Figure 3. Optogenetic stimulation of the tongue in Pkd2l1-Cre, ChR2 mice elicits a robust, tastant-like nerve response. A, Chorda tympani (CT) and glossopharyngeal (GN) nerve responses to acidic stimuli and a 470 nm light pulse stimulus in Pkd2l1-Cre, ChR2 mice. B, CT nerve responses to citric acid and blue light in a Cre-negative control mouse. C, CT nerve responses to blue light in a Pkd2l1-Cre, ChR2 mouse before and after the application of purinergic receptor blocker AF353 to the tongue. D, CT nerve responses to a control tastant stimulus (NH4Cl) and blue light pulses at increasing frequencies (power at 7 mW, duty cycle at 50%). E, CT nerve responses to NH4Cl and blue light pulses at increasing light power (frequency at 5 Hz, duty cycle at 50%). F, CT nerve responses to NH4Cl and blue light pulses at increasing light-on duty cycle percentages (frequency at 5 Hz, power at 7 mW). G, All quantified data in frequency (n = 3), power (n = 4), and duty cycle experiments (n = 3). H, Two example experiments (left and middle) showing the consistency of the blue light response, compared with repeated blocks of 100 mm NH4Cl (black), 10 mm citric acid (CA; red), 500 mm sucrose (yellow), and blue light at 5 Hz pulses, 7 mW power, and 50% duty cycle (blue). All presentations normalized to the first presentation of that stimulus (e.g., CA responses normalized to first presentation of CA, light responses normalized to first presentation of light). Right graph shows all data (n = 6) comparing the consistency of blue light responses (blue) to CA responses (red). Blue light responses were not different from CA responses over presentation blocks (F(7,70) = 0.254, p = 0.9692, two-way ANOVA). I, CT nerve responses to blue (470 nm) and amber (589 nm) light. Graph on right shows all data (n = 4) of varied wavelength stimulation. Stimulus bars denote 30 s of stimulation, except for those in F, which are adjusted to normalize total time of light exposure to the tongue. All error bars denote the SEM.