Evoked and spontaneous corticofugal multiple unit activity during different phases of metrazol infusion in cats

Abstract

Multiple unit activity (MUA) was recorded from the cerebral peduncle during preictal, ictal and postictal phases of Metrazol infusion in cats. During preictal EEG paroxysmal activity MUA activity increased, sustained MUA discharge preceded the onset of tonic EEG seizure activity and bursts of MUA activity coincided with positive transients during late tonic and clonic periods. No MUA discharge was observed during postictal depression. During preictal periods, Metrazol increased the amplitude and duration of the initial MUA burst to stimulation of the ventralis posterolateralis nucleus. The duration and intensity of the MUA suppression following the response was also increased. The burst-suppression pattern of MUA activity during repetitive stimulation was replaced by a burst-sustained discharge pattern. The changes observed in EEG and MUA are correlated with previously described intracellular changes and provide a consistent picture of EEG, neuronal and axonal behaviour during Metrazol administration. Axonal activity provides a more relevant indication of effective corticofugal activity than does intracellular recording. The level of axonal discharge correlates better with the degree of soma-dendritic depolarization than it does to somatic spike generation.