A study of the transition from spindles to spike and wave discharge in feline generalized penicillin epilepsy: Microphysiological features

Abstract

The microphysiological features underlying the evolution of spike and wave discharge from spindles in feline generalized penicillin epilepsy were investigated using extracellular microelectrode recordings. Action potentials generated by single cortical neurons were related to the EEG features of the transition from spindles to spike and waves using statistical methods of analysis on a computer. The probability of an action potential being discharged by a spindle wave was weak. It progressively increased after penicillin during the transformation of the spindle wave into the spike of the spike and wave complex. As this occurred, periods of decreased firing probability coinciding with the slow wave of the spike and wave complex developed immediately after each period of enhanced firing probability. The spike and wave pattern was thus characterized by a remarkable oscillation between periods of increased excitation of cortical neurons corresponding to the spike, and periods of markedly decreased firing probability corresponding to the wave of the spike and wave complex. This was associated with increased synchronization of discharge of neighboring cortical neurons. We propose that the transformation of spindles to spike and waves is the consequence of a single feature: increased excitability of cortical neurons to spindle-inducing thalamocortical volleys. Under those conditions cortical cells discharge action potentials more consistently with each thalamocortical volley. Because of this the high threshold intracortical recurrent inhibitory pathway is recruited into the discharging process and induces recurrent periods of powerful inhibition of cortical neurons.