A Neurophysiologic Study of Ketamine Anesthesia in the Cat

Abstract

The effects of ketamine on CNS electrical activities (EEC and multiple-unit activity of the brain-stem core) and gross behavior were studied in cats with chronically implanted electrodes. Ketamine induced three distinct patterns, related to dose An initial CNS excitation coupled with catatonic behavior was followed by disorganized excitation characterized by a catatonie-anesthetic state and finally, electrographic seizures without clinical correlates. During the initial period multiple-unit activity increased. Following this, the basal level of multiple-unit activity decreased, but the level increased phasically in synchrony with EEG hypersynchrony. During the stage of generalized seizures, the basal level decreased further, while phasic enhancement was not much affected. Comparison of polygraphic findings in the ketamine-induced anesthetic state and during control paradoxical (dream) sleep revealed that there is little or no possibility that ketamine induces dream sleep in the cat. Comparison of ketamine anesthesia and states induced by other hallucinogenic and convulsant drugs, including anesthetics, indicated some possibility that ketamine induces hallucinations. It was concluded that the ketamine-induced anesthetic state is a result of functional disorganization of the CNS rather than CNS depression.