title: Antinociceptive effects of H₃ (R-methylhistamine) and GABA(B) (baclofen)-receptor ligands in an orofacial model of pain in rats.
abstract: The present study explored the antinociceptive effects of H₃ (R-methylhistamine) and GABA(B) (baclofen) receptor ligands in an orofacial model of pain in rats. Orofacial pain was induced by subcutaneous injection of formalin (50 μl, 5 %) in the upper lip region, and the number of jumps and time spent face rubbing was recorded for 40 min. Formalin produced a marked biphasic pain response; first phase, 0-10 min (jumps), and second phase, 15-40 min, (rubbing). Baclofen (50 μg) injected into the rat wiskerpad 5 min before formalin administration suppressed both phases of pain whereas R-alpha-methylhistamine (12.5 μg) abolished the first phase only. Brains were taken immediately after behavioral testing was completed. HPLC/ED analysis showed that 5-hydroxytryptamine (5-HT) turnover was increased in hippocampus, thalamus, and brain stem of all formalin groups, excepting the baclofen group in which the balance of 5-HT metabolism was restored to control values. These findings demonstrate that GABA(B) receptors represent peripheral targets for analgesia. Consequently, locally administered baclofen may be a useful approach in treating inflammatory trigeminal pain.
authors: Department of Toxicology and Health Protection, Medical University of Silesia, Str Medyków 18, 40-752 Katowice, Poland. pnowak@sum.edu.pl
authors: Przemysław
authors: P
authors: Nowak
authors: Magdalena
authors: M
authors: Kowalińska-Kania
authors: Damian
authors: D
authors: Nowak
authors: Richard M
authors: RM
authors: Kostrzewa
authors: Jolanta
authors: J
authors: Malinowska-Borowska
mesh_terms: D000818:Animals; D001418:Baclofen / Q000008:administration & dosage*; D004195:Disease Models, Animal; D005157:Facial Pain / Q000188:drug therapy* / Q000378:metabolism; D005260:Female; D058786:GABA-B Receptor Agonists / Q000008:administration & dosage*; D017442:Histamine Agonists / Q000008:administration & dosage*; D007279:Injections, Subcutaneous; D008024:Ligands; D008297:Male; D008761:Methylhistamines / Q000008:administration & dosage*; D010147:Pain Measurement / Q000187:drug effects / Q000379:methods; D051381:Rats; D017208:Rats, Wistar
chemical_list: D058786:GABA-B Receptor Agonists; D017442:Histamine Agonists; D008024:Ligands; D008761:Methylhistamines; D001418:Baclofen