title: Effect of microinjection of histamine into the dorsal hippocampus on the orofacial formalin-induced pain in rats.
abstract: Brain neuronal histamine, through its receptors, is involved in central pain perception. In the present study, the effect of microinjection of histamine, mepyramine (a histamine H(1) receptor antagonist) and ranitidine (a histamine H(2) receptor antagonist) into the dorsal hippocampus was investigated on a model of orofacial pain in rats. Orofacial pain was induced by subcutaneous injection of formalin (1%, 50 microl) in the upper lip in rats, and the time spent of face rubbing was measured in 3-min blocks for 45 min. Formalin induced a marked biphasic (first phase: 0-3 min; second phase: 15-33 min) pain. Intra-hippocampal injection of histamine at doses of 0.25, 0.5 microg attenuated the second phase, and at a dose of 1 microg, histamine suppressed both phases of pain. Intra-hippocampal injections of mepyramine and ranitidine at the same doses of 1, 2 and 4 microg produced no effects when used alone. Pretreatments with mepyramine and ranitidine at a same dose of 4 microg prevented histamine (1 microg)-induced antinociception. These results indicate that the activation of brain neuronal histamine at the levels of the hippocampus may produce antinociception. Hippocampal histamine-induced antinociception may be mediated thorough its H(1) and H(2) receptors.
authors.affiliation: Division of Physiology, Department of Basic Sciences, Faculty of Veterinary Medicine, Urmia University, Urmia, Iran.
authors.forename: Amir
authors.initials: A
authors.lastname: Erfanparast
authors.forename: Esmaeal
authors.initials: E
authors.lastname: Tamaddonfard
authors.forename: Amir Abbas
authors.initials: AA
authors.lastname: Farshid
authors.forename: Emad
authors.initials: E
authors.lastname: Khalilzadeh
mesh_terms: D000700:Analgesics / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D005157:Facial Pain / Q000139:chemically induced* / Q000188:drug therapy* / Q000378:metabolism / Q000503:physiopathology; D005557:Formaldehyde / Q000494:pharmacology*; D006624:Hippocampus / Q000187:drug effects* / Q000378:metabolism / Q000503:physiopathology; D006632:Histamine / Q000008:administration & dosage* / Q000494:pharmacology* / Q000627:therapeutic use; D006634:Histamine H1 Antagonists / Q000494:pharmacology; D006635:Histamine H2 Antagonists / Q000494:pharmacology; D007279:Injections, Subcutaneous; D008046:Lip; D008297:Male; D008845:Microinjections; D010147:Pain Measurement; D011738:Pyrilamine / Q000494:pharmacology; D011899:Ranitidine / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D011969:Receptors, Histamine H1 / Q000378:metabolism; D011970:Receptors, Histamine H2 / Q000378:metabolism
chemical_list: D000700:Analgesics; D006634:Histamine H1 Antagonists; D006635:Histamine H2 Antagonists; D011969:Receptors, Histamine H1; D011970:Receptors, Histamine H2; D005557:Formaldehyde; D006632:Histamine; D011899:Ranitidine; D011738:Pyrilamine