Figure 3

bReaChES expression confers high sensitivity to light. (A) Membrane potential recordings in response to light flashes of increasing durations (bottom to top: 1.5, 4.5, 40, 365 ms and 9.9 s) and constant intensity (14.4 log photons cm⁻² s⁻¹). A 1.5 ms flash produced a subthreshold response (bottom trace). Increase in flash duration elicited action potentials and increased the number of action potentials. (B) Duration-response function of the bReaChES-induced spike response. Number of spikes increased with duration. Stimulus intensity = 15.5 log photons cm⁻² s⁻¹. (C) Intensity-response function of the magnitude of the bReaChES-induced EPSP-like depolarization (action potentials were filtered out). A 1 ms flash was delivered at 6 different intensities (14.9 to 16.3 log photons cm⁻² s⁻¹). Symbols indicate mean ± SEM (n = 6 cells). (D) Membrane potential responses to sinusoidal modulation of light at 1, 3, 5, 10 and 30 Hz (top to bottom) in a RGC of a bReaChES-expressing dystrophic mouse. Sinusoidal stimulation resulted in reliable action potential firing for frequencies up to 30 Hz. Peak intensity of sinusoidal inputs = 14.24 log photons cm⁻² s⁻¹. (E) Latency to first spike elicited by 5 sinusoidal frequencies (n = 4 cells). (F) Short duration (1 ms, 16.9 log photons cm⁻² s⁻¹, λ = 470 nm) square pulses delivered to a 27.5 µm × 27.5 µm patch area over the cell soma reliably elicited action potentials in an RGC of bReaChES-expressing dystrophic mouse. (G) Instantaneous firing rate for the first cycle at each frequency (filled triangles) and for the first second of stimulation (empty circles). (H) Comparison of membrane potential responses to 3 current injection (left, 150 pA) and light (right, 15.1 log photons cm⁻² s⁻¹) pulses for 3 different durations (bottom to top: 2, 5 and 100 ms). Responses (except in panel F) were elicited by full-field illumination with λ = 565 nm following bleaching by intense white light (see methods).