Figure 2.

Imaging APs in a hippocampal slice from a thy1-hVOS 2.0 mouse. A, Probe fluorescence in mossy fiber axons in the sl originating from dentate granule cells. Image shows the CA3 region (see Fig. 1A) with selected locations numbered in the sl. The stimulating electrode is in the sl to the left of location 1. On the right are hVOS traces (10-trial averages) from the indicated locations; arrows indicate time of stimulation. The latency increased with distance from the stimulus electrode. Stimulus = 200 µA; [DPA] = 4 µM. B, Probe fluorescence in mossy cell axons in the iml. The bright iml is flanked by the darker stratum granulosum below and middle molecular layer above. The stimulating electrode is just outside the field of view from the lower left corner. Numbered locations are indicated in the iml, and traces to the right show 10-trial averages from those locations. Note the longer time scale in B compared with A due to slower propagation in mossy cell axons compared with mossy fibers. Traces in A and B were normalized. Stimulus = 200 µA; [DPA] = 4 µM. C, AP broadening by 10 mM TEA in CA3 mossy fibers. D, AP broadening by 10 mM TEA in mossy cell axons. Solid, control trace; dotted, in TEA; dashed, after TEA washout. TEA reversibly broadened APs by slowing repolarization. Upper traces were not normalized; lower traces were normalized to peak amplitude. Stimulus = 75 µA (C) and 100 µA (D). [DPA] = 2 µM. 10-trial averages.