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 verus 5HT₂ selectivity that prohibits the use of [¹²⁵I]SCH 23982 to label D₁ receptors in human cortex.