EFFECTS OF KETAMINE ENANTIOMERS ON SCHEDULE-CONTROLLED BEHAVIOR IN THE RAT

Abstract

Male Sprague-Dawley rats were trained to barpress under a FI-300 [fixed interval 300 s] schedule of food presentation until responding patterns were stable. The effects of the ketamine [2-(O-chlorophenyl)-2-(methylamino)cyclohexanone hydrochloride] optical isomers (enantiomers) on this schedule-controlled behavior were examined over a dose range of 3.75-60 mg/kg i.p. At doses of 15 mg/kg and above, (-)-ketamine increasd rate of responding, with a maximum increase of .apprx. 3 times control rate. This effect was rate-dependent, being more marked at lower control rates. (+)-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.