Age-dependent reductions in the level of glial fibrillary acidic protein in the prefrontal cortex in major depression

Glial pathology in an animal model of depression: reversal of stress-induced cellular, metabolic and behavioral deficits by the glutamate-modulating drug riluzole

Growing evidence indicates that glia pathology and amino-acid neurotransmitter system abnormalities contribute to the pathophysiology and possibly the pathogenesis of major depressive disorder. This study investigates changes in glial function occurring in the rat prefrontal cortex (PFC) after chronic unpredictable stress (CUS), a rodent model of depression. Furthermore, we analyzed the effects of riluzole, a Food and Drug Administration-approved drug for the treatment of amyotrophic laterosclerosis, known to modulate glutamate release and facilate glutamate uptake, on CUS-induced glial dysfunction and depressive-like behaviors. We provide the first experimental evidence that chronic stress impairs cortical glial function. Animals exposed to CUS and showing behavioral deficits in sucrose preference and active avoidance exhibited significant decreases in 13C-acetate metabolism reflecting glial cell metabolism, and glial fibrillary associated protein (GFAP) mRNA expression in the PFC. The cellular, metabolic and behavioral alterations induced by CUS were reversed and/or blocked by chronic treatment with the glutamate-modulating drug riluzole. The beneficial effects of riluzole on CUS-induced anhedonia and helplessness demonstrate the antidepressant action of riluzole in rodents. Riluzole treatment also reversed CUS-induced reductions in glial metabolism and GFAP mRNA expression. Our results are consistent with recent open-label clinical trials showing the drug's effect in mood and anxiety disorders. This study provides further validation of hypothesis that glial dysfunction and disrupted amino-acid neurotransmission contribute to the pathophysiology of depression and that modulation of glutamate metabolism, uptake and/or release represent viable targets for antidepressant drug development.

Is there a CSF biomarker profile related to depression in elderly women?

In light of our previous observation of higher levels of cerebrospinal fluid (CSF) amyloid beta-42 (Abeta42) and CSF/serum albumin ratio in major depressive disorder (MDD), we analyzed two additional CSF biomarkers reflecting neurodegeneration-neurofilament protein light (NFL) and glial fibrillary acidic protein (GFAp)-in relationship to prevalent geriatric depression. Neuropsychiatric, physical, and lumbar puncture examinations, with DSM-III-R-based depression diagnoses and measurement of CSF levels of NFL and GFAp, were evaluated among a population-based sample of 78 elderly women (mean age, 73.9+/-3.2 years) without dementia for at least 10 years after CSF collection. Eleven (13.1%) women had MDD, and higher levels of NFL compared with women without depression. A multivariate model including age, NFL, Abeta42 and the CSF/serum albumin ratio showed that each biomarker was independently and positively associated with MDD, and that this biomarker profile explained more variation in the model compared with single or combined biomarkers. A CSF profile with higher levels of NFL, Abeta42, and CSF/serum albumin ratio may indicate neuropathological and vascular events in depression etiology. This contrasts with the well-characterized pattern of low Abeta42, higher CSF/serum albumin ratio, and higher NFL in Alzheimer's disease.

DHA deficiency and prefrontal cortex neuropathology in recurrent affective disorders

Increasing evidence suggests that docosahexaenoic acid [DHA, 22:6(n-3)], the principal (n-3) fatty acid in brain gray matter, has neurotrophic and neuroprotective properties. Preliminary clinical evidence also suggests that the perinatal accrual, and the subsequent dietary maintenance of, cortical DHA is positively associated with cortical gray matter volumes. The pathophysiology of recurrent affective disorders, including unipolar and bipolar depression, is associated with (n-3) fatty acid deficiency, DHA deficits, impaired astrocyte mediated vascular coupling, neuronal shrinkage, and reductions in gray matter volume in the prefrontal cortex (PFC). Preclinical studies have also observed neuronal shrinkage and indices of astrocyte pathology in the DHA-deficient rat brain. Together, this body of evidence supports the proposition that DHA deficiency increases vulnerability to neuronal atrophy in the PFC of patients with affective disorders. Because projections from the PFC modulate multiple limbic structures involved in affective regulation, this represents one plausible mechanism by which (n-3) fatty acid deficiency may increase vulnerability to recurrent affective disorders.

Astrocytes: biology and pathology

Astrocytes are specialized glial cells that outnumber neurons by over fivefold. They contiguously tile the entire central nervous system (CNS) and exert many essential complex functions in the healthy CNS. Astrocytes respond to all forms of CNS insults through a process referred to as reactive astrogliosis, which has become a pathological hallmark of CNS structural lesions. Substantial progress has been made recently in determining functions and mechanisms of reactive astrogliosis and in identifying roles of astrocytes in CNS disorders and pathologies. A vast molecular arsenal at the disposal of reactive astrocytes is being defined. Transgenic mouse models are dissecting specific aspects of reactive astrocytosis and glial scar formation in vivo. Astrocyte involvement in specific clinicopathological entities is being defined. It is now clear that reactive astrogliosis is not a simple all-or-none phenomenon but is a finely gradated continuum of changes that occur in context-dependent manners regulated by specific signaling events. These changes range from reversible alterations in gene expression and cell hypertrophy with preservation of cellular domains and tissue structure, to long-lasting scar formation with rearrangement of tissue structure. Increasing evidence points towards the potential of reactive astrogliosis to play either primary or contributing roles in CNS disorders via loss of normal astrocyte functions or gain of abnormal effects. This article reviews (1) astrocyte functions in healthy CNS, (2) mechanisms and functions of reactive astrogliosis and glial scar formation, and (3) ways in which reactive astrocytes may cause or contribute to specific CNS disorders and lesions.

Neurocircuitry of mood disorders

This review begins with a brief historical overview of attempts in the first half of the 20th century to discern brain systems that underlie emotion and emotional behavior. These early studies identified the amygdala, hippocampus, and other parts of what was termed the 'limbic' system as central parts of the emotional brain. Detailed connectional data on this system began to be obtained in the 1970s and 1980s, as more effective neuroanatomical techniques based on axonal transport became available. In the last 15 years these methods have been applied extensively to the limbic system and prefrontal cortex of monkeys, and much more specific circuits have been defined. In particular, a system has been described that links the medial prefrontal cortex and a few related cortical areas to the amygdala, the ventral striatum and pallidum, the medial thalamus, the hypothalamus, and the periaqueductal gray and other parts of the brainstem. A large body of human data from functional and structural imaging, as well as analysis of lesions and histological material indicates that this system is centrally involved in mood disorders.

Neuronal damage and protection in the pathophysiology and treatment of psychiatric illness: stress and depression

The discovery that stress and depression, as well as other psychiatric illnesses, are characterized by structural alterations, and that these changes result from atrophy and loss of neurons and glia in specific limbic regions and circuits, has contributed to a fundamental change in our understanding of these illnesses. These structural changes are accompanied by dysregulation of neuroprotective and neurotrophic signaling mechanisms that are required for the maturation, growth, and survival of neurons and glia. Conversely, behavioral and therapeutic interventions can reverse these structural alterations by stimulating neuroprotective and neurotrophic pathways and by blocking the damaging, excitotoxic, and inflammatory effects of stress. Lifetime exposure to cellular and environmental stressors and interactions with genetic factors contribute to individual susceptibility or resilience. This exciting area of research holds promise and potential for further elucidating the pathophysiology of psychiatric illness and for development of novel therapeutic interventions.

Suicide neurobiology

In this review, we examine the history of the neurobiology of suicide, as well as the genetics, molecular and neurochemical findings in suicide research. Our analysis begins with a summary of family, twin, and adoption studies, which provide support for the investigation of genetic variation in suicide risk. This leads to an overview of neurochemical findings restricted to neurotransmitters and their receptors, including recent findings in whole genome gene expression studies. Next, we look at recent studies investigating lipid metabolism, cell signalling with a particular emphasis on growth factors, stress systems with a focus on the role of polyamines, and finally, glial cell pathology in suicide. We conclude with a description of new ideas to study the neurobiology of suicide, including subject-specific analysis, protein modification assessment, neuroarchitecture studies, and study design strategies to investigate the complex suicide phenotype.

Targeting glial physiology and glutamate cycling in the treatment of depression

Accumulating evidence indicates that dysfunction in amino acid neurotransmission contributes to the pathophysiology of depression. Consequently, the modulation of amino acid neurotransmission represents a new strategy for antidepressant development. While glutamate receptor ligands are known to have antidepressant effects, mechanisms regulating glutamate cycling and metabolism may be viable drug targets as well. In particular, excitatory amino acid transporters (EAATs) that are embedded in glial processes constitute the primary means of clearing extrasynaptic glutamate. Therefore, the decreased glial number observed in preclinical stress models, and in postmortem tissue from depressed patients provides intriguing, yet indirect evidence for a role of disrupted glutamate homeostasis in the pathophysiology of depression. More direct evidence for this hypothesis comes from studies using magnetic resonance spectroscopy (MRS), a technique that non-invasively measures in vivo concentrations of glutamate and other amino acids under different experimental conditions. Furthermore, when combined with the infusion of (13)C-labeled metabolic precursors, MRS can measure flux through discrete metabolic pathways. This approach has recently shown that glial amino acid metabolism is reduced by chronic stress, an effect that provides a link between environmental stress and the decreased EAAT activity observed under conditions of increased oxidative stress in the brain. Furthermore, administration of riluzole, a drug that enhances glutamate uptake through EAATs, reversed this stress-induced change in glial metabolism. Because riluzole has antidepressant effects in both animal models and human subjects, it may represent the prototype for a novel class of antidepressants with the modulation of glial physiology as a primary mechanism of action.

Neonatal separation stress reduces glial fibrillary acidic protein- and S100beta-immunoreactive astrocytes in the rat medial precentral cortex

The interactions between the mother/parents and their offspring provides socioemotional input, which is essential for the establishment and maintenance of synaptic networks in prefrontal and limbic brain regions. Since glial cells are known to play an important role in developmental and experience-driven synaptic plasticity, the effect of an early adverse emotional experience induced by maternal separation for 1 or 6 h on the expression of the glia specific proteins S100beta and glial fibrillary acidic protein (GFAP) was quantitatively analyzed in anterior cingulate cortex, hippocampus, and precentral medial cortex. Three animal groups were analyzed at postnatal day 14: (i) separated for 1 h; (ii) separated for 6 h; (iii) undisturbed (control). Twenty-four hours after stress exposure, the stressed brains showed significantly reduced numbers of S100beta-immunoreactive (ir) cells in the anterior cingulate cortex (6-h stress) and in the precentral medial cortex (1- and 6-h stress). Significantly reduced numbers of GFAP-ir cells were observed only in the medial precentral cortex (1- and 6-h stress); no significant changes were observed in the anterior cingulate cortex. No significant changes of the two glial markers were observed in the hippocampus. Double-labeling experiments with GFAP and pCREB revealed pCREB labeling only in the hippocampus, where the stressed brains (1 and 6 h) displayed significantly reduced numbers of GFAP/pCREB-ir glial cells. The observed downregulation of glia-specific marker proteins is in line with our hypothesis that emotional experience can alter glia cell activation in the juvenile limbic system.

Antidepressant effect detected on proton magnetic resonance spectroscopy in drug-naïve female patients with first-episode major depression

AIM

Recent neuroimaging studies support functional and structural alterations in the dorsolateral prefrontal cortex (DLPFC), particularly on the left side in patients with major depressive disorders (MDD). The aim of the present study was to examine the biochemical characteristics of left DLPFC as measured on proton ((1)H) magnetic resonance spectroscopy (MRS) in patients with drug-naïve first-episode MDD and a healthy control group. A second aim was to assess the effect of antidepressant treatment on the metabolites of DLPFC.

METHODS

Short-echo single-voxel (1)H-MRS was done for the left DLPFC in 17 female drug-free MDD patients (mean age +/- SD, 30.9 +/- 6.9 years) and 13 matched control subjects (mean age +/- SD, 29.1 +/- 6.2 years) and was repeated at 8 weeks following antidepressant treatment.

RESULTS

Comparison of baseline values indicated that there were no significant differences in any of the metabolite ratios (N-acetyl aspartate/creatine [NAA/Cr], myoinositol [Ino]/Cr, and choline [Cho]/Cr) between patients and controls. Significant differences were detected between pre- and post-treatment Ino/Cr ratios (0.67 +/- 0.13, 0.58 +/- 0.22, P = 0.032, respectively), although there was no difference in NAA/Cr and Cho/Cr ratios.

CONCLUSION

Although no significant metabolic alterations exist in female patients with drug-naïve first-episode MDD as evaluated on (1)H-MRS, an increase in Ino/Cr was observed following 8-week antidepressant treatment. These findings give rise to the possibility that non-neuronal cells, particularly glial cells that are probably damaged, play a role in the action of antidepressant treatment.

Biochemical abnormalities of the medial temporal lobe and medial prefrontal cortex in late-life depression

We utilized single-voxel (1)H magnetic resonance spectroscopy (MRS) to investigate biochemical abnormalities related to late-life depression in the medial prefrontal cortex and medial temporal lobe. Fourteen elderly subjects whose depression responded to treatment and 12 nondepressed subjects were enrolled. Subjects were scanned using a GE 3.0 Tesla whole body MR scanner. Metabolite concentrations were quantified using the LC Model software and adjusted for CSF and ratio of gray to white matter. ANCOVA models tested for group differences while controlling for age and sex. Older previously depressed individuals showed significantly reduced concentrations of total N-acetyl aspartate (NAA), choline, and creatine in the prefrontal cortex and significantly elevated left medial temporal lobe concentrations of NAA and myo-inositol. There were no significant group differences in right temporal metabolite concentrations. The prefrontal cortex observations suggest that reduced neuronal, phospolipid, and energy metabolism is present even in clinically improved depression. In contrast, elevated NAA and myo-inositol concentrations in the left medial temporal lobe could be associated with neuronal and glial cell changes in the amygdala.

Elevated levels of NR2A and PSD-95 in the lateral amygdala in depression

Compelling evidence suggests that major depression is associated with dysfunction of the brain glutamatergic transmission, and that the glutamatergic N-methyl-d-aspartate (NMDA) receptor plays a role in antidepressant activity. Recent post-mortem studies demonstrate that depression is associated with altered concentrations of proteins associated with NMDA receptor signalling in the brain. The present study investigated glutamate signalling proteins in the amygdala from depressed subjects, given strong evidence for amygdala pathology in depression. Lateral amygdala samples were obtained from 13-14 pairs of age- sex-, and post-mortem-interval-matched depressed and psychiatrically healthy control subjects. Concentrations of NR1 and NR2A subunits of the NMDA receptor, as well as NMDA receptor-associated proteins such as post-synaptic density protein-95 (PSD-95) and neuronal nitric oxide synthase (nNOS) were measured by Western immunoblotting. Additionally, levels of enzymes involved in glutamate metabolism, including glutamine synthetase and glutamic acid decarboxylase (GAD-67), were measured in the same amygdala samples. NR2A protein levels were markedly and significantly elevated (+115%, p=0.03) in depressed subjects compared to controls. Interestingly, PSD-95 levels were also highly elevated (+128%, p=0.01) in the same depressed subjects relative to controls. Amounts of NR1, nNOS, glutamine synthetase, and GAD-67 were unchanged. Increased levels of NR2A and PSD-95 suggest that glutamate signalling at the NMDA receptor in the amygdala is disrupted in depression.

Neuronal damage and protection in the pathophysiology and treatment of psychiatric illness: stress and depression

The discovery that stress and depression, as well as other psychiatric illnesses, are characterized by structural alterations, and that these changes result from atrophy and loss of neurons and glia in specific limbic regions and circuits, has contributed to a fundamental change in our understanding of these illnesses. These structural changes are accompanied by dysregulation of neuroprotective and neurotrophic signaling mechanisms that are required for the maturation, growth, and survival of neurons and glia. Conversely, behavioral and therapeutic interventions can reverse these structural alterations by stimulating neuroprotective and neurotrophic pathways and by blocking the damaging, excitotoxic, and inflammatory effects of stress. Lifetime exposure to cellular and environmental stressors and interactions with genetic factors contribute to individual susceptibility or resilience. This exciting area of research holds promise and potential for further elucidating the pathophysiology of psychiatric illness and for development of novel therapeutic interventions.

Serum markers support disease-specific glial pathology in major depression

BACKGROUND

Recently, it was shown by histopathological studies that mood disorders are characterized by disease-specific glial pathology.

METHODS

To validate this hypothesis in vivo we measured weekly and simultaneously serum levels of the neuronal marker neuron-specific enolase and S100B, a protein expressed in astro- and oligodendroglia in the human brain, in 10 patients with major depressive disorder and 10 age- and gender-matched control subjects. Furthermore, we conducted a systematic, quantitative meta-analysis of all published studies on S100B involving 193 patients suffering from mood disorders and 132 healthy control subjects by calculating effect sizes.

RESULTS

S100B was elevated at admission and discharge in our patients with major depression compared with control subjects, whereas there were no significant differences for neuron-specific enolase. During treatment S100B decreased slightly, although this effect was not significant. It had no significant impact on neuron-specific enolase. The meta-analysis revealed that serum levels of S100B are consistently elevated in mood disorders during acute major depressive or manic episodes. Additionally, it demonstrated that serum S100B decreases during antidepressive treatment reliably if clinical improvement is sufficient.

LIMITATIONS

As the study measured only serum S100B, future (cell culture) studies have to elucidate molecular mechanisms of this protein in mood disorders. Moreover, results have to be replicated in a larger patient group.

CONCLUSIONS

S100B may represent a biomarker for mood disorders, particularly major depression, and their treatment. Together with unaltered levels of neuron-specific enolase, our results support in vivo the histopathologically generated hypothesis of disease-specific glial pathology in mood disorders.

Glial loss in the prefrontal cortex is sufficient to induce depressive-like behaviors

BACKGROUND

Postmortem studies have repeatedly found decreased density and number of glia in cortical regions, including the prefrontal and cingulate areas, from depressed patients. However, it is unclear whether this glial loss plays a direct role in the expression of depressive symptoms.

METHODS

To address this question, we characterized the effects of pharmacologic glial ablation in the prefrontal cortex (PFC) of adult rats on behavioral tests known to be affected by stress or antidepressant treatments: sucrose preference test (SPT), novelty suppressed feeding test (NSFT), forced swim test (FST), and two-way active avoidance test (AAT). We established the dose and time course for the actions of an astrocyte specific toxin, L-alpha-aminoadipic acid (L-AAA), and compared the behavioral effects of this gliotoxin with the effects of an excitotoxic (ibotenate) lesion and to the effects of chronic stress.

RESULTS

The results demonstrate that L-AAA infusions induced anhedonia in SPT, anxiety in NSFT, and helplessness in FST and AAT. These effects of L-AAA were similar to chronic unpredictable stress (CUS)-induced depressive-like behaviors in these tests. However, ibotenate-induced neurotoxic lesion of the PFC had no effect in these behavioral tests.

CONCLUSIONS

The results demonstrate that glial ablation in the PFC is sufficient to induce depressive-like behaviors similar to chronic stress and support the hypothesis that loss of glia contributes to the core symptoms of depression.

Inflammation, glutamate, and glia in depression: a literature review

Multiple lines of evidence suggest that inflammation and glutamate dysfunction contribute to the pathophysiology of depression. In this review we provide an overview of how these two systems may interact. Excess levels of inflammatory mediators occur in a subgroup of depressed patients. Studies of acute experimental activation of the immune system with endotoxin and of chronic activation during interferon-alpha treatment show that inflammation can cause depression. Peripheral inflammation leads to microglial activation which could interfere with excitatory amino acid metabolism leading to inappropriate glutamate receptor activation. Loss of astroglia, a feature of depression, upsets the balance of anti- and pro-inflammatory mediators and further impairs the removal of excitatory amino acids. Microglia activated by excess inflammation, astroglial loss, and inappropriate glutamate receptor activation ultimately disrupt the delicate balance of neuroprotective versus neurotoxic effects in the brain, potentially leading to depression.

Repeated unpredictable stress and antidepressants differentially regulate expression of the bcl-2 family of apoptotic genes in rat cortical, hippocampal, and limbic brain structures

Apoptosis has been proposed as a contributing cellular mechanism to the structural alterations that have been observed in stress-related mood disorders. Antidepressants, on the other hand, are hypothesized to exert trophic and/or neuroprotective actions. The present study examined the regulation of the major antiapoptotic (Bcl-2, Bcl-xl) and proapoptotic (Bax) genes by repeated unpredictable stress (an animal model of depression) and antidepressant treatments (ADT). In adult rats, exposure to unpredictable stress reduced Bcl-2 mRNA levels in the central nucleus of the amygdala (CeA), cingulate (Cg), and frontal (Fr) cortices. Bcl-xl mRNA was significantly decreased in hippocampal subfields. In contrast, chronic administration of clinically effective antidepressants from four different classes, ie fluoxetine, reboxetine, tranylcypromine, and electroconvulsive seizures (ECS) upregulated Bcl-2 mRNA expression in the Cg, Fr, and CeA. Reboxetine, tranylcypromine, and ECS selectively increased Bcl-xl, but not Bcl-2 mRNA expression in the hippocampus. Chemical ADT but not ECS, robustly enhanced Bcl-2 expression in the medial amygdaloid nucleus and ventromedial hypothalamus. Fluoxetine did not influence Bcl-xl expression in the hippocampus, but it was the only ADT that decreased Bax expression in this region. In the CeA, again in direct contrast to the stress effects, exposure to all classes of ADTs significantly increased Bcl-2 mRNA. The selective regulation of Bcl-xl and Bax in hippocampal subfields and of Bcl-2 in the Cg cortex, amygdala, and hypothalamus suggests that these cellular adaptations contribute to the long-term neural plastic adaptations to stress and ADTs in cortical, hypothalamic, and limbic brain structures.

The immune-mediated alteration of serotonin and glutamate: towards an integrated view of depression

Beside the well-known deficiency in serotonergic neurotransmission as pathophysiological correlate of major depression (MD), recent evidence points to a pivotal role of increased glutamate receptor activation as well. However, cause and interaction of these neurotransmitter alterations are not understood. In this review, we present a hypothesis integrating current concepts of neurotransmission and hypothalamus-pituitary-adrenal (HPA) axis dysregulation with findings on immunological alterations and alterations in brain morphology in MD. An immune activation including increased production of proinflammatory cytokines has repeatedly been described in MD. Proinflammatory cytokines such as interleukin-2, interferon-gamma, or tumor necrosis factor-alpha activate the tryptophan- and serotonin-degrading enzyme indoleamine 2,3-dioxygenase (IDO). Depressive states during inflammatory somatic disorders are also associated with increased proinflammatory cytokines and increased consumption of tryptophan via activation of IDO. An enhanced consumption of serotonin and its precursor tryptophan through IDO activation could well explain the reduced availability of serotonergic neurotransmission in MD. An increased activation of IDO and its subsequent enzyme kynurenine monooxygenase by proinflammatory cytokines, moreover, leads to an enhanced production of quinolinic acid, a strong agonist of the glutamatergic N-methyl-D-aspartate receptor. In inflammatory states of the central nervous system, IDO is mainly activated in microglial cells, which preferentially metabolize tryptophan to the NMDA receptor agonist quinolinic acid, whereas astrocytes - counteracting this metabolism due to the lack of an enzyme of this metabolism - have been observed to be reduced in MD. Therefore the type 1/type 2 immune response imbalance, associated with an astrocyte/microglia imbalance, leads to serotonergic deficiency and glutamatergic overproduction. Astrocytes are further strongly involved in re-uptake and metabolic conversion of glutamate. The reduced number of astrocytes could contribute to both, a diminished counterregulation of IDO activity in microglia and an altered glutamatergic neurotransmission. Further search for antidepressant agents should take into account anti-inflammatory drugs, for example, cyclooxygenase-2 inhibitors, might exert antidepressant effects by acting on serotonergic deficiency, glutamatergic hyperfunction and antagonizing neurotoxic effects of quinolinic acid.

Chronic unpredictable stress decreases cell proliferation in the cerebral cortex of the adult rat

BACKGROUND

One of the most consistent morphologic findings in postmortem studies of brain tissue from depressed patients is a decrease in the number of glia in the prefrontal cortex. However, little is known about the mechanisms that contribute to this decrease in cell number.

METHODS

To address this question, we subjected adult rats to chronic stress, a vulnerability factor for depression, and measured cell proliferation as a potential cellular mechanism that could underlie glial reduction in depression.

RESULTS

We found that exposure to chronic unpredictable stress (CUS) for 15 days significantly decreased cell proliferation in neocortex by approximately 35%. This effect was dependent on the duration, intensity and type of stress, and was region-specific. Analysis of cell phenotype demonstrated that there was a decrease in the number of oligodendrocytes and endothelial cells. Finally, using a CUS paradigm that allows for analysis of anhedonia, we found that chronic antidepressant administration reversed the decrease in cortical cell proliferation, as well as the deficit in sucrose preference.

CONCLUSION

These findings are consistent with the possibility that decreased cell proliferation could contribute to reductions in glia in prefrontal cortex of depressed subjects and further elucidate the cellular actions of stress and antidepressants.

Comparative proteomic analysis with postmortem prefrontal cortex tissues of suicide victims versus controls

BACKGROUND

The origin of suicidal behaviour is multifactorial including genetic, neurobiological and psychosocial correlates. Although there is no doubt that serotonin has a central role, the overall genetic findings with candidate genes of the serotonergic pathway are relatively inconsistent and suggests that other, yet unidentified, genes and gene products are also contributing to the vulnerability of suicidality. Proteomics is a powerful method to investigate modifications in protein expression.

METHODS

We performed comparative proteomic analysis with prefrontal cortex tissues of 17 suicide victims and 9 controls.

RESULTS

Applying two dimensional gel electrophoresis and image analysis we detected five protein spots to differ significantly in intensities between both groups. Three of them appeared only in suicide victims and could be identified by means of MALDI-TOF-MS analysis and protein database search as alpha crystallin chain B (CRYAB), glial fibrillary acidic protein (GFAP) and manganese superoxide dismutase (SOD2). CRYAB belongs to the low molecular heat shock proteins and GFAP is known as a marker of astrocytic activation in gliosis. SOD2 is a major antioxidant enzyme protecting cells against oxidative injury. Two further spots revealed higher intensities in the control group but had no unambiguous protein to match.

CONCLUSIONS

Our findings suggest that proteins, being involved in glial function, neurodegeneration and oxidative stress neuronal injury, might also have an impact upon the neurobiological cascade leading to suicidality. As animal data provide evidence for an up-regulation of GFAP synthesis in astrocytes due to alterations in 5-HT levels, similar mechanisms of interaction might also be relevant in humans.

Gliogenesis and glial pathology in depression

Recent research has changed the perception of glia from being no more than silent supportive cells of neurons to being dynamic partners participating in brain metabolism and communication between neurons. This discovery of new glial functions coincides with growing evidence of the involvement of glia in the neuropathology of mood disorders. Unanticipated reductions in the density and number of glial cells are reported in fronto-limbic brain regions in major depression and bipolar illness. Moreover, age-dependent decreases in the density of glial fibrillary acidic protein (GFAP) - immunoreactive astrocytes and levels of GFAP protein are observed in the prefrontal cortex of younger depressed subjects. Since astrocytes participate in the uptake, metabolism and recycling of glutamate, we hypothesize that an astrocytic deficit may account for the alterations in glutamate/GABA neurotransmission in depression. Reductions in the density and ultrastructure of oligodendrocytes are also detected in the prefrontal cortex and amygdala in depression. Pathological changes in oligodendrocytes may be relevant to the disruption of white matter tracts in mood disorders reported by diffusion tensor imaging. Factors such as stress, excess of glucocorticoids, altered gene expression of neurotrophic factors and glial transporters, and changes in extracellular levels of neurotransmitters released by neurons may modify glial cell number and affect the neurophysiology of depression. Therefore, we will explore the role of these events in the possible alteration of glial number and activity, and the capacity of glia as a promising new target for therapeutic medications. Finally, we will consider the temporal relationship between glial and neuronal cell pathology in depression.

Glia mechanisms in mood regulation: a novel model of mood disorders

INTRODUCTION

Recent evidence in clinical and preclinical studies has implicated glutamate neurotransmissions in pathophysiology of mood disorders. The regulation of amino acid neurotransmission, i.e., glutamate and gamma-aminobutyric acid (GABA) involves coordinated mechanisms of uptake and transport within a tripartite synaptic system that includes neurons and glia. Newly appreciated role of the glia, more specifically astrocytes on neuronal functions combined with reported postmortem abnormalities of glia in patients with mood disorders further supports the role of glia in mood disorders.

MATERIALS AND METHODS

This report presents some of our preliminary results utilizing glia-selective toxins and other pharmacological tools to suppress glial function within the limbic system to study the resulting behavioral abnormalities, and thus, elucidate glial involvement in the development of mood disorders.

RESULTS AND DISCUSSION

We demonstrate that chronic blockade of glutamate uptake by a glial/neuronal transporter antagonist L-trans-pyrrolidine-2,4-dicarboxylic acid (PDC) within the amygdala, a key area implicated in mood regulation, results in dose-dependent reduction in social exploratory behavior and disrupts circadian activity patterns consistent with symptoms of mood disorders. Similarly, the selective astrocytic glutamate transporter type 1 (GLT-1) blocker dihydrokainic acid (DHK) injected into the amygdala also results in reduced social interaction that is blocked by selective glutamate N-methyl-D-aspartate (NMDA) type receptor antagonist AP5. The results are discussed in the context of glial and glutamate mechanisms in mood disorders and potential therapeutic avenues to address these mechanisms.

Distribution of ICAM-1 immunoreactivity during aging in the human orbitofrontal cortex

Neurological and psychiatric alterations during aging are associated with increased cerebrovascular disturbances and inflammatory markers such as Intercellular Adhesion Molecule-1 (ICAM-1). We investigated whether the distribution of ICAM-1 immunoreactivity (ICAM-1-I) in histological sections from the left orbitofrontal cortex (ORB) was altered during normal aging. Postmortem tissue from the ORB of nine younger (27-54 years old) and 10 older (60-86) human subjects was collected. Cryostat sections were immunostained only with antibodies to ICAM-1 or together with an antibody to glial fibrillary acidic protein (GFAP). The total area fraction of ICAM-1-I, and the fraction of vascular and extravascular ICAM-1-I were quantified in the gray matter. Furthermore, we examined the association of extravascular ICAM-1-I to GFAP immunoreactive (GFAP-IR) astrocytes. In all subjects, brain blood vessels were similarly ICAM-1 immunoreactive, and in some subjects there was a variable number of extravascular patches of ICAM-1-I. The area fraction of ICAM-1-I was 120% higher (p<.0001) in the old subjects than in the young subjects. This increase localized mostly to the extravascular ICAM-1-I in register with GFAP-IR astrocytes. A much smaller, also age-dependent increase occurred in vascular ICAM-1-I. Our results indicate a dramatic increase in extravascular ICAM-1-I associated to GFAP-IR astrocytes in the ORB in normal aging. This increase may contribute to an enhanced risk for brain inflammatory processes during aging, although a role of extravascular ICAM-1 as a barrier to further inflammation cannot be ruled out.

Neuroimmune-endocrine crosstalk in schizophrenia and mood disorders

This review focuses on possible causes and the impact of different immune states in schizophrenia and major depression. It discusses the fact that, in schizophrenia, an over-activation of the type 2 immune response may dominate, while the type 1 and the pro-inflammatory immune responses are over-activated in major depression. The consequence of these diverse immune states is the activation and, respectively, inhibition of different enzymes in tryptophan/kynurenine metabolism, which may lead to an overemphasis of N-methyl-D-aspartate (NMDA) receptor antagonism in schizophrenia and of NMDA-receptor agonism in depression, resulting in glutamatergic hypofunction in schizophrenia and glutamatergic hyperfunction in major depression. In addition, the activation of the type 1 and the pro-inflammatory immune responses in major depression result in increased serotonin degradation and a serotonergic deficit. While antipsychotics and antidepressants today mainly act on the dopaminergic-glutamatergic and the noradrenergic-serotonergic neurotransmission, anti-inflammatory and immune-modulating therapies might act more basically at the pathophysiological mechanism. The limitations of this concept, however, are critically discussed.

Age, rapid-cycling, and pharmacotherapy effects on ventral prefrontal cortex in bipolar disorder: a cross-sectional study

BACKGROUND

Neuroimaging data suggest that deficits in ventral prefrontal cortex (VPFC) function in bipolar disorder (BD) progress during adolescence and young adulthood. However, the developmental trajectory of VPFC morphological abnormalities in BD is unknown. This study investigated potential age-dependent volume abnormalities in VPFC in BD.

METHODS

Thirty-seven individuals diagnosed with BD I (14 adolescents, 10 young adults and 13 older adults) and 56 healthy comparison subjects (HC) participated in imaging. Gray and white matter volumes of VPFC were measured using high-resolution structural magnetic resonance imaging (MRI). We used a mixed model, repeated measures analysis to examine VPFC volumes across age groups while co-varying for total brain volume. Potential effects of illness features including rapid-cycling and medication were explored.

RESULTS

VPFC volumes declined with age (p < .001). The diagnosis-by-age group interaction was significant (p = .01). Relative to HC subjects, VPFC gray and white matter volumes were significantly smaller in BD patients only in young adulthood (p = .04). In participants with BD, VPFC volumes were significantly smaller in participants with rapid-cycling than participants without rapid-cycling (p = .02). Conversely, current use of medication was associated with larger VPFC gray matter volumes (p = .005), independent of age.

CONCLUSIONS

These preliminary findings suggest the presence of a more rapid initial decline in VPFC volumes with age in adolescents and young adults with BD than HC. These findings also suggest that the rapid-cycling subtype of BD is associated with larger VPFC volume deficits than the non-rapid-cycling subtype, and that pharmacotherapy may have trophic or protective effects on VPFC volumes in BD patients.

Beyond monoamines: glutamatergic function in mood disorders

The monoamine theory has implicated abnormalities in serotonin and norepinephrine in the pathophysiology of major depression and bipolar illness and contributed greatly to our understanding of mood disorders and their treatment. Nevertheless, some limitations of this model still exist that require researchers and clinicians to seek further explanation and develop novel interventions that reach beyond the confines of the monoaminergic systems. Recent studies have provided strong evidence that glutamate and other amino acid neurotransmitters are involved in the pathophysiology and treatment of mood disorders. Studies employing in vivo magnetic resonance spectroscopy have revealed altered cortical glutamate levels in depressed subjects. Consistent with a model of excessive glutamate-induced excitation in mood disorders, several antiglutamatergic agents, such as riluzole and lamotrigine, have demonstrated potential antidepressant efficacy. Glial cell abnormalities commonly associated with mood disorders may at least partly account for the impairment in glutamate action since glial cells play a primary role in synaptic glutamate removal. A hypothetical model of altered glutamatergic function in mood disorders is proposed in conjunction with potential antidepressant mechanisms of antiglutamatergic agents. Further studies elucidating the role of the glutamatergic system in the pathophysiology of mood and anxiety disorders and studies exploring the efficacy and mechanism of action of antiglutamatergic agents in these disorders, are likely to provide new targets for the development of novel antidepressant agents.

Prominent reduction in pyramidal neurons density in the orbitofrontal cortex of elderly depressed patients

BACKGROUND

Elderly depressed patients have more vascular hyperintensities in frontal white matter and basal ganglia than elderly control subjects. Cell pathology that might be related to increased vascular hyperintensities has not been examined.

METHODS

Postmortem samples from the orbitofrontal cortex (ORB) were collected in 15 elderly subjects with major depressive disorder (MDD) and 11 age-matched control subjects. Cell packing density of neurons and glia, density of pyramidal and nonpyramidal neurons, and cortical and laminar width were measured.

RESULTS

The overall (layers I-VI) packing density of ORB neurons with pyramidal morphology was markedly decreased in MDD (by 30%) as compared with control subjects. Further laminar analysis of pyramidal neurons density revealed significant reductions in layers IIIc and V in MDD. In contrast, in MDD the density of nonpyramidal neurons and glia and cortical and laminar width were comparable to control values.

CONCLUSIONS

In elderly subjects with depression, the density of pyramidal neurons in the ORB was particularly low in cortical layers V and III, the origin of prefronto-striatal and prefronto-cortical and prefronto-amygdalar projections. Degeneration of neurons furnishing these projections might be related to the white matter hyperintensities previously observed. Neuronal pathology seems to be more severe in elderly than in younger subjects with MDD.

Proton spectroscopy study of the left dorsolateral prefrontal cortex in pediatric depressed patients

The dorsolateral prefrontal cortex (DLPFC) plays an essential role in mood regulation and integration of cognitive functions that are abnormal in major depressive disorder (MDD). Few neuroimaging studies have evaluated the still maturing DLPFC in depressed children and adolescents. We conducted single voxel proton magnetic resonance spectroscopy ((1)H MRS) of the left DLPFC in 14 depressed children and adolescents (13.3 +/- 2.3 years old, 10 males) and 22 matched healthy controls (13.6 +/- 2.8 years old, 13 males). Depressed subjects had significantly lower levels of glycerophosphocholine plus phosphocholine (GPC + PC; or choline-containing compounds) and higher myo-inositol levels in the left DLPFC compared to healthy controls. In the depressed subjects, we found significant inverse correlations between glutamate levels and both duration of illness and number of episodes. In healthy controls there was a significant direct correlation between age and glutamine levels, which was not present in the patient group. Lower GPC + PC levels in pediatric MDD may reflect lower cell membrane content per volume in the DLPFC. Increased myo-inositol levels in MDD may represent a disturbed secondary messenger system. GPC + PC and myo-inositol abnormalities further demonstrate the involvement of DLPFC in pediatric MDD.

Lower packing density of glial fibrillary acidic protein-immunoreactive astrocytes in the prelimbic cortex of alcohol-naive and alcohol-drinking alcohol-preferring rats as compared with alcohol-nonpreferring and Wistar rats

BACKGROUND

Low packing density of glial cells, possibly astrocytes, has been described in the prefrontal cortex and hippocampus of "uncomplicated" alcoholics. Astrocytes perform crucial support functions in the processing of neurotransmitters and transfer of energy substrates from blood to cortical neurons. It is still unknown whether attrition in the numbers of astrocytes is only a consequence of prolonged alcohol abuse or also predates the exposure to alcohol in subjects at risk for alcohol dependence.

METHODS

We used alcohol-preferring (P) rats exposed ad libitum for 2 or 6 months to either water only or 10% ethanol and alcohol-nonpreferring (NP) rats and nonselected Wistar rats exposed only to water for 2 months. Sections through the rat frontal cortex were immunostained for glial fibrillary acidic protein (GFAP), a specific marker of astrocytes. The packing density of GFAP-immunoreactive (IR) astrocytes and the area fraction of GFAP immunoreactivity were measured in the prelimbic cortex (PLC) using the dissector probe and analysis of binary images of GFAP immunostaining, respectively.

RESULTS

The packing density of GFAP-IR astrocytes was significantly lower in both alcohol-naive and alcohol-exposed P rats than in NP rats or Wistar rats. The area fraction of GFAP immunoreactivity was significantly lower in the alcohol-exposed P rats than in NP rats, Wistar rats, and alcohol-naive P rats.

CONCLUSION

These results suggest that low density of GFAP-IR astrocytes in the PLC of P rats predates the exposure to alcohol and might be a factor contributing to the increased risk for alcohol dependence. In addition, prolonged free-choice alcohol drinking may reduce the extent of GFAP-IR processes in the PLC of P rats.

Proteomic analysis of glial fibrillary acidic protein in Alzheimer's disease and aging brain

Chronic inflammation is known to play an important role in the heterogeneous pathogenesis of Alzheimer's disease (AD). Activated astrocytes expressing glial fibrillary acidic protein (GFAP) are closely associated with AD pathology, such as tangles, neuritic plaques and amyloid depositions. Altogether, 46 soluble isoforms of GFAP were separated and most of them quantified by two-dimensional immunoblotting in frontal cortices of AD patients and age-matched controls. A 60% increase in the amount of more acidic isoforms of GFAP was observed in AD and these isoforms were both phosphorylated and N-glycosylated, while more basic isoforms were O-glycosylated and exhibited no quantitative differences between post-mortem AD and control brains. These data highlight the importance of exploring isoform-specific levels of proteins in pathophysiological conditions since modifications of proteins determine their activity state, localization, turnover and interaction with other molecules. Mechanisms, structures and functional consequences of modification of GFAP isoforms remain to be clarified.

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.

Depression, cytokines, and glial function

It has been known for some time that cytokines made and released during systemic illness can result in a constellation of symptoms strikingly similar to those observed in depression. The overlap of the symptoms of depression and systemic illness raises the intriguing possibility that cytokines may be involved in the development and maintenance of mood disorders. Cytokines are small ubiquitous pleiotropic molecules that are made and released in response to a variety of stimuli. They have a multitude of actions throughout the body, including actions on the central and peripheral nervous systems. Alterations in the levels of circulating cytokines, especially the key proinflammatory cytokines, interleukin 6 and tumor necrosis factor alpha , have been linked to a variety of disease states including those involving central nervous system depression. In this brief review, epidemiological and clinical data on depression, as well as findings from relevant animal models, are examined for links between cytokine expression and depression. We suggest that glial cells, both as a source and target of cytokines, represent the overlooked targets involved in the etiology of depression.

Aging, stress and the hippocampus

Functional loss often occurs in many body systems (e.g., endocrine, cognitive, motor) with the passage of years, but there is great individual variation in the degree of compromise shown. The current focus on brain aging will continue because demographic trends indicate that the average lifespan will show a continued increase. There is increasing emphasis on understanding how aging contributes to a decline in brain functions, cognition being a prime example. This is due in part to the fact that dementias and other losses in brain function that sometimes accompany aging cause an obvious decline in the quality of life and these deficits are of more concern as the number of elderly increase. Stress also is a ubiquitous aspect of life and there is now a greater interest in understanding the role of stress and the stress response in brain aging. The key role of the hippocampus and its related brain structures in cognition, as well as in the feedback control of the response to stress, have made this brain area a logical focus of investigation for those interested in the impact of stress on brain aging. Here, we describe how the hippocampus changes with age and we examine the idea that age-related changes in the secretion patterns of the hypothalamic-pituitary adrenal (HPA) axis can contribute to aging of this structure. We also examine the proposal that stress, perhaps due to compromised HPA axis function, can contribute to hippocampal aging through exposure to excessive levels of glucocorticoids. The aging hippocampus does not appear to suffer a generalized loss of cells or synapses, although atrophy of the structure may occur in humans. Thus, age-related cognitive impairments are likely related to other neurobiological alterations that could include changes in the signaling, information encoding, plasticity, electrophysiological or neurochemical properties of neurons or glia. Although excessive levels of glucocorticoids are able to interfere with cognition, as well as hippocampal neuronal integrity, and aging is sometimes accompanied by an increase in these steroids because of inadequate feedback control of the HPA axis, none of these are a foregone consequence of aging. The general preservation of cells and the plastic potential of the hippocampus provide a focus for the development of pharmacological, nutritive or lifestyle strategies to combat age-related declines in the hippocampus as well as other brain areas.