Extracellular fluid conductivity analysis by dielectric spectroscopy forin vitrodetermination of cortical tissue vitality

Abstract

Brain tissue is extremely metabolically active in part due to its need to constantly maintain a precise extracellular ionic environment. Under pathological conditions, unhealthy cortical tissue loses its ability to maintain this precise environment and there is a net efflux of charged particles from the cells. Typically, this ionic efflux is measured using ion-selective microelectrodes, which measure a single ionic species at a time. In this paper, we have used a bio-sensing method, dielectric spectroscopy (DS), which allows for the simultaneous measurement of the net efflux of all charged particles from cells by measuring extracellular conductivity. We exposed cortical brain slices from the mouse to different solutions that mimic various pathological states such as hypokalemia, hyperkalemia and ischemia (via oxygen-glucose deprivation). We have found that the changes in conductivity of the extracellular solutions were proportional to the severity of the pathological insult experienced by the brain tissue. Thus, DS allows for the measurement of changes in extracellular conductivity with enough sensitivity to monitor the health of brain tissue in vitro.

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“…conductivity of Tyrode's solution as σ T = 1.59 S/m [21][22][23] and the conductivity of cardiac tissue as σ C = 0.6 S/m [20]. Note that the solution of the Laplace equation depends on only the ratio σ T /σ C , so variations in σ T or σ C with frequency do not affect our solution as long as they have the same frequency dependency.…”