Definition of the in-vivo accumulation of [3H]spiperone in brain using haloperidol and sulpiride to determine functional dopamine receptor occupation.

Abstract

The in-vivo administration of [3H]spiperone caused an accumulation of radioactivity in the substantia nigra, tuberculum olfactorium, nucleus accumbens, striatum and frontal cortex when compared with cerebellar levels. Haloperidol (0.01-1.0 mg kg-1 i.p.) dose-dependently prevented the accumulation of [3H]spiperone in the substantia nigra, tuberculum olfactorium, striatum and nucleus accumbens. Sulpiride (10-160 mg kg-1 i.p.) dose-dependently prevented the accumulation of [3H]spiperone only in the substantia nigra. The effects of sulpiride on other areas were not consistent; there was a suggestion of a reduction in the accumulation of [3H]spiperone in tuberculum olfactorium and striatum, but not in nucleus accumbens. Neither haloperidol (0.01-1.0 mg kg-1 i.p.) nor sulpiride (10-160 mg kg-1 i.p.) caused displacement of [3H]spiperone from the frontal cortex. Both haloperidol (0.01-0.5 mg kg-1) and sulpiride (10-80 mg kg-1) increased striatal and mesolimbic HVA concentrations. Haloperidol potently blocked apomorphine-induced stereotypy but sulpiride was only effective at the highest dose employed. The functional effect produced by haloperidol correlated with its ability to define [3H]spiperone binding in-vivo to dopamine receptors in the substantia nigra, striatum and tuberculum olfactorium. In contrast, there was no correlation between functional effect of sulpiride and its ability to define [3H]spiperone binding in-vivo.