Concurrent evaluation of locomotor response to novelty and propensity toward cocaine conditioned place preference in mice.

Neural and physiological factors underlying individual differences in the vulnerability to drug abuse are the major questions remained to be determined. The present study described new methods that concurrently assess the relationship between locomotor response to novelty and conditioned place preference (CPP) for cocaine in mice using a novel activity monitor, SCANET. The activity monitor simultaneously measured the distance traveled and the amount of time spent in each side of a two-compartment CPP chamber, and the latency to the first entry into the other side of the CPP chamber. Mice were divided into two groups according to their locomotor response to the first exposure to the CPP chamber during a preconditioning session; high-responder (HR) and low-responder (LR) mice. Following conditioning sessions, the CPP score was shown to be higher in LR mice than in HR mice, especially at low doses of cocaine. In a separate experiment with SCANET, we measured the latency to the first entry into the white-floored compartment from the black-floored compartment of the CPP chamber as an index of anxiety-like behavior. The latency was significantly prolonged in the LR group as compared with the HR group. Thus, the new methods described here are considered to be useful for examining animal models of drug addiction with respect to anxiety-like behavior.