Fast sodium action potentials are generated in the distal apical dendrites of rat hippocampal CA1 pyramidal cells

Intracellular recording techniques were used to monitor the evoked responses in hippocampal CA1 pyramidal cells following focal stimulation of the proximally and distally located apical dendritic synapses. The local anaesthetic, QX-314, when injected into individual cells, caused a complete time-dependent blockade of the proximal and then the distal action potentials at both threshold and suprathreshold levels of stimulation. This progressive blockade of proximal and distal voltage-dependent sodium channels suggests that sodium action potentials can be generated in the distal apical dendrites of CA1 pyramidal cells.