[H-3] NEMONAPRIDE AND [H-3] SPIPERONE LABEL EQUIVALENT NUMBERS OF D-2AND 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 dopa minergic systems in vitro and in vivo, but it has been reported that [ H-3] nemonapride and [H-3]spiperone give markedly different B-max valu es for preparations of D-2 dopamine receptors from recombinant cell li nes or animal tissues. We have used the two radioligands in parallel t o 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 d iffer by an average of <20%, independent of receptor type or buffer co nditions. All competition experiments show that the two ligands compet e 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-lik e receptors.