Reduced inhibition and sensitivity to neurosteroids in hippocampus of mice lacking the GABA(A) receptor delta subunit

J Neurophysiol. 2003 Aug;90(2):903-10. doi: 10.1152/jn.01022.2002. Epub 2003 Apr 17.


The delta subunit of the gamma-aminobutyric acid (A) receptor (GABA(A)R) is expressed postnatally mostly in the cerebellum, thalamus, and dentate gyrus. Previous studies in mice with a targeted disruption of the delta subunit revealed a considerable attenuation of behavioral responses to neuroactive steroids but not to other neuromodulatory drugs. Here we show that delta subunit loss leads to a concomitant reduction in hippocampal alpha4 subunit levels. These changes were accompanied by faster decay of evoked inhibitory postsynaptic potentials (IPSPs) in dentate granule neurons of -/- mutants (decay tau = 25 ms) compared with +/+ controls (tau = 50 ms). Furthermore, the GABA(A)R-mediated miniature inhibitory postsynaptic currents (mIPSCs) also decayed faster in delta-mutants (tau = 6.3 ms) than controls (tau = 7.2 ms) and had decreased frequency (controls, 10.5 Hz; mutants, 6.6 Hz). Prolongation of mIPSCs by the neuroactive steroid anesthetic, alphaxalone (1-10 microM), was smaller in delta-mutants (at 10 microM, 65% increase) compared with +/+ littermates (308% increase). In competition binding experiments, alphaxalone (0.03-1 microM) modulation of [35S]t-butylbicyclophosphorothionate binding was reduced in delta-mutant brain homogenates, indicating that the decreased alphaxalone effects on mIPSCs were due to changes in the GABA(A)R protein. Faster decay of evoked IPSPs and mIPSCs in delta-mutants suggests presence of the delta subunit at both synaptic and extrasynaptic GABA(A)Rs. Decreased synaptic and extrasynaptic inhibition likely contributes to the pro-epileptic phenotype of delta-mutants. Reduced neurosteroid sensitivity might also contribute to seizure susceptibility. While the simplest explanation is that delta subunit-containing GABA(A)Rs represent the actual target of neurosteroids, it is possible that the behavioral and physiological sensitivity to neuroactive steroids is indirectly altered in the delta -/- mice.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Anesthetics / pharmacology
  • Animals
  • Blotting, Western
  • Electrophysiology
  • Female
  • Hippocampus / drug effects
  • Hippocampus / physiology*
  • Male
  • Mice
  • Mice, Knockout
  • Neural Inhibition* / drug effects
  • Neural Inhibition* / genetics
  • Neurons / drug effects
  • Neurons / physiology*
  • Pregnanediones / pharmacology
  • Receptors, GABA-A / deficiency*
  • Receptors, GABA-A / drug effects
  • Receptors, GABA-A / genetics
  • Receptors, GABA-A / physiology*


  • Anesthetics
  • Pregnanediones
  • Receptors, GABA-A
  • alphaxalone