The interaction of serotonin transporter gene polymorphisms and early adverse life events on vulnerability for major depression

Hippocampal PPARα Plays a Role in the Pharmacological Mechanism of Vortioxetine, a Multimodal-Acting Antidepressant

As a well-known multimodal-acting antidepressant, vortioxetine is thought to aim at several serotonin (5-HT) receptors and the 5-HT transporter. However, recently more and more proteins besides 5-HT are being reported to participate in the antidepressant mechanism of vortioxetine. As a widely known nuclear hormone receptor, peroxisome proliferator activated receptor α (PPARα) possesses transcriptional activity and is very important in the brain. Several reports have suggested that hippocampal PPARα is implicated in antidepressant responses. Here we speculate that hippocampal PPARα may participate in the antidepressant mechanism of vortioxetine. In this study, chronic unpredictable mild stress (CUMS), chronic social defeat stress (CSDS), behavioral tests, the western blotting and adenovirus associated virus (AAV)-mediated gene knockdown methods were used together. It was found that vortioxetine administration significantly reversed the inhibitory actions of both CUMS and CSDS on the hippocampal PPARα expression. Pharmacological blockade of PPARα notably prevented the antidepressant actions of vortioxetine in the CUMS and CSDS models. Moreover, genetic knockdown of PPARα in the hippocampus also significantly blocked the protecting effects of vortioxetine against both CUMS and CSDS. Therefore, the antidepressant effects of vortioxetine in mice require hippocampal PPARα.

Association of Serotonin Transporter (SERT) Polymorphisms with Opioid Dependence and Dimensional Aspects of Cocaine Use in a Caucasian Cohort of Opioid Users

INTRODUCTION

A functional tandem repeat polymorphism in the promoter of the serotonin transporter (SERT) gene (SLC6A4) has been studied for association to neuropsychiatric conditions, including substance use disorders. Short (S) forms of this repeat result in reduced transcription, and presumably greater synaptic levels of serotonin, which are involved in opioid and cocaine-induced reward. Dual exposure to heroin and cocaine is a common pattern of poly-drug use and is associated with considerable morbidity. We hypothesize that SLC6A4 variants are associated with cocaine exposure in subjects with an opioid dependence diagnosis (OD), and also in non-dependent opioid users (NOD). Other single nucleotide polymorphisms (SNPs) of SLC6A4 may also be likewise associated.

MATERIALS AND METHODS

This study determined whether variants of the SLC6A4 promoter repeats and two intronic SNPs, rs16965628 and rs2066713, are associated with categorical diagnoses of opioid dependence (DSM-IV criteria) and with dimensional aspects of cocaine use, in a Caucasian cohort (n=591). Three groups of subjects were examined: (1) 276 subjects with opioid dependence diagnosis (OD); (2) 163 subjects who had used opioids for non-medical reasons but never had an opioid dependence diagnosis (NOD); (3) 152 healthy controls (HC).

RESULTS

Aside from high exposure to heroin in the OD group, relatively high exposure to cocaine was detected in both OD and NOD groups. The SERT repeat genotype (classified as "long-long" [LL] versus "short-long" plus "short-short" [SL+SS]) was not associated with categorical opioid dependence diagnoses. A nominally significant association was identified with the [SL+SS] genotype of SLC6A4 and cocaine KMSK scores ≥"cutpoint" for a cocaine dependence diagnosis (p=0.026). The [SL+SS] genotype was associated with more rapid cocaine escalation than the LL genotype. No significant associations of rs16965628 and rs2066713 SNPs were found overall.

CONCLUSION

The functional SERT promoter tandem repeat genotype may be associated to heavy cocaine exposure and more rapid escalation of cocaine use, in persons with and without opioid dependence diagnosis.

Toward Serotonin Fluorescent False Neurotransmitters: Development of Fluorescent Dual Serotonin and Vesicular Monoamine Transporter Substrates for Visualizing Serotonin Neurons

Ongoing efforts in our laboratories focus on design of optical reporters known as fluorescent false neurotransmitters (FFNs) that enable the visualization of uptake into, packaging within, and release from individual monoaminergic neurons and presynaptic sites in the brain. Here, we introduce the molecular probe FFN246 as an expansion of the FFN platform to the serotonergic system. Combining the acridone fluorophore with the ethylamine recognition element of serotonin, we identified FFN54 and FFN246 as substrates for both the serotonin transporter and the vesicular monoamine transporter 2 (VMAT2). A systematic structure-activity study revealed the basic structural chemotype of aminoalkyl acridones required for serotonin transporter (SERT) activity and enabled lowering the background labeling of these probes while maintaining SERT activity, which proved essential for obtaining sufficient signal in the brain tissue (FFN246). We demonstrate the utility of FFN246 for direct examination of SERT activity and SERT inhibitors in 96-well cell culture assays, as well as specific labeling of serotonergic neurons of the dorsal raphe nucleus in the living tissue of acute mouse brain slices. While we found only minor FFN246 accumulation in serotonergic axons in murine brain tissue, FFN246 effectively traces serotonin uptake and packaging in the soma of serotonergic neurons with improved photophysical properties and loading parameters compared to known serotonin-based fluorescent tracers.

Mental Health Effects of Stress over the Life Span of Refugees

Information about the relative impact of stressful events across the lifespan on the mental health of refugees is needed. Cross-sectional data from a community sample of 135 Kurdish and 117 Vietnamese refugees were fit to a path model about the effects of non-war stress, war-related stress, and post-migration stress on mental health. Kurdish and Vietnamese data were generally consistent with the model. However, war-related stress produced no direct but a large indirect effect through post-migration stress on mental health in Kurds. Vietnamese data indicated a modest direct war-related stress effect but no indirect influence through post-migration stress. Different types of stressful events lead to adverse mental health of displaced refugees in a somewhat group-dependent manner. Implications for prevention and treatment are discussed.

Associations of endocrine stress-related gene polymorphisms with risk of autism spectrum disorders: Evidence from an integrated meta-analysis

Autism spectrum disorders (ASD) are related to serotonin transporter (5-HTT) and catechol-O-methyl transferase (COMT) as two most monoaminergic polymorphic variations. However, multiple studies assessing rs4680 and 5-HTTLPR variants in ASD have reported inconsistent results. Therefore, we conducted an integrated meta-analysis to combine case-control and transmission/disequilibrium test (TDT) studies to determine whether COMT and 5-HTT are associated with ASD. We searched multiple electronic databases (PubMed, EmBase and Web of Science) to identify studies assessing the rs4680 and 5-HTTLPR variants in ASD from Jan 1997 to Dec 2016. Then allelic data from case-control and TDT studies were analyzed by the Catmap package in the R software. A total of 5 studies were eligible for the meta-analysis of rs4680, including 3 case-control, 1 TDT and 1 TDT & case-control studies. Meanwhile, 22 studies of 5-HTTLPR were available, including 16 TDT, 4 case-control and 2 TDT & case-control studies. The current meta-analysis included 814 ASD cases, 741 controls and 311 families related to rs4680; 749 ASD cases, 1,118 controls and 1,861 families relevant to 5-HTTLPR were also evaluated. For rs4680, the pooled OR was 1.18 (95% CI = 0.87-1.59, P = 0.29, P_{heterogeneity}  < 0.00001). There was no significant association of rs4680 with risk of ASD between the two subgroups. For 5-HTTLPR, the pooled OR was 1.05 (95% CI = 0.92-1.20, P = 0.4652, P_{heterogeneity}  < 0.00001). Meanwhile, we found no significant risk in individual case-control or TDT studies. The above findings indicated that neither COMT rs4680 nor 5-HTT 5-HTTLPR polymorphism significantly affects ASD risk. Autism Res 2017, 10: 1722-1736. © 2017 International Society for Autism Research, Wiley Periodicals, Inc.

LAY SUMMARY

Our results showed no evidence of significant association of either COMT rs4680 or 5-HTT 5-HTTLPR variants with ASD, showing that these two genes may not be major susceptible genetic factors in ASD occurrence, and may have a reciprocal action with each other in combination with environmental factors. These findings further provide evidence that a single gene variant may not dictate autism occurrence, but possibly contributes to a specific phenotype or subtype of ASD.

Vulnerability or Sensitivity to the Environment? Methodological Issues, Trends, and Recommendations in Gene-Environment Interactions Research in Human Behavior

Research on the potential role of gene-environment interactions (GxE) in explaining vulnerability to psychopathology in humans has witnessed a shift from a diathesis-stress perspective to differential susceptibility approaches. This paper critically reviews methodological issues and trends in this body of research. Databases were screened for studies of GxE in the prediction of personality traits, behavior, and mental health disorders in humans published between January 2002 and January 2015. In total, 315 papers were included. Results showed that 34 candidate genes have been included in GxE studies. Independent of the type of environment studied (early or recent life events, positive or negative environments), about 67-83% of studies have reported significant GxE interactions, which is consistent with a social susceptibility model. The percentage of positive results does not seem to differ depending on the gene studied, although publication bias might be involved. However, the number of positive findings differs depending on the population studied (i.e., young adults vs. older adults). Methodological considerations limit the ability to draw strong conclusions, particularly as almost 90% (n = 283/315) of published papers are based on samples from North America and Europe, and about 70% of published studies (219/315) are based on samples that were also used in other reports. At the same time, there are clear indications of methodological improvements over time, as is shown by a significant increase in longitudinal and experimental studies as well as in improved minimum genotyping. Recommendations for future research, such as minimum quality assessment of genes and environmental factors, specifying theoretical models guiding the study, and taking into account of cultural, ethnic, and lifetime perspectives, are formulated.

Ultrasound of alternating frequencies and variable emotional impact evokes depressive syndrome in mice and rats

Emotional stress is primarily triggered by the cognitive processing of negative input; it is regarded as a serious pathogenetic factor of depression that is challenging to model in animals. While available stress paradigms achieve considerable face and construct validity in modelling depressive disorders, broader use of naturalistic stressors instead of the more prevalent models with artificial challenges inducing physical discomfort or pain may substantially contribute to the development of novel antidepressants. Here, we investigated whether a 3-week exposure of Wistar rats and Balb/c mice to unpredictably alternating frequencies of ultrasound between the ranges of 20-25 and 25-45kHz, which are known to correspond with an emotionally negative and with a neutral emotional state, respectively, for small rodents in nature, can induce behavioural and molecular depressive-like changes. Both rats and mice displayed decreased sucrose preference, elevated "despair" behaviour in a swim test, reduced locomotion and social exploration. Rats showed an increased expression of SERT and 5-HT2A receptor, a decreased expression of 5-HT1A receptor in the prefrontal cortex and hippocampus, diminished BDNF on gene and protein levels in the hippocampus. Fluoxetine, administered to rats at the dose of 10mg/kg, largely precluded behavioural depressive-like changes. Thus, the here applied paradigm of emotional stress is generating an experimental depressive state in rodents, which is not related to any physical stressors or pain. In essence, this ultrasound stress model, besides enhancing animal welfare, is likely to provide improved validity in the modelling of clinical depression and may help advance translational research and drug discovery for this disorder.

Depression

PURPOSE OF REVIEW

Depression is a presenting symptom of common psychiatric disorders such as major depressive disorder, bipolar disorder, and schizophrenia. Depression can also be the presenting symptom of several neurodegenerative disorders, including Alzheimer disease, dementia with Lewy bodies, frontotemporal dementia, and Parkinson disease. Depression can also cause cognitive impairment and is a risk factor for dementia. As a result of the intimate relationship between depression and dementia, differentiating between a psychiatric and a neurologic cause of depression and dementia can sometimes be very difficult. The purpose of this review is to discuss the diagnosis and treatment of depression and to demonstrate how new diagnostic tools are helping to identify the differential diagnosis of depression.

RECENT FINDINGS

It is a time of great advancement in the management of depression. Innovative new medications, psychotherapeutic modalities, and new and investigational somatic treatments (eg, transcranial magnetic stimulation, deep brain stimulation) are making it possible to ameliorate and manage symptoms more effectively in more patients.

SUMMARY

With our greater ability to improve the lives of patients with depression, it is important for neurologists to recognize depression and work with our psychiatric colleagues to help patients access the newest and best treatments.

Association between serotonin transporter gene polymorphisms and childhood asthma

BACKGROUND

Asthma is a common chronic inflammatory disease of the airways in which genetic factors play a major role in its pathogenesis. High serotonin serum levels in patients with asthma suggest that serotonin is involved in the pathophysiology of the disease. Serotonin clearance is mediated by the serotonin reuptake transporter, and functional polymorphisms in this gene lead to altered serotonin reuptake efficiency.

OBJECTIVE

The aim of this study was to investigate the relationship between serotonin transporter gene polymorphisms and asthma.

METHODS

Serotonin transporter gene polymorphisms (5-HTTLPR, rs35521 and STin2.VNTR) were assessed by PCR-based methods in 100 children with mild to moderate persistent asthma and compared with 100 healthy controls.

RESULTS

There were no significant differences in allele, genotype or haplotype frequencies between patients and controls. No association was observed between SERT gene polymorphisms after stratification of patients for sex, age, spirometry indices, family history, passive smoking behavior and concomitant allergic rhinitis. Significant differences were observed in the distribution of 5-HTTLPR alleles (p = 0.025) and genotypes (p = 0.021) between patients with and without atopic dermatitis.

CONCLUSIONS

Despite strong evidence suggesting the role of serotonin in the pathophysiology of asthma, we found no association between serotonin transporter gene polymorphisms and mild to moderate persistent asthma. Further serotonin transporter gene analyses in patients with severe asthma may open up new horizons in the utilization of common serotonin regulators to treat asthma, based on their pharmacogenetic effects. However, serotonin may also be indirectly influenced by emotional stress during asthma attacks.

Presence of autism, hyperserotonemia, and severe expressive language impairment in Williams-Beuren syndrome

BACKGROUND

Deletion of the Williams-Beuren syndrome (WBS) critical region (WBSCR), at 7q11.23, causes a developmental disorder commonly characterized by hypersociability and excessive talkativeness and often considered the opposite behavioral phenotype to autism. Duplication of the WBSCR leads to severe delay in expressive language. Gene-dosage effects on language development at 7q11.23 have been hypothesized.

METHODS

Molecular characterization of the WBSCR was performed by fluorescence in situ hybridization and high-resolution single-nucleotide polymorphism array in two individuals with severe autism enrolled in a genetic study of autism who showed typical WBS facial dysmorphism on systematic clinical genetic examination. The serotonin transporter promoter polymorphism (5-HTTLPR, locus SLC6A4) was genotyped. Platelet serotonin levels and urinary 6-sulfatoxymelatonin excretion were measured. Behavioral and cognitive phenotypes were examined.

RESULTS

The two patients had common WBSCR deletions between proximal and medial low copy repeat clusters, met diagnostic criteria for autism and displayed severe impairment in communication, including a total absence of expressive speech. Both patients carried the 5-HTTLPR ss genotype and exhibited platelet hyperserotonemia and low melatonin production.

CONCLUSIONS

Our observations indicate that behaviors and neurochemical phenotypes typically associated with autism can occur in patients with common WBSCR deletions. The results raise intriguing questions about phenotypic heterogeneity in WBS and regarding genetic and/or environmental factors interacting with specific genes at 7q11.23 sensitive to dosage alterations that can influence the development of social communication skills. Thus, the influence of WBSCR genes on social communication expression might be dramatically modified by other genes, such as 5-HTTLPR, known to influence the severity of social communication impairments in autism, or by environmental factors, such as hyperserotonemia, given that hyperserotonemia is found in WBS associated with autism but not in WBS without autism. In this regard, WBS provides a potentially fruitful model with which to develop integrated genetic, cognitive, behavioral and neurochemical approaches to study genotype-phenotype correlations, possible gene-environment interactions and genetic background effects. The results underscore the importance of considering careful clinical and molecular genetic examination of individuals diagnosed with autism.

Psychiatric neural networks and neuropharmacology: Selected advances and novel implications

Psychiatric disorders are often considered as simple imbalances between a limited number of cerebral neurotransmitters. In fact, it is more complicated than this "simple approach" and each psychiatric disorder constitutes network dysfunction within which several agents and factors are implicated. Thus, the therapeutical perspectives and implications are as vast and as numerous as the diversity of those network dysfunctions. Furthermore, the description of factors influencing diseases prognoses and treatment efficacy indicates new elements to consider both in therapies and drug researches.

Peripuberty stress leads to abnormal aggression, altered amygdala and orbitofrontal reactivity and increased prefrontal MAOA gene expression

Although adverse early life experiences have been found to increase lifetime risk to develop violent behaviors, the neurobiological mechanisms underlying these long-term effects remain unclear. We present a novel animal model for pathological aggression induced by peripubertal exposure to stress with face, construct and predictive validity. We show that male rats submitted to fear-induction experiences during the peripubertal period exhibit high and sustained rates of increased aggression at adulthood, even against unthreatening individuals, and increased testosterone/corticosterone ratio. They also exhibit hyperactivity in the amygdala under both basal conditions (evaluated by 2-deoxy-glucose autoradiography) and after a resident-intruder (RI) test (evaluated by c-Fos immunohistochemistry), and hypoactivation of the medial orbitofrontal (MO) cortex after the social challenge. Alterations in the connectivity between the orbitofrontal cortex and the amygdala were linked to the aggressive phenotype. Increased and sustained expression levels of the monoamine oxidase A (MAOA) gene were found in the prefrontal cortex but not in the amygdala of peripubertally stressed animals. They were accompanied by increased activatory acetylation of histone H3, but not H4, at the promoter of the MAOA gene. Treatment with an MAOA inhibitor during adulthood reversed the peripuberty stress-induced antisocial behaviors. Beyond the characterization and validation of the model, we present novel data highlighting changes in the serotonergic system in the prefrontal cortex-and pointing at epigenetic control of the MAOA gene-in the establishment of the link between peripubertal stress and later pathological aggression. Our data emphasize the impact of biological factors triggered by peripubertal adverse experiences on the emergence of violent behaviors.

The role of 5-HTT LPR and GNβ3 825C>T polymorphisms and gene-environment interactions in irritable bowel syndrome (IBS)

BACKGROUND

Smaller studies have evaluated SLC6A4 5-HTTLPR and GNβ3 825C>T polymorphisms in IBS, and interactions between 5-HTT LPR with life events have been reported in the psychiatric literature, but gene-environment studies in IBS are lacking.

AIMS

The purpose of this study was to assess the association of two polymorphisms with IBS and age of onset, and whether there are gene-environment interactions with IBS.

METHODS

Outpatients with IBS and controls completed a validated questionnaire and provided blood for DNA. Comparisons of genotype/allele frequencies between cases and controls were performed with logistic regression. Linear regression was used to evaluate the association between the variants and age of onset. Environmental variables tested included abuse, parental alcohol abuse, parental psychiatric disorders, and gastrointestinal infections.

RESULTS

Genotyping was performed in 385 cases and 262 controls with median age of 50 years (range, 18.0-70.0) and 498 (77 %) females. The IBS subtype distribution among cases was: 102 (26 %) D-IBS, 40 (10 %) C-IBS, 125 (32 %) M-IBS, 118 (31 %) other. No association was observed between IBS or age of onset and both variants. Significant interactions were observed between GI infection and the GNβ3 825T allele. For those reporting gastrointestinal infection, the OR for IBS was 3.9 (95 % CI 1.2-12.7) whereas the OR was 0.86 (95 % CI 0.65-1.13) for those without prior infection.

CONCLUSIONS

There was a significant interaction between the GNβ3 polymorphism and infection in the development of IBS, suggesting that its etiology is the result of a combination of specific genetic and environmental risk factors.

Clinical implications of genetic variation in the serotonin transporter promoter region: a review

OBJECTIVE

To determine the state of the art in understanding the role of genetic variation in the serotonin transporter (5-HTT) promoter region (5-HTTLPR) in the development of a depressive episode and in its response to treatment.

DATA SOURCES

PubMed and Ovid were used to search for articles published prior to December 2007 utilizing the key words serotonin transporter, 5-HTT, 5-HTTLPR, serotonin transporter gene, and SLC6A4.

STUDY SELECTION

All studies were reviewed, but case reports and small case series were excluded.

DATA EXTRACTION

All relevant articles were read by at least 2 of the coauthors and notes regarding study design, measures, data analysis, and findings were later used to construct the review.

DATA SYNTHESIS

A common genetic variant, the short allele, in which 44 base pairs are missing from the promoter of SLC6A4, is associated with a greater risk for developing a major depressive disorder in patients following exposure to adversity. This association appears to be most important in the early stages of the depressive disorder. Additionally, the likelihood of a positive response to antidepressant treatment may be reduced in these patients in terms of delayed response, greater adverse event load, or, in bipolar patients, mania induction and rapid cycling.

CONCLUSIONS

Selected genetic testing of patients with a recent history of significant adversity may be a reasonable tool that can enlighten treatment options and the course of illness. Ongoing work with the short allele of 5-HTT may also inform clinical guidelines of long-term treatment with antidepressants.

Association of the 5-HTT gene-linked promoter region (5-HTTLPR) polymorphism with psychiatric disorders: review of psychopathology and pharmacotherapy

Serotonin (5-HT) regulates important biological and psychological processes including mood, and may be associated with the development of several psychiatric disorders. An association between psychopathology and genes that regulate 5-HT neurotransmission is a robust area of research. Identification of the genes responsible for the predisposition, development, and pharmacological response of various psychiatric disorders is crucial to the advancement of our understanding of their underlying neurobiology. This review highlights research investigating 5-HT transporter (5-HTTLPR) polymorphism, because studies investigating the impact of the 5-HTTLPR polymorphism have demonstrated significant associations with many psychiatric disorders. Decreased transcriptional activity of the S allele ("risk allele") may be associated with a heightened amygdala response leading to anxiety-related personality traits, major depressive disorder, suicide attempts, and bipolar disorder. By contrast, increased transcriptional activity of the L allele is considered protective for depression but is also associated with completed suicide, nicotine dependence, and attention deficit hyperactivity disorder. For some disorders, such as post-traumatic stress disorder and major depressive disorder, the research suggests that treatment response may vary by allele (such as an enhanced response to serotonin specific reuptake inhibitors in patients with major depressive disorder and post-traumatic stress disorder with L alleles), and for alcohol dependence, the association and treatment for S or L alleles may vary with alcoholic subtype. While some studies suggest that 5-HTTLPR polymorphism can moderate the response to pharmacotherapy, the association between 5-HTTLPR alleles and therapeutic outcomes is inconsistent. The discovery of triallelic 5-HTTLPR alleles (L(A)/L(G)/S) may help to explain some of the conflicting results of many past association studies, while concurrently providing more meaningful data in the future. Studies assessing 5-HTTLPR as the solitary genetic factor contributing to the etiology of psychiatric disorders continue to face the challenges of statistically small effect sizes and limited replication.

Ontogeny and regulation of the serotonin transporter: providing insights into human disorders

Serotonin (5-hydroxytryptamine, 5-HT) was one of the first neurotransmitters for which a role in development was identified. Pharmacological and gene knockout studies have revealed a critical role for 5-HT in numerous processes, including cell division, neuronal migration, differentiation and synaptogenesis. An excess in brain 5-HT appears to be mechanistically linked to abnormal brain development, which in turn is associated with neurological disorders. Ambient levels of 5-HT are controlled by a vast orchestra of proteins, including a multiplicity of pre- and post-synaptic 5-HT receptors, heteroreceptors, enzymes and transporters. The 5-HT transporter (SERT, 5-HTT) is arguably the most powerful regulator of ambient extracellular 5-HT. SERT is the high-affinity uptake mechanism for 5-HT and exerts tight control over the strength and duration of serotonergic neurotransmission. Perturbation of its expression level or function has been implicated in many diseases, prominent among them are psychiatric disorders. This review synthesizes existing information on the ontogeny of SERT during embryonic and early postnatal development though adolescence, along with factors that influence its expression and function during these critical developmental windows. We integrate this knowledge to emphasize how inappropriate SERT expression or its dysregulation may be linked to the pathophysiology of psychiatric, cardiovascular and gastrointestinal diseases.

Neurobiological and psychiatric consequences of child abuse and neglect

The effects of early-life trauma and its consequences for the treatment of depression are reviewed. The prevalence and clinical sequelae of early sexual and physical abuse, neglect and parental loss are described. An overview of preclinical studies that help guide clinical research and practice is presented. Human clinical studies on the neurobiological consequences of early trauma are summarized. Moderating factors, such as genetic variation and sex differences, are discussed. The few current treatment outcome studies relevant to this research area are described. Guidance for the management of patients with depression and a history of child abuse and neglect are provided. Most patients who have experienced early traumatic experiences are likely best treated with a combination of psychotherapy and pharmacotherapy. This review is dedicated to the memory of Seymour Levine who pioneered the field of early experience research and to a considerable extent inspired the clinical studies described in this review.

Interleukin-1 receptor activation by systemic lipopolysaccharide induces behavioral despair linked to MAPK regulation of CNS serotonin transporters

Serotonin (5-hydroxytryptamine, 5-HT) has long been implicated in regulation of mood. Medications that block the neuronal 5-HT transporter (SERT) are used as major pharmacological treatment for mood disorders. Conversely, stimuli that enhance SERT activity might be predicted to diminish synaptic 5-HT availability and increase the risk for 5-HT-related CNS disorders. We have shown that the inflammatory cytokines enhance brain SERT activity in cultured serotonergic cells and nerve terminal preparations in vitro. In this study, we establish that intraperitoneal injection of the cytokine-inducer lipopolysaccharide (LPS) stimulates brain SERT activity, acting at doses below those required to induce overt motor suppression. SERT stimulation by LPS is paralleled by increased immobility in both the tail suspension test (TST) and the forced swim test (FST); antidepressant-sensitive alterations are thought to model aspects of behavioral despair. Both the stimulation of SERT activity and induced immobility are absent when LPS is administered to interleukin-1 receptor (IL-1R)-deficient mice and in the presence of SB203580, an inhibitor of IL-1R-stimulated p38 MAPK. Moreover, the ability of LPS to enhance immobility in TST is lost in SERT knockout mice. These findings reveal an ability of peripheral inflammatory stimuli to enhance brain SERT activity through IL-1R and p38 MAPK pathways in vivo and identify a requirement for SERT expression in immune-system-modulated despair behaviors. Our studies identify IL-1R- and p38 MAPK-dependent regulation of SERT as one of the mechanisms by which environmentally driven immune system activation can trigger despair-like behavior in an animal model, encouraging future analysis of the pathway for risk factors in neuropsychiatric disorders.

Rotating disk electrode voltammetric measurements of serotonin transporter kinetics in synaptosomes

Altered serotonin (5-HT) signaling is implicated in several neuropsychiatric disorders, including depression, anxiety, obsessive-compulsive disorder, and autism. The 5-HT transporter (SERT) modulates 5-HT neurotransmission strength and duration. This is the first study using rotating disk electrode voltammetry (RDEV) to measure 5-HT clearance. SERT kinetics were measured in whole brain synaptosomes. Uptake kinetics of exogenous 5-HT were measured using glassy carbon electrodes rotated in 500 μL glass chambers containing synaptosomes from SERT-knockout (-/-), heterozygous (+/-), or wild-type (+/+) mice. RDEV detected 5-HT concentrations of 5nM and higher. Initial velocities were kinetically resolved with K(m) and V(max) values of 99±35 standard error of regression (SER) nM and 181±11 SER fmol/(s×mg protein), respectively in wild-type synaptosomes. The method enables control over drug and chemical concentrations, facilitating interpretation of results. Results are compared in detail to other techniques used to measure SERT kinetics, including tritium labeled assays, chronoamperometry, and fast scan cyclic voltammetry. RDEV exhibits decreased 5-HT detection limits, decreased vulnerability to 5-HT oxidation products that reduce electrode sensitivity, and also overcomes diffusion limitations via forced convection by providing a continuous, kinetically resolved signal. Finally, RDEV distinguishes functional differences between genotypes, notably, between wild-type and heterozygous mice, an experimental problem with other experimental approaches.

Real-time, spatially resolved analysis of serotonin transporter activity and regulation using the fluorescent substrate, ASP+

The serotonin transporter (SERT) mediates clearance of serotonin from the synapse, thereby, regulating extracellular serotonin concentrations. Radioligand uptake techniques are typically used to assess SERT function in tissue and heterologous expression systems. The need for sufficient protein in samples, however, requires use of homogenate preparations, potentially masking effects limited to specific cell populations. 4-(4-(dimethylamino)-styryl)-N-methylpyridinium (ASP(+)) is a fluorescent monoamine transporter substrate that has been used for real-time monitoring of dopamine and norepinephrine transporter function in single cells. The present live cell imaging studies examine the utility of ASP(+) for quantifying human SERT function in HEK293 and neuroblastoma cells. We show rapid membrane binding and intracellular ASP(+) accumulation in human SERT-expressing cells. Accumulation is saturable; dependent on temperature and the presence of sodium and chloride in the media, and attenuated by serotonin. Acute or prolonged exposure of cells to serotonin re-uptake inhibitors produces a concentration-dependent decrease in accumulation. Similar effects are produced by protein kinase C activation whereas p38 MAPK activation increases ASP(+) accumulation. These data demonstrate the validity of ASP(+) as a probe for monitoring SERT function in living cells. Alterations in SERT binding and uptake can be quantified in the same cell and use of a within-cell design permits analysis of time-related alterations in SERT function.

A prospective study of predictors of depression symptoms in police

Police work is one of the most stressful occupations. Previous research has indicated that work stress and trauma exposure may place individuals at heightened risk for the development of depression symptomatology. This prospective longitudinal study was designed to examine predictors of depression symptoms in police service. Participants comprised 119 healthy police recruits from an ongoing prospective study. They completed baseline measures of depression symptoms, childhood trauma exposure, neuroticism, and self-worth during academy training. Follow-up measures of depression symptoms, PTSD symptoms, critical incident exposure, negative life events, and routine work environment stress were assessed after 12 months of police service. Hierarchical linear regression analysis was conducted to examine predictors of current levels of depression symptoms, controlling for baseline depression symptoms and current PTSD symptoms. Greater childhood trauma exposure, lower self-worth during training, and greater perceived work stress in the first year of police service predicted greater depression symptoms at 12 months. Depression symptoms at 1 year of police service were partly independent from PTSD symptoms at 12 months. Greater childhood trauma exposure and lower self-worth during training may be important variables to screen as risk factors for duty-related depression. Strategies to reduce routine work environment stress have the potential to decrease duty-related depression in law enforcement.

The development of peripartum depressive symptoms is associated with gene polymorphisms of MAOA, 5-HTT and COMT

BACKGROUND

Polymorphisms of monoamine-related genes have been associated with depression following life events. The peripartum is a physiologically and psychologically challenging period, characterized by fluctuations in depressive symptoms, therefore facilitating prospective investigations in this gene x environment (G x E) interaction.

METHODS

Eighty nine pregnant women filled in two Edinburgh Postpartum Depression Scale (EPDS) questionnaires during pregnancy and two in the postpartum period. MAOA, COMT and 5-HTT polymorphisms were analyzed.

RESULTS

We found a significant interaction between the development of depressive symptoms in the course of pregnancy and polymorphisms in 5-HTT (p=0.019); MAOA (p=0.044) and COMT (p=0.026), and MAOA x COMT (p<0.001). Particularly, women carrying the combination of low activity variants of MAOA and COMT showed increased EPDS scores at week 36 of pregnancy and 6 weeks postpartum, but not during early pregnancy or 12 weeks postpartum.

CONCLUSION

We found that MAOA in combination with COMT appears to regulate not only the stress response in laboratory experiments, but also seems to influence the stress-evoked onset of mood during normal, mild, stressful events, such as experienced in the peripartum period. These findings support the GxE concept for depression, but they underline the complexity of this concept, as the cumulating effects of these polymorphic genes (i.e. MAOA+COMT) might be needed and the effects of these polymorphic genes becomes apparent in special environmental or physiological conditions (i.e. the peripartum period). We therefore suggest that G x E interactions become especially noticeable from longitudinal study designs in specific physiological or social challenging periods.

Dynorphin, stress, and depression

Stress is most often associated with aversive states. It rapidly induces the release of hormones and neuropeptides including dynorphin, which activates kappa opioid receptors (KORs) in the central and peripheral nervous systems. In animal models, many aversive effects of stress are mimicked or exacerbated by stimulation of KORs in limbic brain regions. Although KOR signaling during acute stress may increase physical ability (by producing analgesia) and motivation to escape a threat (by producing aversion), prolonged KOR signaling in response to chronic or uncontrollable stress can lead to persistent expression of behavioral signs that are characteristic of human depressive disorders (i.e., "prodepressive-like" signs). Accumulating evidence suggests that KORs contribute to the progressive amplification (sensitization) of stress-induced behaviors that occurs with repeated exposure to stress. Many of the aversive effects of stress are blocked by KOR antagonists, suggesting that these agents may have potential as therapeutics for stress-related conditions such as depression and anxiety disorders. This review summarizes current data on how KOR systems contribute to the acute (rapid), delayed, and cumulative molecular and behavioral effects of stress. We focus on behavioral paradigms that provide insight on interactions between stress and KOR function within each of these temporal categories. Using a simplified model, we consider the time course and mechanism of KOR-mediated effects in stress and suggest future directions that may be useful in determining whether KOR antagonists exert their therapeutic effects by preventing the development of stress-induced behaviors, the expression of stress-induced behaviors, or both.

Influence of sex and corticotropin-releasing factor pathways as determinants in serotonin sensitivity

Stress sensitivity and sex are predictive factors in affective disorder susceptibility. Serotonin (5-HT) pathway recruitment by corticotropin-releasing factor (CRF) during stress is necessary in adaptive coping behaviors, but sex differences in such responses have not been investigated. Using selective 5-HT reuptake inhibitor (SSRI) administration to acutely elevate 5-HT in a genetic model of stress sensitivity, we examined behavioral and physiological responses in male and female stress-sensitive CRF receptor-2-deficient (R2KO) mice. Chronic SSRI treatment was used to confirm outcomes were specific to acute 5-HT elevation and not antidepressant efficacy. We hypothesized that R2KO mice would show a greater sensitivity to acute changes in 5-HT and that, because females typically are more stress sensitive, R2KO females would be the most responsive. Our results supported this hypothesis because females of both genotypes and R2KO males showed a greater sensitivity to an acute 10 mg/kg dose of citalopram in a tail suspension test, displaying decreased immobile time and increased latency to immobility. Furthermore, acute citalopram promoted significant anxiogenic-like effects that were specific to R2KO females in the elevated plus maze and light-dark box tests. Chronic citalopram did not produce these behavioral changes, supporting specificity to acute 5-HT modulation. Mechanistically, females had decreased hippocampal 5-HT transporter (SERT) levels, whereas R2KO mice showed reduced SERT in the prefrontal cortex, supporting a possible intersection of sex and genotype where R2KO females would have the lowest SERT to be blocked by the SSRI. This sensitivity to 5-HT-mediated anxiety in females may underlie a heightened vulnerability to stress-related affective disorders.

Kappa-opioid ligands in the study and treatment of mood disorders

The biological basis of mood is not understood. Most research on mood and affective states has focused on the roles of brain systems containing monoamines (e.g., dopamine, norepinephrine, serotonin). However, it is becoming clear that endogenous opioid systems in the brain may also be involved in the regulation of mood. In this review, we focus on the potential utility of kappa-opioid receptor (KOR) ligands in the study and treatment of psychiatric disorders. Research from our group and others suggests that KOR antagonists might be useful for depression, KOR agonists might be useful for mania, and KOR partial agonists might be useful for mood stabilization. Currently available KOR agents have some unfavorable properties that might be addressed through medicinal chemistry. The development of KOR-selective agents with improved drug-like characteristics would facilitate preclinical and clinical studies designed to evaluate the possibility that KORs are a feasible target for new medications.

Gene-Environment Interactions in Depression Research

Recent studies on life stress, depression, and polymorphisms in the promoter region of the serotonin transporter gene (5-HTTLPR) are characterized by powerful genetic techniques, but are also characterized by unconventional and inconsistent approaches to assessing life stress. The present review addresses this problem by critically evaluating this rapidly growing literature with regard to the concepts and procedures employed to assess life stress and the research designs used to test causal associations. The existing body of evidence is seriously compromised by the predominance of ad hoc approaches for measuring life stress and by a lack of attention to key issues concerning research design. Principles and procedures for more refined and rigorous stress measurement are outlined. Improved guidelines are needed to direct future research on interactive effects of life stress and genes in psychopathology, pathophysiological processes, and disease.

The contribution of gene-environment interaction to psychopathology

The study of gene-environment interaction (G x E) constitutes an area of significant social and clinical significance. Different types of research study designs are being used to investigate the contribution of G x E to psychopathology, although the term G x E has also been used and interpreted in different ways. Despite mixed evidence that G x E contributes to psychopathology, some promising and consistent findings are emerging. Evidence is reviewed in relation to depression, antisocial behavior, schizophrenia, and attention-deficit/hyperactivity disorder. Although findings from various research designs have different meaning, interestingly much of the evidence with regard to the contribution of G x E that has arisen from twin and adoption studies has been for antisocial behavior and depression. It is for these same forms of psychopathology that molecular genetic evidence of G x E has also been most convincing. Finally, current and anticipated methodological challenges and implications for future research in this area are considered.

Changes in midbrain serotonin transporter availability in atypically depressed subjects after one year of psychotherapy

BACKGROUND

Psychotherapy is an effective treatment method for depression, but no differences in the psychotherapy response have been found between the subtypes of depression. The effect of psychotherapy on neurotransmitter transporter functions has never been recorded in depressed subjects.

METHODS

Depressive outpatients (N=19) received psychodynamic psychotherapy for 12 months. All subjects fulfilled the DSM-IV criteria for depression, and 8 were classified as having atypical depression. The severity of depression was assessed with the 29-item Hamilton Depression Rating Scale (HAM-D-29). Midbrain serotonin transporter (SERT) and striatum dopamine transporter (DAT) densities were recorded using single photon emission computed tomography (SPECT) brain imaging with the [123I]nor-beta-CIT radioligand before and after psychotherapy.

RESULTS

Midbrain SERT density significantly increased during psychotherapy in atypicals but not in nonatypicals. There were no changes in the levels of DAT.

CONCLUSIONS

The psychotherapy-related SERT elevation of atypically depressed subjects may be due to some unknown adaptive mechanisms inducing an increase in either the levels of SERT or serotonergic nerve terminals and therefore enhancing serotonergic activity and improving mood.

Serotonin transporter polymorphism, memory and hippocampal volume in the elderly: association and interaction with cortisol

The s allele variant of the serotonin transporter gene (5-HTT) has recently been observed to moderate the relationship of stress to depression and anxiety. To date no study has considered interactive effects of 5-HTT genotype, stress and hypothalamic-pituitary-adrenal (HPA) function on cognition in healthy, older adults, which may reflect developmental, functional or neurodegenerative effects of the serotonin transporter polymorphism. We investigated whether 5-HTT genotype interacts with cumulative life stress and HPA-axis measures of waking and diurnal cortisol slope to impact cognition in 154 non-depressed, older adults. Structural images of hippocampal volume were acquired on a subsample of 56 participants. The 5-HTT s allele was associated with both significantly lower delayed recall and higher waking cortisol levels. Presence of the s allele interacted with higher waking cortisol to negatively impact memory. We also observed a significant interaction of higher waking cortisol and the s allele on lower hippocampal volume. Smaller hippocampi and higher cortisol were associated with lower delayed recall only in s allele carriers. No impact or interactions of cumulative life stress with 5-HTT or cortisol were observed. This is the first investigation to identify an association of the 5-HTT s allele with poorer memory function in older adults. The interactive effects of the s allele and waking cortisol levels on reduced hippocampal volume and lower memory suggest that the negative effect of the serotonin polymorphism on memory is mediated by the HPA axis. Further, given the significant association of the s allele with higher waking cortisol in our investigation, future studies may be needed to evaluate the impact of the serotonin transporter polymorphism on any neuropsychiatric or behavioral outcome which is influenced by HPA axis function in older adults.