Figure 3.

Action potential propagation in the axons of granule cells and mossy cells. The hVOS probe illustrated in Fig. 2A was modified to incorporate a motif from GAP43 [36], which resulted in axon targeting [43,45]. In hippocampal slices prepared from a transgenic mouse with this probe on the thy1 promotor, probe expression was evident in the mossy fibers of the stratum lucidum in the CA3 region, formed by granule cell axons (A), and in a population of axons in the inner molecular layer of the dentate gyrus, formed by hilar mossy cells (B). Stimulation near the sites numbered 1 elicited a fluorescence change that propagated to the more distant sites over a few msec (recording sites numbered in the images to the left correspond to numbers of the traces to the right). Plots of time versus distance for granule cell axons (C) and mossy cell axons (D) illustrate propagation with constant velocity. Black diamond and solid line, 2 μM DPA; grey square and dashed gray line, 4 μM DPA. The legend in C also applies to D. Velocities determined from these plots are stated in the text (reproduced from [43]).