Fig. 1. Synaptic currents in organotypic hippocampal slices  in vitro . (  A ) Photograph of a slice maintained  in vitro for 14 days. Note that major structural features are maintained, enabling identification of specific subfields and laminae. Typical positions of the recording and stimulating electrodes are illustrated schematically. CA1 and CA3 = Cornu Ammonis areas 1 and 3; DG = dentate gyrus; EC = entorhinal cortex. (  B–D ) Recordings from a pyramidal-shaped neuron in  stratum pyramidale : (  B ) under control conditions, with no drugs added to the artificial cerebrospinal fluid (ACSF); (  C ) in the presence of the ionotropic glutamate antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and (2R)-amino-5-phosphonovaleric acid (APV), which reveals abundant large-amplitude spontaneous inhibitory postsynaptic currents; (  D ) after the addition of tetrodotoxin (TTX), which leaves only small-amplitude miniature (action potential-independent) inhibitory postsynaptic currents.