[H-3] Nemonapride And [H-3] Spiperone Label Equivalent Numbers Of D-2 And D-3 Dopamine-Receptors In A Range Of Tissues And Under Different Conditions

[H-3]Nemonapride and [H-3]spiperone are very widely used to study dopaminergic systems in vitro and in vivo, but it has been reported that [H-3] nemonapride and [H-3]spiperone give markedly different B-max values for preparations of D-2 dopamine receptors from recombinant cell lines or animal tissues. We have used the two radioligands in parallel to study a range of dopamine receptors [D-2(short), D-2(long), and D-3] in different buffers. B-max values derived using either radioligand differ by an average of <20%, independent of receptor type or buffer conditions. All competition experiments show that the two ligands compete at a single site. It seems that [H-3]spiperone and [H-3]nemonapride do not differentiate between different forms or populations of D-2-like receptors.