Action potentials rely on voltage-gated sodium channels to propagate into the dendrite. Action potentials rely on voltage-gated sodium channels to propagate into the dendrite. A, Confocal z-projection of a voltage-sensitive dye-filled interneuron. Colored boxes indicate dendritic regions of interest during imaging. B, Electrical and optical signals corresponding to an action potential or an injected action potential waveform in control or 1 μm TTX conditions. Black trace is the action potential recorded by the electrode at the soma during control. This action potential served as the injected waveform in the presence of TTX. Colored traces correspond to data obtained from somatic and dendritic regions of interest seen in A during control conditions (average of three trials). Gray traces are fluorescence changes in response to the injected action potential waveform (average of 5 trials). C, Relative amplitude of the fluorescence (TTX/Control) plotted against distance along the dendrite. Gray circles represent somatic change. Black circles represent dendritic changes. D, Plot of action potential amplitude (ΔF/F) during TTX and control conditions. Gray circles represent somatic ΔF/F. Black circles represent dendritic ΔF/F. Black line represents unity. Only optical signals were compared at the soma. N = 5 cells. Amanda E. Casale, and David A. McCormick J. Neurosci. 2011;31:18289-18302 ©2011 by Society for Neuroscience