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Effects of tryptophan depletion on anxiety, a systematic review. Transl Psychiatry 2021; 11:118. [PMID: 33574223 PMCID: PMC7878770 DOI: 10.1038/s41398-021-01219-8] [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] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/14/2020] [Revised: 10/30/2020] [Accepted: 11/16/2020] [Indexed: 12/11/2022] Open
Abstract
Vulnerability markers for onset of anxiety disorders are scarce. In depression, patients at risk tend to respond with a negative mood to 'acute tryptophan depletion' (ATD), while healthy volunteers and current patients do not. The serotonergic system thus provides indications for vulnerability for depression. It is unknown whether ATD reveals vulnerability in anxiety too. This study systematically reviews the effects of ATD on anxiety and assesses whether challenging anxiety modifies the response. PubMed, Embase and PsychInfo were systematically searched up to April 2019 for studies in which (1) healthy volunteers or patients with a (remitted) anxiety disorder underwent ATD and (2) levels of anxiety were reported. In total, 21 studies were included. Studies conducted in healthy volunteers (n = 13), and patients with a remitted (n = 6) or current (panic, social or generalised) anxiety disorder (n = 4). Studies were mostly of poor quality and heterogeneous regarding population, challenge test used and outcome measures. ATD did not consistently affect anxiety in any of the groups. Moreover, a challenge test after ATD (n = 17 studies) did not consistently provoke anxiety in healthy volunteers or remitted patients. A 35% CO2 challenge did consistently increase anxiety in patients with a current panic disorder (PD). To conclude, this systematic review found no clear indications that ATD provokes anxiety in those at risk for anxiety disorders. Hence, unlike in depression, ATD does not indicate vulnerability to develop an anxiety disorder. Because included studies were heterogeneous and mostly of poor quality, there is an urgent need for high quality research in homogeneous samples.
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Kim YK, Jeon SW. Neuroinflammation and the Immune-Kynurenine Pathway in Anxiety Disorders. Curr Neuropharmacol 2018; 16:574-582. [PMID: 28901278 PMCID: PMC5997870 DOI: 10.2174/1570159x15666170913110426] [Citation(s) in RCA: 83] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2017] [Revised: 07/10/2017] [Accepted: 08/16/2017] [Indexed: 01/01/2023] Open
Abstract
BACKGROUND Recently, neuroinflammation and the immune-kynurenine pathway have received increased attention in the psychoimmunology field of major depressive disorder (MDD), while studies related to anxiety disorders have been very limited. OBJECTIVE This study reviewed possible mechanisms by which stress or inflammation modulate anxiety through tryptophan metabolism and the kynurenine pathway. METHODS Relevant literature was identified through a search of MEDLINE via PubMed. RESULTS Accumulating evidence has indicated the modulatory effects of the immune-kynurenine pathway on anxiety. The tryptophan catabolites (TRYCATs) in the kynurenine pathway imbalanced by stress or inflammation induce serotonin and melatonin deficiency, making anxiety reactions more sensitive. In addition, TRYCATs cause or sustain anxiety by acting as endogenous anxiogens or anxiolytics, an NMDA agonist or antagonist, or a free radical generator. CONCLUSION We hope that our understanding of the psychoimmunological mechanisms of anxiety will be expanded and anxiety-related studies will receive greater attention.
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Affiliation(s)
| | - Sang Won Jeon
- Address correspondence to this author at the Department of Psychiatry, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, 29 Saemunan-ro, Jongno-gu, Seoul 03181, Republic of Korea; Tel: +82-2-2001-2073; Fax: +82-2-2001-2211; E-mail:
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Brummett BH, Babyak MA, Kuhn CM, Siegler IC, Williams RB. A functional polymorphism in the HTR2C gene associated with stress responses: a validation study. Biol Psychol 2014; 103:317-21. [PMID: 25457638 DOI: 10.1016/j.biopsycho.2014.10.006] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2014] [Revised: 09/08/2014] [Accepted: 10/10/2014] [Indexed: 12/20/2022]
Abstract
Previously we have shown that a functional nonsynonymous single nucleotide polymorphism (SNP), rs6318 on the HTR2C gene located on the X-chromosome, is associated with hypothalamic-pituitary-adrenal axis response to a laboratory stress recall task. The present paper reports a validation of the cortisol response to stress in a second, independent sample. The study population consisted of 60 adult participants (73.3% males). Consistent with our prior findings, compared to Cys23 G allele carriers, persons homozygous for the Ser23C allele had a significantly greater average cortisol response (p=0.007) and area under the curve (p=0.021) over the course of an emotional stress recall protocol. Also parallel to our prior report, the change in cortisol from baseline to the average during the stress protocol was roughly twice as large among Ser23C homozygotes than among persons with Cys23 G. These findings validate our initial observation of association between rs6318 and cortisol response to an acute stressor, and extend the results to include females.
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Affiliation(s)
- Beverly H Brummett
- Department of Psychiatry and Behavioral Sciences, Duke University Medical Center, Durham, NC, United States.
| | - Michael A Babyak
- Department of Psychiatry and Behavioral Sciences, Duke University Medical Center, Durham, NC, United States
| | - Cynthia M Kuhn
- Department of Psychiatry and Behavioral Sciences, Duke University Medical Center, Durham, NC, United States; Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC, United States
| | - Ilene C Siegler
- Department of Psychiatry and Behavioral Sciences, Duke University Medical Center, Durham, NC, United States
| | - Redford B Williams
- Department of Psychiatry and Behavioral Sciences, Duke University Medical Center, Durham, NC, United States
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Anticevic A, Tang Y, Cho YT, Repovs G, Cole MW, Savic A, Wang F, Krystal JH, Xu K. Amygdala connectivity differs among chronic, early course, and individuals at risk for developing schizophrenia. Schizophr Bull 2014; 40:1105-16. [PMID: 24366718 PMCID: PMC4133672 DOI: 10.1093/schbul/sbt165] [Citation(s) in RCA: 54] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Alterations in circuits involving the amygdala have been repeatedly implicated in schizophrenia neuropathology, given their role in stress, affective salience processing, and psychosis onset. Disturbances in amygdala whole-brain functional connectivity associated with schizophrenia have yet to be fully characterized despite their importance in psychosis. Moreover, it remains unknown if there are functional alterations in amygdala circuits across illness phases. To evaluate this possibility, we compared whole-brain amygdala connectivity in healthy comparison subjects (HCS), individuals at high risk (HR) for schizophrenia, individuals in the early course of schizophrenia (EC-SCZ), and patients with chronic schizophrenia (C-SCZ). We computed whole-brain resting-state connectivity using functional magnetic resonance imaging at 3T via anatomically defined individual-specific amygdala seeds. We identified significant alterations in amygdala connectivity with orbitofrontal cortex (OFC), driven by reductions in EC-SCZ and C-SCZ (effect sizes of 1.0 and 0.97, respectively), but not in HR for schizophrenia, relative to HCS. Reduced amygdala-OFC coupling was associated with schizophrenia symptom severity (r = .32, P < .015). Conversely, we identified a robust increase in amygdala connectivity with a brainstem region around noradrenergic arousal nuclei, particularly for HR individuals relative to HCS (effect size = 1.54), but not as prominently for other clinical groups. These results suggest that deficits in amygdala-OFC coupling could emerge during the initial episode of schizophrenia (EC-SCZ) and may present as an enduring feature of the illness (C-SCZ) in association with symptom severity but are not present in individuals with elevated risk for developing schizophrenia. Instead, in HR individuals, there appears to be increased connectivity in a circuit implicated in stress response.
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Affiliation(s)
| | - Yanqing Tang
- Department of Psychiatry, The First Affiliated Hospital, China Medical University, Shenyang , Liaoning, PR China
| | - Youngsun T Cho
- Department of Psychiatry, Yale University School of Medicine, New Haven, CT
| | - Grega Repovs
- Department of Psychology, University of Ljubljana, Ljubljana, Slovenia
| | - Michael W Cole
- Department of Psychology, Washington University in St Louis, St Louis, MO
| | - Aleksandar Savic
- Department of Psychiatry, Yale University School of Medicine, New Haven, CT; University Psychiatric Hospital Vrapce, University of Zagreb, Zagreb, Croatia
| | - Fei Wang
- Department of Psychiatry, Yale University School of Medicine, New Haven, CT; Department of Radiology, The First Affiliated Hospital, China Medical University, Shenyang , Liaoning, PR China
| | | | - Ke Xu
- Department of Radiology, The First Affiliated Hospital, China Medical University, Shenyang , Liaoning, PR China
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Norepinephrine and impulsivity: effects of acute yohimbine. Psychopharmacology (Berl) 2013; 229:83-94. [PMID: 23559222 PMCID: PMC3742556 DOI: 10.1007/s00213-013-3088-7] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/05/2012] [Accepted: 03/22/2013] [Indexed: 01/24/2023]
Abstract
RATIONALE Rapid-response impulsivity, characterized by inability to withhold response to a stimulus until it is adequately appraised, is associated with risky behavior and may be increased in a state-dependent manner by norepinephrine. OBJECTIVE We assessed effects of yohimbine, which increases norepinephrine release by blocking alpha-2 noradrenergic receptors, on plasma catecholamine metabolites, blood pressure, subjective symptoms, and laboratory-measured rapid-response impulsivity. METHODS Subjects were 23 healthy controls recruited from the community, with normal physical examination and ECG, and negative history for hypertension, cardiovascular illness, and axis I or II disorder. Blood pressure, pulse, and behavioral measures were obtained before and periodically after 0.4 mg/kg oral yohimbine or placebo in a randomized, counterbalanced design. Metabolites of norepinephrine [3-methoxy-4-hydroxyphenylglycol (MHPG) and vanillylmandelic acid (VMA)] and dopamine [homovanillic acid (HVA)] were measured by high-pressure liquid chromatography with electrochemical detection. Rapid-response impulsivity was measured by commission errors and reaction times on the immediate memory task (IMT), a continuous performance test designed to measure impulsivity and attention. RESULTS Yohimbine increased plasma MHPG and VMA but not HVA. Yohimbine increased systolic and diastolic blood pressure and pulse rate. On the IMT, yohimbine increased impulsive errors and impulsive response bias and accelerated reaction times. Yohimbine-associated increase in plasma MHPG correlated with increased impulsive response rates. Time courses varied; effects on blood pressure generally preceded those on metabolites and test performance. CONCLUSIONS These effects are consistent with increased rapid-response impulsivity after pharmacological noradrenergic stimulation in healthy controls. Labile noradrenergic responses, or increased sensitivity to norepinephrine, may increase risk for impulsive behavior.
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Geeraerts B, Van Oudenhove L, Boesmans W, Vos R, Vanden Berghe P, Tack J. Influence of acute tryptophan depletion on gastric sensorimotor function in humans. Am J Physiol Gastrointest Liver Physiol 2011; 300:G228-35. [PMID: 20884888 DOI: 10.1152/ajpgi.00020.2010] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Peripheral serotonin (5-hydrodytryptamine; 5-HT) is involved in the regulation of gastrointestinal motility and sensation, whereas centrally it plays a role in mood regulation. A dysfunctional serotonergic system may provide a plausible link between functional dyspepsia symptoms and its high psychosocial comorbidity such as anxiety and depression. The aim of this study was to evaluate the effect of decreased 5-HT synthesis by acute tryptophan depletion (ATD) on gastric sensorimotor function and nutrient tolerance, anxiety scores, and gastrointestinal mucosal 5-HT concentrations in healthy volunteers. All subjects were studied under a control condition and during ATD. Gastric sensorimotor function and nutrient tolerance were assessed using a barostat (n = 16, mean age 28.8 ± 1.4 yr) and a satiety drinking test (n = 13, mean age 27.3 ± 1.4 yr). Anxiety during the barostat was evaluated using State-Trait Anxiety Inventory (STAI) questionnaire. 5-HT concentrations were measured in fundic and duodenal mucosal biopsies by means of ELISA and immunohistochemistry. ATD significantly decreased plasma tryptophan levels compared with control in every experiment. ATD did not affect gastric sensitivity and compliance but decreased the sensation of nausea during balloon distension (AUC: 17.4 ± 4.3 vs. 11.4 ± 3.4 mm·mmHg, P = 0.030). ATD enhanced the postprandial volume increase (ANOVA, P < 0.05), but this was not accompanied by augmented nutrient tolerance (848 ± 110 vs. 837 ± 99 ml, nonsignificant). ATD had no effect on STAI state anxiety scores. No evidence was found for an effect on the number of enterochromaffin cells, but ATD reduced 5-HT levels in the duodenal mucosa. ATD alters gastric postprandial motor function and distension-induced nausea. These findings confirm involvement of 5-HT in the control of gastric accommodation and sensitivity.
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Affiliation(s)
- Brecht Geeraerts
- Dept. of Gastroenterology, Univ. Hospital Gasthuisberg, Herestraat 49, B-3000 Leuven, Belgium
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Colasanti A, Esquivel G, den Boer E, Horlings A, Dandachi A, Oostwegel JL, van Donkelaar EL, Griez EJ, Schruers K. Effects of tryptophan depletion and tryptophan loading on the affective response to high-dose CO2 challenge in healthy volunteers. Psychopharmacology (Berl) 2011; 215:739-48. [PMID: 21336580 PMCID: PMC3102203 DOI: 10.1007/s00213-011-2177-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/26/2010] [Accepted: 01/07/2011] [Indexed: 12/20/2022]
Abstract
RATIONALE It has been reported that in panic disorder (PD), tryptophan depletion enhances the vulnerability to experimentally induced panic, while the administration of serotonin precursors blunts the response to challenges. OBJECTIVES Using a high-dose carbon dioxide (CO(2)) challenge, we aimed to investigate the effects of acute tryptophan depletion (ATD) and acute tryptophan loading (ATL) on CO(2)-induced panic response in healthy volunteers. METHODS Eighteen healthy volunteers participated in a randomized, double-blind placebo-controlled study. Each subject received ATD, ATL, and a balanced condition (BAL) in separate days, and a double-breath 35% CO(2) inhalation 4.5 h after treatment. Tryptophan (Trp) manipulations were obtained adding 0 g (ATD), 1.21 g (BAL), and 5.15 g (ATL) of l-tryptophan to a protein mixture lacking Trp. Assessments consisted of a visual analogue scale for affect (VAAS) and panic symptom list. A separate analysis on a sample of 55 subjects with a separate-group design has also been performed to study the relationship between plasma amino acid levels and subjective response to CO(2). RESULTS CO(2)-induced subjective distress and breathlessness were significantly lower after ATD compared to BAL and ATL (p < 0.05). In the separate-group analysis, ΔVAAS scores were positively correlated to the ratio Trp:ΣLNAA after treatment (r = 0.39; p < 0.05). CONCLUSIONS The present results are in line with preclinical data indicating a role for the serotonergic system in promoting the aversive respiratory sensations to hypercapnic stimuli (Richerson, Nat Rev Neurosci 5(6):449-461, 2004). The differences observed in our study, compared to previous findings in PD patients, might depend on an altered serotonergic modulatory function in patients compared to healthy subjects.
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Affiliation(s)
- Alessandro Colasanti
- Department of Psychiatry and Neuropsychology, Faculty of Health, Medicine and Life Sciences, School for Mental Health and Neuroscience, Maastricht University, Maastricht, The Netherlands.
| | - Gabriel Esquivel
- Department of Psychiatry and Neuropsychology, Faculty of Health, Medicine and Life Sciences, School for Mental Health and Neuroscience, Maastricht University, Maastricht, The Netherlands
| | - Erik den Boer
- Department of Psychiatry and Neuropsychology, Faculty of Health, Medicine and Life Sciences, School for Mental Health and Neuroscience, Maastricht University, Maastricht, The Netherlands
| | - Annerieke Horlings
- Department of Psychiatry and Neuropsychology, Faculty of Health, Medicine and Life Sciences, School for Mental Health and Neuroscience, Maastricht University, Maastricht, The Netherlands
| | - Abdul Dandachi
- Department of Psychiatry and Neuropsychology, Faculty of Health, Medicine and Life Sciences, School for Mental Health and Neuroscience, Maastricht University, Maastricht, The Netherlands
| | | | - Eva L. van Donkelaar
- Department of Psychiatry and Neuropsychology, Faculty of Health, Medicine and Life Sciences, School for Mental Health and Neuroscience, Maastricht University, Maastricht, The Netherlands
| | - Eric J. Griez
- Department of Psychiatry and Neuropsychology, Faculty of Health, Medicine and Life Sciences, School for Mental Health and Neuroscience, Maastricht University, Maastricht, The Netherlands
| | - Koen Schruers
- Department of Psychiatry and Neuropsychology, Faculty of Health, Medicine and Life Sciences, School for Mental Health and Neuroscience, Maastricht University, Maastricht, The Netherlands
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Samuels ER, Szabadi E. Functional neuroanatomy of the noradrenergic locus coeruleus: its roles in the regulation of arousal and autonomic function part I: principles of functional organisation. Curr Neuropharmacol 2010; 6:235-53. [PMID: 19506723 PMCID: PMC2687936 DOI: 10.2174/157015908785777229] [Citation(s) in RCA: 472] [Impact Index Per Article: 33.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2007] [Revised: 02/25/2008] [Accepted: 06/06/2008] [Indexed: 01/09/2023] Open
Abstract
The locus coeruleus (LC) is the major noradrenergic nucleus of the brain, giving rise to fibres innervating extensive areas throughout the neuraxis. Recent advances in neuroscience have resulted in the unravelling of the neuronal circuits controlling a number of physiological functions in which the LC plays a central role. Two such functions are the regulation of arousal and autonomic activity, which are inseparably linked largely via the involvement of the LC. The LC is a major wakefulness-promoting nucleus, resulting from dense excitatory projections to the majority of the cerebral cortex, cholinergic neurones of the basal forebrain, cortically-projecting neurones of the thalamus, serotoninergic neurones of the dorsal raphe and cholinergic neurones of the pedunculopontine and laterodorsal tegmental nucleus, and substantial inhibitory projections to sleep-promoting GABAergic neurones of the basal forebrain and ventrolateral preoptic area. Activation of the LC thus results in the enhancement of alertness through the innervation of these varied nuclei. The importance of the LC in controlling autonomic function results from both direct projections to the spinal cord and projections to autonomic nuclei including the dorsal motor nucleus of the vagus, the nucleus ambiguus, the rostroventrolateral medulla, the Edinger-Westphal nucleus, the caudal raphe, the salivatory nuclei, the paraventricular nucleus, and the amygdala. LC activation produces an increase in sympathetic activity and a decrease in parasympathetic activity via these projections. Alterations in LC activity therefore result in complex patterns of neuronal activity throughout the brain, observed as changes in measures of arousal and autonomic function.
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Affiliation(s)
- E R Samuels
- Psychopharmacology Section, University of Nottingham, Division of Psychiatry, Queen's Medical Centre, Nottingham, NG7 2UH, UK
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Kang EH, Shim HB, Kim KJ, Park JE, Lee IS, Yu BH. Platelet serotonin transporter function after short-term paroxetine treatment in patients with panic disorder. Psychiatry Res 2010; 176:250-3. [PMID: 20207008 DOI: 10.1016/j.psychres.2008.12.007] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/27/2008] [Revised: 09/23/2008] [Accepted: 12/22/2008] [Indexed: 10/19/2022]
Abstract
Dysfunctions in serotonin neurotransmission have been implicated in some psychiatric disorders, and in particular, altered serotonin transporter function has been noted in panic disorder. In this study, the authors compared platelet [(3)H]serotonin uptake parameters, including maximum velocities (V(max)) and affinity constants (K(m)), in patients with panic disorder not undergoing treatment (n=21) and in healthy subjects (n=20). V(max) and K(m) values were re-examined after 12 weeks of paroxetine treatment. Values of V(max) and K(m) were lower in panic disorder patients at baseline than in healthy subjects. After treatment, K(m) normalized in panic patients, whereas V(max) did not change. A significant inverse correlation was found between increased K(m) and changes in anxiety levels. These results support a hypothesis of serotonergic transporter abnormalities in panic disorder, and suggest that increased K(m) values of platelet serotonin transporters parallel clinical improvement after short-term pharmacotherapy in panic disorder.
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Affiliation(s)
- Eun-Ho Kang
- Department of Psychiatry, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul 135-710, Republic of Korea
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Lazary J, Lazary A, Gonda X, Benko A, Molnar E, Hunyady L, Juhasz G, Bagdy G. Promoter variants of the cannabinoid receptor 1 gene (CNR1) in interaction with 5-HTTLPR affect the anxious phenotype. Am J Med Genet B Neuropsychiatr Genet 2009; 150B:1118-27. [PMID: 19725030 DOI: 10.1002/ajmg.b.31024] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Anxiety is a polygenic condition, and the recently discovered Endocannabinoid System (ECS) is one plausible candidate. Experimental data suggest that the ECS can modulate several neurotransmitter systems, including the serotonergic system, which itself plays a significant role in anxiety. However, to date there is no evidence of gene-gene interactions; indeed genetic studies focusing separately on the two systems provide conflicting data. Thus, the aim of our study was to analyze the interaction of the promoter regions of the serotonin transporter (SLC6A4) and cannabinoid receptor 1 (CNR1) genes on anxiety. We genotyped 706 individuals for the 5-HTTLPR in the SLC6A4 promoter and 4 SNPs located in the CNR1 promoter region. Anxiety was measured by the State-Trait Anxiety Inventory (STAI-S, STAI-T), the anxiety subscale of TEMPS-A (TEMPS-Anx), and the Brief Symptom Inventory (BSI-Anx). Significant 5-HTTLPR x CNR1 promoter-promoter interaction was observed using STAI-T (P = 0.0006) and TEMPS-Anx (P = 0.0013). The risk of high anxiety scores on BSI-Anx was 4.6-fold greater in homozygous 'GG' rs2180619 in combination with homozygous 'SS' 5-HTTLPR (P = 0.0005) compared to other genotypes. The effect of previously described "TGC" haplotype in the alternative promoter of CNR1 depended both on the conventional promoter polymorphism and the 5-HTTLPR. Our haplotype and putative transcription binding profile analyses strongly suggest that certain constellations of CB1-receptor and 5-HTT promoters yield extremely high or low synaptic 5-HT concentrations, and these are associated with an anxious phenotype. In conclusion, genetically determined serotonergic and endocannabinoid dysfunctions could lead to a vulnerability causing anxiety disorders and possibly depression.
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Affiliation(s)
- Judit Lazary
- Department of Pharmacology and Pharmacotherapy, Semmelweis University, Budapest, Hungary
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Abstract
A considerable body of evidence suggests the involvement of serotonin neurotransmission in the pathogenesis of panic disorder. Research on pathways and functions of tryptophan, an essential amino acid converted into serotonin, may advance our understanding of serotonergic actions in panic disorder and related phenomena. The investigative approaches in this field include manipulations of tryptophan availability as well as genetic association and functional brain imaging studies. In this review we examine the principle findings of these studies and propose further research directions.
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Affiliation(s)
- Eduard Maron
- Research Department of Mental Health, The North Estonian Regional Hospital, Psychiatry Clinic, Tallinn, Estonia
- Department of Psychiatry, University of Tartu, Tartu, Estonia
- Estonian Genome Project, University of Tartu, Estonia
| | - Jakov Shlik
- Department of Psychiatry, University of Ottawa, Ottawa, Ontario, Canada
| | - David J. Nutt
- Department of Community Based Medicine, Psychopharmacology Unit, University of Bristol, U.K
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Tõru I, Shlik J, Maron E, Vasar V, Nutt DJ. Tryptophan depletion does not modify response to CCK-4 challenge in patients with panic disorder after treatment with citalopram. Psychopharmacology (Berl) 2006; 186:107-12. [PMID: 16541242 DOI: 10.1007/s00213-006-0351-1] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/30/2005] [Accepted: 02/13/2006] [Indexed: 12/18/2022]
Abstract
RATIONALE Data by [Bell et al. J Psychopharmacol (2002) 16:5-14] suggest that a decrease in 5-HT neurotransmission predisposes to panic attacks and that the antipanic effect of SSRIs depends upon the availability of 5-HT in the brain. OBJECTIVES Our aim was to assess the effect of acute tryptophan depletion (TD) on cholecystokinin-tetrapeptide (CCK-4)- induced symptoms in patients with panic disorder (PD) who had responded to a 10-week treatment with a selective serotonin (5-HT) reuptake inhibitor (SSRI), citalopram. MATERIALS AND METHODS A total of 18 patients (6 males and 12 females, mean age 34.5 years) received a tryptophan-free amino acid drink and a control drink, each followed by a CCK-4 challenge (25 microg), 1 week apart in a double-blind crossover design. RESULTS The results showed no significant differences in response to the CCK-4 challenge between the TD and the control conditions. Panic rate after the CCK-4 challenge was 27.8% after depletion and 33.3% after control drink (chi2=0.13, p=0.72). No significant effects of TD were observed in panic intensity scores, subjective anxiety, or cardiovascular indices. CONCLUSIONS This study demonstrates that an acute lowering of brain 5-HT availability with TD does not affect response to a CCK-4 challenge in PD patients successfully treated with citalopram. Thus, the reduction of CCK-4 sensitivity following SSRI-treatment in patients with PD may be related to mechanisms other than 5-HT availability in the brain, possibly to a reduction in brain cholecystokinin receptor sensitivity.
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Affiliation(s)
- Innar Tõru
- Department of Psychiatry, University of Tartu, Tartu, Estonia.
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Abstract
OBJECTIVE This is the second of two articles reviewing the modern dietary technique of acute tryptophan depletion (ATD), a method of transiently reducing central serotonin levels in both healthy volunteers and clinical populations. This article details the clinical studies to date and discusses the implications of this research methodology. METHOD The authors present a review of clinical ATD studies collated from a MEDLINE search, unpublished communications and the authors' considerable experience with this paradigm. RESULTS Following from the initial use of ATD in subjects with depressive illness, studies of anxiety disorders and other psychiatric illnesses have been reported. Sleep, aggressive and cognitive effects are also active areas of research and are reviewed here. CONCLUSIONS Acute tryptophan depletion remains a useful psychiatric research tool. The findings from the clinical studies reviewed here are summarized and implications for future research detailed.
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Affiliation(s)
- Caroline J Bell
- Department of Psychological Medicine, Christchurch School of Medicine and Health Sciences, New Zealand
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Gordon JA, Hen R. The serotonergic system and anxiety. Neuromolecular Med 2004; 5:27-40. [PMID: 15001810 DOI: 10.1385/nmm:5:1:027] [Citation(s) in RCA: 125] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2003] [Accepted: 08/06/2003] [Indexed: 11/11/2022]
Abstract
The wide use of serotonin reuptake inhibitors and serotonin receptor agonists in anxiety disorders has suggested a key role for the modulatory neurotransmitter in anxiety. However, serotonin's specific role is still uncertain. This article reviews the literature concerning how and where serotonergic agents modulate anxiety. Varying and sometimes conflicting data from human and animal studies argue for both anxiolytic and anxiogenic roles for serotonin, depending on the specific disorder, structure, or behavioral task studied. However, recent data from molecular genetic studies in the mouse point toward two important roles for the serotonin 1A receptor. In development, serotonin acts through this receptor to promote development of the circuitry necessary for normal anxiety-like behaviors. In adulthood, serotonin reuptake inhibitors act through the same receptor to stimulate neurogenesis and reduce anxiety-like behaviors. These studies highlight that the complex serotonin system likely plays various roles in the regulation of anxiety both during development and in adulthood.
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Affiliation(s)
- Joshua A Gordon
- Department of Psychiatry, Center for Neurobiology and Behavior, Columbia University, and the New York State Psychiatric Institute, NY, USA
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Pyle AC, Argyropoulos SV, Nutt DJ. The role of serotonin in panic: evidence from tryptophan depletion studies. Acta Neuropsychiatr 2004; 16:79-84. [PMID: 26984000 DOI: 10.1111/j.0924-2708.2004.0081.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
There has been growing interest in the role of serotonin (5-hydroxytryptamine, 5-HT) in anxiety, including pathological states such as panic disorder. The technique of tryptophan depletion (TD), which causes an acute, temporary and reversible reduction in brain 5-HT levels, is a useful minimally invasive paradigm to aid the research of the role of 5-HT in various disorders. This review discusses the evidence supporting the hypothesis that 5-HT function is of importance in the neurobiology of panic disorder and considers in more detail how our understanding has been influenced by work using the technique of TD. Possible avenues for future research are also discussed.
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Klaassen T, Riedel WJ, van Praag HM, Menheere PPCA, Griez E. Neuroendocrine response to meta-chlorophenylpiperazine and ipsapirone in relation to anxiety and aggression. Psychiatry Res 2002; 113:29-40. [PMID: 12467943 DOI: 10.1016/s0165-1781(02)00250-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The aim of this study was to establish the association of trait anxiety and anger with hormonal responses to acute challenges with two different 5-HT agonists in a mixed group of patients with depressed mood. Fifteen patients and 16 normal controls received single oral doses of 0.5 mg/kg meta-chlorophenylpiperazine (MCPP), a 5-HT(2C) agonist, and 10 mg of ipsapirone, a 5-HT(1A) agonist, according to a double-blind, placebo-controlled, cross-over design. Dutch-adapted versions of the Spielberger Trait-Anxiety Inventory and the Spielberger Trait-Anger Scale administered assessed at study entry. Hormonal responses, expressed as drug-placebo differences, to MCPP and ipsapirone (changes in cortisol, ACTH and prolactin) were measured. Blood levels of MCPP and ipsapirone were also measured. MCPP and ipsapirone elevated cortisol, ACTH and prolactin. In the patient group, there was a significant correlation between trait anxiety and the cortisol response to MCPP. No significant correlations between the ACTH and prolactin responses to MCPP and levels of anxiety/anger were observed in the patients. No significant correlations could be established between levels of anxiety/anger and hormonal responses to ipsapirone. This study provided evidence for an association between measures of anxiety/aggression and the hormonal response to MCPP. Thus, in subjects with depressed mood, high levels of anxiety suggest a higher probability of 5-HT(2C) disturbances.
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Affiliation(s)
- Tineke Klaassen
- Departments of Psychiatry and Neuropsychology, University of Maastricht, PO Box 616, 6200 MD, Maastricht, The Netherlands.
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Berman RM, Sanacora G, Anand A, Roach LM, Fasula MK, Finkelstein CO, Wachen RM, Oren DA, Heninger GR, Charney DS. Monoamine depletion in unmedicated depressed subjects. Biol Psychiatry 2002; 51:469-73. [PMID: 11922881 DOI: 10.1016/s0006-3223(01)01285-9] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
BACKGROUND Although significant evidence suggests that diminished monoamine function is associated with clinical depression, catecholamine or indoleamine depletion alone has not been associated with significant mood changes in unmedicated depressed subjects or never-depressed control subjects. This study assesses the integrated role of these monoamine systems in depressed patients. METHODS Unmedicated depressed subjects underwent a 2-week, double-blind, random-ordered crossover study consisting of the following active and control conditions respectively: indoleamine (via tryptophan depletion) plus catecholamine (via alpha-methyl-paratyrosine administration) depletion and, separately, indoleamine plus sham (via diphenhydramine administration) catecholamine depletion. Ten subjects completed both conditions; two subjects were withdrawn after active testing and one after control testing. RESULTS Mean Hamilton Depression Rating Scale (HDRS) scores decreased progressively throughout the study days (baseline 26.7 points +/- 1.7 SEM and termination 20.0 +/- 2.4, active depletion; baseline 26.1 points +/- 2.3 SEM and termination 23.2 +/- 2.6, control testing) but did not differ between groups. Only three patients demonstrated 20% or greater increases from baseline HDRS at any point during the observation days. CONCLUSIONS Overall, results show that simultaneous disruptions of indoleamine and catecholamine function do not exacerbate symptoms in unmedicated depressed subjects, thus lending further support to the notion that monoamines regulate mood in actively depressed patients via indirect mechanisms.
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Affiliation(s)
- Robert M Berman
- Abraham Ribicoff Center Clinical Neuroscience Research Unit of the Connecticut Mental Health Center, New Haven, Connecticut, USA
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Bell C, Forshall S, Adrover M, Nash J, Hood S, Argyropoulos S, Rich A, Nutt DJ. Does 5-HT restrain panic? A tryptophan depletion study in panic disorder patients recovered on paroxetine. J Psychopharmacol 2002; 16:5-14. [PMID: 11949771 DOI: 10.1177/026988110201600116] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The neurobiological basis of panic disorder has not been clearly established, although a role for serotonin (5-HT) has been postulated. It is clear that drugs which increase 5-HT neurotransmission are effective in treating the condition but how they do so remains a point of debate. The aim of this study was to determine if lowering brain serotonin activity using the technique of tryptophan depletion provoked a short-term relapse of panic symptoms in patients with panic disorder who had responded to drug treatment. Fourteen patients with panic disorder who had responded to treatment with the selective serotonin reuptake inhibitor (SSRI) paroxetine received a tryptophan-free amino acid drink on one occasion and a control drink on the other in a double-blind crossover design. In addition, they received an infusion of flumazenil (used as a pharmacological challenge) and placebo on each day. The tryptophan depleted drink produced an 87% reduction in plasma tryptophan concentration. Flumazenil produced a panic attack (defined by changes in the panic inventory) in seven out of 14 patients when tryptophan depleted and one out of 14 on the control day (p < 0.02). Three patients also experienced temporary depressive symptoms when tryptophan depleted, with no mood changes being seen on the control days. We conclude that rapid lowering of brain serotonin function can allow the precipitation of panic symptoms in response to flumazenil in panic disorder patients who have responded to treatment with an SSRI. This implies that in panic disorder increased 5-HT availability is important in maintaining the response to SSRIs.
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Affiliation(s)
- Caroline Bell
- Psychopharmacology Unit, School of Medical Sciences, University of Bristol, UK
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Abstract
BACKGROUND Over the past 10 years the technique of tryptophan depletion has been used increasingly as a tool for studying brain serotonergic systems. AIMS To review the technique of tryptophan depletion and its current status as a tool for investigating psychiatric disorders. METHOD Systematic review of preclinical and clinical studies. RESULTS Tryptophan depletion produces a marked reduction in plasma tryptophan and consequently brain serotonin (5-HT) synthesis and release. In healthy volunteers the effects of tryptophan depletion are influenced by the characteristics of the subjects and include some mood lowering, some memory impairment and an increase in aggression. In patients with depression tryptophan depletion tends to result in no worsening of depression in untreated subjects but a relapse in those who have responded to antidepressants (particularly serotonergic agents). In panic disorder the results are similar. CONCLUSIONS The findings that tryptophan depletion produces a relapse of symptoms in patients with depression and panic disorder who have responded to treatment with antidepressants suggests that enhanced 5-HT function is important in maintaining response in these conditions.
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Affiliation(s)
- C Bell
- Psychopharmacology Unit, School of Medical Sciences, Bristol, UK
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Abstract
BACKGROUND The number of studies using tryptophan depletion (TD) challenge has increased markedly in the past few years. Recently, a number of negative results have been published, implicating that the effect of TD on mood may be less consistent than previously thought. METHODS The literature on the mood effects of TD in psychiatric patients and healthy volunteers was reviewed. RESULTS TD has a mood-lowering effect in subgroups of recovered depressed patients, patients with seasonal affective disorder and vulnerable healthy subjects. The mood effect in former patients is of a different quality, however, than the effect in healthy subjects. Some recent negative studies in depression might be explained by insufficient lowering of plasma tryptophan levels. Preliminary evidence exists for an effect of TD on bulimia nervosa, autism, aggression and substance dependence. CONCLUSIONS The effects of TD on mood may be more consistent than suggested by a number of recent negative studies. Response to TD in recovered depressed patients is associated with prior treatment. However, even in SSRI-treated patients the relapse rates are not higher than 50-60%, which needs to be explained. The clinical usefulness of the response to TD in recovered patients (prediction of relapse after treatment discontinuation) and in symptomatic patients (prediction of treatment refractoriness) deserves more research attention. Further suggestions for future research include the cognitive effects of TD in recovered depressed patients and the effect of dietary habits on response to TD.
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Affiliation(s)
- A J Van der Does
- Departments of Psychology and Psychiatry, Leiden University, Wassenaarseweg 52, 2333 AK, Leiden, The Netherlands.
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Zald DH, Depue RA. Serotonergic functioning correlates with positive and negative affect in psychiatrically healthy males. PERSONALITY AND INDIVIDUAL DIFFERENCES 2001. [DOI: 10.1016/s0191-8869(00)00011-8] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Anderson IM, Mortimore C. 5-HT and human anxiety. Evidence from studies using acute tryptophan depletion. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2000; 467:43-55. [PMID: 10721037 DOI: 10.1007/978-1-4615-4709-9_6] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/15/2023]
Abstract
There is abundant evidence that serotonin (5-hydroxytryptamine, 5-HT) is involved in anxiety in both animals and humans but there is conflicting evidence for the precise role it plays. Acute tryptophan depletion provides a technique for investigating a global reduction in brain 5-HT function and we have investigated its effect on anxiety in drug-free panic disorder patients and normal volunteers. We found little effect on general levels of anxiety but it enhanced the effect of a panic challenge using 5% carbon dioxide (5%CO2) in panic disorder patients. The effect in normal volunteers was less clear with no overall effect following 5%CO2 challenge or the psychological challenge of a simulated public speaking task. These results are discussed in relation to the literature and are broadly supportive of the hypothesis that 5-HT acts to inhibit panic anxiety at the level of the periaqueductal grey but facilitates general and conditioned anxiety at the level of medial temporal lobe structures.
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Affiliation(s)
- I M Anderson
- Neuroscience and Psychiatry Unit, University of Manchester, UK.
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Monteiro-dos-Santos PC, Graeff FG, dos-Santos JE, Ribeiro RP, Guimarães FS, Zuardi AW. Effects of tryptophan depletion on anxiety induced by simulated public speaking. Braz J Med Biol Res 2000; 33:581-7. [PMID: 10775890 DOI: 10.1590/s0100-879x2000000500013] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Several lines of evidence point to the participation of serotonin (5HT) in anxiety. Its specific role, however, remains obscure. The objective of the present study was to evaluate the effect of reducing 5HT-neurotransmission through an acute tryptophan depletion on anxiety induced by a simulated public speaking (SPS) test. Two groups of 14-15 subjects were submitted to a 24-h diet with a low or normal content of tryptophan and received an amino acid mixture without (TRY-) or with (TRY+) tryptophan under double-blind conditions. Five hours later they were submitted to the SPS test. The state-trait anxiety inventory (STAI) and the visual analogue mood scale (VAMS) were used to measure subjective anxiety. Both scales showed that SPS induced a significant increase in anxiety. Although no overall difference between groups was found, there was a trend (P = 0.078) to an interaction of group x gender x phases of the SPS, and a separate analysis of each gender showed an increase in anxiety measured by the STAI in females of the TRY- group. The results for the female TRY- group also suggested a greater arousing effect of the SPS test. In conclusion, the tryptophan depletion procedure employed in the present study did not induce a significant general change in subjective anxiety, but tended to induce anxiety in females. This suggests a greater sensitivity of the 5HT system to the effects of the procedure in this gender.
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Schruers K, Klaassen T, Pols H, Overbeek T, Deutz NE, Griez E. Effects of tryptophan depletion on carbon dioxide provoked panic in panic disorder patients. Psychiatry Res 2000; 93:179-87. [PMID: 10760376 DOI: 10.1016/s0165-1781(00)00117-7] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Results of an earlier study in healthy volunteers suggest that the serotonergic system is involved in anxiety-related mechanisms. We studied the influence of tryptophan depletion on the response to a 35% carbon dioxide challenge. Twenty-four panic disorder patients received a mixture of amino acids, either with or without tryptophan, under double-blind conditions. There was a significant increase in anxiety as well as in neurovegetative symptoms in the depletion group, compared to the placebo condition. Furthermore, when we compare the results of the placebo group with earlier panic provocation studies, it also seems that a balanced amino acid mixture might have a protective effect against a panic provocation. We conclude that the panic-enhancing effect of tryptophan depletion as well as the potential protective effect of tryptophan administration in panic disorder patients can be explained by the Deakin-Graeff theory of anxiety.
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Affiliation(s)
- K Schruers
- Department of Psychiatry & Neuropsychology, Maastricht University, P. O. Box 88, 6200 AB, Maastricht, The Netherlands.
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Miller HE, Deakin JF, Anderson IM. Effect of acute tryptophan depletion on CO2-induced anxiety in patients with panic disorder and normal volunteers. Br J Psychiatry 2000; 176:182-8. [PMID: 10755058 DOI: 10.1192/bjp.176.2.182] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
BACKGROUND Uncertainties remain about the role of serotonin in the aetiology and treatment of panic disorder. AIMS To investigate the effect of reducing brain serotonin function on anxiety at rest, and following 5% CO2 provocation in normal controls and patients with panic disorder. METHOD Twenty drug-free patients with DSM-III-R panic disorder and 19 controls received a tryptophan-free amino acid drink on one occasion and a control drink on the other in a double-blind, balanced protocol. 5% CO2 was given as a panic challenge after 270 minutes. RESULTS Plasma tryptophan fell by more than 80% both patients and controls after the tryptophan-free drink. Tryptophan depletion did not alter resting anxiety. In patients alone, tryptophan depletion caused a greater anxiogenic response and an increased rate of panic attacks (9 v. 2, P < 0.05) after 5% CO2 challenge. No normal volunteers panicked. CONCLUSIONS Serotonin may directly modulate panic anxiety in patients with panic disorder. This may underlie the efficacy of serotonergic antidepressants in treating panic disorder.
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Affiliation(s)
- H E Miller
- Department of Psychiatry, Manchester Royal Infirmary
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Klaassen T, Klumperbeek J, Deutz NE, van Praag HM, Griez E. Effects of tryptophan depletion on anxiety and on panic provoked by carbon dioxide challenge. Psychiatry Res 1998; 77:167-74. [PMID: 9707299 DOI: 10.1016/s0165-1781(98)00004-3] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Results of several studies suggest that anxiety is under serotonergic control. We studied the influence of tryptophan depletion on generalized anxiety and on the response to a 35% carbon dioxide (CO2) challenge. Fifteen healthy male volunteers received both a mixture of amino acids without tryptophan and a placebo mixture under double-blind conditions. The tryptophan-free mixture led to an 80% decrease in blood tryptophan levels compared to the placebo. There was a significant increase in anxiety on the Spielberger Anxiety Inventory and a trend towards more tension on the Profile of Mood States-'tension' items, both of which were interpreted as increased nervousness. Furthermore, a significant increase in neurovegetative panic symptoms occurred after the CO2 challenge. We conclude that the serotonergic system is causally involved in anxiety-related mechanisms and that it may be worth pursuing the role of tryptophan depletion on CO2-induced panic in patients with anxiety disorders.
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Affiliation(s)
- T Klaassen
- Department of Psychiatry and Neuropsychology, Maastricht University, The Netherlands
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Reilly JG, McTavish SF, Young AH. Rapid depletion of plasma tryptophan: a review of studies and experimental methodology. J Psychopharmacol 1998; 11:381-92. [PMID: 9443529 DOI: 10.1177/026988119701100416] [Citation(s) in RCA: 116] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Evidence that the neurotransmitter serotonin (5-hydroxytryptamine, 5-HT) plays a role in the pathophysiology of mood disorders has been accumulating over the past three decades. Recent studies on this neurotransmitter have extended across the spectrum of psychiatric disorder, suggesting a role for 5-HT in psychosis, aggression, eating disorders and addiction. However, much of the evidence has come from post-mortem examination of the brain or measures of peripheral rather than central 5-HT function. The technique of tryptophan depletion allows investigation of brain 5-HT function in living subjects by examining the behavioural responses to this pharmacological challenge. This review considers the current status of tryptophan depletion as an experimental technique and discusses the implications of findings both in affective disorders and in a range of other psychiatric syndromes. MEDLINE and PSYCHLIT searches were completed for the years 1966 to November 1996 using the key words 'serotonin', '5-hydroxytryptamine', 'tryptophan' and 'depletion'. In addition relevant journals were hand-searched for the period from 1980 to December 1996. Forty-four double-blind studies in humans and three clinical case reports were identified; these cover a range of psychiatric disorders including mood disorders and psychoses, anxiety and eating disorders and specific behaviours such as appetite, aggression and craving. The studies reviewed utilized a variety of differing methodologies reducing the extent to which results can be generalized. A series of studies in depressed patients (before and after treatment with antidepressants) and their first-degree relatives have shown the importance of an intact 5-HT system in the action of antidepressants and offer new insights into the biology of affective disorder. The mood change induced by tryptophan depletion may predict those patients likely to respond to 5-HT-specific drugs. Rapid tryptophan depletion has also been reported to exacerbate both panic and aggression in vulnerable individuals. Effects in other disorders are conflicting and further research is needed to clarify these findings.
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Affiliation(s)
- J G Reilly
- Division of Psychiatry, School of Neurosciences, University of Newcastle, Royal Victoria Infirmary, Newcastle Upon Tyne, UK
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Barr LC, Heninger GR, Goodman W, Charney DS, Price LH. Effects of fluoxetine administration on mood response to tryptophan depletion in healthy subjects. Biol Psychiatry 1997; 41:949-54. [PMID: 9110100 DOI: 10.1016/s0006-3223(96)00224-7] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Short-term reduction in plasma tryptophan (tryptophan depletion) produces a relapse of depressive symptoms in 60% of previously depressed patients recently recovered with serotonin reuptake inhibitor treatment. Tryptophan depletion does not consistently increase depressive symptoms in unmedicated depressed patients or in depressed patients whose symptoms are remitted with a norepinephrine reuptake inhibitor. These data suggest that serotonin reuptake inhibitor treatment itself may confer vulnerability to the development of depressive symptoms during tryptophan depletion. In order to further investigate this possibility, six healthy individuals underwent double-blind placebo-controlled tryptophan depletion before and following six weeks of treatment with fluoxetine 20 mg/day. No increased vulnerability to the mood-lowering effects of tryptophan depletion occurred as a result of fluoxetine treatment. Additionally, fluoxetine treatment itself was not associated with changes in mood or quality of life in these healthy volunteers. These data indicate that serotonin reuptake inhibitor treatment alone does not produce the depressive effects of tryptophan depletion that are observed in serotonin reuptake inhibitor-treated depressed and obsessive compulsive disorder patients.
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Affiliation(s)
- L C Barr
- Clinical Neuroscience Research Unit, Abraham Ribicoff Research Facilities, Connecticut Mental Health Center, Department of Psychiatry, Yale University School of Medicine, New Haven, USA
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Koszycki D, Zacharko RM, Le Melledo JM, Young SN, Bradwejn J. Effect of acute tryptophan depletion on behavioral, cardiovascular, and hormonal sensitivity to cholecystokinin-tetrapeptide challenge in healthy volunteers. Biol Psychiatry 1996; 40:648-55. [PMID: 8886299 DOI: 10.1016/0006-3223(95)00479-3] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Recent data suggest that serotonergic (5-HT) mechanisms may mediate the anxiogenic effects of cholecystokinin (CCK)-related peptides. Accordingly, we investigated the effect of lowering plasma tryptophan to the elicitation of behavioral, cardiovascular, and hormonal changes in healthy volunteers challenged with the tetrapeptide CCK agonist, CCK-4. Forty men without personal or family history of psychiatric disorders were randomly assigned to either a tryptophan-free amino acid mixture, which decreases central 5-HT concentrations, or a control mixture. Five hours after administration of the amino acid mixture, all subjects received a single intravenous injection of CCK-4. The main finding of the study was that acute depletion of tryptophan failed to modify the panicogenic and cardiovascular effects of CCK-4, although it did enhance CCK-4-mediated increases in ACTH/cortisol and prolactin secretion. While these findings suggest that at least part of the neuroendocrine action of CCK-4 is mediated through the 5-HT system, the locus of the 5-HT-CCK interaction and the specific 5-HT receptor subtype involved remains to be determined.
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Affiliation(s)
- D Koszycki
- Psychobiology and Clinical Trials Research Unit in Anxiety, Clarke Institute of Psychiatry, Toronto, Ontario, Canada
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Aronson SC, Black JE, McDougle CJ, Scanley BE, Jatlow P, Kosten TR, Heninger GR, Price LH. Serotonergic mechanisms of cocaine effects in humans. Psychopharmacology (Berl) 1995; 119:179-85. [PMID: 7659765 DOI: 10.1007/bf02246159] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The objective of this study was to investigate the role of serotonin (5-HT) in mediating the effects of cocaine in humans. To accomplish this, 12 subjects each participated in two randomized, double-blind test sessions separated by 1 week. In one session, subjects underwent acute depletion of the 5-HT amino acid precursor tryptophan (TRP), followed by a test dose of intranasal cocaine. In the other session, the cocaine test dose was preceded by sham depletion. Subject ratings of cocaine "high" were significantly lower following active TRP depletion than after the sham procedure. Subjects also showed an earlier but less sustained rise in self-rated nervousness during active TRP depletion. These findings are consistent with the hypothesis that 5-HT may be involved in mediating the euphorigenic and modulating the anxiogenic effects of cocaine in humans, either directly or through actions on other (e.g., dopaminergic) systems.
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Affiliation(s)
- S C Aronson
- Department of Psychiatry, Yale University School of Medicine, New Haven, CT 06519, USA
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