Chronic lithium treatment decreases NG2 cell proliferation in rat dentate hilus, amygdala and corpus callosum

Adult Neural Stem Cells as Promising Targets in Psychiatric Disorders

The development of new therapies for psychiatric disorders is of utmost importance, given the enormous toll these disorders pose to society nowadays. This should be based on the identification of neural substrates and mechanisms that underlie disease etiopathophysiology. Adult neural stem cells (NSCs) have been emerging as a promising platform to counteract brain damage. In this perspective article, we put forth a detailed view of how NSCs operate in the adult brain and influence brain homeostasis, having profound implications at both behavioral and functional levels. We appraise evidence suggesting that adult NSCs play important roles in regulating several forms of brain plasticity, particularly emotional and cognitive flexibility, and that NSC dynamics are altered upon brain pathology. Furthermore, we discuss the potential therapeutic value of utilizing adult endogenous NSCs as vessels for regeneration, highlighting their importance as targets for the treatment of multiple mental illnesses, such as affective disorders, schizophrenia, and addiction. Finally, we speculate on strategies to surpass current challenges in neuropsychiatric disease modeling and brain repair.

Clinical Findings Documenting Cellular and Molecular Abnormalities of Glia in Depressive Disorders

Depressive disorders are complex, multifactorial mental disorders with unknown neurobiology. Numerous theories aim to explain the pathophysiology. According to the “gliocentric theory”, glial abnormalities are responsible for the development of the disease. The aim of this review article is to summarize the rapidly growing number of cellular and molecular evidences indicating disturbed glial functioning in depressive disorders. We focus here exclusively on the clinical studies and present the in vivo neuroimaging findings together with the postmortem molecular and histopathological data. Postmortem studies demonstrate glial cell loss while the in vivo imaging data reveal disturbed glial functioning and altered white matter microstructure. Molecular studies report on altered gene expression of glial specific genes. In sum, the clinical findings provide ample evidences on glial pathology and demonstrate that all major glial cell types are affected. However, we still lack convincing theories explaining how the glial abnormalities develop and how exactly contribute to the emotional and cognitive disturbances. Abnormal astrocytic functioning may lead to disturbed metabolism affecting ion homeostasis and glutamate clearance, which in turn, affect synaptic communication. Abnormal oligodendrocyte functioning may disrupt the connectivity of neuronal networks, while microglial activation indicates neuroinflammatory processes. These cellular changes may relate to each other or they may indicate different endophenotypes. A theory has been put forward that the stress-induced inflammation—mediated by microglial activation—triggers a cascade of events leading to damaged astrocytes and oligodendroglia and consequently to their dysfunctions. The clinical data support the “gliocentric” theory, but future research should clarify whether these glial changes are truly the cause or simply the consequences of this devastating disorder.

A New Outlook on Mental Illnesses: Glial Involvement Beyond the Glue

Mental illnesses have long been perceived as the exclusive consequence of abnormalities in neuronal functioning. Until recently, the role of glial cells in the pathophysiology of mental diseases has largely been overlooked. However recently, multiple lines of evidence suggest more diverse and significant functions of glia with behavior-altering effects. The newly ascribed roles of astrocytes, oligodendrocytes and microglia have led to their examination in brain pathology and mental illnesses. Indeed, abnormalities in glial function, structure and density have been observed in postmortem brain studies of subjects diagnosed with mental illnesses. In this review, we discuss the newly identified functions of glia and highlight the findings of glial abnormalities in psychiatric disorders. We discuss these preclinical and clinical findings implicating the involvement of glial cells in mental illnesses with the perspective that these cells may represent a new target for treatment.

Proliferating cells in the adolescent rat amygdala: Characterization and response to stress

The amygdala is a heterogeneous group of nuclei that plays a role in emotional and social learning. As such, there has been increased interest in its development in adolescent animals, a period in which emotional/social learning increases dramatically. While many mechanisms of amygdala development have been studied, the role of cell proliferation during adolescence has received less attention. Using bromodeoxyuridine (BrdU) injections in adolescent and adult rats, we previously found an almost fivefold increase in BrdU-positive cells in the amygdala of adolescents compared to adults. Approximately one third of BrdU-labeled cells in the amygdala contained the putative neural marker doublecortin (DCX), suggesting a potential for neurogenesis. To further investigate this possibility in adolescents, we examined the proliferative dynamics of DCX/BrdU-labeled cells. Surprisingly, DCX/BrdU-positive cells were found to comprise a stable subpopulation of BrdU-containing cells across survivals up to 56 days, and there was no evidence of neural maturation by 28 days after BrdU injection. Additionally, we found that approximately 50% of BrdU+ cells within the adolescent amygdala contain neural-glial antigen (NG2) and are therefore presumptive oligodendrocyte precursors (OPCs). We next characterized the response to a short-lived stressor (3-day repeated variable stress, RVS). The total BrdU-labeled cell number decreased by ∼30% by 13 days following RVS (10 days post-BrdU injection) as assessed by stereologic counting methods, but the DCX/BrdU-labeled subpopulation was relatively resistant to RVS effects. In contrast, NG2/BrdU-labeled cells were strongly influenced by RVS. We conclude that typical neurogenesis is not a feature of the adolescent amygdala. These findings point to several possibilities, including the possibility that DCX/BrdU cells are late-developing neural precursors, or a unique subtype of NG2 cell that is relatively resistant to stress. In contrast, many proliferating OPCs are significantly impacted by a short-lived stressor, suggesting consequences for myelination in the developing amygdala.

Role of NG2 expressing cells in addiction: a new approach for an old problem

Neuron-glial antigen 2 (NG2) is a proteoglycan expressed predominantly in oligodendrocyte progenitor cells (OPCs). NG2-expressing OPCs (NG2-OPCs) are self-renewing cells that are widely distributed in the gray and white matter areas of the central nervous system. NG2-OPCs can mature into premyelinating oligodendrocytes and myelinating oligodendroglia which serve as the primary source of myelin in the brain. This review characterizes NG2-OPCs in brain structure and function, conceptualizes the role of NG2-OPCs in brain regions associated with negative reinforcement and relapse to drug seeking and discusses how NG2-OPCs are regulated by neuromodulators linked to motivational withdrawal. We hope to provide the readers with an overview of the role of NG2-OPCs in brain structure and function in the context of negative affect state in substance abuse disorders and to integrate our current understanding of the physiological significance of the NG2-OPCs in the adult brain.

Evidence for morphological alterations in prefrontal white matter glia in schizophrenia and bipolar disorder

BACKGROUND

Brain imaging studies suggest that volume reductions and compromised white matter integrity occur in schizophrenia and bipolar disorder (BD). However, the cellular correlates have not yet been identified. To address this issue we assessed oligodendrocyte, astrocyte and microglial populations in postmortem white matter from schizophrenia, BD and nonpsychiatric control samples.

METHODS

The density, areal fraction and spatial distribution of glial fibrillary acidic protein (GFAP)-expressing astrocytes and ionized calcium-binding adaptor molecule-1 (IBA-1)-expressing microglia as well as the density, nuclear size and spatial distribution of Nissl-stained oligodendrocytes were quantified in postmortem white matter adjacent to the dorsolateral prefrontal cortex (Brodmann area 9) in schizophrenia, BD and control samples (n = 20). In addition, the oligodendrocyte-associated proteins myelin basic protein and 2,3-cyclic-nucleotide 3-phosphodiesterase (CNPase) were quantified in the same samples by enzyme-linked immunosorbent assay and immunoblotting.

RESULTS

Oligodendrocyte density (p = 0.012) and CNPase protein levels (p = 0.038) differed between groups, being increased in BD compared with control samples. The GFAP area fraction (p = 0.05) and astrocyte spatial distribution (p = 0.040) also differed between groups, reflecting decreased area fraction and increased cell clustering in both schizophrenia and BD samples.

LIMITATIONS

Oligodendrocytes were identified using morphological criteria.

CONCLUSION

This study provides evidence for glial pathology in prefrontal white matter in schizophrenia and BD. Changes in oligodendrocyte and astrocyte populations in white matter in the major psychiatric disorders may reflect disruptions in structural or metabolic support of axons.

Differences in amygdala cell proliferation between adolescent and young adult rats

Adolescence is characterized by changes in both behavior and neural organization. During this period, the amygdala, a structure that mediates social and emotional behaviors, is changing in terms of neural and glia density. We examined cell proliferation within the amygdala of adolescent (post natal day (PND) 31) and adult (PND 70) male Sprague-Dawley rats using BrdU (bromodeoxyuridine) to label dividing cells. BrdU-labeled cells were distributed throughout the amygdala, often found in fibers surrounding major nuclei. Using two independent cell counting strategies under light and confocal microcopy, respectively, we found significantly more labeled cells in the amygdala in adolescent compared to adult animals (239.3 ± 87.18 vs. 44.75 ± 13.68; n=4/group; p<.05). BrdU/doublecortin (DCX) positive cells constitute approximately 30% of all dividing cells in the amygdala in both adolescents and adults. These data suggest that compared to young adulthood, adolescence is a relatively active period of cell proliferation in the amygdala. Moreover, the normal decline in dividing cells with age does not preferentially affect cells co-containing DCX-immunoreactivity.

NG2 cells, a new trail for Alzheimer's disease mechanisms?

Background

Neuron Glial 2 (NG2) cells are glial cells known to serve as oligodendrocyte progenitors as well as modulators of the neuronal network. Altered NG2 cell morphology and up-regulation as well as increased shedding of the proteoglycan NG2 expressed on the cell surface have been described in rodent models of brain injury. Here we describe alterations in the human NG2 cell population in response to pathological changes characteristic of Alzheimer’s disease (AD).

Results

Immunohistological stainings of postmortem brain specimens from clinically diagnosed and postmortem verified AD patients and non-demented controls revealed reduced NG2 immunoreactivity as well as large numbers of NG2 positive astrocytes in individuals with high amyloid beta plaque load. Since fibrillar amyloid beta (Aβ)1-42 is the major component of AD-related senile plaques, we exposed human NG2 cells to oligomer- and fibril enriched preparations of Aβ1-42. We found that both oligomeric and fibrillar Aβ1-42 induced changes in NG2 cell morphology. Further, in vitro exposure to fibrillar Aβ1-42 decreased the NG2 concentrations in both cell lysates and supernatants. Interestingly, we also found significantly decreased levels of soluble NG2 in the cerebrospinal fluid (CSF) from clinically diagnosed AD patients compared to non-demented individuals. Additionally, the CSF NG2 levels were found to significantly correlate with the core AD biomarkers Aß1-42, T-tau and P-tau.

Conclusion

Our results demonstrate major alterations in the NG2 cell population in relation to AD pathology which highlights the NG2 cell population as a new attractive research target in the search for cellular mechanisms associated with AD pathogenesis.

Electronic supplementary material

The online version of this article (doi:10.1186/2051-5960-1-7) contains supplementary material, which is available to authorized users.

The clinical implications of cognitive impairment and allostatic load in bipolar disorder

BACKGROUND

Allostatic load (AL) relates to the neural and bodily "wear and tear" that emerge in the context of chronic stress. This paper aims to provide clinicians with a comprehensive overview of the role of AL in patophysiology of bipolar disorder (BD) and its practical implications.

METHODS

PubMed searches were conducted on English-language articles published from 1970 to June 2011 using the search terms allostatic load, oxidative stress, staging, and bipolar disorder cross-referenced with cognitive impairment, comorbidity, mediators, prevention.

RESULTS

Progressive neural and physical dysfunction consequent to mood episodes in BD can be construed as a cumulative state of AL. The concept of AL can help to reconcile cognitive impairment and increased rates of clinical comorbidities that occur over the course of cumulative BD episodes.

CONCLUSIONS

Data on transduction of psychosocial stress into the neurobiology of mood episodes converges to the concept of AL. Mood episodes prevention would not only alleviate emotional suffering, but also arrest the cycle of AL, cognitive decline, physical morbidities and, eventually, related mortality. These objectives can be achieved by focusing on effective prophylaxis from the first stages of the disorder, providing mood-stabilizing agents and standardized psychoeducation and, potentially, addressing cognitive deficits by the means of specific medication and neuropsychological interventions.

Understanding aberrant white matter development in schizophrenia: an avenue for therapy?

Although historically gray matter changes have been the focus of neuropathological and neuroradiological studies in schizophrenia, in recent years an increasing body of research has implicated white matter structures and its constituent components (axons, their myelin sheaths and supporting oligodendrocytes). This article summarizes this body of literature, examining neuropathological, neurogenetic and neuroradiological evidence for white matter pathology in schizophrenia. We then look at the possible role that antipsychotic medication may play in these studies, examining both its role as a potential confounder in studies examining neuronal density and brain volume, but also the possible role that these medications may play in promoting myelination through their effects on oligodendrocytes. Finally, the role of potential novel therapies is discussed.

Lithium suppresses astrogliogenesis by neural stem and progenitor cells by inhibiting STAT3 pathway independently of glycogen synthase kinase 3 beta

Transplanted neural stem and progenitor cells (NSCs) produce mostly astrocytes in injured spinal cords. Lithium stimulates neurogenesis by inhibiting GSK3b (glycogen synthetase kinase 3-beta) and increasing WNT/beta catenin. Lithium suppresses astrogliogenesis but the mechanisms were unclear. We cultured NSCs from subventricular zone of neonatal rats and showed that lithium reduced NSC production of astrocytes as well as proliferation of glia restricted progenitor (GRP) cells. Lithium strongly inhibited STAT3 (signal transducer and activator of transcription 3) activation, a messenger system known to promote astrogliogenesis and cancer. Lithium abolished STAT3 activation and astrogliogenesis induced by a STAT3 agonist AICAR (5-aminoimidazole-4-carboxamide 1-beta-D-ribofuranoside), suggesting that lithium suppresses astrogliogenesis by inhibiting STAT3. GSK3β inhibition either by a specific GSK3β inhibitor SB216763 or overexpression of GID5-6 (GSK3β Interaction Domain aa380 to 404) did not suppress astrogliogenesis and GRP proliferation. GSK3β inhibition also did not suppress STAT3 activation. Together, these results indicate that lithium inhibits astrogliogenesis through non-GSK3β-mediated inhibition of STAT. Lithium may increase efficacy of NSC transplants by increasing neurogenesis and reducing astrogliogenesis. Our results also may explain the strong safety record of lithium treatment of manic depression. Millions of people take high-dose (>1 gram/day) lithium carbonate for a lifetime. GSK3b inhibition increases WNT/beta catenin, associated with colon and other cancers. STAT3 inhibition may reduce risk for cancer.

Canonical Wnt signalling requires the BMP pathway to inhibit oligodendrocyte maturation

OLs (oligodendrocytes) are the myelinating cells of the CNS (central nervous system), wrapping axons in conductive sheathes to ensure effective transmission of neural signals. The regulation of OL development, from precursor to mature myelinating cell, is controlled by a variety of inhibitory and inductive signalling factors. The dorsal spinal cord contains signals that inhibit OL development, possibly to prevent premature and ectopic precursor differentiation. The Wnt and BMP (bone morphogenic protein) signalling pathways have been identified as dorsal spinal cord signals with overlapping temporal activity, and both have similar inhibitory effects on OL differentiation. Both these pathways feature prominently in many developmental processes and demyelinating events after injury, and they are known to interact in complex inductive, inhibitive and synergistic manners in many developing systems. The interaction between BMP and Wnt signalling in OL development, however, has not been extensively explored. In the present study, we examine the relationship between the canonical Wnt and BMP pathways. We use pharmacological and genetic paradigms to show that both Wnt3a and BMP4 will inhibit OL differentiation in vitro. We also show that when the canonical BMP signalling pathway is blocked, neither Wnt3a nor BMP4 have inhibitory effects on OL differentiation. In contrast, abrogating the Wnt signalling pathway does not alter the actions of BMP4 treatment. Our results indicate that the BMP signalling pathway is necessary for the canonical Wnt signalling pathway to exert its effects on OL development, but not vice versa, suggesting that Wnt signals upstream of BMP.

The effects of lithium and anticonvulsants on brain structure in bipolar disorder

OBJECTIVE

To investigate the effect of lithium, anticonvulsants and antipsychotics on brain structure in bipolar disorder (BD).

METHOD

A cross-sectional structural brain magnetic resonance imaging study of 74 remitted patients with BD, aged 18-65, who were receiving long-term prophylactic treatment with lithium or anticonvulsants or antipsychotics. Global and regional grey matter, white matter, and cerebrospinal fluid volumes were compared between treatment groups.

RESULTS

Grey matter in the subgenual anterior cingulate gyrus on the right (extending into the hypothalamus) and in the postcentral gyrus, the hippocampus/amygdale complex and the insula on the left was greater in BD patients on lithium treatment compared to all other treatment groups.

CONCLUSION

Lithium treatment in BD has a significant effect on brain structure particularly in limbic/paralimbic regions associated with emotional processing.

Astrocytes in the amygdala

The amygdala has received considerable attention because of its established role in specific behaviors and disorders such as anxiety, depression, and autism. Studies have revealed that the amygdala is a complex and dynamic brain region that is highly connected with other areas of the brain. Previous works have focused on neurons, demonstrating that the amygdala in rodents is highly plastic and sexually dimorphic. However, our more recent work explores sex differences in nonneuronal cells, joining a rich literature concerning glia in the amygdala. Prior investigation of glia in the amygdala can generally be divided into disease-related and hormone-related categories, with both areas of research producing interesting findings concerning glia in this important brain region. Despite a wide range of research topics, the collected findings make it clear that glia in the amygdala are sensitive and plastic cells that respond and develop in a highly region specific manner.