Serotonin 2A receptor (5-HT2A) gene promoter variant interacts with chronic perceived stress to modulate resting parasympathetic activity in humans

Heart rate variability: Evaluating a potential biomarker of anxiety disorders

Establishing quantifiable biological markers associated with anxiety will increase the objectivity of phenotyping and enhance genetic research of anxiety disorders. Heart rate variability (HRV) is a physiological measure reflecting the dynamic relationship between the sympathetic and parasympathetic nervous systems, and is a promising target for further investigation. This review summarizes evidence evaluating HRV as a potential physiological biomarker of anxiety disorders by highlighting literature related to anxiety and HRV combined with investigations of endophenotypes, neuroimaging, treatment response, and genetics. Deficient HRV shows promise as an endophenotype of pathological anxiety and may serve as a noninvasive index of prefrontal cortical control over the amygdala, and potentially aid with treatment outcome prediction. We propose that the genetics of HRV can be used to enhance the understanding of the genetics of pathological anxiety for etiological investigations and treatment prediction. Given the anxiety-HRV link, strategies are offered to advance genetic analytical approaches, including the use of polygenic methods, wearable devices, and pharmacogenetic study designs. Overall, HRV shows promising support as a physiological biomarker of pathological anxiety, potentially in a transdiagnostic manner, with the heart-brain entwinement providing a novel approach to advance anxiety treatment development.

Does heart rate variability mediate the association between chronic stress, cardiorespiratory fitness, and working memory in young adults?

Young adulthood is a demanding development phase rendering individuals at risk for high levels of stress. While chronic stress may impair working memory maintenance, cardiorespiratory fitness is suggested to have a protective effect. Heart rate variability (HRV) contributes to this cognitive domain, but also retaliates to stress and aerobic exercise. Therefore, the present study investigated the mediating role of resting HRV on the association between chronic stress, cardiorespiratory fitness, and working memory maintenance in young healthy adults. Healthy participants (N = 115, 48% female) aged 18-35 years (M = 24.1, SD = 3.8) completed the Åstrand test on a bicycle ergometer to estimate maximal oxygen consumption [ V ̇ O 2 max $$ \dot{\mathrm{V}}{\mathrm{O}}_{2\max } $$ (ml/min/kg)]. In addition, working memory maintenance was assessed using the modified Sternberg task with low (three items) and high cognitive load (six items). Using electrocardiography, HRV was recorded and the LF/HF ratio was extracted for mediation analyses. Path analysis revealed that cardiorespiratory fitness was significantly associated with accuracy on high cognitive load trials (β = 0.19, p = 0.035), but not on trials with low cognitive load. Perceived levels of chronic stress failed to show a significant association with working memory maintenance, independently of cognitive load. The pattern of results remained unchanged after introduction of HRV as a mediator (β = 0.18, p = 0.045). In conclusion, higher cardiorespiratory fitness is associated with better maintenance of verbal information in working memory. However, this association cannot be explained by vagal influences on memory processing driven by the autonomic nervous system.

Serotonin Modulates the Correlations between Obsessive-compulsive Trait and Heart Rate Variability in Normal Healthy Subjects: A SPECT Study with [123I]ADAM and Heart Rate Variability Measurement

Objective

The impact of serotonergic system on obsessive-compulsive disorder (OCD) is well studied. However, the correlation between OC presentations and autonomic nervous system (ANS) is still unclear. Furthermore, whether the correlation might be modulated by serotonin is also uncertain.

Methods

We recruited eighty-nine healthy subjects. Serotonin transporter (SERT) availability by [¹²³I]ADAM and heart rate variability (HRV) tests were measured. Symptoms checklist-90 was measured for the OC presentations. The interaction between HRV and SERT availability were calculated and the correlation between HRV and OC symptoms were analyzed after stratified SERT level into two groups, split at medium.

Results

The interactions were significant in the factors of low frequency (LF), high frequency (HF), and root mean square of successive differences (RMSSD). Furthermore, the significantly negative correlations between OC symptoms and the above HRV indexes existed only in subjects with higher SERT availability.

Conclusion

OC symptoms might be correlated with ANS regulations in subjects with higher SERT availability.

Associations and interactions of the serotonin receptor genes 5-HT1A, 5-HT2A, and childhood trauma with alexithymia in two independent general-population samples

Previous studies suggested that childhood trauma and a disturbed serotonergic neurotransmission are involved in the pathogenesis of alexithymia. Specifically, genetic polymorphisms of the serotonin receptors 5-HT1A and 5-HT2A were found to be associated with alexithymia. However, it is unclear whether these factors show main or interaction effects with childhood trauma on alexithymia. Data from two independent general-population cohorts of the Study of Health in Pomerania (SHIP-Trend: N=3,706, Age: range=20-83, 51.6% female, SHIP-LEGEND: N=2,162, Age: range=20-80, 52.5% female) were used. The Toronto Alexithymia Scale-20 (TAS-20) and the Childhood Trauma Questionnaire (CTQ) were applied. Genotypes of rs6295 of 5-HT1A and rs6311 of 5-HT2A were determined. Ordinary least-squared regression models with robust standard errors were applied to investigate associations of the main and interaction effects of childhood maltreatment and the polymorphisms with alexithymia. Childhood trauma, but none of the investigated polymorphisms showed main effects on alexithymia. However, childhood trauma showed significant CTQ sum score x rs6295 interactions in male subjects in both samples such that the presence of the G-allele diminished the CTQ associated increase in the TAS-20 sum scores. Our results support a strong role of early life stress and interactions with rs6295 on alexithymic personality features at least in male subjects.

Pivotal mental states

This paper introduces a new construct, the 'pivotal mental state', which is defined as a hyper-plastic state aiding rapid and deep learning that can mediate psychological transformation. We believe this new construct bears relevance to a broad range of psychological and psychiatric phenomena. We argue that pivotal mental states serve an important evolutionary function, that is, to aid psychological transformation when actual or perceived environmental pressures demand this. We cite evidence that chronic stress and neurotic traits are primers for a pivotal mental state, whereas acute stress can be a trigger. Inspired by research with serotonin 2A receptor agonist psychedelics, we highlight how activity at this particular receptor can robustly and reliably induce pivotal mental states, but we argue that the capacity for pivotal mental states is an inherent property of the human brain itself. Moreover, we hypothesize that serotonergic psychedelics hijack a system that has evolved to mediate rapid and deep learning when its need is sensed. We cite a breadth of evidences linking stress via a variety of inducers, with an upregulated serotonin 2A receptor system (e.g. upregulated availability of and/or binding to the receptor) and acute stress with 5-HT release, which we argue can activate this primed system to induce a pivotal mental state. The pivotal mental state model is multi-level, linking a specific molecular gateway (increased serotonin 2A receptor signaling) with the inception of a hyper-plastic brain and mind state, enhanced rate of associative learning and the potential mediation of a psychological transformation.

Sex-specific pathways among tri-allelic serotonin transporter polymorphism, trait neuroticism and generalized anxiety disorder

BACKGROUND

Neuroticism personality trait is recognized as an important endophenotypic predictor of generalized anxiety disorder (GAD). Furthermore, endophenotype-based pathway approaches have recently been shown to have greater advantages for gene-finding strategies than traditional case-control studies. In the present study, in addition to conventional case-control methods, we used pathway analyses to test whether the tri-allelic serotonin transporter promoter polymorphism (combining 5-HTTLPR and rs25531) is associated with risk of GAD through its effects on trait neuroticism.

METHODS

We included 2236 Han Chinese adults in this study, including 736 patients with GAD and 1500 healthy participants. We genotyped the 5-HTTLPR and rs25531 polymorphisms using the polymerase chain reaction restriction fragment length polymorphism method. We used the Neuroticism scale of the Maudsley Personality Inventory (MPI) short version (MPI-Neuroticism) to measure participants' tendency toward neuroticism.

RESULTS

Using endophenotype-based path analyses, we found significant indirect effects of the tri-allelic genotype on risk of GAD, mediated by MPI-Neuroticism in both men and women. Compared to women carrying the S'S' genotype, women carrying the L' allele had higher levels of MPI-Neuroticism, which in turn were associated with higher risk of GAD. Men, however, showed the opposite pattern. Using traditional case-control comparisons, we observed that the effect of tri-allelic genotype on GAD was significant, but only in women.

LIMITATIONS

Participants were restricted to Han Chinese, and we used only 1 questionnaire to assess neuroticism.

CONCLUSION

These findings are the first to show that the triallelic 5-HTTLPR polymorphism is associated with elevated risk of GAD, and that this effect is mediated via increased trait neuroticism, a sex-dependent risk pathway.

The rs6311 of serotonin receptor 2A (5-HT2A) gene is associated with alexithymia and mental health

BACKGROUNDS

Alexithymia, difficulties in identifying and describing one's own feelings, is related to substantial clinical practice. Inspired by the links between serotonin functions and affective disorders, this study investigated associations of the serotonin receptor 2A (5-HT2A) gene with alexithymia and mental health.

METHODS

We differentiated subjects according to two functional polymorphisms (i.e., rs6311 and rs6313) of 5-HT2A gene and scored alexithymia and mental health of college students with the Toronto Alexithymia Scale (TAS-20) and the Symptom Check List-90 (SCL-90), respectively.

RESULTS

The analyses basing on sample 1 (N = 566) and sample 2 (N = 602) indicated that the G allele of rs6311 was related to higher score on the TAS-20 as compared to the AA genotype. The analysis with 467 individuals from sample 2 indicated that the rs6311 was associated with mental health, and this association was mediated by alexithymia.

LIMITATIONS

The potential confounding variables such as depression and anxiety were neglected in the analyses.

CONCLUSIONS

These findings demonstrate the contribution of the 5-HT2A to alexithymia, and highlight the link between alexithymia and mental health at genetic level.

Age-dependent association of polymorphisms in the promoter and 5'-untranslated region of the norepinephrine transporter gene with generalized anxiety disorder

BACKGROUND

Norepinephrine transporter (NET), which regulates synaptic norepinephrine for noradrenergic signaling, is involved in the pathogenesis of anxiety, while expression of the NET gene differs at different ages. Here, we examine whether genetic variants in the NET gene are associated, in an age-specific manner, with increased risk of generalized anxiety disorder (GAD), one of the most disabling anxiety disorders.

METHODS

Three common single-nucleotide polymorphisms (SNPs) in the promoter (rs168924: A/G; rs2242446: T/C) and 5'-untranslated region (5'-UTR) (rs2397771: G/C) of the NET gene were genotyped in 2,317 Han-Chinese participants (791 GAD patients and 1,526 controls; age: 20-65). Potential confounding factors, such as gender, stress levels and psychiatric comorbidities, were included as covariates.

RESULTS

An interaction between age and NET genotypes and haplotypes was found for the risk of GAD. In the younger participants, rs168924 minor allele G homozygotes had the lowest incidence of GAD; however, older subjects displayed an inverse pattern, with homozygous G/G carriers presenting the highest prevalence of GAD. Additionally, younger individuals carrying 2 copies of the GGT haplotype composed of rs2397771-rs168924-rs2242446 had the lowest rate of GAD. However, those with 2 copies of the same haplotype exhibited the highest risk of GAD in the older groups.

LIMITATIONS

Only 3 common SNPs in the promoter and 5'-UTR of the NET gene were analyzed.

CONCLUSIONS

Our findings are the first to demonstrate that potentially functional SNPs in the NET promoter and 5'-UTR are associated with an increased risk of GAD, and that such associations are determined in an age-specific way.

Minimally-invasive methods for examining biological changes in response to chronic stress: A scoping review

BACKGROUND

Nurse researchers are increasingly interested in incorporating biological indicators related to chronic stress, or repeated or constant exposure to psychological stressors. Minimally invasive collection methods may improve access to vulnerable populations.

OBJECTIVE

To map biological indicators measured through minimally invasive methods investigating biological changes in response to chronic stress.

DESIGN, DATA SOURCES, AND METHODS

The paper seeks to answer two questions: What are the characteristics of the minimally-invasive methods used to measure the biological correlates of chronic stress? What are the limitations regarding the use of the minimally-invasive methods and/or biological indicators identified above? Authors completed a scoping review following guidelines from the Joanna Briggs Institute Manual and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) extension for Scoping Reviews. A literature search was completed in PubMed, PsycINFO, and Scopus. 2518 articles were screened and 145 studies were included. Data were extracted using a standardized extraction tool, compiled, and coded.

RESULTS

Studies included minimally-invasive methods to measure the hypothalamic-adrenal-pituitary axis (N = 173), immune and inflammatory markers (N = 118), and adult neurogenesis (N = 6). Cortisol was most frequently measured (N = 136), usually in saliva (N = 86). Studies included a variety of limitations for the methods and indicators, including concerns about timing and accuracy of collection, frequency of sampling, and controlling for acute stressors.

CONCLUSIONS

Nurse researchers have access to many minimally-invasive methods to measure altered biological processes related to chronic stress. A gap identified by this review is the paucity of minimally-invasive methods for investigating neurogenesis; the measurement of brain derived neurotrophic factor in plasma is a distal proxy and further research is needed to test the response of peripheral levels to psychosocial stress interventions. Additionally, while this scoping review allows nurse researchers to consider possible biological indicators to include in their research, future research is still needed on some of the basic premises of stress research, including agreement on the conceptualization of chronic stress.

Age-specific associations among functional COMT Val158Met polymorphism, resting parasympathetic nervous control and generalized anxiety disorder

The functional Val¹⁵⁸Met polymorphism (rs4680) of the Catechol-O-Methyltransferase (COMT) gene has been implicated in generalized anxiety disorder (GAD); however, the underlying neural mechanisms remain unexamined. Recent evidence reveals that low resting parasympathetic (vagal) control is an endophenotypic predictor of anxiety, while the effect of COMT rs4680 differs at different ages. Thus, we examined whether the COMT Val¹⁵⁸Met variant could increase the risk of GAD through decreased resting parasympathetic nervous control in an age-specific manner. COMT rs4680 polymorphism was genotyped in 1,655 Han Chinese adults (1,142 healthy subjects and 513 patients with GAD; age: 20-65). High-frequency power (HF) of heart rate variability (HRV) was used to measure resting state parasympathetic nervous regulation. Non-genetic factors, such as gender, smoking status, medication use and comorbidity conditions, were treated as covariates. After adjusting for relevant covariates, there was a significant age x COMT genotype interaction on resting HF of HRV. In younger adults, Met allele carriers had a significantly lower HF index; however, older adults exhibited the opposite pattern, with Val/Val homozygotes exhibiting decreased HF values. Moreover, reduced HF-HRV is associated with increased risk of GAD. Finally, pathway analysis revealed a significant indirect effect of COMT on the risk of GAD via reduced resting HF-HRV, in the aforementioned age-dependent manner. Our findings are the first to demonstrate that COMT Val¹⁵⁸Met polymorphism is associated with risk of GAD via reduced resting parasympathetic nervous control, an age-specific risk pathway.

Childhood Adversity Moderates the Effects of HTR2A Epigenetic Regulatory Polymorphisms on Rumination

The serotonin system has been suggested to moderate the association between childhood maltreatment and rumination, with the latter in its turn reported to be a mediator in the depressogenic effect of childhood maltreatment. Therefore, we investigated whether the associations of two epigenetic regulatory polymorphisms in the HTR2A serotonin receptor gene with Ruminative Responses Scale rumination and its two subtypes, brooding and reflection, are moderated by childhood adversity (derived from the Childhood Trauma Questionnaire) among 1,501 European white adults. We tested post hoc whether the significant associations are due to depression. We also tested the replicability of the significant results within the two subsamples of Budapest and Manchester. We revealed two significant models: both the association of methylation site rs6311 with rumination and that of miRNA binding site rs3125 (supposed to bind miR-1270, miR-1304, miR-202, miR-539 and miR-620) with brooding were a function of childhood adversity, and both interaction findings were significantly present both in the never-depressed and in the ever-depressed group. Moreover, the association of rs3125 with brooding could be replicated across the separate subsamples, and remained significant even when controlling for lifetime depression and the Brief Symptom Inventory depression score. These findings indicate the crucial importance of involving stress factors when considering endophenotypes and suggest that brooding is a more promising endophenotype than a broader measure of rumination. Transdiagnostic relevance of the brooding endophenotype and the potential of targeting epigenetic regulatory polymorphisms of HTR2A in primary and secondary prevention of depression and possibly of other disorders are also discussed.

Prefrontal cortex modulates the correlations between brain-derived neurotrophic factor level, serotonin, and the autonomic nervous system

Top-down regulation in the human brain and anatomical connections between the prefrontal cortex (PFC) and specific catecholamine-related regions have been well-studied. However, the way in which the PFC modulates downstream neuro-networks in terms of serotonin and the autonomic nervous system (ANS) by variation in the level of brain-derived neurotrophic factor (BDNF) is still unclear. We recruited sixty-seven healthy subjects. Serotonin transporter (SERT) availability was examined by SPECT with [¹²³I]ADAM analysis; heart rate variability (HRV) testing was performed, and the BDNF level was measured. The Wisconsin card-sorting test (WCST), which assesses PFC activation, was also conducted. The interactions of BDNF level and SERT availability were significant in relation to the HRV indexes of low frequency, high frequency, total power, and mean heart rate range. Moderate to significant positive correlations between SERT availability and the above-mentioned HRV indexes existed only in subjects with a low BDNF level. Furthermore, in the low BDNF level group, only those with high WCST perseveration errors or low category completions exhibited significant positive correlations between SERT availability and HRV indexes. A lower BDNF level and poorer PFC function might modulate the synergistic effects of serotonergic and ANS systems in order to maintain brain physiological and psychological homeostasis.

The Association between 5HT2A T102C and Behavioral and Psychological Symptoms of Dementia in Alzheimer's Disease: A Meta-Analysis

The serotonin receptor gene (5-HT2A) has been reported to be a susceptible factor in behavioral and psychological symptoms of dementia (BPSD) in Alzheimer's disease (AD). However, previous results were conflicting. We aim to investigate the association of 5-HT2A T102C with BPSD in AD using a meta-analysis. Studies were collected using PubMed, Web of Science, the Cochrane Library databases, Chinese National Knowledge Infrastructure (CNKI), and Embase. Pooled odds ratios (ORs) with 95% confidence intervals (CIs) were used to assess associations. Nine studies with 1899 AD patients with/without BPSD were included in this meta-analysis. The 102C and CC genotypes were associated with psychosis in AD (102C: p < 0.00001, OR [95% CI] = 3.19 [2.12-4.79]; CC: p < 0.00001, OR [95% CI] = 7.24 [3.60-14.59]). The TT genotype was significantly associated with hallucinations, aberrant motor behavior, and psychosis in AD (hallucinations: p = 0.001, OR [95% CI] = 0.52 [0.36-0.77]; aberrant motor behavior: p = 0.03, OR [95% CI] = 0.58 [0.35-0.95]; and psychosis: p = 0.002, OR [95% CI] = 0.34 [0.17-0.67]). No association was observed between T102C alleles or genotypes and delusions, agitation/aggression, depression, and apathy (p > 0.05). Thus, the 5HT2A T102C might be a susceptible factor for hallucinations, aberrant motor behavior, and psychosis in AD. The potential mechanism of this polymorphism in BPSD in AD requires further exploration.

Chronic Stress in Adolescents and Its Neurobiological and Psychopathological Consequences: An RDoC Perspective

The Research Domain Criteria (RDoC) initiative provides a strategy for classifying psychopathology based on behavioral dimensions and neurobiological measures. Neurodevelopment is an orthogonal dimension in the current RDoC framework; however, it has not yet been fully incorporated into the RDoC approach. A combination of both a neurodevelopmental and RDoC approach offers a multidimensional perspective for understanding the emergence of psychopathology during development. Environmental influence (e.g., stress) has a profound impact on the risk for development of psychiatric illnesses. It has been shown that chronic stress interacts with the developing brain, producing significant changes in neural circuits that eventually increase the susceptibility for development of psychiatric disorders. This review highlights effects of chronic stress on the adolescent brain, as adolescence is a period characterized by a combination of significant brain alterations, high levels of stress, and emergence of psychopathology. The literature synthesized in this review suggests that chronic stress-induced changes in neurobiology and behavioral constructs underlie the shared vulnerability across a number of disorders in adolescence. The review particularly focuses on depression and substance use disorders; however, a similar argument can also be made for other psychopathologies, including anxiety disorders. The summarized findings underscore the need for a framework to integrate neurobiological findings from disparate psychiatric disorders and to target transdiagnostic mechanisms across disorders.

5-HT2A receptor deficiency alters the metabolic and transcriptional, but not the behavioral, consequences of chronic unpredictable stress

Chronic stress enhances risk for psychiatric disorders, and in animal models is known to evoke depression-like behavior accompanied by perturbed neurohormonal, metabolic, neuroarchitectural and transcriptional changes. Serotonergic neurotransmission, including serotonin_2A (5-HT_2A) receptors, have been implicated in mediating specific aspects of stress-induced responses. Here we investigated the influence of chronic unpredictable stress (CUS) on depression-like behavior, serum metabolic measures, and gene expression in stress-associated neurocircuitry of the prefrontal cortex (PFC) and hippocampus in 5-HT_2A receptor knockout (5-HT2A−/−) and wild-type mice of both sexes. While 5-HT2A−/− male and female mice exhibited a baseline reduced anxiety-like state, this did not alter the onset or severity of behavioral despair during and at the cessation of CUS, indicating that these mice can develop stress-evoked depressive behavior. Analysis of metabolic parameters in serum revealed a CUS-evoked dyslipidemia, which was abrogated in 5-HT2A−/− female mice with a hyperlipidemic baseline phenotype. 5-HT2A−/− male mice in contrast did not exhibit such a baseline shift in their serum lipid profile. Specific stress-responsive genes (Crh, Crhr1, Nr3c1, and Nr3c2), trophic factors (Bdnf, Igf1) and immediate early genes (IEGs) (Arc, Fos, Fosb, Egr1-4) in the PFC and hippocampus were altered in 5-HT2A−/− mice both under baseline and CUS conditions. Our results support a role for the 5-HT_2A receptor in specific metabolic and transcriptional, but not behavioral, consequences of CUS, and highlight that the contribution of the 5-HT_2A receptor to stress-evoked changes is sexually dimorphic.

Increased temporal discounting after chronic stress in CHL1-deficient mice is reversed by 5-HT2C agonist Ro 60-0175

Schizophrenia is a neurodevelopmental disorder in which impaired decision-making and goal-directed behaviors are core features. One of the genes associated with schizophrenia is the Close Homolog of L1 (CHL1); CHL1-deficient mice are considered a model of schizophrenia-like deficits, including sensorimotor gating, interval timing and spatial memory impairments. Here we investigated temporal discounting in CHL1-deficient (KO) mice and their wild-type littermates. Although no discounting differences were found under baseline conditions, CHL1-KO mice showed increased impulsive choice following chronic unpredictable stress (fewer % larger-later choices, and reduced area under the discounting curve). Stressed CHL1-KO mice also showed decreased neuronal activation (number of cFos positive neurons) in the discounting task in the prelimbic cortex and dorsal striatum, areas thought to be part of executive and temporal processing circuits. Impulsive choice alterations were reversed by the 5-HT2C agonist Ro 60-0175. Our results provide evidence for a gene x environment, double-hit model of stress-related decision-making impairments, and identify CHL1-deficient mice as a mouse model for these deficits in regard to schizophrenia-like phenotypes.