Active properties of dendritic membrane examined by current source density analysis in hippocampal CA1 pyramidal neurons.

The laminar profile of extracellular field potentials evoked by alveus or stratum radiatum stimulation was recorded at the CA1 region of guinea pig hippocampal slices. One-dimensional approximation of the current source density analysis method was applied to the data. When the alveus was stimulated, the location of inward membrane current (sink) moved from the cell body layer to the dendritic region for a distance of at least 200 micron at a velocity of 0.16 +/- 0.03 m/s (n = 6). This sink movement was not blocked by either low- Ca2+ or Ca2+-free/high-Mg2+ medium, but was blocked by tetrodotoxin application restricted to the dendritic region by a local perfusion method. When the stratum radiatum was stimulated, sink movement from the dendritic region to the cell body layer was not distinct. Retrograde sink movement from the cell body layer to the dendritic region subsequent to the cell body spike was not observed. These findings indicated that the dendrites of the CA1 pyramidal neurons can generate action potentials which propagate along the dendrite and that they might primarily be mediated by Na ion.