Spatial profile of calcium transients evoked by backpropagating action potential in human cortical pyramidal dendrites.

Backpropagating action potentials play important role in synaptic plasticity, dendritic excitability and compartment specific intracellular Ca2+ dynamics. Signal propagation in human dendrites shows potentially species and dendritic region specific properties and we asked whether action potential backpropagation in human dendrites follows a uniform or a segment regulated pattern. We studied human cortical layer 2/3 pyramidal apical dendrites in acute brain slices with somatic whole-cell stimulation and simultaneous dendritic two-photon Ca2+ imaging. Single action potentials produced detectable Ca2+ influx in segments of apical dendrites up to 270 μm from the soma of human pyramidal neurons. Evoked Ca2+ signals showed a stereotyped spatial profile along dendrites: the amplitude of the Ca2+ transients increased with distance from the soma, reached the maximum level on the dendritic region 50-100 µm from the soma then decreased towards the distal dendritic regions of primary and higher order dendrites. Non-specific blockage of Ca2+ channels and blockade of voltage-gated Na+ channels significantly reduced and completely abolished Ca2+ transients, respectively. Various Ca2+ channel types contributed to the Ca2+ signals as shown by selective blockade with N-type, L-type, T-type, or R-type Ca2+ channel subtypes. These results suggest a booster region in primary dendrites of human pyramidal cells for backpropagation induced Ca2+ influx in the dendritic tree. Declaration of Interest Statement: None