Blockage of Cortical Spreading Depression by Picrotoxin Foci of Paroxysmal Activity

1% Picrotoxin placed on cortex of rat caused paroxysmal ECoG discharges with concomitant increase in [Ke+]from 3 to 6.7 mM with oscillations corresponding to ictal (maximum) and interictal (minimum) spiking. Invasion of the epileptogenic focus by spreading depression was blocked when the amplitude of oscillations of [Ke+] reached 2.6 mM. Epileptogenic activity induced by topical 10% Pentazol caused a less marked increase in [Ke+] (4.6 mM) and did not prevent depression from invading the focal area, but did diminish [Ke+] from the normal of 60 to 70 mM to 39 mM. It is concluded that seizure‐induced depolarization of neural elements in deep cortical layers, though inadequate to trigger spreading depression, does prevent it from spreading, in part by activating the sodium pump.

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