Extracellular potentials in low-density dissociated neuronal cultures.

The detection of extracellular potentials by means of multi-electrode arrays (MEA) is a useful technique for multi-site long-term monitoring of cultured neuronal activity with single-cell resolution. To optimize the geometry of the MEA it is advantageous to localize the cellular compartments that constitute the generators of these signals. For this purpose, an in vitro technique for the detection of extracellular signals with subcellular resolution has been developed. It makes use of easy-to-manufacture large-tip pipettes, monitoring of electrode-cell gap resistance for precise electrode positioning and low-density (100 cells/mm(2)) dissociated hippocampal cultures. Negative monophasic extracellular spikes, typically 60 microV, were measured over putative axonal processes and monophasic, biphasic and triphasic signals were recorded over the soma. A compartmental simulation suggests that different somatic conductance densities of Na(+) (1-10 mS/cm(2)) and K(+) (5-10 mS/cm(2)) channels can produce characteristic somatic extracellular potentials, with a variety of shapes similar to those observed experimentally.