Electrophysiological Characterization of AMPA and NMDA Receptors in Rat Dorsal Striatum

The striatum receives glutamatergic afferents from the cortex and thalamus, and these synaptic transmissions are mediated by alpha-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.