title: Dopamine D3 receptor-dependent changes in alpha6 GABAA subunit expression in striatum modulate anxiety-like behaviour: Responsiveness and tolerance to diazepam.
abstract: Increasing evidence indicates that central dopamine (DA) neurotransmission is involved in pathophysiology of anxiety, in particular the DA receptor subtype 3 (D3R). We previously reported that D3R null mice (D3R(-/-)) exhibit low baseline anxiety levels and that acutely administrated diazepam is more effective in D3R(-/-) than in wild type (WT) when tested in the elevated plus maze test (EPM). Here we tested the hypothesis that genetic deletion or pharmacological blockade of D3R affect GABAA subunit expression, which in turn modulates anxiety-like behaviour as well as responsiveness and tolerance to diazepam. D3R(-/-) mice exhibited tolerance to diazepam (0.5mg/kg, i.p.), assessed by EPM, as fast as after 3 day-treatment, performing similarly to untreated D3R(-/-) mice; conversely, WT exhibited tolerance to diazepam after a 14-21 day-treatment. Analysis of GABAA α6 subunit mRNA expression by qPCR in striatum showed that it was about 15-fold higher in D3R(-/-) than in WT. Diazepam treatment did not modify α6 expression in D3R(-/-), but progressively increased α6 expression in WT, to the level of untreated D3R(-/-) after 14-21 day-treatment. BDNF mRNA expression in striatum was remarkably (>10-fold) increased after 3 days of diazepam-treatment in both WT and D3R(-/-); such expression level, however, slowly declined below control levels, by 14-21 days. Following a 7 day-treatment with the selective D3R antagonist SB277011A, WT exhibited a fast tolerance to diazepam accompanied by a robust increase in α6 subunit expression. In conclusion, genetic deletion or pharmacological blockade of D3R accelerate the development of tolerance to repeated administrations of diazepam and increase α6 subunit expression, a GABAA subunit that has been linked to diazepam insensitivity. Modulation of GABAA receptor by DA transmission may be involved in the mechanisms of anxiety and, if occurring in humans, may have therapeutic relevance following repeated use of drugs targeting D3R.
authors.affiliation: Department of Clinical and Molecular Biomedicine, Section of Pharmacology and Biochemistry, Catania University, Catania, Italy.
authors.forename: Gian Marco
authors.initials: GM
authors.lastname: Leggio
authors.affiliation: Department of Clinical and Molecular Biomedicine, Section of Pharmacology and Biochemistry, Catania University, Catania, Italy.
authors.forename: Sebastiano Alfio
authors.initials: SA
authors.lastname: Torrisi
authors.affiliation: Department of Bio-Medical Sciences, Catania University, Catania, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Castorina
authors.affiliation: Department of Clinical and Molecular Biomedicine, Section of Pharmacology and Biochemistry, Catania University, Catania, Italy.
authors.forename: Chiara Bianca Maria
authors.initials: CB
authors.lastname: Platania
authors.affiliation: Department of Clinical and Molecular Biomedicine, Section of Pharmacology and Biochemistry, Catania University, Catania, Italy.
authors.forename: Agata Antonia Rita
authors.initials: AA
authors.lastname: Impellizzeri
authors.affiliation: Department of Clinical and Molecular Biomedicine, Section of Pharmacology and Biochemistry, Catania University, Catania, Italy.
authors.forename: Annamaria
authors.initials: A
authors.lastname: Fidilio
authors.affiliation: Department of Educational Sciences, Catania University, Catania, Italy; IRCCS Associazione Oasi Maria S.S., Institute for Research on Mental Retardation and Brain Aging, Troina, Italy.
authors.forename: Filippo
authors.initials: F
authors.lastname: Caraci
authors.affiliation: Department of Clinical and Molecular Biomedicine, Section of Pharmacology and Biochemistry, Catania University, Catania, Italy.
authors.forename: Claudio
authors.initials: C
authors.lastname: Bucolo
authors.affiliation: Department of Clinical and Molecular Biomedicine, Section of Pharmacology and Biochemistry, Catania University, Catania, Italy.
authors.forename: Filippo
authors.initials: F
authors.lastname: Drago
authors.affiliation: Department of Clinical and Molecular Biomedicine, Section of Pharmacology and Biochemistry, Catania University, Catania, Italy. Electronic address: salomone@unict.it.
authors.forename: Salvatore
authors.initials: S
authors.lastname: Salomone
mesh_terms: D000818:Animals; D014151:Anti-Anxiety Agents / Q000494:pharmacology*; D001007:Anxiety / Q000188:drug therapy / Q000378:metabolism*; D019208:Brain-Derived Neurotrophic Factor / Q000378:metabolism; D003342:Corpus Striatum / Q000187:drug effects / Q000378:metabolism*; D003975:Diazepam / Q000494:pharmacology*; D018492:Dopamine Antagonists / Q000494:pharmacology; D004361:Drug Tolerance / Q000502:physiology; D008297:Male; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009043:Motor Activity / Q000187:drug effects / Q000502:physiology; D009570:Nitriles / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D050637:Receptors, Dopamine D3 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D011963:Receptors, GABA-A / Q000378:metabolism*; D044005:Tetrahydroisoquinolines / Q000494:pharmacology
chemical_list: D014151:Anti-Anxiety Agents; D019208:Brain-Derived Neurotrophic Factor; D018492:Dopamine Antagonists; C493594:Drd3 protein, mouse; C546172:Gabra6 protein, mouse; D009570:Nitriles; D012333:RNA, Messenger; D050637:Receptors, Dopamine D3; D011963:Receptors, GABA-A; C409982:SB 277011; D044005:Tetrahydroisoquinolines; D003975:Diazepam
keywords: Alpha6 subunit; Anxiety; BDNF; Diazepam; Dopamine D3 receptor; GABAA