Abstract: Ingestive behavior was evolutionarily important for survival in animals. A serial of studies demonstrated that dizocilpine (MK-801) increased but naloxone decreased the food intake in rats. However, it was elusive how they mediated ingestive behavior in rats. Food craving was one of the most important factors to impact food intake. In the present experiment, the effects of naloxone and dizocilpine on food craving of the rats were investigated with conditioned place preference (CPP) paradigm. After received 3 conditioning sessions with food, the rats were injected with saline, naloxone (1.0 mg˙kg -1) and MK-801 (0.1 mg˙kg -1) during the expression of CPP test, and the time spent in the food-associated compartment were observed. The results showed the rats developed significant preference for food-paired side, and MK-801 potentiated the expression of food-induced CPP, but naloxone had no effect on the expression of food CPP. The present data suggested that the enhancement of food craving was one of the possibilities of MK-801-induced increase of food intake, but it might not be the reduction of food craving that led to the naloxone-induced decrease of food intake. The psychological mechanism of ingestive behavior meditated by naloxone and MK-801 may be disassociated.

Key words: food craving, naloxone, MK-801, expression of conditioned place preference