Longitudinal brain magnetic resonance imaging study of the alcohol-preferring rat. Part II: effects of voluntary chronic alcohol consumption

Alcohol Use Disorder and Dementia: A Review

PURPOSE

By 2040, 21.6% of Americans will be over age 65, and the population of those older than age 85 is estimated to reach 14.4 million. Although not causative, older age is a risk factor for dementia: every 5 years beyond age 65, the risk doubles; approximately one-third of those older than age 85 are diagnosed with dementia. As current alcohol consumption among older adults is significantly higher compared to previous generations, a pressing question is whether drinking alcohol increases the risk for Alzheimer's disease or other forms of dementia.

SEARCH METHODS

Databases explored included PubMed, Web of Science, and ScienceDirect. To accomplish this narrative review on the effects of alcohol consumption on dementia risk, the literature covered included clinical diagnoses, epidemiology, neuropsychology, postmortem pathology, neuroimaging and other biomarkers, and translational studies. Searches conducted between January 12 and August 1, 2023, included the following terms and combinations: "aging," "alcoholism," "alcohol use disorder (AUD)," "brain," "CNS," "dementia," "Wernicke," "Korsakoff," "Alzheimer," "vascular," "frontotemporal," "Lewy body," "clinical," "diagnosis," "epidemiology," "pathology," "autopsy," "postmortem," "histology," "cognitive," "motor," "neuropsychological," "magnetic resonance," "imaging," "PET," "ligand," "degeneration," "atrophy," "translational," "rodent," "rat," "mouse," "model," "amyloid," "neurofibrillary tangles," "α-synuclein," or "presenilin." When relevant, "species" (i.e., "humans" or "other animals") was selected as an additional filter. Review articles were avoided when possible.

SEARCH RESULTS

The two terms "alcoholism" and "aging" retrieved about 1,350 papers; adding phrases-for example, "postmortem" or "magnetic resonance"-limited the number to fewer than 100 papers. Using the traditional term, "alcoholism" with "dementia" resulted in 876 citations, but using the currently accepted term "alcohol use disorder (AUD)" with "dementia" produced only 87 papers. Similarly, whereas the terms "Alzheimer's" and "alcoholism" yielded 318 results, "Alzheimer's" and "alcohol use disorder (AUD)" returned only 40 citations. As pertinent postmortem pathology papers were published in the 1950s and recent animal models of Alzheimer's disease were created in the early 2000s, articles referenced span the years 1957 to 2024. In total, more than 5,000 articles were considered; about 400 are herein referenced.

DISCUSSION AND CONCLUSIONS

Chronic alcohol misuse accelerates brain aging and contributes to cognitive impairments, including those in the mnemonic domain. The consensus among studies from multiple disciplines, however, is that alcohol misuse can increase the risk for dementia, but not necessarily Alzheimer's disease. Key issues to consider include the reversibility of brain damage following abstinence from chronic alcohol misuse compared to the degenerative and progressive course of Alzheimer's disease, and the characteristic presence of protein inclusions in the brains of people with Alzheimer's disease, which are absent in the brains of those with AUD.

Role of inflammation in alcohol-related brain abnormalities: a translational study

Brain abnormalities observed in alcohol use disorder are highly heterogeneous in nature and severity, possibly because chronic alcohol consumption also affects peripheral organs leading to comorbidities that can result in exacerbated brain alterations. Despite numerous studies focussing on the effects of alcohol on the brain or liver, few studies have simultaneously examined liver function and brain damage in alcohol use disorder, and even fewer investigated the relationship between them except in hepatic encephalopathy. And yet, liver dysfunction may be a risk factor for the development of alcohol-related neuropsychological deficits and brain damage well before the development of liver cirrhosis, and potentially through inflammatory responses. The use of animal models enables a better understanding of the pathophysiological mechanisms underlying liver–brain relationships in alcohol use disorder, and more particularly of the inflammatory response at the tissue, cerebral and hepatic levels. The objective of this translational study was to investigate, both in alcohol use disorder patients and in a validated animal model of alcohol use disorder, the links between peripheral inflammation, liver damage and brain alterations. To do this, we conducted an in vivo neuroimaging examination and biological measures to evaluate brain volumes, liver fibrosis and peripheral cytokines in alcohol use disorder patients. In selectively bred Sardinian alcohol-preferring rats, we carried out ex vivo neuroimaging examination and immunohistochemistry to evaluate brain and liver inflammatory responses after chronic (50 consecutive weeks) alcohol drinking. In recently abstinent and non-cirrhotic alcohol use disorder patients, the score of liver fibrosis positively correlated with subcortical regions volumes (especially in right and left putamen) and level of circulating proinflammatory cytokines. In Sardinian alcohol-preferring rats, we found macrostructural brain damage and microstructural white matter abnormalities similar to those found in alcohol use disorder patients. In addition, in agreement with the results of peripheral inflammation observed in the patients, we revealed, in Sardinian alcohol-preferring rats, inflammatory responses in the brain and liver were caused by chronic alcohol consumption. Since the liver is the main source of cytokines in the human body, these results suggest a relationship between liver dysfunction and brain damage in alcohol use disorder patients, even in the absence of major liver disease. These findings encourage considering new therapeutic strategies aiming at treating peripheral organs to limit alcohol-related brain damage.

Jacobian Mapping Reveals Converging Brain Substrates of Disruption and Repair in Response to Ethanol Exposure and Abstinence in 2 Strains of Rats

BACKGROUND

In a previous study using Jacobian mapping to evaluate the morphological effects on the brain of binge (4-day) intragastric ethanol (EtOH) on wild-type Wistar rats, we reported reversible thalamic shrinkage and lateral ventricular enlargement, but persistent superior and inferior colliculi shrinkage in response to binge EtOH treatment.

METHODS

Herein, we used similar voxel-based comparisons of Magnetic Resonance Images collected in EtOH-exposed relative to control animals to test the hypothesis that regardless of the intoxication protocol or the rat strain, the hippocampi, thalami, and colliculi would be affected.

RESULTS

Two experiments [binge (4-day) intragastric EtOH in Fisher 344 rats and chronic (1-month) vaporized EtOH in Wistar rats] showed similarly affected brain regions including retrosplenial and cingulate cortices, dorsal hippocampi, central and ventroposterior thalami, superior and inferior colliculi, periaqueductal gray, and corpus callosum. While most of these regions showed significant recovery, volumes of the colliculi and periaqueductal gray continued to show response to each proximal EtOH exposure but at diminished levels with repeated cycles.

CONCLUSIONS

Given the high metabolic rate of these enduringly affected regions, the current findings suggest that EtOH per se may affect cellular respiration leading to brain volume deficits. Further, responsivity greatly diminished likely reflecting neuroadaptation to repeated alcohol exposure. In summary, this unbiased, in vivo-based approach demonstrating convergent brain systems responsive to 2 EtOH exposure protocols in 2 rat strains highlights regions that warrant further investigation in both animal models of alcoholism and in humans with alcohol use disorder.

Age-Related Regional Network Covariance of Magnetic Resonance Imaging Gray Matter in the Rat

Healthy human aging has been associated with brain atrophy in prefrontal and selective temporal regions, but reductions in other brain areas have been observed. We previously found regional covariance patterns of gray matter with magnetic resonance imaging (MRI) in healthy humans and rhesus macaques, using multivariate network Scaled Subprofile Model (SSM) analysis and voxel-based morphometry (VBM), supporting aging effects including in prefrontal and temporal cortices. This approach has yet to be applied to neuroimaging in rodent models of aging. We investigated 7.0T MRI gray matter covariance in 10 young and 10 aged adult male Fischer 344 rats to identify, using SSM VBM, the age-related regional network gray matter covariance pattern in the rodent. SSM VBM identified a regional pattern that distinguished young from aged rats, characterized by reductions in prefrontal, temporal association/perirhinal, and cerebellar areas with relative increases in somatosensory, thalamic, midbrain, and hippocampal regions. Greater expression of the age-related MRI gray matter pattern was associated with poorer spatial learning in the age groups combined. Aging in the rat is characterized by a regional network pattern of gray matter reductions corresponding to aging effects previously observed in humans and non-human primates. SSM MRI network analyses can advance translational aging neuroscience research, extending from human to small animal models, with potential for evaluating mechanisms and interventions for cognitive aging.

Differential Effects of Chronic Alcohol Consumption on Cortical and Subcortical Brain Volume in Adolescent Nonhuman Primates

Highlighted Research Paper:Chronic Alcohol Drinking Slows Brain Development in Adolescent and Young Adult Nonhuman Primates, by Tatiana A. Shnitko, Zheng Liu, Xiaojie Wang, Kathleen A. Grant, and Christopher D. Kroenke.

Chronic Alcohol Drinking Slows Brain Development in Adolescent and Young Adult Nonhuman Primates

The transition from adolescence to adulthood is associated with brain remodeling in the final stages of developmental growth. It is also a period when a large proportion of this age group engages in binge alcohol drinking (occasional consumption of four to five drinks leading to intoxication) and heavy alcohol drinking (binge drinking on ≥5 d in a month). Here we report on magnetic resonance imaging of developmental changes in the brain occurring during late adolescence and early adulthood (3.5-7.5 years of age) in a rhesus macaque model of alcohol self-administration. Monkeys were imaged prior to alcohol exposure, and following ∼6 and ∼12 months of daily (22 h/d) access to ethanol and water. The results revealed that the brain volume increases by 1 ml/1.87 years throughout the late adolescence and early adulthood in controls. Heavy alcohol drinking reduced the rate of brain growth by 0.25 ml/year per 1 g/kg daily ethanol. Cortical volume increased throughout this period with no significant effect of alcohol drinking on the cortical growth rate. In subcortical regions, age-dependent increases in the volumes of globus pallidus, thalamus, brainstem, and cerebellum were observed. Heavy drinking attenuated the growth rate of the thalamus. Thus, developmental brain volume changes in the span of late adolescence to young adulthood in macaques is altered by excessive alcohol, an insult that may be linked to the continuation of heavy drinking throughout later adult life.

Transient CNS responses to repeated binge ethanol treatment

The effects of ethanol (EtOH) on in vivo magnetic resonance (MR)-detectable brain measures across repeated exposures have not previously been reported. Of 28 rats weighing 340.66 ± 21.93 g at baseline, 15 were assigned to an EtOH group and 13 to a control group. Animals were exposed to five cycles of 4 days of intragastric (EtOH or dextrose) treatment and 10 days of recovery. Rats in both groups had structural MR imaging and whole-brain MR spectroscopy (MRS) scans at baseline, immediately following each binge period and after each recovery period (total = 11 scans per rat). Blood alcohol level at each of the five binge periods was ~300 mg/dl. Blood drawn at the end of the experiment did not show group differences for thiamine or its phosphate derivatives. Postmortem liver histopathology provided no evidence for hepatic steatosis, alcoholic hepatitis or alcoholic cirrhosis. Cerebrospinal fluid volumes of the lateral ventricles and cisterns showed enlargement with each binge EtOH exposure but recovery with each abstinence period. Similarly, changes in MRS metabolite levels were transient: levels of N-acetylaspartate and total creatine decreased, while those of choline-containing compounds and the combined resonance from glutamate and glutamine increased with each binge EtOH exposure cycle and then recovered during each abstinence period. Changes in response to EtOH were in expected directions based on previous single-binge EtOH exposure experiments, but the current MR findings do not provide support for accruing changes with repeated binge EtOH exposure.

Widespread effects of alcohol on white matter microstructure

BACKGROUND

Evidence suggests that chronic misuse of alcohol may preferentially affect the integrity of frontal white matter (WM) tracts, which can impact executive functions important to achieve and maintain abstinence.

METHODS

Global and regional WM microstructure was assessed using diffusion magnetic resonance measures of fractional anisotropy (FA) for 31 abstinent alcoholics (ALC) with an average of 25 years of abuse and approximately 5 years of sobriety and 20 nonalcoholic control (NC) participants. Data processing was conducted with FreeSurfer and FSL processing streams. Voxelwise processing of the FA data was carried out using tract-based spatial statistics. Clusters of significance were created to provide a quantitative summary of highly significant regions within the voxelwise analysis.

RESULTS

Widespread, bilateral reductions in FA were observed in ALC as compared to NC participants in multiple frontal, temporal, parietal, and cerebellar WM tracts. FA in the left inferior frontal gyrus was associated with drinking severity.

CONCLUSIONS

This study found widespread reductions in WM integrity in a group of ALC compared to NC participants, with most pronounced effects in frontal and superior tracts. Decreased FA throughout the frontostriatal circuits that mediate inhibitory control may result in impulsive behavior and inability to maintain sobriety.

Monkeys that voluntarily and chronically drink alcohol damage their brains: a longitudinal MRI study

Neuroimaging has consistently documented reductions in the brain tissue of alcoholics. Inability to control comorbidity, environmental insult, and nutritional deficiency, however, confound the ability to assess whether ethanol itself is neurotoxic. Here we report monkey oral ethanol self-administration combined with MR imaging to characterize brain changes over 15 months in 18 well-nourished rhesus macaques. Significant brain volume shrinkage occurred in the cerebral cortices of monkeys drinking ≥ 3 g/kg ethanol/day (12 alcoholic drinks) at 6 months, and this persisted throughout the period of continuous access to ethanol. Correlation analyses revealed a cerebral cortical volumetric loss of ~0.11% of the intracranial vault for each daily drink (0.25 g/kg), and selective vulnerability of cortical and non-cortical brain regions. These results demonstrate for the first time a direct relation between oral ethanol intake and measures of decreased brain gray matter volume in vivo in primates. Notably, greater volume shrinkage occurred in monkeys with younger drinking onset that ultimately became heavier drinkers than monkeys with older drinking onset. The pattern of volumetric changes observed in nonhuman primates following 15 months of drinking suggests that cerebral cortical gray matter changes are the first macroscopic manifestation of chronic ethanol exposure in the brain.

Peri-adolescent ethanol vapor exposure produces reductions in hippocampal volume that are correlated with deficits in prepulse inhibition of the startle

BACKGROUND

Epidemiological studies suggest that excessive alcohol consumption is prevalent among adolescents and may have lasting neurobehavioral consequences. The use of animal models allows for the separation of the effects of adolescent ethanol (EtOH) exposure from genetic background and other environmental insults. In this study, the effects of moderate EtOH vapor exposure, during adolescence, on structural diffusion tensor imaging (DTI) and behavioral measures were evaluated in adulthood.

METHODS

A total of 53 Wistar rats were received at postnatal day (PD) 21 and were randomly assigned to EtOH vapor (14 hours on/10 hours off/day) or air exposure for 35 days from PD 23 to 58 (average blood ethanol concentration: 169 mg%). Animals were received in 2 groups that were subsequently sacrificed at 2 time points following withdrawal from EtOH vapor: (i) at 72 days of age, 2 weeks following withdrawal or (ii) at day 128, 10 weeks following withdrawal. In the second group, behavior in the light/dark box and prepulse inhibition (PPI) of the startle was also evaluated. Fifteen animals in each group were scanned, postmortem, for structural DTI.

RESULTS

There were no significant differences in body weight between EtOH and control animals. Volumetric data demonstrated that total brain, hippocampal, corpus callosum but not ventricular volume were significantly larger in the 128-day-sacrificed animals as compared to the 72 day animals. The hippocampus was smaller and the ventricles larger at 128 days as compared to 72 days, in the EtOH-exposed animals, leading to a significant group × time effect. EtOH-exposed animals sacrificed at 128 days also had diminished PPI, and more rears in the light box were significantly correlated with hippocampal size.

CONCLUSIONS

These studies demonstrate that DTI volumetric measures of hippocampus are significantly impacted by age and peri-adolescent EtOH exposure and withdrawal in Wistar rats.

Periadolescent ethanol vapor exposure persistently reduces measures of hippocampal neurogenesis that are associated with behavioral outcomes in adulthood

Excessive alcohol consumption is prevalent among adolescents and may result in lasting neurobehavioral consequences. The use of animal models to study adolescent alcohol exposure has the advantage of allowing for the control necessary in order to evaluate the effects of ethanol on the brain and separate such effects from genetic background and other environmental insults. In the present study the effects of moderate ethanol vapor exposure, during adolescence, on measures of neurogenesis and behavioral measures were evaluated at two different times following ethanol withdrawal, in adulthood. The two groups of Wistar rats were both exposed to intermittent ethanol vapor (14 h on/10h off/day) for 35-36 days from PD 23 to PD 58 (average blood ethanol concentration: 163 mg%). In the first group, after rats were withdrawn from vapor they were subsequently assessed for locomotor activity, conflict behavior in the open field, and behaviors in the forced swim test (FST) and then sacrificed at 72 days of age. The second group of rats were withdrawn from vapor and injected for 5 days with Bromo-deoxy-Uridine (BrdU). Over the next 8 weeks they were also assessed for locomotor activity, conflict behavior in the open field, and behaviors in the FST and then sacrificed at 113/114 days of age. All rats were perfused for histochemical analyses. Ethanol vapor-exposed rats displayed hypoactivity in tests of locomotion and less anxiety-like and/or more "disinhibitory" behavior in the open field conflict. Quantitative analyses of immunoreactivity revealed a significant reduction in measures of neurogenesis, progenitor proliferation, as indexed by doublecortin (DCX), Ki67, and increased markers of cell death as indexed by cleaved caspase-3, and Fluoro-Jade at 72 days, and decreases in DCX, and increases in cleaved caspase-3 at 114 days in the ethanol vapor-exposed rats. Progenitor survival, as assessed by BrdU+, was reduced in the vapor-exposed animals that were sacrificed at 114 days. The reduction seen in DCX labeled in cell counts was significantly correlated with hypoactivity at 24h after withdrawal as well as less anxiety-like and/or more "disinhibitory" behavior in the open field conflict test at 2 and 8 weeks following termination of vapor exposure. These studies demonstrate that behavioral measures of disinhibitory behavior correlated with decreases in neurogenesis are all significantly and persistently impacted by periadolescent ethanol exposure and withdrawal in Wistar rats.

A mouse model for adolescent alcohol abuse: stunted growth and effects in brain

BACKGROUND

Adolescent alcohol abuse remains a serious public health concern, with nearly a third of high school seniors reporting heavy drinking in the previous month.

METHODS

Using the high ethanol-consuming C57BL/6J mouse strain, we examined the effects of ethanol (3.75 g/kg, IP, daily for 45 days) on body weight and brain region mass (cerebral cortex, cerebellum, corpus callosum) during peri-adolescence (postnatal day [P]25 to 70) or adulthood (P180 to 225) of both males and females.

RESULTS

In control peri-adolescent animals, body weight gain was greater in males compared with females. In the peri-adolescent exposure group, ethanol significantly reduced body weight gain to a similar extent in both male and female mice (82 and 84% of controls, respectively). In adult animals, body weight gain was much less than that of the peri-adolescent mice, with ethanol having a small but significant effect in males but not females. Between the control peri-adolescent and adult cohorts (measurements taken at P70 and 225, respectively), there were no significant differences in the mass of the cerebral cortex or the cerebellum from either male or female mice, although the rostro-caudal length of the corpus callosum increased slightly but significantly (6.1%) between these time points.

CONCLUSIONS

Ethanol treatment significantly reduced the mass of the cerebral cortex in peri-adolescent (-3.1%), but not adult, treated mice. By contrast, ethanol significantly reduced the length of the corpus callosum in adult (-5.4%), but not peri-adolescent, treated mice. Future studies at the histological level may yield additional details concerning ethanol and the peri-adolescent brain.

The translational role of diffusion tensor image analysis in animal models of developmental pathologies

Diffusion tensor magnetic resonance imaging (DTI) has proven itself a powerful technique for clinical investigation of the neurobiological targets and mechanisms underlying developmental pathologies. The success of DTI in clinical studies has demonstrated its great potential for understanding translational animal models of clinical disorders, and preclinical animal researchers are beginning to embrace this new technology to study developmental pathologies. In animal models, genetics can be effectively controlled, drugs consistently administered, subject compliance ensured, and image acquisition times dramatically increased to reduce between-subject variability and improve image quality. When pairing these strengths with the many positive attributes of DTI, such as the ability to investigate microstructural brain organization and connectivity, it becomes possible to delve deeper into the study of both normal and abnormal development. The purpose of this review is to provide new preclinical investigators with an introductory source of information about the analysis of data resulting from small animal DTI studies to facilitate the translation of these studies to clinical data. In addition to an in-depth review of translational analysis techniques, we present a number of relevant clinical and animal studies using DTI to investigate developmental insults in order to further illustrate techniques and to highlight where small animal DTI could potentially provide a wealth of translational data to inform clinical researchers.

Brain injury and recovery following binge ethanol: evidence from in vivo magnetic resonance spectroscopy

BACKGROUND

The binge-drinking model in rodents using intragastric injections of ethanol (EtOH) for 4 days results in argyrophilic corticolimbic tissue classically interpreted as indicating irreversible neuronal degeneration. However, recent findings suggest that acquired argyrophilia can also identify injured neurons that have the potential to recover. The current in vivo magnetic resonance (MR) imaging and spectroscopy study was conducted to test the hypothesis that binge EtOH exposure would injure but not cause the death of neurons as previously ascertained postmortem.

METHODS

After baseline MR scanning, 11 of 19 rats received a loading dose of 5 g/kg EtOH via oral gavage, then a maximum of 3 g/kg every 8 hours for 4 days, for a total average cumulative EtOH dose of 43 +/- 1.2 g/kg and average blood alcohol levels of 258 +/- 12 mg/dL. All animals were scanned after 4 days of gavage (post-gavage scan) with EtOH (EtOH group) or dextrose (control [Con] group) and again after 7 days of abstinence from EtOH (recovery scan).

RESULTS

Tissue shrinkage at the post-gavage scan was reflected by significantly increased lateral ventricular volume in the EtOH group compared with the Con group. At the post-gavage scan, the EtOH group had lower dorsal hippocampal N-acetylaspartate and total creatine and higher choline-containing compounds than the Con group. At the recovery scan, neither ventricular volume nor metabolite levels differentiated the groups.

CONCLUSIONS

Rapid recovery of ventricular volume and metabolite levels with removal of the causative agent argues for transient rather than permanent effects of a single EtOH binge episode in rats.

Neuroimaging of the Wernicke-Korsakoff syndrome

AIM

Presented is the neuroradiological signature of acute Wernicke's encephalopathy (WE), derived from different types of magnetic resonance imaging (MRI) sequences. WE results from thiamine depletion, and its most typical antecedent is chronic alcohol dependence. Brain regions observed with in vivo MRI affected in acute WE include the mammillary bodies, periaqueductal and periventricular gray matter, collicular bodies and thalamus. These affected areas are usually edematous and are best visualized and quantified with MRI sequences that highlight such tissue. Following the acute WE phase and resolution of edema and inflammation of affected brain tissue, WE, if not adequately treated with thiamine repletion, can herald Korsakoff's syndrome (KS), with its symptomatic hallmark of global amnesia, that is, the inability to commit newly encountered (episodic) information to memory for later recall or recognition.

METHODS

Neuropathology of KS detectable with MRI has a different neuroradiological signature from the acute stage and can be observed as tissue shrinkage or atrophy of selective brain structures, including the mammillary bodies and thalamus and ventricular expansion, probably indicative of atrophy of surrounding gray matter nuclei. Quantification of these and additional gray matter structures known to underlie global amnesia reveal substantial bilateral volume deficits in the hippocampus, in addition to the mammillary bodies and thalamus, and modest deficits in the medial septum/diagonal band of Broca. The infratentorium is also affected, exhibiting volume deficits in cerebellar hemispheres, anterior superior vermis and pons, contributing to ataxia of gait and stance.

RESULTS

Consideration of WKS structural brain changes in the context of the neuropathology of non-WKS alcoholism revealed a graded pattern of volume deficits, from mild in non-WKS alcoholics to moderate or severe in WKS, in the mammillary bodies, hippocampus, thalamus, cerebellum and pons. The development and resolution of brain structures affected in acute, chronic and treated WE was verified in longitudinal MRI study of rats that modeled of the interaction of extensive alcohol consumption and thiamine depletion and repletion.

CONCLUSIONS

Thus, neuroradiological examination with MRI is valuable in the diagnosis of acute WE and enables in vivo tracking of the progression of the brain pathology of WE from the acute pathological phase to resolution with thiamine treatment or to progression to KS without treatment. Further, in vivo MRI facilitates translational studies to model antecedent conditions contributing to the development, sequelae and treatment of WE.

Abstinence from moderate alcohol self-administration alters progenitor cell proliferation and differentiation in multiple brain regions of male and female P rats

BACKGROUND

Acute and chronic ethanol exposure has been found to decrease hippocampal neurogenesis, reduce dendritic differentiation of new neurons, and increase cell death. Interestingly, abstinence from such treatment increases hippocampal neurogenesis and microglial genesis across several brain regions. The goal of the current investigation was to study cellular alterations on neuro- and cell-genesis during abstinence following alcohol self-administration using alcohol-preferring rats (P rats).

METHODS

Male and female P rats were given the choice of drinking 10% alcohol in water or pure water for 7 weeks. Social interaction behavioral assessments were conducted at 5 hours upon removal of alcohol, followed by bromo-deoxyuridine (BrdU, 150 mg/kg x 1/d x 14 d) injections to label proliferating cells. Animals were then killed 4 weeks later to conduct immunohistochemical and confocal analyses using antibodies against BrdU and other phenotypic markers (NeuN for mature neurons; Iba-1 for microglia; GFAP for astrocytes; and NG(2) for oligodendrocyte progenitors).

RESULTS

Mild alcohol withdrawal anxiety was detected by reduction in social interactions. The number of hippocampal BrdU(+) cells was increased approximately 50% during alcohol abstinence (26 +/- 2.8 in controls vs. 39 +/- 4 in alcohol group). BrdU(+) cells were also increased in the substantia nigra (SN) approximately 65% in the alcohol abstinent group (12 +/- 1 in controls vs. 19 +/- 1.5 in alcohol group). No gender differences were found. Confocal analyses indicated that approximately 75% of co-localization of BrdU(+) cells with NeuN in the hippocampal dentate gyrus (DG) resulting a net increase in neurogenesis in the alcohol abstinent group compared to controls. In cingulum, greater proportion of BrdU(+) cells were co-localized with NG(2) in the alcohol abstinent group indicating increased differentiation toward oligodendrocyte progenitors in both genders. However, the phenotype of the BrdU(+) cells in SN and other brain regions were not identified by NeuN, Iba-1, GFAP, or NG(2) suggesting that these BrdU(+) cells probably remain in a nondifferentiated stage.

CONCLUSIONS

These data indicate that abstinence from moderate alcohol drinking increases hippocampal neurogenesis, cingulate NG(2) differentiation, and SN undifferentiated cell proliferation in both males and females. Such cellular alteration during abstinence could contribute to the spontaneous partial restoration of cognitive deficits upon sobriety.

Ventricular expansion in wild-type Wistar rats after alcohol exposure by vapor chamber

BACKGROUND

Structural magnetic resonance imaging (MRI) reveals widespread brain damage manifest as tissue shrinkage and complementary ventriculomegaly in human alcoholism. For an animal model to parallel the human condition, high alcohol exposure should produce similar radiologically detectable neuropathology. Our previous structural MRI study demonstrated only modest brain dysmorphology of the alcohol-preferring (P) rat with average blood alcohol levels(BALs) of 125 mg/dl achieved with voluntary consumption. Here, we tested the hypothesis that wild-type Wistar rats, exposed to vaporized alcohol ensuring higher BALs than typically achieved with voluntary consumption in rodents, would model MRI findings in the brains of humans with chronic alcoholism.

METHODS

The longitudinal effects of vaporized alcohol exposure on the brains of 10 wild-type Wistar rats compared with 10 sibling controls were investigated with structural MRI, conducted before (MRI 1) and after (MRI 2) 16 of alcohol exposure and after an additional 8 weeks at a higher concentration of alcohol (MRI 3).

RESULTS

Two rats in the alcohol group died prior to MRI 2. The remaining vapor-exposed rats(n = 8) achieved BALs of 293 mg/dl by MRI 2 and 445 mg/dl by MRI 3. Whereas the controls gained 17% of their body weight from MRI 1 to MRI 3, the alcohol-exposed group lost 6%.MRI, quantified with atlas-based parcellation, revealed a profile of significant ventricular expansion,after alcohol vapor exposure, in 9 contiguous slices, extending from the dorsolateral to ventrolateral ventricles. In particular, from MRI 1 to MRI 2, this ventricular volume expanded by an average of 6.5% in the controls and by 27.1% in the alcohol-exposed rats but only an additional 1.5% in controls and 2.4% in alcohol-exposed rats from MRI 2 to MRI 3. The midsagittal volume of the full anterior-to-posterior extent of the corpus callosum grew between the first 2 MRIs in both groups followed by regression in the alcohol group by MRI 3. Although group differences were statistically significant, among animals there was substantial variability of the effects of alcohol exposure on brain morphology; some animals showed profound effects, whereas others were essentially unaffected.

CONCLUSIONS

The ventricular dilatation and callosal shrinkage produced in wild-type rats following involuntary alcohol exposure yielded a modestly successful model of neurodysmorphology phenotypes of human alcoholism. As is the case for the human condition, however, in which some individuals express greater alcoholism-related neuropathology than others, some rats maybe more susceptible than others to extreme alcohol exposure.

Interaction of thiamine deficiency and voluntary alcohol consumption disrupts rat corpus callosum ultrastructure

The relative roles of alcohol and thiamine deficiency in causing brain damage remain controversial in alcoholics without the Wernicke-Korsakoff syndrome. Experimental control over alcohol consumption and diet are impossible in humans but can be accomplished in animal models. This experiment was designed to differentiate the separate and combined effects on the macro- and ultrastructure of the corpus callosum of thiamine deficiency and voluntary alcohol consumption. Adult male alcohol-preferring (P) rats (9 chronically alcohol-exposed and 9 water controls) received a thiamine-deficient diet for 2 weeks. There were four groups: five rats previously exposed to alcohol were treated with pyrithiamine (a thiamine phosphorylation inhibitor); five rats never exposed to alcohol were treated with pyrithiamine; four alcohol-exposed rats were treated with thiamine; and four rats never exposed to alcohol were treated with thiamine. On day 14, thiamine was restored in all 18 rats; 2 weeks later the 10 pyrithiamine-treated rats received intraperitoneal thiamine. The rats were perfused 61 days post-pyrithiamine treatment at age 598 days. Brains were dissected and weight and volumes were calculated. Sagittal sections were stained to measure white matter structures. The corpus callosum was examined using transmission electron microscopy to determine density of myelinated fibers, fiber diameter, and myelin thickness. The corpus callosum in the alcohol/pyrithiamine group was significantly thinner, had greater fiber density, higher percentage of small fibers, and myelin thinning than in the alcohol/thiamine and water/thiamine groups. Several measures showed a graded effect, where the alcohol/pyrithiamine group had greater pathology than the water/pyrithiamine group, which had greater pathology than the two thiamine-replete groups. Across all 16 rats, thinner myelin sheaths correlated with higher percentage of small fibers. Myelin thickness and axon diameter together accounted for 71% of the variance associated with percentage of small fibers. Significant abnormalities in the alcohol/pyrithiamine group and lack of abnormality in the alcohol-exposed/thiamine-replete group indicate that thiamine deficiency caused white matter damage. The graded abnormalities across the dually to singly treated animals support a compounding effect of alcohol exposure and thiamine depletion, and indicate the potential for interaction between alcohol and thiamine deficiency in human alcohol-related brain damage.

Development and resolution of brain lesions caused by pyrithiamine- and dietary-induced thiamine deficiency and alcohol exposure in the alcohol-preferring rat: a longitudinal magnetic resonance imaging and spectroscopy study

Wernicke's encephalopathy (WE) is characterized by lesions in thalamus, hypothalamus (including mammillary nuclei), and inferior colliculi, results in serious disabilities, has an etiology of thiamine deficiency, is treatable with thiamine, and occurs most commonly with alcoholism. Despite decades of study, whether alcohol exposure exacerbates the neuropathology or retards its resolution remains controversial. To examine patterns of brain damage and recovery resulting from thiamine deprivation with and without alcohol exposure, we conducted in vivo magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) at 3 T in alcohol-preferring (P) rats, which had voluntarily consumed large amounts of alcohol before thiamine manipulation. A total of 18 adult male P rats (nine alcohol-exposed) received a thiamine-deficient diet for 2 weeks: 10 (five alcohol-exposed) received intraperitoneal (i.p.) pyrithiamine (PT) and eight (four alcohol-exposed) received i.p. thiamine supplementation. Neurological signs developed by day 14. Rats were scanned before thiamine depletion and 18 and 35 days after thiamine repletion. Two-dimensional J-resolved MRS single-voxel spectra with water reference were collected in a voxel subtending the thalamus; metabolite quantification was corrected for voxel tissue content. MRI identified significant enlargement of dorsal ventricles and increase in signal intensities in thalamus, inferior colliculi, and mammillary nuclei of PT compared with thiamine-treated (TT) groups from MRI 1-2, followed by significant normalization from MRI 2-3 in thalamus and colliculi, but not mammillary nuclei and lateral ventricles. Voxel-by-voxel analysis revealed additional hyperintense signal clusters in the dorsal and ventral hippocampus and enlargement of the fourth ventricle. MRS showed a significant decline and then partial recovery in thalamic N-acetylaspartate, a marker of neuronal integrity, in PT compared with TT rats, with no change detected in creatine, choline, or glutamate. PT rats with prior alcohol exposure exhibited attenuated recovery in the thalamus and arrested growth of the corpus callosum; further, two of the five alcohol-exposed PT rats died prematurely. Parenchymal and ventricular changes with thiamine manipulation concur with human radiological signs of WE. The enduring macrostructural and neurochemical abnormalities involving critical nodes of Papez circuit carry liabilities for development of amnesia and incomplete recovery from other cognitive and motor functions subserved by the affected neural systems.