R.A. Locock

Displacement of serotonin from binding sites in rat cortex: The effects of biogenic “trace” amines

The concentrations for 50 percent inhibition of binding (IC50s) to specific in vitro serotonin binding sites (5-HT1 and 5-HT2) of rat cerebral cortex were determined for the trace amines 2-phenylethylamine, m- and p-tyramine, tryptamine, and (+)- and (-)- alpha-methyltryptamine. Tryptamine gave an IC50 of 66.7 +/- 4.8 nM (n = 7) at the 5-HT1 site and an IC50 of 3.85 +/- 0.16 microM (n = 7) for the 5-HT2 binding site. The IC50 values for all the other compounds were in the micromolar range and were different at the two binding sites except for p-tyramine (IC50, 5-HT1 = IC50, 5-HT2 = 17 microM. The trace amines may have different functional roles as evidenced by their different degrees of displacement of serotonin at 5-HT1 and 5-HT2 binding sites in the brain.

Interaction of Trace Amines with Serotonin Recognition Sites in Rat Brain

The “trace” amines such as 2-phenylethylamine, m-and p-tyramine and tryptamine accumulate in brain after administration of monoamine oxidase inhibitor antidepressant drugs (Boulton and Juorio, 1982). Accumulated quantities of these substances, in addition to having effects by themselves, may have important interactions with neurotransmitter receptor systems. In the study reported here we have examined the in vitro interactions of these trace amines with serotonin (5-hydroxytryptamine; 5-HT) recognition sites (5-HT1 and 5-HT2) of rat cerebral cortex. Modulation of serotonin receptors by the central neurotransmitter, norepinephrine, has been recognized recently (Scott and Crews, 1985); the trace amines also may have important interactions with the serotonin receptors.