title: α-Conotoxin Vc1.1 inhibits human dorsal root ganglion neuroexcitability and mouse colonic nociception via GABABreceptors.
abstract: α-Conotoxin Vc1.1 is a small disulfide-bonded peptide from the venom of the marine cone snailConus victoriae. Vc1.1 has antinociceptive actions in animal models of neuropathic pain, but its applicability to inhibiting human dorsal root ganglion (DRG) neuroexcitability and reducing chronic visceral pain (CVP) is unknown.
  
  
  
  We determined the inhibitory actions of Vc1.1 on human DRG neurons and on mouse colonic sensory afferents in healthy and chronic visceral hypersensitivity (CVH) states. In mice, visceral nociception was assessed by neuronal activation within the spinal cord in response to noxious colorectal distension (CRD). Quantitative-reverse-transcription-PCR, single-cell-reverse-transcription-PCR and immunohistochemistry determined γ-aminobutyric acid receptor B (GABABR) and voltage-gated calcium channel (CaV2.2, CaV2.3) expression in human and mouse DRG neurons.
  
  
  
  Vc1.1 reduced the excitability of human DRG neurons, whereas a synthetic Vc1.1 analogue that is inactive at GABABR did not. Human DRG neurons expressed GABABR and its downstream effector channels CaV2.2 and CaV2.3. Mouse colonic DRG neurons exhibited high GABABR, CaV2.2 and CaV2.3 expression, with upregulation of the CaV2.2 exon-37a variant during CVH. Vc1.1 inhibited mouse colonic afferents ex vivo and nociceptive signalling of noxious CRD into the spinal cord in vivo, with greatest efficacy observed during CVH. A selective GABABR antagonist prevented Vc1.1-induced inhibition, whereas blocking both CaV2.2 and CaV2.3 caused inhibition comparable with Vc1.1 alone.
  
  
  
  Vc1.1-mediated activation of GABABR is a novel mechanism for reducing the excitability of human DRG neurons. Vc1.1-induced activation of GABABR on the peripheral endings of colonic afferents reduces nociceptive signalling. The enhanced antinociceptive actions of Vc1.1 during CVH suggest it is a novel candidate for the treatment for CVP.
authors.affiliation: Visceral Pain Group, Centre for Nutrition and Gastrointestinal Diseases, Discipline of Medicine, Faculty of Health Sciences, The University of Adelaide, South Australian Health and Medical Research Institute (SAHMRI), Adelaide, South Australia, Australia.
authors.forename: Joel
authors.initials: J
authors.lastname: Castro
authors.affiliation: Visceral Pain Group, Centre for Nutrition and Gastrointestinal Diseases, Discipline of Medicine, Faculty of Health Sciences, The University of Adelaide, South Australian Health and Medical Research Institute (SAHMRI), Adelaide, South Australia, Australia.
authors.forename: Andrea M
authors.initials: AM
authors.lastname: Harrington
authors.affiliation: Visceral Pain Group, Centre for Nutrition and Gastrointestinal Diseases, Discipline of Medicine, Faculty of Health Sciences, The University of Adelaide, South Australian Health and Medical Research Institute (SAHMRI), Adelaide, South Australia, Australia.
authors.forename: Sonia
authors.initials: S
authors.lastname: Garcia-Caraballo
authors.affiliation: Visceral Pain Group, Centre for Nutrition and Gastrointestinal Diseases, Discipline of Medicine, Faculty of Health Sciences, The University of Adelaide, South Australian Health and Medical Research Institute (SAHMRI), Adelaide, South Australia, Australia.
authors.forename: Jessica
authors.initials: J
authors.lastname: Maddern
authors.affiliation: Visceral Pain Group, Centre for Nutrition and Gastrointestinal Diseases, Discipline of Medicine, Faculty of Health Sciences, The University of Adelaide, South Australian Health and Medical Research Institute (SAHMRI), Adelaide, South Australia, Australia.
authors.forename: Luke
authors.initials: L
authors.lastname: Grundy
authors.affiliation: Anabios, San Diego, California, USA.
authors.forename: Jingming
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Anabios, San Diego, California, USA.
authors.forename: Guy
authors.initials: G
authors.lastname: Page
authors.affiliation: Anabios, San Diego, California, USA.
authors.forename: Paul E
authors.initials: PE
authors.lastname: Miller
authors.affiliation: Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, University of Queensland, Brisbane, Queensland, Australia.
authors.forename: David J
authors.initials: DJ
authors.lastname: Craik
authors.affiliation: Illawarra Health & Medical Research Institute (IHMRI), University of Wollongong, Wollongong, NSW, Australia.
authors.forename: David J
authors.initials: DJ
authors.lastname: Adams
authors.affiliation: Visceral Pain Group, Centre for Nutrition and Gastrointestinal Diseases, Discipline of Medicine, Faculty of Health Sciences, The University of Adelaide, South Australian Health and Medical Research Institute (SAHMRI), Adelaide, South Australia, Australia.
authors.forename: Stuart M
authors.initials: SM
authors.lastname: Brierley
mesh_terms: D000818:Animals; D001418:Baclofen / Q000494:pharmacology; D020864:Calcium Channels, N-Type / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D020908:Calcium Channels, R-Type / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D027682:Cation Transport Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D059350:Chronic Pain / Q000517:prevention & control; D003106:Colon / Q000502:physiology*; D020916:Conotoxins / Q000494:pharmacology*; D004195:Disease Models, Animal; D004594:Electrophysiology; D005260:Female; D058786:GABA-B Receptor Agonists / Q000494:pharmacology; D058788:GABA-B Receptor Antagonists / Q000494:pharmacology; D005727:Ganglia, Spinal / Q000737:chemistry / Q000187:drug effects / Q000502:physiology*; D015870:Gene Expression; D006801:Humans; D008297:Male; D051379:Mice; D009475:Neurons, Afferent / Q000737:chemistry / Q000187:drug effects / Q000502:physiology*; D059225:Nociception / Q000187:drug effects*; D018080:Receptors, GABA-B / Q000032:analysis* / Q000235:genetics* / Q000378:metabolism; D015854:Up-Regulation; D059265:Visceral Pain / Q000517:prevention & control; D055815:Young Adult
chemical_list: C500545:CACNA1B protein, human; C423009:CACNA1E protein, human; C500963:Cacna1b protein, mouse; C498916:Cacna1e protein, mouse; D020864:Calcium Channels, N-Type; D020908:Calcium Channels, R-Type; D027682:Cation Transport Proteins; D020916:Conotoxins; D058786:GABA-B Receptor Agonists; D058788:GABA-B Receptor Antagonists; D018080:Receptors, GABA-B; C507383:alpha-conotoxin Vc1.1; D001418:Baclofen
keywords: ABDOMINAL PAIN; ION CHANNELS; IRRITABLE BOWEL SYNDROME; REAL TIME PCR; VISCERAL NOCICEPTION