Changes in Locomotor Activity and Naloxone-Induced Jumping in Mice Produced by WIN 35,197-2 (Ethylketazocine) and Morphine

Abstract. Acute i.p. administration of morphine or cocaine produced increase in locomotor activity in Swiss-Webster female mice that were maximal at 32-100 mg/kg for morphine and at 32 mg/kg for cocaine. WIN35,197-2 produced dose-dependent decreases in locomotor activity from 3.2- 32 mg/kg. Chronic ad-ministration of WIN35,197-2 led to a 6- 10 fold shift to the right in the locomotor activity decreasing effect of the drug, but WIN35,197-2-tolerant mice retained their sensitivity to the locomotor stimulant effects of morphine and cocaine. Acute administration of WIN35,197-2 failed to sensitize mice to naloxone-induced jumping, although morphine did so. Chronic administration of WIN35,197-2 did lead to sensiti-zation to naloxone, but WIN 35,197-2 was much less efficacious in this regard than morphine. These behav-ioral effects of WIN35,197-2 may be helpful in the classification of modes of action of different narcotic agonists