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

Brain serotonin and serotonin transporter expression in male and female postnatal rat offspring in response to perturbed early life dietary exposures

Introduction

Serotonin (5-HT) is critical for neurodevelopment and the serotonin transporter (SERT) modulates serotonin levels. Perturbed prenatal and postnatal dietary exposures affect the developing offspring predisposing to neurobehavioral disorders in the adult. We hypothesized that the postnatal brain 5-HT-SERT imbalance associated with gut dysbiosis forms the contributing gut-brain axis dependent mechanism responsible for such ultimate phenotypes.

Methods

Employing maternal diet restricted (IUGR, n=8) and high fat+high fructose (HFhf, n=6) dietary modifications, rodent brain serotonin was assessed temporally by ELISA and SERT by quantitative Western blot analysis. Simultaneously, colonic microbiome studies were performed.

Results

At early postnatal (P) day 2 no changes in the IUGR, but a ~24% reduction in serotonin (p = 0.00005) in the HFhf group occurred, particularly in the males (p = 0.000007) revealing a male versus female difference (p = 0.006). No such changes in SERT concentrations emerged. At late P21 the IUGR group reared on HFhf (IUGR/HFhf, (n = 4) diet revealed increased serotonin by ~53% in males (p = 0.0001) and 36% in females (p = 0.023). While only females demonstrated a ~40% decrease in serotonin (p = 0.010), the males only trended lower without a significant change within the HFhf group (p = 0.146). SERT on the other hand was no different in HFhf or IUGR/RC, with only the female IUGR/HFhf revealing a 28% decrease (p = 0.036). In colonic microbiome studies, serotonin-producing Bacteriodes increased with decreased Lactobacillus at P2, while the serotonin-producing Streptococcus species increased in IUGR/HFhf at P21. Sex-specific changes emerged in association with brain serotonin or SERT in the case of Alistipase, Anaeroplasma, Blautia, Doria, Lactococcus, Proteus, and Roseburia genera.

Discussion

We conclude that an imbalanced 5-HT-SERT axis during postnatal brain development is sex-specific and induced by maternal dietary modifications related to postnatal gut dysbiosis. We speculate that these early changes albeit transient may permanently alter critical neural maturational processes affecting circuitry formation, thereby perturbing the neuropsychiatric equipoise.

Tracing Superoxide Anion in Serotonergic Neurons of Living Mouse Brains with Depression by Small-Molecule Fluorescence Probes

In brains, the serotonergic neurons are the unique resource of the neurotransmitter serotonin, which plays a pivotal role in the physiology of the brain. The dysfunction of serotonergic neurons caused by oxidative stress in the brain is closely related to the occurrence and development of various mental diseases, such as depression. As the biomarker of oxidative stress, the superoxide anion radical (O2•-) can cause oxidative damage to proteins, nucleic acids and lipids, disturbing the function of neurons and brains. A serotonin transporter (SERT) specifically expresses in serotonergic neurons, which is the biomarker of serotonergic neurons. Thus, we created two novel small molecular fluorescent probes (PA-CA and HT-CA) for imaging O2•- in serotonergic neurons of living brains of mice based on specific targeting groups of SERT. Both PA-CA and HT-CA exert excellent SERT-targetable and glorious selectivity for O2•-. Those two probes could monitor the boost of O2•- in living hsert-HEK293 cells that specifically express SERT under oxidative stress. With two-photon fluorescence imaging, we revealed for the first time that O2•- is significantly increased in serotonergic neurons in living brains of mice with depression. More importantly, proteomic analyses suggested that O2•- could oxidize cysteine and histidine in the active site of SERT, which is involved in the development of depression. This work provides new materials for living brain imaging and offers new strategy for unraveling the pathophysiology of depression.

Serotonin and the serotonin transporter in the adrenal gland

The adrenal glands are key components of the mammalian endocrine system, helping maintain physiological homeostasis and the coordinated response to stress. Each adrenal gland has two morphologically and functionally distinct regions, the outer cortex and inner medulla. The cortex is organized into three concentric zones which secrete steroid hormones, including aldosterone and cortisol. Neural crest-derived chromaffin cells in the medulla are innervated by preganglionic sympathetic neurons and secrete catecholamines (epinephrine, norepinephrine) and neuropeptides into the bloodstream, thereby functioning as the neuroendocrine arm of the sympathetic nervous system. In this article we review serotonin (5-HT) and the serotonin transporter (SERT; SLC6A4) in the adrenal gland. In the adrenal cortex, 5-HT, primarily sourced from resident mast cells, acts as a paracrine signal to stimulate aldosterone and cortisol secretion through 5-HT4/5-HT7 receptors. Medullary chromaffin cells contain a small amount of 5-HT due to SERT-mediated uptake and express 5-HT1A receptors which inhibit secretion. The atypical mechanism of the 5-HT1A receptors and interaction with SERT fine tune this autocrine pathway to control stress-evoked catecholamine secretion. Receptor-independent signaling by SERT/intracellular 5-HT modulates the amount and kinetics of transmitter release from single vesicle fusion events. SERT might also influence stress-evoked upregulation of tyrosine hydroxylase transcription. Transient signaling via 5-HT3 receptors during embryonic development can limit the number of chromaffin cells found in the mature adrenal gland. Together, this emerging evidence suggests that the adrenal medulla is a peripheral hub for serotonergic control of the sympathoadrenal stress response.

Maternal LPS Exposure Enhances the 5-HT Level in the Prefrontal Cortex of Autism-like Young Offspring

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by reduced social interactions, impaired communication, and stereotyped behavior. The aim of this research is to investigate the changes in serotonin (5-HT) in the medial prefrontal cortex (PFC) of autism-like offspring induced by maternal lipopolysaccharide (LPS) exposure. Pregnant Sprague-Dawley rats were intraperitoneally injected with LPS to establish an autism-like model in their offspring. Offspring prenatally exposed to LPS showed autism-like behavior. The serotonin level in the mPFC of 2-week-old offspring was noticeably increased after maternal LPS exposure. Differentially expressed genes (DEGs) were enriched in pathways related to tryptophan metabolism and the serotonin system, as shown in RNA-seq findings. Consistently, tryptophan and serotonin metabolisms were altered in 2-week-old LPS-exposed offspring. The mRNA expression levels of 5-HT catabolic enzymes were remarkably reduced or tended to decrease. Moreover, maternal LPS exposure resulted in a higher serotonin 1B receptor (5-HT_1BR) expression level in the mPFC but no difference in tryptophan hydroxylase 2 (TPH2) or serotonin reuptake transporter (SERT). The concentrations of 5-HT in serum and colon were increased in LPS-exposed offspring. Meanwhile, the expression level of tryptophan hydroxylase 1 (TPH1) in the colon was increased after maternal LPS treatment, whereas SERT was reduced. Furthermore, Golgi-Cox staining showed that neuronal dendritic length and spine density were significantly reduced in the mPFC of LPS-exposed offspring. The current study reveals that maternal LPS treatment resulted in an exaltation of the 5-HT of mPFC in ASD-like young rats, which may partly be caused by the abnormal elevation of 5-HT metabolism in its colon.

Multi-omics analysis reveals changes in tryptophan and cholesterol metabolism before and after sexual maturation in captive macaques

Rhesus macaques (Macaca mulatta, RMs) are widely used in sexual maturation studies due to their high genetic and physiological similarity to humans. However, judging sexual maturity in captive RMs based on blood physiological indicators, female menstruation, and male ejaculation behavior can be inaccurate. Here, we explored changes in RMs before and after sexual maturation based on multi-omics analysis and identified markers for determining sexual maturity. We found that differentially expressed microbiota, metabolites, and genes before and after sexual maturation showed many potential correlations. Specifically, genes involved in spermatogenesis (TSSK2, HSP90AA1, SOX5, SPAG16, and SPATC1) were up-regulated in male macaques, and significant changes in gene (CD36), metabolites (cholesterol, 7-ketolithocholic acid, and 12-ketolithocholic acid), and microbiota (Lactobacillus) related to cholesterol metabolism were also found, suggesting the sexually mature males have stronger sperm fertility and cholesterol metabolism compared to sexually immature males. In female macaques, most differences before and after sexual maturity were related to tryptophan metabolism, including changes in IDO1, IDO2, IFNGR2, IL1Β, IL10, L-tryptophan, kynurenic acid (KA), indole-3-acetic acid (IAA), indoleacetaldehyde, and Bifidobacteria, indicating that sexually mature females exhibit stronger neuromodulation and intestinal immunity than sexually immature females. Cholesterol metabolism-related changes (CD36, 7-ketolithocholic acid, 12-ketolithocholic acid) were also observed in female and male macaques. Exploring differences before and after sexual maturation through multi-omics, we identified potential biomarkers of sexual maturity in RMs, including Lactobacillus (for males) and Bifidobacterium (for females) valuable for RM breeding and sexual maturation research.

Effect of citalopram and sertraline on the expression of miRNA- 124, 132, and 16 and their protein targets in patients with depression

Objectives

This study aimed to evaluate the effect of SSRIs on the expression of miRNAs and their protein targets.

Materials and Methods

In a 100 day open-label study of citalopram (n=25) and sertraline (n=25), levels of miRNA 16, 132, and 124 and glucocorticoid receptor (GR), Brain-derived neurotrophic factor (BDNF), and serotonin transporter (SERT) protein expression were measured by QRT-PCR and western blot in healthy control (n=20), patients with depression at the baseline, and same patients after 100 days of treatment.

Results

Expression levels of GR and BDNF proteins were lower in the depressed group before treatment as compared with the healthy group (P<0.0001). The SERT level was higher among the depressed group before treatment in comparison with the healthy group (P<0.0001). The level of GR and BDNF significantly increased, and SERT expression decreased after receiving sertraline (P<0.05). When the depressed group received citalopram, only SERT and GR were altered (P<0.05). Among the microRNAs' expression investigated, mir-124 and mir-132 were higher, and mir-16 was lower among the depressed compared with the healthy group (P<0.0001). Individuals receiving citalopram only showed an increase in the expression of mir-16 while administration of sertraline led to a significant increase in the expression of mir-16 and a decrease in mir-124 and mir-132 (P<0.05).

Conclusion

This elucidated the relationship between antidepressant treatment and the expression of different microRNA that control gene expression in various pathways involved in depressed patients. Receiving SSRI can affect the level of these proteins and their relevant microRNAs.

Maternal Western-style diet reduces social engagement and increases idiosyncratic behavior in Japanese macaque offspring

Recent evidence in humans and animals indicates an association between maternal obesity and offspring behavioral outcomes. In humans, increased maternal body mass index has been linked to an increased risk of children receiving a diagnosis of early-emerging neurodevelopmental disorders such as Attention Deficit/Hyperactivity Disorder (ADHD) and/or Autism Spectrum Disorder (ASD). However, a limited number of preclinical studies have examined associations between maternal Western-Style Diet (mWSD) exposure and offspring social behavior. To our knowledge, this is the first study to investigate relationships between mWSD exposure and social behavior in non-human primates. Since aberrant social behavior is a diagnostic criterion for several neurodevelopmental disorders, the current study focuses on examining the influence of maternal nutrition and metabolic state on offspring social behavior in Japanese macaques (Macaca fuscata). We found that mWSD offspring initiated less affiliative social behaviors as well as proximity to a peer. Using path analysis, we found that the association between mWSD consumption and reduced offspring social engagement was statistically mediated by increased maternal interleukin (IL)-12 during the third trimester of pregnancy. Additionally, mWSD offspring displayed increased idiosyncratic behavior, which was related to alterations in maternal adiposity and leptin in the third trimester. Together, these results suggest that NHP offspring exposed to mWSD exhibit behavioral phenotypes similar to what is described in some early-emerging neurodevelopmental disorders. These results provide evidence that mWSD exposure during gestation may be linked to increased risk of neurodevelopmental disorders and provides targets for prevention and intervention efforts.

The Influence of Maternal Metabolic State and Nutrition on Offspring Neurobehavioral Development: A Focus on Preclinical Models

The prevalence of both obesity and neurodevelopmental disorders has increased substantially over the last several decades. Early environmental factors, including maternal nutrition and metabolic state during gestation, influence offspring neurodevelopment. Both human and preclinical models demonstrate a link between poor maternal nutrition, altered metabolic state, and risk of behavioral abnormalities in offspring. This review aims to highlight evidence from the current literature connecting maternal nutrition and the associated metabolic changes with neural and behavioral outcomes in the offspring, as well as identify possible mechanisms underlying these neurodevelopmental outcomes. Owing to the highly correlated nature of poor nutrition and obesity in humans, preclinical animal models are important in distinguishing the unique effects of maternal nutrition and metabolic state on offspring brain development. We use a translational lens to highlight results from preclinical animal models of maternal obesogenic diet related to alterations in behavioral and neurodevelopmental outcomes in offspring. Specifically, we aim to highlight results that resemble behavioral phenotypes described in the diagnostic criteria of neurodevelopmental conditions in humans. Finally, we examine the proinflammatory nature of maternal obesity and consumption of a high-fat diet as a mechanism for neurodevelopmental alterations that may alter offspring behavior later in life. It is important that future studies examine potential therapeutic interventions and prevention strategies to interrupt the transgenerational transmission of the disease. Given the tremendous risk to the next generation, changes need to be made to ensure that all pregnant people have access to nutritious food and are informed about the optimal diet for their developing child.

Role of the cAMP-PKA-CREB-BDNF pathway in abnormal behaviours of serotonin transporter knockout mice

Serotonin transporter gene-linked polymorphic region polymorphisms are associated with anxiety, neuroticism, affective disorders and vulnerability to stressful life events; however, the relevant physiological mechanisms are not well understood. Serotonin transporter knockout mice have been widely used as a model of allelic variation of serotonin transporter function in humans; herein, wild-type mice and heterozygous and homozygous knockout mice models were established to explore the behavioural changes related to different genotypes and the possible physiological mechanisms. Behavioural changes were assessed using behavioural tests, namely, elevated plus maze, open field, Morris water maze and rotarod tests. Serum indicators were detected using the enzyme-linked immunosorbent assay. Compared with wild-type mice, homozygous mice showed significant anxiety-like behaviours in the plus maze and open field tests; conversely, anxiety-like behaviours in heterozygous mice were less pronounced. Homozygous mice also showed cognitive impairment and motor inhibition in the Morris water maze and rotarod tests. Serotonin levels decreased in both heterozygous and homozygous mice, and 5-hydroxytryptophan, protein kinase A, adenylyl cyclase, cyclic adenosine monophosphate response element-binding protein and brain-derived neurotrophic factor levels were lower in homozygous mice than in wild-type and heterozygous mice, whereas no statistical differences were found between wild-type and heterozygous mice. Additionally, there was a correlation between serological and behavioural indicators. This study provided experimental evidence that the cyclic adenosine monophosphate-protein kinase A-cyclic adenosine monophosphate response element-binding protein-brain-derived neurotrophic factor pathway may be involved in the regulation of polymorphism to stress and enriched the behavioural and physiological characteristics of serotonin transporter knockout mice.

The complex interactions among serotonin, insulin, leptin, and glycolipid metabolic parameters in human obesity

OBJECTIVE

To provide evidence to the link between serotonin (5-HT), energy metabolism, and the human obese phenotype, the present study investigated the binding and function of the platelet 5-HT transporter (SERT), in relation to circulating insulin, leptin, and glycolipid metabolic parameters.

METHODS

Seventy-four drug-free subjects were recruited on the basis of divergent body mass index (BMIs) (16.5-54.8 Kg/m2). All subjects were tested for their blood glycolipid profile together with platelet [3H]-paroxetine ([3H]-Par) binding and [3H]-5-HT reuptake measurements from April 1st to June 30th, 2019.

RESULTS

The [3H]-Par Bmax (fmol/mg proteins) was progressively reduced with increasing BMIs (P < .001), without changes in affinity. Moreover, Bmax was negatively correlated with BMI, waist/hip circumferences (W/HC), triglycerides (TD), glucose, insulin, and leptin, while positively with high-density lipoprotein (HDL) cholesterol (P < .01). The reduction of 5-HT uptake rate (Vmax, pmol/min/109 platelets) among BMI groups was not statistically significant, but Vmax negatively correlated with leptin and uptake affinity values (P < .05). Besides, [3H]-Par affinity values positively correlated with glycemia and TD, while [3H]-5-HT reuptake affinity with glycemia only (P < .05). Finally, these correlations were specific of obese subjects, while, from multiple linear-regression analysis conducted on all subjects, insulin (P = .006) resulting negatively related to Bmax independently from BMI.

CONCLUSIONS

Present findings suggest the presence of a possible alteration of insulin/5-HT/leptin axis in obesity, differentially impinging the density, function, and/or affinity of the platelet SERT, as a result of complex appetite/reward-related interactions between the brain, gut, pancreatic islets, and adipose tissue. Furthermore, they support the foremost cooperation of peptides and 5-HT in maintaining energy homeostasis.

Bipolar women's antepartum psychotropic exposure and offspring risk of attention-deficit/hyperactivity disorder and autism spectrum disorder

BACKGROUND

Women with bipolar disorder (BD) may continue psychotropics during pregnancy. The association of exposure to antidepressant, antipsychotics, and mood stabilizers with offspring risks of attention-deficit/hyperactivity disorder (ADHD) and autism spectrum disorder (ASD) remains unexplored in mothers with BD.

METHODS

A total of 5669 pregnant women with BD and 5669 psychiatrically healthy controls were identified between 2002 and 2011 from the Taiwan Longitudinal Health Insurance Database. We analyzed the odds ratios (ORs) of psychotropic types and exposure periods (3 months before pregnancy [3MbPreg] and first, second, and third trimesters [T1, T2, T3, respectively]) on the risk of ADHD and ASD by using adjusted logistic regression analyses.

RESULTS

Antidepressant exposure during 3MbPreg (OR=2.15, 95% CI=1.45-3.20), T1 (OR=2.62, 95% CI=1.68-4.09), T2 (OR=2.33, 95% CI=1.18-4.63), and T3 (OR=2.33, 95% CI=1.67-6.61) was associated with increased offspring risk of ADHD, particularly for selective serotonin reuptake inhibitor and serotonin norepinephrine reuptake inhibitor. Mood stabilizer exposure during 3MbPreg increased the risks of ADHD (OR=2.39, 95% CI=1.45-3.95) and ASD (OR=3.89, 95% CI=1.30-11.65); a higher ADHD risk was associated with valproic acid (OR=2.43, 95% CI=1.32-4.47) and lamotrigine exposure (OR=8.24, 95% CI = 1.49-45.67); ASD risk was higher for lithium exposure (OR=6.75, 95% CI=1.41-32.28).

LIMITATION

In claims-data analyses, several clinical parameters or potential confounders may be incompletely captured.

CONCLUSIONS

Antidepressants were associated with higher offspring risk of ADHD over all gestation periods among mothers with BD than psychiatrically healthy controls, while mood stabilizers were associated with higher risk of ADHD and ASD during 3MbPreg.

The edible Lactobacillus paracasei X11 with Konjac glucomannan promotes intestinal motility in zebrafish

BACKGROUND

Constipation is a gastrointestinal symptom with high incidence rate and large number of patients. It is becoming one of the urgent medical problems. Poor intestinal motility is one of the important causes of constipation. Current drug treatments for constipation are associated with many side effects; thus, it is necessary to study more effective treatment methods and potential mechanism.

METHODS

A zebrafish model of intestinal motility obstruction was established by loperamide hydrochloride to evaluate the effect of probiotic, food ingredients, and combination on intestinal peristalsis according to intestinal peristalsis frequency counts. The gastrointestinal survival ability of the best probiotics was evaluated by surface hydrophobicity, self-aggregation, acid and bile salt tolerance, and gastrointestinal transit tolerance. Interactions between probiotics and food ingredients were studied in vivo and in vitro. The expression of 5-HT was detected by ELISA and fluorescence immunoassay, and 5-HT related genes were detected by RT-PCR.

KEY RESULTS

We obtained the probiotics, food ingredients, and combination that effectively promoted intestinal peristalsis, X11 and YRL577, P. persica and KGM, KGM + X11, respectively. Both KGM and P. persica promoted colonization of probiotics in vivo. KGM + X11 could effectively promote the increase in 5-HT synthesis in zebrafish via up-regulating gene expression of TPH-1, TPH-2, and 5-HT_R and down-regulating gene expression of SERT. The specific in-depth mechanism needs further study.

CONCLUSIONS AND INFERENCES

The combinations of KGM with X11 effectively promoted intestinal peristalsis. We provide a theoretical basis for new modalities that can promote intestinal peristalsis and alleviate constipation.

Organic Cation Transporters in Psychiatric Disorders

Selective serotonin reuptake inhibitors (SSRIs) are the most commonly prescribed medications for psychiatric disorders, yet they leave the majority of patients without full symptom relief. Therefore, a major research challenge is to identify novel targets for the improved treatment of these disorders. SSRIs act by blocking the serotonin transporter (SERT), the high-affinity, low-capacity, uptake-1 transporter for serotonin. Other classes of antidepressant work by blocking the norepinephrine or dopamine transporters (NET and DAT), the high-affinity, low-capacity uptake-1 transporters for norepinephrine and dopamine, or by blocking combinations of SERT, NET, and DAT. It has been proposed that uptake-2 transporters, which include organic cation transporters (OCTs) and the plasma membrane monoamine transporter (PMAT), undermine the therapeutic utility of uptake-1 acting antidepressants. Uptake-2 transporters for monoamines have low affinity for these neurotransmitters, but a high capacity to transport them. Thus, activity of these transporters may limit the increase of extracellular monoamines thought to be essential for ultimate therapeutic benefit. Here preclinical evidence supporting a role for OCT2, OCT3, and PMAT in behaviors relevant to psychiatric disorders is presented. Importantly, preclinical evidence revealing these transporters as targets for the development of novel therapeutics for psychiatric disorders is discussed.

Pediatric Drug-Drug Interaction Evaluation: Drug, Patient Population, and Methodological Considerations

Hospitalized pediatric patients and those with complex or chronic conditions treated on an outpatient basis are commonly prescribed multiple drugs, resulting in increased risk for drug-drug interactions (DDIs). Although dedicated DDI evaluations are routinely performed in healthy adult volunteers during drug development, they are rarely performed in pediatric patients because of ethical, logistical, and methodological challenges. In the absence of pediatric DDI evaluations, adult DDI data are often extrapolated to pediatric patients. However, the magnitude of a DDI in pediatric patients may differ from adults because of age-dependent physiological changes that can impact drug disposition or response and because of other factors related to the drug (eg, dose, formulation) and the patient population (eg, disease state, obesity). Therefore, the DDI magnitude needs to be assessed in children separately from adults, although a lack of clinical DDI data in pediatric populations makes this evaluation challenging. As a result, pediatric DDI assessment relies on the predictive performance of the pharmacometric approaches used, such as population and physiologically based pharmacokinetic modeling. Therefore, careful consideration needs to be given to adequately account for the age-dependent physiological changes in these models to build high confidence for such untested DDI scenarios. This review article summarizes the key considerations related to the drug, patient population, and methodology, and how they can impact DDI evaluation in the pediatric population.

Fecal Microbiome Transplantation from Children with Autism Spectrum Disorder Modulates Tryptophan and Serotonergic Synapse Metabolism and Induces Altered Behaviors in Germ-Free Mice

To determine the relationship of the gut microbiota and its metabolites with autism spectrum disorder (ASD)-like behaviors and preliminarily explore the potential molecular mechanisms, the fecal microbiota from donors with ASD and typically developing (TD) donors were transferred into germ-free (GF) mice to obtain ASD-FMT mice and TD-FMT mice, respectively. Behavioral tests were conducted on these mice after 3 weeks. 16S rRNA gene sequencing of the cecal contents and untargeted metabolomic analysis of the cecum, serum, and prefrontal cortex were performed. Untargeted metabolomics was also used to analyze fecal samples of TD and ASD children. Western blotting detected the protein expression levels of tryptophan hydroxylase 1 (TPH1), serotonin transporter (SERT), and serotonin 1A receptor (5-HT1AR) in the colon and TPH2, SERT, and 5-HT1AR in the prefrontal cortex of mice. ASD-FMT mice showed ASD-like behavior and a microbial community structure different from that of TD-FMT mice. Tryptophan and serotonin metabolisms were altered in both ASD and TD children and ASD-FMT and TD-FMT mice. Some microbiota may be related to tryptophan and serotonin metabolism. Compared with TD-FMT mice, ASD-FMT mice showed low SERT and 5-HT1AR and high TPH1 expression levels in the colon. In the prefrontal cortex, the expression levels of TPH2 and SERT were increased in the ASD-FMT group relative to the TD-FMT group. Therefore, the fecal microbiome of ASD children can lead to ASD-like behaviors, different microbial community structures, and altered tryptophan and serotonin metabolism in GF mice. These changes may be related to changes in some key proteins involved in the synthesis and transport of serotonin.

IMPORTANCE The relationship between the gut microbiota and ASD is not yet fully understood. Numerous studies have focused on the differences in intestinal microbial and metabolism profiles between TD and ASD children. However, it is still not clear if these microbes and metabolites cause the development of ASD symptoms. Here, we collected fecal samples from TD and ASD children, transplanted them into GF mice, and found that the fecal microbiome of ASD children can lead to ASD-like behaviors, different microbial community structures, and altered tryptophan and serotonin metabolism in GF mice. We also demonstrated that tryptophan and serotonin metabolism was also altered in ASD and TD children. Together, these findings confirm that the microbiome from children with ASD may lead to ASD-like behavior of GF mice through metabolites, especially tryptophan and serotonin metabolism.

Developing Brain Glucose Transporters, Serotonin, Serotonin Transporter, and Oxytocin Receptor Expression in Response to Early-Life Hypocaloric and Hypercaloric Dietary, and Air Pollutant Exposures

Perturbed maternal diet and prenatal exposure to air pollution (AP) affect the fetal brain, predisposing to postnatal neurobehavioral disorders. Glucose transporters (GLUTs) are key in fueling neurotransmission; deficiency of the neuronal isoform GLUT3 culminates in autism spectrum disorders. Along with the different neurotransmitters, serotonin (5-HT) and oxytocin (OXT) are critical for the development of neural connectivity. Serotonin transporter (SERT) modulates synaptic 5-HT levels, while the OXT receptor (OXTR) mediates OXT action. We hypothesized that perturbed brain GLUT1/GLUT3 regulated 5-HT-SERT imbalance, which serves as a contributing factor to postnatal neuropsychiatric phenotypes, with OXT/OXTR providing a counterbalance. Employing maternal diet restriction (intrauterine growth restriction [IUGR]), high-fat (HF) dietary modifications, and prenatal exposure to simulated AP, fetal (E19) murine brain 5-HT was assessed by ELISA with SERT and OXTR being localized by immunohistochemistry and measured by quantitative Western blot analysis. IUGR with lower head weights led to a 48% reduction in male and female fetal brain GLUT3 with no change in GLUT1, when compared to age- and sex-matched controls, with no significant change in OXTR. In addition, a ∼50% (p = 0.005) decrease in 5-HT and SERT concentrations was displayed in fetal IUGR brains. In contrast, despite emergence of microcephaly, exposure to a maternal HF diet or AP caused no significant changes. We conclude that in the IUGR during fetal brain development, reduced GLUT3 is associated with an imbalanced 5-HT-SERT axis. We speculate that these early changes may set the stage for altering the 5HT-SERT neural axis with postnatal emergence of associated neurodevelopmental disorders.

General Overview of Organic Cation Transporters in Brain

Inhibitors of Na⁺/Cl^- dependent high affinity transporters for norepinephrine (NE), serotonin (5-HT), and/or dopamine (DA) represent frequently used drugs for treatment of psychological disorders such as depression, anxiety, obsessive-compulsive disorder, attention deficit hyperactivity disorder, and addiction. These transporters remove NE, 5-HT, and/or DA after neuronal excitation from the interstitial space close to the synapses. Thereby they terminate transmission and modulate neuronal behavioral circuits. Therapeutic failure and undesired central nervous system side effects of these drugs have been partially assigned to neurotransmitter removal by low affinity transport. Cloning and functional characterization of the polyspecific organic cation transporters OCT1 (SLC22A1), OCT2 (SLC22A2), OCT3 (SLC22A3) and the plasma membrane monoamine transporter PMAT (SLC29A4) revealed that every single transporter mediates low affinity uptake of NE, 5-HT, and DA. Whereas the organic transporters are all located in the blood brain barrier, OCT2, OCT3, and PMAT are expressed in neurons or in neurons and astrocytes within brain areas that are involved in behavioral regulation. Areas of expression include the dorsal raphe, medullary motoric nuclei, hypothalamic nuclei, and/or the nucleus accumbens. Current knowledge of the transport of monoamine neurotransmitters by the organic cation transporters, their interactions with psychotropic drugs, and their locations in the brain is reported in detail. In addition, animal experiments including behavior tests in wildtype and knockout animals are reported in which the impact of OCT2, OCT3, and/or PMAT on regulation of salt intake, depression, mood control, locomotion, and/or stress effect on addiction is suggested.

Pharmacodynamic Gene Testing in Prader-Willi Syndrome

Prader-Willi syndrome (PWS) is a rare genetic disorder with a complex neurobehavioral phenotype associated with considerable psychiatric co-morbidity. This clinical case series, for the first time, describes the distribution and frequency of polymorphisms of pharmacodynamic genes (serotonin transporter, serotonin 2A and 2C receptors, catechol-o-methyltransferase, adrenergic receptor 2A, methylene tetrahydrofolate reductase, and human leucocytic antigens) across the two major molecular classes of PWS in a cohort of 33 referred patients who met medical criteria for testing. When results were pooled across PWS genetic subtypes, genotypic and allelic frequencies did not differ from normative population data. However, when the genetic subtype of PWS was examined, there were differences observed across all genes tested that may affect response to psychotropic medication. Due to small sample size, no statistical significance was found, but results suggest that pharmacodynamic gene testing should be considered before initiating pharmacotherapy in PWS. Larger scale studies are warranted.

Fetal brain and placental programming in maternal obesity: A review of human and animal model studies

Both human epidemiologic and animal model studies demonstrate that prenatal and lactational exposure to maternal obesity and high-fat diet are associated with adverse neurodevelopmental outcomes in offspring. Neurodevelopmental outcomes described in offspring of obese women include cognitive impairment, autism spectrum disorder (ASD), attention deficit hyperactivity disorder, anxiety and depression, disordered eating, and propensity for reward-driven behavior, among others. This review synthesizes human and animal data linking maternal obesity and high-fat diet consumption to abnormal fetal brain development, and neurodevelopmental and psychiatric morbidity in offspring. It highlights key mechanisms by which maternal obesity and maternal diet impact fetal and offspring development, and sex differences in offspring programming. In addition, we review placental effects of maternal obesity, and the role the placenta might play as an indicator vs mediator of fetal programming.

An atlas of the protein-coding genes in the human, pig, and mouse brain

The brain, with its diverse physiology and intricate cellular organization, is the most complex organ of the mammalian body. To expand our basic understanding of the neurobiology of the brain and its diseases, we performed a comprehensive molecular dissection of 10 major brain regions and multiple subregions using a variety of transcriptomics methods and antibody-based mapping. This analysis was carried out in the human, pig, and mouse brain to allow the identification of regional expression profiles, as well as to study similarities and differences in expression levels between the three species. The resulting data have been made available in an open-access Brain Atlas resource, part of the Human Protein Atlas, to allow exploration and comparison of the expression of individual protein-coding genes in various parts of the mammalian brain.

Maternal neglect and the serotonin system are associated with daytime sleep in infant rhesus monkeys

Environmental and biological factors contribute to sleep development during infancy. Parenting plays a particularly important role in modulating infant sleep, potentially via the serotonin system, which is itself involved in regulating infant sleep. We hypothesized that maternal neglect and serotonin system dysregulation would be associated with daytime sleep in infant rhesus monkeys. Subjects were nursery-reared infant rhesus macaques (n = 287). During the first month of life, daytime sleep-wake states were rated bihourly (0800-2100). Infants were considered neglected (n = 16) if before nursery-rearing, their mother repeatedly failed to retrieve them. Serotonin transporter genotype and concentrations of cerebrospinal fluid 5-hydroxyindoleacetic acid (5-HIAA) were used as markers of central serotonin system functioning. t tests showed that neglected infants were observed sleeping less frequently, weighed less, and had higher 5-HIAA than non-neglected nursery-reared infants. Regression revealed that serotonin transporter genotype moderated the relationship between 5-HIAA and daytime sleep: in subjects possessing the Ls genotype, there was a positive correlation between 5-HIAA and daytime sleep, whereas in subjects possessing the LL genotype there was no association. These results highlight the pivotal roles that parents and the serotonin system play in sleep development. Daytime sleep alterations observed in neglected infants may partially derive from serotonin system dysregulation.

Antidepressant prescriptions, discontinuation, depression and perinatal outcomes, including breastfeeding: A population cohort analysis

Objectives

To explore associations between exposure to antidepressants, their discontinuation, depression [medicated or unmediated] and preterm birth [<37 and <32 weeks], small for gestational age (SGA) [<10th and <3rd centiles], breastfeeding [any] at 6–8 weeks.

Methods

Design: A population-based cohort study.

Setting: The Secure Anonymised Information Linkage [SAIL] databank in Wales, linking maternal primary care data with infant outcomes.

Participants: 107,573, 105,331, and 38,725 infants born 2000–2010 with information on prematurity, SGA and breastfeeding respectively, after exclusions.

Exposures: Maternal antidepressant prescriptions in trimesters 2 or 3, discontinuation after trimester 1, recorded diagnosis of depression [medicated or unmediated] in pregnancy.

Methods: Odds ratios for adverse pregnancy outcomes were calculated, adjusted for smoking, parity, socio-economic status, and depression.

Results

Exclusive formula feeding at 6–8 weeks was associated with prescriptions in trimesters 2 or 3 for any antidepressants (adjusted odds ratio [aOR] 0.81, 95% confidence intervals 0.67–0.98), SSRIs [aOR 0.77, 0.62–0.95], particularly higher doses [aOR 0.45, 0.23–0.86], discontinuation of antidepressants or SSRIs after trimester 1 (aOR 0.70, 0.57–0.83 and 0.66, 0.51–0.87), diagnosis of depression aOR 0.76 [0.70–0.82), particularly if medicated (aOR 0.70, 0.58–0.85), rather than unmedicated (aOR 0.87, 0.82–0.92). Preterm birth at <37 and <32 weeks’ gestation was associated with diagnosis of depression (aOR 1.27, 1.17–1.38, and 1.33, 1.09–1.62), particularly if medicated (aOR 1.56, 1.23–1.96, and 1.63, 0.94–2.84); birth at <37 weeks was associated with antidepressants, (aOR 1.24, 1.04–1.49]. SGA <3rd centile was associated with antidepressants (aOR 1.43, 1.07–1.90), and SSRIs (aOR 1.46, 1.06–2.00], particularly higher doses [aOR 2.10, 1.32–3.34]. All adverse outcomes were associated with socio-economic status and smoking.

Implications

Exposure to antidepressants or depression increased risks of exclusive formula feeding at 6–8 weeks, and prescription of antidepressants was associated with SGA <3^rd centile. Prescription of antidepressants offers a useful marker to target additional support and additional care before and during pregnancy and lactation.

Differential serotonin transporter (5-HTT) and 5-HT2 receptor density in limbic and neocortical areas of adults and children with autism spectrum disorders: implications for selective serotonin reuptake inhibitor efficacy

As selective serotonin reuptake inhibitors (SSRIs) are among the most commonly prescribed medications in autism, we aimed to determine whether targets for SSRIs are differentially affected in three cortical areas in children and adults with autism compared to neurotypical individuals. Utilizing a large cohort of postmortem brain tissue (n = 14–19 per group), saturation ligand binding assays were conducted on sections from the anterior cingulate cortex (ACC), posterior cingulate cortex, and fusiform gyrus (FG). Specific binding to the 5‐HT transporter (5‐HTT) as well as to 5‐HT2 and 1A receptors (5‐HT₂, 5‐HT_1A) was quantified in superficial and deep layers of each region using the ligands [³H]‐citalopram (5‐HTT), [³H]‐ketanserin (5‐HT₂), and [³H]‐8‐OH‐DPAT (5‐HT_1A). A Welch’s t‐test was utilized to compare receptor densities (B_max), revealing a statistically significant decrease in 5‐HTT within the ACC of the entire autism cohort. There was also a decrease in 5‐HT₂ receptor density in the ACC in the adult cohort, but not in child postmortem autism cases as compared to controls. Comparing linear regression lines of B_max values plotted against age, shows a significantly lower intercept for 5‐HTT in autism (p = 0.025). 5‐HT₂ density increases with age in control cases, whereas in autism there is a decrease with age and significantly different slopes between regression lines (p = 0.032). This suggests a deficit in 5‐HTT within the ACC in individuals with autism, while decreases in 5‐HT₂ density are age‐dependent. There were no differences in receptor densities in the posterior cingulate cortex or FG in autism and no differences in ligand affinity (K_D) across all regions and ligands examined.

Neuroinflammation as a risk factor for attention deficit hyperactivity disorder

Attention Deficit Hyperactivity Disorder (ADHD) is a persistent, and impairing pediatric-onset neurodevelopmental condition. Its high prevalence, and recurrent controversy over its widespread identification and treatment, drive strong interest in its etiology and mechanisms. Emerging evidence for a role for neuroinflammation in ADHD pathophysiology is of great interest. This evidence includes 1) the above-chance comorbidity of ADHD with inflammatory and autoimmune disorders, 2) initial studies indicating an association with ADHD and increased serum cytokines, 3) preliminary evidence from genetic studies demonstrating associations between polymorphisms in genes associated with inflammatory pathways and ADHD, 4) emerging evidence that early life exposure to environmental factors may increase risk for ADHD via an inflammatory mechanism, and 5) mechanistic evidence from animal models of maternal immune activation documenting behavioral and neural outcomes consistent with ADHD. Prenatal exposure to inflammation is associated with changes in offspring brain development including reductions in cortical gray matter volume and the volume of certain cortical areas -parallel to observations associated with ADHD. Alterations in neurotransmitter systems, including the dopaminergic, serotonergic and glutamatergic systems, are observed in ADHD populations. Animal models provide strong evidence that development and function of these neurotransmitters systems are sensitive to exposure to in utero inflammation. In summary, accumulating evidence from human studies and animal models, while still incomplete, support a potential role for neuroinflammation in the pathophysiology of ADHD. Confirmation of this association and the underlying mechanisms have become valuable targets for research. If confirmed, such a picture may be important in opening new intervention routes.

Targeting Serotonin Transporters in the Treatment of Juvenile and Adolescent Depression

Depression is a serious public health concern. Many patients are not effectively treated, but in children and adolescents this problem is compounded by limited pharmaceutical options. Currently, the Food and Drug Administration approves only two antidepressants for use in these young populations. Both are selective serotonin reuptake inhibitors (SSRIs). Compounding matters further, they are therapeutically less efficacious in children and adolescents than in adults. Here, we review clinical and preclinical literature describing the antidepressant efficacy of SSRIs in juveniles and adolescents. Since the high-affinity serotonin transporter (SERT) is the primary target of SSRIs, we then synthesize these reports with studies of SERT expression/function during juvenile and adolescent periods. Preclinical literature reveals some striking parallels with clinical studies, primary among them is that, like humans, juvenile and adolescent rodents show reduced antidepressant-like responses to SSRIs. These findings underscore the utility of preclinical assays designed to screen drugs for antidepressant efficacy across ages. There is general agreement that SERT expression/function is lower in juveniles and adolescents than in adults. It is well established that chronic SSRI treatment decreases SERT expression/function in adults, but strikingly, SERT expression/function in adolescents is increased following chronic treatment with SSRIs. Finally, we discuss a putative role for organic cation transporters and/or plasma membrane monoamine transporter in serotonergic homeostasis in juveniles and adolescents. Taken together, fundamental differences in SERT, and putatively in other transporters capable of serotonin clearance, may provide a mechanistic basis for the relative inefficiency of SSRIs to treat pediatric depression, relative to adults.

Extreme enhancement or depletion of serotonin transporter function and serotonin availability in autism spectrum disorder

A variety of human and animal studies support the hypothesis that serotonin (5-hydroxytryptamine or 5-HT) system dysfunction is a contributing factor to the development of autism in some patients. However, many questions remain about how developmental manipulation of various components that influence 5-HT signaling (5-HT synthesis, transport, metabolism) persistently impair social behaviors. This review will summarize key aspects of central 5-HT function important for normal brain development, and review evidence implicating perinatal disruptions in 5-HT signaling in the pathophysiology of autism spectrum disorder. We discuss the importance, and relative dearth, of studies that explore the possible correlation to autism in the interactions between important intrinsic and extrinsic factors that may disrupt 5-HT homeostasis during development. In particular, we focus on exposure to 5-HT transport altering mechanisms such as selective serotonin-reuptake inhibitors or genetic polymorphisms in primary or auxiliary transporters of 5-HT, and how they relate to neurological stores of serotonin and its precursors. A deeper understanding of the many mechanisms by which 5-HT signaling can be disrupted, alone and in concert, may contribute to an improved understanding of the etiologies and heterogeneous nature of this disorder. We postulate that extreme bidirectional perturbations of these factors during development likely compound or synergize to facilitate enduring neurochemical changes resulting in insufficient or excessive 5-HT signaling, that could underlie the persistent behavioral characteristics of autism spectrum disorder.

Enterochromaffin cells and gastrointestinal diseases

Enterochromaffin cells (ECs), known for their special histochemical characteristics, originate from enteroblasts. For their important role in physiological and pathophysiological conditions, ECs in the gut could synthesize and secrete about 95% of 5-hydroxytryptamine (5-HT) in the body, which is an important humoral factor. As a chemosensor, ECs can regulate nutrition absorption and satiety through the sensory neural pathways. In addition, ECs participate in immune regulation. What's more, ECs and 5-HT are closely related to many kinds of gastrointestinal diseases.

Study of gastrointestinal tract viability and motility via modulation of serotonin in a zebrafish model by probiotics

Investigated gastrointestinal tract viability and effect of potential probiotics on intestinal motility and the synthesis of serotonin in a zebrafish model.

Prenatal metformin exposure or organic cation transporter 3 knock-out curbs social interaction preference in male mice

Poorly managed gestational diabetes can lead to severe complications for mother and child including fetal overgrowth, neonatal hypoglycemia and increased autism risk. Use of metformin to control it is relatively new and promising. Yet safety concerns regarding gestational metformin use remain, as its long-term effects in offspring are unclear. In light of beneficial findings with metformin for adult mouse social behavior, we hypothesized gestational metformin treatment might also promote offspring sociability. To test this, metformin was administered to non-diabetic, lean C57BL/6 J female mice at mating, with treatment discontinued at birth or wean. Male offspring exposed to metformin through birth lost social interaction preference relative to controls by time in chambers, but not by sniffing measures. Further, prenatal metformin exposure appeared to enhance social novelty preference only in females. However due to unbalanced litters and lack of statistical power, firm establishment of any sex-dependency of metformin's effects on sociability was not possible. Since organic cation transporter 3 (OCT3) transports metformin and is dense in placenta, social preferences of OCT3 knock-out males were measured. Relative to wild-type, OCT3 knock-outs had reduced interaction preference. Our data indicate gestational metformin exposure under non-diabetic conditions, or lack of OCT3, can impair social behavior in male C57BL6/J mice. Since OCT3 transports serotonin and tryptophan, impaired placental OCT3 function is one common mechanism that could persistently impact central serotonin systems and social behavior. Yet no gross alterations in serotonergic function were evident by measure of serotonin transporter density in OCT3, or serotonin turnover in metformin-exposed offspring brains. Mechanisms underlying the behavioral outcomes, and if with gestational diabetes the same would occur, remain unclear. Metformin's impacts on placental transporters and serotonin metabolism or AMPK activity in fetal brain need further investigation to clarify benefits and risks to offspring sociability from use of metformin to treat gestational diabetes.

Computation-guided analysis of paroxetine binding to hSERT reveals functionally important structural elements and dynamics

The serotonin transporter (SERT) is one of the primary targets for medications to treat neuropsychiatric disorders and functions by exploiting pre-existing ion gradients of Na⁺, Cl^-, and K⁺ to translocate serotonin from the synaptic cleft into the presynaptic neuron. Although recent hSERT crystal structures represent a milestone for structure-function analyses of mammalian neurotransmitter:sodium symporters, they are all derived from thermostabilized but transport-deficient constructs. Two of these structures are in complex with paroxetine, the most potent selective serotonin reuptake inhibitor known. In this study, by carrying out and analyzing the results of extensive and comparative molecular dynamics simulations while also re-evaluating the transport and binding properties of the thermostabilized constructs, we identified functionally important structural elements that are perturbed by these mutations, revealed unexpected dynamics in the central primary binding site of SERT, and uncovered a conceivable ambiguity in paroxetine's binding orientation. We propose that the favored entropy contribution plays a significant role in paroxetine's extraordinarily high affinity for SERT. Our findings lay the foundation for future mechanistic studies and rational design of high-affinity SERT inhibitors. This article is part of the issue entitled 'Special Issue on Neurotransmitter Transporters'.

Serotonin Transporter Gene Polymorphism in Women With Suspected Ischemia

Introduction:

Association of serotonin transporter gene ( 5-HTTLPR) polymorphisms with adverse cardiovascular (CV) events in women with suspected ischemia has not yet been reported. We hypothesized an association of 5-HTTLPR polymorphisms with risk of adverse CV events in women with suspected ischemic heart disease (IHD) referred for coronary angiography enrolled in the Women’s Ischemia Syndrome Evaluation (WISE).

Method:

We studied clinical and angiographic data and DNA from a cohort of 437 Caucasian women enrolled in the WISE genotyped for the long (L) and short (S) variant of the 5-HTTLPR polymorphism. Women were followed yearly for adverse CV events (defined as first occurrence of all-cause death, myocardial infarction, stroke, or heart failure hospitalization) with data collected at WISE 10-year follow-up. Exploratory analyses compared outcomes between genotype groups.

Results:

A total of 437 women, with baseline, angiographic, and long-term follow-up data, were successfully genotyped. Their mean age was 58 ± 11 years and body mass index 29 ± 6; 54% had hypertension, 18% diabetes, 50% dyslipidemia, 20% depression history, and only 34% had obstructive CAD. At 8.9 years median follow-up, the SS genotype was associated with significantly increased risk of adverse CV event versus LL + LS (1.93, confidence interval [CI]: 1.03-3.61, P = .03). Results were not significant for all-cause death (hazard ratio: 1.63, CI: 0.91-2.93, P = .09).

Conclusion:

Among a cohort of Caucasian women with suspected IHD enrolled in the WISE, the SS homozygous genotype for the 5-HTTLPR polymorphism was associated with increased risk of adverse CV outcomes.

Adrenal serotonin derives from accumulation by the antidepressant-sensitive serotonin transporter

Adrenal chromaffin cells comprise the neuroendocrine arm of the sympathetic nervous system and secrete catecholamines to coordinate the appropriate stress response. Deletion of the serotonin (5-HT) transporter (SERT) gene in mice (SERT^-/- mice) or pharmacological block of SERT function in rodents and humans augments this sympathoadrenal stress response (epinephrine secretion). The prevailing assumption is that loss of CNS SERT alters central drive to the peripheral sympathetic nervous system. Adrenal chromaffin cells also prominently express SERT where it might coordinate accumulation of 5-HT for reuse in the autocrine control of stress-evoked catecholamine secretion. To help test this hypothesis, we have generated a novel mouse model with selective excision of SERT in the peripheral sympathetic nervous system (SERT^ΔTH), generated by crossing floxed SERT mice with tyrosine hydroxylase Cre driver mice. SERT expression, assessed by western blot, was abolished in the adrenal gland but not perturbed in the CNS of SERT^ΔTH mice. SERT-mediated [³H] 5-HT uptake was unaltered in midbrain, hindbrain, and spinal cord synaptosomes, confirming transporter function was intact in the CNS. Endogenous midbrain and whole blood 5-HT homeostasis was unperturbed in SERT^ΔTH mice, contrasting with the depleted 5-HT content in SERT^-/- mice. Selective SERT excision reduced adrenal gland 5-HT content by ≈ 50% in SERT^ΔTH mice but had no effect on adrenal catecholamine content. This novel model confirms that SERT expressed in adrenal chromaffin cells is essential for maintaining wild-type levels of 5-HT and provides a powerful tool to help dissect the role of SERT in the sympathetic stress response.

Pathway of Maternal Serotonin to the Human Embryo and Fetus

Serotonin [5-hydroxytryptamine (5-HT)] is essential to intrauterine development, but its source is debated. We used immunocytochemistry to gauge 5-HT, its biosynthetic enzyme tryptophan hydroxylase 1 (TPH1); an importer (serotonin transporter, 5-HTT/SERT/SLC6A); other transporters [P-glycoprotein 1 (P-gp/ABCB1), OCT3/SLC22A3, and gap junction connexin-43]; and the 5-HT degradative enzyme monoamine oxidase A (MAOA) in sections of placentas. In humans, 5-HT was faintly stained only in first-trimester trophoblasts, whereas TPH1 was not seen at any stage. SERT was expressed in syncytiotrophoblasts and, more strongly, in cytotrophoblasts. MAOA was prominent in syncytiotrophoblasts, OCT3 and gap junctions were stained in cytotrophoblasts, and P-gp was present at the apical surfaces of both epithelia. 5-HT added to cultured placental explants accumulated in the trophoblast epithelium and reached the villus core vessels. Trophoblast uptake was blocked by the SERT inhibitor escitalopram. Inhibition of gap junctions with heptanol prevented the accumulation of 5-HT in cytotrophoblasts, whereas blocking OCT3 with decynium-22 and P-gp with mitotane led to its accumulation in cytotrophoblasts. Reducing 5-HT destruction by inhibiting MAOA with clorgyline increased the accumulation of 5-HT throughout the villus. In the mouse fetus, intravascular platelets stained prominently for 5-HT at day 13.5, whereas the placenta and yolk sac endoderm were both negative. TPH1 was not detected, but SERT was prominent in these mouse tissues. We conclude that serotonin is conveyed from the maternal blood stream through syncytiotrophoblasts, cytotrophoblasts and the villus core to the fetus through a physiological pathway that involves at least SERT, gap junctions, P-gp, OCT3, and MAOA.

Serotonin receptor 2B signaling with interstitial cell activation and leaflet remodeling in degenerative mitral regurgitation

AIMS

Mitral valve interstitial cells (MVIC) play an important role in the pathogenesis of degenerative mitral regurgitation (MR) due to mitral valve prolapse (MVP). Numerous clinical studies have observed serotonin (5HT) dysregulation in cardiac valvulopathies; however, the impact of 5HT-mediated signaling on MVIC activation and leaflet remodeling in MVP have been investigated to a limited extent. Here we test the hypothesis that 5HT receptors (5HTRs) signaling contributes to MVP pathophysiology.

METHODS AND RESULTS

Diseased human MV leaflets were obtained during cardiac surgery for MVP; normal MV leaflets were obtained from heart transplants. MV RNA was used for microarray analysis of MVP patients versus control, highlighting genes that indicate the involvement of 5HTR pathways and extracellular matrix remodeling in MVP. Human MV leaflets were also studied in vitro and ex vivo with biomechanical testing to assess remodeling in the presence of a 5HTR2B antagonist (LY272015). MVP leaflets from Cavalier King Charles Spaniels were used as a naturally acquired in vivo model of MVP. These canine MVP leaflets (N=5/group) showed 5HTR2B upregulation. This study also utilized CB57.1ML/6 mice in order to determine the effect of Angiotensin II infusion on MV remodeling. Histological analysis showed that MV thickening due to chronic Angiotensin II remodeling is mitigated by a 5HTR2B antagonist (LY272015) but not by 5HTR2A inhibitors.

CONCLUSION

In humans, MVP is associated with an upregulation in 5HTR2B expression and increased 5HT receptor signaling in the leaflets. Antagonism of 5HTR2B mitigates MVIC activation in vitro and MV remodeling in vivo. These observations support the view that 5HTR signaling is involved not only in previously reported 5HT-related valvulopathies, but it is also involved in the pathological remodeling of MVP.

Inhibition of the Serotonin Transporter Is Altered by Metabolites of Selective Serotonin and Norepinephrine Reuptake Inhibitors and Represents a Caution to Acute or Chronic Treatment Paradigms

Previous studies of transgenic mice carrying a single isoleucine to methionine substitution (I172M) in the serotonin transporter (SERT) demonstrated a loss of sensitivity to multiple antidepressants (ADs) at SERT. However, the ability of AD metabolites to antagonize SERT was not assessed. Here, we evaluated the selectivity and potency of these metabolites for inhibition of SERT in mouse brain-derived synaptosomes and blood platelets from wild-type (I172 mSERT) and the antidepressant-insensitive mouse M172 mSERT. The metabolites norfluoxetine and desmethylsertraline lost the selectivity demonstrated by the parent compounds for inhibition of wild-type mSERT over M172 mSERT, whereas desvenlafaxine and desmethylcitalopram retained selectivity. Furthermore, we show that the metabolite desmethylcitalopram accumulates in the brain and that the metabolites desmethylcitalopram, norfluoxetine, and desvenlafaxine inhibit serotonin uptake in wild-type mSERT at potencies similar to those of their parent compounds, suggesting that metabolites may play a role in effects observed following AD administration in wild-type and M172 mice.

Serotonin and Serotonin Transporters in the Adrenal Medulla: A Potential Hub for Modulation of the Sympathetic Stress Response

Serotonin (5-HT) is an important neurotransmitter in the central nervous system where it modulates circuits involved in mood, cognition, movement, arousal, and autonomic function. The 5-HT transporter (SERT; SLC6A4) is a key regulator of 5-HT signaling, and genetic variations in SERT are associated with various disorders including depression, anxiety, and autism. This review focuses on the role of SERT in the sympathetic nervous system. Autonomic/sympathetic dysfunction is evident in patients with depression, anxiety, and other diseases linked to serotonergic signaling. Experimentally, loss of SERT function (SERT knockout mice or chronic pharmacological block) has been reported to augment the sympathetic stress response. Alterations to serotonergic signaling in the CNS and thus central drive to the peripheral sympathetic nervous system are presumed to underlie this augmentation. Although less widely recognized, SERT is robustly expressed in chromaffin cells of the adrenal medulla, the neuroendocrine arm of the sympathetic nervous system. Adrenal chromaffin cells do not synthesize 5-HT but accumulate small amounts by SERT-mediated uptake. Recent evidence demonstrated that 5-HT1A receptors inhibit catecholamine secretion from adrenal chromaffin cells via an atypical mechanism that does not involve modulation of cellular excitability or voltage-gated Ca2+ channels. This raises the possibility that the adrenal medulla is a previously unrecognized peripheral hub for serotonergic control of the sympathetic stress response. As a framework for future investigation, a model is proposed in which stress-evoked adrenal catecholamine secretion is fine-tuned by SERT-modulated autocrine 5-HT signaling.

Panic Disorder Comorbidity with Medical Conditions and Treatment Implications

Panic disorder (PD) is unique among the anxiety disorders in that panic symptoms are primarily of a physical nature. Consequently, comorbidity with medical illness is significant. This review examines the association between PD and medical illness. We identify shared pathophysiological and psychological correlates and illustrate how physiological activation in panic sufferers underlies their symptom experience in the context of the fight-or-flight response and beyond a situation-specific response pattern. We then review evidence for bodily symptom perception accuracy in PD. Prevalence of comorbidity for PD and medical illness is presented, with a focus on respiratory and cardiovascular illness, irritable bowel syndrome, and diabetes, followed by an outline for potential pathways of a bidirectional association. We conclude by illustrating commonalities in mediating mechanistic pathways and moderating risk factors across medical illnesses, and we discuss implications for diagnosis and treatment of both types of conditions.

Selective Serotonin Reuptake Inhibitor (SSRI) Antidepressants in Pregnancy and Congenital Anomalies: Analysis of Linked Databases in Wales, Norway and Funen, Denmark

Background

Hypothesised associations between in utero exposure to selective serotonin reuptake inhibitors (SSRIs) and congenital anomalies, particularly congenital heart defects (CHD), remain controversial. We investigated the putative teratogenicity of SSRI prescription in the 91 days either side of first day of last menstrual period (LMP).

Methods and Findings

Three population-based EUROCAT congenital anomaly registries- Norway (2004–2010), Wales (2000–2010) and Funen, Denmark (2000–2010)—were linked to the electronic healthcare databases holding prospectively collected prescription information for all pregnancies in the timeframes available. We included 519,117 deliveries, including foetuses terminated for congenital anomalies, with data covering pregnancy and the preceding quarter, including 462,641 with data covering pregnancy and one year either side. For SSRI exposures 91 days either side of LMP, separately and together, odds ratios with 95% confidence intervals (ORs, 95%CI) for all major anomalies were estimated. We also explored: pausing or discontinuing SSRIs preconception, confounding, high dose regimens, and, in Wales, diagnosis of depression. Results were combined in meta-analyses. SSRI prescription 91 days either side of LMP was associated with increased prevalence of severe congenital heart defects (CHD) (as defined by EUROCAT guide 1.3, 2005) (34/12,962 [0.26%] vs. 865/506,155 [0.17%] OR 1.50, 1.06–2.11), and the composite adverse outcome of 'anomaly or stillbirth' (473/12962, 3.65% vs. 15829/506,155, 3.13%, OR 1.13, 1.03–1.24). The increased prevalence of all major anomalies combined did not reach statistical significance (3.09% [400/12,962] vs. 2.67% [13,536/506,155] OR 1.09, 0.99–1.21). Adjusting for socio-economic status left ORs largely unchanged. The prevalence of anomalies and severe CHD was reduced when SSRI prescriptions were stopped or paused preconception, and increased when >1 prescription was recorded, but differences were not statistically significant. The dose-response relationship between severe CHD and SSRI dose (meta-regression OR 1.49, 1.12–1.97) was consistent with SSRI-exposure related risk. Analyses in Wales suggested no associations between anomalies and diagnosed depression.

Conclusion

The additional absolute risk of teratogenesis associated with SSRIs, if causal, is small. However, the high prevalence of SSRI use augments its public health importance, justifying modifications to preconception care.

A Novel Interaction between Tryptophan Hydroxylase 2 (TPH2) Gene Polymorphism (rs4570625) and BDNF Val66Met Predicts a High-Risk Emotional Phenotype in Healthy Subjects

Poor inhibitory processing of negative emotional content is central to many psychiatric disorders, including depression and anxiety. Moreover, increasing evidence suggests that core aspects of emotion-inhibitory processing are largely inherited and as such may represent a key intermediate or risk-related phenotype for common affective diseases (e.g., unipolar depressive, anxiety disorders). The current study employed a candidate-gene approach in order to most effectively examine this complex behavioral phenotype. We examined the novel interaction between BDNF (Val⁶⁶Met) and TPH2 (rs4570625) polymorphisms and their influence on behavioral inhibition of negative emotion in two independent investigations of healthy adults. BDNF Met carriers consistently report greater symptoms of affective disease and display corresponding behavioral rigidity, while TPH2 T carriers display poor inhibitory processing. These genotypes are traditionally perceived as ‘risk’ genotypes when compared to their respective major Val and G homozygous genotypes, but evidence is mixed. Recent studies in humans and mutant mouse models suggest biological epistasis between BDNF and genes involved in serotonin regulation. Moreover, polymorphisms in the TPH2 gene may have greater influence on serotonergic function than other more commonly studied polymorphisms (e.g., 5-HTTLPR). We observed consistent evidence across two different emotion-inhibition paradigms, one with high internal validity (Study 1, n = 119) and one with high ecological validity (Study 2, n = 115) that the combination of Val/Val and G/G genotypes was clearly associated with impaired inhibition of negative emotional content. This was followed by individuals carrying the BDNF—Met allele (including Met/Val and Met/Met) when combined with the TPH2—T allele (including T/G and T/T combinations). The consistency of these results across tasks and studies suggests that these two groups may be particularly vulnerable to the most common psychiatric disorders and should be targets for future clinical investigation.

Kinase-dependent Regulation of Monoamine Neurotransmitter Transporters

Modulation of neurotransmission by the monoamines dopamine (DA), norepinephrine (NE), and serotonin (5-HT) is critical for normal nervous system function. Precise temporal and spatial control of this signaling in mediated in large part by the actions of monoamine transporters (DAT, NET, and SERT, respectively). These transporters act to recapture their respective neurotransmitters after release, and disruption of clearance and reuptake has significant effects on physiology and behavior and has been linked to a number of neuropsychiatric disorders. To ensure adequate and dynamic control of these transporters, multiple modes of control have evolved to regulate their activity and trafficking. Central to many of these modes of control are the actions of protein kinases, whose actions can be direct or indirectly mediated by kinase-modulated protein interactions. Here, we summarize the current state of our understanding of how protein kinases regulate monoamine transporters through changes in activity, trafficking, phosphorylation state, and interacting partners. We highlight genetic, biochemical, and pharmacological evidence for kinase-linked control of DAT, NET, and SERT and, where applicable, provide evidence for endogenous activators of these pathways. We hope our discussion can lead to a more nuanced and integrated understanding of how neurotransmitter transporters are controlled and may contribute to disorders that feature perturbed monoamine signaling, with an ultimate goal of developing better therapeutic strategies.

An interplay between the serotonin transporter (SERT) and 5-HT receptors controls stimulus-secretion coupling in sympathoadrenal chromaffin cells

Adrenal chromaffin cells (ACCs), the neuroendocrine arm of the sympathetic nervous system, secrete catecholamines to mediate the physiological response to stress. Although ACCs do not synthesize 5-HT, they express the serotonin transporter (SERT). Genetic variations in SERT are linked to several CNS disorders but the role(s) of SERT/5-HT in ACCs has remained unclear. Adrenal glands from wild-type mice contained 5-HT at ≈ 750 fold lower abundance than adrenaline, and in SERT(-/-) mice this was reduced by ≈80% with no change in catecholamines. Carbon fibre amperometry showed that SERT modulated the ability of 5-HT1A receptors to inhibit exocytosis. 5-HT reduced the number of amperometric spikes (vesicular fusion events) evoked by KCl in SERT(-/-) cells and wild-type cells treated with escitalopram, a SERT antagonist. The 5-HT1A receptor antagonist WAY100635 blocked the inhibition by 5-HT which was mimicked by the 5-HT1A agonist 8-OH-DPAT but not the 5-HT1B agonist CP93129. There was no effect on voltage-gated Ca(2+) channels, K(+) channels, or intracellular [Ca(2+)] handling, showing the 5-HT receptors recruit an atypical inhibitory mechanism. Spike charge and kinetics were not altered by 5-HT receptors but were reduced in SERT(-/-) cells compared to wild-type cells. Our data reveal a novel role for SERT and suggest that adrenal chromaffin cells might be a previously unrecognized hub for serotonergic control of the sympathetic stress response.

Ontogeny of SERT Expression and Antidepressant-like Response to Escitalopram in Wild-Type and SERT Mutant Mice

Depression is a disabling affective disorder for which the majority of patients are not effectively treated. This problem is exacerbated in children and adolescents for whom only two antidepressants are approved, both of which are selective serotonin reuptake inhibitor (SSRIs). Unfortunately SSRIs are often less effective in juveniles than in adults; however, the mechanism(s) underlying age-dependent responses to SSRIs is unknown. To this end, we compared the antidepressant-like response to the SSRI escitalopram using the tail suspension test and saturation binding of [(3)H]citalopram to the serotonin transporter (SERT), the primary target of SSRIs, in juvenile [postnatal day (P)21], adolescent (P28), and adult (P90) wild-type (SERT+/+) mice. In addition, to model individuals carrying low-expressing SERT variants, we studied mice with reduced SERT expression (SERT+/-) or lacking SERT (SERT-/-). Maximal antidepressant-like effects were less in P21 mice relative to P90 mice. This was especially apparent in SERT+/- mice. However, the potency for escitalopram to produce antidepressant-like effects in SERT+/+ and SERT+/- mice was greater in P21 and P28 mice than in adults. SERT expression increased with age in terminal regions and decreased with age in cell body regions. Binding affinity values did not change as a function of age or genotype. As expected, in SERT-/- mice escitalopram produced no behavioral effects, and there was no specific [(3)H]citalopram binding. These data reveal age- and genotype-dependent shifts in the dose-response for escitalopram to produce antidepressant-like effects, which vary with SERT expression, and may contribute to the limited therapeutic response to SSRIs in juveniles and adolescents.

Brain dopamine and serotonin transporter binding are associated with visual attention bias for food in lean men

BACKGROUND

In rodents, the striatal dopamine (DA) system and the (hypo)thalamic serotonin (5-HT) system are involved in the regulation of feeding behavior. In lean humans, little is known about the relationship between these brain neurotransmitter systems and feeding. We studied the relationship between striatal DA transporters (DAT) and diencephalic 5-HT transporters (SERT), behavioral tasks and questionnaires, and food intake.

METHOD

We measured striatal DAT and diencephalic SERT binding with [123I]FP-CIT SPECT in 36 lean male subjects. Visual attention bias for food (detection speed and distraction time) and degree of impulsivity were measured using response-latency-based computer tasks. Craving and emotional eating were assessed with questionnaires and ratings of hunger by means of VAS scores. Food intake was assessed through a self-reported online diet journal.

RESULTS

Striatal DAT and diencephalic SERT binding negatively correlated with food detection speed (p = 0.008, r = -0.50 and p = 0.002, r = -0.57, respectively), but not with food distraction time, ratings of hunger, craving or impulsivity. Striatal DAT and diencephalic SERT binding did not correlate with free choice food intake, whereas food detection speed positively correlated with total caloric intake (p = 0.001, r = 0.60), protein intake (p = 0.01, r = 0.44), carbohydrate intake (p = 0.03, r = 0.39) and fat intake (p = 0.06, r = 0.35).

CONCLUSIONS

These results indicate a role for the central 5-HT and DA system in the regulation of visual attention bias for food, which contributes to the motivation to eat, in non-obese, healthy humans. In addition, this study confirms that food detection speed, measured with the latency-based computer task, positively correlates with total food and macronutrient intake.

A refined high carbohydrate diet is associated with changes in the serotonin pathway and visceral obesity

Consumption of palatable foods high in refined carbohydrate has been implicated as a contributing factor to the epidemic levels of obesity. Such foods may disrupt appetite regulation in the hypothalamus through alterations in hunger and satiety signalling. This investigation examined whether a palatable high refined carbohydrate (HRC) diet with the potential to induce obesity was linked to modulation of serotonin and dopamine signalling within the hypothalamus of rats. Male Wistar rats were allowed ad libitum access to either a palatable refined carbohydrate enriched (HRC) diet or standard chow (SC). Visceral fat percentage was used as a measure of the animals' weight gain during the trial. Real-time PCR was applied to determine any variation in levels of expression of the serotonin (Slc6A4 or Sert) and dopamine transporter (Slc6A3 or Dat) genes. After 29 weeks, the HRC group showed a significant increase in visceral fat percentage accompanied by increased expression of Sert. Higher levels of circulating triglycerides were also seen. This investigation determined that a refined high carbohydrate diet is associated with visceral obesity, increased circulating lipids in the blood and distorted serotonergic signalling, which possibly alters satiety and hunger signals.

Treating Anxiety Disorders in Older Adults: Current Treatments and Future Directions

Anxiety disorders are highly prevalent among the elderly and are associated with increased disability, poor quality of life, and cognitive impairment. Despite this high prevalence and associated morbidities, anxiety disorders in late life are underreported and understudied. In this article, we discuss the epidemiology, disease presentation, and current treatment of anxiety disorders in older adults. We also discuss limitations in the current understanding of such disorders in this population, as well as future research directions that may reveal the mechanisms and rationale for treatment regimens for anxiety disorders in late life. We present material on the application of the Research Domain Criteria (RDoC) model to geriatric anxiety. Finally, we describe optimal management strategies of anxiety disorders.

Serotonylation and Transamidation of Other Monoamines

Although serotonin was discovered over 65 years ago, it has been only within the past decade that serotonin was found to be involved in a covalent post-translational modification to proteins. The enzyme transglutaminase catalyzes the transamidation of serotonin to a protein-bound glutamine residue; the amino group of serotonin is covalently bound to the gamma carboxamide of glutamine. The term serotonylation is used to describe this transamidation reaction to serotonin. Not only can serotonin be a substrate for transamidation to proteins but also other monoamine neurotransmitters are substrates including histamine, dopamine, and noradrenaline. The term monoaminylation has been coined to describe the transamidation of monoamines to protein substrates. Small G proteins have emerged as the most common substrate for monoaminylation and are activated by this post-translational modification. Fibronectin and cytoskeletal proteins are also substrates for monoaminylation. Serotonylation and monoaminylation are involved in a number of physiological functions, including platelet activation, insulin release, smooth muscle contraction, and regulation of membrane localization of the serotonin transporter. Stimulation of 5-HT2A receptors increases serotonylation and activates the small G protein Rac1, which plays a role in dendritic spine regulation. Monoaminylation is implicated in pathophysiological processes as well such as diabetes and hypertension. The availability of monoamines for monoaminylation is altered by antidepressants that target serotonin transporters, noradrenaline transporters, or the enzymatic degradation of monoamines as well as drugs of abuse such as cocaine and amphetamines. Further research on monoaminylation is needed to elucidate its physiological and pathophysiological roles and to explore monoaminylation as a novel target for drug therapy.

The role of maternal obesity in the risk of neuropsychiatric disorders

Recent evidence indicates that perinatal exposure to maternal obesity, metabolic disease, including diabetes and hypertension, and unhealthy maternal diet has a long-term impact on offspring behavior and physiology. During the past three decades, the prevalence of both obesity and neuropsychiatric disorders has rapidly increased. Epidemiologic studies provide evidence that maternal obesity and metabolic complications increase the risk of attention deficit hyperactivity disorder (ADHD), autism spectrum disorders, anxiety, depression, schizophrenia, eating disorders (food addiction, anorexia nervosa, and bulimia nervosa), and impairments in cognition in offspring. Animal models of maternal high-fat diet (HFD) induced obesity also document persistent changes in offspring behavior and impairments in critical neural circuitry. Animals exposed to maternal obesity and HFD consumption display hyperactivity, impairments in social behavior, increased anxiety-like and depressive-like behaviors, substance addiction, food addiction, and diminished cognition. During development, these offspring are exposed to elevated levels of nutrients (fatty acids, glucose), hormones (leptin, insulin), and inflammatory factors (C-reactive protein, interleukin, and tumor necrosis factor). Such factors appear to permanently change neuroendocrine regulation and brain development in offspring. In addition, inflammation of the offspring brain during gestation impairs the development of neural pathways critical in the regulation of behavior, such as serotoninergic, dopaminergic, and melanocortinergic systems. Dysregulation of these circuits increases the risk of mental health disorders. Given the high rates of obesity in most developed nations, it is critical that the mechanisms by which maternal obesity programs offspring behavior are thoroughly characterized. Such knowledge will be critical in the development of preventative strategies and therapeutic interventions.

Antidepressants and the adolescent brain

Major unipolar depression is a significant global health problem, with the highest incident risk being during adolescence. A depressive illness during this period is associated with negative long-term consequences including suicide, additional psychiatric comorbidity, interpersonal relationship problems, poor educational performance and poor employment attainment well into adult life. Despite previous safety concerns, selective serotonin reuptake inhibitors (SSRIs) remain a key component of the treatment of moderate to severe depression episodes in adolescents. The impact of SSRIs on the developing adolescent brain, however, remains unclear. In this review we first consider what is currently known about the developing brain during adolescence and how these development processes may be affected by a depressive illness. We then review our understanding of the action of SSRIs, their effects on the brain and how these may differ between adults and adolescents. We conclude that there is currently little evidence to indicate that the human adolescent brain is at developmental risk from SSRIs. Furthermore, there is no clear-cut evidence to support the concerns of marked suicidal adverse side effects accruing in depressed adolescents being treated with SSRIs. Neither, however, is there irrefutable evidence to dismiss all such concerns. This makes SSRI prescribing a matter of medical judgement, ensuring the benefits outweigh the risks for the individual patients, as with so much in therapeutics. Overall, SSRIs show clinical benefits that we judge to outweigh the risks to neurodevelopment and are an important therapeutic choice in the treatment of moderate to severe adolescent depression.