title: GABA(A) receptors implicated in REM sleep control express a benzodiazepine binding site.
abstract: It has been reported that non-subtype-selective GABAA receptor antagonists injected into the nucleus pontis oralis (PnO) of rats induced long-lasting increases in REM sleep. Characteristics of these REM sleep increases were identical to those resulting from injection of muscarinic cholinergic agonists. Both actions were blocked by the muscarinic antagonist, atropine. Microdialysis of GABAA receptor antagonists into the PnO resulted in increased acetylcholine levels. These findings were consistent with GABAA receptor antagonists disinhibiting acetylcholine release in the PnO to result in an acetylcholine-mediated REM sleep induction. Direct evidence has been lacking for localization in the PnO of the specific GABAA receptor-subtypes mediating the REM sleep effects. Here, we demonstrated a dose-related, long-lasting increase in REM sleep following injection (60 nl) in the PnO of the inverse benzodiazepine agonist, methyl-6,7-dimethoxy-4-ethyl-β-carboline (DMCM, 10(-2)M). REM sleep increases were greater and more consistently produced than with the non-selective antagonist gabazine, and both were blocked by atropine. Fluorescence immunohistochemistry and laser scanning confocal microscopy, colocalized in PnO vesicular acetylcholine transporter, a presynaptic marker of cholinergic boutons, with the γ2 subunit of the GABAA receptor. These data provide support for the direct action of GABA on mechanisms of acetylcholine release in the PnO. The presence of the γ2 subunit at this locus and the REM sleep induction by DMCM are consistent with binding of benzodiazepines by a GABAA receptor-subtype in control of REM sleep.
authors.affiliation: VA North Texas Health Care System, Research, 4500 South Lancaster Rd., Dallas, TX 75216, USA. Tin.Nguyen@utsouthwestern.edu
authors.forename: Tin Quang
authors.initials: TQ
authors.lastname: Nguyen
authors.forename: Chang-Lin
authors.initials: CL
authors.lastname: Liang
authors.forename: Gerald A
authors.initials: GA
authors.lastname: Marks
mesh_terms: D000818:Animals; D001569:Benzodiazepines / Q000378:metabolism; D001665:Binding Sites; D002243:Carbolines / Q000494:pharmacology; D058785:GABA-A Receptor Agonists / Q000494:pharmacology; D058787:GABA-A Receptor Antagonists / Q000494:pharmacology; D007150:Immunohistochemistry; D008297:Male; D018613:Microscopy, Confocal; D011724:Pyridazines / Q000494:pharmacology; D051381:Rats; D020318:Rats, Long-Evans; D011963:Receptors, GABA-A / Q000378:metabolism*; D012154:Reticular Formation / Q000187:drug effects / Q000378:metabolism*; D012895:Sleep, REM / Q000502:physiology*
chemical_list: D002243:Carbolines; D058785:GABA-A Receptor Agonists; D058787:GABA-A Receptor Antagonists; D011724:Pyridazines; D011963:Receptors, GABA-A; D001569:Benzodiazepines; C034818:methyl 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate; C049853:gabazine
keywords: 4,5,6,7-tetrahydroisoxazolo (5,4-c)pyridin-3(ol); ACh; BZ; DMCM; DMSO; ESZ; GABA(A) receptor; GABA(A) receptor γ2 subunit; GABA(A)R; GBZ; Gabazine; IC; LDT; Muscarinic receptor; NREM; Non-REM; Nucleus pontis oralis; PAG; PBS; PPT; PnO; Rat; S.E.M.; THIP; VAChT; VGAT; VTg; acetylcholine; benzodiazepine; dimethyl sulfoxide; eszopiclone; gabazine; inferior collculus; laterodorsal tegmental nucleus; methyl-6,7-dimethoxy-4-ethyl-β-carboline; nucleus pontis oralis; pedunculopontine tegmental nucleus; periaquiductal grey; phosphate buffered saline; standard error of the mean; ventral tegmental nucleus of Gudden.; vesicular GABA transporter; vesicular acetylcholine transporter