The isolated retina was perfused continuously with normal Ringer by whole chamber and local perfusion systems to accelerate delivery and removal of the test agents. To better monitor NMDA receptor activity, we recorded simultaneously the NMDA-induced whole cell current and the cytosolic Ca2+ signal. Normal Ringer contained 120 mM NaCl, 3 mM KCl, 2 mM CaCl2, 1.2 mM MgSO4, 0.5 mM KH2PO4, 10 mM d-glucose, 26 mM NaHCO3, 0.005 mM strychnine, and 0.02 mM SR95530. Conventional methods for whole-cell patch clamp were used. RGCs were voltage clamped at −70 mV. After whole-cell patch clamp was established, normal Ringer was replaced with 0 Mg2+ Ringer, which was made by removing MgSO4 from normal Ringer and adding 0.02 mM ascorbic acid to it. The normal intracellular (patch pipette) solution contained 125 mM CsCH3SO3, 1 mM MgCl2, 15 mM TEA·Cl, 10 mM HEPES, 4 mM ATP-Mg, 0.5 mM GTP-Na3, 12 mM phosphocreatine, 5 mM QX-314, and 0.1 mM fluo-4. NMDA (100 μM NMDA + 5 μM glycine) was applied for 8 seconds through a multichannel local perfusion system. In experiments using brimonidine or atipamezole, these two agents were added to the whole-chamber and local perfusion systems. Ca2+ images were obtained with a spinning disc confocal system (Nipkow; Solamere Technology Group, Salt Lake City, UT) mounted on a fixed-stage upright microscope (BX51WI; Olympus, Tokyo, Japan).