Characterization of [125I]SCH 23982 binding in human brain: comparison with [3H]SCH 23390.

We studied binding of [125I]SCH 23982 in two regions of human brain, the caudate and the dorsolateral prefrontal cortex. Binding characteristics of [125I]SCH 23982 and of the non-iodinated tritiated analogue, [3H]SCH 23390, were compared. In caudate, binding of [125I]SCH 23982 was consistent with binding to D1 dopamine receptors while in frontal cortex, [125I]SCH 23982 bound mostly to serotonergic 5HT2 receptors. In contrast to [3H]SCH 23390, no evidence of binding of [125I]SCH 23982 to D1 receptors could be found in human frontal cortex. This indicates that iodination of SCH 23390 induces a decrease in its relative D1 versus 5HT2 selectivity that prohibits the use of [125I]SCH 23982 to label D1 receptors in human cortex.