[Individual susceptibility to addiction. Contribution of animal models]

Whereas the main clinical problem in drug addiction lies in individual vulnerability to toxicomania, experimental models of drug abuse usually focus on the brain targets involved in the reinforcing properties of drugs. In this short review, we describe the two main procedures of animal drug self-administration--retention and acquisition paradigms--designed to investigate the neural substrate of drug abuse and the individual susceptibility to toxicomania. Retention procedures have been widely employed since Weeks (1962) to study the reinforcing properties of various addictive substances in experimental animals, particularly opiates and psychostimulants. If the meso-accumbens dopaminergic pathway actually seems to underlie the reinforcing properties of psychostimulants, the question remains unsolved regarding opiates and other drugs of abuse such as benzodiazepines, nicotine or alcohol. Rather than a final common pathway for the reinforcing properties of drugs, the dopaminergic system could be considered as a modulator which enables the expression of addictive properties, supported by the interaction of drugs with other brain structures. Therefore, the neural substrate of drug reinforcement appears redundant and widespread rather than convergent and anatomically circumscribed. On the other hand, acquisition procedures deal with factors that influence the individual vulnerability to drug addiction in animals. This procedure measures the ability of animals to become dependent of low doses of addictive substances. Under various conditions such as stress, food deprivation or isolated housing, it is possible to detect changes in the vulnerability to drug consumption. Moreover, it is possible to detect behavioral characteristics that predict the vulnerability of animals to the spontaneous self-administration of psychostimulants.(ABSTRACT TRUNCATED AT 250 WORDS)