Spatio-temporal pattern of eye movements induced by ketamine in the rat

Eye movements up to seven hours after ketamine injection were recorded in Long-Evans rats by means of a phase detection search coil apparatus. A flutter-like oculomotor pattern immeditely appeared after drug administration, lasting about one hour; it was characterized by unidirectional slow eye movements with superimposed bursts of saccades. While saccadic dynamics was always within the normal range, the eyes were unable to maintain a steady post-saccadic position. Every saccade was followed by a quick drift back towards the initial position. As the rat aroused, paroxysmal ocular motility stopped and spontaneous well isolated, now bidirectional saccades appeared. The post-saccadic drift persisted. Ocular flutter-like behavior could result from a sustained activation of the saccade generator, whereas impairment of gaze holding might be due to the neural integrator suppression.