SOMADENDRITIC BACKPROPAGATION OF ACTION-POTENTIALS IN CORTICAL PYRAMIDAL CELLS OF THE AWAKE RAT

The invasion of fast (Na+) spikes from the soma into dendrites was stu died in single pyramidal cells of the sensorimotor cortex by simultane ous extracellular recordings of the somatic and dendritic action poten tials in freely behaving rats. Field potentials and unit activity were monitored with multiple-site silicon probes along trajectories perpen dicular to the cortical layers at spatial intervals of 100 mu m. Dendr itic action potentials of individual layer V pyramidal neurons could b e recorded up to 400 mu m from the cell body. Action potentials were i nitiated at the somatic recording site and traveled back to the apical dendrite at a velocity of 0.67 m/s. Current source density analysis o f the action potential revealed time shifted dipoles, supporting the v iew of active spike propagation in dendrites. The presented method is suitable for exploring the conditions affecting the somadendritic prop agation action of potentials in the behaving animal.