Subthreshold ASPs from single release sites backpropagate to the soma. (A) Representative current-clamp recordings of six consecutive ASPs (black) and their average (gray) evoked by local Ca²⁺ photolysis in an individual varicosity; the cell was recorded at physiological [Cl⁻]_i (15 mM) and kept at a −70-mV holding potential; the dotted gray line indicates timing of the laser pulse. The reconstruction on the left shows the location of the photolysis spot (arrowhead). (B) Average traces of ASPs evoked in four different release sites from different cells located at 36, 45, 54, and 87 µm from the soma (amplitudes were 6.3, 4.9, 2.8, and 2 mV, respectively; n = 2–10 events per site). (C) Plot of ASP amplitude as a function of the distance between the soma and the release site. Individual points correspond to average amplitudes made from 2 to 26 individual sweeps from single release sites. Continuous line is the exponential fit (D₃₇ = 91 ± 66 µm; n = 21 sites). (D) Plot of ASP amplitude as a function of τ_Rise (continuous line is the linear fit; P > 0.05; Pearson’s coefficient = 0.61; n = 21 sites). (E) Plot of τ_Decay as a function of τ_Rise (continuous line is the linear fit; P > 0.05; Pearson’s coefficient = −0.24; n = 21 sites).