The effects of ketamine enantiomers on schedule-controlled behavior in the rat.

Male Sprague-Dawley rats were trained to barpress under a FL-300 sec schedule of food presentation until responding patterns were stable. The effects of the ketamine optical isomers (enantioners) on this schedule-controlled behavior were examined over a dose range of 3.75 to 60 mg/kg i.p. At doses of 15 mg/kg and above, (-)-ketamine increased rate of responding, with a maximum increase of about 3 times control rate. This effect was rate-dependent, being more marked at lower control rates. In contrast (+)-ketamine did not increase overall fixed-interval response rate at any dose, but decreased rate of responding in a rate-dependent fashion at doses of 30 mg/kg and above. Spontaneous locomotor activity was increased about equally by equimolar doses of both enantiomers.