Figure 10.

AP backpropagation into the distal tuft is frequency dependent. A, Reconstructed prefrontal layer 5 pyramidal neuron showing location of line scans in the distal apical tuft (470-780 μm from the soma). B, One to five APs at 200 Hz were generated by brief somatic current injections (B₁), whereas simultaneous line scans taken across dendrites in the distal apical tuft produce the corresponding calcium transients (B₂). C, Plots of average ΔF/F for five trials similar to that shown in B. Numbers refer to somatic APs generated per trial. Note that a detectable calcium signal is only observed during bursts of three or more APs. D, Plot of peak ΔF/F during high-frequency AP bursts as a function of distance from the soma. The numbers indicate the minimum number of APs needed to evoke a detectable calcium signal at each location. E, Plot of average ΔF/F during AP bursts of three to six APs (200 Hz) under control conditions (black) and during bath application of 10 μm dopamine (gray). F, Summary of peak ΔF/F in control and dopamine (10 μm; n = 4) conditions at distal tuft locations during high-frequency AP bursts. The minimum number of APs needed to evoke a detectable calcium signal under control conditions was used for comparison of control and dopamine responses.