic; D009292:Narcotic Antagonists; D018722:Nicotinic Agonists; D018733:Nicotinic Antagonists; D011725:Pyridines; D005557:Formaldehyde; D009270:Naloxone; D008464:Mecamylamine; D009020:Morphine; C082748:epibatidine
keywords: (+/−)-epibatidine dihydrochloride (PubChem CID: 16219300); Nicotinic acetylcholine receptor; Normal saline (PubChem: 5234); Opioid receptor; Orofacial pain; Rats; Ventral orbital cortex; formaldehyde solution (PubChem CID: 712); mecamylamine hydrochloride (PubChem CID: 13221); morphine sulfate (PubChem CID: 5464280); naloxone hydrochloride (PubChem CID: 5464092)