[Evaluation of the rewarding effects of drugs by conditioned place preference (CPP) paradigm: properties of volatile organic solvents and uncontrolled newly-abused drugs].

The conditioned place preference paradigm has been used to evaluate the motivational effects of drugs. The primary motivational effects of a drug are conditioned to prominent environmental stimuli of a conditioned place preference box, and after several conditionings, animals acquire secondary motivational effects of drugs. If the drug experience produces a positive effect, it is expected that animals will spend more time in the drug-paired place. This technique only requires that the animals carry out a simple operation to approach or avoid the drug-paired place. Place conditioning procedures have been used to assess rewarding and aversive properties of drugs. Abuse of volatile organic solvents among young people is a serious social issue in Japan. Organic solvents are cheap and relatively easy to obtain; hence, they carry the risk of becoming "gate-way drugs" for users. We developed an airtight conditioned place preference system for drug inhalation. Using this system, we found that toluene inhalation produced a rewarding effect in mice. The conditioned place preference paradigm has been used as a tool to delineate the neurochemical substrates mediating the rewarding effect of drugs. This method may be of great help in evaluating the abuse potential of substances (e.g., volatile organic solvents and uncontrolled newly-abused drugs) in animals.