[3H] GBR-12935 Binding to Human Cerebral Cortex Is Not to Dopamine Uptake Sites

Abstract: The binding of the dopamine uptake inhibitor [³H] GBR-12935 to 16 regions of the human brain was investigated in competition experiments with increasing concentrations of GBR-12909, mazindol, and dopamine. The methodology used included a relatively high tissue concentration (8 mg/ml) and addition of 5 m M KCI in the assay buffer. GBR-12909 inhibited 80–90% of the binding in most regions, whereas dopamine only inhibited the binding in the striatum. Mazindol inhibited only part of the cortical binding at concentrations of >1 μ M , whereas the inhibition in the caudate and the putamen also contained a high-affinity component representing the dopamine uptake site. It is concluded that the [³H] GBR-12935 binding sensitive to GBR-12909 cannot be regarded as specific binding to the dopamine uptake site because the displaceable binding most likely is not related to the dopamine uptake site.