Ketamine induces failure of the oculomotor neural integrator in the cat.

We studied the effect of intramuscular injection of low dose of ketamine (1 mg/kg) on the spontaneous ocular movements of the cat. Ketamine is a non-competitive antagonist of the N-methyl-D-aspartate (NMDA) receptors, which is used as an anesthetic agent in human surgery. We found that ketamine administration caused a failure of gaze holding: each saccade was followed by a centripetal post-saccadic drift. This defect was selective: the dynamics of the saccades was not altered (the amplitude/maximum velocity relationship was unaffected by ketamine at the dose of 1 mg/kg). We postulated that the observed effect was due to the fact that NMDA receptors were implicated in the network of the oculomotor neural integrator that converted activity related to the saccade (pulse signal) into activity responsible for gaze holding (step signal).