Dendritic shaft constrictions shape synaptic integration in neurons.

For nearly 150 years, textbooks have described dendritic morphology as optimized for efficient synaptic voltage transfer from spines to the soma, implemented as a tubular design respecting Rall's 3/2 rule for impedance matching at branch points. Here, we reveal that this view is an oversimplification. Using multiple high-resolution imaging techniques, we demonstrate that dendrites in cortical and hippocampal neurons exhibit nanoscale constrictions, termed dendritic shaft constrictions (DSCs), with diameters ranging from ∼100 to 500 nanometers in mice. We also identified DSCs in human hippocampal and cortical neurons. We provide theoretical and experimental lines of evidence that these constrictions effectively partition the dendrite into distinct electrical compartments, shaping dendritic integration of synaptic potentials.