Evidence for the existence of serotonin uptake inhibitor-like substances in human cerebrospinal fluid.

Addition of human cerebrospinal fluid (CSF) induced a marked inhibition of 3H-paroxetine binding to the monkey cortical membranes, while the specific binding of 3H-imipramine was slightly inhibited. Moreover, 3H-serotonin (5-hydroxy-tryptamine, 5-HT) uptake inhibition in the monkey cortical synaptosomes was also increased as the volume of added CSF was increased. Scatchard analysis of specific 3H-paroxetine binding with human CSF showed non-competitive kinetics, although CSF was competitive with 3H-imipramine binding. The inhibitory effect of human CSF on 5-HT uptake was non-competitive in nature. The endogenous substances in human CSF most probably act at the recognition site labeled with 3H-paroxetine. Moreover, occupation of this site by the endogenous substances is likely to inhibit the 5-HT uptake process.