Laminar DC studies of acetylcholine-activated epileptiform discharge in cerebral cortex

Abstract

Epileptiform paroxysms induced by local application of neostigmine and acetylcholine (ACh) to intact and undercut cerebral cortex of the cat have been studied by simultaneous DC recording of electrical activity from the cortical surface together with a penetrating micro-electrode used to plot the field potentials in depth as well as to obtain extracellular records of associated unit discharge. Each spontaneous paroxysm was initiated by a sudden surface negative DC shift upon which was superimposed regular rhythmic oscillating waves at 8–20/sec. The surface negative DC field potential did not show a phase reversal except deep to the Vth layer in the cortical depth, increased in negativity with a maximum in layer V in vicinity of large pyramidal cells. The rhythmic oscillating waves showed a phase reversal in most superficial cortical layers only approximately 200 μ beneath the surface. Rapid unit discharge of deep pyramidal cells accompanied the negative DC shift in intact cortex and was interrupted by gating or inhibitory action of rhythmic waves. ACh paroxysms induced in acutely undercut cortex were not accompanied by detectable unit discharge, raising a puzzling problem about their mode of generation. It is suggested that neuronal depolarization and possibly glial cells may play a role in the generation of the DC shifts of the ACh paroxysm as shown for direct cortical responses and evoked potentials by Castellucci and Goldring (1970).