[New antipsychotic agents: new paths of research on the notion of atypical agents].

The synthesis of new compounds called atypical neuroleptics such as amisulpride, clozapine, risperidone and now olanzapine has roused interest in the psychopharmacology of atypical antipsychotics. Since the synthesis of chlorpromazine in the early 1950s, subsequent therapeutic research has had two main goals: to define the mechanism of action of atypical neuroleptics and to search new compounds with both clinical efficacy and fewer side effects. The first one has widely been achieved, as it is clear that classical neuroleptics exert their effects by blockade of dopamine D2 receptors located in the ventral striatum. As a matter of fact, non specific blockade of dopaminergic receptors in the dorsal striatum also predicts extrapyramidal side effects. Moreover, classical neuroleptics have poor effects on negative and cognitive symptoms. That is why the search for new compounds has focused on two main goals: first, understanding the interactions of the neurotransmitters involved by the new drugs, second, characterizing their brain site of action. Achieving these two goals might enable us to precise the notion of atypicity as well as the classification of these new drugs.