Neuroleptics have identical potencies in human brain limbic and putamen regions

In order to examine whether some neuroleptic drugs were specifically more potent on human limbic dopamine receptors than on striatal dopamine receptors, we tested the potency of eight neuroleptics on their ability to inhibit the binding of [3H]spiperone to D2 dopamine receptors in human putamen and nucleus accumbens. Each of the neuroleptics had an identical potency in both tissues, the IC50 values being 0.2 nM for spiperone, 2.5 nM for haloperidol, 2.6 nM for trifluperidol, 5 nM for fluphenazine, 20 nM for thioridazine, 25 nM for chlorpromazine, 100 nM for metoclopramide and 300 nM for clozapine. There is no evidence, therefore, for the concept of a limbic-specific dopamine receptor antagonist.