Mood changes following acute tryptophan depletion in healthy adults

Association Study of Serotonin 1A Receptor Gene, Personality, and Anxiety in Women with Alcohol Use Disorder

Alcohol use disorder is considered a chronic and relapsing disorder affecting the central nervous system. The serotonergic system, mainly through its influence on the mesolimbic dopaminergic reward system, has been postulated to play a pivotal role in the underlying mechanism of alcohol dependence. The study aims to analyse the association of the rs6295 polymorphism of the 5HTR1A gene in women with alcohol use disorder and the association of personality traits with the development of alcohol dependence, as well as the interaction of the rs6295, personality traits, and anxiety with alcohol dependence in women. The study group consisted of 213 female volunteers: 101 with alcohol use disorder and 112 controls. NEO Five-Factor and State-Trait Anxiety Inventories were applied for psychometric testing. Genotyping of rs6295 was performed by real-time PCR. We did not observe significant differences in 5HTR1A rs6295 genotypes (p = 0.2709) or allele distribution (p = 0.4513). The AUD subjects scored higher on the anxiety trait (p < 0.0001) and anxiety state (p < 0.0001) scales, as well as on the neuroticism (p < 0.0001) and openness (p = 0134) scales. Significantly lower scores were obtained by the AUD subjects on the extraversion (p < 0.0001), agreeability (p < 0.0001), and conscientiousness (p < 0.0001) scales. Additionally, we observed a significant effect of 5HTR1A rs6295 genotype interaction and alcohol dependency, or lack thereof, on the openness scale (p = 0.0016). In summary, this study offers a comprehensive overview of alcohol dependence among women. It offers valuable insights into this complex topic, contributing to a more nuanced understanding of substance use among this specific demographic. Additionally, these findings may have implications for developing prevention and intervention strategies tailored to individual genetic and, most importantly, personality and anxiety differences.

Sex Differences in Tryptophan Metabolism: A Systematic Review Focused on Neuropsychiatric Disorders

Tryptophan (Tryp) is an essential amino acid and the precursor of several neuroactive compounds within the central nervous system (CNS). Tryp metabolism, the common denominator linking serotonin (5-HT) dysfunctions and neuroinflammation, is involved in several neuropsychiatric conditions, including neurological, neurodevelopmental, neurodegenerative, and psychiatric diseases. Interestingly, most of those conditions occur and progress in a sex-specific manner. Here, we explore the most relevant observations about the influence of biological sex on Tryp metabolism and its possible relation to neuropsychiatric diseases. Consistent evidence suggests that women have a higher susceptibility than men to suffer serotoninergic alterations due to changes in the levels of its precursor Tryp. Indeed, female sex bias in neuropsychiatric diseases is involved in a reduced availability of this amino acid pool and 5-HT synthesis. These changes in Tryp metabolism could lead to sexual dimorphism on the prevalence and severity of some neuropsychiatric disorders. This review identifies gaps in the current state of the art, thus suggesting future research directions. Specifically, there is a need for further research on the impact of diet and sex steroids, both involved in this molecular mechanism as they have been poorly addressed for this topic.

Revisiting the serotonin-aggression relation in humans: a meta-analysis

The inverse relation between serotonin and human aggression is often portrayed as "reliable," "strong," and "well established" despite decades of conflicting reports and widely recognized methodological limitations. In this systematic review and meta-analysis, we evaluate the evidence for and against the serotonin deficiency hypothesis of human aggression across 4 methods of assessing serotonin: (a) cerebrospinal fluid levels of 5-hydroxyindoleacetic acid (CSF 5-HIAA), (b) acute tryptophan depletion, (c) pharmacological challenge, and (d) endocrine challenge. Results across 175 independent samples and over 6,500 total participants were heterogeneous, but, in aggregate, revealed a small, inverse correlation between serotonin functioning and aggression, anger, and hostility (r = -.12). Pharmacological challenge studies had the largest mean weighted effect size (r = -.21), and CSF 5-HIAA studies had the smallest (r = -.06). Potential methodological and demographic moderators largely failed to account for variability in study outcomes. Notable exceptions included year of publication (effect sizes tended to diminish with time) and self- versus other-reported aggression (other-reported aggression was positively correlated to serotonin functioning). We discuss 4 possible explanations for the pattern of findings: unreliable measures, ambient correlational noise, an unidentified higher order interaction, and a selective serotonergic effect. Finally, we provide 4 recommendations for bringing much needed clarity to this important area of research: acknowledge contradictory findings and avoid selective reporting practices; focus on improving the reliability and validity of serotonin and aggression measures; test for interactions involving personality and/or environmental moderators; and revise the serotonin deficiency hypothesis to account for serotonin's functional complexity.

Modulation of central serotonin affects emotional information processing in impulsive aggressive personality disorder

BACKGROUND

The mechanistic model whereby serotonin affects impulsive aggression is not completely understood. The purpose of this study was to test the hypothesis that depletion of serotonin reserves by tryptophan depletion affects emotional information processing in susceptible individuals.

METHODS

The effect of tryptophan (vs placebo) depletion on processing of Ekman emotional faces was compared in impulsive aggressive personality disordered, male and female adults with normal controls. All subjects were free of psychotropic medications, medically healthy, nondepressed, and substance free. Additionally, subjective mood state and vital signs were monitored.

RESULTS

For emotion recognition, a significant interaction of Aggression × Drug × Sex (F(1, 31) = 7.687, P = 0.009) was found, with male normal controls but not impulsive aggressive males showing increased recognition of fear. For intensity ratings of emotional faces, a significant interaction was discovered of Drug × Group × Sex (F(1, 31) = 5.924, P = 0.021), with follow-up tests revealing that males with intermittent explosive disorder tended to increase intensity ratings of angry faces after tryptophan depletion. Additionally, tryptophan depletion was associated with increased heart rate in all subjects, and increased intensity of the subjective emotional state of "anger" in impulsive aggressive subjects.

CONCLUSIONS

Individuals with clinically relevant levels of impulsive aggression may be susceptible to effects of serotonergic depletion on emotional information processing, showing a tendency to exaggerate their impression of the intensity of angry expressions and to report an angry mood state after tryptophan depletion. This may reflect heightened sensitivity to the effects of serotonergic dysregulation, and suggests that what underlies impulsive aggression is either supersensitivity to serotonergic disturbances or susceptibility to fluctuations in central serotonergic availability.

From menarche to menopause: exploring the underlying biology of depression in women experiencing hormonal changes

Epidemiologic data consistently report an elevated prevalence of major depressive disorder (MDD) in women. This increase begins during adolescence and continues through the menopausal transition. Population-based clinical studies report an increase in the incidence of MDD during perimenopause compared to either the premenopausal or postmenopausal period. Evidence suggests that fluctuations and decline of hormonal levels are correlated with this observed increase in risk for MDD. A strong predictor of depression in the perimenopausal period is a previous history of MDD. However, recent studies revealed an increased risk of new onset depression in perimenopausal women without a history of MDD. Additionally, recent reports have indicated that the presence of vasomotor symptoms may be associated with an increased the risk for MDD. The objective of this paper is to review evidence that would support our hypothesis that neurotransmitter systems are affected by changes in hormonal status over the course of a woman's life, leading to increase vulnerability to perimenopausal depression. Relevant data from nonclinical experiments will be discussed in the context of observed clinical evidence of the risk for MDD before, during, and after the menopausal transition. A testable hypothesis will be proposed to advance our understanding of hormonal effects on mood.

Mood is indirectly related to serotonin, norepinephrine and dopamine levels in humans: a meta-analysis of monoamine depletion studies

Dysfunction in the monoamine systems of serotonin (5-HT), norepinephrine (NE) and dopamine (DA) may causally be related to major depressive disorder (MDD). Monoamine depletion studies investigate the direct effects of monoamines on mood. Acute tryptophan depletion (ATD) or para-chlorophenylalanine (PCPA) deplete 5-HT, acute phenylalanine/tyrosine depletion (APTD) or alpha-methyl-para-tyrosine (AMPT) deplete NE/DA. Available depletion studies found conflicting results in heterogeneous populations: healthy controls, patients with previous MDD in remission and patients suffering from MDD. The decrease in mood after 5-HT and NE/DA depletion in humans is reviewed and quantified. Systematic search of MEDLINE and EMBASE (1966-October 2006) and cross-references was carried out. Randomized studies applying ATD, PCPA, APTD or AMPT vs control depletion were included. Pooling of results by meta-analyses was stratified for studied population and design of the study (within or between subjects). Seventy-three ATD, 2 PCPA, 10 APTD and 8 AMPT studies were identified of which 45 ATD and 8 APTD studies could be meta-analyzed. 5-HT or NE/DA depletion did not decrease mood in healthy controls. 5-HT or NE/DA depletion slightly lowered mood in healthy controls with a family history of MDD. In drug-free patients with MDD in remission, a moderate mood decrease was found for ATD, without an effect of APTD. ATD induced relapse in patients with MDD in remission who used serotonergic antidepressants. In conclusion, monoamine depletion studies demonstrate decreased mood in subjects with a family history of MDD and in drug-free patients with MDD in remission, but do not decrease mood in healthy humans. Although depletion studies usefully investigate the etiological link of 5-HT and NE with MDD, they fail to demonstrate a causal relation. They presumably clarify a vulnerability trait to become depressed. Directions for further investigation of this vulnerability trait are proposed.

The relation of free plasma tryptophan to anger, hostility, and aggression in a nonpatient sample of adult men and women

BACKGROUND

Dysregulation of central nervous system serotonergic (5-HT) activity is implicated in behavioral states and psychological traits associated with depression and aggression, with some studies suggesting possible gender-related differences.

PURPOSE

This study examined the relation of free plasma tryptophan (TRP) to aggression and depression in a sample of 138 nonsmoking adults recruited from the general community. It was hypothesized that TRP would be associated with anger, hostility, and aggression.

METHODS

To minimize effects of diurnal variation and menstrual cycle, fasting blood samples were collected in the morning, and, for women, during the follicular phase of the menstrual cycle. Participants were administered questionnaires following blood draw. Plasma TRP was determined by high performance liquid chromatography.

RESULTS

In women, but not men, higher levels of TRP were associated with trait hostility, propensity for anger, a tendency to express anger outwardly, and an antagonistic interpersonal style. For men and women, greater severity of depressive symptoms, anger, and the verbal expression of anger were associated with higher TRP. These associations were independent of age, body mass index, fasting albumin, and race and ethnicity.

CONCLUSIONS

These data suggest that in women, but not men, higher plasma levels of TRP, the precursor to 5-HT, are associated with anger-hostility-aggression and that these associations are independent of various potential confounds. Implications of these observations to studies employing acute TRP depletion studies are discussed.

Acute tryptophan depletion. Part II: clinical effects and implications

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.

Monoamine depletion in psychiatric and healthy populations: review

A number of techniques temporarily lower the functioning of monoamines: acute tryptophan depletion (ATD), alpha-methyl-para-tyrosine (AMPT) and acute phenylalanine/tyrosine depletion (APTD). This paper reviews the results of monoamine depletion studies in humans for the period 1966 until December 2002. The evidence suggests that all three interventions are specific, in terms of their short-term effects on one or two neurotransmitter systems, rather than on brain protein metabolism in general. The AMPT procedure is somewhat less specific, affecting both the dopamine and norepinephrine systems. The behavioral effects of ATD and AMPT are remarkably similar. Neither procedure has an immediate effect on the symptoms of depressed patients; however, both induce transient depressive symptoms in some remitted depressed patients. The magnitude of the effects, response rate and quality of response are also comparable. APTD has not been studied in recovered major depressive patients. Despite the similarities, the effects are distinctive in that ATD affects a subgroup of recently remitted patients treated with serotonergic medications, whereas AMPT affects recently remitted patients treated with noradrenergic medications. The evidence also suggests that ATD and APTD affect different cognitive functions, in particular different memory systems. Few studies investigated cognitive effects of the procedures in patients. Patients who are in remission for longer may also be vulnerable to ATD and AMPT, but the relationship with prior treatment is much weaker. For these patients, individual vulnerability markers are the more important determinants of depressive response, making these techniques potentially useful models of vulnerability to depression.