Figure 3.

Optical stimulation of ChR2 can cause both excitation and inhibition in the hippocampus. (A) Schematic representation of optical stimulation of hippocampal slices. The star indicates the location of mossy fiber monopolar stimulation to elicit an orthodromic response in CA3. The 200μm diameter optical fiber was positioned directly over the CA3 pyramidal cell region, and the areas marked by the dashed lines indicate the spatial extent of the optical stimulus (inner line indicating the area of most intense illumination close to the fiber output) as determined by image capture of the illumination (B) of the in vitro transverse hippocampal slice. Scale bar, 500μm. (C–F) Whole-cell patch clamp recordings of neurons in the pyramidal cell layer of the CA3 region of the hippocampus from juvenile Thy1-ChR2 mice. (C) Pulsed optical stimulation using 473nm light (indicated by blue bars) at a power of 20mW applied for 10ms (C, i)), 20ms (C, ii), and 30ms (C, iii) was able to reliably elicit action potential responses. (D) Optical stimulation of a different cell at the same power and pulse durations that caused a large cell depolarization but did not elicit action potential firing. (E) A cell that responded to optical stimulus pulses with an excitation-inhibition response. (F) A pyramidal neuron that exhibited a pure hyperpolarization response to optical pulse stimulation without any depolarization. The resting membrane potential for all cells was −55mV to −60mV.