Figure 2. ChR2-mediated stimulation of the pharynx induces highly regular pumping at frequencies up to 7 Hz.

(a) Pumping in ChR2::mCherry expressing pharynxes, recorded as EPGs, stimulated by light pulses of different length (10, 35, 100, 350 ms), causing accordingly increased pump duration (grey trace), or multiple pumps (top black trace) during 350 ms stimuli. Pharynxes of animals raised without ATR exhibit non-specific pump events (bottom black trace). (b) Pumping can be stimulated at 4 Hz, (470 nm, 10 ms, 1.5 mW/mm²; lower black EPG trace), but not in non-transgenic animals (lower grey trace). Upper traces: Non-transgenic (grey) or transgenic pharynxes in the presence of ATR (black) exhibit normal bouts of spontaneous pumping. (c) Pumping (single EPG trace) stimulated by increasing frequencies of light pulses as in b, as a ‘stress test’ protocol (pacing frequency increased stepwise up to 6 Hz, as indicated below the trace). This pharynx could not lock in to 6 Hz pacing.