Classification of neuroleptics: implications for tardive dyskinesia

The dopamine (DA) receptor blocking effect of neuroleptics is believed to be responsible for their antipsychotic effect. This blockade can be demonstrated in experimental animals by the ability of neuroleptics to antagonize stereotypies induced by DA agonists. Biochemically DA receptor-blocking properties of neuroleptics are illustrated by direct binding to DA receptors or by measuring inhibition of DA-stimulated adenylate cyclase activity. Most pharmacological and biochemical experiments with neuroleptics have concentrated on dopaminergic effects of the compounds both after acute and long-term treatment. After long-term treatment with neuroleptics an increase in DA receptor number and an increase in stereotyped behavior are seen. DA supersensitivity have been implied in the development of tardive dyskinesia (TD) in patients on long-term neuroleptic medication. In search for neuroleptics which would be less prone to induce TD and more effective in treating dyskinesia we have looked at the profile of a series of neuroleptics in in vitro experiments and in acute and long-term in vivo experiments. Since neuroleptics also influence other transmitter systems than the dopaminergic we have investigated interactions with drugs affecting these transmitter systems. According to their differential effects on DA receptors (D1 and D2) and their ability to develop tolerance and supersensitivity, the neuroleptics can be classified into different groups, some of which might be expected to induce less TD and be preferred for treating dyskinesia.