Stimulant and depressant effects of ketamine on neocortical activity in cats

Electroencephalographic (EEG) and behavioural effects of ketamine were examined in chronically-prepared cats carrying recording electrodes for neocortical EEG and a stimulating electrode in the optic chiasma for producing evoked potentials. Ketamine 3-5 mg kg-1 alone acted as a stimulant upon the cortical electrical activity with induced immobility. However, when ketamine was given in combination with barbiturate, it appeared to be a depressant in the sense that the anaesthetic effect of barbiturate was potentiated. Ketamine also failed to excite the neocortex of cats whose mesencephalic reticular formation had been destroyed. These results suggest that ketamine, administered in cats with no pretreatment or lesion, enhanced the neocortical activity via the ascending reticular activating system of the brain stem.