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Colwell MJ, Tagomori H, Shang F, Cheng HI, Wigg CE, Browning M, Cowen PJ, Murphy SE, Harmer CJ. Direct serotonin release in humans shapes aversive learning and inhibition. Nat Commun 2024; 15:6617. [PMID: 39122687 PMCID: PMC11315928 DOI: 10.1038/s41467-024-50394-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2023] [Accepted: 07/09/2024] [Indexed: 08/12/2024] Open
Abstract
The role of serotonin in human behaviour is informed by approaches which allow in vivo modification of synaptic serotonin. However, characterising the effects of increased serotonin signalling in human models of behaviour is challenging given the limitations of available experimental probes, notably selective serotonin reuptake inhibitors. Here we use a now-accessible approach to directly increase synaptic serotonin in humans (a selective serotonin releasing agent) and examine its influence on domains of behaviour historically considered core functions of serotonin. Computational techniques, including reinforcement learning and drift diffusion modelling, explain participant behaviour at baseline and after week-long intervention. Reinforcement learning models reveal that increasing synaptic serotonin reduces sensitivity for outcomes in aversive contexts. Furthermore, increasing synaptic serotonin enhances behavioural inhibition, and shifts bias towards impulse control during exposure to aversive emotional probes. These effects are seen in the context of overall improvements in memory for neutral verbal information. Our findings highlight the direct effects of increasing synaptic serotonin on human behaviour, underlining its role in guiding decision-making within aversive and more neutral contexts, and offering implications for longstanding theories of central serotonin function.
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Affiliation(s)
- Michael J Colwell
- University Department of Psychiatry, University of Oxford, Warneford Hospital, Oxford, UK.
- Oxford Health NHS Foundation Trust, Warneford Hospital, Oxford, UK.
| | - Hosana Tagomori
- University Department of Psychiatry, University of Oxford, Warneford Hospital, Oxford, UK
- Oxford Health NHS Foundation Trust, Warneford Hospital, Oxford, UK
| | - Fei Shang
- University Department of Psychiatry, University of Oxford, Warneford Hospital, Oxford, UK
- Oxford Health NHS Foundation Trust, Warneford Hospital, Oxford, UK
| | - Hoi Iao Cheng
- University Department of Psychiatry, University of Oxford, Warneford Hospital, Oxford, UK
- Oxford Health NHS Foundation Trust, Warneford Hospital, Oxford, UK
| | - Chloe E Wigg
- University Department of Psychiatry, University of Oxford, Warneford Hospital, Oxford, UK
- Oxford Health NHS Foundation Trust, Warneford Hospital, Oxford, UK
| | - Michael Browning
- University Department of Psychiatry, University of Oxford, Warneford Hospital, Oxford, UK
- Oxford Health NHS Foundation Trust, Warneford Hospital, Oxford, UK
| | - Philip J Cowen
- University Department of Psychiatry, University of Oxford, Warneford Hospital, Oxford, UK
- Oxford Health NHS Foundation Trust, Warneford Hospital, Oxford, UK
| | - Susannah E Murphy
- University Department of Psychiatry, University of Oxford, Warneford Hospital, Oxford, UK
- Oxford Health NHS Foundation Trust, Warneford Hospital, Oxford, UK
| | - Catherine J Harmer
- University Department of Psychiatry, University of Oxford, Warneford Hospital, Oxford, UK.
- Oxford Health NHS Foundation Trust, Warneford Hospital, Oxford, UK.
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Colom M, Vidal B, Fieux S, Redoute J, Costes N, Lavenne F, Mérida I, Irace Z, Iecker T, Bouillot C, Billard T, Newman-Tancredi A, Zimmer L. [ 18F]F13640, a 5-HT 1A Receptor Radiopharmaceutical Sensitive to Brain Serotonin Fluctuations. Front Neurosci 2021; 15:622423. [PMID: 33762906 PMCID: PMC7982540 DOI: 10.3389/fnins.2021.622423] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2020] [Accepted: 02/17/2021] [Indexed: 12/30/2022] Open
Abstract
Introduction Serotonin is involved in a variety of physiological functions and brain disorders. In this context, efforts have been made to investigate the in vivo fluctuations of this neurotransmitter using positron emission tomography (PET) imaging paradigms. Since serotonin is a full agonist, it binds preferentially to G-protein coupled receptors. In contrast, antagonist PET ligands additionally interact with uncoupled receptors. This could explain the lack of sensitivity to serotonin fluctuations of current 5-HT1A radiopharmaceuticals which are mainly antagonists and suggests that agonist radiotracers would be more appropriate to measure changes in neurotransmitter release. The present study evaluated the sensitivity to endogenous serotonin release of a recently developed, selective 5-HT1A receptor PET radiopharmaceutical, the agonist [18F]F13640 (a.k.a. befiradol or NLX-112). Materials and Methods Four cats each underwent three PET scans with [18F]F13640, i.e., a control PET scan of 90 min, a PET scan preceded 30 min before by an intravenous injection 1 mg/kg of d-fenfluramine, a serotonin releaser (blocking challenge), and a PET scan comprising the intravenous injection of 1 mg/kg of d-fenfluramine 30 min after the radiotracer injection (displacement challenge). Data were analyzed with regions of interest and voxel-based approaches. A lp-ntPET model approach was implemented to determine the dynamic of serotonin release during the challenge study. Results D-fenfluramine pretreatment elicited a massive inhibition of [18F]F13640 labeling in regions known to express 5-HT1A receptors, e.g., raphe nuclei, hippocampus, thalamus, anterior cingulate cortex, caudate putamen, occipital, frontal and parietal cortices, and gray matter of cerebellum. Administration of d-fenfluramine during PET acquisition indicates changes in occupancy from 10% (thalamus) to 31% (gray matter of cerebellum) even though the dissociation rate of [18F]F13640 over the 90 min acquisition time was modest. The lp-ntPET simulation succeeded in differentiating the control and challenge conditions. Conclusion The present findings demonstrate that labeling of 5-HT1A receptors with [18F]F13640 is sensitive to serotonin concentration fluctuations in vivo. Although the data underline the need to perform longer PET scan to ensure accurate measure of displacement, they support clinical development of [18F]F13640 as a tool to explore experimental paradigms involving physiological or pathological (neurological or neuropsychiatric pathologies) fluctuations of extracellular serotonin.
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Affiliation(s)
- Matthieu Colom
- Lyon Neuroscience Research Center, INSERM, CNRS, Université de Lyon, Université Claude Bernard Lyon 1, Lyon, France.,Hospices Civils de Lyon, Lyon, France
| | - Benjamin Vidal
- Lyon Neuroscience Research Center, INSERM, CNRS, Université de Lyon, Université Claude Bernard Lyon 1, Lyon, France
| | - Sylvain Fieux
- Lyon Neuroscience Research Center, INSERM, CNRS, Université de Lyon, Université Claude Bernard Lyon 1, Lyon, France
| | | | | | | | | | | | | | | | | | | | - Luc Zimmer
- Lyon Neuroscience Research Center, INSERM, CNRS, Université de Lyon, Université Claude Bernard Lyon 1, Lyon, France.,Hospices Civils de Lyon, Lyon, France.,CERMEP-Imagerie du Vivant, Bron, France.,Institut National des Sciences et Techniques Nucléaires, Gif-sur-Yvette, France
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Rush CR, Stoops WW, Lile JA, Alcorn JL, Bolin BL, Reynolds AR, Hays LR, Rayapati AO. Topiramate-phentermine combinations reduce cocaine self-administration in humans. Drug Alcohol Depend 2021; 218:108413. [PMID: 33290875 DOI: 10.1016/j.drugalcdep.2020.108413] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/07/2020] [Revised: 10/30/2020] [Accepted: 11/09/2020] [Indexed: 02/06/2023]
Abstract
RATIONALE Cocaine use disorder is an unrelenting public health concern. Despite nearly four decades of research, an FDA approved medication is not yet available. OBJECTIVES The objective of this human laboratory study was to demonstrate the initial efficacy, safety and tolerability of topiramate-phentermine combinations for cocaine use disorder. METHODS Thirty-one (31) participants with cocaine use disorder completed this mixed-model inpatient laboratory study. Participants were maintained on topiramate (0 [N = 11], 50 [N = 9] or 100 [N = 11] mg/day). Each topiramate group was concurrently maintained on phentermine (0, 15, 30 mg). Drug self-administration, subjective responses and cardiovascular effects following acute doses of intranasal cocaine (0, 40, 80 mg) were determined during separate experimental sessions after at least seven (7) days of maintenance on each condition. RESULTS The three groups of participants were well matched demographically and generally did not differ significantly in their responses to a range of doses of intranasal cocaine (0, 10, 20, 40, 80 mg) during a medical safety session. Maintenance on topiramate and phentermine alone significantly decreased cocaine self-administration although these effects were modest in magnitude. Combining topiramate and phentermine robustly decreased cocaine self-administration. Topiramate and phentermine were well tolerated alone and combined, as well as in conjunction with cocaine. CONCLUSIONS The results of the present study support advancing topiramate-phentermine combinations as a putative pharmacotherapeutic for cocaine use disorder.
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Affiliation(s)
- Craig R Rush
- Department of Behavioral Science, University of Kentucky College of Medicine, 1100 Veterans Drive, Medical Behavioral Science Building, Lexington, KY, 40536-0086, USA.
| | - William W Stoops
- Department of Behavioral Science, University of Kentucky College of Medicine, 1100 Veterans Drive, Medical Behavioral Science Building, Lexington, KY, 40536-0086, USA; Center on Drug and Alcohol Research, University of Kentucky College of Medicine, 845 Angliana Ave, Lexington, KY, 40508, USA
| | - Joshua A Lile
- Department of Behavioral Science, University of Kentucky College of Medicine, 1100 Veterans Drive, Medical Behavioral Science Building, Lexington, KY, 40536-0086, USA; Department of Psychiatry, University of Kentucky College of Medicine, 245 Fountain Court, Lexington, KY, 40509-1810, USA; Department of Psychology, University of Kentucky College of Arts and Sciences, 171 Funkhouser Drive, Lexington, KY, 40506-0044, USA
| | - Joseph L Alcorn
- Department of Behavioral Science, University of Kentucky College of Medicine, 1100 Veterans Drive, Medical Behavioral Science Building, Lexington, KY, 40536-0086, USA
| | - B Levi Bolin
- Department of Behavioral Science, University of Kentucky College of Medicine, 1100 Veterans Drive, Medical Behavioral Science Building, Lexington, KY, 40536-0086, USA
| | - Anna R Reynolds
- Department of Behavioral Science, University of Kentucky College of Medicine, 1100 Veterans Drive, Medical Behavioral Science Building, Lexington, KY, 40536-0086, USA
| | - Lon R Hays
- Department of Psychiatry, University of Kentucky College of Medicine, 245 Fountain Court, Lexington, KY, 40509-1810, USA
| | - Abner O Rayapati
- Department of Psychiatry, University of Kentucky College of Medicine, 245 Fountain Court, Lexington, KY, 40509-1810, USA
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Quinlan MA, Krout D, Katamish RM, Robson MJ, Nettesheim C, Gresch PJ, Mash DC, Keith Henry L, Blakely RD. Human Serotonin Transporter Coding Variation Establishes Conformational Bias with Functional Consequences. ACS Chem Neurosci 2019; 10:3249-3260. [PMID: 30668912 PMCID: PMC6640095 DOI: 10.1021/acschemneuro.8b00689] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The antidepressant-sensitive serotonin (5-HT) transporter (SERT) dictates rapid, high-affinity clearance of the neurotransmitter in both the brain and periphery. In a study of families with multiple individuals diagnosed with autism spectrum disorder (ASD), we previously identified several, rare, missense coding variants that impart elevated 5-HT transport activity, relative to wild-type SERT, upon heterologous expression as well as in ASD subject lymphoblasts. The most common of these variants, SERT Ala56, located in the transporter's cytosolic N-terminus, has been found to confer in transgenic mice hyperserotonemia, an ASD-associated biochemical trait, an elevated brain 5-HT clearance rate, and ASD-aligned behavioral changes. Hyperfunction of SERT Ala56 has been ascribed to a change in 5-HT KM, though the physical basis of this change has yet to be elucidated. Through assessments of fluorescence resonance energy transfer (FRET) between cytosolic N- and C-termini, sensitivity to methanethiosulfonates, and capacity for N-terminal tryptic digestion, we obtain evidence for mutation-induced conformational changes that support an open-outward 5-HT binding conformation in vitro and in vivo. Aspects of these findings were also evident with another naturally occurring C-terminal SERT coding variant identified in our ASD study, Asn605. We conclude that biased conformations of surface resident transporters that can impact transporter function and regulation are an unappreciated consequence of heritable and disease-associated SERT coding variation.
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Affiliation(s)
- Meagan A. Quinlan
- Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN
- Department of Biomedical Science, Charles E. Schmidt College of Medicine
| | - Danielle Krout
- Department of Biomedical Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks, ND
| | - Rania M. Katamish
- Department of Biomedical Science, Charles E. Schmidt College of Medicine
| | - Matthew J. Robson
- Division of Pharmaceutical Sciences, University of Cincinnati, Cincinnati, OH
| | | | - Paul J. Gresch
- Department of Biomedical Science, Charles E. Schmidt College of Medicine
- Brain Institute, Florida Atlantic University, Jupiter, FL
| | - Deborah C. Mash
- Dr. Kiran Patel College of Allopathic Medicine, Nova Southeastern University, Davie, FL
| | - L. Keith Henry
- Department of Biomedical Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks, ND
| | - Randy D. Blakely
- Department of Biomedical Science, Charles E. Schmidt College of Medicine
- Brain Institute, Florida Atlantic University, Jupiter, FL
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Anthenelli RM, Heffner JL, Blom TJ, Daniel BE, McKenna BS, Wand GS. Sex differences in the ACTH and cortisol response to pharmacological probes are stressor-specific and occur regardless of alcohol dependence history. Psychoneuroendocrinology 2018; 94:72-82. [PMID: 29763783 PMCID: PMC6411284 DOI: 10.1016/j.psyneuen.2018.05.007] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/21/2017] [Revised: 04/05/2018] [Accepted: 05/03/2018] [Indexed: 01/24/2023]
Abstract
Women and men differ in their risk for developing stress-related conditions such as alcohol use and anxiety disorders and there are gender differences in the typical sequence in which these disorders co-occur. However, the neural systems underlying these gender-biased psychopathologies and clinical course modifiers in humans are poorly understood and may involve both central and peripheral mechanisms regulating the limbic-hypothalamic-pituitary-adrenal axis. In the present randomized, double blind, placebo-controlled, triple-dummy crossover study, we juxtaposed a centrally-acting, citalopram (2 mg/unit BMI) neuroendocrine stimulation test with a peripherally-acting, dexamethasone (Dex) (1.5 mg)/corticotropin-releasing factor (CRF) (1 μg/kg) test in euthymic women (N = 38) and men (N = 44) with (54%) and without histories of alcohol dependence to determine whether sex, alcohol dependence or both influenced the adrenocorticotropic hormone (ACTH) and cortisol responses to the pharmacological challenges and to identify the loci of these effects. We found that central serotonergic mechanisms, along with differences in pituitary and adrenal sensitivity, mediated sexually-diergic ACTH and cortisol responses in a stressor-specific manner regardless of a personal history of alcohol dependence. Specifically, women exhibited a greater response to the Dex/CRF test than they did the citalopram test while men exhibited the opposite pattern of results. Women also had more robust ACTH, cortisol and body temperature responses to Dex/CRF than men, and exhibited a shift in their adrenal glands' sensitivity to ACTH as measured by the cortisol/log (ACTH) ratio during that session in contrast to the other test days. Our findings indicate that central serotonergic and peripheral mechanisms both play roles in mediating sexually dimorphic, stressor-specific endocrine responses in humans regardless of alcohol dependence history.
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Affiliation(s)
- Robert M. Anthenelli
- Department of Psychiatry, University of California, San Diego, Health Sciences, La Jolla, CA, United States,Corresponding author at: Pacific Treatment and Research Center, Department of Psychiatry (0603), University of California, San Diego, Health Sciences, 9500 Gilman Drive, La Jolla, CA, 92093-0603 United States. (R.M. Anthenelli)
| | | | - Thomas J. Blom
- Department of Psychiatry and Behavioral Neuroscience, University of Cincinnati College of Medicine, Cincinnati, OH, United States
| | - Belinda E. Daniel
- Department of Psychiatry, University of California, San Diego, Health Sciences, La Jolla, CA, United States
| | - Benjamin S. McKenna
- Department of Psychiatry, University of California, San Diego, Health Sciences, La Jolla, CA, United States
| | - Gary S. Wand
- The Johns Hopkins University School of Medicine, Baltimore, MD, United States
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Investigating interactions between phentermine, dexfenfluramine, and 5-HT2C agonists, on food intake in the rat. Psychopharmacology (Berl) 2015; 232:1973-82. [PMID: 25524140 PMCID: PMC4425807 DOI: 10.1007/s00213-014-3829-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/02/2014] [Accepted: 11/20/2014] [Indexed: 10/26/2022]
Abstract
RATIONALE Synergistic or supra-additive interactions between the anorectics (dex)fenfluramine and phentermine have been reported previously in the rat and in the clinic. Studies with 5-HT2C antagonists and 5-HT2C knockouts have demonstrated dexfenfluramine hypophagia in the rodent to be mediated by actions at the 5-HT2C receptor. Given the recent FDA approval of the selective 5-HT2C agonist lorcaserin (BELVIQ®) for weight management, we investigated the interaction between phentermine and 5-HT2C agonists on food intake. OBJECTIVES This study aims to confirm dexfenfluramine-phentermine (dex-phen) synergy in a rat food intake assay, to extend these findings to other 5-HT2C agonists, and to determine whether pharmacokinetic interactions could explain synergistic findings with particular drug combinations. METHODS Isobolographic analyses were performed in which phentermine was paired with either dexfenfluramine, the 5-HT2C agonist AR630, or the 5-HT2C agonist lorcaserin, and inhibition of food intake measured in the rat. Subsequent studies assessed these same phentermine-drug pair combinations spanning both the full effect range and a range of fixed ratio drug combinations. Satellite groups received single doses of each drug either alone or in combination with phentermine, and free brain concentrations were measured. RESULTS Dex-phen synergy was confirmed in the rat and extended to the 5-HT2C agonist AR630. In contrast, although some synergistic interactions between lorcaserin and phentermine were observed, these combinations were largely additive. Synergistic interactions between phentermine and dexfenfluramine or AR630 were accompanied by combination-induced increases in brain levels of phentermine. CONCLUSIONS Dex-phen synergy in the rat is caused by a pharmacokinetic interaction, resulting in increased central concentrations of phentermine.
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Polyunsaturated fatty acid associations with dopaminergic indices in major depressive disorder. Int J Neuropsychopharmacol 2014; 17:383-91. [PMID: 24300434 PMCID: PMC3956108 DOI: 10.1017/s1461145713001399] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Dopaminergic function is thought to be altered in major depression and, in animal studies, is reduced in omega-3 polyunsaturated fatty acid (PUFA) deficiency states. Therefore we studied PUFAs and resting prolactin, a marker for dopaminergic tone, and cerebrospinal fluid homovanillic acid (HVA), the chief dopamine metabolite. In medication-free adults (n = 23) with DSM-IV major depressive disorder (MDD), we measured plasma phospholipid levels of omega-3 PUFAs docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), the omega-6 PUFA arachidonic acid (AA), and plasma prolactin levels before and after administration of dl-fenfluramine (FEN). In a subset of patients (n = 14), cerebrospinal fluid levels of HVA and the serotonin metabolite, 5-hydroxyindoleacetic acid (5-HIAA), were obtained through lumbar puncture. Baseline prolactin was negatively correlated with omega-3 PUFAs (logDHA, F(1,21) = 20.380, p < 0.001; logEPA, F(1,21) = 10.051, p = 0.005) and positively correlated with logAA:DHA (F(1,21) = 15.263, p = 0.001), a measure of omega-6/omega-3 balance. LogDHA was negatively correlated with CSF HVA (Spearman's ρ = -0.675, p = 0.008) but not 5-HIAA (Spearman's ρ = -0.143, p = 0.626) after controlling for sex and HVA - 5-HIAA correlation. PUFAs did not predict the magnitude of the FEN-stimulated change in prolactin, considered to be a serotonin effect. The robust relationship of omega-3 PUFAs with dopaminergic but not serotonergic indices suggests that omega-6:omega-3 balance may impact depression pathophysiology through effects on the dopaminergic system.
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Couch Y, Martin CJ, Howarth C, Raley J, Khrapitchev AA, Stratford M, Sharp T, Sibson NR, Anthony DC. Systemic inflammation alters central 5-HT function as determined by pharmacological MRI. Neuroimage 2013; 75:177-186. [PMID: 23473937 PMCID: PMC4004801 DOI: 10.1016/j.neuroimage.2013.02.046] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2012] [Revised: 02/18/2013] [Accepted: 02/20/2013] [Indexed: 02/02/2023] Open
Abstract
Considerable evidence indicates a link between systemic inflammation and central 5-HT function. This study used pharmacological magnetic resonance imaging (phMRI) to study the effects of systemic inflammatory events on central 5-HT function. Changes in blood oxygenation level dependent (BOLD) contrast were detected in selected brain regions of anaesthetised rats in response to intravenous administration of the 5-HT-releasing agent, fenfluramine (10 mg/kg). Further groups of rats were pre-treated with the bacterial lipopolysaccharide (LPS; 0.5 mg/kg), to induce systemic inflammation, or the selective 5-HT2A receptor antagonist MDL100907 prior to fenfluramine. The resultant phMRI data were investigated further through measurements of cortical 5-HT release (microdialysis), and vascular responsivity, as well as a more thorough investigation of the role of the 5-HT2A receptor in sickness behaviour. Fenfluramine evoked a positive BOLD response in the motor cortex (+15.9±2%) and a negative BOLD response in the dorsal raphe nucleus (-9.9±4.2%) and nucleus accumbens (-7.7±5.3%). In all regions, BOLD responses to fenfluramine were significantly attenuated by pre-treatment with LPS (p<0.0001), but neurovascular coupling remained intact, and fenfluramine-evoked 5-HT release was not affected. However, increased expression of the 5-HT2A receptor mRNA and decreased 5-HT2A-dependent behaviour (wet-dog shakes) was a feature of the LPS treatment and may underpin the altered phMRI signal. MDL100907 (0.5 mg/kg), 5-HT2A antagonist, significantly reduced the BOLD responses to fenfluramine in all three regions (p<0.0001) in a similar manner to LPS. Together these results suggest that systemic inflammation decreases brain 5-HT activity as assessed by phMRI. However, these effects do not appear to be mediated by changes in 5-HT release, but are associated with changes in 5-HT2A-receptor-mediated downstream signalling pathways.
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Affiliation(s)
- Yvonne Couch
- Department of Pharmacology, University of Oxford, Mansfield Rd, Oxford, OX1 3QT, UK; CR-UK/MRC Gray Institute for Radiation Oncology and Biology, Department of Oncology, University of Oxford, Churchill Hospital, Oxford, OX3 7LJ, UK
| | - Chris J Martin
- CR-UK/MRC Gray Institute for Radiation Oncology and Biology, Department of Oncology, University of Oxford, Churchill Hospital, Oxford, OX3 7LJ, UK
| | - Clare Howarth
- CR-UK/MRC Gray Institute for Radiation Oncology and Biology, Department of Oncology, University of Oxford, Churchill Hospital, Oxford, OX3 7LJ, UK
| | - Josie Raley
- CR-UK/MRC Gray Institute for Radiation Oncology and Biology, Department of Oncology, University of Oxford, Churchill Hospital, Oxford, OX3 7LJ, UK
| | - Alexandre A Khrapitchev
- CR-UK/MRC Gray Institute for Radiation Oncology and Biology, Department of Oncology, University of Oxford, Churchill Hospital, Oxford, OX3 7LJ, UK
| | - Michael Stratford
- CR-UK/MRC Gray Institute for Radiation Oncology and Biology, Department of Oncology, University of Oxford, Churchill Hospital, Oxford, OX3 7LJ, UK
| | - Trevor Sharp
- Department of Pharmacology, University of Oxford, Mansfield Rd, Oxford, OX1 3QT, UK
| | - Nicola R Sibson
- CR-UK/MRC Gray Institute for Radiation Oncology and Biology, Department of Oncology, University of Oxford, Churchill Hospital, Oxford, OX3 7LJ, UK.
| | - Daniel C Anthony
- Department of Pharmacology, University of Oxford, Mansfield Rd, Oxford, OX1 3QT, UK
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Arrant AE, Jemal H, Kuhn CM. Adolescent male rats are less sensitive than adults to the anxiogenic and serotonin-releasing effects of fenfluramine. Neuropharmacology 2012; 65:213-22. [PMID: 23103347 DOI: 10.1016/j.neuropharm.2012.10.010] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2012] [Revised: 10/14/2012] [Accepted: 10/18/2012] [Indexed: 11/30/2022]
Abstract
Risk taking behavior increases during adolescence, which is also a critical period for the onset of drug abuse. The central serotonergic system matures during the adolescent period, and its immaturity during early adolescence may contribute to adolescent risk taking, as deficits in central serotonergic function have been associated with impulsivity, aggression, and risk taking. We investigated serotonergic modulation of behavior and presynaptic serotonergic function in adult (67-74 days old) and adolescent (28-34 days old) male rats. Fenfluramine (2 mg/kg, i.p.) produced greater anxiogenic effects in adult rats in both the light/dark and elevated plus maze tests for anxiety-like behavior, and stimulated greater increases in extracellular serotonin in the adult medial prefrontal cortex (mPFC) (1, 2.5, and 10 mg/kg, i.p.). Local infusion of 100 mM potassium chloride into the mPFC also stimulated greater serotonin efflux in adult rats. Adult rats had higher tissue serotonin content than adolescents in the prefrontal cortex, amygdala, and hippocampus, but the rate of serotonin synthesis was similar between age groups. Serotonin transporter (SERT) immunoreactivity and SERT radioligand binding were comparable between age groups in all three brain regions. These data suggest that lower tissue serotonin stores in adolescents limit fenfluramine-stimulated serotonin release and so contribute to the lesser anxiogenic effects of fenfluramine.
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Affiliation(s)
- Andrew E Arrant
- Department of Pharmacology & Cancer Biology, Duke University, Room 100B Research Park Building 2, Box 3813, Duke University Medical Center, Durham, NC 27710, USA
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Wellman P. Effects of acute administration of phentermine, alone or in combination with dexfenfluramine, on pain reactivity in the adult rat. Pharmacol Biochem Behav 2008; 90:339-43. [DOI: 10.1016/j.pbb.2008.03.009] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/05/2007] [Revised: 02/19/2008] [Accepted: 03/14/2008] [Indexed: 11/26/2022]
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Coşkun S, Gönül B, Ozer C, Erdoğan D, Elmas C. The effects of dexfenfluramine administration on brain serotonin immunoreactivity and lipid peroxidation in mice. Cell Biol Toxicol 2006; 23:75-82. [PMID: 17009098 DOI: 10.1007/s10565-006-0107-z] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2006] [Accepted: 07/27/2006] [Indexed: 11/30/2022]
Abstract
Obesity continues to be an increasing health problem in worldwide and antiobesity drugs have commonly been used by obese patients. During the use of anorectic drugs, the antioxidant defense may be affected, especially by reactive oxygen species. It was decided to investigate the effects of dexfenfluramine on body weight, daily food intake, brain thiobarbituric acid-reactive substances (TBARS), glutathione (GSH) and nitric oxide (NO) levels, and 5-HT immunoreactivity. Mice were divided into two groups each containing 8 Swiss Albino adult (6 months) mice. Group 1, untreated, was used as a control; group 2 was treated with dexfenfluramine 0.4 mg/kg per day intraperitoneally for 7 days. Brain TBARS and GSH levels were assayed spectrophotometrically. The stable end-products of NO, nitrite and nitrate, were analyzed spectrophotometrically. Brain tissue 5-HT immunoreactivity was observed using an immunohistochemical method. There were significant decreases in body weight in the dexfenfluramine group (p < 0.05). Although brain GSH and NO(x) levels decreased significantly, brain TBARS levels increased in the dexfenfluramine group (p < 0.05). Brain 5-HT immunoreactivity also increased in the dexfenfluramine-treated group compared to control. In conclusion, our findings show that dexfenfluramine is effective in achieving weight loss and also increases lipid peroxidation in mouse brain.
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Affiliation(s)
- S Coşkun
- Department of Biology, Faculty of Arts and Science, Gazi University, Ankara, Turkey.
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Fletcher PJ, Sinyard J, Higgins GA. The effects of the 5-HT(2C) receptor antagonist SB242084 on locomotor activity induced by selective, or mixed, indirect serotonergic and dopaminergic agonists. Psychopharmacology (Berl) 2006; 187:515-25. [PMID: 16832658 DOI: 10.1007/s00213-006-0453-9] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/10/2006] [Accepted: 05/20/2006] [Indexed: 11/26/2022]
Abstract
RATIONALE The 5-HT(2C) receptor modulates mesolimbic dopamine (DA) function and the expression of DA-dependent behaviors, including stimulant-induced hyperactivity. The 5-HT(2C) receptor may also be involved in drug-induced locomotion that is 5-HT-dependent. OBJECTIVES This study investigated the effects of the 5-HT(2C) receptor antagonist 6-chloro-5-methyl-1-[[2-[(2-methyl-3-pyridyl)oxy]-5-pyridyl]carbamoyl]-indoline (SB242084) on hyperlocomotion induced by psychomotor stimulants with selective, or mixed, actions on serotonergic and/or dopaminergic systems. MATERIALS AND METHODS Male Sprague-Dawley rats were treated in the presence or absence of SB242084 with releasers/reuptake inhibitors of DA (amphetamine and methylphenidate), 5-HT (fenfluramine and citalopram), or both 5-HT and DA (MDMA and cocaine). In addition, the effects of SB242084 combined with nicotine, morphine, or the 5-HT(1A/1B) receptor agonist RU24969 were examined. Locomotor activity was recorded for 2 h. RESULTS SB242084 potentiated hyperactivity induced by MDMA (2.5-5 mg/kg), amphetamine (0.5 mg/kg), fenfluramine (5 mg/kg), cocaine (10 mg/kg), and methylphenidate (5 mg/kg). SB242084 modestly potentiated nicotine-induced (0.2-0.4 mg/kg) and morphine-induced (2.5 mg/kg) hyperactivity. SB242084 failed to influence hyperactivity induced by RU24969 (0.5-1 mg/kg) or citalopram (10-20mg/kg). CONCLUSION SB242084 potentiated the locomotor stimulant effects of both indirect DA and 5-HT agonists. This potentiation may reflect two distinct mechanisms. The first involves direct enhancement of DA activity as shown by potentiation of the effects of amphetamine and methylphenidate. The second mechanism reflects an unmasking of stimulatory 5-HT receptors activated by 5-HT releasers (possibly 5-HT(1B/2A)) through blockade of inhibitory 5-HT(2C) receptors. The failure of SB242084 to potentiate the effect of citalopram might reflect differences between changes in synaptic levels of 5-HT produced by release compared to reuptake inhibition.
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Affiliation(s)
- Paul J Fletcher
- Section of Biopsychology, Centre for Addiction and Mental Health, Toronto, ON, Canada.
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Bishop C, Taylor JL, Kuhn DM, Eskow KL, Park JY, Walker PD. MDMA and fenfluramine reduce L-DOPA-induced dyskinesia via indirect 5-HT1A receptor stimulation. Eur J Neurosci 2006; 23:2669-76. [PMID: 16817869 DOI: 10.1111/j.1460-9568.2006.04790.x] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Chronic L-3,4-dihydroxyphenylalanine (L-DOPA) pharmacotherapy in Parkinson's disease is often accompanied by the development of abnormal and excessive movements known as dyskinesia. Clinical and experimental studies indicate that indirect serotonin agonists can suppress dyskinesia without affecting the efficacy of L-DOPA. While the mechanism by which these effects occur is not clear, recent research suggests that serotonin 5-HT1A receptors may play a pivotal role. To test this, male Sprague-Dawley rats with unilateral 6-hydroxydopamine medial forebrain bundle lesions received 1 week of daily treatment with L-DOPA (12 mg/kg, i.p.) plus benserazide (15 mg/kg, i.p.). Beginning on the 8th day of treatment and every 3rd or 4th day thereafter, rats were pretreated with vehicle (0.9% NaCl), the serotonin and dopamine releaser 3,4-methylenedioxymethamphetamine (MDMA; 0.25 or 2.5 mg/kg, i.p.) or the serotonin releaser fenfluramine (FEN; 0.25 or 2.5 mg/kg, i.p.) 5 min prior to L-DOPA, after which abnormal involuntary movements (AIMs) and rotations were quantified every 20th minute for 2 h. Pretreatment with 2.5 mg/kg of either MDMA or FEN reduced AIMs. To determine the contribution of the 5-HT1A receptor to these effects, another group of L-DOPA-primed 6-hydroxydopamine-lesioned rats were pretreated with the 5-HT1A antagonist WAY100635 (0.5 mg/kg, i.p.), MDMA + WAY100635 (2.5 + 0.5 mg/kg, i.p.) or FEN + WAY100635 (2.5 + 0.5 mg/kg, i.p.) 5 min prior to L-DOPA and subsequent AIMs and rotation tests. The antidyskinetic effects of MDMA and FEN were reversed by cotreatment with WAY100635. These results suggest that 5-HT-augmenting compounds such as MDMA and FEN probably convey antidyskinetic properties in part via stimulation of 5-HT1A receptors.
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Affiliation(s)
- Christopher Bishop
- Behavioural Neuroscience Program, Department of Psychology, State University of New York at Binghamton, 4400 Vestal Parkway East, Binghamton, NY 13902-6000, USA.
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Ozer C, Gönül B, Elmas C, Erdoüan D, Ercan ZS. Effects of dexfenfluramine on serotonin levels of mice ileum, contractility, glutathione and malondialdehyde level. Mol Cell Biochem 2005; 280:151-7. [PMID: 16311917 DOI: 10.1007/s11010-005-8842-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2005] [Accepted: 06/16/2005] [Indexed: 11/30/2022]
Abstract
UNLABELLED Dexfenfluramine is one of the anorectic drugs that suppresses food intake which acts via inhibition of reuptake of serotonin into brain terminal. Gastrointestinal tract is the main source of peripheral serotonin which is involved in the regulation of gastrointestinal motility. During the use of anorectic drugs, the antioxidant defence is affected especially by reactive oxygen species. The purpose of this study to search: The effect of dexfenfluramine on serotonin levels of ileum and the effect of dexfenfluramine on ileal contractility and oxidative stress. MATERIALS AND METHODS Twenty-two adult male Swiss-albino mice were divided two groups (1) Control, (2) Dexfenfluramine treated (i.p. twice a day 0.2 mg kg(-1) in 0.2 ml saline solution for 7 days). Animal body weights were recorded at the beginning and at the end of the experimental period. Ileum tissues contractile responses to different concentrations of KCl and acethycholine were recorded on polygraph. In the meantime ileal tissue malondialdehyde, a product of lipid peroxidation, and glutathione, endogenous antioxidant levels were assessed by spectrophotometric methods. Ileal tissue serotonin level determined by immunohistochemical method. Body weights decrease and ileal contractile response of acethycholine increased significantly by dexfenfluramine treatment. Meanwhile, ileum glutathione levels decreased and malondialdehyde levels increased in dexfenfluramine treated group. Immunohistochemical detection showed that ileal serotonin levels increased by dexfenfluramine treatments. As a conclusion, there is a relationship between increased ileal contractility and oxidant status in dexfenfluramine treated animals. These effects can be related by increased serotonin levels which is induced by dexfenfluramine in ileum.
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Affiliation(s)
- Ciüdem Ozer
- Faculty of Medicine, Department of Physiology, University of Gazi, Ankara, Turkey.
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15
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Abstract
Most psychostimulants interact with monoamine transport proteins. This paper reviews work our laboratory has conducted to investigate the interaction of psychostimulants with monoamine transporters in order to advance our understanding of how these drugs affect the brain. We review two topics: (1) characterization of multiple binding sites for cocaine-like drugs and (2) an examination of the mechanisms of action of amphetamine-type anorectic agents. We conclude that the brain contains high abundance nonclassical binding sites for cocaine-like drugs that have micromolar affinity for cocaine and that none of the clinically available amphetamine-type appetite suppressants are equipotent substrates for dopamine transporter (DAT) and serotonin transporter (SERT) proteins. Future medications discovery efforts should focus on identifying new compounds which possess the equipotent substrate activity at DAT and SERT, but which lack the adverse effects of stimulants developed decades ago.
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Affiliation(s)
- Richard B Rothman
- Clinical Psychopharmacology Section, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, 5500 Nathan Shock Drive, PO Box 5180, Baltimore, MD 21224, USA.
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16
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Kaddoumi A, Nakashima MN, Maki T, Matsumura Y, Nakamura J, Nakashima K. Liquid chromatography studies on the pharmacokinetics of phentermine and fenfluramine in brain and blood microdialysates after intraperitoneal administration to rats. J Chromatogr B Analyt Technol Biomed Life Sci 2003; 791:291-303. [PMID: 12798189 DOI: 10.1016/s1570-0232(03)00231-9] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A highly sensitive and simple HPLC method with fluorescence detection for the determination of phentermine (Phen), fenfluramine (Fen) and norfenfluramine (Norf, the active metabolite of Fen) in rat brain and blood microdialysates has been developed. The brain and blood microdialysates were directly subjected to derivatization with 4-(4,5-diphenyl-1H-imidazol-2-yl) benzoyl chloride (DIB-Cl) in the presence of carbonate buffer (0.1 M, pH 9.0) at room temperature. The chromatographic conditions consisted of an ODS column and mobile phase composition of acetonitrile and water (65:35, v/v) with flow rate set at 1.0 ml/min. The detection was performed at excitation and emission wavelengths of 325 and 430 nm, respectively. Under these conditions, the DIB-derivatives of Phen, Fen and Norf were well separated and showed good linearities in the studied ranges (5-2000 nM for Phen and 10-2000 nM for Norf and Fen) with correlation coefficients greater than 0.999. The obtained detection limits were less than 23 fmol on column (for the three compounds) in both brain and blood microdialysates at a signal-to-noise ratio of 3 (S/N=3). The intra- and the inter-assay precisions were lower than 10%. The method coupled with microdialysis was applied for a pharmacokinetic drug-drug interaction study of Phen and Fen following individual and combined intraperitoneal administration to rats. In addition, since the role of protein binding in drug interactions can be quite involved, the method was applied for the determination of total and free Phen and Fen in rat plasma and ultrafiltrate, respectively. The results showed that Fen and/or Norf significantly altered the pharmacokinetic parameters of Phen in both blood and brain but did not alter its protein binding. On the other hand, there was no significant difference in the pharmacokinetics of Fen when administered with Phen.
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Affiliation(s)
- Amal Kaddoumi
- Course of Pharmaceutical Sciences, Department of Clinical Pharmacy, Graduate School of Biomedical Sciences, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki 852-8521, Japan
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17
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Wellman PJ, Jones SL, Miller DK. Effects of preexposure to dexfenfluramine, phentermine, dexfenfluramine-phentermine, or fluoxetine on sibutramine-induced hypophagia in the adult rat. Pharmacol Biochem Behav 2003; 75:103-14. [PMID: 12759118 DOI: 10.1016/s0091-3057(03)00045-5] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The antiobesity drug sibutramine suppresses food intake via inhibition of reuptake of both norepinephrine (NE) and serotonin (5-HT) into brain terminals. The present study examined whether preexposure to other antiobesity drugs (fluoxetine [FLUOX], phentermine [PHEN], and dexfenfluramine [DEX]) that alter noradrenergic and/or serotonergic activity in brain induces tolerance or sensitization to the subsequent hypophagic action of sibutramine. Accordingly, adult male rats were treated (administered orally once per day for 21 days) with DEX (0, 1, or 3 mg/kg) and/or PHEN (0, 5, or 10 mg/kg), alone and in combination, or with the selective 5-HT reuptake inhibitor FLUOX (0, 15, or 30 mg/kg). Daily administration of PHEN persistently reduced food intake and body weight whereas tolerance developed to the hypophagic action of DEX or of FLUOX within the first week of daily administration. Moreover, low doses of DEX (1 mg/kg) and PHEN (5 mg/kg) interacted in a supra-additive manner to inhibit food intake and water intake and decrease body weight over the 21-day exposure period. After a recovery period of 9 days, a series of food intake trials were conducted to assess the hypophagic action of sibutramine (0, 1, 3, and 9 mg/kg po). Preexposure to PHEN (5 or 10 mg/kg), DEX (3 mg/kg), or FLUOX (30 mg/kg) resulted in a significant attenuation of the hypophagia induced by sibutramine over an 8-h, but not a 2-h, testing period. The pattern of cross-tolerance noted in this study is consistent with the observation that sibutramine inhibits eating via an interaction with noradrenergic and serotonergic mechanisms. Whether PHEN and DEX preexposure in humans alters subsequent sibutramine effectiveness is unknown.
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Affiliation(s)
- P J Wellman
- Department of Psychology, Texas A&M University, College Station, TX 77843-4235, USA.
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Morford LL, Inman-Wood SL, Gudelsky GA, Williams MT, Vorhees CV. Impaired spatial and sequential learning in rats treated neonatally with D-fenfluramine. Eur J Neurosci 2002; 16:491-500. [PMID: 12193193 DOI: 10.1046/j.1460-9568.2002.02100.x] [Citation(s) in RCA: 96] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
D-Fenfluramine, a serotonin releaser, was administered to neonatal rats on postnatal days 11-20 (a stage of hippocampal development analogous to third trimester human ontogeny). As adults, the D-fenfluramine-treated offspring exhibited dose-related impairments of sequential and spatial learning and reference memory in the absence of sensorimotor impairments. Procedures to minimize stress and to control for other performance effects prior to testing for spatial learning demonstrated that nonspecific factors did not account for the selective effects of D-fenfluramine on learning and memory. Developmental D-fenfluramine-induced spatial and sequential learning deficits are similar to previous findings with developmental MDMA treatment. By contrast, recent findings with developmental D-methamphetamine treatment showed spatial learning deficits while sparing sequential learning. The spatial learning effects common to all three drugs suggest that they may share a common mechanism of action, however, the effects are not related to long-lasting changes in hippocampal 5-HT levels as no differences were found in adulthood. Whether the cognitive deficits are related to the effects of substituted amphetamines on corticosteroids, other aspects of the 5-HT system, or some unidentified neuronal substrates is not known, but the data demonstrate that these drugs are all capable of inducing long-term adverse effects on learning.
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Affiliation(s)
- L L Morford
- Division of Developmental Biology, Children's Hospital Research Foundation and University of Cincinnati College of Medicine, Cincinnati, OH 45229-3039, USA
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Tao R, Fray A, Aspley S, Brammer R, Heal D, Auerbach S. Effects on serotonin in rat hypothalamus of D-fenfluramine, aminorex, phentermine and fluoxetine. Eur J Pharmacol 2002; 445:69-81. [PMID: 12065196 DOI: 10.1016/s0014-2999(02)01751-x] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Hypothalamic 5-HT (serotonin) regulates food intake, energy expenditure and bodyweight. Using in vivo microdialysis, we determined the effects of various anorectic drugs on hypothalamic extracellular 5-HT levels during the dark phase when rats predominantly feed. Phentermine and aminorex, which were originally considered to be catecholaminergic drugs, markedly increased 5-HT efflux in rat hypothalamus. Their actions were less profound than D-fenfluramine, but considerably greater than that of the selective 5-HT reuptake inhibitor, fluoxetine. This suggests that enhanced hypothalamic 5-HT function could be involved in their anorectic actions. Pharmacological characterization revealed that D-fenfluramine, aminorex and probably also phentermine potentiate synaptic 5-HT function predominantly by release, whereas fluoxetine acts exclusively by reuptake inhibition. The results also revealed that the combined actions of phentermine and D-fenfluramine on hypothalamic extracellular 5-HT levels were additive, but not synergistic. In contrast, there was a significant negative cooperative effect on extraneuronal 5-HT of combining phentermine with fluoxetine.
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Affiliation(s)
- Rui Tao
- Nelson Laboratories, Department of Cell Biology and Neuroscience, Rutgers University, 604 Allison Road, Piscataway, NJ 08854-8082, USA
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20
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Rothman RB, Blough BE, Baumann MH. Appetite suppressants as agonist substitution therapies for stimulant dependence. Ann N Y Acad Sci 2002; 965:109-26. [PMID: 12105089 DOI: 10.1111/j.1749-6632.2002.tb04155.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Several lines of evidence support a dual-deficit model of stimulant withdrawal in which decreases in synaptic dopamine (DA) and serotonin (5-HT) contribute to withdrawal symptoms, drug craving, and relapse. According to the dual-deficit model, DA dysfunction during withdrawal underlies anhedonia and psychomotor disturbances, whereas 5-HT dysfunction gives rise to depressed mood, obsessive thoughts, and lack of impulse control. The model suggests that medications capable of normalizing stimulant-induced DA and 5-HT deficits should be effective treatment adjuncts. Furthermore, the model may explain why medications targeting only one neurotransmitter system (i.e., DA) have failed to treat cocaine dependence. Amphetamine-type appetite suppressants are logical choices for neurochemical normalization therapy of stimulant dependence, yet few clinical studies have tested anorectics in this regard. The chief purpose of the present work is to profile the activity of various anorectic agents at DA, 5-HT, and NE transporters, in order to identify possible medications for stimulant dependence. Compounds were tested in vitro for their ability to stimulate release and inhibit uptake of [(3)H]DA, [(3)H]NE, and [(3)H]5-HT. Selected compounds were tested in vivo for their ability to elevate extracellular levels of DA and 5-HT in rat nucleus accumbens. The results show that clinically available appetite suppressants display a wide range of activities at monoamine transporters. However, no single medication possesses equal potency at DA and 5-HT transporters, suggesting that none of the anorectics is ideally suited for treatment of stimulant addictions. Future efforts should focus on developing new medications that possess the desired therapeutic activity but lack the adverse effects associated with older amphetamine-type anorectics.
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Affiliation(s)
- Richard B Rothman
- Clinical Psychopharmacology Section, NIDA, NIH, Baltimore, Maryland 21224, USA.
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21
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Choi S, Jonak EM, Simpson L, Patil V, Fernstrom JD. Intermittent, chronic fenfluramine administration to rats repeatedly suppresses food intake despite substantial brain serotonin reductions. Brain Res 2002; 928:30-9. [PMID: 11844469 DOI: 10.1016/s0006-8993(01)03330-3] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The mechanisms by which fenfluramine suppresses food intake and body weight have been linked to its ability to enhance transmission across serotonin synapses in brain. This drug initially lowers body weight and suppresses food intake, yet after repeated administration food intake soon returns to normal and body weight no longer decreases. Fenfluramine also causes rapid and prolonged reductions in brain serotonin concentrations, which might account for its loss of appetite suppression. This possibility has been evaluated in rats by assessing if intermittent, chronic fenfluramine administration could suppress food intake during each treatment period, and if so, whether such an effect occurs in the presence of reduced brain serotonin levels. Rats were injected once daily with 10 mg/kg D,L-fenfluramine for 5 days, and then received no injections for the next 5 days. Control rats received only vehicle injections. This 10-day sequence was repeated five more times. During each period of fenfluramine administration, daily food intake dropped markedly the first 1-2 days of treatment, but returned to pretreatment values by day 5. Daily food intake was normal or slightly above normal during non-injection periods. Body weight dropped modestly during each period of fenfluramine administration, and rose during each subsequent period when injections had ceased. Serotonin concentrations and synthesis rates in several brain regions were markedly reduced at early, middle, and late periods of the experiment. Despite the long-term reduction in brain serotonin pools produced by fenfluramine, the drug continues to reduce food intake and body weight. Several possible interpretations of these findings are considered, based on the multiple mechanisms through which this drug has been proposed to modify synaptic serotonin transmission.
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Affiliation(s)
- SuJean Choi
- Department of Psychiatry, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA.
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22
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Glatz AC, Ehrlich M, Bae RS, Clarke MJ, Quinlan PA, Brown EC, Rada P, Hoebel BG. Inhibition of cocaine self-administration by fluoxetine or D-fenfluramine combined with phentermine. Pharmacol Biochem Behav 2002; 71:197-204. [PMID: 11812523 DOI: 10.1016/s0091-3057(01)00657-8] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Instrumental responding for intravenous cocaine in rats at 85% of free-feeding weight was significantly decreased 50% by D-fenfluramine plus phentermine (D-Fen/Phen, 5 mg/kg of each for 1 day). A similar effect was obtained in normal-weight rats self-administering a cocaine-heroin mixture. Treating normal-weight animals with fluoxetine (5 mg/kg) for 4 days also significantly decreased cocaine self-administration by half, and then adding phentermine caused an additional decrease in cocaine intake. Animals that were well trained to self-administer drug did not self-administer intravenous D-Fen/Phen or Flu/Phen. The present results confirm that serotonergic drugs can decrease cocaine, or cocaine/heroin, self-administration in rats, and that phentermine adds to the effect. Based on related research with the same dose of D-Fen/Phen, it is suggested that effectiveness in reducing cocaine reinforcement is due in part to a satiating effect in which dopamine and acetylcholine are released in the nucleus accumbens.
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Affiliation(s)
- Andrew C Glatz
- Department of Psychology, Princeton University, Princeton, NJ 08544, USA
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Prow MR, Lancashire B, Aspley S, Heal DJ, Kilpatrick IC. Additive effects on rat brain 5HT release of combining phentermine with dexfenfluramine. Int J Obes (Lond) 2001; 25:1450-3. [PMID: 11673764 DOI: 10.1038/sj.ijo.0801717] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/14/2000] [Revised: 02/13/2001] [Accepted: 02/19/2001] [Indexed: 11/08/2022]
Abstract
OBJECTIVE AND DESIGN This study examined the effects of the anti-obesity agents, phentermine and dexfenfluramine given alone or in combination, on in vitro and in vivo 5HT release from rat brain tissue. RESULTS In vitro, phentermine was without effect on basal [3H]5HT efflux from hypothalamic slices whereas dexfenfluramine (10 microM) evoked a 131% increase in [3H]5HT release. In combination, the two drugs did not alter [3H]5HT release beyond that caused by dexfenfluramine alone. At pharmacologically equivalent doses, phentermine (5.7 mg/kg, i.p.) caused a rapid, modest elevation, and dexfenfluramine (3 mg/kg, i.p.) a larger but equally rapid elevation of extracellular 5HT in the microdialysates from the rat anterior hypothalamus. In combination, the increase in extracellular 5HT evoked by these drugs was not significantly greater than the sum of their individual effects. CONCLUSIONS This study provides evidence that phentermine's actions are not restricted to catecholamine systems and indicates that combining phentermine with dexfenfluramine results in an additive increase in neuronal 5HT release.
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Affiliation(s)
- M R Prow
- Knoll Limited, Research and Development, Nottingham, UK
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Abstract
The association between valvular heart disease and diet pills was discovered several years ago in a small cohort of patients. Subsequent uncontrolled surveys and reports suggested a prevalence of cardiac abnormalities as high as 30%. These results led to widespread concern by millions of appetite suppressant users and the withdrawal of both fenfluramine and dexfenfluramine from the market. Through this review of the literature, it becomes apparent that we have better defined the association between valvular heart disease and appetite suppressants; nonetheless, many questions and controversies remain. Most large scale, multicenter, controlled studies have shown that a prevalence of significant valve regurgitation is between 2 and 12% and that the likelihood of disease increases with increasing dose and/or duration of appetite suppressant use, but several other issues, such as the mechanism of action, remain unanswered.
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Affiliation(s)
- N J Weissman
- Cardiovascular Research Institute, Washington Hospital Center, DC 20010, USA.
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Spencer DC, Hwang J, Morrell MJ. Fenfluramine-Phentermine (Fen-Phen) and Seizures: Evidence for an Association. Epilepsy Behav 2000; 1:448-452. [PMID: 12737835 DOI: 10.1006/ebeh.2000.0132] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Fenfluramine-phentermine combination therapy ("fen-phen") became a popular treatment for obesity in the 1990s. Although this treatment causes cardiac toxicity, use of these medications has not previously been associated with seizures. We report five cases with apparent association between use of fenfluramine-phentermine and occurrence of seizures. Three patients with a history of childhood-onset idiopathic generalized epilepsy in remission experienced a recrudescence of seizures following treatment with fenfluramine-phentermine. Two patients presented with new-onset seizures in midlife following use of fenfluramine-phentermine, and seizures persisted following discontinuation of this therapy. One of these patients restarted fenfluramine-phentermine months later, and experienced recurrent seizures. The nature of the association between fenfluramine-phentermine and seizures is uncertain from this preliminary report. There may be a specific association with idiopathic generalized epilepsies, which appeared to be overrepresented in this case series. An effect of fen-phen on seizure threshold appears most likely; however, an epileptogenic effect cannot be excluded.
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Ulus IH, Maher TJ, Wurtman RJ. Characterization of phentermine and related compounds as monoamine oxidase (MAO) inhibitors. Biochem Pharmacol 2000; 59:1611-21. [PMID: 10799660 DOI: 10.1016/s0006-2952(00)00306-3] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Phentermine was shown in the 1970s to inhibit the metabolism of serotonin by monoamine oxidase (MAO), but never was labeled as an MAO inhibitor; hence, it was widely used in combination with fenfluramine, and continues to be used, in violation of their labels, with other serotonin uptake blockers. We examined the effects of phentermine and several other unlabeled MAO inhibitors on MAO activities in rat lung, brain, and liver, and also the interactions of such drugs when administered together. Rat tissues were assayed for MAO-A and -B, using serotonin and beta-phenylethylamine as substrates. Phentermine inhibited serotonin-metabolizing (MAO-A) activity in all three tissues with K(i) values of 85-88 microM. These potencies were similar to those of the antidepressant MAO inhibitors iproniazid and moclobemide. When phentermine was mixed with other unlabeled reversible MAO inhibitors (e.g. pseudoephedrine, ephedrine, norephedrine; estradiol benzoate), the degree of MAO inhibition was additive. The cardiac valvular lesions and primary pulmonary hypertension that have been reported to be associated with fenfluramine-phentermine use may have resulted from the intermittent concurrent blockage of both serotonin uptake and metabolism.
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Affiliation(s)
- I H Ulus
- Department of Pharmacology and Clinical Pharmacology, Uludag University Medical School, Bursa, Turkey
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Rada PV, Hoebel BG. Supraadditive effect of d-fenfluramine plus phentermine on extracellular acetylcholine in the nucleus accumbens: possible mechanism for inhibition of excessive feeding and drug abuse. Pharmacol Biochem Behav 2000; 65:369-73. [PMID: 10683475 DOI: 10.1016/s0091-3057(99)00219-1] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Abstract
The combination of d-fenfluramine plus phentermine (d-FEN/PHEN) provides a tool for exploring neural mechanisms that control food intake and drug abuse. Prior research suggests that dopamine (DA) in the nucleus accumbens can reinforce appetitive behavior and acetylcholine (ACh) inhibits it. When rats were given d-fenfluramine (5 mg/kg, IP) DA increased to 169% (p < 0.01), and ACh decreased slightly. Phentermine (5 mg/kg, IP) increased extracellular DA to 469% of baseline and ACh increased slightly to 124% (both p < 0.01). The d-FEN/PHEN combination, however, increased both DA and ACh with a supraadditive effect on ACh to 172%. One interpretation is that dFEN/PHEN increases DA like a meal or drug of abuse, while also increasing ACh to stop further approach behavior. This leaves the animal "satiated," as defined by reduced intake of food or drugs.
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Affiliation(s)
- P V Rada
- Princeton University, Department of Psychology, Princeton, NJ 08544, USA
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Halladay AK, Fisher H, Wagner GC. Effects of phentermine and fenfluramine on alcohol consumption and alcohol withdrawal seizures in rats. Alcohol 2000; 20:19-29. [PMID: 10680713 DOI: 10.1016/s0741-8329(99)00047-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The drug combination of phentermine plus fenfluramine has been used clinically in both the treatment of obesity and alcoholism. The aim of the current study was to assess the interaction of the two drugs on consumption of both an alcohol-containing and a nonalcoholic diet. Furthermore, the efficacy of the drug combination on suppression of withdrawal seizures was determined. Animals were either maintained on a 6% alcohol-containing diet, free-fed an isocaloric control, or pair-fed the control diet. It was observed that, with regard to body weight growth curves, alcohol provides about 2.5 kcal/g. Both phentermine and fenfluramine caused a decrease in consumption 1 h after administration; however, during the next 23 h, 4 mg/kg phentermine significantly increased consumption of all diets. At doses of 1 and 2 mg/kg, fenfluramine selectively reduced consumption of the alcohol-containing diet as compared to the isocaloric diets. Lower doses of fenfluramine blocked the increases in consumption induced by phentermine. Furthermore, in animals fed the nonalcoholic diet, the drug combination of 2 mg/kg fenfluramine plus 8 mg/kg phentermine produced a 63-82% reduction in consumption, an effect not seen when either drug was administered alone. This greater than additive effect was also seen in the earlier time periods in animals pair-fed the control diet. Neurochemical analysis from these animals revealed that the alcohol-dependent animals displayed a significant reduction of DOPAC and 5-HIAA levels in the striatum, frontal cortex, and hypothalamus after a 9-h withdrawal period, further implicating the serotonergic and dopaminergic systems in mediation of withdrawal symptoms and alcohol craving. Finally, 8 mg/kg phentermine plus 8 mg/kg fenfluramine completely abolished alcohol withdrawal seizures, compared to a 78% rate in saline treated rats. In conclusion, the coadministration of phentermine plus fenfluramine produced a moderate reduction of alcohol consumption and was completely effective at reducing alcohol withdrawal seizures.
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Affiliation(s)
- A K Halladay
- Department of Psychology, Rutgers University, New Brunswick, NJ 08904, USA
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Shively BK, Roldan CA, Gill EA, Najarian T, Loar SB. Prevalence and determinants of valvulopathy in patients treated with dexfenfluramine. Circulation 1999; 100:2161-7. [PMID: 10571975 DOI: 10.1161/01.cir.100.21.2161] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Valve regurgitation has been associated with dexfenfluramine, but its prevalence and severity are uncertain. Additional factors that may contribute to valve regurgitation in patients exposed to this drug are poorly understood. METHODS AND RESULTS Echocardiography was performed on subjects recruited from 26 prescribing sites in 15 states. The total sample of 412 subjects included 172 dexfenfluramine patients and 172 unexposed controls matched for age, sex, and body mass index and 68 unmatched subjects meeting the same entry criteria (51 dexfenfluramine patients and 17 controls). Mean treatment duration was 6.9 months; mean interval from treatment discontinuation to echocardiogram was 8.5 months. Each echocardiogram was interpreted independently by 3 echocardiographers. FDA-grade regurgitation (at least mild aortic regurgitation or at least moderate mitral regurgitation) was significantly more frequent in dexfenfluramine patients (7.6% versus 2.1% for controls; P=0.01; odds ratio, 3.82). This difference was primarily due to more frequent mild aortic regurgitation in dexfenfluramine patients (6.3% versus 1.6% in controls; P<0.02; odds ratio, 4.15). No differences were found in sclerosis or mobility for either the aortic or mitral valve. Factors independently related to FDA-grade regurgitation or any grade of aortic regurgitation were older age, higher diastolic blood pressure at the time of echocardiography, and shorter time from drug discontinuation to echocardiogram. CONCLUSIONS Dexfenfluramine use is associated with an increase in the prevalence of abnormal valve regurgitation. Age and blood pressure may also affect the prevalence of regurgitation. Dexfenfluramine-related valve regurgitation may regress after drug discontinuation.
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Affiliation(s)
- B K Shively
- Cardiology Divisions of Oregon Health Sciences University, Portland, OR, USA.
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Abstract
Phentermine produces a spectrum of concentration-dependent biochemical effects. It interacts with NE transporters at 0.1 microM, DA transporters at about 1 microM, 5-HT transporters at 15 microM and MAO-A at about 100 microM. When administered at typical anorectic doses, phentermine primarily interacts with DA and NE transporters and does not produce biochemical or neurochemical effects which would occur if it were inhibiting MAO-A. Some other explanation other than MAO inhibition must be sought to explain how oral phentermine increases platelet 5-HT, since platelet MAO-B does not metabolize platelet 5-HT, and since amphetamine-type drugs are even weaker inhibitors of MAO-B than MAO-A. Clinical studies in humans have shown that amphetamine, which is a more potent inhibitor of MAO-A than phentermine, does not inhibit MAO-A at therapeutic doses. Neither phentermine alone, fluoxetine alone or their combined use have been associated with cardiac valvulopathy, and clinical experience has shown their combined use to be free of significant adverse effects. Viewed collectively, there appears to be no data to support the hypothesis that phentermine inhibits MAO at typical therapeutic doses.
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