Mechanisms of cell death in cholinergic basal forebrain neurons in chronic alcoholics

Central markers of neuroinflammation in alcohol use disorder: A meta-analysis of neuroimaging, cerebral spinal fluid, and postmortem studies

INTRODUCTION AND AIMS

There is emerging evidence that heavy long-term alcohol consumption may alter the neuroimmune profile. We conducted a meta-analysis of the association between alcohol use disorder (AUD) and the extent of neuroinflammation using cerebrospinal (CSF), PET (Positron Emission Tomography), and postmortem studies.

DESIGN AND METHODS

A comprehensive search of electronic databases was conducted using the Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols (PRISMA-P) for AUD-related terms in combination with neuroinflammatory markers and cytokine- and chemokine-related terms for CSF, PET, and postmortem studies. Participants had to meet established criteria for AUD and/or heavy alcohol consumption with dependence features and be compared with healthy controls. Papers retrieved were assessed for inclusion criteria and a critical appraisal was completed using the Newcastle-Ottawa Scale. A meta-analysis was conducted on postmortem and PET studies.

RESULTS

Eleven papers met the inclusion criteria with CSF, PET, and postmortem studies included in the final analysis. Postmortem studies demonstrate significant heterogeneity (𝑄 (14) = 62.02, 𝑝 < 0.001), with the alcohol group showing higher levels of neuroimmune markers than controls (𝑑 = 1.50 [95% CI 0.56, 2.45]). PET studies demonstrated a lower [11 C] PBR28 total volume of distribution (V T ) for translocator protein in the hippocampus (g = -1.95 [95% CI -2.72, -1.18], p < 0.001) of the alcohol group compared to controls.

CONCLUSION

There is emerging evidence across multiple diagnostic modalities that alcohol impacts neuroimmune signaling in the human brain.

The Inferior Colliculus in Alcoholism and Beyond

Post-mortem neuropathological and in vivo neuroimaging methods have demonstrated the vulnerability of the inferior colliculus to the sequelae of thiamine deficiency as occurs in Wernicke-Korsakoff Syndrome (WKS). A rich literature in animal models ranging from mice to monkeys-including our neuroimaging studies in rats-has shown involvement of the inferior colliculi in the neural response to thiamine depletion, frequently accomplished with pyrithiamine, an inhibitor of thiamine metabolism. In uncomplicated alcoholism (i.e., absent diagnosable neurological concomitants), the literature citing involvement of the inferior colliculus is scarce, has nearly all been accomplished in preclinical models, and is predominately discussed in the context of ethanol withdrawal. Our recent work using novel, voxel-based analysis of structural Magnetic Resonance Imaging (MRI) has demonstrated significant, persistent shrinkage of the inferior colliculus using acute and chronic ethanol exposure paradigms in two strains of rats. We speculate that these consistent findings should be considered from the perspective of the inferior colliculi having a relatively high CNS metabolic rate. As such, they are especially vulnerable to hypoxic injury and may be provide a common anatomical link among a variety of disparate insults. An argument will be made that the inferior colliculi have functions, possibly related to auditory gating, necessary for awareness of the external environment. Multimodal imaging including diffusion methods to provide more accurate in vivo visualization and quantification of the inferior colliculi may clarify the roles of brain stem nuclei such as the inferior colliculi in alcoholism and other neuropathologies marked by altered metabolism.

The fate of the brain cholinergic neurons in neurodegenerative diseases

The aims of this review are: 1) to describe which cholinergic neurons are affected in brain neurodegenerative diseases leading to dementia; 2) to discuss the possible causes of the degeneration of the cholinergic neurons, 3) to summarize the functional consequences of the cholinergic deficit. The brain cholinergic system is basically constituted by three populations of phenotypically similar neurons forming a series of basal forebrain nuclei, the midpontine nuclei and a large population of striatal interneurons. In Alzheimer's disease there is an extensive loss of forebrain cholinergic neurons accompanied by a reduction of the cholinergic fiber network of the cortical mantel and hippocampus. The midpontine cholinergic nuclei are spared. The same situation occurs in the corticobasal syndrome and dementia following alcohol abuse and traumatic brain injury. Conversely, in Parkinson's disease, the midpontine nuclei degenerate, together with the dopaminergic nuclei, reducing the cholinergic input to thalamus and forebrain whereas the forebrain cholinergic neurons are spared. In Parkinson's disease with dementia, Lewis Body Dementia and Parkinsonian syndromes both groups of forebrain and midpontine cholinergic nuclei degenerate. In Huntington's disease a dysfunction of the striatal cholinergic interneurons without cell loss takes place. The formation and accumulation of misfolded proteins such as β-amyloid oligomers and plaques, tau protein tangles and α-synuclein clumps, and aggregated mutated huntingtin play a crucial role in the neuronal degeneration by direct cellular toxicity of the misfolded proteins and through the toxic compounds resulting from an extensive inflammatory reaction. Evidences indicate that β-amyloid disrupts NGF metabolism causing the degeneration of the cholinergic neurons which depend on NGF for their survival, namely the forebrain cholinergic neurons, sparing the midpontine and striatal neurons which express no specific NGF receptors. It is feasible that the latter cholinergic neurons may be damaged by direct toxicity of tau, α-synuclein and inflammations products through mechanisms not fully understood. Attention and learning and memory impairment are the functional consequences of the forebrain cholinergic neuron dysfunction, whereas the loss of midpontine cholinergic neurons results primarily in motor and sleep disturbances.

Enhancing Rehabilitative Therapies with Vagus Nerve Stimulation

Pathological neural activity could be treated by directing specific plasticity to renormalize circuits and restore function. Rehabilitative therapies aim to promote adaptive circuit changes after neurological disease or injury, but insufficient or maladaptive plasticity often prevents a full recovery. The development of adjunctive strategies that broadly support plasticity to facilitate the benefits of rehabilitative interventions has the potential to improve treatment of a wide range of neurological disorders. Recently, stimulation of the vagus nerve in conjunction with rehabilitation has emerged as one such potential targeted plasticity therapy. Vagus nerve stimulation (VNS) drives activation of neuromodulatory nuclei that are associated with plasticity, including the cholinergic basal forebrain and the noradrenergic locus coeruleus. Repeatedly pairing brief bursts of VNS sensory or motor events drives robust, event-specific plasticity in neural circuits. Animal models of chronic tinnitus, ischemic stroke, intracerebral hemorrhage, traumatic brain injury, and post-traumatic stress disorder benefit from delivery of VNS paired with successful trials during rehabilitative training. Moreover, mounting evidence from pilot clinical trials provides an initial indication that VNS-based targeted plasticity therapies may be effective in patients with neurological diseases and injuries. Here, I provide a discussion of the current uses and potential future applications of VNS-based targeted plasticity therapies in animal models and patients, and outline challenges for clinical implementation.

Reduction of brain mitochondrial β-oxidation impairs complex I and V in chronic alcohol intake: the underlying mechanism for neurodegeneration

Neuropathy and neurocognitive deficits are common among chronic alcohol users, which are believed to be associated with mitochondrial dysfunction in the brain. The specific type of brain mitochondrial respiratory chain complexes (mRCC) that are adversely affected by alcohol abuse has not been studied. Thus, we examined the alterations of mRCC in freshly isolated mitochondria from mice brain that were pair-fed the ethanol (4% v/v) and control liquid diets for 7–8 weeks. We observed that alcohol intake severely reduced the levels of complex I and V. A reduction in complex I was associated with a decrease in carnitine palmitoyltransferase 1 (cPT1) and cPT2 levels. The mitochondrial outer (cPT1) and inner (cPT2) membrane transporter enzymes are specialized in acylation of fatty acid from outer to inner membrane of mitochondria for ATP production. Thus, our results showed that alterations of cPT1 and cPT2 paralleled a decrease β-oxidation of palmitate and ATP production, suggesting that impairment of substrate entry step (complex I function) can cause a negative impact on ATP production (complex V function). Disruption of cPT1/cPT2 was accompanied by an increase in cytochrome C leakage, while reduction of complex I and V paralleled a decrease in depolarization of mitochondrial membrane potential (ΔΨ, monitored by JC-1 fluorescence) and ATP production in alcohol intake. We noted that acetyl-L-carnitine (ALC, a cofactor of cPT1 and cPT2) prevented the adverse effects of alcohol while coenzyme Q10 (CoQ10) was not very effective against alcohol insults. These results suggest that understanding the molecular, biochemical, and signaling mechanisms of the CNS mitochondrial β-oxidation such as ALC can mitigate alcohol related neurological disorders.

ZO proteins and redox-dependent processes

SIGNIFICANCE

ZO-1, ZO-2, and ZO-3 are scaffold proteins of the tight junction (TJ) that belong to the MAGUK protein family characterized for exhibiting PDZ, SH3, and GuK domains. ZO proteins are present only in multicellular organisms, being the placozoa the first to have them. ZO proteins associate among themselves and with other integral and adaptor proteins of the TJ, of the ZA and of gap junctions, as with numerous signaling proteins and the actin cytoskeleton. ZO proteins are also present at the nucleus of proliferating cells.

RECENT ADVANCES

Oxidative stress disassembles the TJs of endothelial and epithelial cells.

CRITICAL ISSUES

Oxidative stress alters ZO proteins expression and localization, in conditions like hypoxia, bacterial and viral infections, vitamin deficiencies, age-related diseases, diabetes and inflammation, alcohol and tobacco consumption.

FUTURE DIRECTIONS

Molecules present in the signaling pathways triggered by oxidative stress can be targets for therapeutic intervention.

Effects of yokukansan, a traditional Japanese medicine, on memory disturbance and behavioral and psychological symptoms of dementia in thiamine-deficient rats

Effects of yokukansan (TJ-54) on memory disturbance and behavioral and psychological symptoms of dementia (BPSD) were investigated in thiamine-deficient (TD) rats which were produced by feeding a TD diet for 37 d. Daily oral administration of TJ-54 (0.5, 1.0 g/kg) ameliorated the memory disturbance, anxiety-like behavior, the increase in aggressive behaviors, the decrease in social behaviors, and several neurological symptoms including opisthotonus observed in TD rats, in a dose-dependent manner. In addition, histopathological examinations showed that TJ-54 inhibited the degeneration of neuronal and astroglial cells in the brain stem, hippocampus and cortex in TD rats. Microdialysis experiments showed that TJ-54 inhibited extracellular glutamate rise in the ventral posterior medial thalamus in TD rats. These results suggest that TJ-54 possesses the preventive or progress inhibitive effect against the development of memory disturbance and BPSD-like behaviors induced by the degeneration of neuronal and astroglial cells resulting from TD. TJ-54 may inhibit glutamate-mediated excitotoxicity as one of mechanisms.

Tau oligomers and aggregation in Alzheimer's disease

We are analyzing the physiological function of Tau protein and its abnormal pathological behavior when this protein is self-assemble into pathological filaments. These aggregates of Tau protein are the main components in many diseases such as Alzheimer's disease (AD). Recent studies suggest that Tau acquires complex oligomeric conformations which may be toxic. In this review, we emphasized the possible phenomena implicated in the formation of these oligomers. Studies with chemical inductors indicates that the microtubule-binding domain is the most important region involved in Tau aggregation and showed the requirement of a pre-arrange Tau in abnormal conformation to promote self-assembly. Transgenic animal models and AD neuropathology studies showed that post-translational modifications are also implicated in Tau aggregation and neural cell death during AD development. Therefore, we analyzed some events that could be present during Tau aggregation. Finally, we included a brief discussion of the possible relation between glucose metabolism dysfunction in AD, and data of Tau aggregation by using aggregation inhibitors. In conclusion, the process Tau aggregation deserves further investigations to design possible therapeutic targets to inhibit the toxicity of these aggregates and it is possible that could be extended to other diseases with similar etiology.

Ethanol enhances tau accumulation in neuroblastoma cells that inducibly express tau

Chronic alcohol consumption causes pathological changes in the brain and neuronal loss. Ethanol toxicity may partially result from the perturbation of microtubule-associated proteins, like tau. Tau dysfunction is well known for its involvement in certain neurodegenerative diseases, such as Alzheimer's disease. In the present study, the effect of ethanol on tau was examined using differentiated human neuroblastoma cells that inducibly express the 4R0N isoform of tau via a tetracycline-off expression system. During tau induction, ethanol exposure (1.25-5mg/ml) dose-dependently increased tau protein levels and reduced cell viability. The increase in cell death likely resulted from tau accumulation since increased levels of tau were sufficient to reduce cell viability and ethanol was toxic to cells expressing tau but not to non-induced controls. Tau accumulation did not result from greater tetracycline-off induction since ethanol increased neither tau mRNA expression nor the expression of the tetracycline-controlled transactivator. Additionally, ethanol increased endogenous tau protein levels in neuroblastoma cells lacking the tetracycline-off induction system for tau. Ethanol delayed tau clearance suggesting ethanol impedes its degradation. Though ethanol inhibited neither cathepsin B, cathepsin D, nor chymotrypsin-like activity, it did significantly reduce calpain I expression and activity. Calpain I knockdown by shRNA increased tau levels indicating that calpain participates in tau degradation in this model. Moreover, the activation of calpain, by the calcium ionophore A23187, partially reversed the accumulation of tau resulting from ethanol exposure. Impaired calpain-mediated degradation may thus contribute to the increased accumulation of tau caused by ethanol.

Thiamine-dependent processes and treatment strategies in neurodegeneration

Reductions in brain glucose metabolism and increased oxidative stress invariably occur in Alzheimer's disease (AD) and thiamine (vitamin B1) deficiency. Both conditions cause irreversible cognitive impairment; their behavioral consequences overlap but are not identical. Thiamine-dependent processes are critical in glucose metabolism, and recent studies implicate thiamine in oxidative stress, protein processing, peroxisomal function, and gene expression. The activities of thiamine-dependent enzymes are characteristically diminished in AD, and the reductions in autopsy AD brain correlate highly with the extent of dementia in the preagonal state. Abnormalities in thiamine-dependent processes can be plausibly linked to the pathology of AD. Seemingly paradoxical properties of thiamine-dependent processes may underlie their relation to the pathophysiology of AD: Reduction of thiamine-dependent processes increase oxidative stress. Thiamine can act as a free radical scavenger. Thiamine-dependent mitochondrial dehydrogenase complexes produce oxygen free radicals and are sensitive to oxidative stress. Genetic disorders of thiamine metabolism that lead to neurological disease can be treated with large doses of thiamine. Although thiamine itself has not shown dramatic benefits in AD patients, the available data is scanty. Adding thiamine or more absorbable forms of thiamine to tested treatments for the abnormality in glucose metabolism in AD may increase their efficacy.

Role of mitochondrial dysfunction and oxidative stress in the pathogenesis of selective neuronal loss in Wernicke's encephalopathy

Thiamine deficiency results in Wernicke's encephalopathy and is commonly encountered in chronic alcoholism, gastrointestinal diseases, and HIV AIDS. The earliest metabolic consequence of thiamine deficiency is a selective loss in activity of the thiamine diphosphate-dependent enzyme alpha-ketoglutarate dehydrogenase (alpha-KGDH), a rate-limiting tricarboxylic acid cycle enzyme. Thiamine deficiency is characterized neuropathologically by selective neuronal cell death in the thalamus, pons, and cerebellum. The cause of this region-selective neuronal loss is unknown, but mechanisms involving cellular energy failure, focal lactic acidosis, and NMDA receptor-mediated excitotoxicity have classically been implicated. More recently, evidence supports a role for oxidative stress. Evidence includes increased endothelial nitric oxide synthase, nitrotyrosine deposition, microglial activation, and lipid peroxidation. Reactive oxygen species production results in decreased expression of astrocytic glutamate transporters and decreased activities of alpha-KGDH, resulting in an amplification of cell death mechanisms in thiamine deficiency.

Effect of kami-untan-to on the impairment of learning and memory induced by thiamine-deficient feeding in mice

We have recently reported that thiamine deficient (TD) mice show an impairment of learning and memory on the 20th day after start of TD feeding. Interestingly, it has been reported that the kampo medicine, "kami-untan-to" (KUT) may be useful as a potential therapeutic agent in diseases associated with cholinergic deficit such as Alzheimer's disease. In the present study, we investigated the effects of KUT on the impairment of memory-related behavior concomitant with psychoneuronal symptoms after TD feeding in mice. Oral administration of KUT had no effect on the food intake, body weight or locomotor activity in TD mice, but the mortality rate in the KUT-treated TD group was significantly lower compared with that in the non-treated TD group. Daily administration of KUT from the 1st day of TD feeding protected against the impairment of memory-related behavior induced by TD. The intensity of the choline acetyltransferase fluorescence decreased in the field of CA1 and dentate gyrus in the hippocampus in TD mice compared with pair-fed mice as the control group, and KUT treatment inhibited this decrease. These results suggest that the effect of KUT on the impairment of memory-related behavior induced by TD feeding may be closely related to the activation of cholinergic neurons in the hippocampus.

Neuropathological alterations in alcoholic brains. Studies arising from the New South Wales Tissue Resource Centre

Alcohol dependence and abuse are among the most costly health problems in the world from both social and economic points of view. Patterns of drinking appear to be changing throughout the world with more women and young people drinking heavily. Excessive drinking can lead to impairment of cognitive function and structural brain changes--some permanent, some reversible. Patterns of damage appear to relate to lifetime alcohol consumption but, more importantly, to associated medical complications. The most significant of these is the alcohol-related vitamin deficient state, the Wernicke-Korsakoff syndrome (WKS), which is caused by thiamin deficiency but is seen most commonly in alcoholics. Careful selection and classification of alcoholic cases into those with and without these complications, together with detailed quantitative neuropathological analyses has provided data that gives clues to the most vulnerable regions and cells in the brain. Brain shrinkage is largely accounted for by loss of white matter. Some of this damage appears to be reversible. Alcohol-related neuronal loss has been documented in specific regions of the cerebral cortex (superior frontal association cortex), hypothalamus and cerebellum. No change is found in basal ganglia, nucleus basalis, or serotonergic raphe nuclei. Many of these regions which are normal in uncomplicated alcoholics are damaged in those with the WKS. Dendritic and synaptic changes have been documented in alcoholics and these, together with receptor and transmitter changes, may explain functional changes and cognitive deficits, which precede more severe structural neuronal changes. A resource to provide human brain tissues for these types of studies has been developed at the University of Sydney--the New South Wales Tissue Resource Centre. The aim of this facility is to provide research groups throughout the world with fresh and/or frozen tissues from well-characterized cases of alcohol-related brain damage and matched controls. The development of new technologies in pathology and molecular biology means that many more questions can be addressed using appropriately stored human brain tissues. Examples of the application of some of these techniques, involving neurochemical, neuropharmacological, neuroimaging and gene expression studies are included in this paper. Important public health outcomes have arisen from some of these studies including the enrichment of bread flour with thiamin for the whole of Australia. Researchers with an interest in alcohol studies can access tissues from this brain bank.

The effects of chronic ethanol consumption on neurotrophins and their receptors in the rat hippocampus and basal forebrain

Damage to the basal forebrain frequently results in deficits in learning and memory. Mnenonic dysfunction also occurs following prolonged ethanol consumption in humans and in animal models of chronic ethanol intake, accompanied by specific abnormalities in synaptic transmission between the basal forebrain and hippocampus. The integrity of at least some of the reciprocal neuronal connections between these brain regions is influenced by target-derived neurotrophic factors. We used a semiquantitative reverse transcription polymerase chain reaction technique to measure the messenger RNA for neurotrophins BDNF and NGF, and for their receptors trkB, trkA, and the low affinity receptor, p75(NTR) in the hippocampus and basal forebrain of rats after 28 weeks of alcohol consumption without malnutrition. This chronic ethanol treatment (CET) resulted in a marked and selective reduction in basal forebrain trkA mRNA. Western blotting revealed a similar reduction of basal forebrain trkA protein. CET effects on basal forebrain trkA may reflect impaired NGF signaling that could compromise septohippocampal synaptic connections, cholinergic differentiation, and emergent functional abilities dependent on these properties.

Increased expression of estrogen receptor α and β in the nucleus basalis of Meynert in Alzheimer’s disease

The human nucleus basalis of Meynert (NBM) is severely affected in Alzheimer's disease (AD). Since estrogens may reduce both the risk and severity of AD, possibly by an action on the cholinergic system, we determined whether estrogen receptors are present in the human NBM and what their changes are in normal aging and in AD. ERalpha was expressed to a higher degree than ERbeta and was localized mainly in the cell nucleus, while ERbeta was mainly confined to the cytoplasm. A significant positive correlation between the percentage of ERalpha nuclear positive neurons and age was found in men but not in women, whereas the proportion of ERbeta cytoplasm positive cells increased during aging in both sexes. In AD the proportion of neurons showing nuclear staining for both ERalpha and beta and cytoplasmic staining for ERbeta was markedly increased. The percentage of ERbeta nuclear positive neurons increased in AD only in women but not in men. The ApoE genotype had no effect on ER expression in the NBM in AD. In conclusion, whereas only minor sex- and age-related changes in both ERs were found in the human NBM, a clear upregulation of ERalpha and beta was observed in AD.

Immunohistochemical estimation of brain choline acetyltransferase and somatostatin related to the impairment of avoidance learning induced by thiamine deficiency

We have found that thiamine-deficient (TD) rats show significant impairment of avoidance learning on the 25th day after the start of TD diet, as measured by passive-avoidance task. Administration of physostigmine (0.1 mg/kg, i.p.) from the 14th day after the start of TD diet improved the impairment of avoidance learning to the pair-fed (PF) control level by the 25th day. However, the recovery effect of physostigmine did not occur on the 25th day when the treatment was begun on the 21st day. To ascertain the correlation between the cholinergic neuronal function in rat brain and the avoidance learning impairment induced by TD, the immunohistochemical distribution of brain choline acetyltransferase (ChAT) was determined by fluorescence intensity using two-dimensional microphotometry. The intensity of the ChAT fluorescence started to decrease in the cortex and hippocampus on the 14th day and showed a marked decrease in the cortex, hippocampus and thalamus on the 25th day of TD feeding in comparison with PF controls. The intensity of the somatostatin (SST) fluorescence was unchanged on the 14th day of TD feeding, but on the 25th day, SST was significantly decreased in comparison with PF controls. Furthermore, physostigmine treatment from 14th day after the start of TD diet reversed SST fluorescence intensity to the control level by the 25th day. These results suggest that the impairment of avoidance learning induced by TD may involve not only cholinergic but also somatostatinergic systems.

Immunohistochemical estimation of rat brain somatostatin on avoidance learning impairment induced by thiamine deficiency

In rats, on the 25th day after the start of a thiamine-deficient (TD) diet, impairment of avoidance learning was significantly induced in proportion to the decrease somatostatin (SST) fluorescence intensity in the cortex, amygdala, thalamus, hypothalamus, and hippocampus, including the CA1, CA2, and dentate gyrus (DG). Only a single injection of thiamine HCl (0.5 mg/rat, subcutaneous) on the 14th day after the start of a TD diet improved the amnesia to the level of the pair-fed control and prevented the decrease in the SST level. Whereas these reversal effects of thiamine treatment were not found when the treatment was given on the 21st day after the start of a TD diet. These results indicate that, after a certain degree of thiamine deficiency, TD-induced behavioral effects might be reversible, but some neuronal fibers might be irreversibly damaged, probably due to the reduction of thiamine-dependent enzymes in brain mitochondria. The results also suggest the possibility that SST in the brain may be closely related to the avoidance learning impairment induced by TD.

Plasma thiamine deficiency associated with Alzheimer's disease but not Parkinson's disease

In this study we compared plasma and erythrocyte thiamine levels in a group of patients with idiopathic Parkinson's Disease (iPD) to a group of patients with probable Alzheimer's Disease (pAD). pAD patients had significantly lower plasma thiamine levels (raw and z-score) than iPD patients. A significantly higher number of pAD patients had plasma thiamine deficiencies than iPD patients. The demographics of our patient groups were similar to those reported by other investigators, making age, sex and nutritional status unlikely explanations for our findings. These results suggest that plasma thiamine deficiency is associated with pAD but not with iPD.

The cerebral cortex is damaged in chronic alcoholics

There is some controversy in the literature concerning whether chronic alcohol consumption damages the cerebral cortex. While decreased neuronal density in specific cortical regions is well described in chronic alcoholics, a recent study by Badsberg Jensen and Pakkenberg using unbiased stereological methods questions whether neurodegeneration occurs. In order to assess selective neurodegeneration in the cerebral cortex of chronic alcoholics, regional volumes and unbiased estimates of regional neuronal number (including neuronal identification with calcium-binding proteins) were calculated for 14 chronic alcoholics and 21 controls. Cases were carefully screened to exclude any interfering pathologies. Lifetime and maximum daily alcohol consumption was determined, and homogeneous groups were identified (four chronic alcoholics with Wernicke's encephalopathy and Korsakoff's psychosis, four chronic alcoholics with Wernicke's encephalopathy alone, six chronic alcoholics without Wernicke's encephalopathy or Korsakoff's psychosis, and 21 controls). Brain volume analysis revealed that discrete regions were significantly smaller in the chronic alcoholics compared to controls. As previously shown, white matter regions (particularly in the frontal lobe) were the most significantly reduced in volume. Alcoholics with Wernicke's encephalopathy (either alone or in combination with Korsakoff's psychosis) had significantly smaller white matter volumes than controls or alcoholics without these complications. Medial temporal lobe regions and the thalamus were also reduced in volume. Regression analyses revealed that the volume of both the white matter and thalamus negatively correlated with alcohol consumption. Consistent with the interpretation of previous neuronal density studies, selective neuronal loss was found in the superior frontal association cortex of chronic alcoholics, while no loss occurred from the motor cortex. The number of parvalbumin-, calbindin- and calretinin-immunoreactive neurons was found to be unaltered in chronic alcoholics, suggesting that the neurodegeneration is confined to the non-GABAergic pyramidal neurons. As neurodegeneration was observed in all alcoholic groups, damage to the frontal association cortex is not restricted to alcoholics with the amnesia of Korsakoff's psychosis. These results are consistent with the notion that chronic alcohol consumption is associated with selective neuronal vulnerability. The selective frontal neurodegeneration and the frontal focus of white matter atrophy are supported by neuropsychological, regional blood flow, and magnetic resonance imaging studies of frontal lobe dysfunction in chronic alcoholics and may correlate with abnormalities in working memory.

Chronic alcohol consumption does not cause hippocampal neuron loss in humans

High alcohol consumption for long periods of time causes significant hippocampal neurodegeneration in rodents. A single study using neuronal density measures has reported similar findings in humans. The present study aims to substantiate these findings in human alcoholics using unbiased stereological techniques. Both amnesic (n = 5) and nonamnesic (n = 7) chronic alcoholics were selected and compared with nonalcoholic controls (n = 8) and patients with marked memory loss and hippocampal neurodegeneration caused by Alzheimer's disease (n = 4). Hippocampal volume was significantly reduced in the alcoholics and in patients with Alzheimer's disease. However, in alcoholics the volume reduction occurred exclusively in the white matter, whereas both the gray and white matter were reduced in the patients with Alzheimer's disease. Neuron loss occurred exclusively from the CA1 and subiculum subregions of the hippocampus in Alzheimer's disease. No neuron loss occurred from any subregion of the hippocampus in alcoholics. There were no correlations with age and any of the volume or neuron number measures. Hippocampal volume correlated with brain volume and with the regional gray and white matter volumes within the hippocampus. In addition, hippocampal gray matter volume correlated with the number of CA1 pyramidal neurons. These results do not support the theory that chronic alcohol consumption is neurotoxic to hippocampal pyramidal neurons in humans. Further, the present results suggest that changes observed in rodent models of alcoholism do not parallel those observed in humans, questioning the validity of such models.

Chronic alcoholism in the absence of Wernicke-Korsakoff syndrome and cirrhosis does not result in the loss of serotonergic neurons from the median raphe nucleus

Previous studies have identified alcohol, thiamine deficiency and liver disease as contributing to the neuropathology of alcohol-related brain damage. In order to examine the effects of alcohol toxicity and thiamine deficiency on serotonergic neurons in the median raphe nucleus (MnR), alcoholic and previously published Wernicke-Korsakoff syndrome (WKS) cases without liver disease, were compared with age-matched non-alcoholic controls. While there was no difference between the estimated number of serotonergic neurons in either controls or alcoholics without WKS (means of 63,010 +/- 8,900 and 59,560 +/- 8,010 respectively), a substantial loss of serotonergic neurons was previously found in WKS cases (mean of 19,050 +/- 13,140). Further analysis revealed a significant difference in the maximum daily alcohol consumption between these groups. However, analysis of covariance showed that the number or serotonergic neurons in the MnR did not correlate with the amount of alcohol consumed. Therefore, our results suggest that cell loss in the MnR can be attributed to thiamine deficiency rather than alcohol per se.

Neuropathology of thiamine deficiency: an update on the comparative analysis of human disorders and experimental models

This paper provides a re-examination of the neuroanatomical consequences of thiamine deficiency in light of more recent studies of human disorders and models of experimental thiamine deficiency. A major goal is to elucidate the relative roles of thiamine deficiency and chronic alcohol consumption in the pathogenesis of Wernicke-Korsakoff syndrome (WKS). Particular emphasis is placed on the role of thiamine deficiency in lesions to basal forebrain, raphe, locus coeruleus, white matter and cortex and their role in the cognitive and memory disturbances of human WKS and experimental models of thiamine deficiency.