Serotonergic vulnerability and depression: assumptions, experimental evidence and implications

Balancing plasticity/stability across brain development

The potency of the environment to shape brain function changes dramatically across the lifespan. Neural circuits exhibit profound plasticity during early life and are later stabilized. A focus on the cellular and molecular bases of these developmental trajectories has begun to unravel mechanisms, which control the onset and closure of such critical periods. Two important concepts have emerged from the study of critical periods in the visual cortex: (1) excitatory-inhibitory circuit balance is a trigger; and (2) molecular "brakes" limit adult plasticity. The onset of the critical period is determined by the maturation of specific GABA circuits. Targeting these circuits using pharmacological or genetic approaches can trigger premature onset or induce a delay. These manipulations are so powerful that animals of identical chronological age may be at the peak, before, or past their plastic window. Thus, critical period timing per se is plastic. Conversely, one of the outcomes of normal development is to stabilize the neural networks initially sculpted by experience. Rather than being passively lost, the brain's intrinsic potential for plasticity is actively dampened. This is demonstrated by the late expression of brake-like factors, which reversibly limit excessive circuit rewiring beyond a critical period. Interestingly, many of these plasticity regulators are found in the extracellular milieu. Understanding why so many regulators exist, how they interact and, ultimately, how to lift them in noninvasive ways may hold the key to novel therapies and lifelong learning.

Association between serotonin transporter genotype, brain structure and adolescent-onset major depressive disorder: a longitudinal prospective study

The extent to which brain structural abnormalities might serve as neurobiological endophenotypes that mediate the link between the variation in the promoter of the serotonin transporter gene (5-HTTLPR) and depression is currently unknown. We therefore investigated whether variation in hippocampus, amygdala, orbitofrontal cortex (OFC) and anterior cingulate cortex volumes at age 12 years mediated a putative association between 5-HTTLPR genotype and first onset of major depressive disorder (MDD) between age 13-19 years, in a longitudinal study of 174 adolescents (48% males). Increasing copies of S-alleles were found to predict smaller left hippocampal volume, which in turn was associated with increased risk of experiencing a first onset of MDD. Increasing copies of S-alleles also predicted both smaller left and right medial OFC volumes, although neither left nor right medial OFC volumes were prospectively associated with a first episode of MDD during adolescence. The findings therefore suggest that structural abnormalities in the left hippocampus may be present prior to the onset of depression during adolescence and may be partly responsible for an indirect association between 5-HTTLPR genotype and depressive illness. 5-HTTLPR genotype may also impact upon other regions of the brain, such as the OFC, but structural differences in these regions in early adolescence may not necessarily alter the risk for onset of depression during later adolescence.

Interaction of 5-HTT and HTR1A gene polymorphisms in treatment responses to mirtazapine in patients with major depressive disorder

We tested for the association of HTR1A and 5-HTT genetic polymorphisms with treatment response to mirtazapine and evaluated the interactive effect between the polymorphisms in 283 patients with major depressive disorder. Korean subjects with diagnosis of major depressive disorder using the Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition Axis I disorders were recruited. Clinical symptoms were evaluated using the 17-item Hamilton Depression Rating (HAMD-17) Scale at baseline and after 1, 2, 4, 8, and 12 weeks of treatment with mirtazapine. The genetic association of 5-HTTLPR and HTR1A+272G>A with treatment response was analyzed. We found a significant association of the 12.12-repeat genotype of 5-HTT various number tandem repeat (VNTR) with a large percentage decline in HAMD-17 Scale score after 4, 8, and 12 weeks of treatment with mirtazapine. We also found that the frequency of the 12.12-repeat genotype was higher in responders than in nonresponders at week 8. The HTR1A+272GG genotype was significantly associated with a large percentage decline in HAMD-17 Scale score at 4, 8, and 12 weeks, although the genotypic frequencies were comparable between responders and nonresponders during the study period. Patients with the 12.12-repeat 5-HTT VNTR and GG of HTR1A+272G>A showed the highest HAMD-17 Scale percentage reduction during the study period and a better treatment response status after 4 weeks. These results suggest that the interaction between HTR1A+272G>A and 5-HTT VNTR is involved in the response to mirtazapine treatment and that a combination of these may be a useful marker for predicting treatment response to mirtazapine.

Desvenlafaxine prevents white matter injury and improves the decreased phosphorylation of the rate-limiting enzyme of cholesterol synthesis in a chronic mouse model of depression

Serotonin/norepinephrine reuptake inhibitors antidepressants exert their effects by increasing serotonin and norepinephrine in the synaptic cleft. Studies show it takes 2-3 weeks for the mood-enhancing effects, which indicate other mechanisms may underlie their treatment effects. Here, we investigated the role of white matter in treatment and pathogenesis of depression using an unpredictable chronic mild stress (UCMS) mouse model. Desvenlafaxine (DVS) was orally administrated to UCMS mice at the dose of 10 mg/kg/day 1 week before they went through a 7-week stress procedure and lasted for over 8 weeks before the mice were killed. No significant changes were found for protein markers of neurons and astrocytes in UCMS mice. However, myelin and oligodendrocyte-related proteins were significantly reduced in UCMS mice. DVS prevented the stress-induced injury to white matter and the decrease of phosphorylated 5'-AMP-activated protein kinase and 3-hydroxy-3-methyl-glutaryl-CoA reductase protein expression. DVS increased open arm entries in an elevated plus-maze test, sucrose consumption in the sucrose preference test and decreased immobility in tail suspension and forced swimming tests. These findings suggest that stress induces depression-like behaviors and white matter deficits in UCMS mice. DVS may ameliorate the oligodendrocyte dysfunction by affecting cholesterol synthesis, alleviating the depression-like phenotypes in these mice. We examined the possible role of oligodendrocyte and myelin in the pathological changes of depression with an unpredictable chronic mild stress (UCMS) mouse model. Oligodendrocyte-related proteins in the mouse brain were specifically changed during the stress period. The depressive-like behaviors and oligodendrocyte deficits could be prevented by the administration of desvenlafaxine. Oligodendrocyte and myelin may be an essential target of desvenlafaxine for the treatment of depression.

Effect of sub chronic tryptophan supplementation on stress-induced cortisol and appetite in subjects differing in 5-HTTLPR genotype and trait neuroticism

Stress or negative effect often increases preference for, and intake of, palatable snack foods and this may be influenced by cognitive and genetic factors related to stress and 5-HT vulnerability. The short (S) compared to the long (L) allele of the 5-HT transporter linked polymorphic region (5-HTTLPR) has been associated (i) with decreased 5-HT transporter function and availability and hence, with 5-HT vulnerability, and (ii) with greater stress-responsiveness. Stress-proneness is furthermore promoted by cognitive stress-vulnerability, a key feature of trait neuroticism. Brain 5-HT function can be manipulated by dietary administration of its amino acid precursor tryptophan (Trp), and the beneficial effects of dietary Trp on stress experience and emotional eating may be greatest following repeated administration in both stress- and 5-HT-vulnerable subjects. The aim was to examine the influence of repeated Trp administration on stress responsiveness and emotional eating in homozygous 5-HTTLPR S-allele (N=60) and L-allele (N=58) carriers with high and low neuroticism. Following seven days of Trp or PLC intake, mood, cortisol and appetite were assessed before and after exposure to acute stress and snack intake and preference were measured post-stress. It was hypothesized that Trp would reduce stress experience and emotional eating particularly in S-allele carriers with high neuroticism. Results revealed Trp treatment caused a clear reduction in stress-induced cortisol levels in S/S-allele carriers exclusively, and prevented a stress-induced increase in appetite only in S/S-allele carriers with high trait neuroticism. The findings reveal an advantageous effect of sub chronic Trp treatment on stress experience and appetite depending on stress and (genetic) serotonergic vulnerability.

Serotonin-prefrontal cortical circuitry in anxiety and depression phenotypes: pivotal role of pre- and post-synaptic 5-HT1A receptor expression

Decreased serotonergic activity has been implicated in anxiety and major depression, and antidepressants directly or indirectly increase the long-term activity of the serotonin system. A key component of serotonin circuitry is the 5-HT1A autoreceptor, which functions as the major somatodendritic autoreceptor to negatively regulate the "gain" of the serotonin system. In addition, 5-HT1A heteroreceptors are abundantly expressed post-synaptically in the prefrontal cortex (PFC), amygdala, and hippocampus to mediate serotonin actions on fear, anxiety, stress, and cognition. Importantly, in the PFC 5-HT1A heteroreceptors are expressed on at least two antagonist neuronal populations: excitatory pyramidal neurons and inhibitory interneurons. Rodent models implicate the 5-HT1A receptor in anxiety- and depression-like phenotypes with distinct roles for pre- and post-synaptic 5-HT1A receptors. In this review, we present a model of serotonin-PFC circuitry that integrates evidence from mouse genetic models of anxiety and depression involving knockout, suppression, over-expression, or mutation of genes of the serotonin system including 5-HT1A receptors. The model postulates that behavioral phenotype shifts as serotonin activity increases from none (depressed/aggressive not anxious) to low (anxious/depressed) to high (anxious, not depressed). We identify a set of conserved transcription factors including Deaf1, Freud-1/CC2D1A, Freud-2/CC2D1B and glucocorticoid receptors that may confer deleterious regional changes in 5-HT1A receptors in depression, and how future treatments could target these mechanisms. Further studies to specifically test the roles and regulation of pyramidal vs. interneuronal populations of 5-HT receptors are needed better understand the role of serotonin in anxiety and depression and to devise more effective targeted therapeutic approaches.

An exploration of the dynamic longitudinal relationship between mental health and alcohol consumption: a prospective cohort study

BACKGROUND

Despite intense investigation, the temporal sequence between alcohol consumption and mental health remains unclear. This study explored the relationship between alcohol consumption and mental health over multiple occasions, and compared a series of competing theoretical models to determine which best reflected the association between the two.

METHODS

Data from phases 5 (1997 to 1999), 7 (2002 to 2004), and 9 (2007 to 2009) of the Whitehall II prospective cohort study were used, providing approximately 10 years of follow-up for 6,330 participants (73% men; mean ± SD age 55.8 ± 6.0 years). Mental health was assessed using the Short Form (SF)-36 mental health component score. Alcohol consumption was defined as the number of UK units of alcohol drunk per week. Four dynamic latent change score models were compared: 1) a baseline model in which alcohol consumption and mental health trajectories did not influence each other, 2) and model in which alcohol consumption influenced changes in mental health but mental health exerted no effect on changes in drinking and 3) vice versa, and (4) a reciprocal model in which both variables influenced changes in each other.

RESULTS

The third model, in which mental health influenced changes in alcohol consumption but not vice versa, was the best fit. In this model, the effect of previous mental health on upcoming change in alcohol consumption was negative (γ = -0.31, 95% CI -0.52 to -0.10), meaning that those with better mental health tended to make greater reductions (or shallower increases) in their drinking between occasions.

CONCLUSIONS

Mental health appears to be the leading indicator of change in the dynamic longitudinal relationship between mental health and weekly alcohol consumption in this sample of middle-aged adults. In addition to fuelling increases in alcohol consumption among low-level consumers, poor mental health may also be a maintaining factor for heavy alcohol consumption. Future work should seek to examine whether there are critical levels of alcohol intake at which different dynamic relationships begin to emerge between alcohol-related measures and mental health.

Sleep Disturbances and Common Mental Disorders in College Students

OBJECTIVE

To estimate the prevalence of common mental disorders (CMDs) and examine the association of sleep disorders with presence of CMDs.

METHODS

A self-administered questionnaire was used to ascertain demographic information and behavioral characteristics among 2,645 undergraduate students in Ethiopia. Standard questionnaires were used to assess CMDs, evening chronotype, sleep quality and daytime sleepiness.

RESULTS

A total of 716 students (26.6%) were characterized as having CMDs. Female students had higher prevalence of CMDs (30.6%) compared to male students (25.4%). After adjusting for potential confounders, daytime sleepiness (OR=2.02; 95% CI 1.64-2.49) and poor sleep quality (OR=2.36; 95% CI 1.91-2.93) were associated with increased odds of CMDs.

CONCLUSION

There is a high prevalence of CMDs comorbid with sleep disorders among college students.

Linoleic acid derivative DCP-LA ameliorates stress-induced depression-related behavior by promoting cell surface 5-HT1A receptor translocation, stimulating serotonin release, and inactivating GSK-3β

Impairment of serotonergic neurotransmission is the major factor responsible for depression and glycogen synthase kinase 3β (GSK-3β) participates in serotonergic transmission-mediated signaling networks relevant to mental illnesses. In the forced-swim test to assess depression-like behavior, the immobility time for mice with restraint stress was significantly longer than that for nonstressed control mice. Postsynaptic cell surface localization of 5-HT1A receptor, but not 5-HT2A receptor, in the hypothalamus for mice with restraint stress was significantly reduced as compared with that for control mice, which highly correlated to prolonged immobility time, i.e., depression-like behavior. The linoleic acid derivative 8-[2-(2-pentyl-cyclopropylmethyl)-cyclopropyl]-octanoic acid (DCP-LA) restored restraint stress-induced reduction of cell surface 5-HT1A receptor and improved depression-like behavior in mice with restraint stress. Moreover, DCP-LA stimulated serotonin release from hypothalamic slices and cancelled restraint stress-induced reduction of GSK-3β phosphorylation at Ser9. Taken together, the results of the present study indicate that DCP-LA could ameliorate depression-like behavior by promoting translocation of 5-HT1A receptor to the plasma membrane on postsynaptic cells, stimulating serotonin release, and inactivating GSK-3β.

Novel homozygous DEAF1 variant suspected in causing white matter disease, intellectual disability, and microcephaly

DEAF1 encodes a transcriptional binding factor and is a regulator of serotonin receptor 1A. Its protein has a significant expression in the neurons of different brain regions and is involved in early embryonic development. In addition, its role in neural tube development is evident from the knockout mouse as many homozygotes have exencephaly. Heterozygous mutations of this gene have been linked to intellectual disability in addition to the gene's involvement in major depression, suicidal tendencies, and panic disorder. In this clinical report, we describe two children from a consanguineous family with intellectual disability, microcephaly, and hypotonia. The brain MRI of both patients showed bilateral and symmetrical white matter abnormalities, and one of the patients had a seizure disorder. Using whole exome sequencing combined with homozygosity mapping, a homozygous p.R226W (c.676C>T) mutation in DEAF1 was found in both patients. Furthermore, sequencing analysis confirmed complete segregation in tested family members and absence of the mutation in control cohort (n = 650). The mutation is located in a highly conserved structural domain that mediates DNA binding and therefore regulates transcriptional activity of its target molecules. This study indicates, for the first time to our knowledge, a hereditary role of DEAF1 in white matter abnormalities, microcephaly and syndromic intellectual disability.

Differential influence of the 5-HTTLPR genotype, neuroticism and real-life acute stress exposure on appetite and energy intake

Stress or negative mood often promotes energy intake and overeating. Since the serotonin transporter-linked polymorphic region (5-HTTLPR) is found to mediate stress vulnerability as well as to influence energy intake, this gene may also influence the negative effects of stress exposure on overeating. Moreover, since stress proneness also reflects cognitive stress vulnerability - as often defined by trait neuroticism - this may additionally predispose for stress-induced overeating. In the present study it was investigated whether the 5-HTTLPR genotype interacted with neuroticism on changes in mood, appetite and energy intake following exposure to a real-life academic examination stressor. In a balanced-experimental design, homozygous S-allele and L-allele carriers (N = 94) with the lowest and highest neuroticism scores were selected from a large database of 5-HTTLPR genotyped students. Mood, appetite and energy intake were measured before and after a 2-hour academic examination and compared with a control day. Examination influenced appetite for particular sweet snacks differently depending on 5-HTTLPR genotype and neuroticism. S/S compared with L/L subjects reported greater examination stress, and this was accompanied by a more profound post-stress increase in appetite for sweet snacks. Data also revealed a 5-HTTLPR genotype by trait neuroticism interaction on energy intake, regardless of examination. These results consolidate previous assumptions of 5-HTTLPR involvement in stress vulnerability and suggest 5-HTTLPR and neuroticism may influence stress-induced overeating depending on the type of food available. These findings furthermore link previous findings of increased risk for weight gain in S/S-allele carriers, particularly with high scores on trait neuroticism, to increased energy intake.

Metaplastic regulation of the median raphe nucleus via serotonin 5-HT1A receptor on hippocampal synaptic plasticity is associated with gender-specific emotional expression in rats

Gender differences in psychiatric disorders are considered to be associated with the serotonergic (5-HTergic) system; however the underlying mechanisms have not been clearly elucidated. In this study, possible involvement of the median raphe nucleus (MRN)-hippocampus 5-HTergic system in gender-specific emotional regulation was investigated, focusing on synaptic plasticity in rats. A behavioral study using a contextual fear conditioning (CFC) paradigm showed that the females exhibited low anxiety-like behavior. Extracellular 5-HT levels in the hippocampus were increased by CFC only in the males. Long-term potentiation (LTP) in the hippocampal CA1 field was suppressed after CFC in the males, which was mimicked by the synaptic response to MRN electrical stimulation. In the MRN, 5-HT immunoreactive cells significantly increased in the females compared with those in the males. Pretreatment with the 5-HT1A receptor agonists tandospirone (10 mg/kg, i.p.) and 8-OH DPAT (3 mg/kg, i.p.) significantly suppressed LTP induction in the males. Synaptic responses to CFC and 5-HT1A receptor interventions were not observed in the females. These results suggest that the metaplastic 5-HTergic mechanism via 5-HT1A receptors in the MRN-hippocampus pathway is a key component for gender-specific emotional regulation and may be a cause of psychiatric disorders associated with vulnerability or resistance to emotional stress.

5-HT(1A) [corrected] receptors in mood and anxiety: recent insights into autoreceptor versus heteroreceptor function

RATIONALE

Serotonin (5-HT) neurotransmission is intimately linked to anxiety and depression and a diverse body of evidence supports the involvement of the main inhibitory serotonergic receptor, the serotonin-1A (5-HT(1A)) subtype, in both disorders.

OBJECTIVES

In this review, we examine the function of 5-HT(1A) receptor subpopulations and re-interpret our understanding of their role in mental illness in light of new data, separating both spatial (autoreceptor versus heteroreceptor) and the temporal (developmental versus adult) roles of the endogenous 5-HT(1A) receptors, emphasizing their distinct actions in mediating anxiety and depression-like behaviors.

RESULTS

It is difficult to unambiguously distinguish the effects of different populations of the 5-HT(1A) receptors with traditional genetic animal models and pharmacological approaches. However, with the advent of novel genetic systems and subpopulation-selective pharmacological agents, direct evidence for the distinct roles of these populations in governing emotion-related behavior is emerging.

CONCLUSIONS

There is strong and growing evidence for a functional dissociation between auto- and heteroreceptor populations in mediating anxiety and depressive-like behaviors, respectively. Furthermore, while it is well established that 5-HT(1A) receptors act developmentally to establish normal anxiety-like behaviors, the developmental role of 5-HT(1A) heteroreceptors is less clear, and the specific mechanisms underlying the developmental role of each subpopulation are likely to be key elements determining mood control in adult subjects.

Impact of High Fat Diet-induced Obesity on the Plasma Levels of Monoamine Neurotransmitters in C57BL/6 Mice

Obesity is one of the most serious health problems in developed countries. It negatively affects diverse aspects of human wellbeing. Of these, a relationship between obesity and depression is widely recognized but biomarkers for assessment of obesityassociated mood changes in animal obesity models are rarely known. Here we explored the link between obesity and the plasma levels of monoamine neurotransmitters involved in mood control using a sensitive UPLC/MSMS technique in high fat diet (HFD)- induced obesity model in male C57BL/6 mice to explore the potential utility of plasma tests for obesity-associated mood change. HFD (60% of total calories, 8 weeks) induced significantly higher weight gains in body (+37.8%) and fat tissue (+306%) in male C57BL/6 mice. Bioanalysis of serotonin, dopamine and norepinephrine in plasma at 8 weeks of HFD revealed that serotonin decreased significantly in the obese mice when compared to normal diet-fed mice (2.7 ± 0.6 vs 4.3 ± 2.0 ng/ml, N=8). Notably, a negative correlation was found between the levels of serotonin and body weight gains. Furthermore, principal component analysis (PCA) with the individual levels of neurotransmitters revealed that plasma levels of dopamine and serotonin could apparently differentiate the obese mice from lean ones. Our study demonstrated that blood plasma levels of neurotransmitters can be employed to evaluate the mood changes associated with obesity and more importantly, provided an important clue for understanding of the relationship between obesity and mood disorders.

Obstructive sleep apnea and other sleep-related syndromes

Obstructive sleep apnea syndrome (OSAS) is a common disorder characterized by repetitive episodes of breathing cessation due to complete or partial collapse of the upper airway therefore affecting ventilation. It is quite common, with a prevalence of about 2-4%, has a strong genetic component, and creates a proinflammatory state with elevated TNFα and other cytokines. If untreated, OSA can lead to significant neurological problems that include stroke, cognitive decline, depression, headaches, peripheral neuropathy, and nonarteritic ischemic optic neuropathy (NAION). Treatment reverses some of these neurological problems. Treatment includes continuous positive airway pressure and its variants, oral appliances, weight loss, upper airway surgery, and rarely maxillofacial procedures. Other sleep breathing disorders such as hypoventilation, central sleep apnea, complex sleep apnea, and Cheyne-Stokes respiration are less common and are sometimes associated with neuromuscular disorders causing diaphragmatic paralysis, but can also be seen in opiate exposure and severe obesity.

A Preliminary Study on the Relationship between Platelet Serotonin Transporter Functionality, Depression, and Fatigue in Patients with Untreated Chronic Hepatitis C

Objective and Methods. Although the interaction between fatigue and depression in patients with chronic hepatitis C infection (HCV) has been recognized, the biological correlates of this observation have yet to be reported. We addressed this issue by examining serotonin transporter- (SERT-) driven [(14)C]-serotonin uptake rate (SUR) and serotonin content in platelets of 65 untreated HCV patients and 65 healthy control subjects (HCS). All patients completed report questionnaires for fatigue, depression, and general psychopathology. Structured interviews were conducted by a board-certified psychiatrist. Results. Whereas 36 of the patients experienced fatigue of moderate-to-severe intensity, only 16 reported symptoms of depression (BDI score > 10). Mean SUR in patients with depressive symptoms was significantly higher relative to the HCS, corresponding to a large Cohen's effect size of d = 1.45 (95% CI = 0.66-1.83). Patients who rated their fatigue to have a marked impact on mood and activity displayed a moderate relationship between the BDI score and SUR (n = 18, r = 0.563, P = 0.015), which becomes stronger after controlling for age, gender, and thrombocytopenia (r part = 0.710, P = 0.003). In the univariate analysis, high fatigue interference score, thrombocytopenia, and high SUR were all significant predictors of depression. Conclusions. High SERT activity could be implicated in the expression of depressive symptoms especially in a subgroup of HCV patients who are feeling fatigue as markedly distressing.

Xiaochaihutang prevents depressive-like behaviour in rodents by enhancing the serotonergic system

Objectives

Xiaochaihutang (XCHT) has been used in China for thousands of years to treat ‘Shaoyang syndrome’, which involves depressive-like symptoms. However, no studies were conducted to demonstrate its antidepressant effect and mechanism. This study was designed to confirm the antidepressant effect of XCHT and explore its mechanism using the pharmacological methods.

Methods

Ultra-HPLC and mass spectrometry was used to identify the chemical constituents of XCHT. Forced swimming test (FST) and tail suspension test (TST) were used to determine the antidepressant-like activity of XCHT in mice and rats. The possible mechanism of XCHT was elucidated by the reserpine-induced hypothermia and 5-hydroxytryptophan (5-HTP)-induced head-twitch in mice. The levels of serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were measured in prefrontal cortex and hippocampus tissue of both mice and rats. Moreover, the extracellular 5-HT in rat hippocampus was assessed by using microdialysis coupled to HPLC with electrochemical detection.

Key findings

Forty-four components were detected in XCHT. XCHT significantly reduced immobility time in the TST and the FST, antagonized reserpine-induced depressive-like behaviours, increased 5-HTP-induced head-twitches, elevated 5-HT and 5-HIAA levels, and increased 5-HT turnover at doses that did not affect general activity.

Conclusions

These data demonstrate that XCHT has therapeutic effects in animal models of depression by enhancing the serotoninergic system in the prefrontal cortex and hippocampus.

Stress, serotonin, and hippocampal neurogenesis in relation to depression and antidepressant effects

Chronic stressful life events are risk factors for developing major depression, the pathophysiology of which is strongly linked to impairments in serotonin (5-HT) neurotransmission. Exposure to chronic unpredictable stress (CUS) has been found to induce depressive-like behaviours, including passive behavioural coping and anhedonia in animal models, along with many other affective, cognitive, and behavioural symptoms. The heterogeneity of these symptoms represents the plurality of corticolimbic structures involved in mood regulation that are adversely affected in the disorder. Chronic stress has also been shown to negatively regulate adult hippocampal neurogenesis, a phenomenon that is involved in antidepressant effects and regulates subsequent stress responses. Although there exists an enormous body of data on stress-induced alterations of 5-HT activity, there has not been extensive exploration of 5-HT adaptations occurring presynaptically or at the level of the raphe nuclei after exposure to CUS. Similarly, although hippocampal neurogenesis is known to be negatively regulated by stress and positively regulated by antidepressant treatment, the role of neurogenesis in mediating affective behaviour in the context of stress remains an active area of investigation. The goal of this review is to link the serotonergic and neurogenic hypotheses of depression and antidepressant effects in the context of stress. Specifically, chronic stress significantly attenuates 5-HT neurotransmission and 5-HT1A autoreceptor sensitivity, and this effect could represent an endophenotypic hallmark for mood disorders. In addition, by decreasing neurogenesis, CUS decreases hippocampal inhibition of the hypothalamic-pituitary-adrenal (HPA) axis, exacerbating stress axis overactivity. Similarly, we discuss the possibility that adult hippocampal neurogenesis mediates antidepressant effects via the ventral (in rodents; anterior in humans) hippocampus' influence on the HPA axis, and mechanisms by which antidepressants may reverse chronic stress-induced 5-HT and neurogenic changes. Although data are as yet equivocal, antidepressant modulation of 5-HT neurotransmission may well serve as one of the factors that could drive neurogenesis-dependent antidepressant effects through these stress regulation-related mechanisms.

Neuronal ablation of p-Akt at Ser473 leads to altered 5-HT1A/2A receptor function

The serotonergic system regulates a wide range of behavior, including mood and impulsivity, and its dysregulation has been associated with mood disorders, autism spectrum disorder, and addiction. Diabetes is a risk factor for these conditions. Insulin resistance in the brain is specifically associated with susceptibility to psychostimulant abuse. Here, we examined whether phosphorylation of Akt, a key regulator of the insulin signaling pathway, controls serotonin (5-HT) signaling. To explore how impairment in Akt function regulates 5-HT homeostasis, we used a brain-specific rictor knockout (KO) mouse model of impaired neuronal phosphorylation of Akt at Ser473. Cortical 5-HT1A and 5-HT2A receptor binding was significantly elevated in rictor KO mice. Concomitant with this elevated receptor expression, the 5-HT1A receptor agonist 8-Hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) led to an increased hypothermic response in rictor KO mice. The increased cortical 5-HT1A receptor density was associated with higher 5-HT1A receptor levels on the cortical cell surface. In contrast, rictor KO mice displayed significantly reduced head-twitch response (HTR) to the 5-HT2A/C agonist 2,5-dimethoxy-4-iodoamphetamine (DOI), with evidence of impaired 5-HT2A/C receptor signaling. In vitro, pharmacological inhibition of Akt significantly increased 5-HT1A receptor expression and attenuated DOI-induced 5-HT2A receptor signaling, thereby lending credence to the observed in vivo cross-talk between neuronal Akt signaling and 5-HT receptor regulation. These data reveal that defective central Akt function alters 5-HT signaling as well as 5-HT-associated behaviors, demonstrating a novel role for Akt in maintaining neuronal 5-HT receptor function.

A longitudinal study of SLC6A4 DNA promoter methylation and poststroke depression

Serotonin transporter gene (SLC6A4) has been shown to play an important role in the pathophysiology of mood disorders including poststroke depression (PSD). SLC6A4 expression is influenced by DNA methylation status and the SLC6A4 linked promoter region (5-HTTLPR) polymorphism. This study aimed to investigate whether SLC6A4 methylation status was associated with depression ascertained at two weeks and one year after stroke taking into account the 5-HTTLPR polymorphism. A total of 286 patients were evaluated two weeks after stroke, and 222 (78%) were followed one year later. Depression was diagnosed according to DSM-IV criteria, and depression severity was assessed by the Hamilton Depression Rating Scale (HAMD) at each evaluation point. The effects of SLC6A4 methylation status on PSD status and HAMD scores were investigated using multivariate logistic regression models and partial correlation tests, respectively. Analyses were repeated after stratification by 5-HTTLPR genotype groups ('l/l or l/s' and 's/s'). Higher SLC6A4 promoter methylation status was independently associated with PSD both at 2 weeks and more prominently at 1 year after stroke, and was significantly associated with the worsening of depressive symptoms over one year. These findings were significant only in the presence of the 5-HTTLPR s/s genotype. SLC6A4 methylation profile was supported as a potential diagnostic and prognostic biomarker for PSD; associations with SLC6A4 methylation status may represent a target for drug development.

Regular moderate or intense exercise prevents depression-like behavior without change of hippocampal tryptophan content in chronically tryptophan-deficient and stressed mice

Regular exercise has an antidepressant effect in human subjects. Studies using animals have suggested that the antidepressant effect of exercise is attributable to an increase of brain 5-hydroxytryptamine (5-HT); however, the precise mechanism underlying the antidepressant action via exercise is unclear. In contrast, the effect of 5-HT on antidepressant activity has not been clarified, in part because the therapeutic response to antidepressant drugs has a time lag in spite of the rapid increase of brain 5-HT upon administration of these drugs. This study was designed to investigate the contribution of brain 5-HT to the antidepressant effect of exercise. Mice were fed a tryptophan-deficient diet and stressed using chronic unpredictable stress (CUS) for 4 weeks with or without the performance of either moderate or intense exercise on a treadmill 3 days per week. The findings demonstrated that the onset of depression-like behavior is attributable not to chronic reduction of 5-HT but to chronic stress. Regular exercise, whether moderate or intense, prevents depression-like behavior with an improvement of adult hippocampal cell proliferation and survival and without the recovery of 5-HT. Concomitantly, the mice that exercised showed increased hippocampal noradrenaline. Regular exercise prevents the impairment of not long-term memory but short-term memory in a 5-HT-reduced state. Together, these findings suggest that: (1) chronic reduction of brain 5-HT may not contribute to the onset of depression-like behavior; (2) regular exercise, whether moderate or intense, prevents the onset of chronic stress-induced depression-like behavior independent of brain 5-HT and dependent on brain adrenaline; and (3) regular exercise prevents chronic tryptophan reduction-induced impairment of not long-term but short-term memory.

Association of SLC6A4 methylation with early adversity, characteristics and outcomes in depression

Childhood adversities have been associated with onset and worse clinical presentations of depression. Epigenetic changes may reflect childhood adversities, while their effects on clinical characteristics of depression are unknown. This study aimed to investigate whether epigenetic changes were associated with childhood adversities, pretreatment characteristics, and treatment outcomes in depressive patients. In 108 patients with major depressive disorders, the methylation status in the promoter of gene encoding serotonin transporter (SLC6A4) was measured. Childhood adversities, socio-demographic and clinical characteristics including assessment scales for depression (Hamilton Depression Rating Scale, HAMD), anxiety (Hamilton Anxiety Rating Scale, HAMA), functioning (Social and Occupational Functioning Assessment Scale, SOFAS), disability (World Health Organization Disability Assessment Schedule-12, WHODAS-12), and quality of life (World Health Organization Quality of Life-Abbreviated form, WHOQOL-BREF) were evaluated at baseline. After a 12-week treatment with antidepressants, the assessment scales were reevaluated. To avoid type I error by multiple comparisons, Bonferroni corrections were applied. Higher SLC6A4 promoter methylation status was significantly associated with childhood adversities, worse clinical presentation (family history of depression, higher perceived stress, and more severe psychopathology assessed by SOFAS, WHODAS-12, and WHOQOL-BREF), but was not associated with treatment outcomes after considering multiple comparisons. SLC6A4 methylation status could be a proxy marker for childhood adversities and a clinical biomarker for certain presentations of depression.

[The effects of hormone replacement therapy on mind and brain]

Hormonal fluctuations during the perimenopausal transition lead to physical discomfort but are also frequently accompanied by mood swings, depressive symptoms, anxiety and sleeping disorders. The important role of the neurotransmitter serotonin in the pathogenesis of anxiety disorders and major depression is unquestioned, but only little is known about the influence of sex hormones on the serotonergic system. This review provides an overview of potential risk factors for the occurrence of affective disorders in the menopausal transition and discusses possible therapeutic options. Current research findings from longitudinal studies testing the efficacy of hormone replacement therapy and antidepressants with effects on the serotonergic neurotransmission on physical and mental discomforts during menopause are presented. Furthermore, studies using positron emission tomography and genetic methods that explore the effects of sex steroids on different components of the serotonergic system are shown. The interactions between estrogen, progesterone and the serotonergic system are described, and possible neurobiological and endocrinological mechanisms underlying depressive symptoms in the perimenopause are elucidated.

Pitchfork bifurcation in a receptor theory-based model of the serotonergic system

Abnormalities in the serotonergic system are thought to be a potent cause of several mental diseases. Past research has shown that autoreceptors are the key component. It is thought that the autoreceptor constructs a negative feedback circuit on this system and realizes homeostatic control on its neural activity. This study is mainly organized from the above mentioned knowledge. In this paper, we construct two possible models of the serotonergic system based on receptor theory and provide some predictions for this system with each model. In the first model, we predict that the deficit of serotonin synthesis causes destabilization of the amount of autoreceptors; autoreceptors show an explosive increase if serotonin synthesis drops below a certain threshold value. In the second model, we indicate that the serotonergic system changes its stable property from a monostable one to a bistable one by certain factors. We clarify these factors and show that this changing process is named pitch-fork bifurcation. Additionally, we also suggest another notable phenomena which would appear when we consider a stochastic perturbation on the receptor expressions. Lastly, we suggest some experimental ideas towards the verification of the validity of these models.

Social defeat induces changes in histone acetylation and expression of histone modifying enzymes in the ventral hippocampus, prefrontal cortex, and dorsal raphe nucleus

Chronic exposure to stress is associated with a number of psychiatric disorders, but little is known about the epigenetic mechanisms that underlie the stress response or resilience to chronic stress. We investigated histone acetylation in seven different brain regions of rats exposed to chronic social defeat stress: the dorsal hippocampus (dHPC), ventral hippocampus (vHPC), medial prefrontal cortex (mPFC), basolateral amygdala (BLA), locus coeruleus (LC), paraventricular thalamus (PVT), and dorsal raphe (DR) nucleus. This stress paradigm was unique in that it allowed rats to display resilience in the form of an active coping mechanism. We found that there was an increase in acetylation of H3K9/14 (H3K9/14ac) and bulk acetylation of H4K5,8,12,16 (H4K5,8,12,16ac) in the DR nucleus of rats that were less resilient. Less resilient rats also displayed increased levels of H3K18 acetylation (H3K18ac) in the mPFC when compared to non-stressed controls. In the vHPC, there was an increase in H3K18ac and H4K12 (H4K12ac) in rats that were less resilient when compared to non-stressed control rats. In addition, there was a decrease in levels of H4K8 acetylation (H4K8ac) in both resilient and non-resilient rats as compared to controls. We assessed expression of histone modifying enzymes in the vHPC and the mPFC using quantitative real-time polymerase chain reaction (PCR) and found changes in expression of a number of targets. These included changes in Sirt1 and Sirt2 in the vHPC and changes in Kat5 in the mPFC. Overall, these results suggest that changes in histone acetylation and expression of histone modifying enzymes in these regions correlate with the behavioral response to stress in socially defeated rats.

Rethinking 5-HT1A receptors: emerging modes of inhibitory feedback of relevance to emotion-related behavior

The complexities of the involvement of the serotonin transmitter system in numerous biological processes and psychiatric disorders is, to a substantial degree, attributable to the large number of serotonin receptor families and subtypes that have been identified and characterized for over four decades. Of these, the 5-HT(1A) receptor subtype, which was the first to be cloned and characterized, has received considerable attention based on its purported role in the etiology and treatment of mood and anxiety disorders. 5-HT(1A) receptors function both at presynaptic (autoreceptor) and postsynaptic (heteroreceptor) sites. Recent research has implicated distinct roles for these two populations of receptors in mediating emotion-related behavior. New concepts as to how 5-HT(1A) receptors function to control serotonergic tone throughout life were highlights of the proceedings of the 2012 Serotonin Club Meeting in Montpellier, France. Here, we review recent findings and current perspectives on functional aspects of 5-HT(1A) auto- and heteroreceptors with particular regard to their involvement in altered anxiety and mood states.

Interleukin-1β inhibits the differentiation of hippocampal neural precursor cells into serotonergic neurons

Interleukin-1 beta (IL-1β) is one of pro-inflammatory cytokines. Recent studies have shown that IL-1β impairs hippocampal neurogenesis, mediates proliferation and differentiation of multipotent neural precursor cells (NPCs), and exerts effects of anti-proliferation, anti-neurogenesis, and pro-gliogenesis on embryonic hippocampal NPCs. The aim of this study was to examine the effect of IL-1β on the differentiation of hippocampal NPCs into functional serotonergic neurons, which play important roles in the pathophysiology and treatment of depression. Hippocampal NPCs were prepared from the hippocampus of neonatal rats (within 24h after birth). After three passages and phenotyping, hippocampal NPCs were cultured in a differentiating medium with various concentrations (5, 10, and 20 ng/mL) of IL-1β for 7 days. At the endpoint, the serotonergic differentiation of hippocampal NPCs in IL-1β-treated cultures decreased in a dose-dependent manner and this effect was blocked by IL-1ra, an IL-1 receptor antagonist capable of blocking the effects of IL-1 by binding to the same receptor (IL-1R1) without triggering signaling; serotonin in the lysate of the differentiated hippocampal NPCs decreased in IL-1β-treated cultures; and levels of Bcl-2 and phosphorylated extracellular-regulated kinase (pERK) were also lower in differentiated hippocampal NPCs with IL-1β treatment. These results support the hypothesis that IL-1β is an important factor in the stress-associated neuropathology and psychopathology and has relevance to the treatment of depressive symptoms in patients with depression.

Global decrease of serotonin-1A receptor binding after electroconvulsive therapy in major depression measured by PET

Electroconvulsive therapy (ECT) is a potent therapy in severe treatment-refractory depression. Although commonly applied in psychiatric clinical routine since decades, the exact neurobiological mechanism regarding its efficacy remains unclear. Results from preclinical and clinical studies emphasize a crucial involvement of the serotonin-1A receptor (5-HT(1A)) in the mode of action of antidepressant treatment. This includes associations between treatment response and changes in 5-HT(1A) function and density by antidepressants. Further, alterations of the 5-HT(1A) receptor are consistently reported in depression. To elucidate the effect of ECT on 5-HT(1A) receptor binding, 12 subjects with severe treatment-resistant major depression underwent three positron emission tomography (PET) measurements using the highly selective radioligand [carbonyl-(11)C]WAY100635, twice before (test-retest variability) and once after 10.08±2.35 ECT sessions. Ten patients (~83%) were responders to ECT. The voxel-wise comparison of the 5-HT(1A) receptor binding (BP(ND)) before and after ECT revealed a widespread reduction in cortical and subcortical regions (P<0.05 corrected), except for the occipital cortex and the cerebellum. Strongest reductions were found in regions consistently reported to be altered in major depression and involved in emotion regulation, such as the subgenual part of the anterior cingulate cortex (-27.5%), the orbitofrontal cortex (-30.1%), the amygdala (-31.8%), the hippocampus (-30.6%) and the insula (-28.9%). No significant change was found in the raphe nuclei. There was no significant difference in receptor binding in any region comparing the first two PET scans conducted before ECT. This PET study proposes a global involvement of the postsynaptic 5-HT(1A) receptor binding in the effect of ECT.

The effects of acute tryptophan depletion on impulsivity and mood in adolescents engaging in non-suicidal self-injury

OBJECTIVE

Non-suicidal self-injury (NSSI) is associated with impaired emotion regulation and impulsivity. Low serotonin (5-hydroxytryptamine) function is associated with NSSI, impaired emotion regulation and impulsivity. We investigated the effects of experimentally lowered 5-hydroxytryptamine activity, via acute tryptophan depletion (ATD), on impulsive action, reflection impulsivity and mood in female adolescents engaging in NSSI.

METHODS

Thirty-two female adolescents engaging in NSSI participated in a parallel group ATD study. Following ATD, impulsive action was assessed using the Continuous Performance Test, Identical Pairs Version. Reflection impulsivity was assessed using the Matching Familiar Figures Test. Mood-lowering was examined using the Profile of Mood States.

RESULTS

Following ATD, the participants showed an impulsive response style (as reflected in their low β) and increased attentional capacity (as reflected in their elevated d'). ATD did not affect reflection impulsivity or mood.

CONCLUSIONS

Acute tryptophan depletion caused an impulsive response style and increased attentional capacity. Importantly, the findings suggest that low serotonin function is a vulnerability among female adolescents for engaging in NSSI when in emotional distress.

The 5-HT deficiency theory of depression: perspectives from a naturalistic 5-HT deficiency model, the tryptophan hydroxylase 2Arg439His knockin mouse

A decreased level of brain 5-hydroxytryptamine (5-HT) has been theorized to be a core pathogenic factor in depression for half a century. The theory arose from clinical observations that drugs enhancing extracellular levels of 5-HT (5-HT(Ext)) have antidepressant effects in many patients. However, whether such drugs indeed correct a primary deficit remains unresolved. Still, a number of anomalies in putative biomarkers of central 5-HT function have been repeatedly reported in depression patients over the past 40 years, collectively indicating that 5-HT deficiency could be present in depression, particularly in severely ill and/or suicidal patients. This body of literature on putative 5-HT biomarker anomalies and depression has recently been corroborated by data demonstrating that such anomalies indeed occur consequent to severely reduced 5-HT(Ext) levels in a mouse model of naturalistic 5-HT deficiency, the tryptophan hydroxylase 2 His(439) knockin (Tph2KI) mouse. In this review, we will critically assess the evidence for 5-HT deficiency in depression and the possible role of polymorphisms in the Tph2 gene as a causal factor in 5-HT deficiency, the latter investigated from a clinical as well as preclinical angle.

Environmental stress affects DNA methylation of a CpG rich promoter region of serotonin transporter gene in a nurse cohort

BACKGROUND

Shift-working nurses are exposed to a stressful work environment, which puts them at an increased risk for burnout and depression. We explored the effect of environmental stress on serotonin transporter gene (SLC6A4) promoter methylation among nurses from high and low work stress environments.

METHODOLOGY

Using bisulfite sequencing, we investigated the methylation status of five CpG residues of a CpG-rich region in the promoter of SLC6A4 by comparing female shift working nurses from a high work stress environment (n = 24) to low work stress environment (n = 25). We also analyzed the association of 5-HTTLPR polymorphism at 5' end of SLC6A4. Work stress was assessed by the Karasek's Model and possible signs of burnout or depression were measured by the Maslach Burnout Index General Survey and Beck Depression Index. Methylation levels were assessed by bisulfite sequencing of DNA extracted from peripheral blood leucocytes. Restriction enzyme treatment followed by standard PCR was used to identify 5-HTTLPR genotypes.

PRINCIPAL FINDINGS

We found that nurses in the high stress environment had significantly lower promoter methylation levels at all five CpG residues compared to nurses in the low stress environment (p<0.01). There was no significant interaction of 5-HTTLPR genotype and work stress with methylation (p = 0.58). In unadjusted (bivariate) analysis, burnout was not significantly associated to methylation levels. However, when mutually adjusted for both, burnout and work stress were significant contributors (p = 0.038 and p<0.0001 respectively) to methylation levels.

CONCLUSIONS

Our findings show that environmental stress is concurrent with decreased methylation of the SLC6A4 promoter. This may lead to increased transcriptional activity of the gene, increased reuptake of serotonin from synaptic clefts, and termination of the activity of serotonin. This could present a possible coping mechanism for environmental stress in humans that could eventually increase risk for disturbed functional capability and experience of depressed mood in long-term stress.

Raphe-Hippocampal Serotonin Neurotransmission In The Sex Related Differences of Adaptation to Stress: Focus on Serotonin-1A Receptor

Stress is the major predisposing and precipitating factor in the onset of depression which is the most significant mental health risk for women. Behavioral studies in animal models show that female sex though less affected by an acute stressor; exposure to repeated stressors induces coping deficits to impair adaptation in them. A decrease in the function of 5-hydroxytryptamine (5-HT; serotonin) in the hippocampus and an increased function of the 5-HT-1A receptor in the raphe nucleus coexist in depression. Pharmacological and neurochemical data are relevant that facilitation of serotonin neurotransmission via hippocampus due to desensitization of somatodendritic 5-HT1A receptors may lead to adaptation to stress. The present article reviews research on sex related differences of raphe-hippocampal serotonin neurotransmission to find a possible answer that may account for the sex differences of adaptation to stress reported in preclinical research and greater incidence of depression in women than men.

Mood disorders and risk of lung cancer in the EAGLE case-control study and in the U.S. Veterans Affairs inpatient cohort

Background

Mood disorders may affect lung cancer risk. We evaluated this hypothesis in two large studies.

Methodology/Principal Findings

We examined 1,939 lung cancer cases and 2,102 controls from the Environment And Genetics in Lung cancer Etiology (EAGLE) case-control study conducted in Italy (2002–2005), and 82,945 inpatients with a lung cancer diagnosis and 3,586,299 person-years without a lung cancer diagnosis in the U.S. Veterans Affairs Inpatient Cohort (VA study), composed of veterans with a VA hospital admission (1969–1996). In EAGLE, we calculated odds ratios (ORs) and 95% confidence intervals (CI), with extensive adjustment for tobacco smoking and multiple lifestyle factors. In the VA study, we estimated lung cancer relative risks (RRs) and 95% CIs with time-dependent Poisson regression, adjusting for attained age, calendar year, hospital visits, time within the study, and related previous medical diagnoses. In EAGLE, we found decreased lung cancer risk in subjects with a personal history of mood disorders (OR: 0.59, 95% CI: 0.44–0.79, based on 121 lung cancer incident cases and 192 controls) and family history of mood disorders (OR: 0.62, 95% CI: 0.50–0.77, based on 223 lung cancer cases and 345 controls). The VA study analyses yielded similar results (RR: 0.74, 95% CI: 0.71–0.77, based on 2,304 incident lung cancer cases and 177,267 non-cancer person-years) in men with discharge diagnoses for mood disorders. History of mood disorders was associated with nicotine dependence, alcohol and substance use and psychometric scales of depressive and anxiety symptoms in controls for these studies.

Conclusions/Significance

The consistent finding of a relationship between mood disorders and lung cancer risk across two large studies calls for further research into the complex interplay of risk factors associated with these two widespread and debilitating diseases. Although we adjusted for smoking effects in EAGLE, residual confounding of the results by smoking cannot be ruled out.

Cannabinoids and monoamine neurotransmission with focus on monoamine oxidase

Progress in understanding the mechanisms of action of cannabinoids was made after discovery of cannabinoid receptors and finding their endogenous ligands. New findings are obtained using both endogenous cannabinoids and plant or synthetic cannabinoids. Activation of cannabinoid receptors on synaptic terminals results in regulation of ion channels, neurotransmitter release and synaptic plasticity. Neuromodulation of synapses by cannabinoids is proving to have a wide range of functional effects, making them potential targets as medical preparations in a variety of illnesses, including some neurodegenerative and mental disorders. Brain monoamines are involved in many of the same processes affected by neuropsychiatric disorders and by different psychotropic drugs, including cannabinoids. Basic information is summarized in the paper about mechanisms of action of cannabinoids on monoaminergic systems, with a view to inhibition of monoamine oxidase.

Hippocampal neurogenesis, cognitive deficits and affective disorder in Huntington's disease

Huntington's disease (HD) is a neurodegenerative disorder caused by a tandem repeat expansion encoding a polyglutamine tract in the huntingtin protein. HD involves progressive psychiatric, cognitive, and motor symptoms, the selective pathogenesis of which remains to be mechanistically elucidated. There are a range of different brain regions, including the cerebral cortex and striatum, known to be affected in HD, with evidence for hippocampal dysfunction accumulating in recent years. In this review we will focus on hippocampal abnormalities, in particular, deficits of adult neurogenesis. We will discuss potential molecular mechanisms mediating disrupted hippocampal neurogenesis, and how this deficit of cellular plasticity may in turn contribute to specific cognitive and affective symptoms that are prominent in HD. The generation of transgenic animal models of HD has greatly facilitated our understanding of disease mechanisms at molecular, cellular, and systems levels. Transgenic HD mice have been found to show progressive behavioral changes, including affective, cognitive, and motor abnormalities. The discovery, in multiple transgenic lines of HD mice, that adult hippocampal neurogenesis and synaptic plasticity is disrupted, may help explain specific aspects of cognitive and affective dysfunction. Furthermore, these mouse models have provided insight into potential molecular mediators of adult neurogenesis deficits, such as disrupted serotonergic and neurotrophin signaling. Finally, a number of environmental and pharmacological interventions which are known to enhance adult hippocampal neurogenesis have been found to have beneficial affective and cognitive effects in mouse models, suggesting common molecular targets which may have therapeutic utility for HD and related diseases.

A morphometric, immunohistochemical, and in situ hybridization study of the dorsal raphe nucleus in major depression, bipolar disorder, schizophrenia, and suicide

BACKGROUND

Several lines of evidence implicate 5-hydroxytryptamine (5-HT, serotonin) in the pathophysiology of mood disorders and suicide. However, it is unclear whether these conditions include morphological involvement of the dorsal raphe nucleus (DRN), the origin of most forebrain 5-HT innervation.

METHOD

We used morphometric, immunohistochemical, and molecular methods to compare the DRN in post-mortem tissue of 50 subjects (13 controls, 14 major depressive disorder [MDD], 13 bipolar disorder, 10 schizophrenia; 17 of the cases died by suicide). NeuN and PH8 antibodies were used to assess all neurons and serotonergic neurons respectively; 5-HT(1A) autoreceptor expression was investigated by regional and cellular in situ hybridization. Measurements were made at three rostrocaudal levels of the DRN.

RESULTS

In MDD, the area of the DRN was decreased. In bipolar disorder, serotonergic neuronal size was decreased. Suicide was associated with an increased DRN area, and with a higher density but decreased size of serotonergic neurons. Total neuronal density and 5-HT(1A) receptor mRNA abundance were unaffected by diagnosis or suicide. No changes were seen in schizophrenia.

CONCLUSION

The results show that mood disorders and suicide are associated with differential, limited morphological alterations of the DRN. The contrasting influences of MDD and suicide may explain some of the discrepancies between previous studies, since their design precluded detection of the effect.

Increased serotonin-1A (5-HT1A) autoreceptor expression and reduced raphe serotonin levels in deformed epidermal autoregulatory factor-1 (Deaf-1) gene knock-out mice

Altered regulation of the serotonin-1A (5-HT1A) receptor gene is implicated in major depression and mood disorders. The functional human 5-HT1A C(-1019)G promoter polymorphism (rs6295), which prevents the binding of Deaf-1/NUDR leading to dysregulation of the receptor, has been associated with major depression. In cell models Deaf-1 displays dual activity, repressing 5-HT1A autoreceptor expression in serotonergic raphe cells while enhancing postsynaptic 5-HT1A heteroreceptor expression in nonserotonergic neurons. A functional Deaf-1 binding site on the mouse 5-HT1A promoter was recognized by Deaf-1 in vitro and in vivo and mediated dual activity of Deaf-1 on 5-HT1A gene transcription. To address regulation by Deaf-1 in vivo, Deaf-1 knock-out mice bred to a C57BL/6 background were compared with wild-type siblings for changes in 5-HT1A RNA and protein by quantitative RT-PCR, in situ hybridization, and immunofluorescence. In the dorsal raphe, Deaf-1 knock-out mice displayed increased 5-HT1A mRNA, protein, and 5-HT1A-positive cell counts but reduced 5-HT levels, whereas other serotonergic markers, such as tryptophan hydroxylase (TPH)- or 5-HT-positive cells and TPH2 RNA levels, were unchanged. By contrast, 5-HT1A mRNA and 5-HT1A-positive cells were reduced in the frontal cortex of Deaf-1-null mice, with no significant change in hippocampal 5-HT1A RNA, protein, or cell counts. The region-specific alterations of brain 5-HT1A gene expression and reduced raphe 5-HT content in Deaf-1(-/-) mice indicate the importance of Deaf-1 in regulation of 5-HT1A gene expression and provide insight into the role of the 5-HT1A G(-1019) allele in reducing serotonergic neurotransmission by derepression of 5-HT1A autoreceptors.

Behavioral deficits and exaggerated feedback control over raphe-hippocampal serotonin neurotransmission in restrained rats

Serotonin (5-hydroxytryptamine, 5-HT), acting via the hippocampus, is thought to be critical for the neuroadaptation that alleviates the adverse effects of stress on emotion and behavior. It was hypothesized that a decrease in raphe-hippocampal serotonin neurotransmission caused by exaggerated feedback inhibition of 5-HT synthesis and release significantly contributes to stress-induced behavioral deficits. Acute exposure to 2 h of restraint stress increased 5-HT metabolism in the cortex and raphe region but had no such effect in the hippocampus. Exposure to 2 h of restraint stress elicited anxiety-like behavior, which was monitored in the light-dark transition test the next day. Animals sacrificed 24 h after termination of the stress period exhibited a decrease in the concentration of 5-HT and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the hippocampus but not in the cortex and raphe. 8-Hydroxy-2-di-n-propylaminotetralin (8-OH-DPAT) injected at doses of 0.125, 0.25 and 0.5 mg/kg decreased 5-HT metabolism in the raphe, cortex and hippocampus of restrained and unrestrained animals, and the decreases in the raphe and hippocampus, but not those in the cortex, were greater in restrained than unrestrained animals. Exaggerated feedback control over raphe-hippocampal serotonin neurotransmission may be involved in the inability of the organism to cope with increased stress and elicits behavioral depression.

Developmental influence of the serotonin transporter on the expression of npas4 and GABAergic markers: modulation by antidepressant treatment

Alterations of the serotonergic system are involved in the pathophysiology of mood disorders and represent an important target for its pharmacological treatment. Genetic deletion of the serotonin transporter (SERT) in rodents leads to an anxious and depressive phenotype, and is associated with reduced neuronal plasticity as indicated by decreased brain-derived neurotrophic factor (Bdnf) expression levels. One of the transcription factors regulating Bdnf is the neuronal PAS domain protein 4 (Npas4), which regulates activity-dependent genes and neuroprotection, and has a critical role in the development of GABA synapses. On the basis of these premises, we investigated the expression of Npas4 and GABAergic markers in the hippocampus and prefrontal cortex of homozygous (SERT(-/-)) and heterozygous (SERT(+/-)) knockout rats, and analyzed the effect of long-term duloxetine treatment on the expression of these targets. We found that Npas4 expression was reduced in both the brain structures of adult SERT(+/-) and SERT(-/-) animals. This effect was already present in adolescent SERT(-/-), and could be mimicked by prenatal exposure to the antidepressant fluoxetine. Moreover, SERT(-/-) rats showed a strong impairment of the GABAergic system, as indicated by the reduction of several markers, including the vesicular transporter (Vgat), glutamic acid decarboxylase-67 (Gad67), the receptor subunit GABA A receptor, gamma 2 (GABA(A)-γ2), and calcium-binding proteins that label subgroups of the GABAergic neurons. Interestingly, chronic treatment with the antidepressant duloxetine was able to restore the physiological levels of Npas4 and GABAergic markers in SERT(-/-) rats, although some differences in the modulation of GABAergic genes exist between hippocampus and prefrontal cortex. Our results demonstrate that SERT knockout rats, an animal model of mood disorders, have reduced Npas4 expression that correlates with decreased expression of Bdnf exon I and IV. These changes lead to an impairment of the GABAergic system that may contribute to the anxious and depressive phenotype associated with inherited SERT downregulation.

Antidepressant-like effect of the extracted of Kai Xin San, a traditional Chinese herbal prescription, is explained by modulation of the central monoaminergic neurotransmitter system in mouse

ETHNOPHARMACOLOGICAL RELEVANCE

Kai Xin San (KXS) is a traditional Chinese herbal prescription for the treatment of depression-like disorders, anxiety, and impairment in learning and memory, however, there is very little scientific data concerning the efficacy of this.

AIM OF THE STUDY

The present study aimed to investigate the antidepressant potential of Kai Xin San and its possible mechanisms.

MATERIALS AND METHODS

Mouse models of depression including the tail suspension test (TST) and the forced swim test (FST) were used to evaluate the effects of KXS. A possible mechanism was explored in the tests of antagonism of reserpine-induced ptosis, akinesia and hypothermia and 5-HTP induced head-twitch response in mice. The contents of monoamine neurotransmitters including epinephrine (NE), 5-hydroxytryptamine (5-HT) and dopamine (DA) in mice brain were determined by Elisa. Spontaneous motor activities of mice and rotarod test were performed to find whether KXS has excitatory or inhibitory actions on the central nervous system.

RESULTS

The results showed that intragastric administration of KXS at 175, 350, 700, 1400 mg/kg/day or fluoxetine at 28 mg/kg/day for 3 days significantly reduced the duration of immobility in TST and FST, while it showed no effect on the spontaneous motor activity and rotarod performance in mice. However, the effect was not dose-dependent. The pre-treatment with KXS or fluoxetine for 3 days could elevate the contents of NE, 5-HT and DA in mice brain significantly. When the mice were treated with KXS (350 mg/kg, p.o) or desipramine (30 mg/kg, p.o) for 7 days, both of them could antagonize reserpine-induced ptosis, akinesia and hypothermia. The KXS (350 mg/kg) also increased the accumulative number of the 5-HTP-induced head twitch response in mice in 20 min when KXS at dosages of 175, 350, 700 and 1400 mg/kg/day were performed per os (p.o.) during a 1-day, 3-day or 7-day period.

CONCLUSIONS

Our results suggested that KXS exerts antidepressant-like effect. A possible mechanism, at least in part, is via the central monoaminergic neurotransmitter system and 5-HT plays a major role.

Sertraline delays relapse in recently abstinent cocaine-dependent patients with depressive symptoms

AIMS

Whether the selective serotonin re-uptake inhibitor sertraline at 200 mg/day delays relapse in recently abstinent cocaine-dependent individuals.

DESIGN

The study involved a 12-week, double-blind, placebo-controlled clinical trial with 2-week residential stay followed by 10-week out-patient participation.

SETTING

Veterans Affairs residential unit and out-patient treatment research program.

PARTICIPANTS

Cocaine-dependent volunteers (n = 86) with depressive symptoms (Hamilton score > 15), but otherwise no major psychiatric or medical disorder or contraindication to sertraline.

MEASUREMENTS

Participants were housed on a drug-free residential unit (weeks 1-2) and randomized to receive sertraline or placebo. Participants then participated on an out-patient basis during weeks 3-12 while continuing to receive study medication. Patients participated in a day substance abuse/day treatment program during weeks 1-3 and underwent weekly cognitive behavioral therapy during weeks 4-12. The primary outcome measure was thrice-weekly urine results and the secondary measure was Hamilton Depression scores.

FINDINGS

Pre-hoc analyses were performed on those who participated beyond week 2. Generally, no group differences in retention or baseline characteristics occurred. Sertraline patients showed a trend towards longer time before their first cocaine-positive urine ('lapse', χ(2) = 3.67, P = 0.056), went significantly longer before having two consecutive urine samples positive for cocaine ('relapse', χ(2) = 4.03, P = 0.04) and showed significantly more days to lapse (26.1 ± 16.7 versus 13.2 ± 10.5; Z = 2.89, P = 0.004) and relapse (21.3 ± 10.8 versus 32.3 ± 14.9; Z = 2.25, P = 0.02). Depression scores decreased over time (F = 43.43, P < 0.0001), but did not differ between groups (F = 0.09, P = 0.77).

CONCLUSIONS

Sertraline delays time to relapse relative to placebo in cocaine-dependent patients who initially achieve at least 2 weeks of abstinence.

Classification of 5-HT(1A) receptor agonists and antagonists using GA-SVM method

AIM

To construct a reliable computational model for the classification of agonists and antagonists of 5-HT(1A) receptor.

METHODS

Support vector machine (SVM), a well-known machine learning method, was employed to build a prediction model, and genetic algorithm (GA) was used to select the most relevant descriptors and to optimize two important parameters, C and r of the SVM model. The overall dataset used in this study comprised 284 ligands of the 5-HT(1A) receptor with diverse structures reported in the literatures.

RESULTS

A SVM model was successfully developed that could be used to predict the probability of a ligand being an agonist or antagonist of the 5-HT(1A) receptor. The predictive accuracy for training and test sets was 0.942 and 0.865, respectively. For compounds with probability estimate higher than 0.7, the predictive accuracy of the model for training and test sets was 0.954 and 0.927, respectively. To further validate our model, the receiver operating characteristic (ROC) curve was plotted, and the Area-Under-the-ROC- Curve (AUC) value was calculated to be 0.883 for training set and 0.906 for test set.

CONCLUSION

A reliable SVM model was successfully developed that could effectively distinguish agonists and antagonists among the ligands of the 5-HT(1A) receptor. To our knowledge, this is the first effort for the classification of 5-HT(1A) receptor agonists and antagonists based on a diverse dataset. This method may be used to classify the ligands of other members of the GPCR family.