5HT2 receptor changes in major depression

Early escitalopram administration as a preemptive treatment strategy against spasticity after contusive spinal cord injury in rats

In the majority of spinal cord injury (SCI) patients, spasticity develops in the subacute phase and chronically persists with muscle hypertonia. Among various pathological conditions underlying spasticity, upregulated expression of 5-HT receptors (5-HTR) on the spinal motor neurons due to 5-HT denervation is considered one of crucial factors for hyperexcitability of the spinal circuit. As a 5-HT signal modulator, selective serotonin re-uptake inhibitors (SSRIs) are ordinarily prescribed for diseases associated with 5-HT in the CNS, and are known for their ability to increase 5-HT levels as well as to desensitize 5-HTR. Here, we hypothesized that early SSRI administration as a preemptive treatment strategy would effectively prevent the onset of spasticity. We used a rat model of contusive SCI and administered escitalopram during the first 4 weeks after injury, which is the period required for spasticity development in rodent models. We performed a swimming test to quantify spastic behaviors and conducted the Hoffman reflex test as well as histological analyses for 5-HT_2AR and KCC2 expressions. Four weeks of escitalopram administration suppressed spastic behaviors during the swimming test and reduced the population of spasticity-strong rats. Moreover, the treatment resulted in decreased immunoreactivity of 5-HT_2AR in the spinal motor neurons. Result of the H-reflex test and membrane expression of KCC2 were not significantly altered. In summary, early escitalopram administration could prevent the onset of spastic behaviors via regulation of 5-HT system after SCI, but could not modulate exaggerated spinal reflex. Our results suggest a novel application of SSRIs for preventative treatment of spasticity.

Classical Psychedelics as Therapeutics in Psychiatry - Current Clinical Evidence and Potential Therapeutic Mechanisms in Substance Use and Mood Disorders

Classical psychedelics, primarily psilocybin and lysergic acid diethylamide (LSD), have been used and extensively studied in Western medicine as part of substance-assisted psychotherapy in the 1950s and 1960s. Modern clinical research is currently gaining momentum and provides new evidence for the safety and efficacy of classical psychedelics (primarily psilocybin, but also LSD and ayahuasca) in the treatment of different psychiatric conditions, including substance use and mood disorders.In this review article, we outline common pathological mechanisms of substance use disorders (SUD) and unipolar depression. Next, the current literature on the effects of psychedelics is summarized in order to generate hypotheses regarding their potential therapeutic mechanisms of action in treating these psychiatric conditions. Finally, we review and discuss clinical trials published since 2011 investigating the effects of psychedelics in SUD and depression.While results from those modern clinical trials are promising, most of them do not meet the methodological requirements to allow firm conclusions on the clinical efficacy of psychedelics. Larger, blinded, randomized controlled trials (RCT) with clearly defined patient groups and well-defined primary endpoints are needed. Additionally, the therapeutic mechanisms of classical psychedelics are currently unknown. This review presents hypotheses derived from preclinical and human studies that need to be tested in future trials to better understand the clinical potential of psychedelic substances in modern psychiatry.

Autophagy inhibition plays a protective role against 3, 4-methylenedioxymethamphetamine (MDMA)-induced loss of serotonin transporters and depressive-like behaviors in rats

The 3,4-methylenedioxymethamphetamine (MDMA) is a popular recreational drug, which ultimately leads to serotonergic (5-HT) neurotoxicity and psychiatric disorders. Previous in vitro studies have consistently demonstrated that MDMA provokes autophagic activation, as well as damage of 5-HT axons and nerve fibers. So far, whether autophagy, a well-conserved cellular process that is critical for cell fate, also participates in MDMA-induced neurotoxicity in vivo remains elusive. Here, we first examined time-course of autophagy-related changes during repeated administration of MDMA (10 mg/kg s.c. twice daily for 4 consecutive days) using immunofluorescent staining for tryptophan hydroxylase and microtubule-associated protein 1 light chain 3 beta in rats. We also evaluated the protective effects of 3-methyadanine (3-MA, an autophagy inhibitor, 15 mg/kg i.p.) against MDMA-induced acute and long-term reductions in serotonin transporters (SERT) density in various brain regions using immunohistochemical staining and positron emission tomography (PET) imaging respectively. Plasma corticosterone measurements and forced swim tests were performed to evaluate the depressive performance. The staining results showed that repeated administration of MDMA increased expression of autophagosome and caused reduction in SERT densities of striatum and frontal cortex, which was ameliorated in the presence of 3-MA. PET imaging data also revealed that 3-MA could ameliorate MDMA-induced long-term decreased SERT availability in various brain regions of rats. Furthermore, immobility time of forced swim tests and plasma corticosterone levels were less in the group of MDMA co-injected with 3-MA compared with that of MDMA group. Together, these findings suggest that autophagy inhibition may confer protection against neurobiological and behavioral changes induced by MDMA.

Psilocybin for treating substance use disorders?

INTRODUCTION

Evidence based treatment for Substance use disorders (SUD) includes psychotherapy and pharmacotherapy. However, these are only partially effective. Hallucinogens, such as psilocybin, may represent potential new treatment options for SUD. This review provides a summary of (human) studies on the putative therapeutic effects of psilocybin, and discusses the receptor systems, brain regions and cognitive and emotional processes mediating psilocybin's effects. Psilocybin's chemical structure is similar to that of serotonin. Dysregulations in the serotonin system are associated with alterations in stress hormones, such as cortisol, and mood disorders. After psilocybin administration cortisol levels spike and activate the executive control network, with subsequent increased control over emotional processes, and relief of negative thinking and persistent negative emotions. Preliminary data of ongoing alcohol and smoking addiction studies in humans shows promising effects of psilocybin administration on substance use. Importantly, psilocybin has a low risk of toxicity and dependence and can be used safely under controlled clinical conditions. Areas covered: This paper is a narrative review based on the search terms: psilocybin, substance use disorder, addiction, depression, serotonin. Literature on potential efficacy and mechanisms of action of psilocybin in SUD is discussed. Expert commentary: Recent positive findings with psilocybin need confirmation in well-designed placebo controlled randomized trials employing a large sample size.

Functional constituents of a local serotonergic system, intrinsic to the human coronary artery smooth muscle cells

Human coronary artery smooth muscle cells (HCASMCs) play an important role in the pathogenesis of coronary atherosclerosis and coronary artery diseases (CAD). Serotonin is a mediator known to produce vascular smooth muscle cell mitogenesis and contribute to coronary atherosclerosis. We hypothesize that the HCASMC possesses certain functional constituents of the serotonergic system such as: tryptophan hydroxylase and serotonin transporter. Our aim was to examine the presence of functional tryptophan hydroxylase-1 (TPH1) and serotonin transporter (SERT) in HCASMCs. The mRNA transcripts by qPCR and protein expression by Western blot of TPH1 and SERT were examined. The specificity and accuracy of the primers were verified using DNA gel electrophoresis and sequencing of qPCR products. The functionality of SERT was examined using a fluorescence dye-based serotonin transporter assay. The enzymatic activity of TPH was evaluated using UPLC. The HCASMCs expressed both mRNA transcripts and protein of SERT and TPH. The qPCR showed a single melt curve peak for both transcripts and in sequence analysis the amplicons were aligned with the respective genes. SERT and TPH enzymatic activity was present in the HCASMCs. Taken together, both TPH and SERT are functionally expressed in HCASMCs. These findings are novel and represent an initial step in examining the clinical relevance of the serotonergic system in HCASMCs and its role in the pathogenesis of coronary atherosclerosis and CAD.

Central serotonin-2A (5-HT2A) receptor dysfunction in depression and epilepsy: the missing link?

5-Hydroxytryptamine 2A receptors (5-HT_2A-Rs) are G-protein coupled receptors. In agreement with their location in the brain, they have been implicated not only in various central physiological functions including memory, sleep, nociception, eating and reward behaviors, but also in many neuropsychiatric disorders. Interestingly, a bidirectional link between depression and epilepsy is suspected since patients with depression and especially suicide attempters have an increased seizure risk, while a significant percentage of epileptic patients suffer from depression. Such epidemiological data led us to hypothesize that both pathologies may share common anatomical and neurobiological alteration of the 5-HT_2A signaling. After a brief presentation of the pharmacological properties of the 5-HT_2A-Rs, this review illustrates how these receptors may directly or indirectly control neuronal excitability in most networks involved in depression and epilepsy through interactions with the monoaminergic, GABAergic and glutamatergic neurotransmissions. It also synthetizes the preclinical and clinical evidence demonstrating the role of these receptors in antidepressant and antiepileptic responses.

Converging translational evidence for the involvement of the serotonin 2A receptor gene in major depressive disorder

An association between serotonin 2A receptor (5-HT2AR), encoded by HTR2A gene, and major depressive disorder (MDD) has been suggested. Here, we combined preclinical and ecological clinical approaches to explore the impact of impaired 5-HT2AR-mediated transmission on MDD or anxio-depressive-like phenotype in mice. Htr2a knock-out mice (Htr2a(-/-)) and wild-type mice were compared for the ability of chronic corticosterone to elicit some anxio-depressive-like phenotype in three behavioral paradigms (elevated plus maze, tail suspension test and splash test). Accordingly, two single nucleotide polymorphisms of the HTR2A gene (rs6314 ie His452Tyr and rs6313 ie 102C/T), which specific allelic variants may decrease 5-HT2AR-mediated transmission (as in Htr2a(-/-)mice), were studied in a sample of 485 Caucasian patients with MDD. In response to chronic corticosterone exposure, Htr2a(-/-) mice displayed more pronounced anxiodepressive-like phenotype than wild-type mice, as shown by a significant higher "emotionality score" (p<0.01). In patients, the C allele of rs6313 was more frequent in depressed patients (p=0.019) and was also associated with a more severe major depressive episode (p=0.03). This translational and ecological study involving constitutive Htr2a(-/-) knock-out mice and related SNPs in depressed patients suggests that a lower neurotransmission at the 5-HT2AR may favor the susceptibility and severity of MDE. It also suggests that specific allelic variants of the rs6313 and rs6314 may reduce 5-HT2AR-mediated transmission.

Association of HTR2A T102C and A-1438G polymorphisms with susceptibility to major depressive disorder: a meta-analysis

Serotonin 2A receptor (HTR2A) gene was implicated to be associated with major depressive disorder (MDD) susceptibility due to its role of key neurotransmitter in many physiologic processes. A great number of related studies reported in different populations have emerged. The results of these studies, however, have been inconsistent and thereby definite conclusions are difficult to establish. With the cumulative data in recent years, it was necessary to carry out a comprehensive analysis of previous findings. Electronic databases were systematically searched for studies published before May 2013. Pooled odds ratios (OR) and 95 % confidence interval (CI) were estimated under three different genetic models. Subgroup and sensitivity analyses were also performed. A total of 21 studies, 3,299 patients and 4,092 controls, met the selection criteria. 15 studies included HTR2A T102C polymorphism (with a total of 2,409 patients and 3,130 controls), and 9 studies included HTR2A A-1438G polymorphism (with a total of 1,510 patients and 2,281 controls). Our results showed that no significant association of MDD susceptibility with T102C polymorphism was found in allelic analysis and genotypic analysis (For T vs. C: OR = 1.06, 95 % CI = 0.95-1.18, P = 0.307; For TT + TC vs. CC: OR = 1.07, 95 % CI = 0.90-1.28, P = 0.451; For TT vs. TC + CC: OR = 1.08, 95 % CI = 0.95-1.22, P = 0.235). With respect to A-1438G polymorphism, however, carriers with A allele tend to suffer from MDD (AA + AG vs. GG: OR = 1.20, 95 % CI = 1.02-1.43, P = 0.030). When stratified by race for T102C polymorphism and A-1438G polymorphism of the HTR2A, we found no significant association. In conclusions, our study suggests that the A allele of A-1438G polymorphism might play a role in susceptibility to MDD. On the contrary, T102C polymorphism does not seem to be capable of modifying MDD risk.

Additive antidepressant-like effects of fasting with imipramine via modulation of 5-HT2 receptors in the mice

Recently, studies show that intermittent fasting and caloric restriction may improve symptoms of depression. However, there is little scientific evidence regarding the literature on the antidepressant-like effects of acute fasting. The present study aims to investigate the antidepressant-like effects and its influence on brain levels of the transcription factor cAMP response element-binding protein (CREB) and its phosphorylated form (p-CREB) in different time periods of fasting mice. Furthermore, the additive antidepressant-like effects of fasting with imipramine and the possible involvement of the 5-HT2 receptors were examined. In the present study 9h, but not 3h and 18h of fasting significantly reduced immobility time in the forced swimming test (FST) without alteration in locomotor activity in the open field test. 9h fasting also enhanced the ratio of p-CREB/CREB in the frontal cortex and hippocampus. Co-administration of 9h of fasting and imipramine (30mg/kg, i.p) produced the additive antidepressant-like effects in the FST and increased the ratio of p-CREB/CREB. Meanwhile, the additive effects were partially reversed by treatment with a 5-HT2A/2C receptor agonist, (±)-1-(2, 5-dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride (DOI) (5mg/kg, s.c). Furthermore, the antidepressant-like effects of 9h fasting was also blocked by DOI compared to the non-fasting control group. Serum corticosterone level, but not 5-HT and noradrenaline, was significantly increased in a time-dependent manner following different time periods of fasting. Taken together, these results suggest that acute fasting produces antidepressant-like effects via enhancement of the p-CREB/CREB ratio, and additive antidepressant-like effects of fasting with imipramine may be related to modulating 5-HT2 receptors.

Biological basis of suicide and suicidal behavior

OBJECTIVE

Suicide is a major public health concern as each year 30000 people die by suicide in the USA alone. In the teenage population, it is the second leading cause of death. There have been extensive studies of psychosocial factors associated with suicide and suicidal behavior. However, very little is known about the neurobiology of suicide. Recent research has provided some understanding of the neurobiology of suicide, which is the topic of this review.

METHODS

Neurobiology of suicide has been studied using peripheral tissues such as platelets, lymphocytes, and cerebrospinal fluid obtained from suicidal patients or from the postmortem brains of suicide victims.

RESULTS

These studies have provided encouraging information with regard to the neurobiology of suicide. They show an abnormality of the serotonergic mechanism, such as increased serotonin receptor subtypes and decreased serotonin metabolites (e.g. 5-hydroxyindoleacetic acid). These studies also suggest abnormalities of receptor-linked signaling mechanisms such as phosphoinositide and adenylyl cyclase. Other biological systems that appear to be dysregulated in suicide involve the hypothalamic-pituitary-adrenal axis, and neurotrophins and neurotrophin receptors. More recently, several studies have also indicated abnormalities of neuroimmune functions in suicide.

CONCLUSIONS

Some encouraging information emerged from the present review, primarily related to some of the neurobiological mechanisms mentioned above. It is hoped that neurobiological studies may eventually result in the identification of appropriate biomarkers for suicidal behavior as well as appropriate therapeutic targets for its treatment.

Glucocorticoid treatment increases density of serotonin 5-HT2A receptors in humans

BACKGROUND

Interactions between the serotonergic system and the hypothalamic-pituitary-adrenal axis have been suggested, albeit the details for such interactions have yet to be established. Animal studies have shown that the density of serotonin 5-HT2A receptors is increased after administration of exogenous glucocorticoids.

OBJECTIVE

The objective of this study was to explore possible changes in the pattern of density and affinity of 5-HT2A receptors in humans after treatment with glucocorticoids.

METHODS

Using a radioactive binding assay, the density and affinity (measured as Bmax and Kd) of 5-HT2A serotonin receptors were measured in blood samples drawn from 27 individuals diagnosed with polymyalgia rheumatica and/or giant cell arteritis before and after start of an oral treatment with prednisolone. For each patient Bmax and Kd at baseline before prednisolone treatment were compared with Bmax and Kd in samples drawn at a first and second follow-up clinic visit at an average of 8.8 (±2.5) days and 33.6 (±6.8) days, respectively.

RESULTS

The density of 5-HT2A receptors increased after treatment in 23 individuals. The mean Bmax value at baseline for all patients was 45.2 fmol/mg protein compared with 64.9 fmol/mg protein in the corresponding samples drawn at the second follow-up visit (p=0.001). There also was an association between individuals accumulated prednisolone dose and the magnitude of change in Bmax between baseline and the first follow-up visit. Erythrocyte sedimentation rate, platelet count or gender had no influence on the results. There were no significant differences in Kd during the treatment period. However, a low Kd value at baseline was a predictor for an increase in Bmax following treatment.

CONCLUSIONS

The results of this study showed that the density of 5-HT2A serotonin receptors in man is increased after a subchronic treatment with glucocorticoids. The magnitude of the increase appears to be associated with the affinity of 5-HT2A receptors before treatment and the accumulated dose of glucocorticoid early in the treatment period.

The neurobiology of suicide - A Review of post-mortem studies

The neurobiology of suicidal behaviour, which constitutes one of the most serious problems both in psychiatry and general medical practice, still remains to a large degree unclear. As a result, scientists constantly look for new opportunities of explaining the causes underlying suicidality. In order to elucidate the biological changes occurring in the brains of the suicide victims, studies based on post-mortem brain tissue samples are increasingly being used. These studies employ different research methods to provide an insight into abnormalities in brain functioning on various levels, including gene and protein expression, neuroplasticity and neurotransmission, as well as many other areas. The aim of this paper to summarize the available data on the post-mortem studies, to provide an overview of main research directions and the most up-to-date findings, and to indicate the possibilities of further research in this field.

Depression-like behavior is dependent on age in male SAMP8 mice

Aging is associated with an increased risk of depression in humans. To elucidate the underlying mechanisms of depression and its dependence on aging, here we study signs of depression in male SAMP8 mice. For this purpose, we used the forced swimming test (FST). The total floating time in the FST was greater in SAMP8 than in SAMR1 mice at 9 months of age; however, this difference was not observed in 12-month-old mice, when both strains are considered elderly. Of the two strains, only the SAMP8 animals responded to imipramine treatment. We also applied the dexamethasone suppression test (DST) and studied changes in the dopamine and serotonin (5-HT) uptake systems, the 5-HT2a/2c receptor density in the cortex, and levels of TPH2. The DST showed a significant difference between SAMR1 and SAMP8 mice at old age. SAMP8 exhibits an increase in 5-HT transporter density, with slight changes in 5-HT2a/2c receptor density. In conclusion, SAMP8 mice presented depression-like behavior that is dependent on senescence process, because it differs from SAMR1, senescence resistant strain.

HTR2A-1438A/G polymorphism influences the risk of schizophrenia but not bipolar disorder or major depressive disorder: a meta-analysis

The incidence of psychiatric disorders has been shown to have a strong genetic component, and we conducted this study to investigate whether the -1438A/G polymorphism of the HTR2A gene was associated with susceptibility to schizophrenia (SZ), bipolar disorder (BD), and major depressive disorder (MDD). Pooled odd ratios (ORs) and 95% confidence intervals (95% CIs) were calculated using data obtained from a total 27 studies that investigated an association between the HTR2A -1438A/G polymorphism and SZ (15), BD (7), and MDD (4). We failed to observe an association between the HTR2A -1438A/G polymorphism and BD and MDD, and we found contrary results with regard to SZ. Our results showed that the -1438A/G polymorphism was a risk factor for SZ, especially in Caucasians (allele model: OR, 1.12; 95% CI, 1.05-1.20; I(2) = 17.3%; dominant model: OR, 1.14; 95% CI, 1.03-1.27; I(2) = 15.3%; recessive model: OR, 1.20; 95% CI, 1.06-1.37; I(2) = 0.0%; codominant model 1: OR, 1.16; 95% CI, 1.01-1.32; I(2) = 0.0%). We found that the association of the HTR2A -1438A/G polymorphism with SZ depends on the ethnic origin of the study population, and this genetic variant does not modify the susceptibility to BD or MDD. © 2013 Wiley Periodicals, Inc.

Administration of clomipramine to neonatal mice alters stress response behavior and serotonergic gene expressions in adult mice

Early life exposure to antidepressants frequently occurs when pregnant mothers take the medication during late pregnancy. Previous studies in animal models have shown that early exposure to certain antidepressants can alter some behaviors in adulthood. We examined whether the administration of clomipramine, a serotonin reuptake inhibitor, to neonatal mice could result in depression-related behavioral alterations in adult mice. In addition, in an attempt to uncover the mechanism underlying these behavioral changes, we examined the expression of candidate genes in different areas of the brain. Here we show that mice chronically injected with clomipramine specifically during early postnatal development demonstrated depression-like behavior as well as altered stress responses in adulthood. An analysis of the expression of serotonergic genes after exposure to social defeat stress revealed small but significant changes in the expression of 5-HT1A receptor gene (Htr1a) and 5-HTT gene (Slc6a4) in the mice treated with clomipramine compared with the mice injected with saline. We concluded that antidepressant exposure in early days of life could alter stress-related behavior in adulthood and that the behavioral alterations are accompanied by altered serotonergic gene expressions.

Neurochemical imaging and depressive behaviours

Neurochemical imaging is frequently applied to measure markers of pathological change so as to understand mechanisms that create symptoms of major depressive disorder. For example, indices of greater monoamine oxidase A(MAO-A) level, particularly in the prefrontal and anterior cingulate cortex, are associated with depressed mood states, and high-risk states for onset of major depressive episodes. MAO-A metabolises monoamines, and greater metabolism of monoamines occurs when MAO-A is elevated in brain. Lower extracellular serotonin is associated with greater pessimism in humans and chronic serotonin deficiency is associated with upregulation of 5-HT2A (serotonin2A) receptors in cortex. During major depressive episodes when pessimism is more severe, greater 5-HT2A BPND, an index of density occurs in prefrontal and anterior cingulate cortex. These results argue for a mechanism of lowering extracellular serotonin in the prefrontal and anterior cingulate cortex, consequent to elevated MAO-A level. The relationship between elevated 5-HTT BPND and greater pessimism during major depressive episodes suggests that greater 5-HTT density in the context of elevated MAO-A level further contributes to serotonin deficiency in these brain regions. A similar mechanism may explain the association between neuroimaging indices of greater dorsal striatal D2 density, DAT density and symptoms of motor retardation: Greater MAO-A level and relatively greater DAT density lower extracellular dopamine in the dorsal striatum, leading to motor retardation. Indices of greater 5-HT1A density, particularly in the cingulate cortex, have been associated with major depressive disorder, and well as anxiety disorders, suggesting that this abnormality is mechanistically related to presence of anxiety symptoms. To date, abnormalities of Glx a measure reflecting glutamate and glutamine levels have been most strongly associated with presence of major depressive episodes, with greater levels in occipital cortex, and reduced levels in prefrontal cortex. Ultimately, the future for neurochemical imaging is to better understand the mechanisms that predispose toward onset of MDE so as to create biologically informed, novel, methods of prevention, and superior, more symptom-targeted treatments.

Chronic fluvoxamine treatment changes 5-HT(2A/2C) receptor-mediated behavior in olfactory bulbectomized mice

AIMS

Olfactory bulbectomy (OBX) in rodents represents a valuable experimental model of depression. This study was designed to shed further light on the impact of putative serotonergic neuronal degeneration in OBX mice and to assess the effect of a widely used antidepressant on serotonergic related behavioral changes induced by OBX.

MAIN METHODS

Adult male ddY mice were subject to bilateral OBX or sham surgery. The serotonin (5-HT)(2A/2C) receptor agonist 2,5-dimethoxy-4-iodoamphetamine (DOI) enhanced a head-twitch response (HTR) in OBX mice. Effects of 5-HT(2A), 5-HT(2C) antagonists and fluvoxamine were observed in OBX mice following DOI administration.

KEY FINDINGS

The HTR elicited by the administration of DOI (0.5 mg/kg and 1 mg/kg, i.p.) was increased about twofold in OBX mice when compared with controls on the 14th day after the surgery. The injection of ketanserin (0.025 mg/kg, i.p.), a 5-HT(2A) receptor antagonist, inhibited the enhancement of the DOI-induced HTR after OBX. Likewise, the administration of SB 242084 (1 mg/kg, s.c.), a 5-HT(2C) receptor antagonist, also inhibited the DOI-induced HTR in OBX mice. Chronic but not acute treatment with the antidepressant fluvoxamine, a selective serotonin reuptake inhibitor (SSRI), suppressed the enhancement of DOI-induced HTR after OBX.

SIGNIFICANCE

These findings indicate that OBX, and the subsequent degeneration of neurons projecting from the olfactory bulb, caused a supersensitivity of 5-HT(2A/2C) receptors which may be involved in symptoms of depression.

Neurobiology of chronic mild stress: parallels to major depression

The chronic mild (or unpredictable/variable) stress (CMS) model was developed as an animal model of depression more than 20 years ago. The foundation of this model was that following long-term exposure to a series of mild, but unpredictable stressors, animals would develop a state of impaired reward salience that was akin to the anhedonia observed in major depressive disorder. In the time since its inception, this model has also been used for a variety of studies examining neurobiological variables that are associated with depression, despite the fact that this model has never been critically examined to validate that the neurobiological changes induced by CMS are parallel to those documented in depressive disorder. The aim of the current review is to summarize the current state of knowledge regarding the effects of chronic mild stress on neurobiological variables, such as neurochemistry, neurochemical receptor expression and functionality, neurotrophin expression and cellular plasticity. These findings are then compared to those of clinical research examining common variables in populations with depressive disorders to determine if the changes observed following chronic mild stress are in fact consistent with those observed in major depression. We conclude that the chronic mild stress paradigm: (1) evokes an array of neurobiological changes that mirror those seen in depressive disorders and (2) may be a suitable tool to investigate novel systems that could be disturbed in depression, and thus aid in the development of novel targets for the treatment of depression.

Opposing local effects of endocannabinoids on the activity of noradrenergic neurons and release of noradrenaline: relevance for their role in depression and in the actions of CB(1) receptor antagonists

There is strong evidence that endocannabinoids modulate signaling of serotonin and noradrenaline, which play key roles in the pathophysiology and treatment of anxiety and depression. Most pharmacological and genetic, human and rodent studies suggest that the presence of under-functioning endocannabinoid type-1 (CB(1)) receptors is associated with increased anxiety and elevated extracellular serotonin concentration. In contrast, noradrenaline is presumably implicated in the mediation of depression-type symptoms of CB(1) receptor antagonists. Evidence shows that most CB(1) receptors located on axons and terminals of GABA-ergic, serotonergic or glutamatergic neurons stimulate the activity of noradrenergic neurons. In contrast, those located on noradrenergic axons and terminals inhibit noradrenaline release efficiently. In this latter process, excitatory ionotropic or G protein-coupled receptors, such as the NMDA, alpha1 and beta1 adrenergic receptors, activate local endocannabinoid synthesis at postsynaptic sites and stimulate retrograde endocannabinoid neurotransmission acting on CB(1) receptors of noradrenergic terminals. The underlying mechanisms include calcium signal generation, which activates enzymes that increase the synthesis of both anandamide and 2-arachidonoylglycerol, while G(q/11) protein activation also increases the formation of 2-arachidonoylglycerol from diacylglycerol during the signaling process. In addition, other non-CB(1) receptor endocannabinoid targets such as CB(2), transient receptor potential vanilloid subtype, peroxisome proliferator-activated receptor-alpha and possibly GPR55 can also mediate some of the endocannabinoid effects. In conclusion, both neuronal activation and neurotransmitter release depend on the in situ synthesized endocannabinoids and thus, local endocannabinoid concentrations in different brain areas may be crucial in the net effect, namely in the regulation of neurons located postsynaptically to the noradrenergic synapse.

Long term adequate n-3 polyunsaturated fatty acid diet protects from depressive-like behavior but not from working memory disruption and brain cytokine expression in aged mice

Converging epidemiological studies suggest that dietary essential n-3 polyunsaturated fatty acid (PUFA) are likely to be involved in the pathogenesis of mood and cognitive disorders linked to aging. The question arises as to whether the decreased prevalence of these symptoms in the elderly with high n-3 PUFA consumption is also associated with improved central inflammation, i.e. cytokine activation, in the brain. To answer this, we measured memory performance and emotional behavior as well as cytokine synthesis and PUFA level in the spleen and the cortex of adult and aged mice submitted to a diet with an adequate supply of n-3 PUFA in form of α-linolenic acid (α-LNA) or a n-3 deficient diet. Our results show that docosahexaenoic acid (DHA), the main n-3 PUFA in the brain, was higher in the spleen and cortex of n-3 adequate mice relative to n-3 deficient mice and this difference was maintained throughout life. Interestingly, high level of brain DHA was associated with a decrease in depressive-like symptoms throughout aging. On the opposite, spatial memory was maintained in adult but not in aged n-3 adequate mice relative to n-3 deficient mice. Furthermore, increased interleukin-6 (IL-6) and decreased IL-10 expression were found in the cortex of aged mice independently of the diets. All together, our results suggest that n-3 PUFA dietary supply in the form of α-LNA is sufficient to protect from deficits in emotional behavior but not from memory disruption and brain proinflammatory cytokine expression linked to age.

Nutraceuticals in the treatment of obsessive compulsive disorder (OCD): a review of mechanistic and clinical evidence

Obsessive-compulsive disorder (OCD) is a debilitating mental illness which has a significant impact on quality of life. First-line SSRI treatments for OCD typically are of limited benefit to only 40-60% of patients, and are associated with a range of adverse side effects. Current preclinical research investigating nutraceuticals (natural products) for OCD, reveals encouraging novel activity in modulating key pathways suggested to be involved in the pathogenesis of OCD (glutamatergic and serotonergic pathway dysregulation). Emerging clinical evidence also appears to tentatively support certain nutrients and plant-based interventions with known active constituents which modulate these pathways: N-acetlycysteine, myo-inositol, glycine, and milk thistle (Silybum marianum). The serotonin precursor tryptophan is unlikely to be of use in treating OCD while 5-HTP may possibly be a more effective precursor strategy. However, there is currently no clinical evidence to test the efficacy of either of these substances. Currently the balance of clinical evidence does not support the use of St. John's wort (Hypericum perforatum) in OCD. While clinical research in this area is in its infancy, further research into nutraceuticals is warranted in light of the promising preclinical data regarding their mechanisms of action and their favourable side effect profiles in comparison to current SSRI treatments. It is recommended that future clinical trials of nutraceutical treatments for OCD utilize randomized placebo-controlled study designs and considerably larger sample sizes in order to properly test for efficacy.

N-3 (omega-3) Fatty acids in postpartum depression: implications for prevention and treatment

A growing body of clinical and epidemiological evidence suggests that low dietary intake and/or tissue levels of n-3 (omega-3) polyunsaturated fatty acids (PUFAs) are associated with postpartum depression. Low tissue levels of n-3 PUFAs, particularly docosahexaenoic acid (DHA), are reported in patients with either postpartum or nonpuerperal depression. Moreover, the physiological demands of pregnancy and lactation put childbearing women at particular risk of experiencing a loss of DHA from tissues including the brain, especially in individuals with inadequate dietary n-3 PUFA intake or suboptimal metabolic capabilities. Animal studies indicate that decreased brain DHA in postpartum females leads to several depression-associated neurobiological changes including decreased hippocampal brain-derived neurotrophic factor and augmented hypothalamic-pituitary-adrenal responses to stress. Taken together, these findings support a role for decreased brain n-3 PUFAs in the multifactorial etiology of depression, particularly postpartum depression. These findings, and their implications for research and clinical practice, are discussed.

What can post-mortem studies tell us about the pathoetiology of suicide?

Suicide is a major public health concern; however, its neurobiology is unclear. Post-mortem brain tissue obtained from suicide victims and normal controls offers a useful method for studying the neurobiology of suicide. Despite several limitations, these studies have offered important leads in the neurobiology of suicide. In this article, we discuss some important findings resulting from these studies, focusing on serotonergic mechanisms, signal transduction systems, neuroendocrine studies and immune function abnormalities in suicide. These studies suggest that abnormalities of certain receptor subtypes, components of signaling systems such as protein kinase C and protein kinase A, transcription factors such as cyclic AMP response element-binding protein and neurotrophins may play an important role in the pathophysiology of suicide. These studies also suggest abnormalities of hypothalamic-pituitary-adrenal axis system components, feedback mechanisms and cytokines, which are chemical mediators of the immune functions. Post-mortem brain tissue offers an opportunity for future studies, such as genetic and epigenetic studies.

Polymorphisms in GRIK4, HTR2A, and FKBP5 show interactive effects in predicting remission to antidepressant treatment

Single-nucleotide polymorphisms (SNPs) in the FKBP5, GRIK4, and HTR2A genes have been shown to be associated with response to citalopram treatment in the STAR(*)D sample, but only associations with FKBP5 have so far been tested in the Munich Antidepressant Response Signature (MARS) project. Response and remission of depressive symptoms after 5 weeks of antidepressant treatment were tested against 82 GRIK4 and 37 HTR2A SNPs. Association analysis was conducted in about 300 depressed patients from the MARS project, 10% of whom had bipolar disorder. The most predictive SNPs from these two genes and rs1360780 in FKBP5 were then genotyped in a total of 387 German depressed in-patients to analyze potential additive and interactive effects of these variants. We could not replicate previous findings of the Sequenced Treatment Alternatives to Relieve Depression (STAR(*)D) study in our sample. Although not statistically significant, the effect for the best GRIK4 SNP of STAR(*)D (rs1954787, p=0.076, p(corrected)=0.98) seemed to be in the same direction. On the other hand, the nominally significant association with the top HTR2A SNPs of STAR(*)D (rs7997012, allelic, p=0.043, p(corrected)=0.62) was with the opposite risk allele. The GRIK4 SNP (rs12800734, genotypic, p=0.0019, p(corrected)=0.12) and the HTR2A SNP (rs17288723, genotypic, p=0.0011, p(corrected)=0.02), which showed the strongest association with remission in our sample, had not been reported previously. Associations across all genetic markers within the GRIK4 (genotypic, p=0.022) or HTR2A (genotypic, p=0.012) locus using the Fisher's product method (FPM) were also significant. In all 374 patients, the best predictive model included a main effect for GRIK4 rs12800734 and two significant interactions between GRIK4 rs12800734 and FKBP5 rs1360780, and GRIK4 rs12800734 and HTR2A rs17288723. This three SNP model explained 13.1% of the variance for remission after 5 weeks (p=0.00051 for the model). Analyzing a sub-sample of 194 patients, plasma ACTH (p=0.002) and cortisol (p=0.021) responses of rs12800734 GG (GRIK4) carriers, who also showed favorable treatment response, were significantly lower in the second combined dexamethasone (dex)/corticotrophin-releasing hormone (CRH) test before discharge compared with the other two genotype groups. Despite large differences in ethnicity and design compared with the STAR(*)D study, our results from the MARS study further support both independent and interactive involvement of GRIK4, HTR2A and FKBP5 in antidepressant treatment response.

Depression and antidepressants: molecular and cellular aspects

Clinical depression is viewed as a physical and psychic disease process having a neuropathological basis, although a clear understanding of its ethiopathology is still missing. The observation that depressive symptoms are influenced by pharmacological manipulation of monoamines led to the hypothesis that depression results from reduced availability or functional deficiency of monoaminergic transmitters in some cerebral regions. However, there are limitations to current monoamine theories related to mood disorders. Recently, a growing body of experimental data has showed that other classes of endogenous compounds, such as neuropeptides and amino acids, may play a significant role in the pathophysiology of affective disorders. With the development of neuroscience, neuronal networks and intracellular pathways have been identified and characterized, describing the existence of the interaction between monoamines and receptors in turn able to modulate the expression of intracellular proteins and neurotrophic factors, suggesting that depression/antidepressants may be intermingled with neurogenesis/neurodegenerative processes.

Test-retest variability of high resolution positron emission tomography (PET) imaging of cortical serotonin (5HT2A) receptors in older, healthy adults

Background

Position emission tomography (PET) imaging using [¹⁸F]-setoperone to quantify cortical 5-HT_2A receptors has the potential to inform pharmacological treatments for geriatric depression and dementia. Prior reports indicate a significant normal aging effect on serotonin 5HT_2A receptor (5HT_2AR) binding potential. The purpose of this study was to assess the test-retest variability of [¹⁸F]-setoperone PET with a high resolution scanner (HRRT) for measuring 5HT_2AR availability in subjects greater than 60 years old. Methods: Six healthy subjects (age range = 65–78 years) completed two [¹⁸F]-setoperone PET scans on two separate occasions 5–16 weeks apart.

Results

The average difference in the binding potential (BP_ND) as measured on the two occasions in the frontal and temporal cortical regions ranged between 2 and 12%, with the lowest intraclass correlation coefficient in anterior cingulate regions.

Conclusion

We conclude that the test-retest variability of [¹⁸F]-setoperone PET in elderly subjects is comparable to that of [¹⁸F]-setoperone and other 5HT_2AR radiotracers in younger subject samples.

Both acute and chronic buspirone treatments have different effects on regional 5-HT synthesis in Flinders Sensitive Line rats (a rat model of depression) than in control rats

The main objective of this investigation was to evaluate the effects of buspirone, a 5-HT(1A) agonist with some partial agonist properties and also an antidepressant, on regional 5-HT synthesis in Flinders Sensitive Line (FSL) rats ("depressed"), and to compare the effects to the Flinders Resistant Line (FRL) control rats (not "depressed"). In addition results were compared to those previously reported in normal Sprague-Dawley (SPD) rats (normal control). Serotonin synthesis in both FSL and FRL rats was measured following acute and chronic treatments with buspirone. Both of these strains were derived from the SPD rats. No direct comparison was done between the FSL saline and FRL saline groups, or the FSL buspirone and FRL buspirone groups, because the objective of the studies was to evaluate effects of buspirone in these two strains. The results show that acute treatment with buspirone elevates 5-HT synthesis throughout the brain in the FRL rats. In the FSL rats, there were reductions in some brain regions (e.g., dorsal and median raphe, amygdala, anterior olfactory nucleus, substantia nigra reticulate), while in other regions, there were increases in the synthesis observed (e.g., frontal, parietal, visual and somatosensory cortices, ventral hippocampus). In 20 out of the 30 brain regions investigated in the FSL rats, there was no significant change in the synthesis following acute buspirone treatment. During the chronic treatment, buspirone produced a significant reduction of 5-HT synthesis in 15 out of 30 brain regions in the FRL rats. In the FSL rats, buspirone produced a significant elevation of the synthesis in 10 out of 30 brain regions. In both the FSL and FRL rats, buspirone produced rather different effects than those reported previously for SPD (normal) rats. The acute effect in the FSL rats was somewhat similar to the effect reported previously for the SPD rats, while in the FRL rats, the acute buspirone treatment produced an effect observed previously in treatments with 5-HT(1A) antagonists suggesting an action of buspirone as partial agonist in FRL rats. The data suggest that with respect to 5-HT synthesis, FRL rats differ from SPD rats (a natural control; normal rats) and, as such, indicate that when the effects related to the serotonergic system (e.g., influence of serotonergic drugs) are studied in the FSL rats and compared to those in the FRL rats, any conclusions drawn may not reflect differences relative to a normal rat.

Applying neuroimaging ligands to study major depressive disorder

The recent increase in radioligands available for neuroimaging major depressive disorder has led to advancements in our understanding of the pathophysiology of this illness and improved antidepressant development. Major depressive disorder can be defined as an illness of recurrent major depressive episodes of persistently low mood, dysregulated sleep, appetite and weight, anhedonia, cognitive impairment, and suicidality. The main target sites investigated with radioligand neuroimaging include receptor sites that regulate in response to lowered monoamine levels, targets related to removal of monoamines, uptake of ligands related to regional brain function, and target sites of antidepressants.

CB1 knockout mice display impaired functionality of 5-HT1A and 5-HT2A/C receptors

Interaction between brain endocannabinoid (EC) and serotonin (5-HT) systems was investigated by examining 5-HT-dependent behavioral and biochemical responses in CB(1) receptor knockout mice. CB(1) knockout animals exhibited a significant reduction in the induction of head twitches and paw tremor by the 5-HT(2A/C) receptor selective agonist (+/-) DOI, as well as a reduced hypothermic response following administration of the 5-HT(1A) receptor agonist (+/-)-8-OH-DPAT. Additionally, exposure to the tail suspension test induced enhanced despair responses in CB(1) knockout mice. However, the tricyclic antidepressant imipramine and the 5-HT selective reuptake inhibitor fluoxetine induced similar decreases in the time of immobility in the tail suspension test in CB(1) receptor knockout and wild-type mice. No differences were found between both genotypes with regard to 5-HT(2A) receptor and 5-HT(1A) receptors levels, measured by autoradiography in different brain areas. However, a significant decrease in the ability of both, the 5-HT(1A) receptor agonist (+/-)-8-OH-DPAT and the 5-HT(2A/C) receptor agonist (-)DOI, to stimulate [(35)S]GTPgammaS binding was detected in the hippocampal CA(1) area and fronto-parietal cortex of CB(1) receptor knockout mice, respectively. This study provides evidence that CB(1) receptors are involved in the regulation of serotonergic responses mediated by 5-HT(2A/C) and 5-HT(1A) receptors, and suggests that a reduced coupling of 5-HT(1A) and 5-HT(2A) receptors to G proteins might be involved in these effects.

Novel 5-HTTLPR allele associates with higher serotonin transporter binding in putamen: a [(11)C] DASB positron emission tomography study

BACKGROUND

The serotonin transporter (5-HTT)-linked polymorphic region (5-HTTLPR) has two frequent alleles, designated long (L), and short (S). The S allele is associated with lower levels of 5-HTT mRNA and lower 5-HTT expression in human cell lines. A functional single nucleotide variant was detected within L, designated L(A) and L(G). Only L(A) is associated with high levels of in vitro 5-HTT expression, whereas L(G) is low expressing and more similar to S. We examined the possible influence of the long (A/G) variant on 5-HTT density in the living human brain using 3-(11)C-amino-4-(2-dimethylaminomethylphenyl-sulfanyl) benzonitrile ([(11)C]DASB) positron emission tomography.

METHODS

The 5-HTT binding potential (5-HTT BP), an index of 5-HTT density, was found in 43 healthy subjects genotyped for 5-HTTLPR long (A/G), and in an ethnically homogenous subsample of 30 Caucasian-Canadians.

RESULTS

The L(A)/L(A) was associated with higher 5-HTT BP in putamen (p = .026, not corrected). This association became stronger in the Caucasian subsample (p = .004) and was significant even after correcting for multiple comparisons.

CONCLUSIONS

The 5-HTTLPR long (A/G) polymorphism influences 5-HTT density leading to higher putamen 5-HTT BP in healthy L(A)/L(A) carriers of Caucasian ancestry. This finding extends the role of this polymorphism from in vitro reports of higher 5-HTT expression with the L(A)/L(A) genotype into in vivo brains of healthy human subjects.

Tandem regulation of phosphoinositide signaling and acute behavioral effects induced by antidepressant agents in rats

RATIONALE

Antidepressants increase synaptic monoamine concentrations, but the subsequent signaling events that produce the beneficial clinical effects remain unclear. Diverse antidepressants increase CDP-diacylglycerol, a crucial step in phosphoinositide signaling. Serotonin 5HT(2) receptors, implicated in depression or the actions of some antidepressants, signal through phosphoinositide hydrolysis. Thus, cross talk between antidepressant-induced CDP-diacylglycerol and 5HT(2) signaling could contribute to the antidepressant mechanism.

OBJECTIVE

The objective of the study was to test the hypotheses that antidepressants enhance net signaling via 5HT(2) receptors by augmenting the supply of phosphoinositide substrates and that this action contributes to the behavioral effects of the drugs.

MATERIALS AND METHODS

Brain slices pre-labeled with [(3)H]inositol in the presence of various antidepressant concentrations were washed and incubated with the 5HT(2) agonist, alpha-methylserotonin, followed by measuring phosphoinositide synthesis and inositol phosphate accumulation. Further, rats administered antidepressants after pretreatment with neomycin to inhibit metabolic utilization of phosphoinositides were behaviorally evaluated in the forced swim test.

RESULTS

Diverse antidepressants significantly enhanced phosphoinositide synthesis. While alpha-methylserotonin increased inositol phosphate accumulation, this effect was significantly accentuated in hippocampal or cortical tissues pre-incubated in the presence of imipramine, desipramine, fluoxetine, paroxetine, or maprotiline. Drug-induced behavioral antidepressant effects were reversed by neomycin pretreatment, whereas neomycin alone did not alter basal immobility times.

CONCLUSIONS

Antidepressants probably exert tandem neurochemical effects by increasing synaptic monoamine concentrations and by producing phosphoinositides used in 5HT(2) receptor signaling. This combination of actions may constitute the mechanism of at least the acute behavioral effects of the drugs and could implicate aberrant neurolipid signaling in the pathophysiology of depression.

5-HT2A: its role in frontally mediated executive function and related psychopathology

Serotonin (5-HT)2A receptors are widely distributed, with high levels in the frontal cortex, where postsynaptic activation may increase activity in pyramidal glutamatergic neurons and mediate various executive functions. More specifically, reciprocal cortical-raphe pathways may allow the ventral prefrontal cortex to inhibit stress-induced neural activity in the brainstem when stressors are perceived as controllable. However, early adversity and negative attitudes may be associated with higher frontal 5-HT2A receptor levels and greater risk for stress-induced psychopathology, and certain 5-HT2A gene variants have been associated with increased risk for impulsive behavior. Conversely, many antidepressants result in decreased levels of 5-HT2A receptor levels, and blockade of 5-HT2A receptors has proven useful in the treatment of a number of psychiatric disorders.

Polymorphisms in the regulatory region of the human serotonin 5-HT2A receptor gene (HTR2A) influence gene expression

BACKGROUND

Genomic variation in the regulatory region of the serotonin (5-HT) 2A receptor gene (HTR2A) may contribute to altered levels of 5-HT2A receptor and to psychiatric disease.

METHODS

Frequency and linkage disequilibrium (LD) were determined for promoter single nucleotide polymorphisms (SNPs) -1438A/G, -1420C/T, and -783A/G in 156 subjects. Functional relevance of -1438A/G and -783A/G was assayed in vitro using a luciferase reporter assay and ex vivo using quantitative real time polymerase chain reaction in a set of human fibroblast cell lines.

RESULTS

Significant LD was observed between SNPs -1438A/G and -783A/G. In vitro assays showed no significant differences in promoter activity between the A- and G-allele of -1438 locus when expressed with the major alleles at -1420C/T and -783A/G; however, when the minor allele G at -783 was expressed with G-allele at -1438, promoter activity was significantly decreased. 5-HT2A receptor mRNA expression in human fibroblast cell lines confirmed that -783A/G polymorphism significantly modified the effects of -1438A/G SNP.

CONCLUSIONS

Our results demonstrate that SNP -783A/G modifies the effects of the major SNP -1438A/G. Future studies examining the association of -1438A/G polymorphism with diseases and 5-HT2A receptor expression analyses should account for this epistasis.

Brain 5-HT synthesis in the Flinders Sensitive Line rat model of depression: An autoradiographic study

Alterations of serotonin (5-HT) levels and serotonergic transmission have been associated with depression. 5-HT synthesis is an important factor of serotonergic neurotransmission that may also be altered in depression. Many studies of the relationships between brain serotonergic functions and affective disorders have been performed in different animal models. In this study, brain regional 5-HT synthesis was examined using the alpha-[(14)C]methyl-L-tryptophan (alpha-MTrp) autoradiographic method in a genetic rat model of depression, Flinders Sensitive Line (FSL) rats, and was compared to both the Flinders Resistant Line (FRL) rats and the control Sprague-Dawley (SD) rats. The plasma concentration of free tryptophan in the FSL rats was not significantly different (p > 0.05; ANOVA and post-hoc Bonferroni correction) when compared to that of the FRL and SD rats. The FSL rats had significantly lower 5-HT synthesis (one sample two-tailed t-test on the ratio) than both the FRL and SD rats (the mean ratios were 0.78 +/- 0.12 and 0.73 +/- 0.15, respectively). Overall, the 5-HT synthesis in the FRL rats was not significantly different (p > 0.05) from that in the SD rats (one sample two-tailed t-test on the ratio and the mean ratio was 0.93 +/- 0.13). Studies of individual brain structures, such as the raphe nuclei and their many terminal areas, including the nucleus accumbens, cingulate and frontal cortex, hippocampus, amygdala, and thalamus revealed significant reductions (typically 25-50%) in 5-HT synthesis in the FSL rats compared to the non-depressive FRL and SD rats. These results suggest that significantly reduced 5-HT synthesis in the raphe nuclei and limbic areas in FSL rats may contribute to their depressive features.

Serotonin receptor 2A gene polymorphism (-1438A/G) and short-term treatment response to citalopram

The 5-HTR2A gene is a candidate gene for influencing the clinical response to antidepressant treatment. The purpose of this study was to determine the relationship between the -1438A/G polymorphism in the 5-HTR2A gene and the response to citalopram in a Korean population with major depressive disorder (MDD). Citalopram was administered for 4 weeks to the 71 patients who completed this study. We found significant differences in genotype, allele, and carrier distribution between the normal group and MDD patients (genotypes: chi(2) = 6.473, d.f. = 2, p = 0.039; alleles: chi(2) = 5.589, d.f. = 1, p = 0.018; OR = 0.618, 95% CI = 0.414-0.922; allele carriers: chi(2) = 5.383, d.f. = 1, p = 0.020; OR = 0.473, 95% CI = 0.249-0.879). The frequency of the -1438G allele was much higher in MDD patients than in the normal group (allele carriers: chi(2) = 5.383, d.f. = 1, p = 0.020; OR = 0.473, 95% CI = 0.249-0.879). There were also significant differences in response to citalopram according to the -1438A/G variation of 5-HTR2A in MDD patients. The group of remitters carried a higher frequency of the GG allele than of the AA and AG alleles. More of nonremitters carried the A allele than were without it (genotype: chi(2) = 8.016, p = 0.018; allele carrier: chi(2) = 4.512, p = 0.034; OR = 0.324, 95% CI = 0.112-0.936). The response to citalopram differed with the -1438A/G polymorphism genotype and allele carriers. The -1438G/-1438G genotype appeared to be associated with a better response to citalopram, with especially the G allele being related to core depressive symptoms and psychic anxiety improvement (p<0.05). These results suggest that the G allele of the -1438A/G polymorphism in the 5-HTR2A gene is associated with MDD, and that patients with -1438G/-1438G have a better response to citalopram treatment than patients with -1438A/-1438A or -1438A/-1438G.

Increased cerebral serotonin-2A receptor binding in depressed patients with myocardial infarction

Serotonin (5-HT) has been implicated in the pathophysiology of depression. It is not known whether depression in post-myocardial infarction (MI) patients is also serotonin-mediated. In somatically healthy depressed persons, increased brain 5-HT(2A) receptor binding has been reported in some studies. In animal studies, decreased serotonin activity was found after induction of MI. In the present study, it was hypothesized that depressed post-MI patients would exhibit increased brain 5-HT(2A) receptor binding compared with non-depressed post-MI patients. Single photon emission computed tomography (SPECT) with the radioligand 123I-5-I-R91150, a 5-HT(2A) receptor antagonist, was used to study 5-HT(2A) receptor binding. SPECT scans were performed in nine depressed post-MI patients, 10 non-depressed post-MI patients and 10 healthy control subjects. Results were analysed using statistical parametric mapping. Depressed post-MI patients showed increased 5-HT(2A) receptor binding compared with non-depressed post-MI patients, and MI patients showed decreased 5-HT(2A) receptor binding compared with control persons. Both post-MI depression and MI seem to be associated with changes in 5-HT(2A) receptor binding.

Association of BDNF serum concentrations with central serotonergic activity: evidence from auditory signal processing

Disturbances of serotonergic neurotransmission in the brain have been implicated in the pathogenesis and maintenance of several psychiatric disorders. According to recent preclinical and clinical studies, the loudness dependence of auditory evoked potentials (LD) is related to the central serotonergic neurotransmission in humans. As the serotonergic phenotype has been reported to be associated with brain-derived neurotrophic factor (BDNF), we studied whether BDNF serum concentrations are related to LD in 109 healthy human volunteers (62 male, 47 female, age: 42.5+/-13.1 years). Pearson correlation showed a significant negative correlation between the BDNF serum concentrations and the LD measured at Fz (r=-0.259, p=0.007) and a trend for the Cz electrode (r=-0.185, p=0.055). Although this association needs to be replicated, the results are in line with the assumption that low serum BDNF levels reflect low central serotonergic neurotransmission as indicated by a strong LD.

Mechanisms of action of antidepressants: from neurotransmitter systems to signaling pathways

Antidepressants are commonly used in the treatment of anxiety and depression, medical conditions that affect approximately 17-20% of the population. The clinical effects of antidepressants take several weeks to manifest, suggesting that these drugs induce adaptive changes in brain structures affected by anxiety and depression. In order to develop shorter-acting and more effective drugs for the treatment of anxiety and depression, it is important to understand how antidepressants bring about their beneficial effects. Recent reports suggest that antidepressants can induce neurogenesis in the adult brain, although the mechanisms involved are not clearly understood. In this review, we describe the different neurotransmitter systems that are affected by anxiety and depression and how they are modulated by antidepressant treatment with a focus on signaling molecules and pathways that are activated during neurotransmitter receptor induced neurogenesis.

Electroconvulsive shock decreases binding to 5-HT2 receptors in nonhuman primates: an in vivo positron emission tomography study with [18F]setoperone

BACKGROUND

Dysfunction within the serotonin (5-HT) system plays a major role in the etiology of human depression, and treatment with antidepressant drugs downregulates 5-HT(2) receptors in rodents and humans. The consequences of another effective antidepressant treatment, electroconvulsive therapy (ECT), on 5-HT(2) receptors are less established.

METHODS

We studied the effects of a course of electroconvulsive shock (ECS) on 5-HT(2) receptor binding in nonhuman primates in vivo using positron emission tomography (PET) and the radiotracer [(18)F]setoperone. Seven adult male rhesus monkeys received two bilateral ECS treatments per week for 3 weeks; PET scans were performed before treatment, and 24 hours, 1 week, and 4-6 weeks after completion of the course of ECS. Regions of interest were placed throughout the cortex, and the data analyzed as the ratio of specific:nonspecific radioactivity accumulation, with the cerebellum used as a measure of nonspecific binding.

RESULTS

Serotonin 5-HT(2) binding was significantly decreased at 24 hours and 1 week post-ECS, but returned to baseline 4-6 weeks posttreatment.

CONCLUSIONS

These results show for the first time in a primate species that chronic ECS decreases binding to 5-HT(2) receptors and indicate that 5-HT(2) receptor downregulation may be a common effect of both pharmacologic and nonpharmacologic antidepressant treatments.

Negative impact of depression on outcomes in patients with coronary artery disease: mechanisms, treatment considerations, and future directions

Depressive symptoms are common in coronary artery disease (CAD) patients, and are associated with increased cardiac risk. Although an important relation exists between depression and CAD prognosis, the underlying pathophysiological mechanisms are poorly understood. Additionally, evidence including the recently published ENRICHD (Enhancing Recovery in Coronary Heart Disease Patients) trial suggests that depression treatments do not lower recurrent cardiac risk. The reason for the observed lack of benefit with depression treatment in CAD patients is unclear. In this review, we discuss the impact of depression in CAD patients, the possible mechanisms involved, the studies that have examined the effects of psychological and antidepressant therapies on recurrent cardiac events, and the direction that future research should take.