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Serotonin Transporters, Serotonin Release, and the Mechanism of Fenfluramine Neurotoxicity
Author(s) -
BAUMANN MICHAEL H.,
AYESTAS MARIO A.,
DERSCH CHRISTINA M.,
PARTILLA JOHN S.,
ROTHMAN RICHARD B.
Publication year - 2000
Publication title -
annals of the new york academy of sciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.712
H-Index - 248
eISSN - 1749-6632
pISSN - 0077-8923
DOI - 10.1111/j.1749-6632.2000.tb05194.x
Subject(s) - fenfluramine , serotonin , pharmacology , chemistry , microdialysis , dopamine , nucleus accumbens , amphetamine , in vivo , mdma , forebrain , 5 ht receptor , endocrinology , medicine , central nervous system , biology , biochemistry , receptor , microbiology and biotechnology
Administration of d,l ‐fenfluramine (FEN), or the more active isomer d ‐fenfluramine (dFEN), causes long‐term depletion of forebrain serotonin (5‐HT) in animals. The mechanism underlying FEN‐induced 5‐HT depletion is not known, but appears to involve 5‐HT transporters (SERTs) in the brain. Some investigators have postulated that 5‐HT release evoked by FEN is responsible for the deleterious effects of the drug. In the present work, we sought to examine the relationship between drug‐induced 5‐HT release and long‐term 5‐HT depletion. The acute 5‐HT‐releasing effects of dFEN and the non‐amphetamine 5‐HT agonist 1‐( m ‐chlorophenyl)piperazine (mCPP) were evaluated using in vivo microdialysis in rat nucleus accumbens. The ability of dFEN and mCPP to interact with SERTs was assessed using in vitro assays for [ 3 H]‐transmitter uptake and release in rat forebrain synaptosomes. Drugs were subsequently tested for potential long‐lasting effects on brain tissue 5‐HT after repeated dosing (2.7 or 8.1 mg/kg, ip × 4). dFEN and mCPP were essentially equipotent in their ability to stimulate acute 5‐HT release in vivo and in vitro . Both drugs produced very selective effects on 5‐HT with minimal effects on dopamine. Interestingly, when dFEN or mCPP was administered repeatedly, only dFEN caused long‐term 5‐HT depletion in the forebrain at 2 weeks later. These data suggest that acute 5‐HT release per se does not mediate the long‐term 5‐HT depletion associated with dFEN. We hypothesize that dFEN and other amphetamine‐type releasers gain entrance into 5‐HT neurons via interaction with SERTs. Once internalized in nerve terminals, drugs accumulate to high concentrations, causing damage to cells. The relevance of this hypothesis for explaining clinical side effects of FEN and dFEN, such as cardiac valvulopathy and primary pulmonary hypertension, warrants further study.