Transcortical Polarization in Rat Inhibits Spreading Depression

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Abstract
In cerebral cortex of rats single spreading depressions (SD) were elicited by a slight needle prick. SDs were monitored by recording changes of direct current (DC) potential via an array of four glass mi-croelectrodes providing a simultaneous depth profile. Using an epicortical Ag-AgCl wire electrode surrounding the recording site and a contralateral Ag-AgCl electrode penetrating the whole grey matter, a polarization current was applied starting 5 min before and ending 3 min after eliciting a SD. By anodic polarization of the cortical surface with intensities of 10 to 20 μA the SD was blocked in the whole grey matter. Restitution of SD in course and amplitudes was found only 45 min to 60 min after ending the polarization. Cathodic polarization of the cortical surface resulted in similar effects. Both polarizing and restitution effects were replicable in the same animal. The results are relevant for further investigations to discover the particular role of glial cells in regulation of extracellular potassium concentration during SD.