title: Hypothalamic GPR40 signaling activated by free long chain fatty acids suppresses CFA-induced inflammatory chronic pain.
abstract: GPR40 has been reported to be activated by long-chain fatty acids, such as docosahexaenoic acid (DHA). However, reports studying functional role of GPR40 in the brain are lacking. The present study focused on the relationship between pain regulation and GPR40, investigating the functional roles of hypothalamic GPR40 during chronic pain caused using a complete Freund's adjuvant (CFA)-induced inflammatory chronic pain mouse model. GPR40 protein expression in the hypothalamus was transiently increased at day 7, but not at days 1, 3 and 14, after CFA injection. GPR40 was co-localized with NeuN, a neuron marker, but not with glial fibrillary acidic protein (GFAP), an astrocyte marker. At day 1 after CFA injection, GFAP protein expression was markedly increased in the hypothalamus. These increases were significantly inhibited by the intracerebroventricular injection of flavopiridol (15 nmol), a cyclin-dependent kinase inhibitor, depending on the decreases in both the increment of GPR40 protein expression and the induction of mechanical allodynia and thermal hyperalgesia at day 7 after CFA injection. Furthermore, the level of DHA in the hypothalamus tissue was significantly increased in a flavopiridol reversible manner at day 1, but not at day 7, after CFA injection. The intracerebroventricular injection of DHA (50 µg) and GW9508 (1.0 µg), a GPR40-selective agonist, significantly reduced mechanical allodynia and thermal hyperalgesia at day 7, but not at day 1, after CFA injection. These effects were inhibited by intracerebroventricular pretreatment with GW1100 (10 µg), a GPR40 antagonist. The protein expression of GPR40 was colocalized with that of β-endorphin and proopiomelanocortin, and a single intracerebroventricular injection of GW9508 (1.0 µg) significantly increased the number of neurons double-stained for c-Fos and proopiomelanocortin in the arcuate nucleus of the hypothalamus. Our findings suggest that hypothalamic GPR40 activated by free long chain fatty acids might have an important role in this pain control system.
authors.affiliation: Department of Clinical Pharmacy, School of Pharmaceutical Sciences, Kobe Gakuin University, Kobe, Japan.
authors.forename: Kazuo
authors.initials: K
authors.lastname: Nakamoto
authors.affiliation: Department of Clinical Pharmacy, School of Pharmaceutical Sciences, Kobe Gakuin University, Kobe, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Nishinaka
authors.affiliation: Department of Clinical Pharmacy, School of Pharmaceutical Sciences, Kobe Gakuin University, Kobe, Japan.
authors.forename: Naoya
authors.initials: N
authors.lastname: Sato
authors.affiliation: Bizen Kasei Chemical Co. Ltd., Okayama, Japan.
authors.forename: Mitsumasa
authors.initials: M
authors.lastname: Mankura
authors.affiliation: Laboratory of Pharmacology, Faculty of Pharmacy, Osaka Ohtani University, Osaka, Japan.
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Koyama
authors.affiliation: Biochemical Toxicology Laboratory, Faculty of Pharmaceutical Sciences, Kobe Gakuin University, Kobe, Japan.
authors.forename: Fumiyo
authors.initials: F
authors.lastname: Kasuya
authors.affiliation: Department of Clinical Pharmacy, School of Pharmaceutical Sciences, Kobe Gakuin University, Kobe, Japan.
authors.forename: Shogo
authors.initials: S
authors.lastname: Tokuyama
mesh_terms: D000818:Animals; D001111:Arcuate Nucleus of Hypothalamus / Q000187:drug effects* / Q000378:metabolism / Q000503:physiopathology; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism; D001565:Benzoates / Q000494:pharmacology; D059350:Chronic Pain / Q000139:chemically induced / Q000188:drug therapy* / Q000378:metabolism / Q000503:physiopathology; D004268:DNA-Binding Proteins; D004195:Disease Models, Animal; D004281:Docosahexaenoic Acids / Q000494:pharmacology*; D005419:Flavonoids / Q000494:pharmacology; D005620:Freund's Adjuvant; D015870:Gene Expression; D005904:Glial Fibrillary Acidic Protein; D006930:Hyperalgesia / Q000188:drug therapy* / Q000378:metabolism / Q000503:physiopathology; D007276:Injections, Intraventricular; D008297:Male; D008744:Methylamines / Q000494:pharmacology; D051379:Mice; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D009457:Neuroglia / Q000187:drug effects / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D059408:Pain Management; D010880:Piperidines / Q000494:pharmacology; D011333:Pro-Opiomelanocortin / Q000235:genetics / Q000378:metabolism; D011422:Propionates / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D043562:Receptors, G-Protein-Coupled / Q000819:agonists / Q000037:antagonists & inhibitors / Q000235:genetics*; D015398:Signal Transduction; D013997:Time Factors; D001615:beta-Endorphin / Q000235:genetics / Q000378:metabolism
chemical_list: D001565:Benzoates; D004268:DNA-Binding Proteins; C473036:Ffar1 protein, mouse; D005419:Flavonoids; C515631:GW1100; C515630:GW9508; D005904:Glial Fibrillary Acidic Protein; D008744:Methylamines; D009419:Nerve Tissue Proteins; C492380:NeuN protein, mouse; D009687:Nuclear Proteins; D010880:Piperidines; D011422:Propionates; D011743:Pyrimidines; D043562:Receptors, G-Protein-Coupled; C528900:glial fibrillary astrocytic protein, mouse; D004281:Docosahexaenoic Acids; C077990:alvocidib; D001615:beta-Endorphin; D011333:Pro-Opiomelanocortin; D005620:Freund's Adjuvant