DL-AP4 (500 μM) reduces the tonic inward current by closing ion channels at holding potentials of -33 mV in isolated rod bipolar cells[1]. DL-AP4 (0.1 M; 1h) antagonizes the excitatory action of glutamate applied iontophoretically to receptors present in the locust muscle membrane[2]. DL-AP4 (compound 2) antagonizes excitatory synapses in the lateral perforant path of the rat hippocampal slice with an apparent K d of 2.5 μM[3]. DL-AP4 (50 μM; 0-2 seconds) blocks the light response of a series of 10 ms 405-nm flashes, at the following strengths: 3, 10, 30, 100, 300, 990, 3000, 9900 photons μm -2[4].