title: Alpha5GABAA receptor activity sets the threshold for long-term potentiation and constrains hippocampus-dependent memory.
abstract: Synaptic plasticity, which is the neuronal substrate for many forms of hippocampus-dependent learning, is attenuated by GABA type A receptor (GABA(A)R)-mediated inhibition. The prevailing notion is that a synaptic or phasic form of GABAergic inhibition regulates synaptic plasticity; however, little is known about the role of GABA(A)R subtypes that generate a tonic or persistent inhibitory conductance. We studied the regulation of synaptic plasticity by alpha5 subunit-containing GABA(A)Rs (alpha5GABA(A)Rs), which generate a tonic inhibitory conductance in CA1 pyramidal neurons using electrophysiological recordings of field and whole-cell potentials in hippocampal slices from both wild-type and null mutant mice for the alpha5 subunit of the GABA(A)R (Gabra5(-/-) mice). In addition, the strength of fear-associated memory was studied. The results showed that alpha5GABA(A)R activity raises the threshold for induction of long-term potentiation in a highly specific band of stimulation frequencies (10-20 Hz) through mechanisms that are predominantly independent of inhibitory synaptic transmission. The deletion or pharmacological inhibition of alpha5GABA(A)Rs caused no change in baseline membrane potential or input resistance but increased depolarization during 10 Hz stimulation. The encoding of hippocampus-dependent memory was regulated by alpha5GABA(A)Rs but only under specific conditions that generate moderate but not robust forms of fear-associated learning. Thus, under specific conditions, alpha5GABA(A)R activity predominates over synaptic inhibition in modifying the strength of both synaptic plasticity in vitro and certain forms of memory in vivo.
authors.affiliation: Department of Physiology, Institute of Medical Science, University of Toronto, Toronto, Ontario M5S 1A8, Canada. ljmartin@bu.edu
authors.forename: Loren J
authors.initials: LJ
authors.lastname: Martin
authors.forename: Agnieszka A
authors.initials: AA
authors.lastname: Zurek
authors.forename: John F
authors.initials: JF
authors.lastname: MacDonald
authors.forename: John C
authors.initials: JC
authors.lastname: Roder
authors.forename: Michael F
authors.initials: MF
authors.lastname: Jackson
authors.forename: Beverley A
authors.initials: BA
authors.lastname: Orser
mesh_terms: D000818:Animals; D001245:Association Learning; D056547:CA1 Region, Hippocampal / Q000187:drug effects / Q000502:physiology; D017097:Electric Impedance; D004558:Electric Stimulation / Q000379:methods; D005239:Fear; D058787:GABA-A Receptor Antagonists; D006624:Hippocampus / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D017774:Long-Term Potentiation / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008568:Memory / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D017966:Pyramidal Cells / Q000187:drug effects / Q000502:physiology; D011963:Receptors, GABA-A / Q000235:genetics / Q000378:metabolism*; D017470:Receptors, Glutamate / Q000378:metabolism; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology
chemical_list: D058787:GABA-A Receptor Antagonists; C496250:Gabra5 protein, mouse; D011963:Receptors, GABA-A; D017470:Receptors, Glutamate
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