Molecular Neuropathology of Astrocytes and Oligodendrocytes in Alcohol Use Disorders.

Postmortem studies reveal structural and molecular alterations of astrocytes and oligodendrocytes in both the gray and white matter (GM and WM) of the prefrontal cortex (PFC) in human subjects with chronic alcohol abuse or dependence. These glial cellular changes appear to parallel and may largely explain structural and functional alterations detected using neuroimaging techniques in subjects with alcohol use disorders (AUDs). Moreover, due to the crucial roles of astrocytes and oligodendrocytes in neurotransmission and signal conduction, these cells are very likely major players in the molecular mechanisms underpinning alcoholism-related connectivity disturbances between the PFC and relevant interconnecting brain regions. The glia-mediated etiology of alcohol-related brain damage is likely multifactorial since metabolic, hormonal, hepatic and hemodynamic factors as well as direct actions of ethanol or its metabolites have the potential to disrupt distinct aspects of glial neurobiology. Studies in animal models of alcoholism and postmortem human brains have identified astrocyte markers altered in response to significant exposures to ethanol or during alcohol withdrawal, such as gap-junction proteins, glutamate transporters or enzymes related to glutamate and gamma-aminobutyric acid (GABA) metabolism. Changes in these proteins and their regulatory pathways would not only cause GM neuronal dysfunction, but also disturbances in the ability of WM axons to convey impulses. In addition, alcoholism alters the expression of astrocyte and myelin proteins and of oligodendrocyte transcription factors important for the maintenance and plasticity of myelin sheaths in WM and GM. These changes are concomitant with epigenetic DNA and histone modifications as well as alterations in regulatory microRNAs (miRNAs) that likely cause profound disturbances of gene expression and protein translation. Knowledge is also available about interactions between astrocytes and oligodendrocytes not only at the Nodes of Ranvier (NR), but also in gap junction-based astrocyte-oligodendrocyte contacts and other forms of cell-to-cell communication now understood to be critical for the maintenance and formation of myelin. Close interactions between astrocytes and oligodendrocytes also suggest that therapies for alcoholism based on a specific glial cell type pathology will require a better understanding of molecular interactions between different cell types, as well as considering the possibility of using combined molecular approaches for more effective therapies.

Length of axons expressing the serotonin transporter in orbitofrontal cortex is lower with age in depression.

Studies of major depressive disorder (MDD) in postmortem brain tissue report enhanced binding to inhibitory serotonin-1A autoreceptors in midbrain dorsal raphe and reductions in length of axons expressing the serotonin transporter (SERT) in dorsolateral prefrontal cortex. The length density of axons expressing SERT in the orbitofrontal cortex (OFC) was determined in 18 subjects with MDD and 17 age-matched control subjects. A monoclonal antibody was used to immunohistochemically label the SERT in fixed sections of OFC. The 3-dimensional length density of SERT-immunoreactive (ir) axons in layer VI of OFC was estimated. The age of subjects with MDD was negatively correlated with SERT axon length (r=-0.77, p<0.0005). The significant effect of age persisted when removing four depressed subjects with an antidepressant medication present at the time of death, or when removing nine depressed subjects that had a recent prescription for an antidepressant medication. Neither gender, tissue pH, postmortem interval, 5-HTTLPR genotype, time in fixative, nor death by suicide had a significant effect on axon length. The age-related decrease in SERT-ir axon length in MDD may reflect pathology of ascending axons passing through deep white matter hyperintensities. Greater length of axons expressing SERT in younger subjects with MDD may result in a significant deficit in serotonin availability in OFC.

Basolateral amygdala volume and cell numbers in major depressive disorder: a postmortem stereological study.

Functional imaging studies consistently report abnormal amygdala activity in major depressive disorder (MDD). Neuroanatomical correlates are less clear: imaging studies have produced mixed results on amygdala volume, and postmortem neuroanatomic studies have only examined cell densities in portions of the amygdala or its subregions in MDD. Here, we present a stereological analysis of the volume of, and the total number of, neurons, glia, and neurovascular (pericyte and endothelial) cells in the basolateral amygdala in MDD. Postmortem tissues from 13 subjects with MDD and 10 controls were examined. Sections (~15/subject) taken throughout the rostral-caudal extent of the basolateral amygdala (BLA) were stained for Nissl substance and utilized for stereological estimation of volume and cell numbers. Results indicate that depressed subjects had a larger lateral nucleus than controls and a greater number of total BLA neurovascular cells than controls. There were no differences in the number or density of neurons or glia between depressed and control subjects. These findings present a more detailed picture of BLA cellular anatomy in depression than has previously been available. Further studies are needed to determine whether the greater number of neurovascular cells in depressed subjects may be related to increased amygdala activity in depression.

Markers of apoptosis induction and proliferation in the orbitofrontal cortex in alcohol dependence.

BACKGROUND: Alcohol-dependent (ALC) subjects exhibit glial and neuronal pathology in the prefrontal cortex (PFC). However, in many patients, neurophysiological disturbances are not associated with catastrophic cell depletion despite prolonged alcohol abuse. It is still unclear how some relevant markers of a cell's propensity to degenerate or proliferate are changed in the PFC of ALC subjects without major neurological disorders. METHODS: Levels of pro-apoptotic caspase 8 (C8), X-linked inhibitor of apoptosis protein (XIAP), direct IAP binding protein with low pI (DIABLO), proliferating cell nuclear antigen (PCNA), and density of cells immunoreactive for proliferation marker Ki-67 (Ki-67-IR) were measured postmortem in the left orbitofrontal cortex (OFC) of 29 subjects with alcohol dependence and 23 nonpsychiatric comparison subjects. RESULTS: Alcohol subjects had significantly higher levels of the 14 kDa C8 fragment (C8-14), an indicator of C8 activation. However, there was no change in the levels of DIABLO, XIAP, or in the DIABLO/XIAP ratio. PCNA protein level and density of Ki-67-IR cells were not significantly changed in alcoholics, although PCNA levels were increased in older ALC subjects as compared to controls. CONCLUSIONS: Significant increase of a C8 activation indicator was found in alcoholism, but without significant changes in XIAP level, DIABLO/XIAP ratio, or Ki-67 labeling. These results would help to explain the absence of catastrophic cell loss in the PFC of many Brigman subjects, while still being consistent with an alcoholism-related vulnerability to slow decline in glial cells and neurons in the OFC of alcoholics.

Apoptosis-related proteins and proliferation markers in the orbitofrontal cortex in major depressive disorder.

BACKGROUND: In major depressive disorder (MDD), lowered neural activity and significant reductions of markers of cell resiliency to degeneration occur in the prefrontal cortex (PFC). It is still unclear whether changes in other relevant markers of cell vulnerability to degeneration and markers of cell proliferation are associated with MDD. METHODS: Levels of caspase 8 (C8), X-linked inhibitor of apoptosis protein (XIAP), direct IAP binding protein with low pI (DIABLO), proliferating cell nuclear antigen (PCNA) and density of cells immunoreactive (-IR) for proliferation marker Ki-67 were measured in postmortem samples of the left orbitofrontal cortex (OFC) of subjects with MDD, and psychiatrically-normal comparison subjects. RESULTS: There was significant increase in C8, a higher ratio of DIABLO to XIAP, lower packing density of Ki-67-IR cells, and an unexpected age-dependent increase in PCNA in subjects with MDD vs. controls. PCNA levels were significantly higher in MDD subjects unresponsive to antidepressants or untreated with antidepressants. The DIABLO/XIAP ratio was higher in MDD subjects without antidepressants than in comparison subjects. LIMITATIONS: Qualitative nature of responsiveness assessments; definition of resistance to antidepressant treatment is still controversial; and unclear role of PCNA. CONCLUSIONS: Markers of cell vulnerability to degeneration are increased and density of Ki67-positive cells is low MDD, but accompanied by normal XIAP levels. The results suggest increased vulnerability to cell pathology in depression that is insufficient to cause morphologically conspicuous cell death. Persistent but low-grade vulnerability to cell degeneration coexisting with reduced proliferation readiness may explain age-dependent reductions in neuronal densities in the OFC of depressed subjects.

Decreased expression of Freud-1/CC2D1A, a transcriptional repressor of the 5-HT1A receptor, in the prefrontal cortex of subjects with major depression.

Serotonin1A (5-HT(1A)) receptors are reported altered in the brain of subjects with major depressive disorder (MDD). Recent studies have identified transcriptional regulators of the 5-HT(1A) receptor and have documented gender-specific alterations in 5-HT(1A) transcription factor and 5-HT(1A) receptors in female MDD subjects. The 5' repressor element under dual repression binding protein-1 (Freud-1) is a calcium-regulated repressor that negatively regulates the 5-HT(1A) receptor gene. This study documented the cellular expression of Freud-1 in the human prefrontal cortex (PFC) and quantified Freud-1 protein in the PFC of MDD and control subjects as well as in the PFC of rhesus monkeys chronically treated with fluoxetine. Freud-1 immunoreactivity was present in neurons and glia and was co-localized with 5-HT(1A) receptors. Freud-1 protein level was significantly decreased in the PFC of male MDD subjects (37%, p=0.02) relative to gender-matched control subjects. Freud-1 protein was also reduced in the PFC of female MDD subjects (36%, p=0.18) but was not statistically significant. When the data was combined across genders and analysed by age, the decrease in Freud-1 protein level was greater in the younger MDD subjects (48%, p=0.01) relative to age-matched controls as opposed to older depressed subjects. Similarly, 5-HT(1A) receptor protein was significantly reduced in the PFC of the younger MDD subjects (48%, p=0.01) relative to age-matched controls. Adult male rhesus monkeys administered fluoxetine daily for 39 wk revealed no significant change in cortical Freud-1 or 5-HT(1A) receptor proteins compared to vehicle-treated control monkeys. Reduced protein expression of Freud-1 in MDD subjects may reflect dysregulation of this transcription factor, which may contribute to the altered regulation of 5-HT(1A) receptors observed in subjects with MDD. These data may also suggest that reductions in Freud-1 protein expression in the PFC may be associated with early onset of MDD.

Elevated level of metabotropic glutamate receptor 2/3 in the prefrontal cortex in major depression.

Clinical, postmortem and preclinical research strongly implicates dysregulation of glutamatergic neurotransmission in major depressive disorder (MDD). Recently, metabotropic glutamate receptors (mGluRs) have been proposed as attractive targets for the discovery of novel therapeutic approaches against depression. The aim of this study was to examine mGluR2/3 protein levels in the prefrontal cortex (PFC) from depressed subjects. In addition, to test whether antidepressants influence mGluR2/3 expression we also studied levels of mGluR2/3 in fluoxetine-treated monkeys. Postmortem human prefrontal samples containing Brodmann's area 10 (BA10) were obtained from 11 depressed and 11 psychiatrically healthy controls. Male rhesus monkeys were treated chronically with fluoxetine (dose escalated to 3mg/kg, p.o.; n=7) or placebo (n=6) for 39 weeks. The mGluR2/3 immunoreactivity was investigated using Western blot method. There was a robust (+67%) increase in the expression of the mGlu2/3 protein in the PFC of depressed subjects relative to healthy controls. The expression of mGlu2/3 was unchanged in the PFC of monkeys treated with fluoxetine. Our findings provide the first evidence that mGluR2/3 is elevated in the PFC in MDD. This observation is consistent with reports showing that mGluR2/3 antagonists exhibit antidepressant-like activity in animal models and demonstrates that these receptors are promising targets for the discovery of novel antidepressants.

Reduced glial and neuronal packing density in the orbitofrontal cortex in alcohol dependence and its relationship with suicide and duration of alcohol dependence.

BACKGROUND: Reduced metabolism, blood flow, and tissue volume have been detected in the dorsolateral prefrontal cortex (dlPFC) of neurologically intact alcoholic subjects and these deficits are accompanied by lower density of neurons and glial cells. Another prefrontal region, the orbitofrontal cortex (ORB), functionally and structurally differentiated from the dlPFC, and heavily involved in decision-making processes, also shows functional alterations in alcoholic subjects. However, it is unknown whether changes in the packing density of neurons or glial cells also occur in the ORB and whether that density may be related to the increased suicide probability of alcoholic subjects or to the duration of alcohol dependence. METHODS: The present study used a 3-dimensional cell-counting method in postmortem brain tissue to determine the packing density of neurons and glial cells in the ORB (area 47) of 15 subjects with alcohol dependence (8 suicides, 7 nonsuicides) and 8 normal controls and to determine whether cell density is correlated with suicide and duration of alcohol dependence. RESULTS: There was a significantly lower density of both neurons (by 27%) and glial cells (by 25%) in the ORB of alcoholic subjects compared with controls. Packing density of either neurons or glial cells was not significantly different in alcoholic suicides compared with alcoholic nonsuicides. Age was not correlated with neuronal or glial density in either group. However, the duration of alcohol dependence and the ratio of that duration to the length of life span were significantly and negatively correlated to the overall density of neurons. CONCLUSION: The present results indicate that alcohol dependence is associated with a decrease in the packing density of neurons and glia in the ORB and that the reduction in neuronal but not glial density progresses with the duration of alcohol dependence.

Cerebral cortex astroglia and the brain of a genius: a propos of A. Einstein's.

The glial fibrillary acidic protein immunoreactive astroglial layout of the cerebral cortex from Albert Einstein and other four age-matched human cases lacking any known neurological disease was analyzed using quantification of geometrical features mathematically defined. Several parameters (parallelism, relative depth, tortuosity) describing the primate-specific interlaminar glial processes did not show individually distinctive characteristics in any of the samples analyzed. However, A. Einstein's astrocytic processes showed larger sizes and higher numbers of interlaminar terminal masses, reaching sizes of 15 microm in diameter. These bulbous endings are of unknown significance and they have been described occurring in Alzheimer's disease. These observations are placed in the context of the general discussion regarding the proposal--by other authors--that structural, postmortem characteristics of the aged brain of Albert Einstein may serve as markers of his cognitive performance, a proposal to which the authors of this paper do not subscribe, and argue against.

Comparison of prefrontal cell pathology between depression and alcohol dependence.

Chronic alcohol abuse is often co-morbid with depression symptoms and in many cases it appears to induce major depressive disorder. Structural and functional neuroimaging has provided evidence supporting some degree of neuropathological convergence of alcoholism and mood disorders. In order to understand the cellular neuropathology of alcohol dependence and mood disorders, postmortem morphometric studies have tested the possibility of alterations in the number and size of cells in the prefrontal cortex and other brain regions. The present review compares the cell pathology in the prefrontal cortex between alcohol dependence and depression, and reveals both similarities and differences. One of the most striking similarities is that, although pathology affects both neuronal and glial cells, effects on glia are more dramatic than on neurons in both alcohol dependence comorbid with depression and idiopathic depression. Moreover, prefrontal cortical regions are commonly affected in both depression and alcoholism. However, the cellular changes are more prominent and spread across cortical layers in alcohol dependent subjects than in subjects with mood disorders, and changes in glial nucleus size are opposite in alcoholism and depression. It could be argued that one defining factor in the manifestation of the depressive pathology is a reduction in the glial distribution in the dlPFC that is reflected in a reduced glial density. In alcoholism reduced glial nuclear size might be related to the cytotoxic effects of prolonged alcohol exposure, while in MDD, in the absence of alcohol abuse, other processes might be responsible for the increase in average size of glial nuclei. In either case abnormal function related to glial reduction would be associated with depression due to insufficient glial support to the surrounding neurons.