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Electrocorticographic recordings were analyzed in two groups of Wistar rats with end-to-side portacaval shunt and sham portacaval shunt. The main electrical abnormalities observed in the shunted rats concerned slow wave sleep. Quantitative evaluation of these disturbances was made by measuring the duration of spindles normally present in this phase of sleep. Longer duration of the spindles appears to be a reliable index of electrocorticographic disorders after portacaval shunt in the rat.

The level of wakefulness in rats with portacaval shunt has been evaluated by measurement of the reactivity of the reticulocortical system by electric stimulation of the brain stem reticular formation during slow wave sleep. The voltage level of stimulus necessary to provoke cortical awakening is significantly decreased after portacaval shunt. This modification of the level of wakefulness is in accordance with the diminution of total sleep and the decrease in threshold of reaction to painful stimuli observed in rats after portacaval shunt. The measurement of the reactivity of the reticulocortical system is a simple procedure which permits quantification of post-shunt encephalopathy in the rat.