The influence of barbiturates on paroxysmal EEG activity induced by hippocampal and/or thalamic cobalt foci

Abstract

Epileptiform 7–9/sec spike and wave and polyspike EEG discharges were induced in male albino rats by chronic cobalt-gelatine implantation into the dorsal hippocampus and/or non-specific thalamus.

Low doses of allobarbital and thiopental (10–20 mg/kg) markedly reduced the incidence of the epileptiform manifestations simultaneously with the appearance of slow-wave EEG activity. After desynchronization by reticular or sensory stimulation, the paroxysmal EEG patterns often reappeared. The presence of sleep cycles with alternation of slow-wave and paradoxical sleep phases made it difficult to measure the duration of the effect. Low doses of barbiturates seemed to influence the 7–9/sec spike and wave and polyspike discharges mainly indirectly by depressing the level of vigilance.

High doses (40–50 mg/kg) of the barbiturates caused an almost complete disappearance of the epileptiform manifestations lasting for several hours.

The frequency of spike and wave complexes or spikes within the epileptiform episodes (when present) slightly increased after barbiturate administration.

In the first 5 min after the injection of low doses of barbiturate a transitory facilitation of the incidence of the paroxysmal discharge was sometimes observed together with the disappearance of spontanous movements. During the second half of anaesthesia after high doses reticular stimulation in some cases triggered polyspike or spike and wave discharges lasting for minutes.