Journal List > Korean J Physiol Pharmacol > v.13(3) > 1025603

Jeun, Cho, Kim, Li, and Sung: Electrophysiological Characterization of AMPA and NMDA Receptors in Rat Dorsal Striatum

Abstract

The striatum receives glutamatergic afferents from the cortex and thalamus, and these synaptic transmissions are mediated by α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) and N-methyl-D-aspartate (NMDA) receptors. The purpose of this study was to characterize glutamate receptors by analyzing NMDA/AMPA ratio and rectification of AMPA and NMDA excitatory postsynaptic currents (EPSCs) using a whole-cell voltage-clamp method in the dorsal striatum. Receptor antagonists were used to isolate receptor or subunit specific EPSC, such as (DL)-2-amino-5-phosphonovaleric acid (APV), an NMDA receptor antagonist, ifenprodil, an NR2B antagonist, CNQX, an AMPA receptor antagonist and IEM-1460, a GluR2-lacking AMPA receptor blocker. AMPA and NMDA EPSCs were recorded at −70 and +40 mV, respectively. Rectification index was calculated by current ratio of EPSCs between +50 and −50 mV. NMDA/AMPA ratio was 0.20±0.05, AMPA receptor ratio of GluR2-lacking/GluR2-containing subunit was 0.26±0.05 and NMDA receptor ratio of NR2B/NR2A subunit was 0.32±0.03. The rectification index (control 2.39±0.27) was decreased in the presence of both APV and combination of APV and IEM-1460 (1.02±0.11 and 0.93±0.09, respectively). These results suggest that the major components of the striatal glutamate receptors are GluR2-containing AMPA receptors and NR2A-containing NMDA receptors. Our results may provide useful information for corticostriatal synaptic transmission and plasticity studies.

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Fig. 1.
Pharmacological isolation of AMPA receptors. (A) Sample traces of EPSCs with continuously added specific antagonist such as APV (NMDA receptor antagonist, 50 μM), and IEM-1460 (GluR2-lacking AMPA receptor blocker, 100 μM), respectively. (B) Plot graph shows baseline, addition of APV, and IEM-1460 by 10 min interval, tendency decreased EPSCs by APV and IEM-1460 (n=6). (C) Bar graph shows average peak data normalized to control (open bar) currents. ∗p<0.05, when compared to control versus APV and APV versus IEM-1460. (D) Bar graph shows NMDA/AMPA ratio and GluR2-lacking AMPA receptor/GluR2-containing AMPA receptor ratio calculated by data from Fig. 1C. Data are expressed as mean±S.E.M.
kjpp-13-209f1.tif
Fig. 2.
Pharmacological isolation of NMDA receptors. (A) Sample traces of EPSCs with continuously added specific antagonist such as CNQX (AMPA receptor antagonist, 10 μM), and ifenprodil (NMDA receptor subunit NR2B blocker, 3 μM), respectively. (B) Plot graph shows baseline, addition of CNQX, and ifenprodil by 10 min interval, tendency decreased EPSCs by CNQX, and ifenprodil (n=6). (C) Bar graph shows average peak data normalized to control (open bar) currents. ∗p<0.05, when compared to control versus CNQX and CNQX versus ifenprodil. (D) Bar graph shows NMDA/AMPA ratio and NR2B NMDA receptor subunit/NR2A NMDA receptor subunit ratio calculated by data from Fig. 2C. Data are expressed as mean±S.E.M.
kjpp-13-209f2.tif
Fig. 3.
Rectification pattern of synaptic responses in rat striatum. Current/voltage curve and bar graph shows the rectification pattern and the rectification index. (A) Current/voltage curve showing the rectification pattern of control, APV, combination of IEM-1460 and APV, CNQX and combination of ifenprodil and CNQX. (B) Bar graph showing the rectification index (current ratio between +50 mV and −50 mV) of control, APV and combination of APV and IEM-1460 (n=7). Data are expressed as mean±S.E.M.
kjpp-13-209f3.tif
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