The binding of [3H]-5-hydroxytryptamine to homogenates of human brain

The binding of [3H]-5-hydroxytryptamine ([3H]-5-HT) to homogenates of human brain has been studied. The specific binding is saturable, with a Kd (frontal cortex) of 12 /+- 2 nM, and is inhibited by non-radioactive 5-HT (IC50=26 nM) and D-Lysergic acid diethylamide (IC50=20 nM). Specific, but not non-specific binding of [3H]-5-TH was inhibited by incubation of the homogenates at 50 degrees C. The binding of [3H]-5-HT across the human brain was not uniform, the highest binding being found in the substantia nigra and hippocampus, and the lowest in the thalamus and pons. The Kd of the binding sites towards 5-HT did, however, appear to be similar for the different brain regions.