Hippocampal network hyperactivity after selective reduction of tonic inhibition in GABA A receptor alpha5 subunit-deficient mice

J Neurophysiol. 2006 May;95(5):2796-807. doi: 10.1152/jn.01122.2005. Epub 2006 Feb 1.


Functionally, gamma-aminobutyric acid receptor (GABAR)-mediated inhibition can be classified as phasic (synaptic) and tonic (extrasynaptic). The GABARs underlying tonic inhibition assemble from subunits different from those responsible for phasic inhibition. We wanted to assess the excitability of hippocampal pyramidal cell (PC) networks following a selective impairment of tonic inhibition. This is difficult to accomplish by pharmacological means. Because the GABAR alpha5 subunits mostly mediate the tonic inhibition in CA1 and CA3 PCs, we quantified changes in tonic inhibition and examined network excitability in slices of adult gabra5-/- mice. In gabra5-/- CA1 and CA3 PCs tonic inhibitory currents were 60 and 53%, respectively, of those recorded in wild type (WT), with no alterations in phasic inhibition. The amount of tonic inhibition recorded in slices was significantly affected by the method of slice storage (interface or submerged chamber). Field recordings in gabra5-/- CA3 pyramidal layer showed an increased network excitability that was decreased by the GABAR agonist muscimol at a concentration that restored the tonic inhibition of gabra5-/- PCs to the WT level without altering phasic inhibition. Through a battery of pharmacological experiments, we have identified delta subunit-containing GABARs as the mediators of the residual tonic inhibition in gabra5-/- PCs. Our study is consistent with an important role of tonic inhibition in the control of hippocampal network excitability and highlights selective enhancers of tonic inhibition as promising therapeutic approaches for diseases involving network hyperexcitability.

Publication types

  • Comparative Study
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Analysis of Variance
  • Animals
  • Animals, Newborn
  • Bicuculline / analogs & derivatives
  • Bicuculline / pharmacology
  • Dose-Response Relationship, Radiation
  • Drug Interactions
  • Electric Stimulation / methods
  • Evoked Potentials / drug effects
  • Evoked Potentials / physiology
  • Evoked Potentials / radiation effects
  • GABA Agonists / pharmacology
  • GABA Antagonists / pharmacology
  • Hippocampus / cytology*
  • In Vitro Techniques
  • Male
  • Membrane Potentials / drug effects
  • Membrane Potentials / physiology
  • Membrane Potentials / radiation effects
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Muscimol / pharmacology
  • Nerve Net / drug effects
  • Nerve Net / physiology*
  • Nerve Net / radiation effects
  • Neural Inhibition / drug effects
  • Neural Inhibition / physiology*
  • Neural Inhibition / radiation effects
  • Nipecotic Acids / pharmacology
  • Oximes / pharmacology
  • Patch-Clamp Techniques / methods
  • Pyramidal Cells / drug effects
  • Pyramidal Cells / physiology*
  • Receptors, GABA-A / deficiency*
  • gamma-Aminobutyric Acid / pharmacology


  • GABA Agonists
  • GABA Antagonists
  • Gabra5 protein, mouse
  • Nipecotic Acids
  • Oximes
  • Receptors, GABA-A
  • NNC 711
  • Muscimol
  • bicuculline methiodide
  • gamma-Aminobutyric Acid
  • Bicuculline