Effect of barbiturate anesthesia on Discharge patterns in nucleus reticularis thalami

Abstract

In unanesthetized preparations spontaneous EEG spindles are accompanied by a tonic increase in neuronal firing in the rostral pole of nucleus reticularis thalami. The effect of Brevital on this relationship was investigated in encephàle isolé cats in the present report. Small doses of the drug consistently decreased the firing frequency inbetween the appearance of cortical spindles, whereas the effect on the intraspindle discharge rate as well as the averaged overall firing frequency varied from cell to cell. The ratio of intra- vs. interspindle discharge frequency was enhanced during light and moderate anesthesia, and the tonic spindle-related firing was broken up into bursts which were in phase with individual EEG waves. An increase in dosage to a level producing persistent slow waves in the EEG was followed by continuous irregular reticularis firing with no apparent relationship to the slow EEG waves. Massive doses of Brevital resulting in a flat cortical EEG arrested spontaneous firing completely. The results are viewed as supporting the hypothesis that neurons in the rostral part of nucleus reticularis exert a tonic inhibitory influence on dorsal thalamic cells.