title: Microinjection of histamine into the dentate gyrus produces antinociception in the formalin test in rats.
abstract: The present study was aimed to investigate the effects of microinjection of histamine, chlorpheniramine (a histamine H(1) receptor antagonist), ranitidine (a histamine H(2) receptor antagonist) and thioperamide (a histamine H(3) receptor antagonist) into the dentate gyrus on the formalin-induced pain. A biphasic pattern (first phase: 0-5min and second phase: 15-60min) in nociceptive responses was induced after subcutaneous injection of formalin (50μl, 2.5%) into the ventral surface of the right hind paw. Microinjection of histamine (1 and 2μg) into the dentate gyrus decreased the intensity of nociceptive responses. Intra-dentate gyrus microinjection of chlorpheniramine and ranitidine at the same doses of 1 and 4μg had no effects, whereas thioperamide at a dose of 4μg suppressed both phases of formalin-induced pain. Pretreatments with chlorpheniramine and ranitidine at the same dose of 4μg prevented histamine (2μg)-induced antinociception, while thioperamide (4μg) increased histamine (2μg)-induced antinociception. These results indicated that activation of brain neuronal histamine at the levels of dentate gyrus produced antinociception. The post-synaptic H(1), H(2) receptors and pre-synaptic H(3) receptors of histamine may be involved in the histamine-induced antinociception at the level of the dentate gyrus.
authors.affiliation: Division of Physiology, Department of Basic Sciences, Faculty of Veterinary Medicine, P.O. Box 1177, Urmia University, Urmia 57135, Iran.
authors.forename: Emad
authors.initials: E
authors.lastname: Khalilzadeh
authors.forename: Esmaeal
authors.initials: E
authors.lastname: Tamaddonfard
authors.forename: Amir Abbas
authors.initials: AA
authors.lastname: Farshid
authors.forename: Amir
authors.initials: A
authors.lastname: Erfanparast
mesh_terms: D000700:Analgesics; D000818:Animals; D002744:Chlorpheniramine / Q000494:pharmacology; D018891:Dentate Gyrus / Q000502:physiology*; D006632:Histamine / Q000008:administration & dosage / Q000494:pharmacology*; D006634:Histamine H1 Antagonists / Q000494:pharmacology; D006635:Histamine H2 Antagonists / Q000494:pharmacology; D054828:Histamine H3 Antagonists / Q000494:pharmacology; D008297:Male; D008845:Microinjections; D010147:Pain Measurement / Q000187:drug effects*; D010880:Piperidines / Q000494:pharmacology; D011899:Ranitidine / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar
chemical_list: D000700:Analgesics; D006634:Histamine H1 Antagonists; D006635:Histamine H2 Antagonists; D054828:Histamine H3 Antagonists; D010880:Piperidines; D002744:Chlorpheniramine; D006632:Histamine; D011899:Ranitidine; C052075:thioperamide