Lack of modulation of nicotinic acetylcholine alpha-7 receptor currents by kynurenic acid in adult hippocampal interneurons

PLoS One. 2012;7(7):e41108. doi: 10.1371/journal.pone.0041108. Epub 2012 Jul 25.

Abstract

Kynurenic acid (KYNA), a classical ionotropic glutamate receptor antagonist is also purported to block the α7-subtype nicotinic acetylcholine receptor (α7* nAChR). Although many published studies cite this potential effect, few have studied it directly. In this study, the α7*-selective agonist, choline, was pressure-applied to interneurons in hippocampal subregions, CA1 stratum radiatum and hilus of acute brain hippocampal slices from adolescent to adult mice and adolescent rats. Stable α7* mediated whole-cell currents were measured using voltage-clamp at physiological temperatures. The effects of bath applied KYNA on spontaneous glutamatergic excitatory postsynaptic potentials (sEPSC) as well as choline-evoked α7* currents were determined. In mouse hilar interneurons, KYNA totally blocked sEPSC whole-cell currents in a rapid and reversible manner, but had no effect on choline-evoked α7* whole-cell currents. To determine if this lack of KYNA effect on α7* function was due to regional and/or species differences in α7* nAChRs, the effects of KYNA on choline-evoked α7* whole-cell currents in mouse and rat stratum radiatum interneurons were tested. KYNA had no effect on either mouse or rat stratum radiatum interneuron choline-evoked α7* whole-cell currents. Finally, to test whether the lack of effect of KYNA was due to unlikely slow kinetics of KYNA interactions with α7* nAChRs, recordings of a7*-mediated currents were made from slices that were prepared and stored in the presence of 1 mM KYNA (>90 minutes exposure). Under these conditions, KYNA had no measurable effect on α7* nAChR function. The results show that despite KYNA-mediated blockade of glutamatergic sEPSCs, two types of hippocampal interneurons that express choline-evoked α7* nAChR currents fail to show any degree of modulation by KYNA. Our results indicate that under our experimental conditions, which produced complete KYNA-mediated blockade of sEPSCs, claims of KYNA effects on choline-evoked α7* nAChR function should be made with caution.

Publication types

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

MeSH terms

  • Animals
  • Evoked Potentials / drug effects*
  • Excitatory Amino Acid Antagonists / pharmacology*
  • Excitatory Postsynaptic Potentials / drug effects*
  • Hippocampus / cytology
  • Hippocampus / metabolism*
  • Interneurons / cytology
  • Interneurons / metabolism*
  • Kynurenic Acid / pharmacology*
  • Male
  • Mice
  • Rats
  • Rats, Sprague-Dawley
  • Receptors, Nicotinic / metabolism*
  • alpha7 Nicotinic Acetylcholine Receptor

Substances

  • Chrna7 protein, mouse
  • Chrna7 protein, rat
  • Excitatory Amino Acid Antagonists
  • Receptors, Nicotinic
  • alpha7 Nicotinic Acetylcholine Receptor
  • Kynurenic Acid