Effect of Intravenous Thiopental on Spontaneous and Evoked Eye Movements in Cats

¹ From the Departments of Physiology and Anatomy, University of California at Los Angeles Medical Center, Los Angeles, California

The effect of small intravenous injections of thiopental has been studied on spontaneous and evoked eye movements in the encéphale isolé cat. Spontaneous movements of the eyes decrease and tend to become dissociated for some minutes after thiopental. Electromyographic recordings from the extraocular muscles reveal a sharp reduction in spontaneous discharge during and after the injection, followed by a gradual recovery. Stimulation of brainstem sites which yielded conjugate deviations before thiopental frequently results in mid-positioning of the eyes after the injection, usually after a period of complete unresponsiveness. Recovery of the original evoked conjugate deviation may occur within 6 minutes upon stimulation of a site in the tegmentum of the medulla; it takes 20 minutes or longer for sites located in the midbrain tegmentum. Cortically evoked conjugate eye movements disappear for longer periods of time following thiopental injection. Some of the possible mechanisms of thiopental action are discussed with particular reference to the mid-positioning response so readily obtained on stimulation in an animal lightly anesthetized with a barbiturate.