Atypical neuroleptics can be defined as dopamine (DA) receptor blockers which differ from typical neuroleptics in that they have a markedly lower or absent propensity for the induction of parkinsonian side effects of tardive dyskinesias. Some of them, but not all, are also more effective in treating schizophrenic patients, i.e. those with negative symptoms or who resist to classical treatments. There may be four classes of potential atypical neuroleptics: 1) Antipsychotics such as sulpiride and remoxipride that block a subgroup of D2 receptors; 2) D1 antagonists that may prove to be a valuable new type of antipsychotic drug; 3) Partial D2 agonists and 4) Antipsychotics such as clozapine and risperidone which block DA as well as other receptors and which appear to have the most pronounced antipsychotic effect. The differences between typical and atypical neuroleptics may first relate to regional specificity in site of actions. Animal studies suggest that atypical neuroleptics may act preferentially on mesolimbic and mesocortical as opposed to striatal DA systems. Most studies which have attempted to define the biological mechanisms which subserve the differences between atypical and typical neuroleptic drugs have focused on receptor binding profile of these drugs. Relatively higher affinity for the serotonin (5HT2) receptor than for the D2 receptor may be important to the action of clozapine-like compounds. However, many other systems might be involved and it seems likely that the atypical neuroleptic profile could be achieved in more than one way.(ABSTRACT TRUNCATED AT 250 WORDS)
Antipsychotic Agents Humans