Brain sigma receptors labelled by [3H]nemonapride.

Binding of [3H]nemonapride and [3H]raclopride was examined in the brain areas of three species (rat, cow and human). The results indicated that [3H]nemonapride binding is inhibited by selective sigma receptor ligands in frontal cortex, striatum and cerebellum. Only the striatum showed significant dopaminergic sites as defined by sulpiride. Use of the subtraction method of [3H]nemonapride minus [3H]raclopride binding as a measure of D4 dopamine receptor binding may, therefore, also include a sigma receptor component.