title: Interaction between the dopaminergic and opioidergic systems in dorsal hippocampus in modulation of formalin-induced orofacial pain in rats.
abstract: The hippocampus is a region of the brain that serves several functions. The dopaminergic system acts through D1- and D2-like receptors to interfere in pain modulation and the opioid receptors play major roles in analgesic processes and there are obvious overlaps between these two systems. The present study investigated the interaction between the opioidergic and dopaminergic systems in the dorsal hippocampus (CA1) region for formalin-induced orofacial pain. Two guide cannulae were stereotaxically implanted in the CA1 region and morphine (0.5, 1, 2 and 4 μg/0.5 μl saline) and naloxone (0.3, 1 and 3 μg/0.5 μl saline) were used as the opioid receptor agonist and antagonist, respectively. SKF-38393 (1 μg/0.5 μl saline) was used as a D1-like receptor agonist, quinpirole (2 μg/0.5 μl saline) as a D2-like receptor agonist, SCH-23390 (0.5 μg/0.5 μl saline) as a D1-like receptor antagonist and sulpiride (3 μg/0.5 μl DMSO) as a D2-like receptor antagonist. To induce orofacial pain, 50 μl of 1% formalin was subcutaneously injected into the left side of the upper lip. Our results showed that different doses of morphine significantly reduced orofacial pain in both phases induced by formalin. Naloxone (1 and 3 μg) reversed morphine induced analgesia in CA1. SKF-38393 and quinpirole with naloxone (1 μg) significantly decreased formalin-induced orofacial pain in both phases. SCH-23390 had no effect on the antinociceptive response of morphine in both phases of orofacial pain. Sulpiride reversed the antinociceptive effects of morphine only in the first phase, but this result was not significant. Our findings suggest that there is cross-talk between the opioidergic and dopaminergic systems. Opioidergic neurons also exerted antinociceptive effects by modulation of the dopaminergic system in the CA1 region of the brain.
authors: Physiology-Pharmacology Research Center, Rafsanjan University of Medical Sciences, Rafsanjan, Iran.
authors: Zahra
authors: Z
authors: Reisi
authors: Neuroscience Research Center, Shahid Beheshti University of Medical Sciences, PO Box 19615-1178, Tehran, Iran; Faculty of Dentistry, International Branch of Shahid Beheshti University of Medical Sciences, Tehran, Iran.
authors: Amir
authors: A
authors: Haghparast
authors: School of Medicine, Hamadan University of Medical Sciences, Hamadan, Iran.
authors: Pouyan
authors: P
authors: Pahlevani
authors: Physiology-Pharmacology Research Center, Rafsanjan University of Medical Sciences, Rafsanjan, Iran.
authors: Ali
authors: A
authors: Shamsizadeh
authors: Neuroscience Research Center, Shahid Beheshti University of Medical Sciences, PO Box 19615-1178, Tehran, Iran. Electronic address: haghparast@yahoo.com.
authors: Abbas
authors: A
authors: Haghparast
mesh_terms: D000818:Animals; D001552:Benzazepines / Q000494:pharmacology; D056547:CA1 Region, Hippocampal / Q000503:physiopathology*; D004298:Dopamine / Q000502:physiology*; D018491:Dopamine Agonists / Q000008:administration & dosage; D018492:Dopamine Antagonists / Q000008:administration & dosage; D005157:Facial Pain / Q000139:chemically induced* / Q000503:physiopathology; D005557:Formaldehyde / Q000633:toxicity*; D008297:Male; D009270:Naloxone / Q000008:administration & dosage; D009292:Narcotic Antagonists / Q000008:administration & dosage; D018847:Opioid Peptides / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D001552:Benzazepines; D018491:Dopamine Agonists; D018492:Dopamine Antagonists; D009292:Narcotic Antagonists; D018847:Opioid Peptides; C534628:SCH 23390; D005557:Formaldehyde; D009270:Naloxone; D004298:Dopamine
keywords: Dopamine receptor; Formalin test; Hippocampus; Opioid receptor; Orofacial pain; Rat