Role of Monoamine Oxidase Inhibition and Monoamine Depletion in Fenfluramine‐Induced Neurotoxicity and Serotonin Release

Abstract

Abstract: The role of both monoamine synthesis and monoamine oxidase inhibition in mediating the fenfluramine‐induced damage to serotonin neurones was examined; as pretreatment agents, both alpha‐methyl‐para‐tyrosine (AMPT) and para‐chlorophenylalanine (PCPA) were used to deplete dopamine and serotonin, respectively, while clorgyline and deprenyl were used to inhibit monoamine oxidase types A and B. While both AMPT and deprenyl did not alter fenfluramine‐induced serotonin or 5‐hydroxyindoleacetic acid (5‐HIAA) depletion in any area, PCPA did partially reduce the serotonin depletion in the hippocampus and hypothalamus. Although pretreatment with clorgyline did not significantly alter fenfluramine‐induced serotonin depletion, it did produce a 65% mortality rate in animals treated with both drugs. Both PCPA and clorgyline significantly increased the depletion of striatal 5‐HIAA concentration consequent to fenfluramine; however, these drugs also produced a long‐term depletion of striatal 5‐HIAA when administered alone, therefore, the changes seen after the coadministration with fenfluramine may be viewed as additive. Finally, acute PCPA pretreatment attenuated the rapid rise in 3,4‐dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (homovanillic acid) induced by fenfluramine, and acute clorgyline reversed the drop in serotonin and rise in 5‐HIAA induced by fenfluramine. These results indicate that the rapid increase in dopamine activity induced by fenfluramine is partially dependent on serotonin concentration and release and that the mechanism of fenfluramine‐induced toxicity is unlike that of the other substituted amphetamines.