Figure 2. Fruit acid tastants activate a subset of bitter neurons.

a. Representative traces of recordings obtained from S-b labellar sensilla of wild-type flies. Vertical bar = 1 mV; horizontal bar = 100 ms. b. Representative 10 mM caffeine traces and mean firing rates of the bitter neuron obtained before and after stimulation with acid tastants. n=9. P = 0.305, Student’s t-test. Independent recordings were acquired over 2 days. Vertical bar = 1 mV; horizontal bar = 100 ms. c. Mean responses of S-b and I-b classes of bitter-responsive sensilla to indicated acid tastants and 30 mM tricholine citrate electrolyte control (0). S-b: n=30 (“0” control), n=9–14 (acetic), n=10–11 (citric), n=8–9 (glycolic), n=10–11 (tartaric). I-b: n=22 (“0” control), n=6–12 (acetic), n=6–10 (citric), n=7–10 (glycolic), n= 9–10 (tartaric). For each sensillum-stimulus series, independent recordings were acquired over 2–6 days. d. Scatter plots of mean responses of S-b and I-b sensilla to acid tastants tested at 0.1%, 1%, and 10% from c, against pH of the stimulus mixtures. Three independent pH measurements were taken and averaged for each stimulus solution. Best fit lines and R² values were calculated in Excel. e. Mean responses of wild-type S-a and I-a classes of bitter-responsive sensilla to indicated acid tastants and 30 mM tricholine citrate electrolyte alone (control). S-a: n=29 (“0” control), n=8–14 (acetic), n=10–14 (citric), n=8–11 (glycolic), n=9–11 (tartaric); Ia: n=7 (“0” control), n=9–10 (acetic), n=8–9 (citric), n=9 (glycolic), n=9 (tartaric). For each sensillum-stimulus series, independent recordings were acquired over 2–6 days. f. Scatter plots of mean responses of indicated sensilla to acid tastants tested at 0.1%, 1%, and 10%, against pH of the stimulus mixtures. Three independent pH measurements were taken and averaged for each stimulus solution. Best fit lines and R² values were calculated in Excel. Error bars = s.e.m.