Fig. 5. NMDA-induced depletion of cell-surface AMPA receptors. Slices were treated with 3 µM NMDA for 10 minutes and immediately fixed with 4% paraformaldehyde and then the immunohistochemical localization of the GluR1 subunit was analyzed with a confocal microscope. (A) Representative confocal sections through the CA1 stratum pyramidale (SP) and the stratum radiatum (SR) show the cellular distribution of GluR1. AMPA receptors containing GluR1 on the cell surface were labeled with antibody under nonpermeant conditions (Surface GluR1) and the total GluR1 population was probed under permeant conditions (Total GluR1). (B) NMDA-induced reduction of cell-surface GluR1 was assessed in the CA1 stratum pyramidale (a) and the CA1 stratum radiatum (b) by using quantitative colorimetric assay. NMDA induced a decrease in cell-surface GluR1 subunits (Surface) without affecting the total number of GluR1 (Total), resulting in a lower proportion of surface AMPA receptors. The GluR1 internalization was predominantly observed in the dendrite-rich area (SR), as compared with the soma-rich zone (SP). *P<0.05 versus Control. Data represent the means±s.e.m. of eight slices.