Modification of the behavioral effects of phencyclidine by repeated drug exposure and body weight changes

In the first experiment, the effects of phencyclidine (PCP) on intake of sweetened condensed milk by rats were compared before and during a period of repeated daily injections of PCP or saline. A shift to the right in the PCP dose-effect function was found in rats receiving daily PCP injections indicating tolerance development to the effects of PCP on milk intake. The dose-effect function of PCP was shifted to the right in animals receiving daily saline as well. However, when body weight changes were controlled for in this groups of animals, the effects of PCP were the same as they had been initially, implicating body weight as a determinant of the behavioral effects of PCP. In the second experiment, a direct comparison of the behavioral effects of PCP in high- and low-weight animals revealed diminished effects of PCP in high-weight animals. When these animals were treated with 3H-PCP, brain total radioactivity as well as 3H-PCP in the high-weight animals were significantly lower than those in the low-weight animals.