[H-3] GBR-12935 BINDING TO HUMAN CEREBRAL-CORTEX IS NOT TO DOPAMINE UPTAKE SITES

The binding of the dopamine uptake inhibitor [H-3]GBR-12935 to 16 regi ons of the human brain was investigated in competition experiments wit h increasing concentrations of GBR-12909, mazindol, and dopamine. The methodology used included a relatively high tissue concentration (8 mg /ml) and addition of 5 mM KCI in the assay buffer. GBR-12909 inhibited 80-90% of the binding in most regions, whereas dopamine only inhibite d the binding in the striatum. Mazindol inhibited only part of the cor tical binding at concentrations of > 1 mu 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 [H-3]G BR-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.