Figure 1

Method setup. (A) Image of rat hippocampal slice culture setup for recording CA1 pyramidal neuron currents with optical stimulation of Schaffer collaterals. The CA3 region was injected with an AAV expressing ChR2 tagged with mCherry, and mCherry fluorescence can be seen in both the CA3 pyramidal neuron cell bodies and axons (Schaffer collaterals). A biolistically transfected CA1 pyramidal neuron is also visible by its tdTomato fluorescence. (B) Schematic illustration of a CA3-CA1 synapse in our setup. ChR2-mCherry is expressed in the presynaptic Schaffer collaterals via AAV virus, and biolistically-transfected tdTomato is optionally expressed postsynaptically in the CA1 pyramidal neuron. (C) Schematic illustration of experimental setup. Virally transduced CA3 pyramidal neurons expressing ChR2 are stimulated optically using 470 nm blue light to evoke a postsynaptic response in CA1 pyramidal neurons. Whole-cell recordings of a CA1 pyramidal neuron were made simultaneously with extracellular field recordings in the Schaffer Collaterals. (D) Optically-induced extracellular field recording trace (blue) merged with postsynaptic whole-cell recording trace (red), verifying that the two traces align in time and illustrating the presynaptic fiber volley. Scale bar: 20 ms. (E) Presynaptic fiber volley amplitude and postsynaptic current amplitude scale with light stimulus intensity. Scale bar: 20 ms.