title: Tonic Inhibitory Control of Dentate Gyrus Granule Cells by α5-Containing GABAA Receptors Reduces Memory Interference.
abstract: Interference between similar or overlapping memories formed at different times poses an important challenge on the hippocampal declarative memory system. Difficulties in managing interference are at the core of disabling cognitive deficits in neuropsychiatric disorders. Computational models have suggested that, in the normal brain, the sparse activation of the dentate gyrus granule cells maintained by tonic inhibitory control enables pattern separation, an orthogonalization process that allows distinct representations of memories despite interference. To test this mechanistic hypothesis, we generated mice with significantly reduced expression of the α5-containing GABAA (α5-GABAARs) receptors selectively in the granule cells of the dentate gyrus (α5DGKO mice). α5DGKO mice had reduced tonic inhibition of the granule cells without any change in fast phasic inhibition and showed increased activation in the dentate gyrus when presented with novel stimuli. α5DGKO mice showed impairments in cognitive tasks characterized by high interference, without any deficiencies in low-interference tasks, suggesting specific impairment of pattern separation. Reduction of fast phasic inhibition in the dentate gyrus through granule cell-selective knock-out of α2-GABAARs or the knock-out of the α5-GABAARs in the downstream CA3 area did not detract from pattern separation abilities, which confirms the anatomical and molecular specificity of the findings. In addition to lending empirical support to computational hypotheses, our findings have implications for the treatment of interference-related cognitive symptoms in neuropsychiatric disorders, particularly considering the availability of pharmacological agents selectively targeting α5-GABAARs.
  
  
  CONCLUSIONS
  Interference between similar memories poses a significant limitation on the hippocampal declarative memory system, and impaired interference management is a cognitive symptom in many disorders. Thus, understanding mechanisms of successful interference management or processes that can lead to interference-related memory problems has high theoretical and translational importance. This study provides empirical evidence that tonic inhibition in the dentate gyrus (DG), which maintains sparseness of neuronal activation in the DG, is essential for management of interference. The specificity of findings to tonic, but not faster, more transient types of neuronal inhibition and to the DG, but not the neighboring brain areas, is presented through control experiments. Thus, the findings link interference management to a specific mechanism, proposed previously by computational models.
authors.affiliation: Laboratory of Genetic Neuropharmacology and Department of Psychiatry, Harvard Medical School, Boston, Massachusetts 02215, eengin@mclean.harvard.edu.
authors.forename: Elif
authors.initials: E
authors.lastname: Engin
authors.affiliation: Department of Anesthesiology, University of Wisconsin, Madison, Wisconsin 53792, and.
authors.forename: Ewa D
authors.initials: ED
authors.lastname: Zarnowska
authors.affiliation: Institute of Pharmacology and Toxicology, University of Zurich, CH-8057 Zurich, Switzerland.
authors.forename: Dietmar
authors.initials: D
authors.lastname: Benke
authors.affiliation: Cellular Neurobiology Laboratory, McLean Hospital, Belmont, Massachusetts 02478, Department of Psychiatry, Harvard Medical School, Boston, Massachusetts 02215.
authors.forename: Evgeny
authors.initials: E
authors.lastname: Tsvetkov
authors.affiliation: Laboratory of Genetic Neuropharmacology and Department of Psychiatry, Harvard Medical School, Boston, Massachusetts 02215.
authors.forename: Maksim
authors.initials: M
authors.lastname: Sigal
authors.affiliation: Institute of Pharmacology and Toxicology, University of Zurich, CH-8057 Zurich, Switzerland.
authors.forename: Ruth
authors.initials: R
authors.lastname: Keist
authors.affiliation: Cellular Neurobiology Laboratory, McLean Hospital, Belmont, Massachusetts 02478, Department of Psychiatry, Harvard Medical School, Boston, Massachusetts 02215.
authors.forename: Vadim Y
authors.initials: VY
authors.lastname: Bolshakov
authors.affiliation: Department of Anesthesiology, University of Wisconsin, Madison, Wisconsin 53792, and.
authors.forename: Robert A
authors.identifier: http://orcid.org/0000-0002-1516-6260
authors.initials: RA
authors.lastname: Pearce
authors.affiliation: Laboratory of Genetic Neuropharmacology and Department of Psychiatry, Harvard Medical School, Boston, Massachusetts 02215.
authors.forename: Uwe
authors.initials: U
authors.lastname: Rudolph
mesh_terms: D000818:Animals; D018891:Dentate Gyrus / Q000166:cytology*; D004192:Discrimination, Psychological / Q000502:physiology; D005106:Exploratory Behavior / Q000502:physiology; D018755:GABA Agonists / Q000493:pharmacokinetics; D005786:Gene Expression Regulation / Q000187:drug effects / Q000235:genetics; D007093:Imidazoles / Q000493:pharmacokinetics; D066298:In Vitro Techniques; D053444:Inhibitory Postsynaptic Potentials / Q000187:drug effects / Q000235:genetics; D018782:Maze Learning / Q000502:physiology; D008568:Memory / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009433:Neural Inhibition / Q000235:genetics*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D011963:Receptors, GABA-A / Q000235:genetics / Q000378:metabolism*; D021641:Recognition, Psychology / Q000502:physiology; D013550:Swimming / Q000523:psychology
chemical_list: D018755:GABA Agonists; C496250:Gabra5 protein, mouse; D007093:Imidazoles; C105490:L 655,708; D016760:Proto-Oncogene Proteins c-fos; D011963:Receptors, GABA-A
keywords: GABAA receptors; alpha5 subunit; dentate gyrus; interference; pattern separation; reversal learning