A Detailed Model of Signal Transmission in Excitable Dendrites of Rat Neocortical Pyramidal Neurons

Abstract

Simultaneous patch clamp recordings from the soma and dendrites of neocortical pyramidal neurons of young rats show that, independent of the synaptic input location, the sodium action potential (AP) always starts at the soma and is then carried along the axon, but also propagates backward decrementally into the dendritic tree¹. This back-propagating AP is supported by a low density (${\bar g_{Na}} = \sim 4mS/c{m^2}$ mS/cm²) of Na⁺ in the dendrites and soma membrane of the pyramidal neurons.

In the work described here we built a detailed biophysical model, based on a fully reconstructed layer V pyramidal cell. Data obtained from electrophysiological measurements were used to restrict the model. By investigating model parameters, which reproduced the findings of Stuart and Sakmann, we were able to address the following questions: 1. Under what conditions will the AP always be seen first at the soma and only later in the dendrites? 2. What is the degree of amplification of the back-propagating AP due to the Na⁺ channels in the dendrites? 3. How resistant is the back propagating AP to background synaptic perturbation?

The model presented here can then be used to predict how the back-propagating AP will be seen in different locations in the dendrites and what will be its functional role.