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Comparative Study
. 2014 May;39(6):1355-65.
doi: 10.1038/npp.2013.331. Epub 2013 Nov 28.

Evidence for a role of transporter-mediated currents in the depletion of brain serotonin induced by serotonin transporter substrates

Michael H Baumann  1 , Simon Bulling  2 , Tova S Benaderet  1 , Kusumika Saha  2 , Mario A Ayestas  1 , John S Partilla  1 , Syed F Ali  3 , Thomas Stockner  2 , Richard B Rothman  1 , Walter Sandtner  2 , Harald H Sitte  2
Affiliations
Comparative Study

Evidence for a role of transporter-mediated currents in the depletion of brain serotonin induced by serotonin transporter substrates

Michael H Baumann et al. Neuropsychopharmacology. 2014 May.

Abstract

Serotonin (5-HT) transporter (SERT) substrates like fenfluramine and 3,4-methylenedioxymethamphetamine cause long-term depletion of brain 5-HT, while certain other substrates do not. The 5-HT deficits produced by SERT substrates are dependent upon transporter proteins, but the exact mechanisms responsible are unclear. Here, we compared the pharmacology of several SERT substrates: fenfluramine, d-fenfluramine, 1-(m-chlorophenyl)piperazine (mCPP) and 1-(m-trifluoromethylphenyl)piperainze (TFMPP), to establish relationships between acute drug mechanisms and the propensity for long-term 5-HT depletions. In vivo microdialysis was carried out in rat nucleus accumbens to examine acute 5-HT release and long-term depletion in the same subjects. In vitro assays were performed to measure efflux of [(3)H]5-HT in rat brain synaptosomes and transporter-mediated ionic currents in SERT-expressing Xenopus oocytes. When administered repeatedly to rats (6 mg/kg, i.p., four doses), all drugs produce large sustained elevations in extracellular 5-HT (>5-fold) with minimal effects on dopamine. Importantly, 2 weeks after dosing, only rats exposed to fenfluramine and d-fenfluramine display depletion of brain 5-HT. All test drugs evoke fluoxetine-sensitive efflux of [(3)H]5-HT from synaptosomes, but d-fenfluramine and its bioactive metabolite d-norfenfluramine induce significantly greater SERT-mediated currents than phenylpiperazines. Our data confirm that drug-induced 5-HT release probably does not mediate 5-HT depletion. However, the magnitude of transporter-mediated inward current may be a critical factor in the cascade of events leading to 5-HT deficits. This hypothesis warrants further study, especially given the growing popularity of designer drugs that target SERT.

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Figures

Figure 1
Figure 1
Effects of repeated i.p. administrations of saline, fenfluramine (fen), d-fenfluramine (d-fen), mCPP, and TFMPP on extracellular 5-HT and dopamine (DA) in rats undergoing microdialysis in nucleus accumbens. Panel a depicts the effects of fen, d-fen, and saline on dialysate 5-HT, whereas panel b shows dialysate dopamine. Panel c depicts effects of mCPP, TFMPP, and saline on dialysate 5-HT, whereas panel d shows dialysate dopamine. Arrows indicate time of injections. Data are mean±SEM expressed as % baseline for N=5 rats per group.
Figure 2
Figure 2
Effects of repeated doses of saline, fenfluramine (fen), d-fenfluramine (d-fen), mCPP, or TFMPP on post-mortem tissue levels of 5-HT and dopamine (DA) in rat nucleus accumbens, measured 2 weeks after injections. Panel a shows the effects of fenfluramines while panel c shows the effects of phenylpiperazines. Post-mortem tissue data (a, c) are mean±SEM expressed as % control amine N=5 rats per group. The relationship between dialysate 5-HT and post-mortem tissue 5-HT is illustrated for fenfluramines and phenylpiperazine in panels b and d, respectively. Pearson's correlation coefficient (r) was calculated for effects of fenfluramines (b) or piperazines (d), based on mean dialysate 5-HT during the sampling period (pg/5 μl) and post-mortem tissue levels of 5-HT (ng/100 mg) for individual subjects. N=15 rats per plot.
Figure 3
Figure 3
Release of preloaded [3H]5-HT from rat brain synaptosomes evoked by d-fenfluramine (d-fen), d-norfenfluramine (d-norfen), mCPP, and TFMPP. Drug-induced [3H]-5-HT release was measured in the presence or absence of 10 nM fluoxetine for d-fen (a), d-norfen (b), mCPP (c), and TFMPP (d). Data are mean±SD for N=3 separate experiments.
Figure 4
Figure 4
SERT-generated currents in Xenopus oocytes induced by increasing concentrations of d-fenfluramine, d-norfenfluramine, mCPP, TFMPP, or MTA in comparison with the physiological substrate 5-HT (10 μM). Sample traces are shown in panels a–e, and drug concentrations are given in μM.
Figure 5
Figure 5
(a) Concentration-response curves, pooled from different oocytes and (b) comparison of the maximal current (Cmax) for d-fenfluramine, d-norfenfluramine, mCPP, TFMPP, and MTA compared in the same oocyte. Maximal current for d-fenfluramine was measured at 10 μM and for d-norfenfluramine at 100 μM, whereas maximal current for mCPP, TFMPP, and MTA was measured at 3 μM. Statistical analysis revealed significant differences at a level of p<0.01 (***).
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References

    1. Adams SV, Defelice LJ. Ionic currents in the human serotonin transporter reveal inconsistencies in the alternating access hypothesis. Biophys J. 2003;85:1548–1559. - PMC - PubMed
    1. Appel NM, Mitchell WM, Contrera JF, De Souza EB. Effects of high-dose fenfluramine treatment on monoamine uptake sites in rat brain: assessment using quantitative autoradiography. Synapse. 1990;6:33–44. - PubMed
    1. Auerbach SB, Kamalakannan N, Rutter JJ. TFMPP and RU24969 enhance serotonin release from rat hippocampus. Eur J Pharmacol. 1990;190:51–57. - PubMed
    1. Baumann MH, Ayestas MA, Dersch CM, Rothman RB. 1-(M-chlorophenyl)piperazine (mCPP) dissociates in vivo serotonin release from long-term serotonin depletion in rat brain. Neuropsychopharmacology. 2001;24:492–501. - PubMed
    1. Baumann MH, Ayestas MA, Partilla JS, Sink JR, Shulgin AT, Daley PF, et al. The designer methcathinone analogs, mephedrone and methylone, are substrates for monoamine transporters in brain tissue. Neuropsychopharmacology. 2012;37:1192–1203. - PMC - PubMed

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