The effects of acute tryptophan depletion and serotonin transporter polymorphism on emotional processing in memory and attention

Impact of psychotropic medications on cognition among older adults: a systematic review

OBJECTIVES

The aim of this systematic review is to examine the cognitive impact of psychotropic medications including benzodiazepines, antidepressants, mood stabilizers, antipsychotics, or a combination of these drugs on older adults.

DESIGN

Systematic review.

SETTING

We searched Medline, PsycINFO, and Embase through the Ovid platform, CINAHL through EBSCO, and Web of Science.

PARTICIPANTS AND INTERVENTIONS

Randomized control trials (RCTs) and cohort studies that used a validated scale to measure cognition with a follow-up period of at least six months were included.

MEASUREMENT

The primary outcome of interest was cognitive change associated with psychotropic medication use.

RESULTS

A total of 7551 articles were identified from the primary electronic literature search across the five databases after eliminating duplicates. Based on full-text analysis, 27 articles (two RCTs, 25 cohorts) met the inclusion criteria. Of these, nine each examined the impact of benzodiazepines and antidepressants, five examined psychotropic combinations, three on antipsychotic drugs, and one on the effects of mood stabilizers.

CONCLUSIONS

This is the first systematic review to examine the cognitive impact of multiple psychotropic drug classes in older adults over an extended follow-up period (six months or more) using robust sample sizes, drug-free control groups, and validated cognitive instruments. We found evidence to indicate cognitive decline with the cumulative use of benzodiazepines and the use of antidepressants, especially those with anticholinergic properties among older adults without cognitive impairment at baseline. Further, the use of antipsychotics and psychotropic combinations is also associated with cognitive decline in older adults.

Brain gain-Is the cognitive performance of domestic hens affected by a functional polymorphism in the serotonin transporter gene?

The serotonin transporter (5-HTT) plays an important role in regulating serotonergic transmission via removal of serotonin (5-HT) from synaptic clefts. Alterations in 5-HTT expression and subsequent 5-HT transmission have been found to be associated with changes in behaviour, such as fearfulness or activity, in humans and other vertebrates. In humans, alterations in 5-HTT expression have been suggested to be able to lead to better learning performance, with more fearful persons being better at learning. Similar effects of the variation in the 5-HTT on fearfulness have been found in chickens, and in this study, we investigated effects on learning. Therefore, we tested 52 adult laying hens, differing in their functional 5-HTT genotype (W/W, W/D and D/D) in an operant learning paradigm in three different phases (initial learning, reversal learning and extinction) and in a tonic immobility test for fearfulness. We found that the 5-HTT polymorphism affects the initial learning performance of laying hens, with homogeneous wild-type (W/W) hens being the slowest learners, and the most fearful birds. W/W hens, showed significantly more choices to solve the initial learning task (LME, p = 0.031) and had the highest latencies in a tonic immobility test (p = 0.039), indicating the highest fearfulness. Our results provide interesting first insights into the role of 5-HTT in chickens and its sensitive interaction with the environment. We further suggest that the 5-HTT gene can be an interesting target gene for future breeding strategies as well as for further experimental studies.

The role of serotonin in declarative memory: A systematic review of animal and human research

The serotonergic system is involved in diverse cognitive functions including memory. Of particular importance to daily life are declarative memories that contain information about personal experiences, general facts, and events. Several psychiatric or neurological diseases, such as depression, attention-deficit-hyperactivity disorder (ADHD), and dementia, show alterations in serotonergic signalling and attendant memory disorders. Nevertheless, understanding serotonergic neurotransmission and its influence on memory remained a challenge until today. In this systematic review, we summarize recent psychopharmacological studies in animals and humans from a psychological memory perspective, in consideration of task-specific requirements. This approach has the advantage that comparisons between serotonin (5-HT)-related neurochemical mechanisms and manipulations are each addressing specific mnemonic circuits. We conclude that applications of the same 5-HT-related treatments can differentially affect unrelated tasks of declarative memories. Moreover, the analysis of specific mnemonic phases (e.g., encoding vs. consolidation) reveals opposing impacts of increased or decreased 5-HT tones, with low 5-HT supporting spatial encoding but impairing the consolidation of objects and verbal memories. Promising targets for protein synthesis-dependent consolidation enhancements include 5-HT₄ receptor agonists and 5-HT₆ receptor antagonists, with the latter being of special interest for the treatment of age-related decline. Further implications are pointed out as base for the development of novel therapeutic targets for memory impairment of neuropsychiatric disorders.

Serotonergic sensitivity alleles moderate relations between attachment security at age three and socioemotional competence at age five

Children with higher socioemotional competence are more likely to build constructive relationships with others and experience more positive adjustment outcomes in later periods. Securely attached children are likely to develop better socioemotional competence, but genetic moderation of associations between attachment and later socioemotional competence has received less attention. Using structural equation modeling, this study analyzed data collected from 1,337 children (51% male) born from 1998 to 2000 in the Fragile Families and Child Wellbeing study. The results demonstrated that relations between attachment security at age 3 years and their social competence at age 5 years differed by two serotonin transporter variants (5-HTTLPR, STin2). Effect sizes of these interactions were larger than effect sizes of main effects and the benefit of having sensitive alleles was consistently supported. This implies that having more secure attachment in the early developmental period is advantageous especially for children with minor alleles who have greater environmental sensitivity.

Serotonergic Plasticity in the Dorsal Raphe Nucleus Characterizes Susceptibility and Resilience to Anhedonia

Chronic stress induces anhedonia in susceptible but not resilient individuals, a phenomenon observed in humans as well as animal models, but the molecular mechanisms underlying susceptibility and resilience are not well understood. We hypothesized that the serotonergic system, which is implicated in stress, reward, and antidepressant therapy, may play a role. We found that plasticity of the serotonergic system contributes to the differential vulnerability to stress displayed by susceptible and resilient animals. Stress-induced anhedonia was assessed in adult male rats using social defeat and intracranial self-stimulation, while changes in serotonergic phenotype were investigated using immunohistochemistry and in situ hybridization. Susceptible, but not resilient, rats displayed an increased number of neurons expressing the biosynthetic enzyme for serotonin, tryptophan-hydroxylase-2 (TPH2), in the ventral subnucleus of the dorsal raphe nucleus (DRv). Further, a decrease in the number of DRv glutamatergic (VGLUT3+) neurons was observed in all stressed rats. This neurotransmitter plasticity is activity-dependent, as was revealed by chemogenetic manipulation of the central amygdala, a stress-sensitive nucleus that forms a major input to the DR. Activation of amygdalar corticotropin-releasing hormone (CRH)+ neurons abolished the increase in DRv TPH2+ neurons and ameliorated stress-induced anhedonia in susceptible rats. These findings show that activation of amygdalar CRH+ neurons induces resilience, and suppresses the gain of serotonergic phenotype in the DRv that is characteristic of susceptible rats. This molecular signature of vulnerability to stress-induced anhedonia and the active nature of resilience could be targeted to develop new treatments for stress-related disorders like depression.SIGNIFICANCE STATEMENT Depression and other mental disorders can be induced by chronic or traumatic stressors. However, some individuals are resilient and do not develop depression in response to chronic stress. A complete picture of the molecular differences between susceptible and resilient individuals is necessary to understand how plasticity of limbic circuits is associated with the pathophysiology of stress-related disorders. Using a rodent model, our study identifies a novel molecular marker of susceptibility to stress-induced anhedonia, a core symptom of depression, and a means to modulate it. These findings will guide further investigation into cellular and circuit mechanisms of resilience, and the development of new treatments for depression.

Effects of Acute Tryptophan Depletion on Repetitive Behavior in Laying Hens

Repetitive pecking at the feather cover of other birds (FP) is one of the most important welfare problems in domestic birds. It is not only characterized by motor symptoms, but also by an innate vulnerability of the serotonergic system. Moreover, the serotonergic system influences cognitive function. Acute tryptophan depletion (ATD) is a widely used method for studying serotonergic function in mammals and has been recently validated in birds. However, a tryptophan-deficient amino acid mixture has never been tested on groups of birds to impact their social behavior, including repetitive feather pecking, nor has it been given to potentially impact their cognition and motor performance. One hundred and sixty White Leghorn laying hens consisting of two genetic lines divergently selected to perform high (H) or low (L) levels of FP, and an unselected control line (UC), were kept in 10 groups consisting of 4 H, 3 L, and 9 UC genotypes. In a counterbalanced order, half of the groups were first subjected to an ATD treatment, while the other half were first given a balanced control (BC) treatment, and vice versa, after which their feather pecking behavior was observed. The effect of ATD/BC on repetitive pecking, motor performance, and cognition was investigated in a 5-s delayed reward task in an operant chamber with 10 phenotypic feather peckers, 10 recipients of feather pecking, and 10 bystanders (who neither performed nor received feather pecks). ATD given to groups of birds induced gentle, repetitive feather pecking in all genotypes. Following ATD, phenotypic feather peckers performed more poorly during the delayed reward task, as seen by their higher number of repetitive, non-rewarded key, and non-key pecks in the operant chamber. In conclusion, ATD impacted the hens' social behavior by increasing the number of repetitive gentle feather pecks at conspecifics. Furthermore, feather peckers were more likely to peck while waiting for a reward after ATD, suggesting a role for the serotonergic system on cognition in these birds.

Allelic variation in dopamine D2 receptor gene is associated with attentional impulsiveness on the Barratt Impulsiveness Scale (BIS-11)

OBJECTIVES

Previous studies have postulated that noradrenergic and/or dopaminergic gene variations are likely to underlie individual differences in impulsiveness, however, few have shown this. The current study examined the relationship between catecholamine gene variants and self-reported impulsivity, as measured by the Barratt Impulsiveness Scale (Version 11; BIS-11) Methods: Six hundred and seventy-seven non-clinical adults completed the Barratt Impulsiveness Scale (BIS-11). DNA was analysed for a set of 142 single-nucleotide polymorphisms (SNPs) across 20 autosomal catecholamine genes. Association was tested using an additive regression model with permutation testing used to control for the influence of multiple comparison.

RESULTS

Analysis revealed an influence of rs4245146 of the dopamine D2 receptor (DRD2) gene on the BIS-11 attention first-order factor, such that self-reported attentional impulsiveness increased in an additive fashion with each copy of the T allele.

CONCLUSIONS

These findings provide preliminary evidence that allelic variation in DRD2 may influence impulsiveness by increasing the propensity for attentional lapses.

The interaction between 5-HTTLPR and stress exposure influences connectivity of the executive control and default mode brain networks

We recently reported that the serotonin transporter polymorphism 5-HTTLPR moderates the relation between stress exposure and attention-deficit/hyperactivity disorder (ADHD) severity. This gene-environment interaction (GxE) has been previously tied to the processing of emotional stimuli, which is increasingly recognized to be a key factor in ADHD-related impairment. The executive control and default mode brain networks play an important role in the regulation of emotion processing, and altered connectivity of these networks has also been associated with ADHD. We therefore investigated whether resting-state connectivity of either of these networks mediates the relation of 5-HTTLPR and stress exposure with ADHD severity. Resting-state functional magnetic resonance imaging, genetic, and stress exposure questionnaire data was available for 425 adolescents and young adults (average age 17.2 years). We found that 5-HTTLPR S-allele carriers showed a more negative relation between stress exposure and connectivity of the executive control network than L-allele homozygotes, specifically in the pre/postcentral gyrus, striatum, and frontal pole. In the default mode network, we found a positive association between the GxE and supramarginal gyrus connectivity. Connectivity of either network did not significantly mediate the effect of this GxE on ADHD. Opposite effects of stress exposure on connectivity in the executive and default mode networks may contribute to findings that stress exposure is associated with lowered cognitive control and heightened levels of rumination and worrying, for S-allele carriers but not L-allele homozygotes. When combined, these effects on connectivity of both networks may relate to the emotional problems seen in individuals with ADHD.

Gene-environment interaction of monoamine oxidase A in relation to antisocial behaviour: current and future directions

Since the pioneering finding of Caspi and co-workers in 2002 that exposure to childhood maltreatment predicted later antisocial behaviour (ASB) in male carriers of the low-activity MAOA-uVNTR allele, frequent replication studies have been published. Two meta-analyses, one in 2006 and the other in 2014, confirmed the original findings by Caspi and co-workers. In the present paper, we review the literature, note some methodological aspects of candidate gene–environment interaction (cG×E) studies and suggest some future directions. Our conclusions are as follows. (1) The direction of the effect in a cG×E model may differ according to the positive and negative environmental background of the population. (2) There is a predictor-intersection problem such that when measuring one type of maltreatment in a person, other kinds of maltreatment often co-occur. Other forms of abuse are implicitly considered in statistical models; therefore, it is difficult to draw conclusions about the effects of timing and the severity of different forms of stressful life events in relation to ASB. (3) There is also an outcome-intersection problem because of the major intersection of ASB and other forms of mental health problems. It is likely that the G×E with MAOA is related to a common unmeasured factor. (4) For the G×E model, in which the effect of the gene on the outcome variable is dependent on other predictor variables, theoretically, hypothesis-driven statistical modelling is needed.

Individual biological sensitivity to environmental influences: testing the differential susceptibility properties of the 5HTTLPR polymorphism in relation to depressive symptoms and delinquency in two adolescent general samples

The gene–environment interaction research field in psychiatry has traditionally been dominated by the diathesis–stress framework, where certain genotypes are assumed to confer increased risk for adverse outcomes in a stressful environment. In later years, theories of differential susceptibility, or biological sensitivity, suggest that candidate genes that interact with environmental events do not exclusively confer a risk for behavioural or psychiatric disorders but rather seem to alter the sensitivity to both positive and negative environmental influences. The present study investigates the susceptibility properties of the serotonin transporter-linked polymorphic region (5HTTLPR) in relation to depressive symptoms and delinquency in two separate adolescent community samples: n = 1457, collected in 2006; and n = 191, collected in 2001. Two-, three-, and four-way interactions between the 5HTTLPR, positive and negative family environment, and sex were found in relation to both depressive symptoms and delinquency. However, the susceptibility properties of the 5HTTLPR were distinctly less pronounced in relation to depressive symptoms. If the assumption that the 5HTTLPR induces differential susceptibility to both positive and negative environmental influences is correct, the previous failures to measure and control for positive environmental factors might be a possible explanation for former inconsistent findings within the research field.

Neurological and neuropsychological effects of low and moderate prenatal alcohol exposure

Several explanations for the diverse results in research on foetal alcohol spectrum disorders or alcohol-related neurodevelopmental disorder might be at hand: timing, amount and patterns of alcohol exposure, as well as complex epigenetic responses. The genetic background of the offspring and its interaction with other prenatal and post-natal environmental cues are likely also of importance. In the present report, key findings about the possible effects of low and moderate doses of maternal alcohol intake on the neuropsychological development of the offspring are reviewed and plausible mechanisms discussed. Special focus is put on the serotonergic system within developmental and gene-environment frameworks. The review also suggests guidelines for future studies and also summarizes some of to-be-answered questions of relevance to clinical practice. Contradictory findings and paucity of studies on the effects of exposure to low alcohol levels during foetal life for the offspring's neuropsychological development call for large prospective studies, as well as for studies including neuroimaging and multi-omics analyses to dissect the neurobiological underpinnings of alcohol exposure-related phenotypes and to identify biomarkers. Finally, it remains to be investigated whether any safe threshold of alcohol drinking during pregnancy can be identified.

Genetic analysis of impulsive personality traits: Examination of a priori candidates and genome-wide variation

Impulsive personality traits are heritable risk factors and putative endophenotypes for addiction and other psychiatric disorders involving disinhibition. This study examined the genetic basis of impulsive personality traits, defined as scores on the Barratt Impulsiveness Scale (BIS-11) and the UPPS-P Impulsive Behavior Scale (UPPS-P). In 983 healthy young adults of European ancestry, the study examined genetic variation in relation to a combined phenotype of seven subscales based on high phenotypic intercorrelations. The study first tested 14 a priori loci that have previously been associated impulsive personality traits or closely related constructs. Second, the study included an exploratory genome-wide scan (i.e., GWAS), acknowledging that only relatively large effects would be detectable in a sample size of ~ 1000. A priori SNP analyses revealed a significant association between the combined impulsivity phenotype and two SNPs within the 5-HT2a receptor gene (HTR2A; rs6313 and rs6311). Follow-up analyses suggested that the effects were specific to the Motor and Non-planning subscales on the BIS-11, and also that the two loci were in linkage disequilibrium. The GWAS yielded no statistically significant findings. This study further implicates loci within HTR2A with certain forms of self-reported impulsivity and identifies candidates for future investigation from the genome-wide analyses.

Effects of tryptophan depletion on selective serotonin reuptake inhibitor-remitted patients with obsessive compulsive disorder

BACKGROUND

Serotonergic antidepressants are first-line medication therapies for obsessive-compulsive disorder, however it is not known if synaptic serotonin availability is important for selective serotonin reuptake inhibitor efficacy. The present study tested the hypothesis that temporary reduction in central serotonin transmission, through acute tryptophan depletion, would result in an increase in anxiety in selective serotonin reuptake inhibitor-remitted obsessive-compulsive disorder patients.

METHODS

Eight patients (four males) with obsessive-compulsive disorder who showed sustained clinical improvement with selective serotonin reuptake inhibitor treatment underwent acute tryptophan depletion in a randomized, double-blind, placebo-controlled, within-subjects design, over two days one week apart. Five hours after consumption of the depleting/sham drink the participants performed a personalized obsessive-compulsive disorder symptom exposure task. Psychological responses were measured using the Spielberger State Anxiety Inventory, Yale-Brown Obsessive Compulsive Scale and Visual Analogue Scales.

RESULTS

Free plasma tryptophan to large neutral amino acid ratio decreased by 93% on the depletion day and decreased by 1% on the sham day, as anticipated. Psychological rating scores as measured by Visual Analogue Scale showed a significant decrease in perceived control and increase in interfering thoughts at the time of provocation on the depletion day but not on the sham day. A measure of convergent validity, namely Visual Analogue Scale Similar to past, was significantly higher at the time of provocation on both the depletion and sham days. Both the depletion and time of provocation scores for Visual Analogue Scale Anxiety, Spielberger State Anxiety Inventory, Yale-Brown Obsessive Compulsive Scale and blood pressure were not significant.

CONCLUSIONS

Acute tryptophan depletion caused a significant decrease in perceived control and increase in interfering thoughts at the time of provocation. Acute tryptophan depletion had no effect on the Spielberger State Anxiety Inventory or Visual Analogue Scale Anxiety measures, which suggests that the mechanism of action of selective serotonin reuptake inhibitors may be different to that seen in panic, social anxiety and post-traumatic stress disorder. Successful selective serotonin reuptake inhibitor treatment of obsessive-compulsive disorder may involve the ability of serotonin to switch habitual responding to goal-directed behaviour.

Involvement of the Serotonin Transporter Gene in Accurate Subcortical Speech Encoding

A flourishing line of evidence has highlighted the encoding of speech sounds in the subcortical auditory system as being shaped by acoustic, linguistic, and musical experience and training. And while the heritability of auditory speech as well as nonspeech processing has been suggested, the genetic determinants of subcortical speech processing have not yet been uncovered. Here, we postulated that the serotonin transporter-linked polymorphic region (5-HTTLPR), a common functional polymorphism located in the promoter region of the serotonin transporter gene (SLC6A4), is implicated in speech encoding in the human subcortical auditory pathway. Serotonin has been shown as essential for modulating the brain response to sound both cortically and subcortically, yet the genetic factors regulating this modulation regarding speech sounds have not been disclosed. We recorded the frequency following response, a biomarker of the neural tracking of speech sounds in the subcortical auditory pathway, and cortical evoked potentials in 58 participants elicited to the syllable /ba/, which was presented >2000 times. Participants with low serotonin transporter expression had higher signal-to-noise ratios as well as a higher pitch strength representation of the periodic part of the syllable than participants with medium to high expression, possibly by tuning synaptic activity to the stimulus features and hence a more efficient suppression of noise. These results imply the 5-HTTLPR in subcortical auditory speech encoding and add an important, genetically determined layer to the factors shaping the human subcortical response to speech sounds.

SIGNIFICANCE STATEMENT

The accurate encoding of speech sounds in the subcortical auditory nervous system is of paramount relevance for human communication, and it has been shown to be altered in different disorders of speech and auditory processing. Importantly, this encoding is plastic and can therefore be enhanced by language and music experience. Whether genetic factors play a role in speech encoding at the subcortical level remains unresolved. Here we show that a common polymorphism in the serotonin transporter gene relates to an accurate and robust neural tracking of speech stimuli in the subcortical auditory pathway. This indicates that serotonin transporter expression, eventually in combination with other polymorphisms, delimits the extent to which lifetime experience shapes the subcortical encoding of speech.

Association between the serotonin transporter gene polymorphism and verbal learning in older adults is moderated by gender

The S allele of the functional 5-HTTLPR polymorphism has previously been associated with reductions in memory function. Given the change in function of the serotonergic system in older adults, and the functional consequences of memory decline in this age group, further investigation into the impact of 5-HTTLPR in healthy older adults is required. This investigation examined the effect of 5-HTTLPR variants (S carriers versus L/L homozygotes) on verbal and visual episodic memory in 438 healthy older adults participating in the Tasmanian Healthy Brain Project (age range 50-79 years, M=60.35, s.d.=6.75). Direct effects of 5-HTTLPR on memory processes, in addition to indirect effects through interaction with age and gender, were assessed. Although no direct effects of 5-HTTLPR on memory processes were identified, our results indicated that gender significantly moderated the impact that 5-HTTLPR variants exerted on the relationship between age and verbal episodic memory function as assessed by the Rey Auditory Verbal Learning Test. No significant direct or indirect effects were identified in relation to visual memory performance. Overall, this investigation found evidence to suggest that 5-HTTLPR genotype affects the association of age and verbal episodic memory for males and females differently, with the predicted negative effect of S carriage present in males but not females. Such findings indicate a gender-dependent role for 5-HTTLPR in the verbal episodic memory system of healthy older adults.

Interactive effect of 5-HTTLPR genotype and age on sources of cortical rhythms in healthy women

This study was aimed to localize the effects of 5-HTTLPR (serotonin-transporter-linked polymorphic region) on the age differences of spontaneous EEG activity in women using neuroimaging analysis sLORETA (Standardized Low Resolution brain Electromagnetic Tomography). DNA samples extracted from cheek swabs and resting-state EEG recorded at 60 standard leads were collected from young (YW, N=86, 18-35years) and older (OW, N=45; 55-80years) healthy women. We have shown that advanced age was associated with increased posterior EEG desynchronization in S'/S'. S' (LG allele was grouped with S alleles owing to its functional equivalence and this group was labeled as S') genotype carriers denoted by decrease of delta - beta1 current source density, and to a lesser extent in L/L homozygotes denoted by decrease in delta activity. In heterozygotes OW, as compared with heterozygotes YW, higher source density estimates of beta1 in frontal and temporal cortex were observed. Age differences were more pronounced in the right hemisphere in S'/S' and L/L carriers and in the left hemisphere in heterozygotes. We also found that in OW, current source density estimates of theta, alpha1, alpha2, alpha3 and beta1 sources in the right occipital lobe were higher in S'/L than in S'/S' carriers. These results may have implications for understanding 5-HTT-dependent variation in the effect of aging on brain activity.

Interplay between stress response genes associated with attention-deficit hyperactivity disorder and brain volume

The glucocorticoid receptor plays a pivotal role in the brain's response to stress; a haplotype of functional polymorphisms in the NR3C1 gene encoding this receptor has been associated with attention-deficit hyperactivity disorder (ADHD). The serotonin transporter (5-HTT) gene polymorphism 5-HTTLPR is known to influence the relation between stress exposure and ADHD severity, which may be partly because of its reported effects on glucocorticoid levels. We therefore investigated if NR3C1 moderates the relation of stress exposure with ADHD severity and brain structure, and the potential role of 5-HTTLPR. Neuroimaging, genetic and stress exposure questionnaire data were available for 539 adolescents and young adults participating in the multicenter ADHD cohort study NeuroIMAGE (average age: 17.2 years). We estimated the effects of genetic variation in NR3C1 and 5-HTT, stress exposure and their interactions on ADHD symptom count and gray matter volume. We found that individuals carrying the ADHD risk haplotype of NR3C1 showed significantly more positive relation between stress exposure and ADHD severity than non-carriers. This gene-environment interaction was significantly stronger for 5-HTTLPR L-allele homozygotes than for S-allele carriers. These two- and three-way interactions were reflected in the gray matter volume of the cerebellum, parahippocampal gyrus, intracalcarine cortex and angular gyrus. Our findings illustrate how genetic variation in the stress response pathway may influence the effects of stress exposure on ADHD severity and brain structure. The reported interplay between NR3C1 and 5-HTT may further explain some of the heterogeneity between studies regarding the role of these genes and hypothalamic-pituitary-adrenal axis activity in ADHD.

Brain-Derived Neurotrophic Factor (Val66Met) and Serotonin Transporter (5-HTTLPR) Polymorphisms Modulate Plasticity in Inhibitory Control Performance Over Time but Independent of Inhibitory Control Training

Several studies reported training-induced improvements in executive function tasks and also observed transfer to untrained tasks. However, the results are mixed and there is a large interindividual variability within and across studies. Given that training-related performance changes would require modification, growth or differentiation at the cellular and synaptic level in the brain, research on critical moderators of brain plasticity potentially explaining such changes is needed. In the present study, a pre-post-follow-up design (N = 122) and a 3-weeks training of two response inhibition tasks (Go/NoGo and Stop-Signal) was employed and genetic variation (Val66Met) in the brain-derived neurotrophic factor (BDNF) promoting differentiation and activity-dependent synaptic plasticity was examined. Because Serotonin (5-HT) signaling and the interplay of BDNF and 5-HT are known to critically mediate brain plasticity, genetic variation in the 5-HTT gene-linked polymorphic region (5-HTTLPR) was also addressed. The overall results show that the kind of training (i.e., adaptive vs. non-adaptive) did not evoke genotype-dependent differences. However, in the Go/NoGo task, better inhibition performance (lower commission errors) were observed for BDNF Val/Val genotype carriers compared to Met-allele ones supporting similar findings from other cognitive tasks. Additionally, a gene-gene interaction suggests a more impulsive response pattern (faster responses accompanied by higher commission error rates) in homozygous l-allele carriers relative to those with the s-allele of 5-HTTLPR. This, however, is true only in the presence of the Met-allele of BDNF, while the Val/Val genotype seems to compensate for such non-adaptive responding. Intriguingly, similar results were obtained for the Stop-Signal task. Here, differences emerged at post-testing, while no differences were observed at T1. In sum, although no genotype-dependent differences between the relevant training groups emerged suggesting no changes in the trained inhibition function, the observed genotype-dependent performance changes from pre- to post measurement may reflect rapid learning or memory effects linked to BDNF and 5-HTTLPR. In line with ample evidence on BDNF and BDNF-5-HT system interactions to induce (rapid) plasticity especially in hippocampal regions and in response to environmental demands, the findings may reflect genotype-dependent differences in the acquisition and consolidation of task-relevant information, thereby facilitating a more adaptive responding to task-specific requirements.

5-HTTLPR, victimization and ecological executive function of adolescents

Executive function (EF) plays an important role in guiding peer relationship, school performance and behavior control. Children exposed to traumatic environments have been reported to perform poorer in EF tasks. We explored if the relationship between victimization and EF was dependent on the functional variation 5-HTTLPR in a non-clinical sample of adolescents. Data on demographics, victimization and daily life EF were collected from school students (Han Chinese, n=2125). All those reporting executive dysfunction (n=169), and classmate controls (n=208), were genotyped for the 5-HTTLPR. It was shown that the number of victimizations associated positively with executive dysfunction (ED). This association was particularly strong in those homozygous for the short allele of 5-HTTLPR, whilst a statistical 5-HTTLPR×victimization interaction on ED was found. Our findings suggest that adolescents with a genotype conferring a low 5-HTT activity are more vulnerable to a childhood adversity-associated ED in their daily life.

The Association Between Breastfeeding Exposure and Duration, Neuropsychological Deficits, and Psychopathic Personality Traits in Offspring: The Moderating Role of 5HTTLPR

A wealth of research has revealed that a shorter duration of breastfeeding during infancy can increase the risk of various maladaptive traits, including neuropsychological deficits. Despite the number of studies that have been conducted on the topic, few studies have explored whether the effects of breastfeeding on neuropsychological functioning and personality features persist into adulthood. Furthermore, very little research to date has examined whether this relationship is moderated by specific indicators of genetic risk. The current study examines the direct and interactive effects of breastfeeding experiences and the serotonin transporter polymorphism (5HTTLPR) on neuropsychological deficits and psychopathic personality traits. Using data from the National Longitudinal study of Adolescent Health, we find that no exposure to breastfeeding and a shorter duration of breastfeeding significantly increase the risk of exhibiting neuropsychological deficits during adolescence and early adulthood as well as psychopathic personality traits during adulthood. The results also reveal a number of gene × environment interactions between 5HTTLPR, breastfeeding exposure and breastfeeding duration in the prediction of neuropsychological deficits, but not in the prediction of psychopathic personality traits.

Hippocampal 5-HT1A Receptor and Spatial Learning and Memory

Spatial cognition is fundamental for survival in the topographically complex environments inhabited by humans and other animals. The hippocampus, which has a central role in spatial cognition, is characterized by high concentration of serotonin (5-hydroxytryptamine; 5-HT) receptor binding sites, particularly of the 1A receptor (5-HT1A) subtype. This review highlights converging evidence for the role of hippocampal 5-HT1A receptors in spatial learning and memory. We consider studies showing that activation or blockade of the 5-HT1A receptors using agonists or antagonists, respectively, lead to changes in spatial learning and memory. For example, pharmacological manipulation to induce 5-HT release, or to block 5-HT uptake, have indicated that increased extracellular 5-HT concentrations maintain or improve memory performance. In contrast, reduced levels of 5-HT have been shown to impair spatial memory. Furthermore, the lack of 5-HT1A receptor subtype in single gene knockout mice is specifically associated with spatial memory impairments. These findings, along with evidence from recent cognitive imaging studies using positron emission tomography (PET) with 5-HT1A receptor ligands, and studies of individual genetic variance in 5-HT1A receptor availability, strongly suggests that 5-HT, mediated by the 5-HT1A receptor subtype, plays a key role in spatial learning and memory.

Impact of 5-HTTLPR on hippocampal subregional activation in older adults

Studies have shown that a functional polymorphism of the serotonin transporter gene (5-HTTLPR) impacts performance on memory-related tasks and the hippocampal structures that subserve these tasks. The short (s) allele of 5-HTTLPR has been linked to greater susceptibility for impaired memory and smaller hippocampal volume compared to the long allele (l). However, previous studies have not examined the associations between 5-HTTLPR allele and activation in subregions of the hippocampus. In this study, we used functional magnetic resonance imaging (fMRI) to measure activation in hippocampal and temporal lobe subregions in 36 elderly non-clinical participants performing a face-name encoding and recognition task. Although there were no significant differences in task performance between s allele carriers and l homozygotes, right CA1 and right parahippocampal activation during recognition errors was significantly greater in individuals bearing the s allele. In an exploratory analysis, we determined that these effects were more pronounced in s allele carriers with the apolipoprotein ɛ4 allele. Our results suggest that older individuals with the s allele inefficiently allocate neural resources while making errors in recognizing face-name associations, which could negatively impact memory performance during more challenging tasks.

Interactive effects of citalopram and serotonin transporter genotype on neural correlates of response inhibition and attentional orienting

The brain's serotonergic (5-HT) system has been implicated in controlling impulsive behavior and attentional orienting and linked to impulse control and anxiety related disorders. However, interactions between genotypical variation and responses to serotonergic drugs impede both treatment efficacy and neuroscientific research. We examine behavioral and electrophysiological responses to acute intravenous administration of a selective serotonin reuptake inhibitor (SSRI) while controlling for major genetic differences regarding 5-HT transporter (5-HTT) genotypes. Out of a genotyped sample of healthy Caucasian subjects (n=878) two extreme-groups regarding 5-HTT genotypes were selected (n=32). A homozygous high-expressing group based on tri-allelic 5-HTTLPR and rs25532 (LAC/LAC=LL) was compared to homozygous S allele carriers (SS). Both groups were administered a low dose of citalopram (10mg) intravenously in a double blind crossover fashion and performed a novelty NoGo paradigm while high density EEG was recorded. Interactions between drug and genotype were seen on both behavioral and neurophysiological levels. Reaction slowing following inhibitory events was decreased by the administration of citalopram in the LL but not SS group. This was accompanied by decreases in the amplitude of the inhibitory N2 EEG component and the P3b in the LL group, which was not seen in the SS group. SS subjects showed an increase in P3a amplitudes following SSRI administration to any type of deviant stimulus possibly reflecting increased attentional capture. The acute SSRI response on inhibitory processes and attentional orienting interacts with genotypes regulating 5-HTT gene expression. SS subjects may show increased attentional side effects reflected in increases in P3a amplitudes which could contribute to treatment discontinuation. Inhibitory processes and their neural correlates are affected only in LL subjects. These findings may indicate an underlying mechanism that could relate genotypical differences to altered side effect profiles and drug responses and are compatible with a non-monotonic relationship between 5-HT levels and optimal functioning.

Aversive emotional interference impacts behavior and prefronto-striatal activity during increasing attentional control

Earlier studies have demonstrated that emotional stimulation modulates attentional processing during goal-directed behavior and related activity of a brain network including the inferior frontal gyrus (IFG) and the caudate nucleus. However, it is not clear how emotional interference modulates behavior and brain physiology during variation in attentional control, a relevant question for everyday life situations in which both emotional stimuli and cognitive load vary. The aim of this study was to investigate the impact of negative emotions on behavior and activity in IFG and caudate nucleus during increasing levels of attentional control. Twenty two healthy subjects underwent event-related functional magnetic resonance imaging while performing a task in which neutral or fearful facial expressions were displayed before stimuli eliciting increasing levels of attentional control processing. Results indicated slower reaction time (RT) and greater right IFG activity when fearful compared with neutral facial expressions preceded the low level of attentional control. On the other hand, fearful facial expressions preceding the intermediate level of attentional control elicited faster behavioral responses and greater activity in the right and left sides of the caudate. Finally, correlation analysis indicated a relationship between behavioral correlates of attentional control after emotional interference and right IFG activity. All together, these results suggest that the impact of negative emotions on attentional processing is differentially elicited at the behavioral and physiological levels as a function of cognitive load.

Serotonin versus catecholamine deficiency: behavioral and neural effects of experimental depletion in remitted depression

Despite immense efforts into development of new antidepressant drugs, the increases of serotoninergic and catecholaminergic neurotransmission have remained the two major pharmacodynamic principles of current drug treatments for depression. Consequently, psychopathological or biological markers that predict response to drugs that selectively increase serotonin and/or catecholamine neurotransmission hold the potential to optimize the prescriber's selection among currently available treatment options. The aim of this study was to elucidate the differential symptomatology and neurophysiology in response to reductions in serotonergic versus catecholaminergic neurotransmission in subjects at high risk of depression recurrence. Using identical neuroimaging procedures with [(18)F] fluorodeoxyglucose positron emission tomography after tryptophan depletion (TD) and catecholamine depletion (CD), subjects with remitted depression were compared with healthy controls in a double-blind, randomized, crossover design. Although TD induced significantly more depressed mood, sadness and hopelessness than CD, CD induced more inactivity, concentration difficulties, lassitude and somatic anxiety than TD. CD specifically increased glucose metabolism in the bilateral ventral striatum and decreased glucose metabolism in the bilateral orbitofrontal cortex, whereas TD specifically increased metabolism in the right prefrontal cortex and the posterior cingulate cortex. Although we found direct associations between changes in brain metabolism and induced depressive symptoms following CD, the relationship between neural activity and symptoms was less clear after TD. In conclusion, this study showed that serotonin and catecholamines have common and differential roles in the pathophysiology of depression.

Mood and cognition in healthy older European adults: the Zenith study

BACKGROUND

The study aim was to determine if state and trait intra-individual measures of everyday affect predict cognitive functioning in healthy older community dwelling European adults (n = 387), aged 55-87 years.

METHODS

Participants were recruited from centres in France, Italy and Northern Ireland. Trait level and variability in positive and negative affect (PA and NA) were assessed using self-administered PANAS scales, four times a day for four days. State mood was assessed by one PANAS scale prior to assessment of recognition memory, spatial working memory, reaction time and sustained attention using the CANTAB computerized test battery.

RESULTS

A series of hierarchical regression analyses were carried out, one for each measure of cognitive function as the dependent variable, and socio-demographic variables (age, sex and social class), state and trait mood measures as the predictors. State PA and NA were both predictive of spatial working memory prior to looking at the contribution of trait mood. Trait PA and its variability were predictive of sustained attention. In the final step of the regression analyses, trait PA variability predicted greater sustained attention, whereas state NA predicted fewer spatial working memory errors, accounting for a very small percentage of the variance (1-2%) in the respective tests.

CONCLUSION

Moods, by and large, have a small transient effect on cognition in this older sample.

The serotonin transporter linked polymorphic region and brain-derived neurotrophic factor valine to methionine at position 66 polymorphisms and maternal history of depression: associations with cognitive vulnerability to depression in childhood

Preliminary work indicates that cognitive vulnerability to depression may be associated with variants of the serotonin transporter promoter polymorphism (5-HTTLPR) and the valine to methionine at position 66 (val66met) polymorphism of the brain-derived neurotrophic factor (BDNF) gene; however, existing reports come from small samples. The present study sought to replicate and extend this research in a sample of 375 community-dwelling children and their parents. Following a negative mood induction, children completed a self-referent encoding task tapping memory for positive and negative self-descriptive traits. Consistent with previous work, we found that children with at least one short variant of the 5-HTTLPR had enhanced memory for negative self-descriptive traits. The BDNF val66met polymorphism had no main effect but was moderated by maternal depression, such that children with a BDNF methionine allele had a heightened memory for negative self-descriptive traits when mothers had experienced depression during children's lifetimes; in contrast, children with a methionine allele had low recall of negative traits when mothers had no depression history. The findings provide further support for the notion that the 5-HTTLPR is associated with cognitive markers of depression vulnerability and that the BDNF methionine allele moderates children's sensitivity to contextual factors.

Influences of COMT and 5-HTTLPR polymorphisms on cognitive flexibility in healthy women: inhibition of prepotent responses and memory updating

Understanding genetic factors that affect monoamine neurotransmitters flux in prefrontal cortex may help to further specify the complex neurobiological processes that underlie cognitive function and dysfunction in health and illness. The current study examined the associations between the polymorphisms of dopaminergic (COMT Met158Val) and serotoninergic (5-HTTLPR) genes and the sequential pattern of responses in a motor random generation task providing well-established indexes for executive functioning in a large sample of 255 healthy women. Participants homozygous for the Met allele of the COMT polymorphism showed impaired inhibition of prepotent responses, whereas individuals homozygous for the s-allele of the 5-HTTLPR showed a restricted ability to update information in working memory. Taken together the results indicate differentiated influences of dopaminergic and serotonergic genes on important and definite executive sub-processes related to cognitive flexibility.

Carriers of the COMT Met/Met allele have higher degrees of hypnotizability, provided that they have good attentional control: a case of gene-trait interaction

Genetic factors may explain part of the interindividual variability in hypnotizability. A new avenue that may provide more comprehensive understanding of the phenotypic effects of genetic variations is the study of gene-trait interaction. In this study, the authors investigate the relationship of the dopamine-related COMT and the serotonin-related 5-HTTLPR polymorphisms to hypnotizability by taking individual differences in executive attention into account. Homozygosity for the COMT Met allele, putatively linked to the capability or proneness to dissociate from reality, was associated with high hypnotizability only if paired with high-attention ability. The finding can be integrated into hypnosis theory and represents a case of gene-trait interaction suggesting that investigating the effects of a gene in the context of relevant psychological traits may further elucidate gene-brain-behavior relationships.

5-HTT deficiency affects neuroplasticity and increases stress sensitivity resulting in altered spatial learning performance in the Morris water maze but not in the Barnes maze

The purpose of this study was to evaluate whether spatial hippocampus-dependent learning is affected by the serotonergic system and stress. Therefore, 5-HTT knockout (-/-), heterozygous (+/-) and wildtype (+/+) mice were subjected to the Barnes maze (BM) and the Morris water maze (WM), the latter being discussed as more aversive. Additionally, immediate early gene (IEG) expression, hippocampal adult neurogenesis (aN), and blood plasma corticosterone were analyzed.

While the performance of 5-HTT-/- mice in the BM was undistinguishable from both other genotypes, they performed worse in the WM. However, in the course of the repeated WM trials 5-HTT-/- mice advanced to wildtype level. The experience of a single trial of either the WM or the BM resulted in increased plasma corticosterone levels in all genotypes. After several trials 5-HTT-/- mice exhibited higher corticosterone concentrations compared with both other genotypes in both tests. Corticosterone levels were highest in 5-HTT-/- mice tested in the WM indicating greater aversiveness of the WM and a greater stress sensitivity of 5-HTT deficient mice.

Quantitative immunohistochemistry in the hippocampus revealed increased cell counts positive for the IEG products cFos and Arc as well as for proliferation marker Ki67 and immature neuron marker NeuroD in 5-HTT-/- mice compared to 5-HTT+/+ mice, irrespective of the test. Most differences were found in the suprapyramidal blade of the dentate gyrus of the septal hippocampus. Ki67-immunohistochemistry revealed a genotype x environment interaction with 5-HTT genotype differences in naïve controls and WM experience exclusively yielding more Ki67-positive cells in 5-HTT+/+ mice. Moreover, in 5-HTT-/- mice we demonstrate that learning performance correlates with the extent of aN.

Overall, higher baseline IEG expression and increased an in the hippocampus of 5-HTT-/- mice together with increased stress sensitivity may constitute the neurobiological correlate of raised alertness, possibly impeding optimal learning performance in the more stressful WM.

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.

Triallelic relationships between the serotonin transporter polymorphism and cognition among healthy older adults

The biallelic serotonin transporter polymorphism (5-hydroxytryptamine transporter linked polymorphic region (5-HTTLPR)) is a common genetic sequence associated with serotonin transporter (5-hydroxytryptamine transporter (5-HTT)) expression, which is further modulated by a triallelic single-nucleotide polymorphism (rs25531). Recent studies using the biallelic 5-HTTLPR have identified a beneficial role of low 5-HTT expression on cognitive performance, although no studies have examined the impact of the triallelic 5-HTTLPR/rs25531 marker on cognitive performance among healthy older adults. In the present study, we addressed this issue in 84 healthy older adults genotyped for biallelic and triallelic variants of 5-HTT. Groups were created based on low, medium and high levels of expression, as indicated by the triallelic marker. Results indicated that individuals with low 5-HTT expression performed significantly better on a test of memory compared with individuals with medium 5-HTT expression. This suggests that possession of low-expressing genetic variants of 5-HTT is modestly associated with enhanced cognitive performance among healthy older adults.

Prenatal serotonin reuptake inhibitor (SRI) antidepressant exposure and serotonin transporter promoter genotype (SLC6A4) influence executive functions at 6 years of age

Prenatal exposure to serotonin reuptake inhibitor (SRI) antidepressants and maternal depression may affect prefrontal cognitive skills (executive functions; EFs) including self-control, working memory and cognitive flexibility. We examined long-term effects of prenatal SRI exposure on EFs to determine whether effects are moderated by maternal mood and/or genetic variations in SLC6A4 (a gene that codes for the serotonin transporter [5-HTT] central to the regulation of synaptic serotonin levels and behavior). Children who were exposed to SRIs prenatally (SRI-exposed N = 26) and non-exposed (N = 38) were studied at age 6 years (M = 6.3; SD = 0.5) using the Hearts & Flowers task (H&F) to assess EFs. Maternal mood was measured during pregnancy (3rd trimester) and when the child was age 6 years (Hamilton Depression Scale). Parent reports of child behavior were also obtained (MacArthur Health & Behavior Questionnaire). Parents of prenatally SRI-exposed children reported fewer child externalizing and inattentive (ADHD) behaviors. Generalized estimate equation modeling showed a significant 3-way interaction between prenatal SRI exposure, SLC6A4 variant, and maternal mood at the 6-year time-point on H&F accuracy. For prenatally SRI-exposed children, regardless of maternal mood, the H&F accuracy of children with reduced 5HTT expression (a short [S] allele) remained stable. Even with increasing maternal depressive symptoms (though all below clinical threshold), EFs of children with at least one short allele were comparable to children with the same genotype whose mothers reported few if any depressive symptoms—in this sense they showed resilience. Children with two long (L) alleles were more sensitive to context. When their mothers had few depressive symptoms, LL children showed extremely good EF performance—better than any other group. When their mothers reported more depressive symptoms, LL children's EF performance was worse than that of any other group. In the face of a mother with a more depressed mood, EFs were best preserved in children prenatally exposed to SRIs and with at least one short SLC6A4 allele. Yet, prenatally-exposed LL children hold out promise of possibly superior EF if their mother's mood remains euthymic or improves.

The role of the serotonergic and GABA system in translational approaches in drug discovery for anxiety disorders

There is ample evidence that genetic factors play an important role in anxiety disorders. In support, human genome-wide association studies have implicated several novel candidate genes. However, illumination of such genetic factors involved in anxiety disorders has not resulted in novel drugs over the past decades. A complicating factor is the heterogeneous classification of anxiety disorders in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR) and diverging operationalization of anxiety used in preclinical and clinical studies. Currently, there is an increasing focus on the gene × environment (G × E) interaction in anxiety as genes do not operate in isolation and environmental factors have been found to significantly contribute to the development of anxiety disorders in at-risk individuals. Nevertheless, extensive research on G × E mechanisms in anxiety has not resulted in major breakthroughs in drug discovery. Modification of individual genes in rodent models has enabled the specific study of anxiety in preclinical studies. In this context, two extensively studied neurotransmitters involved in anxiety are the gamma-aminobutyric acid (GABA) and 5-HT (5-hydroxytryptamine) system. In this review, we illustrate the complex interplay between genes and environment in anxiety processes by reviewing preclinical and clinical studies on the serotonin transporter (5-HTT), 5-HT1A receptor, 5-HT2 receptor, and GABAA receptor. Even though targets from the serotonin and GABA system have yielded drugs with known anxiolytic efficacy, the relation between the genetic background of these targets and anxiety symptoms and development of anxiety disorders is largely unknown. The aim of this review is to show the vast complexity of genetic and environmental factors in anxiety disorders. In light of the difficulty with which common genetic variants are identified in anxiety disorders, animal models with translational validity may aid in elucidating the neurobiological background of these genes and their possible role in anxiety. We argue that, in addition to human genetic studies, translational models are essential to map anxiety-related genes and to enhance our understanding of anxiety disorders in order to develop potentially novel treatment strategies.

Serotonin transporter gene moderates associations between mood, memory and hippocampal volume

BACKGROUND

The short (S) allele of the serotonin transporter gene (5-HTTLPR) is associated with reduced serotonin turnover compared to the long (L) allele in Caucasians. Few studies have examined its impact on memory and brain structure in healthy young adults.

METHODS

Participants included 51 healthy young adults (25 female; ages 18-25). Multiple regressions examined the independent contribution of 5-HTTLPR biomarker genotype and its interactions with gender and sub-clinical depressive symptoms on hippocampal volumes and memory.

RESULTS

The 5-HTTLPR genotype significantly interacted with gender in predicting larger left hippocampal volumes in S-carrying females and smaller hippocampal volumes in males (p<.03). Gender also moderated the impact of the 5-HTTLPR on neurocognition. In females, S allele carriers had poorer visual recall compared to L carriers (p<.05). A three-way interaction between 5-HTTLPR, gender, and depressive symptoms was also observed (p<.04). In females, larger left hippocampal volumes were associated with increased depressive symptoms while the opposite was seen in males. Finally, in male and female S carriers, increased depressive symptoms were marginally associated with poorer verbal memory (p<.09).

CONCLUSIONS

In females, the 5-HTTLPR S allele was associated with poorer memory performance, increased depressive symptoms and larger hippocampal volumes. In males, the S allele predicted smaller hippocampal volumes and increased depressive symptoms. The opposite morphometric patterns likely reflect gender differences in adolescent hippocampal development. Larger longitudinal studies are needed to examine whether the impact of 5-HTTLPR genotype on neurocognition across development differs according to extent of mood symptoms and gender.

Variation in key genes of serotonin and norepinephrine function predicts gamma-band activity during goal-directed attention

Recent evidence shows that genetic variations in key regulators of serotonergic (5-HT) signaling explain variance in executive tasks, which suggests modulatory actions of 5-HT on goal-directed selective attention as one possible underlying mechanism. To investigate this link, 130 volunteers were genotyped for the 5-HT transporter gene-linked polymorphic region (5-HTTLPR) and for a variation (TPH2-703 G/T) of the TPH2 gene coding for the rate-limiting enzyme of 5-HT synthesis in the brain. Additionally, a functional polymorphism of the norepinephrine transporter gene (NET -3081 A/T) was considered, which was recently found to predict attention and working memory processes in interaction with serotonergic genes. The flanker-based Attention Network Test was used to assess goal-directed attention and the efficiency of attentional networks. Event-related gamma-band activity served to indicate selective attention at the intermediate phenotype level. The main findings were that 5-HTTLPR s allele and TPH2 G-allele homozygotes showed increased induced gamma-band activity during target processing when combined with the NET A/A genotype compared with other genotype combinations, and that gamma activity mediates the genotype-specific effects on task performance. The results further support a modulatory role of 5-HT and NE function in the top-down attentional selection of motivationally relevant over competing or irrelevant sensory input.

Estrogen and the prefrontal cortex: towards a new understanding of estrogen's effects on executive functions in the menopause transition

Midlife decline in cognition, specifically in areas of executive functioning, is a frequent concern for which menopausal women seek clinical intervention. The dependence of executive processes on prefrontal cortex function suggests estrogen effects on this brain region may be key in identifying the sources of this decline. Recent evidence from rodent, nonhuman primate, and human subject studies indicates the importance of considering interactions of estrogen with neurotransmitter systems, stress, genotype, and individual life events when determining the cognitive effects of menopause and estrogen therapy.

Perceived parental rejection mediates the influence of serotonin transporter gene (5-HTTLPR) polymorphisms on impulsivity in Japanese adults

This study examined (1) the interrelationships among 5-HTTLPR genotype, perceived parental rejection, and impulsivity, and (2) meditational models in which perceived paternal/maternal rejection mediates the relationship between the 5-HTTLPR genotype and impulsive behaviour. Participants included 403 adults (152 males and 252 females, mean age = 24.20) who provided genetic data and a set of the questionnaires (BIS11; Barratt Impulsiveness Scale-11 and EMBU; Egna Minnen av Bätraffande Uppfostran). Using SEM (Structural Equation Modeling), we evaluated 3 models for both direct and indirect relationships between 5-HTTLPR (5HTT) and Impulsivity (IMP), via maternal/fraternal rejection (MAT/FAT). In model 1, the direct path from 5HTT and IMP was not significant across the mother’s and father’s analysis. Models 2 and 3 assessed the indirect influence of 5HTT on IMP through MOT/FAT. The paths of models 2 and 3 were all significant and showed a good fit between the hypothesized model and data. Furthermore, the effects of the 5-HTTLPR genotype on impulsiveness in this Japanese sample were particularly accounted for by perceived rejection from the mother or father. The effects from the parents appeared to be robust especially among males. These results may help elucidate the specific pathways of risk in relation to genetic and environment influences on impulsive phenotypes.

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.

Toward an integration of cognitive and genetic models of risk for depression

There is growing interest in integrating cognitive and genetic models of depression risk. We review two ways in which these models can be meaningfully integrated. First, information-processing biases may represent intermediate phenotypes for specific genetic influences. These genetic influences may represent main effects on specific cognitive processes or may moderate the impact of environmental influences on information-processing biases. Second, cognitive and genetic influences may combine to increase reactivity to environmental stressors, increasing risk for depression in a gene×cognition×environment model of risk. There is now growing support for both of these ways of integrating cognitive and genetic models of depression risk. Specifically, there is support for genetic influences on information-processing biases, particularly the link between 5-HTTLPR and attentional biases, from both genetic association and gene×environment (G×E) studies. There is also initial support for gene×cognition×environment models of risk in which specific genetic influences contribute to increased reactivity to environmental influences. We review this research and discuss important areas of future research, particularly the need for larger samples that allow for a broader examination of genetic and epigenetic influences as well as the combined influence of variability across a number of genes.

Serotonin transporter gene promoter polymorphism and alexithymia

BACKGROUND

Recent neurobiological studies have reported that alexithymia may result from altered brain function related to emotional processing. Serotonin (5-hydroxytryptamine, 5-HT) has been shown to regulate central nervous system development associated with psychological processing. We investigated the possibility that polymorphism of the 5-HT transporter-linked promoter region (5-HTTLPR) is associated with alexithymia.

METHODS

This study included 304 healthy Japanese volunteers (148 males, 156 females). The subjects were categorized according to genotype (L/L, L/S, S/S) and results of the 20-item Toronto Alexithymia Scale (TAS-20), State-Trait Anxiety Inventory (STAI) and Self-Rating Depression Scale (SDS).

RESULTS

Subjects with the L/L genotype showed significantly higher TAS-20 scores, as well as significantly higher scores on the difficulty identifying feeling (DIF) subscale, than those with the L/S or S/S genotype (p < 0.05). There was a gender difference in the association between 5-HTTLPR genotype and DIF score. Female subjects with the L/L genotype showed significantly higher DIF scores than those with the L/S or S/S genotype (p ≤ 0.001). Neither STAI nor SDS was significantly associated with the 5-HTTLPR genotype.

CONCLUSION

These results suggest a link between low synaptic 5-HT and alexithymia.

Differential susceptibility in spillover between interparental conflict and maternal parenting practices: evidence for OXTR and 5-HTT genes

Guided by the affective spillover hypothesis and the differential susceptibility to environmental influence frameworks, the present study examined how associations between interparental conflict and mothers' parenting practices were moderated by serotonin transporter (5-HTT) and oxytocin receptor (OXTR) genes. A sample of 201 mothers and their 2-year old child participated in a laboratory-based research assessment. Results supported differential susceptibility hypotheses within spillover frameworks. With respect to OXTR rs53576, mothers with the GG genotype showed greater differential maternal sensitivity across varying levels of interparental conflict. Mothers with one or two copies of the 5-HTTLPR S allele demonstrated differential susceptibility for both sensitive and harsh/punitive caregiving behaviors. Finally, analyses examined whether maternal depressive symptoms and emotional closeness to their child mediated the moderating effects. Findings suggest that maternal emotional closeness with their child indirectly linked OXTR with maternal sensitivity. The results highlight how molecular genetics may explain heterogeneity in spillover models with differential implications for specific parenting behaviors. Implications for clinicians and therapists working with maritally distressed parents are discussed.

Influence of threat and serotonin transporter genotype on interference effects

Emotion-cognition interactions are critical in goal-directed behavior and may be disrupted in psychopathology. Growing evidence also suggests that emotion-cognition interactions are modulated by genetic variation, including genetic variation in the serotonin system. The goal of the current study was to examine the impact of threat-related distracters and serotonin transporter promoter polymorphism (5-HTTLPR/rs25531) on cognitive task performance in healthy females. Using a novel threat-distracter version of the Multi-Source Interference Task specifically designed to probe emotion-cognition interactions, we demonstrate a robust and temporally dynamic modulation of cognitive interference effects by threat-related distracters relative to other distracter types and relative to no-distracter condition. We further show that threat-related distracters have dissociable and opposite effects on cognitive task performance in easy and difficult task conditions, operationalized as the level of response interference that has to be surmounted to produce a correct response. Finally, we present evidence that the 5-HTTLPR/rs25531 genotype in females modulates susceptibility to cognitive interference in a global fashion, across all distracter conditions, and irrespective of the emotional salience of distracters, rather than specifically in the presence of threat-related distracters. Taken together, these results add to our understanding of the processes through which threat-related distracters affect cognitive processing, and have implications for our understanding of disorders in which threat signals have a detrimental effect on cognition, including depression and anxiety disorders.

Interactive effects of estrogen and serotonin on brain activation during working memory and affective processing in menopausal women

While cognitive changes and mood instability are frequent symptoms reported by menopausal women, the degree to which the decline in estrogen production is responsible is not yet clear. Several lines of evidence suggest that estrogen may produce its effects on cognition and mood through modulation of serotonergic function. To test this hypothesis, we used the tryptophan depletion (TD) paradigm to lower central serotonin levels and pharmacologically manipulated estrogen levels in healthy menopausal women. We examined the individual and combined effects of estradiol and serotonin on working memory, emotion processing and task-related brain activation. Eight healthy predominantly early postmenopausal women underwent TD or sham depletion followed by functional magnetic resonance imaging (fMRI) both before and after short-term transdermal estradiol 75-150 μg/d administration. There was an estradiol treatment by TD interaction for brain activation during performance on both the N-back Task (working memory) and Emotion Identification Task (affective processing). During the 2-back condition, TD attenuated activation prior to, but not after, estradiol treatment in the right and left dorsal lateral prefrontal and middle frontal/cingulate gyrus. During emotion identification, TD heightened activation in the orbital frontal cortex and bilateral amygdala, and this effect was attenuated by estradiol treatment. These results provide preliminary evidence that serotonergic effects directly mediate the impact of estrogen on brain activation during working memory and affective processing.

Polymorphisms in the 5-HTTLPR gene mediate storage capacity of visual working memory

Working memory (WM) is a limited capacity system that permeates nearly all levels of cognition, ranging from perceptual awareness to intelligence. Through behavioral, electrophysiological, and neuroimaging work, substantial gains have been made in understanding this capacity-limited system. In the current work, we examined genetic contributions to the storage capacity of WM. Multiple studies have demonstrated a link between the serotonin transporter-linked polymorphic region (5-HTTLPR) and cognition, where better performance is observed in individuals possessing a copy of the short (s) variant of the polymorphism compared with individuals homozygous for the long (l) variant. We predicted the same profile in WM performance, such that estimated capacities of l/l carriers should be smaller than s/s and s/l carriers. To measure WM capacity, we implemented a change detection task, which requires observers to actively maintain the color and spatial location of briefly presented squares over a short retention interval. In line with our prediction, we observed similar WM performance between s/s and s/l groups, and these individuals performed better than the l/l group. We then discuss the distribution of the serotonin transporter system and parallels between WM and attention to provide insight into how variation in the 5-HTT polymorphism could lead to individual differences in the storage capacity of WM.