title: Glutamate dysregulation in the trigeminal ganglion: a novel mechanism for peripheral sensitization of the craniofacial region.
abstract: In the trigeminal ganglion (TG), satellite glial cells (SGCs) form a functional unit with neurons. It has been proposed that SGCs participate in regulating extracellular glutamate levels and that dysfunction of this SGC capacity can impact nociceptive transmission in craniofacial pain conditions. This study investigated whether SGCs release glutamate and whether elevation of TG glutamate concentration alters response properties of trigeminal afferent fibers. Immunohistochemistry was used to assess glutamate content and the expression of excitatory amino acid transporter (EAAT)1 and EAAT2 in TG sections. SGCs contained glutamate and expressed EAAT1 and EAAT2. Potassium chloride (10 mM) was used to evoke glutamate release from cultured rat SGCs treated with the EAAT1/2 inhibitor (3S)-3-[[3-[[4-(trifluoromethyl)ben zoyl]amino]phenyl]methoxy]-L-aspartic acid (TFB-TBOA) or control. Treatment with TFB-TBOA (1 and 10 μM) significantly reduced the glutamate concentration from 10.6 ± 1.1 to 5.8 ± 1.4 μM and 3.0 ± 0.8 μM, respectively (p<0.05). Electrophysiology experiments were conducted in anaesthetized rats to determine the effect of intraganglionic injections of glutamate on the response properties of ganglion neurons that innervated either the temporalis or masseter muscle. Intraganglionic injection of glutamate (500 mM, 3 μl) evoked afferent discharge and significantly reduced muscle afferent mechanical threshold. Glutamate-evoked discharge was attenuated bythe N-methyl-D-aspartate receptor antagonist 2-amino-5-phosphonovalerate (APV) and increased by TFB-TBOA, whereas mechanical sensitization was only sensitive to APV. Antidromic invasion of muscle afferent fibers by electrical stimulation of the caudal brainstem (10 Hz) or local anesthesia of the brainstem with lidocaine did not alter glutamate-induced mechanical sensitization. These findings provide a novel mechanism whereby dysfunctional trigeminal SGCs could contribute to cranial muscle tenderness in craniofacial pain conditions such as migraine headache.
authors.affiliation: Center for Sensory-Motor Interaction, Department of Health Science and Technology, Faculty of Medicine, Aalborg University, Fredrik Bajers Vej 7D3, DK-9220 Aalborg East, Denmark.
authors.forename: J C
authors.initials: JC
authors.lastname: Laursen
authors.affiliation: Center for Sensory-Motor Interaction, Department of Health Science and Technology, Faculty of Medicine, Aalborg University, Fredrik Bajers Vej 7D3, DK-9220 Aalborg East, Denmark; Faculty of Pharmaceutical Sciences, The University of British Columbia, 2405 Wesbrook Mall, Vancouver, BC V6T 1Z3, Canada.
authors.forename: B E
authors.initials: BE
authors.lastname: Cairns
authors.affiliation: Faculty of Pharmaceutical Sciences, The University of British Columbia, 2405 Wesbrook Mall, Vancouver, BC V6T 1Z3, Canada; College of Stomatology, Tianjin Medical University, Tianjin 300071, China.
authors.forename: X D
authors.initials: XD
authors.lastname: Dong
authors.affiliation: Faculty of Pharmaceutical Sciences, The University of British Columbia, 2405 Wesbrook Mall, Vancouver, BC V6T 1Z3, Canada.
authors.forename: U
authors.initials: U
authors.lastname: Kumar
authors.affiliation: Faculty of Pharmaceutical Sciences, The University of British Columbia, 2405 Wesbrook Mall, Vancouver, BC V6T 1Z3, Canada.
authors.forename: R K
authors.initials: RK
authors.lastname: Somvanshi
authors.affiliation: Center for Sensory-Motor Interaction, Department of Health Science and Technology, Faculty of Medicine, Aalborg University, Fredrik Bajers Vej 7D3, DK-9220 Aalborg East, Denmark.
authors.forename: L
authors.initials: L
authors.lastname: Arendt-Nielsen
authors.affiliation: Center for Sensory-Motor Interaction, Department of Health Science and Technology, Faculty of Medicine, Aalborg University, Fredrik Bajers Vej 7D3, DK-9220 Aalborg East, Denmark. Electronic address: gazerani@hst.aau.dk.
authors.forename: P
authors.initials: P
authors.lastname: Gazerani
mesh_terms: D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects; D000779:Anesthetics, Local / Q000494:pharmacology; D000818:Animals; D001224:Aspartic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000378:metabolism* / Q000494:pharmacology; D066298:In Vitro Techniques; D008012:Lidocaine / Q000494:pharmacology; D008297:Male; D051379:Mice; D018482:Muscle, Skeletal / Q000294:innervation; D009431:Neural Conduction / Q000187:drug effects; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012684:Sensory Thresholds / Q000187:drug effects / Q000502:physiology*; D013997:Time Factors; D012668:Trigeminal Ganglion / Q000378:metabolism*
chemical_list: C508240:(2S,3S)-3-(3-(4-(trifluoromethyl)benzoylamino)benzyloxy)aspartate; D000779:Anesthetics, Local; D018691:Excitatory Amino Acid Antagonists; D001224:Aspartic Acid; D018698:Glutamic Acid; D011189:Potassium Chloride; D015763:2-Amino-5-phosphonovalerate; D008012:Lidocaine
keywords: (3S)-3-[[3-[[4-(trifluoromethyl)ben zoyl]amino]phenyl]methoxy]-l-aspartic acid; 2-amino-5-phosphonovalerate; ANOVA; APV; CGRP; CV; DMEM; DRG; Dulbecco’s modified minimum essential medium; EAAT; GS; KCl; N-methyl-d-aspartate; NMDA; PBS; PNS; Phosphate-buffered saline; RT; SGCs; TFB-TBOA; TG; Vc; analysis of variance; calcitonin gene-related peptide; conduction velocity; craniofacial pain; dorsal root ganglion; excitatory amino acid transporter; excitatory amino acid transporters; glutamate; glutamine synthetase; peripheral nervous system; potassium chloride; room temperature; satellite glial cells; trigeminal ganglion; trigeminal nucleus caudalis