Fig. 7.

Field potential (top trace) and [K⁺]_o (bottomtrace) recordings in the middle layers of the entorhinal cortex during application of 4AP. The GABA-mediated field potentials are associated with transient increases in [K⁺]_o (left panel in A), while a sustained elevation is seen during the tonic phase of the ictal discharge; note that the ictal discharge is initiated by an increase in [K⁺]_o that is larger than the elevations associated with the isolated GABA-mediated field potential. Note in B that distinct increases in [K⁺]_o accompany clonic discharges during return of [K⁺]_o toward baseline values (asterisk) and that a pronounced undershoot follows the termination of the ictal discharge.