Not so very long ago brain scientists believed that dendrites were entirely passive. It’s become clear over the past 10 years or so that dendrites are much more complex and include regenerative voltage phenomena. One of these is the back-propagation of action potentials from the axon initial segment, through the soma, and into the dendrites. Voltage-gated sodium channels are responsible for much of the action potentials positive current and are known to be highly concentrated in the axons.

The recent paper “Molecular Identity of Dendritic Voltage-Gated Sodium Channels” published May 14, 2010 in Science looked at voltage-gated sodium channel density throughout the dendritic tree of pyramidal cells in the cornu ammonis 1 (CA1) of the hippocampus.

They found that the Nav1.6 subunit, a building block of voltage-gated sodium channels, was key to enabling dendritic excitability.

They measured voltage-gated sodium channel density at:

• 5 channels per square micrometer plasma membrane in soma and proximal apical dendrites
• 3 channels per square micrometer plasma membrane in proximal oblique dendrites
• 2 channels per square micrometer plasma membrane in distal apical dendrites

These measures will be very useful in computer models of these pyramidal cells.