Figure 1.

SynaptopHluorin fluorescence reliably reflects nerve stimulation. A, Transgenic mouse motor nerve terminal expressing spH before stimulation (left), at the end of a stimulus train (100 Hz for 8 s; middle), and 1 min after the train ended (right). Images were background subtracted. Scale bar, 10 μm. B, The average fluorescence (F) of the terminal, which increased ∼50% during the train (horizontal bar) and then decayed exponentially with a time constant of 14 s. C, The robust reliability of the fluorescence rise during repeated trains (each 100 Hz for 0.5 s) is clearly evident. Successive peak amplitudes decayed by ∼3%. D, Fluorescence of 23 different terminals (background subtracted), offset (no scaling) to equal zero immediately before the train. Open circles show mean ± SEM. E, Same data as D, normalized to peak F values to show variation in recovery after the stimulus train ended. The best-fit exponential (open circles) has a decay time constant of 27 s (r² = 0.996). a.u., Arbitrary units.