title: The muscle relaxant thiocolchicoside is an antagonist of GABAA receptor function in the central nervous system.
abstract: Thiocolchicoside (TCC) is used clinically for its muscle relaxant, anti-inflammatory, and analgesic properties, and it has been shown to interact with gamma-aminobutyric acid (GABA) type A receptors (GABAARs) and strychnine-sensitive glycine receptors in the rat central nervous system. In contrast to a proposed agonistic action at these two types of inhibitory receptors, pharmacological evidence has shown that, under certain conditions, TCC manifests convulsant activity in animals and humans. We now show that the phasic and tonic GABAAR-mediated currents recorded from Purkinje cells and granule neurons, respectively, in parasagittal cerebellar slices from adult male rats were inhibited by TCC in a concentration-dependent manner. The median inhibitory concentrations of TCC for these effects were approximately 0.15 and approximately 0.9 microM, respectively. TCC did not potentiate GABABR-mediated currents in hippocampal slices, suggesting that its muscle relaxant action is not mediated by GABABRs. Intraperitoneal injection of TCC in rats either alone or in combination with negative modulators of GABAergic transmission revealed convulsant and proconvulsant actions of this drug. Our data, consistent with clinical observations of the epileptogenic effect of this compound, suggest that TCC is a potent competitive antagonist of GABAAR function.
authors.affiliation: Department of Experimental Biology Bernardo Loddo, Section of Neuroscience, University of Cagliari, Cittadella Universitaria, SS 554, Km 4.5, Monserrato, Cagliari 09123, Italy. mcarta@unica.it
authors.forename: Mario
authors.initials: M
authors.lastname: Carta
authors.forename: Luca
authors.initials: L
authors.lastname: Murru
authors.forename: Paolo
authors.initials: P
authors.lastname: Botta
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Talani
authors.forename: GianPietro
authors.initials: G
authors.lastname: Sechi
authors.forename: PierLuigi
authors.initials: P
authors.lastname: De Riu
authors.forename: Enrico
authors.initials: E
authors.lastname: Sanna
authors.forename: Giovanni
authors.initials: G
authors.lastname: Biggio
mesh_terms: D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D002478:Cells, Cultured; D002490:Central Nervous System / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D003078:Colchicine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation / Q000379:methods; D005071:Evoked Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D018756:GABA Antagonists / Q000737:chemistry / Q000494:pharmacology*; D066298:In Vitro Techniques; D008297:Male; D008959:Models, Neurological; D009415:Nerve Net / Q000187:drug effects; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D009474:Neurons / Q000187:drug effects; D018408:Patch-Clamp Techniques / Q000379:methods; D051381:Rats; D017207:Rats, Sprague-Dawley; D018079:Receptors, GABA / Q000502:physiology*
chemical_list: D018756:GABA Antagonists; D018079:Receptors, GABA; D003078:Colchicine; C004280:thiocolchicoside; D001640:Bicuculline