High-dose fenfluramine administration decreases serotonin transporter binding, but not serotonin transporter protein levels, in rat forebrain.
Administration of D-fenfluramine (D-FEN) or parachloroamphetamine (PCA) can produce long-lasting decreases in serotonin transporter (SERT) binding and tissue levels of serotonin (5-HT) in rat forebrain. These changes have been viewed as evidence for 5-HT neurotoxicity, but no studies have measured SERT protein levels. In the present study, we determined the effect of high-dose D-FEN or PCA, administered according to a "neurotoxic" dosing regimen, on the density of SERT sites using ligand binding methods and on SERT protein levels using Western blots. Rats were sacrificed 2 days and 2 weeks after administration of drug or saline. The density of SERT was determined in homogenates of caudate and whole brain minus caudate. D-FEN and PCA decreased SERT binding by 30-60% in both tissues and at both time points. Similarly, D-FEN and PCA administration profoundly decreased tissue 5-HT and 5-HIAA in frontal cortex. Despite the large decreases in SERT binding and depletion of tissue 5-HT that occurred with D-FEN administration, SERT protein expression, as determined by Western blot analysis, did not change in either tissue or time point. PCA administration decreased SERT protein by about 20% only at the 2-day point in the caudate. Drug treatments did not change expression of glial fibrillary acidic protein (GFAP), a hallmark indicator of neuronal damage, in whole brain minus caudate in the 2-week group. These results support the hypothesis that decreases in tissue 5-HT and SERT binding sites induced by D-FEN and PCA reflect neuroadaptive changes, rather than neurotoxic effects.
D000818:Animals; D015153:Blotting, Western; D002352:Carrier Proteins / Q000187:drug effects* / Q000378:metabolism; D005277:Fenfluramine / Q000008:administration & dosage / Q000633:toxicity*; D006897:Hydroxyindoleacetic Acid / Q000378:metabolism; D008297:Male; D008562:Membrane Glycoproteins / Q000187:drug effects* / Q000378:metabolism; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D016548:Prosencephalon / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000378:metabolism*; D018490:Serotonin Agents / Q000008:administration & dosage / Q000633:toxicity*; D050486:Serotonin Plasma Membrane Transport Proteins; D010133:p-Chloroamphetamine / Q000008:administration & dosage / Q000633:toxicity*
D002352:Carrier Proteins; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D018490:Serotonin Agents; D050486:Serotonin Plasma Membrane Transport Proteins; C493232:Slc6a4 protein, rat; D005277:Fenfluramine; D012701:Serotonin; D006897:Hydroxyindoleacetic Acid; D010133:p-Chloroamphetamine