Histopathology of the prefrontal cortex in major depression: what does it tell us about dysfunctional monoaminergic circuits?

The relationship between BDNF and physical activity on depression

BACKGROUND/OBJECTIVE

Major depressive disorder (MDD) is one of the leading causes of disease burden and disability worldwide. Brain-derived neurotrophic factor (BDNF) seems to have an important role in the molecular mechanisms underlying MDD aetiology, given its implication in regulating neuronal plasticity. There is evidence that physical activity (PA) improves depressive symptoms, with a key role of BDNF in this effect. We aim to perform a systematic review examining the relationship between the BDNF Val66Met polymorphism and the BDNF protein, PA and MDD.

METHODS

Both observational and experimental design original articles or systematic reviews were selected, according to the PRISMA statement.

RESULTS

Six studies evaluated the Val66Met polymorphism, suggesting a greater impact of physical activity on depression depending on the Val66Met genotype. More discordant findings were observed among the 13 studies assessing BDNF levels with acute or chronic exercise interventions, mainly due to the high heterogeneity found among intervention designs, limited sample size, and potential bias.

CONCLUSIONS

Overall, there is cumulative evidence supporting the potential role of BDNF in the interaction between PA and MDD. However, this review highlights the need for further research with more homogeneous and standardised criteria, and pinpoints important confounding factors that must be considered in future studies to provide robust conclusions.

Not Just a Mood Disorder─Is Depression a Neurodevelopmental, Cognitive Disorder? Focus on Prefronto-Thalamic Circuits

Depression is one of the most burdensome psychiatric disorders, affecting hundreds of millions of people worldwide. The disease is characterized not only by severe emotional and affective impairments, but also by disturbed vegetative and cognitive functions. Although many candidate mechanisms have been proposed to cause the disease, the pathophysiology of cognitive impairments in depression remains unclear. In this article, we aim to assess the link between cognitive alterations in depression and possible developmental changes in neuronal circuit wiring during critical periods of susceptibility. We review the existing literature and propose a role of serotonin signaling during development in shaping the functional states of prefrontal neuronal circuits and prefronto-thalamic loops. We discuss how early life insults affecting the serotonergic system could be important in the alterations of these local and long-range circuits, thus favoring the emergence of neurodevelopmental disorders, such as depression.

The role of serotonin in depression-A historical roundup and future directions

Depression is one of the most common psychiatric disorders worldwide, affecting approximately 280 million people, with probably much higher unrecorded cases. Depression is associated with symptoms such as anhedonia, feelings of hopelessness, sleep disturbances, and even suicidal thoughts. Tragically, more than 700 000 people commit suicide each year. Although depression has been studied for many decades, the exact mechanisms that lead to depression are still unknown, and available treatments only help a fraction of patients. In the late 1960s, the serotonin hypothesis was published, suggesting that serotonin is the key player in depressive disorders. However, this hypothesis is being increasingly doubted as there is evidence for the influence of other neurotransmitters, such as noradrenaline, glutamate, and dopamine, as well as larger systemic causes such as altered activity in the limbic network or inflammatory processes. In this narrative review, we aim to contribute to the ongoing debate on the involvement of serotonin in depression. We will review the evolution of antidepressant treatments, systemic research on depression over the years, and future research applications that will help to bridge the gap between systemic research and neurotransmitter dynamics using biosensors. These new tools in combination with systemic applications, will in the future provide a deeper understanding of the serotonergic dynamics in depression.

An integrative network analysis framework for identifying molecular functions in complex disorders examining major depressive disorder as a test case

In addition to the psychological depressive phenotype, major depressive disorder (MDD) patients are also associated with underlying immune dysregulation that correlates with metabolic syndrome prevalent in depressive patients. A robust integrative analysis of biological pathways underlying the dysregulated neural connectivity and systemic inflammatory response will provide implications in the development of effective strategies for the diagnosis, management and the alleviation of associated comorbidities. In the current study, focusing on MDD, we explored an integrative network analysis methodology to analyze transcriptomic data combined with the meta-analysis of biomarker data available throughout public databases and published scientific peer-reviewed articles. Detailed gene set enrichment analysis and complex protein–protein, gene regulatory and biochemical pathway analysis has been undertaken to identify the functional significance and potential biomarker utility of differentially regulated genes, proteins and metabolite markers. This integrative analysis method provides insights into the molecular mechanisms along with key glycosylation dysregulation underlying altered neutrophil-platelet activation and dysregulated neuronal survival maintenance and synaptic functioning. Highlighting the significant gap that exists in the current literature, the network analysis framework proposed reduces the impact of data gaps and permits the identification of key molecular signatures underlying complex disorders with multiple etiologies such as within MDD and presents multiple treatment options to address their molecular dysfunction.

Effect of voluntary running on expression of myokines in brains of rats with depression

This study aimed to demonstrate the histopathology and immunoexpression of exercise-derived myokines in dentate gyrus (DG), medial prefrontal cortex (mPFC) and cerebellum of depressed Wistar rats during depression and after practising voluntary running. Depression was developed by forced swimming for 2 weeks. Voluntary running was performed by voluntary running for 3 weeks. Brain sections were processed and immunostained to detect brain-derived neurotrophic factor (BDNF), macrophage migration inhibitory factor (MIF), vascular endothelial growth factor (VEGF) and interleukin-6 (IL-6). ImageJ software was used to measure the optical density (OD). BDNF was expressed in neurons in DG, mPFC and granular and Purkinje cells in cerebellum. MIF was expressed in neurons of sub-granular zone in DG, mPFC and Purkinje cells. VEGF was expressed in many neurons in DG, mPFC and Purkinje cells. IL-6 was expressed in some neurons in DG, in neuropil of mPFC and in Purkinje cells. In depression, the OD of studied myokines significantly decreased in all examined areas. After voluntary running, the OD of myokines significantly increased in all areas. This study defines the immunohistochemical expression of myokines in brain areas in depression and after voluntary running and reveals the involvement of the mPFC and cerebellum in the pathophysiology of depression.

Sex differences in antidepressant efficacy

Sex differences have been observed across many psychiatric diseases, especially mood disorders. For major depression, the most prevalent psychiatric disorder, females show a roughly two-fold greater risk as compared to males. Depression is sexually dimorphic with males and females exhibiting differences in clinical presentation, course, and response to antidepressant treatment. In this review, we first discuss sex differences observed in depressed patients, as well as animal models that reveal potential underlying mechanisms. We then discuss antidepressant treatments including their proposed mechanism of action and sex differences observed in treatment response. We include possible mechanisms underlying these sex differences with particular focus on synaptic transmission.

Brain-Derived Neurotrophic Factor, Depression, and Physical Activity: Making the Neuroplastic Connection

Brain-derived neurotrophic factor (BDNF) is a neurotrophin that is vital to the survival, growth, and maintenance of neurons in key brain circuits involved in emotional and cognitive function. Convergent evidence indicates that neuroplastic mechanisms involving BDNF are deleteriously altered in major depressive disorder (MDD) and animal models of stress. Herein, clinical and preclinical evidence provided that stress-induced depressive pathology contributes to altered BDNF level and function in persons with MDD and, thereby, disruptions in neuroplasticity at the regional and circuit level. Conversely, effective therapeutics that mitigate depressive-related symptoms (e.g., antidepressants and physical activity) optimize BDNF in key brain regions, promote neuronal health and recovery of function in MDD-related circuits, and enhance pharmacotherapeutic response. A greater knowledge of the interrelationship between BDNF, depression, therapeutic mechanisms of action, and neuroplasticity is important as it necessarily precedes the derivation and deployment of more efficacious treatments.

The Role of Norepinephrine and Its α-Adrenergic Receptors in the Pathophysiology and Treatment of Major Depressive Disorder and Schizophrenia: A Systematic Review

Norepinephrine (NE) is recognized as having a key role in the pathophysiology of major depressive disorder (MDD) and schizophrenia, although its distinct actions via α-adrenergic receptors (α-ARs) are not well defined. We performed a systematic review examining the roles of NE and α-ARs in MDD and schizophrenia. PubMed and ProQuest database searches were performed to identify English language papers published between 2008 and 2015. In total, 2,427 publications (PubMed, n = 669; ProQuest, n = 1,758) were identified. Duplicates, articles deemed not relevant, case studies, reviews, meta-analyses, preclinical reports, or articles on non-target indications were excluded. To limit the review to the most recent data representative of the literature, the review further focused on publications from 2010 to 2015, which were screened independently by all authors. A total of 16 research reports were identified: six clinical trial reports, six genetic studies, two biomarker studies, and two receptor studies. Overall, the studies provided indirect evidence that α-AR activity may play an important role in aberrant regulation of cognition, arousal, and valence systems associated with MDD and schizophrenia. Characterization of the NE pathway in patients may provide clinicians with information for more personalized therapy of these heterogeneous diseases. Current clinical studies do not provide direct evidence to support the role of NE α-ARs in the pathophysiology of MDD and schizophrenia and in the treatment response of patients with these diseases, in particular with relation to specific valence systems. Clinical studies that attempt to define associations between specific receptor binding profiles of psychotropics and particular clinical outcomes are needed.

Imaging the neuroplastic effects of ketamine with VBM and the necessity of placebo control

In the last years a plethora of studies have investigated morphological changes induced by behavioural or pharmacological interventions using structural T1-weighted MRI and voxel-based morphometry (VBM). Ketamine is thought to exert its antidepressant action by restoring neuroplasticity. In order to test for acute impact of a single ketamine infusion on grey matter volume we performed a placebo-controlled, double-blind investigation in healthy volunteers using VBM. 28 healthy individuals underwent two MRI sessions within a timeframe of 2 weeks, each consisting of two structural T1-weighted MRIs within a single session, one before and one 45min after infusion of S-ketamine (bolus of 0.11mg/kg, followed by an maintenance infusion of 0.12mg/kg) or placebo (0.9% NaCl infusion) using a crossover design. In the repeated-measures ANOVA with time (post-infusion/pre-infusion) and medication (placebo/ketamine) as factors, no significant effect of interaction and no effect of medication was found (FWE-corrected). Importantly, further post-hoc t-tests revealed a strong "decrease" of grey matter both in the placebo and the ketamine condition over time. This effect was evident mainly in frontal and temporal regions bilaterally with t-values ranging from 4.95 to 5.31 (FWE-corrected at p<0.05 voxel level). The vulnerabilities of VBM have been repeatedly demonstrated, with reports of influence of blood flow, tissue water and direct effects of pharmacological compounds on the MRI signal. Here again, we highlight that the relationship between intervention and VBM results is apparently subject to a number of physiological influences, which are partly unknown. Future studies focusing on the effects of ketamine on grey matter should try to integrate known influential factors such as blood flow into analysis. Furthermore, the results of this study highlight the importance of a carefully performed placebo condition in pharmacological fMRI studies.

Neurobiology of hedonic tone: the relationship between treatment-resistant depression, attention-deficit hyperactivity disorder, and substance abuse

Anhedonia, defined as the state of reduced ability to experience feelings of pleasure, is one of the hallmarks of depression. Hedonic tone is the trait underlying one's characteristic ability to feel pleasure. Low hedonic tone represents a reduced capacity to experience pleasure, thus increasing the likelihood of experiencing anhedonia. Low hedonic tone has been associated with several psychopathologies, including major depressive disorder (MDD), substance use, and attention-deficit hyperactivity disorder (ADHD). The main neural pathway that modulates emotional affect comprises the limbic-cortical-striatal-pallidal-thalamic circuits. The activity of various components of the limbic-cortical-striatal-pallidal-thalamic pathway is correlated with hedonic tone in healthy individuals and is altered in MDD. Dysfunction of these circuits has also been implicated in the relative ineffectiveness of selective serotonin reuptake inhibitors used to treat anxiety and depression in patients with low hedonic tone. Mood disorders such as MDD, ADHD, and substance abuse share low hedonic tone as well as altered activation of brain regions involved in reward processing and monoamine signaling as their features. Given the common features of these disorders, it is not surprising that they have high levels of comorbidities. The purpose of this article is to review the neurobiology of hedonic tone as it pertains to depression, ADHD, and the potential for substance abuse. We propose that, since low hedonic tone is a shared feature of MDD, ADHD, and substance abuse, evaluation of hedonic tone may become a diagnostic feature used to predict subtypes of MDD, such as treatment-resistant depression, as well as comorbidities of these disorders.

Altered Expression of Endoplasmic Reticulum Stress Associated Genes in Hippocampus of Learned Helpless Rats: Relevance to Depression Pathophysiology

The unfolded protein response (UPR) is an evolutionarily conserved defensive mechanism that is used by cells to correct misfolded proteins that accumulate in the endoplasmic reticulum. These proteins are misfolded as a result of physical stress on a cell and initiate a host of downstream effects that govern processes ranging from inflammation to apoptosis. To examine whether UPR system plays a role in depression, we examined the expression of genes that are part of the three different pathways for UPR activation, namely GRP78, GRP94, ATF6, XBP-1, ATF4, and CHOP using an animal model system that distinguishes vulnerability (learned helpless, LH) from resistance (non-learned helpless, NLH) to develop depression. Rats were exposed to inescapable shock on days 1 and 7 and were tested for escape latency on day 14. Rats not given shock but tested for escape latency were used as tested control (TC). Plasma corticosterone (CORT) levels were measured. Expression levels of various UPR associated genes were determined in hippocampus using qPCR. We found that the CORT level was higher in LH rats compared with TC and NLH rats. Expression of GRP78, GRP94, ATF6, and XBP-1 were significantly upregulated in LH rats compared with TC or NLH rats, whereas NLH rats did not show such changes. Expression levels of ATF4 and CHOP showed trends toward upregulation but were not significantly altered in LH or NLH group. Our data show strong evidence of altered UPR system in depressed rats, which could be associated with development of depressive behavior.

Emerging role of microRNAs in major depressive disorder: diagnosis and therapeutic implications

Major depressive disorder (MDD) is a major public health concern. Despite tremendous advances, the pathogenic mechanisms associated with MDD are still unclear. Moreover, a significant number of MDD subjects do not respond to the currently available medication. MicroRNAs (miRNAs) are a class of small noncoding RNAs that control gene expression by modulating translation, messenger RNA (mRNA) degradation, or stability of mRNA targets. The role of miRNAs in disease pathophysiology is emerging rapidly. Recent studies demonstrating the involvement of miRNAs in several aspects of neural plasticity, neurogenesis, and stress response, and more direct studies in human postmortem brain provide strong evidence that miRNAs can not only play a critical role in MDD pathogenesis, but can also open up new avenues for the development of therapeutic targets. Circulating miRNAs are now being considered as possible biomarkers in disease pathogenesis and in monitoring therapeutic responses because of the presence and/or release of miRNAs in blood cells as well as in other peripheral tissues. In this review, these aspects are discussed in a comprehensive and critical manner.

Resting-state brain activation correlates with short-time antidepressant treatment outcome in drug-naïve patients with major depressive disorder

OBJECTIVE

A resting-state functional magnetic resonance imaging study (fMRI) to investigate pretreatment regional differences in brain function, in patients with early treatment responsive (ERD) and early treatment nonresponsive (END) major depressive disorder (MDD).

METHODS

Patients with MDD and healthy control subjects underwent fMRI. Intrinsic neural activity at baseline was evaluated via amplitude of low-frequency fluctuations (ALFF). Antidepressant treatment was initiated after MRI. All patients received selective serotonin reuptake inhibitor type antidepressants at the minimum effective dose.

RESULTS

There were significant differences in brain activity between patients (n = 56) and control subjects (n = 33). Brain activity in patients with ERD (n = 26) differed from those with END (n = 30) in the lingual gyrus and cerebellum. There was a significantly correlation between activity in these regions and disease duration in patients with ERD, and with amelioration of depressive symptoms in patients with END.

CONCLUSIONS

Brain regions related to the neural mechanism of MDD early treatment outcome were identified. These regions may have important implications for the treatment of MDD.

Neurobiology of major depressive disorder

We survey studies which relate abnormal neurogenesis to major depressive disorder. Clinically, descriptive gene and protein expression analysis and genetic and functional studies revised here show that individual alterations of a complex signaling network, which includes the hypothalamic-pituitary-adrenal axis; the production of neurotrophins and growth factors; the expression of miRNAs; the production of proinflammatory cytokines; and, even, the abnormal delivery of gastrointestinal signaling peptides, are able to induce major mood alterations. Furthermore, all of these factors modulate neurogenesis in brain regions involved in MDD, and are functionally interconnected in such a fashion that initial alteration in one of them results in abnormalities in the others. We highlight data of potential diagnostic significance and the relevance of this information to develop new therapeutic approaches. Controversial issues, such as whether neurogenesis is the basis of the disease or whether it is a response induced by antidepressant treatments, are also discussed.

Chronic stress-induced disruption of the astrocyte network is driven by structural atrophy and not loss of astrocytes

Chronic stress is well recognized to decrease the number of GFAP⁺ astrocytes within the prefrontal cortex (PFC). Recent research, however, has suggested that our understanding of how stress alters astrocytes may be incomplete. Specifically, chronic stress has been shown to induce a unique form of microglial remodelling, but it is not yet clear whether astrocytes also undergo similar structural modifications. Such alterations may be significant given the role of astrocytes in modulating synaptic function. Accordingly, in the current study we have examined changes in astrocyte morphology following exposure to chronic stress in adult rats, using three-dimensional digital reconstructions of astrocytes. Our analysis indicated that chronic stress produced profound atrophy of astrocyte process length, branching and volume. We additionally examined changes in astrocyte-specific S100β, which are both a putative astrocyte marker and a protein whose expression is associated with astrocyte distress. While we found that S100β levels were increased by stress, this increase was not correlated with atrophy. We further established that while chronic stress was associated with a decrease in astrocyte numbers when GFAP labelling was used as a marker, we could find no evidence of a decrease in the total number of cells, based on Nissl staining, or in the number of S100β⁺ cells. This finding suggests that chronic stress may not actually reduce astrocyte numbers and may instead selectively decrease GFAP expression. The results of the current study are significant as they indicate stress-induced astrocyte-mediated disturbances may not be due to a loss of cells but rather due to significant remodeling of the astrocyte network.

α(2A) adrenoceptor-mediated presynaptic inhibition of GABAergic transmission in rat tuberomammillary nucleus neurons

Histaminergic neurons within the tuberomammillary nucleus (TMN) play an important role in the regulation of sleep-wakefulness. Here, we report the adrenergic modulation of GABAergic transmission in rat TMN histaminergic neurons using a conventional whole-cell patch clamp technique. Norepinephrine (NE) reversibly decreased the amplitude of action potential-dependent GABAergic inhibitory post-synaptic currents (IPSCs) and increased the paired pulse ratio. The NE-induced inhibition of GABAergic IPSCs was mimicked by clonidine, a selective α2 adrenoceptor agonist. However, cirazoline and isoproterenol, nonselective α1 and β adrenoceptor agonists, respectively, had no effect on GABAergic IPSCs. The NE-induced inhibition of GABAergic IPSCs was significantly blocked by BRL44408, a selective α2A adrenoceptor antagonist, but not imiloxan or JP1302, a selective α2B and α2C adrenoceptor antagonists. The extent of NE-induced inhibition of GABAergic IPSCs was inversely proportional to the extracellular Ca(2+) concentration. Pharmacological agents affecting the activities of adenylyl cyclase or G-protein-coupled inwardly rectifying K(+) channels did not affect the NE-induced inhibition of GABAergic IPSCs. However, NE had no effect on the frequency and amplitude of GABAergic miniature IPSCs. These results suggest that NE acts on presynaptic α2A adrenoceptor to inhibit action potential-dependent GABA release via the inhibition of Ca(2+) influx from the extracellular space to GABAergic nerve terminals, and that this α2A adrenoceptor-mediated modulation of GABAergic transmission may be involved in regulating the excitability of TMN histaminergic neurons.

Bridging the gap between neuroscientific and psychodynamic models in child and adolescent psychiatry

This article provides a selective review of the neuroscience and child-psychoanalytic literature, focusing on areas of significant overlap and emphasizing comprehensive theories in developmental neuroscience and child psychoanalysis with testable mechanisms of action. Topics include molecular biology and genetics findings relevant to psychotherapy research, neuroimaging findings relevant to psychotherapy, brain regions of interest for psychotherapy, neurobiologic changes caused by psychotherapy, use of neuroimaging to predict treatment outcome, and schemas as a bridging concept between psychodynamic and cognitive neuroscience models. The combined efforts of neuroscientists and psychodynamic clinicians and theorists are needed to unravel the mechanisms of human mental functioning.

Enhancing synaptic plasticity and cellular resilience to develop novel, improved treatments for mood disorders

There is mounting evidence that recurrent mood disorders - once considered “good prognosis diseases”- are, in fact, often very severe and life-threatening illnesses. Furthermore, although mood disorders have traditionally been conceptualized as neurochemical disorders, there is now evidence from a variety of sources demonstrating regional reductions in central nervous system (CNS) volume, as well as reductions in the numbers and/or sizes ofglia and neurons in discrete brain areas. Although the precise cellular mechanisms underlying these morphometric changes remain to be fully elucidated, the data suggest that mood disorders are associated with impairments of synaptic plasticity and cellular resilience. In this context, it is noteworthy that there is increasing preclinical evidence that antidepressants regulate the function of the glutamatergic system. Moreover, although clearly preliminary, the available clinical data suggest that attenuation of N-methyl-D-aspartate (NMDA) function has antidepressant effects. Recent preclinical and clinical studies have shown that signaling pathways involved in regulating cell survival and cell death are long-term targets for the actions of antidepressant agents. Antidepressants and mood stabilizers indirectly regulate a number of factors involved in cell survival pathways, including cyclic adenosine monophosphate (cAMP) response element binding protein (CREB), brain-derived neurotrophic factor (BDNF), the antiapoptotic protein bcl-2, and mitogen-activated protein (MAP) kinases, and may thus bring about some of their delayed long-term beneficial effects via underappreciated neurotrophic effects. There is much promise for the future development of treatments that more directly target molecules in critical CNS signaling pathways regulating synaptic plasticity and cellular resilience. These will represent improved long-term treatments for mood disorders.

Personality traits in rats predict vulnerability and resilience to developing stress-induced depression-like behaviors, HPA axis hyper-reactivity and brain changes in pERK1/2 activity

Emerging evidence indicates that certain behavioral traits, such as anxiety, are associated with the development of depression-like behaviors after exposure to chronic stress. However, single traits do not explain the wide variability in vulnerability to stress observed in outbred populations. We hypothesized that a combination of behavioral traits might provide a better characterization of an individual's vulnerability to prolonged stress. Here, we sought to determine whether the characterization of relevant behavioral traits in rats could aid in identifying individuals with different vulnerabilities to developing stress-induced depression-like behavioral alterations. We also investigated whether behavioral traits would be related to the development of alterations in the hypothalamic-pituitary-adrenal axis and in brain activity - as measured through phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2)--in response to an acute stressor following either sub-chronic (2 weeks) or chronic (4 weeks) unpredictable stress (CUS). Sprague-Dawley rats were characterized using a battery of behavioral tasks, and three principal traits were identified: anxiety, exploration and activity. When combined, the first two traits were found to explain the variability in the stress responses. Our findings confirm the increased risk of animals with high anxiety developing certain depression-like behaviors (e.g., increased floating time in the forced swim test) when progressively exposed to stress. In contrast, the behavioral profile based on combined low anxiety and low exploration was resistant to alterations related to social behaviors, while the high anxiety and low exploration profile displayed a particularly vulnerable pattern of physiological and neurobiological responses after sub-chronic stress exposure. Our findings indicate important differences in animals' vulnerability and/or resilience to the effects of repeated stress, particularly during initial or intermediate levels of stress exposure, and they highlight that the behavioral inhibition profile of an animal provides a particular susceptibility to responding in a deleterious manner to stress.

Neuron density and serotonin receptor binding in prefrontal cortex in suicide

Although serotonin receptor and cytoarchitectonic alterations are reported in prefrontal cortex (PFC) in suicide and depression, no study has considered binding relative to neuron density. Therefore, we measured neuron density and serotonin transporter (SERT), 5-HT1A and 5-HT2A binding in matched suicides and controls. Suicides and normal controls (n=15 matched pairs) were psychiatrically characterized. Neuron density and binding were determined in dorsal [Brodmann area (BA) 9] and ventral (BA 47) PFC by stereology and quantitative autoradiography in near-adjacent sections. Binding index was defined as the ratio of receptor binding to neuron density. Suicides had lower neuron density in the gyrus of both areas. The binding index was lower for SERT in BA 47 but not in BA9; the 5-HT1A binding index was higher in BA 9 but not in BA 47, while the 5-HT2A binding index was not different between groups. SERT binding was lower in suicides in BA 47 but not BA 9, while 5-HT1A binding was higher in BA 9 but not BA 47. SERT binding negatively correlated with 5-HT1A binding in BA 47 in suicides. Neuron density decreased with age. The 5-HT1A binding index was higher in females than males. We found lower neuron density and lower SERT binding index in both PFC regions in suicides. More 5-HT1A binding with less SERT binding and the negative correlation in depressed suicides suggests post-synaptic receptor up-regulation, and it is independent of the difference in neuron density. Thus, abnormalities in both cortical neurons and in their serotonergic innervation are present in suicides and future studies will need to determine whether cortical changes reflect the trophic effect of altered serotonin innervation.

Evidence demonstrating role of microRNAs in the etiopathology of major depression

Major depression is a debilitating disease. Despite a tremendous amount of research, the molecular mechanisms associated with the etiopathology of major depression are not clearly understood. Several lines of evidence indicate that depression is associated with altered neuronal and structural plasticity and neurogenesis. MicroRNAs are a newly discovered prominent class of gene expression regulators that have critical roles in neural development, are needed for survival and optimal health of postmitotic neurons, and regulate synaptic functions, particularly by regulating protein synthesis in dendritic spines. In addition, microRNAs (miRNAs) regulate both embryonic and adult neurogenesis. Given that miRNAs are involved in neural plasticity and neurogenesis, the concept that miRNAs may play an important role in psychiatric illnesses, including major depression, is rapidly advancing. Emerging evidence demonstrates that the expression of miRNAs is altered during stress, in the brain of behaviorally depressed animals, and in human postmortem brain of depressed subjects. In this review article, the possibility that dysregulation of miRNAs and/or altered miRNA response may contribute to the etiology and pathophysiology of depressive disorder is discussed.

Dose-dependent modulation of apoptotic processes by fluoxetine in maturing neuronal cells: an in vitro study

OBJECTIVES

Recent studies indicate that the selective serotonin reuptake inhibitor (SSRI) fluoxetine is not solely effective by the instant inhibition of the serotonin transporter (SERT) but also by its influence on mitotic and/or apoptotic processes.

METHODS

To investigate the effects of the compound in vitro, we treated neurons from different brain areas with increasing concentrations of fluoxetine. Additionally, human embryonic kidney (HEK-293) cells and HEK-293 cells stably expressing the SERT were used. Cell viability was quantified by MTT-assay and apoptosis via fluorescence-activated cell-sorting analyses. Fluoxetine's effect on the γ-aminobutyric acid (GABA) receptor was electrophysiologically investigated to test the hypothesis if a GABA-mimetic effect exists that might lead - additionally to the well-known N-methyl-D-aspartate (NMDA)-antagonism - to increased apoptosis in immature neurons.

RESULTS

In hippocampal, cortical, and both types of HEK-293 cells, viability decreased and apoptosis increased in a dose-dependent manner (0.5-75 μM). In contrast, in mesencephalic and striatal cells the viability was unchanged or even slightly stimulated up to 20 μM fluoxetine. An anti-apoptotic effect of concentrations below 10 μM was observed in these cells. The GABA(A) receptor was directly activated by fluoxetine.

CONCLUSIONS

We conclude that fluoxetine affects apoptotic processes independently from SERT expression. Since especially the combined GABA-mimetic and NMDA-antagonistic effects increase apoptosis in developing neuronal cells, whereas both effects are neuroprotective in adult neurons we hypothesise that these mechanisms explain the discrepancy of in vitro and in vivo studies.

The MRL/lpr mouse strain as a model for neuropsychiatric systemic lupus erythematosus

To date, CNS disease and neuropsychiatric symptoms of systemic lupus erythematosus (NP-SLE) have been understudied compared to end-organ failure and peripheral pathology. In this review, we focus on a specific mouse model of lupus and the ways in which this model reflects some of the most common manifestations and potential mechanisms of human NP-SLE. The mouse MRL lymphoproliferation strain (a.k.a. MRL/lpr) spontaneously develops the hallmark serological markers and peripheral pathologies typifying lupus in addition to displaying the cognitive and affective dysfunction characteristic of NP-SLE, which may be among the earliest symptoms of lupus. We suggest that although NP-SLE may share common mechanisms with peripheral organ pathology in lupus, especially in the latter stages of the disease, the immunologically privileged nature of the CNS indicates that early manifestations of particularly mood disorders maybe derived from some unique mechanisms. These include altered cytokine profiles that can activate astrocytes, microglia, and alter neuronal function before dysregulation of the blood-brain barrier and development of clinical autoantibody titres.

13-Cis-retinoic acid decreases hypothalamic cell number in vitro

13-Cis-retinoic acid (13-cis-RA) causes depression-related behavior in mice. Hypothalamic dysregulation has been implicated in clinical depression. In fact, apoptosis of hypothalamic neurons may lead to depression after myocardial infarction. Our objective was to determine if 13-cis-RA affects cultured hypothalamic cell number. Treatment of GT1-7 hypothalamic cells with 10μM 13-cis-RA for 48h decreased cell growth to 45.6±13% of control. To determine if this decrease in cell number was due to 13-cis-RA acting as an oxidant, cells were treated with 13-cis-RA and ascorbic acid or butylated hydroxyanisole (BHA) for 24 or 48h. Neither antioxidant alleviated the inhibitory affects of 13-cis-RA. In addition, 13-cis-RA treatment did not increase superoxide anion production, indicating 13-cis-RA was not acting as an oxidant. To determine if 13-cis-RA was acting via retinoic acid receptors (RARs) to decrease cell number, GT1-7 cells were treated with 13-cis-RA and the RAR pan-antagonist, AGN 193109. Treatment with the RAR-antagonist blocked the ability of 13-cis-RA to decrease cell number, indicating this phenomenon was a RAR-independent mechanism. We hypothesize that the ability of 13-cis-RA to decrease hypothalamic cell number may contribute to the increased depression-related behaviors observed in mice.

Alcohol-induced depressive-like behavior is associated with cortical norepinephrine reduction

Although strong positive association between alcoholism and depression is a common epidemiological observance, the causal relationship and the neurobiological substrates of such observations are far from clear. We have reported that chronic daily exposure to a relatively high dose of alcohol in rats can induce or exacerbate an already existing depressive-like behavior (Pharm Biochem Behav 91:97-103, 2008). Moreover, these effects of alcohol were blocked by pretreatment with desipramine, a tricyclic antidepressant, implicating a role for the biogenic amines in this type of depressive symptoms. In order to further delineate the involvement of specific neurotransmitters in alcohol-induced depressive symptoms, we examined the concentrations of norepinephrine (NE), dopamine (DA) and serotonin (5-HT) in the frontal cortex and hippocampus following alcohol administration as well as pretreatment with two antidepressants, nomifensine and imipramine selective NE/DA and NE/5-HT uptake inhibitors, respectively. Adult female Wistar and Wistar-Kyoto (WKY) rats were exposed to alcohol via inhalation chambers (3h/day for 10 days) to achieve daily blood alcohol concentration of approximately 150 mg%. On day 11, the animals were evaluated for general locomotor activity (LCA) and performance in the forced swim test (FST), followed by neurochemical analyses. As expected WKY rats had lower LCA and higher immobility in the FST compared to Wistar rats. WKY rats also had lower levels of all three biogenic amines compared to Wistar rats in both areas. However, only cortical NE was reduced in both strains following alcohol administration. Treatments with nomifensine and imipramine blocked the behavioral and most of the neurochemical deficits caused by alcohol in both strains. These results implicate cortical NE as a major player in alcohol-induced depression. Moreover, it is suggested that selective NE uptake inhibitors may be of particular therapeutic potential in co-morbid condition of alcoholism and depression.

Brain-derived neurotrophic factor: role in depression and suicide

Depression and suicidal behavior have recently been shown to be associated with disturbances in structural and synaptic plasticity. Brain-derived neurotrophic factor (BDNF), one of the major neurotrophic factors, plays an important role in the maintenance and survival of neurons and in synaptic plasticity. Several lines of evidence suggest that BDNF is involved in depression, such that the expression of BDNF is decreased in depressed patients. In addition, antidepressants up-regulate the expression of BDNF. This has led to the proposal of the "neurotrophin hypothesis of depression". Increasing evidence demonstrates that suicidal behavior is also associated with lower expression of BDNF, which may be independent from depression. Recent genetic studies also support a link of BDNF to depression/suicidal behavior. Not only BDNF, but abnormalities in its cognate receptor tropomycin receptor kinase B (TrkB) and its splice variant (TrkB.T1) have also been reported in depressed/suicidal patients. It has been suggested that epigenetic modulation of the Bdnf and Trkb genes may contribute to their altered expression and functioning. More recently, impairment in the functioning of pan75 neurotrophin receptor has been reported in suicide brain specimens. pan75 neurotrophin receptor is a low-affinity neurotrophin receptor that, when expressed in conjunction with low availability of neurotropins/Trks, induces apoptosis. Overall, these studies suggest the possibility that BDNF and its mediated signaling may participate in the pathophysiology of depression and suicidal behavior. This review focuses on the critical evidence demonstrating the involvement of BDNF in depression and suicide.

Targeting glutamatergic signaling for the development of novel therapeutics for mood disorders

There have been no recent advances in drug development for mood disorders in terms of identifying drug targets that are mechanistically distinct from existing ones. As a result, existing antidepressants are based on decades-old notions of which targets are relevant to the mechanisms of antidepressant action. Low rates of remission, a delay of onset of therapeutic effects, continual residual depressive symptoms, relapses, and poor quality of life are unfortunately common in patients with mood disorders. Offering alternative options is requisite in order to reduce the individual and societal burden of these diseases. The glutamatergic system is a promising area of research in mood disorders, and likely to offer new possibilities in therapeutics. There is increasing evidence that mood disorders are associated with impairments in neuroplasticity and cellular resilience, and alterations of the glutamatergic system are known to play a major role in cellular plasticity and resilience. Existing antidepressants and mood stabilizers have prominent effects on the glutamate system, and modulating glutamatergic ionotropic or metabotropic receptors results in antidepressant-like properties in animal models. Several glutamatergic modulators targeting various glutamate components are currently being studied in the treatment of mood disorders, including release inhibitors of glutamate, N-methyl-D-aspartate (NMDA) antagonists, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) throughput enhancers, and glutamate transporter enhancers. This paper reviews the currently available knowledge regarding the role of the glutamatergic system in the etiopathogenesis of mood disorders and putative glutamate modulators.

Reduced levels of NR2A and NR2B subunits of NMDA receptor and PSD-95 in the prefrontal cortex in major depression

Recent neuroimaging and postmortem studies have demonstrated abnormalities in glutamatergic transmission in major depression. Glutamate NMDA (N-methyl-d-aspartate) receptors are one of the major mediators of excitatory neurotransmission in the central nervous system. At synaptic sites, NMDA receptors are linked with postsynaptic density protein-95 (PSD-95) that plays a key role in mediating trafficking, clustering, and downstream signaling events, following receptor activation. In this study, we examined the expression of NMDA receptor subunits NR1, NR2A, and NR2B as well as PSD-95 in the anterior prefrontal cortex (PFC) using Western blot method. Cortical samples were obtained from age, gender and postmortem interval matched depressed and psychiatrically healthy controls. The results revealed that there was a reduced expression of the NMDA receptor subunits NR2A (-54%) and NR2B (-48%), and PSD-95 protein level (-40%) in the PFC of depressed subjects relative to controls, with no change in the NR1 subunit. The alterations in NMDA receptor subunits, especially the NR2A and NR2B, as well as PSD-95 suggest an abnormality in the NMDA receptor signaling in the PFC in major depression. Our findings in conjunction with recent clinical, cellular, and neuroimaging studies further implicate the involvement of glutamate neurotransmission in the pathophysiology of depression. This study provides additional evidence that NMDA receptor complex is a target for discovery of novel antidepressants.

Persistent working memory dysfunction following traumatic brain injury: evidence for a time-dependent mechanism

The prefrontal cortex is highly vulnerable to traumatic brain injury (TBI) resulting in the dysfunction of many high-level cognitive and executive functions such as planning, information processing speed, language, memory, attention, and perception. All of these processes require some degree of working memory. Interestingly, in many cases, post-injury working memory deficits can arise in the absence of overt damage to the prefrontal cortex. Recently, excess GABA-mediated inhibition of prefrontal neuronal activity has been identified as a contributor to working memory dysfunction within the first month following cortical impact injury of rats. However, it has not been examined if these working memory deficits persist, and if so, whether they remain amenable to treatment by GABA antagonism. Our findings show that working memory dysfunction, assessed using both the delay match-to-place and delayed alternation T-maze tasks, following lateral cortical impact injury persists for at least 16 weeks post-injury. These deficits were found to be no longer the direct result of excess GABA-mediated inhibition of medial prefrontal cortex neuronal activity. Golgi staining of prelimbic pyramidal neurons revealed that TBI causes a significant shortening of layers V/VI basal dendrite arbors by 4 months post-injury, as well as an increase in the density of both basal and apical spines in these neurons. These changes were not observed in animals 14 days post-injury, a time point at which administration of GABA receptor antagonists improves working memory function. Taken together, the present findings, along with previously published reports, suggest that temporal considerations must be taken into account when designing mechanism-based therapies to improve working memory function in TBI patients.

Stress-induced prefrontal reorganization and executive dysfunction in rodents

The prefrontal cortex (PFC) mediates a range of higher order 'executive functions' that subserve the selection and processing of information in such a way that behavior can be planned, controlled and directed according to shifting environmental demands. Impairment of executive functions typifies many forms of psychopathology, including schizophrenia, mood and anxiety disorders and addiction, that are often associated with a history of trauma and stress. Recent research in animal models demonstrates that exposure to even brief periods of intense stress is sufficient to cause significant structural remodeling of the principle projection neurons within the rodent PFC. In parallel, there is growing evidence that stress-induced alterations in PFC neuronal morphology are associated with deficits in rodent executive functions such as working memory, attentional set-shifting and cognitive flexibility, as well as emotional dysregulation in the form of impaired fear extinction. Although the molecular basis of stress-induced changes in PFC morphology and function are only now being elucidated, an understanding of these mechanisms could provide important insight into the pathophysiology of executive dysfunction in neuropsychiatric disease and foster improved strategies for treatment.

Morphometric changes of gray matter in Parkinson's disease with depression: a voxel-based morphometry study

The origin of the high rate of depression in idiopathic Parkinson's disease (PD) is unknown. We applied voxel-based morphometry (VBM), as a sensitive tool in detection of gray matter MR density alterations, to find differences in depressed and nondepressed PD patients. Patients with idiopathic PD were classified into depressed (DPD) and nondepressed (NDPD) groups based on the Montgomery-Asberg Depression Rating Scale (MADRS). Subsequently, a group comparisons were performed between depressed PD (n = 23), nondepressed PD (n = 27) and normal healthy controls (NC, n = 16). There was no difference in gray matter density comparing healthy controls to any PD groups. However, when NDPD and DPD cohorts were compared, density alteration of the bilateral orbitofrontal, bilateral rectal gyrus, and also the right superior temporal pole was detected in the depressed subgroup. Exploratory analyses revealed an inverse correlation of MADRS scores and severity of VBM alteration in these regions beside the right medial temporal gyrus, anterior and medial cingular gyrus, and parahippocampal gyrus. These results suggest that depression in PD is related to gray matter decrease in the bilateral orbitofrontal and right temporal regions as well as the limbic system.

Preliminary findings of uncoupling of flow and metabolism in unipolar compared with bipolar affective illness and normal controls

Cerebral metabolism (CMR for glucose or oxygen) and blood flow (CBF) have been reported to be closely correlated in healthy controls. Altered relationships between CMR and CBF have been reported in some brain disease states, but not others. This study examined relationships between global and regional CMRglu vs. CBF in controls and medication-free primary affective disorder patients. Nine bipolars, eight unipolars, and nine healthy controls had [15O]-water positron emission tomography (PET) scans at rest, and [18F]-fluorodeoxyglucose PET scans during an auditory continuous performance task. Patients had [15O]-water and FDG PET scans in tandem the same day; controls had an average of 45+/-27 days between scans. Maps of regional coupling were constructed for each subject group. In controls and bipolars, global and virtually all regional correlation coefficients for CMRglu and CBF were positive, albeit more robustly so in controls. However, correlative relationships in unipolars were qualitatively different, such that global and most regional measures of flow and metabolism were not positively related. Unipolars had significantly fewer positive regional correlation coefficients than healthy controls and bipolars. These were significantly different from controls in orbital cortex, anterior cingulate, posterior cingulate, and posterior temporal cortex, and different from bipolars in pregenual anterior cingulate. In unipolars, the degree of flow-metabolism uncoupling was inversely correlated with Hamilton depression scores, indicating the severity of uncoupling was directly related to the severity of depression. These preliminary data suggest abnormal relationships between cerebral metabolism and blood flow globally and regionally in patients with unipolar depression that warrant replication and extension to potential pathophysiological implications.

Suicide brain is associated with decreased expression of neurotrophins

BACKGROUND

Neurotrophins mediate diverse biological responses, including maintenance and growth of neurons and synaptic plasticity in adult brain. This study examined whether suicide brain is associated with changes in the expression of neurotrophins.

METHODS

Messenger ribonucleic acid (mRNA) levels of nerve growth factor (NGF), neurotrophin (NT)-3, NT-4/5, and of cyclophilin and neuron-specific enolase (NSE) were measured by quantitative reverse transcriptase polymerase chain reaction, whereas protein levels of neurotrophins were determined by enzyme-linked immunosorbent assay, in prefrontal cortex (PFC) and hippocampus from 28 suicide victims and 21 control subjects.

RESULTS

In hippocampus of suicide subjects compared with control subjects mRNA levels of NGF (p < .001), NT-3 (p < .001), and NT-4/5 (p < .001) were decreased, whether or not they were expressed as a ratio to cyclophilin or NSE. This was accompanied by a decrease in their respective protein levels (NGF [p < .001], NT-3 [p < .001], and NT-4/5 [p < .001]). In PFC, however, mRNA (p = .001) and protein (p < .001) levels of NT-4/5 and only protein level of NGF (p < .001) were decreased; NT-3 levels were unchanged.

CONCLUSIONS

Given the role of neurotrophins in synaptic plasticity and maintenance of adult neurons, our findings of altered expression of neurotrophins in postmortem brain of suicide victims suggest that these molecules might play a vital role in the pathophysiology of suicide.

Decreased prefrontal Myo-inositol in major depressive disorder

BACKGROUND

Postmortem studies have shown robust prefrontal cortex glial losses and more subtle neuronal changes in major depressive disorder (MDD). Earlier proton magnetic resonance spectroscopy (1H-MRS) studies of the glial marker myo-inositol in MDD were subject to potential confounds. The primary hypothesis of this study was that MDD patients would show reduced prefrontal/anterior cingulate cortex levels of myo-inositol.

METHODS

Thirteen nonmedicated moderate-severe MDD patients and 13 matched control subjects were studied (six male, seven female per group). Proton magnetic resonance spectroscopy stimulated echo acquisition mode spectra (3.0 T; echo time=168 msec; mixing time=28 msec; repetition time=3000 msec) were obtained from prefrontal/anterior cingulate cortex. Metabolite data were adjusted for tissue composition.

RESULTS

Patients with MDD showed significantly lower myo-inositol/creatine ratios (.94+/-.23) than control subjects (1.32+/-.37) [F(1,23)=6.9; p=.016].

CONCLUSIONS

These data suggest a reduction of myo-inositol in prefrontal/anterior cingulate cortex in MDD, which could be a consequence of glial loss or altered glial metabolism. Additional in vivo studies of glial markers could add to the understanding of the pathophysiology of MDD.

Neuroplasticity: from MRI to depressive symptoms

Morphological and functional changes have been repeatedly reported in the brain organization of depressed patients. The main modifications demonstrated by structural magnetic resonance imaging (MRI) are a reduction in the gray matter volume within the prefrontal cortex, the hippocampus, and the striatum. The reduction in gray matter volume and the morphological atrophy are probably due to an excess of neural loss (apoptosis) and an altered regulation of the neurotrophic processes. Hence, a deficit in neurotrophic factor synthesis (brain-derived neurotrophic factor [BDNF], neurotrophin [NT]-3, NT-4/5, Bcl-2, etc.) may be responsible for increased apoptosis in the hippocampus and prefrontal cortex corresponding to the cognitive impairment described in depression. This hypothesis seems to be confirmed by the decreased expression of neurotrophic factors (e.g., BDNF mRNA) in animal models of depression. In parallel, the neural plasticity (functional aspects of synaptic connectivity and long-term potential activity [LTP]) is decreased. However, the most interesting data concern the possible reversibility of this dysregulation with antidepressant treatment. For example, communication between the hippocampus and the prefrontal cortex could be re-established, enabling in a way the cognitive processes to be "reset." From a clinical point of view, the consequences of such a phenomenon are manifold:

Alterations of neuroplasticity in depression: the hippocampus and beyond

Early hypotheses on the pathophysiology of major depression were based on aberrant intrasynaptic concentrations of mainly the neurotransmitters serotonin and norepinephrine. However, recent neuroimaging studies have demonstrated selective structural changes across various limbic and nonlimbic circuits in the brains of depressed patients. In addition, postmortem morphometric studies revealed decreased glial and neuron densities in selected brain structures supporting the idea that major depression may be related to impairments of structural plasticity. Stressful life events are among the major predisposing risk factors for developing depression. Using the chronic psychosocial stress paradigm in male tree shrews, an animal model with a high validity for the pathophysiology of depressive disorders, we found that 1 month of stress reduced the in vivo concentrations of the brain metabolites N-acetyl-aspartate, choline-containing compounds, and (phospho)-creatine, as well as the proliferation rate in the dentate gyrus and the hippocampal volume. Even though long-lasting social conflict does not lead to a loss of principal cells, the hippocampal changes were accompanied by modifications in the incidence of apoptosis. Notably, these suppressive effects of social conflict on hippocampal structure could be counteracted by treatment with the antidepressant tianeptine. These findings support current theories proposing that major depressive disorders may be associated with impairment of structural plasticity and neural cellular resilience, and that antidepressants may act by correcting this dysfunction.

Mirtazapine-induced corelease of dopamine and noradrenaline from noradrenergic neurons in the medial prefrontal and occipital cortex

The novel antidepressant mirtazapine has been shown to increase extracellular noradrenaline and dopamine in the medial prefrontal cortex. Our previous studies indicate that extracellular dopamine in the cerebral cortex originates largely from noradrenergic terminals, such release being controlled by alpha(2)-adrenoceptors. Because mirtazapine inhibits alpha(2)-adrenoceptors, the possibility that it might corelease dopamine and noradrenaline was investigated. By means of microdialysis, the effect of mirtazapine on extracellular dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC) and noradrenaline in the medial prefrontal cortex, densely innervated by dopaminergic and noradrenergic neurons, and in the occipital cortex, receiving equal noradrenergic but scarce dopaminergic projections, was compared. Basal extracellular concentration of noradrenaline was similar in both cortices, while dopamine in the occipital cortex was only about 50% lower than in the medial prefrontal cortex, reflecting noradrenergic rather than dopaminergic projections. The intraperitoneal (i.p.) administration of mirtazapine (5 and 10 mg/kg) increased extracellular dopamine, DOPAC and noradrenaline to approximately the same extent in both cortices, an effect totally suppressed by the alpha(2)-adrenoceptors agonist clonidine (0.15 mg/kg, i.p.). To exclude the possibility that mirtazapine-induced increase in dopamine might result from reduced dopamine removal from extracellular space, noradrenaline and dopamine uptake mechanisms were blocked by perfusing 100 microM desipramine into either cortex. The combined i.p. administration of mirtazapine (5 mg/kg) and the local perfusion of desipramine produced an additional increase in extracellular dopamine, DOPAC and noradrenaline in the medial prefrontal cortex and occipital cortex compared with the increase produced by either drug given alone. The results suggest that mirtazapine by inhibiting alpha(2)-adrenoceptors produces a corelease of noradrenaline and dopamine from noradrenergic terminals in the cerebral cortex.

Changes in brain metabolism associated with remission in unipolar major depression

OBJECTIVE

Functional brain correlates of remission in patients with major depressive disorder (MDD) are measured with positron emission tomography (PET) and 18F-fluorodeoxyglucose.

METHOD

Glucose metabolism was measured in patients (n = 41) with moderate to severe MDD during acute depression and in the remitted state defined as a period of asymptomatic condition over 12 weeks. Data analyses used a region-of-interest (ROI) approach and statistical parametric mapping (SPM).

RESULTS

There were significant decreases in metabolism upon remission with respect to the baseline scan in left prefrontal, anterior temporal and anterior cingulate cortex and bilateral thalamus (SPM analysis) and bilateral putamen and cerebellum (SPM and ROI analyses). There was a significant asymmetry in prefrontal and anterior cingulate cortex metabolism with lower metabolism in the left hemisphere that persisted despite clinical remission.

CONCLUSION

These findings support the hypothesis that selective monoamine reuptake inhibition leads to an attenuation of a brain circuit that mediates depressive symptomatology.

Emerging experimental therapeutics for bipolar disorder: insights from the molecular and cellular actions of current mood stabilizers

Bipolar disorder afflicts approximately 1-3% of both men and women, and is coincident with major economic, societal, medical, and interpersonal consequences. Current mediations used for its treatment are associated with variable rates of efficacy and often intolerable side effects. While preclinical and clinical knowledge in the neurosciences has expanded at a tremendous rate, recent years have seen no major breakthroughs in the development of novel types of treatment for bipolar disorder. We review here approaches to develop novel treatments specifically for bipolar disorder. Deliberate (ie not by serendipity) treatments may come from one of two general mechanisms: (1) Understanding the mechanism of action of current medications and thereafter designing novel drugs that mimics these mechanism(s); (2) Basing medication development upon the hypothetical or proven underlying pathophysiology of bipolar disorder. In this review, we focus upon the first approach. Molecular and cellular targets of current mood stabilizers include lithium inhibitable enzymes where lithium competes for a magnesium binding site (inositol monophosphatase, inositol polyphosphate 1-phosphatase, glycogen synthase kinase-3 (GSK-3), fructose 1,6-bisphosphatase, bisphosphate nucleotidase, phosphoglucomutase), valproate inhibitable enzymes (succinate semialdehyde dehydrogenase, succinate semialdehyde reductase, histone deacetylase), targets of carbamazepine (sodium channels, adenosine receptors, adenylate cyclase), and signaling pathways regulated by multiple drugs of different classes (phosphoinositol/protein kinase C, cyclic AMP, arachidonic acid, neurotrophic pathways). While the task of developing novel medications for bipolar disorder is truly daunting, we are hopeful that understanding the mechanism of action of current mood stabilizers will ultimately lead clinical trials with more specific medications and thus better treatments those who suffer from this devastating illness.

Dysregulation in the suicide brain: mRNA expression of corticotropin-releasing hormone receptors and GABA(A) receptor subunits in frontal cortical brain region

Corticotropin-releasing hormone (CRH) and GABA have been implicated in depression, and there is reason to believe that GABA may influence CRH functioning. The levels of CRH, and mRNA for CRH-binding protein, CRH1, and CRH2 receptors, as well as various GABA(A) receptor subunits (alpha1, alpha2, alpha3, alpha4, alpha5, delta, and gamma2), were determined in several frontal cortical brain regions of depressed suicide victims and nondepressed individuals who had not died by suicide. Relative to the comparison group, CRH levels were elevated in frontopolar and dorsomedial prefrontal cortex, but not in the ventrolateral prefrontal cortex of suicide victims. Conversely, using quantitative PCR analyses, it was observed that, in frontopolar cortex, mRNA for CRH1, but not CRH2, receptors were reduced in suicide brains, possibly secondary to the high levels of CRH activity. In addition, mRNA of the alpha1, alpha3, alpha4, and delta receptor subunits was reduced in the frontopolar region of suicide victims. Interestingly, a partial analysis of the GABA(A) receptor functional genome revealed high cross-correlations between subunit expression in cortical regions of nondepressed individuals, suggesting a high degree of coordinated gene regulation. However, in suicide brains, this regulation was perturbed, independent of overall subunit abundance. These findings raise the possibility that the CRH and GABA(A) receptor subunit changes, or the disturbed coordination between these GABA(A) receptor subunits, contribute to depression and/or suicidality or are secondary to the illness/distress associated with it.

Increased stress vulnerability after a prefrontal cortex lesion in female rats

Neuroimaging studies in patients suffering from affective disorders have shown decreased volume and reduced regional cerebral blood flow in multiple areas of the prefrontal cortex, including the medial prefrontal cortex and the orbitofrontal cortex. This aberrant brain activity is among other things attributed to chronic stress. Affective disorders occur more often in women than in men. In the current experiment, female mPFC-lesioned and non-lesioned rats were subjected to 3 weeks of chronic unpredictable stress in order to determine the role of the mPFC in dealing with chronic stress, and the consequences of mPFC damage for coping with consecutive stressful events. mPFC damage in female rats intensified the stress-induced activation of the dorsomedial nucleus of the hypothalamus and the paraventricular nucleus of the hypothalamus as measured with Fos expression changes and markedly increased plasma catecholamine levels after 3 weeks of unpredictable stress. Additionally, an mPFC lesion significantly reduced the time of appearance of stress-induced behavioral changes in the open field. Altogether, mPFC dysfunction affects the way female rats react to chronic stress, it not only increased the activation of brain regions involved in neuroendocrine and autonomic responses to stress but it also significantly reduced the time of onset of behavioral changes.

State and trait influences on mood regulation in bipolar disorder: blood flow differences with an acute mood challenge

BACKGROUND

Even in remission, patients with bipolar disorder (BD) remain sensitive to external stressors that can trigger new episodes. Imitating such stressors by the controlled transient exposure to an emotional stimulus may help to identify brain regions modulating this sensitivity.

METHODS

Transient sadness was induced in 9 euthymic and in 11 depressed subjects with BD. Regional blood flow (rCBF) changes were measured using (15)O-water positron emission tomography.

RESULTS

Common changes in both groups were increased rCBF in anterior insula and cerebellum and decreased rCBF in dorsal-ventral-medial frontal cortex, posterior cingulate, inferior parietal, and temporal cortices. Decreases in dorsal ventral medial frontal cortices occurred in both groups, but subjects in remission showed a greater magnitude of change. Unique to remitted subjects with BD were rCBF increases in dorsal anterior cingulate and in premotor cortex. Lateral prefrontal rCBF decreases were unique to depressed subjects with BD. At baseline, remitted subjects showed a unique increase in dorsal anterior cingulate and orbitofrontal cortex.

CONCLUSIONS

Common rCBF changes in remitted and depressed subjects identifies potential sites of disease vulnerability. Unique cingulate and orbitofrontal changes both at baseline and with induced sadness seen in the absence of prefrontal rCBF decreases may identify regional interactions important to the euthymic state in this population.

Glutamate and Depression

The past decade has seen a steady accumulation of evidence supporting a role for the excitatory amino acid (EAA) neurotransmitter, glutamate, and its receptors in depression and antidepressant activity. To date, evidence has emerged indicating that N-methyl-d-aspartate (NMDA) receptor antagonists, group I metabotropic glutamate receptor (mGluR1 and mGluR5) antagonists, as well as positive modulators of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors have antidepressant-like activity in a variety of preclinical models. Moreover, antidepressant-like activity can be produced not only by drugs modulating the glutamatergic synapse, but also by agents that affect subcellular signaling systems linked to EAA receptors (e.g., nitric oxide synthase). In view of the extensive colocalization of EAA and monoamine markers in nuclei such as the locus coeruleus and dorsal raphe, it is likely that an intimate relationship exists between regulation of monoaminergic and EAA neurotransmission and antidepressant effects. Further, there is also evidence implicating disturbances in glutamate metabolism, NMDA, and mGluR1,5 receptors in depression and suicidality. Finally, recent data indicate that a single intravenous dose of an NMDA receptor antagonist is sufficient to produce sustained relief from depressive symptoms. Taken together with the proposed role of neurotrophic factors in the neuroplastic responses to stressors and antidepressant treatments, these findings represent exciting and novel avenues to both understand depressive symptomatology and develop more effective antidepressants.

Involvement of serotonin in depression: evidence from postmortem and imaging studies of serotonin receptors and the serotonin transporter

Definitive conclusions on the role of serotonin receptors and transporter in suicide and depression have been elusive in studies of postmortem brain tissue. A number of methodological differences in these studies have made it difficult to reach a consensus, but crucial issues are being identified and incorporated into newer studies. This review will follow the evolution of serotonin receptor and transporter studies in postmortem tissues that initially focused on suicide and gradually incorporated depressive disorders as psychiatric assessments were increasingly performed. Studies in postmortem tissues on the serotonin-1A and serotonin-2A receptors and the serotonin transporter will be reviewed and compared with imaging studies of the same sites in depressed subjects. Critical issues to control in future studies of serotonin receptors in postmortem tissues include variables such as the cause of death (i.e. suicide), the specific psychiatric diagnoses of the subjects, whether the disorder was in remission at the time of death, long-term medication histories, psychoactive substance use disorders, the smoking history, the hemisphere from which tissues were dissected, and the specific cytoarchitectonic region to be evaluated. Carefully controlled studies in postmortem tissues will ensure a greater likelihood of reaching a consensus on the involvement of monoamine measures in the etiology of depression.