Figure 3.

Presynaptic bouton recordings reveal AP broadening in axon collaterals. (A) 2P fluorescence overview image of a demyelinated layer 5 pyramidal neuron loaded with Alexa 568 (200 μM), Yellow arrows, BP locations. Image has been modified for clarity by subtracting the background noise extensively to highlight the collateral tree. A loose-seal recording is indicated schematically. Scale bar, 20 μm. (B) Temporally aligned overlay of eight somatic APs and their corresponding bouton axonal spikes. Bouton loose-seal patch APs (bottom) were recorded by repetitively eliciting somatic single APs (top) through brief (3 ms; middle) square current pulse. Scale bar, 0.5 ms; 10 mV; 5 pA. (C) Example traces of aligned APs recorded in control (black) and demyelinated (blue) axon collaterals (~149 μm from the AP initiation). Scale bar, 1 ms; 5 pA. (D) Plots of the average half-widths of the inward and outward current components of the recorded bouton APs. Cuprizone, blue circles, n = 16 boutons from 14 cells. Control, gray circles, n = 15 boutons from 14 cells. Individual recordings plotted as open circles. M-W test, *P = 0.0010, **P = 0.0002, respectively. Data are presented as mean ± SEM.