Differential effects of 5-HTTLPR genotypes on mood, memory, and attention bias following acute tryptophan depletion and stress exposure

Alteration of the α5 GABA receptor and 5HTT lead to cognitive deficits associated with major depressive-like behaviors in a 14-day combined stress rat model

INTRODUCTION

Current models used to study the pathophysiology of major depressive disorder (MDD) are laborious and time consuming. This study examined the effect of a 14-day combined stress model (CS; corticosterone injection and restraint stress) in male Sprague-Dawley rats and also compare the effect of CS versus 28-day corticosterone treatment on depressive-like behaviour and cognitive deficits.

MATERIEL AND METHODS

Depressive-like behaviours and cognitive deficits were assessed in the forced swim test (FST), sucrose preference (SPT), Morris water maze (MWM) and novel object recognition (NORT) tests. Real-time PCR and ELISA were respectively used to detect expression of the serotonin transporter (5-HTT), serotonin 1 A receptor (5-HT1A), α5 GABAA receptor, and the concentrations of corticosterone (plasma), GABA and acetylcholinesterase (AChE) in the hippocampus and Prefrontal cortex (PFC).Results CS group showed increased immobility time in the FST, time to reach the MWM platform, higher corticosterone level, and increased expressions of hippocampal and PFC 5-HT1A and α5 GABAA receptors, and AChE compared to their control groups. In contrast, reductions in SPT ratio, discrimination index in NORT, time in target quadrant, and hippocampal 5-HTT expression was noted relative to their control group. Compared to the 28-day corticosterone only group, PFC 5-HT1A, Hippocampal 5-HTT were reduced, while PFC 5-HTT, Hippocampal α5 GABAA receptors, and AChE concentrations were higher in the CS group.

CONCLUSION

Our CS model induced depressive-like behaviour with early cognitive deficits in rats affecting both hippocampus and PFC. The CS model may be useful in investigating new and comprehensive treatment strategies for MDD.

Genetic risk of depression is different in subgroups of dietary ratio of tryptophan to large neutral amino acids

Manipulation of intake of serotonin precursor tryptophan has been exploited to rapidly induce and alleviate depression symptoms. While studies show that this latter effect is dependent on genetic vulnerability to depression, the effect of habitual tryptophan intake in the context of predisposing genetic factors has not been explored. Our aim was to investigate the effect of habitual tryptophan intake on mood symptoms and to determine the effect of risk variants on depression in those with high and low tryptophan intake in the whole genome and specifically in serotonin and kynurenine pathways. 63,277 individuals in the UK Biobank with data on depressive symptoms and tryptophan intake were included. We compared two subpopulations defined by their habitual diet of a low versus a high ratio of tryptophan to other large amino acids (TLR). A modest protective effect of high dietary TLR against depression was found. NPBWR1 among serotonin genes and POLI in kynurenine pathway genes were significantly associated with depression in the low but not in the high TLR group. Pathway-level analyses identified significant associations for both serotonin and kynurenine pathways only in the low TLR group. In addition, significant association was found in the low TLR group between depressive symptoms and biological process related to adult neurogenesis. Our findings demonstrate a markedly distinct genetic risk profile for depression in groups with low and high dietary TLR, with association with serotonin and kynurenine pathway variants only in case of habitual food intake leading to low TLR. Our results confirm the relevance of the serotonin hypothesis in understanding the neurobiological background of depression and highlight the importance of understanding its differential role in the context of environmental variables such as complexity of diet in influencing mental health, pointing towards emerging possibilities of personalised prevention and intervention in mood disorders in those who are genetically vulnerable.

The serotonin transporter gene variants modulate acute stress-induced hippocampus and dorsomedial prefrontal cortex activity during memory retrieval

The short (s) allele of a polymorphism in the promoter region of the serotonin transporter gene (5-HTTLPR) is related to reduced serotonin transporter efficiency and an increased vulnerability to stress and mental disorders. In the present study, we investigated how 5-HTTLPR impacts on memory retrieval under stress and related neural activity by reanalyzing a small genetic neuroimaging data set. Twenty-seven healthy male volunteers participated in both the Trier Social Stress Test (TSST) and a respective control procedure and then their brain activity was measured with functional MRI (fMRI) while they performed an emotional-face-recognition task. Sixteen participants were carriers of the short allele (ss/sl carriers) and 11 were homozygous for the long allele (ll carriers). Genotype groups were compared with respect to stress-related physiological changes, memory performance, and brain activity. No significant genotype-dependent effects on memory performance or cortisol levels were found. The ss/sl carriers showed significantly higher systolic and diastolic blood pressure than the ll carriers, independent of stress. The ss/sl carriers reported stronger stress-induced nervous mood than the ll carriers. Our fMRI data revealed that the ss/sl carriers showed significantly weaker left hippocampus activation and stronger dorsomedial prefrontal cortex (dmPFC) deactivation when retrieving memories under stress as compared with the ll carriers. Subsequent analyses revealed that the distinct hippocampal activation pattern in both genotypes was associated with stress-induced cortisol elevation, while the distinct dmPFC activation pattern in both genotypes was associated with stress-induced changes in reaction times. Our results thus add new evidence that serotonin signaling modulates neural activity in the hippocampus and dmPFC during memory retrieval under acute psychosocial stress.

Effects of 5-HTTLPR genotype and cognitive rumination on long-term cortisol reactivity measured in human hair

Ample experimental and associative studies have shown that carrying two short (S) alleles of the serotonin transporter gene (5-HTTLPR) contributes to an increased vulnerability for stress and related affective disorders. Recent findings indicate that this relationship might become even more profound when also possessing a negative ruminative (stress-related) thinking style. However, previous studies on the relationship among 5-HTTLPR, stress, and stress-responsiveness almost exclusively measured salivary cortisol concentrations during exposure to a single acute (laboratory) stressor. Measuring cortisol concentrations over longer periods of time might better reflect (chronic) Gene by biological (HPA) stress responsiveness associations. In recent years, the strategy to assess hair cortisol concentration (HCC) has been established as a more reliable marker for chronic HPA activations. The current study explored associations between 3-months accumulated HCC and the tendency to ruminate about negative events in 27 S/S and 27 L/L 5-HTTLPR-carriers (screened from a large n = 827 DNA database). Hierarchical regression (including moderation) analyses revealed clear significant interactions between Genotype and Rumination (p < 0.01, f²=0.26); indicating greatest accumulation of HCC in high ruminating S/S-allele carriers. These findings implicate that the combined possession of a genetic (S-allele 5-HTTLPR) and cognitive (Rumination) stress-vulnerability might meaningfully increases long-term stress responsiveness; most likely due to increased daily (chronic) stress experiences. Lay summary   The current study investigated whether the combined possession of a biological (genetic) and cognitive (negative thinking pattern) stress vulnerability may lead to a greater vulnerability to experience daily stress. This hypothesis was confirmed as a higher accumulation of the cortisol stress hormone was found over the past 3 months in scalp hair of participants that carried both vulnerability factors in combination.

Intake of tryptophan-enriched whey protein acutely enhances recall of positive loaded words in patients with multiple sclerosis

BACKGROUND & AIMS

Multiple sclerosis (MS) has physiological and/or immunological characteristics that diminish serotonin metabolism, a neurotransmitter associated with affective and cognitive functions. The aim was examine the acute and dose-dependent effects of a dietary tryptophan (TRP) enrichment on affective and cognitive functions in MS patients. We hypothesized that increased dietary availability of the amino acid TRP enhances serotonin concentrations and improves neuropsychological functions.

METHODS

In a double-blind, placebo-controlled, crossover study, MS patients with (n = 15) and without (n = 17) depressed mood ingested a whey protein mixture with 4 different amounts of TRP. Mood states, total plasma TRP and plasma TRP/ΣLNAA ratio were measured during each test session and cognitive tasks were conducted three hours after dietary intake.

RESULTS

A fast, transient and dose-dependent increase of total plasma TRP and TRP/ΣLNAA ratio was found. Ratings of negative mood decreased over time, independent of the TRP dose. Relative to whey-only, immediate word recall and delayed recognition improved after ingestion of the lowest added TRP dose and was mainly due to better recollection for positive loaded words. Executive functions were not affected by a difference in TRP availability.

CONCLUSIONS

A moderate addition of TRP to whey protein enhances memory processes without improving the mood state in MS. ccmo-registration number is NL32316.096.10.

Evaluation of acute tryptophan depletion and sham depletion with a gelatin-based collagen peptide protein mixture

Acute Tryptophan Depletion (ATD) is a dietary method used to modulate central 5-HT to study the effects of temporarily reduced 5-HT synthesis. The aim of this study is to evaluate a novel method of ATD using a gelatin-based collagen peptide (CP) mixture. We administered CP-Trp or CP+Trp mixtures to 29 healthy volunteers; 13 from a randomized, double-blinded crossover study and sixteen from a randomized, double-blinded study run in our laboratory. Plasma amino acids, mood, side effects, cortisol concentrations, mean arterial blood pressure and heart rate were measured at multiple time-points. Repeated measures analysis of variance and Wilcoxon or Mann-Whitney U non-parametric tests were used to analyze the effects of intervention. Intake of the CP-Trp mixture efficiently reduced plasma Trp; however, the CP+Trp mixture induced a large significant increase in plasma Trp. No other significant effects of CP-Trp compared to CP+Trp were observed. The transient increase in plasma Trp after CP+Trp may impair comparison to the CP-Trp and we therefore recommend in future studies to use a smaller dose of Trp supplement to the CP mixture.

Changes in serotonin transporter (5-HTT) gene expression in peripheral blood cells after MDMA intake

RATIONALE

3,4-Methylenedioxymethamphetamine (MDMA, ecstasy) is an amphetamine derivative abused worldwide. Although data report that relatively high doses of MDMA deplete serotonin (5-HT) content and decrease the availability of serotonin transporters (5-HTT), there is no available evidence as to the adaptive mechanisms taking place in 5-HTT gene expression following MDMA intake in humans.

OBJECTIVE

To evaluate the pharmacological effects of MDMA on 5-HTT gene expression, using peripheral mononuclear cells as a biomarker of the central nervous system, and study whether an association exists between 5-HTT gene expression and psychobiological scores.

METHODS

A randomized, double-blind, controlled trial was conducted in 18 (nine women) healthy recreational MDMA users. Subjects were genotyped for 5-HTT linked polymorphism region (5-HTTLPR). MDMA 75 mg or placebo was administered; Profile of Mood States (POMS) and 5-HTT gene expression measures were performed at baseline, 90, and 165 min post administration. POMS scores were correlated with changes in gene expression.

RESULTS

The administration of 75 mg MDMA induced a significant twofold increase in 5-HTT gene expression after 165 min of drug administration. Significant associations were found between gene expression and POMS scores after MDMA administration. Results for each gender and 5-HTTLPR genotype are also reported.

CONCLUSIONS

Preliminary results show that MDMA causes substantial regulatory changes in the expression of serotonergic markers, likely being modulated by the 5-HTTLPR polymorphism. Changes in 5-HTT gene expression may play an important role in the regulation of mood state.

Serotonin transporter gene polymorphisms: Relation with platelet serotonin level in patients with primary Sjogren's syndrome

Significantly lower platelet serotonin level (PSL) in patients with primary Sjogren's syndrome (pSS) than in healthy controls has been reported in our prior studies. In the present report, we demonstrated effect of functional polymorphisms in the serotonin transporter gene (5-HTT) on PSL. We describe a group of 61 pSS patients and 100 healthy individuals subjects, who received PSL measurement in our prior study. All subjects were genotyped for the promoter 5-HTTLPR (L/S), rs25531 (A/G) and intronic 5-HTTVNTRin2 (l/s) polymorphisms. Overall, the presence of 5-HTTVNTRin2 ss genotype was associated with significantly lower PSL in pSS patients, not in healthy controls. Reduced PSL in pSS patients is in line with hypothesis of association between chronic immunoinflammation and 5-HT system dysregulation, identifying additional mechanisms such as altered 5-HT transport as potential genetic factor contributing to PSL depletion.

Sucrose preload reduces snacking after mild mental stress in healthy participants as a function of 5-hydroxytryptamine transporter gene promoter polymorphism

Brain serotonin (5-hydroxytryptamine, 5-HT) dysfunction is considered to promote food intake and eating-related disturbances, especially under stress or negative mood. Vulnerability for 5-HT disturbances is considered to be genetically determined, including a short (S) allele polymorphism in the serotonin transporter gene (5-HTTLPR) that is associated with lower serotonin function. Since 5-HT function may be slightly increased by carbohydrate consumption, S-allele 5-HTTLPR carriers in particular may benefit from a sugar-preload due to their enhanced 5-HT vulnerability. The aim of the current study was to investigate whether a sugar-containing preload may reduce appetite and energy intake after exposure to stress to induce negative mood, depending on genetic 5-HT vulnerability. From a population of 771 healthy young male and female genotyped college students 31 S/S carriers (8 males, 23 females) and 26 long allele (L/L) carriers (9 males, 17 females) (mean ± S.D. 22 ± 1.6 years; body mass index, BMI, 18-33 kg/m(2)) were monitored for changes in appetite and snacking behavior after stress exposure. Results revealed an increased energy intake after mild mental stress (negative mood) mainly for high-fat sweet foods, which was significantly greater in S/S carriers, and only in these genotypes this intake was significantly reduced by a sucrose-containing preload. Although alternative explanations are possible, it is suggested that S/S participants may have enhanced brain (hypothalamic) 5-HT responsiveness to food that makes them more susceptible to the beneficial satiation effects of a sucrose-preload as well as to the negative effects of mild mental stress on weight gain.

Bright ambient light conditions reduce the effect of tryptophan depletion in healthy females

INTRODUCTION

Tryptophan depletion (TD) is an established method to influence the serotonergic system and mood. The purpose of this study was to examine the effect of TD under different ambient light conditions, measured through serotonin-associated plasma levels and a visual analog scale (VAS), on healthy females.

METHODS

Thirty-eight healthy female s-allele carriers of the serotonin transporter promoter gene (5-HTTLPR) were administered a TD under dim light conditions (75 lx). A sub-group of 8 participants repeated the procedure randomized in two additional light conditions (585 lx and 1530 lx respectively). Prior to, and 5h following administration of TD, various variables (serotonin-associated plasma levels, VAS) were measured. Due to not normal distributed data, non-parametric statistical tests were used.

RESULTS

Overall analysis showed a significant mood lowering effect of TD. Moreover, TD decreased all measured serotonin-associated plasma levels significantly. Significant differences in varying light conditions were found for the VAS and plasma tryptophan, with the greatest effect of TD in the 75 lx condition.

CONCLUSION

Results of our study showed an influence of even slight differences in ambient light intensity on the effect of TD concerning mood as well as on the serotonergic system.

Food-derived serotonergic modulators: effects on mood and cognition

The most frequently described drugs in the treatment of mood disorders are selective serotonin reuptake and monoamine oxidase (MAO) inhibitors, enhancing serotonin levels in the brain. However, side-effects have been reported for these drugs. Because serotonin levels in the brain are dependent on the availability of the food-derived precursor tryptophan, foods such as chicken, soyabeans, cereals, tuna, nuts and bananas may serve as an alternative to improve mood and cognition. Here we discuss the effects of high- or low-tryptophan-containing food, as well as plant extracts with a modest monoamine reuptake and MAO-A inhibition functional profile, on mood and cognition in healthy and vulnerable human subjects and rodents. Together the studies suggest that there is an inverted U-shaped curve for plasma tryptophan levels, with low and too high tryptophan levels impairing cognition, and moderate to high tryptophan levels improving cognition. This relationship is found for both healthy and vulnerable subjects. Whereas this relationship may also exist for mood, the inverted U-shaped curve for plasma tryptophan levels and mood may be based on different tryptophan concentrations in healthyv.vulnerable individuals. Animal studies are emerging and allow further understanding of effects and the mode of action of food-derived serotonergic components on mood, cognition and mechanisms. Ultimately, insight into the concentrations of tryptophan and other serotonergic components in food having beneficial effects on mood and cognition in healthy, but particularly vulnerable, subjects may support well-being in our highly demanding society.

Epistasis between 5-HTTLPR and ADRA2B polymorphisms influences attentional bias for emotional information in healthy volunteers

Individual differences in emotional processing are likely to contribute to vulnerability and resilience to emotional disorders such as depression and anxiety. Genetic variation is known to contribute to these differences but they remain incompletely understood. The serotonin transporter (5-HTTLPR) and α2B-adrenergic autoreceptor (ADRA2B) insertion/deletion polymorphisms impact on two separate but interacting monaminergic signalling mechanisms that have been implicated in both emotional processing and emotional disorders. Recent studies suggest that the 5-HTTLPR s allele is associated with a negative attentional bias and an increased risk of emotional disorders. However, such complex behavioural traits are likely to exhibit polygenicity, including epistasis. This study examined the contribution of the 5-HTTLPR and ADRA2B insertion/deletion polymorphisms to attentional biases for aversive information in 94 healthy male volunteers and found evidence of a significant epistatic effect (p<0.001). Specifically, in the presence of the 5-HTTLPR s allele, the attentional bias for aversive information was attenuated by possession of the ADRA2B deletion variant whereas in the absence of the s allele, the bias was enhanced. These data identify a cognitive mechanism linking genotype-dependent serotonergic and noradrenergic signalling that is likely to have implications for the development of cognitive markers for depression/anxiety as well as therapeutic drug effects and personalized approaches to treatment.

Alterations in grooming activity and syntax in heterozygous SERT and BDNF knockout mice: the utility of behavior-recognition tools to characterize mutant mouse phenotypes

Serotonin transporter (SERT) and brain-derived neurotrophic factor (BDNF) are key modulators of molecular signaling, cognition and behavior. Although SERT and BDNF mutant mouse phenotypes have been extensively characterized, little is known about their self-grooming behavior. Grooming represents an important behavioral domain sensitive to environmental stimuli and is increasingly used as a model for repetitive behavioral syndromes, such as autism and attention deficit/hyperactivity disorder. The present study used heterozygous ((+/-)) SERT and BDNF male mutant mice on a C57BL/6J background and assessed their spontaneous self-grooming behavior applying both manual and automated techniques. Overall, SERT(+/-) mice displayed a general increase in grooming behavior, as indicated by more grooming bouts and more transitions between specific grooming stages. SERT(+/-) mice also aborted more grooming bouts, but showed generally unaltered activity levels in the observation chamber. In contrast, BDNF(+/-) mice displayed a global reduction in grooming activity, with fewer bouts and transitions between specific grooming stages, altered grooming syntax, as well as hypolocomotion and increased turning behavior. Finally, grooming data collected by manual and automated methods (HomeCageScan) significantly correlated in our experiments, confirming the utility of automated high-throughput quantification of grooming behaviors in various genetic mouse models with increased or decreased grooming phenotypes. Taken together, these findings indicate that mouse self-grooming behavior is a reliable behavioral biomarker of genetic deficits in SERT and BDNF pathways, and can be reliably measured using automated behavior-recognition technology.

Variations in the promoter region of the serotonin transporter gene and biased attention for emotional information: a meta-analysis

BACKGROUND

Selective attention to negative information has been strongly implicated in the etiology and maintenance of anxiety and offered as a potential intermediate phenotype for anxiety disorders. Attention biases have been studied in relation to a polymorphism in the promoter region of the serotonin transporter gene (5-HTTLPR) offering equivocal findings. The present meta-analysis tested whether the extant published data support the notion that variation in the 5-HTTLPR genotype modulates selective attention to negative information.

METHODS

Eleven relevant samples from 10 published articles were identified through a systematic literature search (total n = 807). Relevant attention bias and 5-HTTLPR data were extracted based on specific coding rules, and Cohen's d effect size index was used to calculate all outcome measures. Publication bias was assessed using various methods.

RESULTS

Carriers of the low (SS, SL(G), L(G)L(G)) transmission efficacy genotype display attentional vigilance toward negatively valenced stimuli, a pattern not found in the intermediate (SL(A), L(A)L(G)) and high (L(A)L(A)) efficacy genotypes. This phenomenon emerges as of medium effect size.

CONCLUSIONS

The meta-analysis supports the notion that allele variants of the 5-HTTLPR are associated with selective attention to negative stimuli. More studies are needed to fully establish the consistency of this effect. Future studies applying systematic attention bias modification may shed further light on the role of 5-HTTLPR in the development of anxiety disorders and in the prediction of clinical response to attention bias modification treatments.

Genetic polymorphisms in the serotonergic system and symptom clusters of major depressive disorder

BACKGROUND

It has been suggested that the symptoms of major depressive disorder (MDD) are composed of some clusters, which are linked to distinct genetic mechanisms. The purpose of this study was to examine the associations of genetic polymorphisms in the serotonergic system with three factors of the Montgomery-Åsberg Depression Rating Scale (MADRS), i.e., dysphoria, retardation, and vegetative symptoms.

METHODS

The subjects were 132 Japanese patients of MDD. The genotypes of tryptophan hydroxylase 218A/C, serotonin transporter gene-linked polymorphic region (5HTTLPR), and 5HT2A receptor -1438G/A polymorphisms were determined by PCR methods. Statistical analyses were performed by the multiple regression analysis.

RESULTS

The A allele of 5HT2A polymorphism was associated with higher vegetative scores (p=0.001) and total MADRS scores (p=0.005), while the S allele of 5HTTLPR was related to higher dysphoric scores (p=0.012). The tryptophan hydroxylase genotype was not related to any factor scores or total MADRS scores.

LIMITATIONS

The sample size was relatively small, and the subjects were composed of Japanese only.

CONCLUSION

This study suggests that the genetic polymorphisms in 5HT2A receptor and serotonin transporter are linked to discrete symptom clusters of MDD.

Implication of serotonin-transporter (5-HTT) gene polymorphism in subjective memory complaints and mild cognitive impairment (MCI)

Serotonin-transporter-linked polymorphism (5-HTTLPR) is involved in neuropsychiatric diseases and recently the S-isoform has been correlated with a higher risk of developing emotion-induced retrograde amnesia. In order to better clarify the possible role of the 5-HTT S/L polymorphism and its effects on cognitive ability, especially on memory skills, we report here the distributions of the 5-HTT genetic variant and the Apolipoprotein E (ApoE) ɛ-4 allele and their association with neuropsychological measures in older adults reporting problems with everyday memory. Moreover, we verified the presence of a possible association between the S-allele with depression and the personal trait of neuroticism. Our results indicate an association between the 5-HTTLPR S-allele and the risk of developing MCI. No association was found in the other three groups. We found a positive dose-dependent association between the S-allele and the Rey-Osterrieth complex figure test (recall) score. Finally, our data did not find an association between the same allele and depression or neuroticism. This data, in our opinion shows a slight, non-established influence of 5-HTTLPR on memory skills exhibited in challenging memory tests but no influence on other extra-mnesic cognitive abilities.

Effects of acute psychosocial stress exposure on endocrine and affective reactivity in college students differing in the 5-HTTLPR genotype and trait neuroticism

Enhanced stress vulnerability has been implicated in the pathogenesis of affective disorders. Although both genetic (5-HTTLPR) and cognitive (neuroticism) factors are known to increase stress vulnerability, no experimental study has investigated the interaction between these two factors on psychobiological reactivity following acute stress exposure. This study used a balanced experimental design to examine the interaction between the 5-HTTLPR genotype and trait neuroticism in neuroendocrine and affective stress responses. From a large group of 771 students, 48 carriers of the short/short (S/S) allele and 48 carriers of the long/long (L/L) allele with the lowest and the highest neuroticism scores (77 females, 19 males; mean age ± SD: 20.6 ± 2 years) were selected and exposed to an acute psychosocial stressor. Mood was assessed before and after the stressor, and salivary cortisol concentrations were measured before and at 20, 30, and 60 min after stressor onset. Acute stress increased salivary cortisol concentration regardless of either 5-HTTLPR genotype or neuroticism, but it caused a less profound negative mood change in L/L compared to S/S-allele carriers with the lowest neuroticism scores. The 5-HTTLPR genotype influences affective reactivity to acute stress conditional upon neuroticism, improving resilience to acute stress in L/L-allele carriers if they do not already possess high cognitive-affective (neuroticism) vulnerability.

WITHDRAWN: Is acute tryptophan depletion a valid method to assess central serotonergic function?

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Cognitive effects of genetic variation in monoamine neurotransmitter systems: a population-based study of COMT, MAOA, and 5HTTLPR

Individual differences in cognitive function are highly heritable and most likely driven by multiple genes of small effect. Well-characterized common functional polymorphisms in the genes MAOA, COMT, and 5HTTLPR each have predictable effects on the availability of the monoamine neurotransmitters dopamine, noradrenaline, and serotonin. We hypothesized that 5HTTLPR genotype would show little association with prefrontal cognitive performance, but that COMT and MAOA would have interacting effects on cognition through their shared influence on prefrontal catecholamine availability. We assessed the individual and epistatic effects of functional polymorphisms in COMT, MAOA, and 5HTTLPR on children's prefrontal cognitive function in nearly 6,000 children from the population-based Avon Longitudinal Study of Parents and Children (ALSPAC). Neither MAOA nor 5HTTLPR polymorphisms showed significant effects on cognitive function. In boys but not girls, there was a modest but statistically significant interaction between MAOA and COMT genotypes such that increased prefrontal catecholamine availability was associated with better working memory. These results suggest that assessment of multiple genes within functionally related systems may improve our understanding of the genetic basis of cognition.

Differential effects of 5-HTTLPR genotypes on inhibition of negative emotional information following acute stress exposure and tryptophan challenge

Previous data suggest that a polymorphism at the serotonin (5-HT) transporter gene (5-HTTLPR) may influence stress resilience and stress-related depression symptoms due to interactions between brain 5-HT dysfunction and stress exposure. Although attentional bias for emotional information has been reliably observed in depression, the interaction between 5-HT transporter-linked promoter region (5-HTTLPR), brain 5-HT vulnerability, and acute stress on affective information processing has not yet been investigated. This study examines the effects of tryptophan (TRP) augmentation (indicating 5-HT manipulation) on inhibition of negative emotional information under stress in mainly female S'/S'- vs L'/L'-allele carriers. A total of 15 female homozygotic short-allele 5-HTTLPR (S'/S'=S/S, S/L(G), L(G)/L(G)) and 13 female homozygotic long-allele 5-HTTLPR (L'/L'=L(A)/L(A)) subjects were tested for mood and inhibition of emotional information in a double-blind, placebo-controlled design before and after stress exposure following TRP manipulation. Stress exposure significantly impaired inhibition of negative affective information only in S'/S' carriers, whereas L'/L' carriers even showed increased inhibition of negative information. The S'/S' allele 5-HTTLPR genotype increases cognitive-attentional bias for negative emotional information under acute stress. As this bias is an important component of depression, this may be a mediating mechanism making S'/S'-allele carriers more vulnerability for stress-induced depression symptoms. Moreover, current data suggest that L'/L'-allele genotypes are more resilient, even increasing cognitive emotional (inhibitory) control after stress.

Serotonin transporter gene polymorphisms and treatment-resistant depression

Major Depression Disorder (MDD) is a serious mental illness that is one of the most disabling diseases worldwide. In addition, approximately 15% of depression patients are defined treatment-resistant (TRD). Preclinical and genetic studies show that serotonin modulation dysfunction exists in patients with TRD. Some polymorphisms in the promoter region of the serotonin transporter gene (SLC6A4) are likely to be involved in the pathogenesis/treatment of MDD; however, no data are available concerning TRD. Therefore, in order to investigate the possible influence of SLC6A4 polymorphisms on the risk of TRD, we genotyped 310 DSM-IV MDD treatment-resistant patients and 284 healthy volunteers. We analysed the most studied polymorphism 5-HTTLPR (L/S) and a single nucleotide substitution, rs25531 (A/G), in relation to different functional haplotype combinations. However the correct mapping of rs25531 is still debated whether it is within or outside the insertion. Our sequencing analysis showed that rs25531 is immediately outside of the 5-HTTLPR segment. Differences in 5-HTTLPR allele (p=0.04) and in L allele carriers (p<0.05) were observed between the two groups. Concerning the estimated haplotype analyses, L(A)L(A) homozygote haplotype was more represented among the control subjects (p=0.01, OR=0.64 95%CI: 0.45-0.91). In conclusion, this study reports a protective effect of the L(A)L(A) haplotype on TRD, supporting the hypothesis that lower serotonin transporter transcription alleles are correlated to a common resistant depression mechanism.

Serotonin, genetic variability, behaviour, and psychiatric disorders--a review

Brain monoamines, and serotonin in particular, have repeatedly been shown to be linked to different psychiatric conditions such as depression, anxiety, antisocial behaviour, and dependence. Many studies have implicated genetic variability in the genes encoding monoamine oxidase A (MAOA) and the serotonin transporter (5HTT) in modulating susceptibility to these conditions. Paradoxically, the risk variants of these genes have been shown, in vitro, to increase levels of serotonin, although many of the conditions are associated with decreased levels of serotonin. Furthermore, in adult humans, and monkeys with orthologous genetic polymorphisms, there is no observable correlation between these functional genetic variants and the amount or activity of the corresponding proteins in the brain. These seemingly contradictory data might be explained if the association between serotonin and these behavioural and psychiatric conditions were mainly a consequence of events taking place during foetal and neonatal brain development. In this review we explore, based on recent research, the hypothesis that the dual role of serotonin as a neurotransmitter and a neurotrophic factor has a significant impact on behaviour and risk for neuropsychiatric disorders through altered development of limbic neurocircuitry involved in emotional processing, and development of the serotonergic neurons, during early brain development.

AGN-2979, an inhibitor of tryptophan hydroxylase activation, does not affect serotonin synthesis in Flinders Sensitive Line rats, a rat model of depression, but produces a significant effect in Flinders Resistant Line rats

The neurotransmitter, serotonin, is involved in several brain functions, including both normal, physiological functions, and pathophysiological functions. Alterations in any of the normal parameters of serotonergic neurotransmission can produce several different psychiatric disorders, including major depression. In many instances, brain neurochemical variables are not able to be studied properly in humans, thus making the use of good animal models extremely valuable. One of these animal models is the Flinders Sensitive Line (FSL) of rats, which has face, predictive and constructive validities in relation to human depression. The objective of this study was to quantify the effect of the tryptophan hydroxylase (TPH) activation inhibitor, AGN-2979, on the FSL rats (rats with depression-like behaviour), and compare it to the effect on the Flinders Resistant Line (FRL) of rats used as the control rats. The effect was evaluated by measuring changes in regional serotonin synthesis in the vehicle treated rats (FSL-VEH and FRL-VEH) relative to those measured in the AGN-2979 treated rats (FSL-AGN and FRL-AGN). Regional serotonin synthesis was measured autoradiographically in more than 30 brain regions. The measurements were performed using alpha-[(14)C]methyl-l-tryptophan as the tracer. The results indicate that AGN-2979 did not produce a significant reduction of TPH activity in the AGN-2979 group relative to the vehicle group (a reduction would have been observed if there had been an activation of TPH by the experimental setup) in the FSL rats. On the other hand, there was a highly significant reduction of synthesis in the FRL rats treated by AGN-2979, relative to the vehicle group. Together, the results demonstrate that in the FSL rats, AGN-2979 does not affect serotonin synthesis. This suggests that there was no activation of TPH in the FSL rats during the experimental procedure, but such activation did occur in the FRL rats. Because of this finding, it could be hypothesized that TPH in the FSL rats cannot be easily activated. This may contribute to the development of depressive-like symptoms in the FSL rats ("depressed" rats), as they cannot easily modulate their need for elevated amounts of this neurotransmitter, and possibly other neurotransmitters. Further, because these rats represent a very good model of human depression, one can hypothesize that humans who do not have readily activated TPH may be more prone to develop depression.