Neuronal loss in hippocampus induced by prolonged ethanol consumption in rats

Neuroimmune Activation and Microglia Reactivity in Female Rats Following Alcohol Dependence

The rates of alcohol use disorder among women are growing, yet little is known about how the female brain is affected by alcohol. The neuroimmune system, and specifically microglia, have been implicated in mediating alcohol neurotoxicity, but most preclinical studies have focused on males. Further, few studies have considered changes to the microglial phenotype when examining the effects of ethanol on brain structure and function. Therefore, we quantified microglial reactivity in female rats using a binge model of alcohol dependence, assessed through morphological and phenotypic marker expression, coupled with regional cytokine levels. In a time- and region-dependent manner, alcohol altered the microglial number and morphology, including the soma and process area, and the overall complexity within the corticolimbic regions examined, but no significant increases in the proinflammatory markers MHCII or CD68 were observed. The majority of cytokine and growth factor levels examined were similarly unchanged. However, the expression of the proinflammatory cytokine TNFα was increased, and the anti-inflammatory IL-10, decreased. Thus, female rats showed subtle differences in neuroimmune reactivity compared to past work in males, consistent with reports of enhanced neuroimmune responses in females across the literature. These data suggest that specific neuroimmune reactions in females may impact their susceptibility to alcohol neurotoxicity and other neurodegenerative events with microglial contributions.

Astrocyte Reactivity and Neurodegeneration in the Female Rat Brain Following Alcohol Dependence

Recent evidence suggests that alcohol use disorder (AUD) may manifest itself differently in women compared to men. Women experience AUDs on an accelerated timeline and may have certain regional vulnerabilities. In male rats, neuronal cell death and astrocyte reactivity are noted following induction of alcohol dependence in an animal model of an AUD. However, the regional and temporal patterns of neurodegeneration and astrocyte reactivity have yet to be fully examined in females using this model. Therefore, adult female rats were exposed to a 4-day binge model of alcohol dependence followed by different periods of abstinence. Histological markers for FluoroJade B, a label of degenerating neurons, and vimentin, a marker for reactive astrocytes, were utilized. The expression of these markers in cortical and limbic regions was quantified immediately after their last dose (e.g., T0), or 2, 7, and 14 days later. Significant neuronal cell death was noted in the entorhinal cortex and the hippocampus, similar to previous reports in males, but also in several cortical regions not previously observed. Vimentin immunoreactivity was noted in the same regions as previously reported, in addition to three novel regions. Vimentin immunoreactivity also occurred at earlier and later time points in some cortical and hippocampal regions. These data suggest that both neuronal cell death and astrocyte reactivity could be more widespread in females compared to males. Therefore, this study provides a framework for specific regions and time points which should be examined in future studies of alcohol-induced damage that include female rats.

The neuroimmune system - Where aging and excess alcohol intersect

As the percentage of the global population over age 65 grows, and with it a subpopulation of individuals with alcohol use disorder (AUD), understanding the effect of alcohol on the aged brain is of utmost importance. Neuroinflammation is implicated in both natural aging as well as alcohol use, and its role in alterations to brain morphology and function may be exacerbated in aging individuals who drink alcohol to excess. The neuroimmune response to alcohol in aging is complex. The few studies investigating this issue have reported heightened basal activity and either hypo- or hyper-reactivity to an alcohol challenge. This review of preclinical research will first introduce key players of the immune system, then explore changes in neuroimmune function with aging or alcohol alone, with discussion of vulnerable brain regions, changes in cytokines, and varied reactions of microglia and astrocytes. We will then consider different levels of alcohol exposure, relevant animal models of AUD, and neuroimmune activation by alcohol across the lifespan. By identifying key findings, challenges, and targets for future research, we hope to bring more attention and resources to this underexplored area of inquiry.

Evaluating signs of hippocampal neurotoxicity induced by a revisited paradigm of voluntary ethanol consumption in adult male and female Sprague-Dawley rats

BACKGROUND

Binge alcohol drinking is considered a prominent risk factor for the development of alcohol-use disorders, and could be model in rodents through the standard two-bottle preference choice test. The goal was to recreate an intermittent use of alcohol during 3 consecutive days each week to ascertain its potential impact on hippocampal neurotoxicity (neurogenesis and other neuroplasticity markers), and including sex as a biological variable, given the well-known sex differences in alcohol consumption.

METHODS

Ethanol access was granted to adult Sprague-Dawley rats for 3 consecutive days per week, followed by 4 days of withdrawal, during 6 weeks, mimicking the most common pattern of intake in people, drinking over the weekends in an intensive manner. Hippocampal samples were collected to evaluate signs of neurotoxicity.

RESULTS

Female rats consumed significantly more ethanol than males, although intake did not escalate over time. Ethanol preference levels remained below 40% over time and did not differ between sexes. Moderate signs of ethanol neurotoxicity were observed in hippocampus at the level of decreased neuronal progenitors (NeuroD + cells), and these effects were independent of sex. No other signs of neurotoxicity were induced by ethanol voluntary consumption when measured through several key cell fate markers (i.e., FADD, Cyt c, Cdk5, NF-L) by western blot analysis.

CONCLUSIONS

Overall, the present results suggest that even though we modeled a situation where no escalation in ethanol intake occurred across time, mild signs of neurotoxicity emerged, suggesting that even the use of ethanol during adulthood in a recreational way could lead to certain brain harm.

Adult alcohol drinking and emotional tone are mediated by neutral sphingomyelinase during development in males

Alcohol use, abuse, and addiction, and resulting health hazards are highly sex-dependent with unknown mechanisms. Previously, strong links between the SMPD3 gene and its coded protein neutral sphingomyelinase 2 (NSM) and alcohol abuse, emotional behavior, and bone defects were discovered and multiple mechanisms were identified for females. Here we report strong sex-dimorphisms for central, but not for peripheral mechanisms of NSM action in mouse models. Reduced NSM activity resulted in enhanced alcohol consumption in males, but delayed conditioned rewarding effects. It enhanced the acute dopamine response to alcohol, but decreased monoaminergic systems adaptations to chronic alcohol. Reduced NSM activity increased depression- and anxiety-like behavior, but was not involved in alcohol use for the self-management of the emotional state. Constitutively reduced NSM activity impaired structural development in the brain and enhanced lipidomic sensitivity to chronic alcohol. While the central effects were mostly opposite to NSM function in females, similar roles in bone-mediated osteocalcin release and its effects on alcohol drinking and emotional behavior were observed. These findings support the view that the NSM and multiple downstream mechanism may be a source of the sex-differences in alcohol use and emotional behavior.

Cdk5 Promotes Mitochondrial Fission via Drp1 Phosphorylation at S616 in Chronic Ethanol Exposure-Induced Cognitive Impairment

Excessive alcohol consumption can lead to alterations in brain structure and function, even causing irreversible learning and memory disorders. The hippocampus is one of the most sensitive areas to alcohol neurotoxicity in the brain. Accumulating evidence indicates that mitochondrial dysfunction contributes to alcohol neurotoxicity. However, little is known about the underlying molecular mechanisms. In this study, we found that chronic exposure to ethanol caused abnormal mitochondrial fission/fusion and morphology by activating the mitochondrial fission protein dynamin-related protein 1 (Drp1) and upregulating Drp1 receptors, such as fission protein 1 (Fis1), mitochondrial dynamics protein of 49 kDa (Mid49), and mitochondrial fission factor (Mff), combined with decreasing optic atrophy 1 (Opa1) and mitochondrial fusion protein mitofusin 1 (Mfn1) levels. In addition, mitochondrial division inhibitor 1 (mdivi-1) abrogated ethanol-induced mitochondrial dysfunction and improved hippocampal synapses and cognitive function in ethanol-exposed mice. Chronic ethanol exposure also resulted in cyclin-dependent kinase 5 (Cdk5) overactivation, as shown by the increase in the levels of Cdk5 and its activator P25 in the hippocampus. Furthermore, a Cdk5/P25 inhibitor (roscovitine) or Cdk5 knockdown using small interfering RNA (LVi-Cdk5) exerted neuroprotection by inhibiting abnormal mitochondrial fission through Drp1 phosphorylation at Ser616 and mitochondrial translocation after chronic ethanol exposure. Taken together, the present study demonstrated that inhibition of aberrant Cdk5 activation attenuates hippocampal neuron injury and cognitive deficits induced by chronic exposure to ethanol through Drp1-mediated mitochondrial fission and mitochondrial dysfunction. Interfering with this pathway might serve as a potential therapeutic approach to prevent ethanol-induced neurotoxicity in the brain.

Consequences of adolescent alcohol use on adult hippocampal neurogenesis and hippocampal integrity

Alcohol is the most commonly used drug among adolescents. Their decreased sensitivity to self-regulating cues to stop drinking coincides with an enhanced vulnerability to negative outcomes of excessive drinking. In adolescents, the hippocampus is one brain region that is particularly susceptible to alcohol-induced neurodegeneration. While cell death is causal, alcohol effects on adult neurogenesis also impact hippocampal structure and function. This review describes what little is known about adolescent-specific effects of alcohol on adult neurogenesis and its relationship to hippocampal integrity. For example, alcohol intoxication inhibits neurogenesis persistently in adolescents but produces aberrant neurogenesis after alcohol dependence. Little is known, however, about the role of adolescent-born neurons in hippocampal integrity or the mechanisms of these effects. Understanding the role of neurogenesis in adolescent alcohol use and misuse is critical to our understanding of adolescent susceptibility to alcohol pathology and increased likelihood of developing alcohol problems in adulthood.

Functional Activation of Newborn Neurons Following Alcohol-Induced Reactive Neurogenesis

Abstinence after alcohol dependence leads to structural and functional recovery in many regions of the brain, especially the hippocampus. Significant increases in neural stem cell (NSC) proliferation and subsequent "reactive neurogenesis" coincides with structural recovery in hippocampal dentate gyrus (DG). However, whether these reactively born neurons are integrated appropriately into neural circuits remains unknown. Therefore, adult male rats were exposed to a binge model of alcohol dependence. On day 7 of abstinence, the peak of reactive NSC proliferation, rats were injected with bromodeoxyuridine (BrdU) to label dividing cells. After six weeks, rats underwent Morris Water Maze (MWM) training then were sacrificed ninety minutes after the final training session. Using fluorescent immunohistochemistry for c-Fos (neuronal activation), BrdU, and Neuronal Nuclei (NeuN), we investigated whether neurons born during reactive neurogenesis were incorporated into a newly learned MWM neuronal ensemble. Prior alcohol exposure increased the number of BrdU+ cells and newborn neurons (BrdU+/NeuN+ cells) in the DG versus controls. However, prior ethanol exposure had no significant impact on MWM-induced c-Fos expression. Despite increased BrdU+ neurons, no difference in the number of activated newborn neurons (BrdU+/c-Fos+/NeuN+) was observed. These data suggest that neurons born during alcohol-induced reactive neurogenesis are functionally integrated into hippocampal circuitry.

Sex differences in cholinergic circuits and behavioral disruptions following chronic ethanol exposure with and without thiamine deficiency

BACKGROUND

Few studies have investigated differences in the vulnerabilities of males and females to alcohol use disorder and alcohol-related brain damage (ARBD). According to epidemiological and clinical findings, females appear to be more sensitive to the effects of alcohol and thiamine deficiency and have a worse prognosis in recovery from neurocognitive deficits compared with males. This study aimed to characterize the effects of chronic ethanol (EtOH) toxicity and thiamine deficiency across the sexes using rodent models.

METHODS

Male and female Sprague Dawley rats were assigned to chronic forced EtOH treatment (CET), pyrithiamine-induced thiamine deficiency (PTD), combined CET-PTD, or pair-fed (PF) control treatment conditions. Following treatments, spatial working memory was assessed during a spontaneous alternation task while measuring acetylcholine (ACh) in the prefrontal cortex (PFC) and the hippocampus (HPC). The animals also underwent an operant-based attentional set-shifting task (ASST) for the analysis of behavioral flexibility.

RESULTS

Female and male rats did not differ in terms of EtOH consumption; however, the CET and CET-PTD-treated female rats had lower BECs than male rats. Compared with the PF group, the CET, PTD, and CET-PTD groups exhibited spatial working memory impairments with corresponding reductions in ACh efflux in the PFC and HPC. The ASST revealed that CET-PTD-treated males and females displayed impairments marked by increased latency to make decisions. Thalamic shrinkage was prominent only in the CET-PTD and PTD treatment conditions, but no sex-specific effects were observed.

CONCLUSIONS

Although the CET and CET-PTD-treated females had lower BECs than the males, they demonstrated similar cognitive impairments. These results provide evidence that female rats experience behavioral and neurochemical disruptions at lower levels of alcohol exposure than males and that chronic EtOH and thiamine deficiencies produce a unique behavioral profile.

Neutral sphingomyelinase mediates the co-morbidity trias of alcohol abuse, major depression and bone defects

Mental disorders are highly comorbid and occur together with physical diseases, which are often considered to arise from separate pathogenic pathways. We observed in alcohol-dependent patients increased serum activity of neutral sphingomyelinase. A genetic association analysis in 456,693 volunteers found associations of haplotypes of SMPD3 coding for NSM-2 (NSM) with alcohol consumption, but also with affective state, and bone mineralisation. Functional analysis in mice showed that NSM controls alcohol consumption, affective behaviour, and their interaction by regulating hippocampal volume, cortical connectivity, and monoaminergic responses. Furthermore, NSM controlled bone-brain communication by enhancing osteocalcin signalling, which can independently supress alcohol consumption and reduce depressive behaviour. Altogether, we identified a single gene source for multiple pathways originating in the brain and bone, which interlink disorders of a mental-physical co-morbidity trias of alcohol abuse-depression/anxiety-bone disorder. Targeting NSM and osteocalcin signalling may, thus, provide a new systems approach in the treatment of a mental-physical co-morbidity trias.

Recovery of Hippocampal-Dependent Learning Despite Blunting Reactive Adult Neurogenesis After Alcohol Dependence

Background:

The excessive alcohol drinking that occurs in alcohol use disorder (AUD) causes neurodegeneration in regions such as the hippocampus, though recovery may occur after a period of abstinence. Mechanisms of recovery are not clear, though reactive neurogenesis has been observed in the hippocampal dentate gyrus following alcohol dependence and correlates to recovery of granule cell number.

Objective:

We investigated the role of neurons born during reactive neurogenesis in the recovery of hippocampal learning behavior after 4-day binge alcohol exposure, a model of an AUD. We hypothesized that reducing reactive neurogenesis would impair functional recovery.

Methods:

Adult male rats were subjected to 4-day binge alcohol exposure and two approaches were tested to blunt reactive adult neurogenesis, acute doses of alcohol or the chemotherapy drug, temozolomide (TMZ).

Results:

Acute 5 g/kg doses of EtOH gavaged T6 and T7 days post binge did not inhibit significantly the number of Bromodeoxyuridine-positive (BrdU+) proliferating cells in EtOH animals receiving 5 g/kg EtOH versus controls. A single cycle of TMZ inhibited reactive proliferation (BrdU+ cells) and neurogenesis (NeuroD+ cells) to that of controls. However, despite this blunting of reactive neurogenesis to basal levels, EtOH-TMZ rats were not impaired in their recovery of acquisition of the Morris water maze (MWM), learning similarly to all other groups 35 days after 4-day binge exposure.

Conclusions:

These studies show that TMZ is effective in decreasing reactive proliferation/neurogenesis following 4-day binge EtOH exposure, and baseline levels of adult neurogenesis are sufficient to allow recovery of hippocampal function.

Activation of Melanocortin-4 Receptor by a Synthetic Agonist Inhibits Ethanolinduced Neuroinflammation in Rats

BACKGROUND

High ethanol intake induces a neuroinflammatory response resulting in the subsequent maintenance of chronic alcohol consumption. The melanocortin system plays a pivotal role in the modulation of alcohol consumption. Interestingly, it has been shown that the activation of melanocortin-4 receptor (MC4R) in the brain decreases the neuroinflammatory response in models of brain damage other than alcohol consumption, such as LPS-induced neuroinflammation, cerebral ischemia, glutamate excitotoxicity, and spinal cord injury.

OBJECTIVES

In this work, we aimed to study whether MC4R activation by a synthetic MC4R-agonist peptide prevents ethanol-induced neuroinflammation, and if alcohol consumption produces changes in MC4R expression in the hippocampus and hypothalamus.

METHODS

Ethanol-preferring Sprague Dawley rats were selected offering access to 20% ethanol on alternate days for 4 weeks (intermittent access protocol). After this time, animals were i.p. administered an MC4R agonist peptide in the last 2 days of the protocol. Then, the expression of the proinflammatory cytokines interleukin 6 (IL-6), interleukin 1-beta (IL-1β), and tumor necrosis factor-alpha (TNF-α) were measured in the hippocampus, hypothalamus and prefrontal cortex. It was also evaluated if ethanol intake produces alterations in the expression of MC4R in the hippocampus and the hypothalamus.

RESULTS

Alcohol consumption increased the expression of MC4R in the hippocampus and the hypothalamus. The administration of the MC4R agonist reduced IL-6, IL-1β and TNF-α levels in hippocampus, hypothalamus and prefrontal cortex, to those observed in control rats that did not drink alcohol.

CONCLUSION

High ethanol consumption produces an increase in the expression of MC4R in the hippocampus and hypothalamus. The administration of a synthetic MC4R-agonist peptide prevents neuroinflammation induced by alcohol consumption in the hippocampus, hypothalamus, and prefrontal cortex. These results could explain the effect of α-MSH and other synthetic MC4R agonists in decreasing alcohol intake through the reduction of the ethanol-induced inflammatory response in the brain.

Effect of Alcohol on Hippocampal-Dependent Plasticity and Behavior: Role of Glutamatergic Synaptic Transmission

Problematic alcohol drinking and alcohol dependence are an increasing health problem worldwide. Alcohol abuse is responsible for approximately 5% of the total deaths in the world, but addictive consumption of it has a substantial impact on neurological and memory disabilities throughout the population. One of the better-studied brain areas involved in cognitive functions is the hippocampus, which is also an essential brain region targeted by ethanol. Accumulated evidence in several rodent models has shown that ethanol treatment produces cognitive impairment in hippocampal-dependent tasks. These adverse effects may be related to the fact that ethanol impairs the cellular and synaptic plasticity mechanisms, including adverse changes in neuronal morphology, spine architecture, neuronal communication, and finally an increase in neuronal death. There is evidence that the damage that occurs in the different brain structures is varied according to the stage of development during which the subjects are exposed to ethanol, and even much earlier exposure to it would cause damage in the adult stage. Studies on the cellular and cognitive deficiencies produced by alcohol in the brain are needed in order to search for new strategies to reduce alcohol neuronal toxicity and to understand its consequences on memory and cognitive performance with emphasis on the crucial stages of development, including prenatal events to adulthood.

Aging with alcohol-related brain damage: Critical brain circuits associated with cognitive dysfunction

Alcoholism is associated with brain damage and impaired cognitive functioning. The relative contributions of different etiological factors, such as alcohol, thiamine deficiency and age vulnerability, to the development of alcohol-related neuropathology and cognitive impairment are still poorly understood. One reason for this quandary is that both alcohol toxicity and thiamine deficiency produce brain damage and cognitive problems that can be modulated by age at exposure, aging following alcohol toxicity or thiamine deficiency, and aging during chronic alcohol exposure. Pre-clinical models of alcohol-related brain damage (ARBD) have elucidated some of the contributions of ethanol toxicity and thiamine deficiency to neuroinflammation, neuronal loss and functional deficits. However, the critical variable of age at the time of exposure or long-term aging with ARBD has been relatively ignored. Acute thiamine deficiency created a massive increase in neuroimmune genes and proteins within the thalamus and significant increases within the hippocampus and frontal cortex. Chronic ethanol treatment throughout adulthood produced very minor fluctuations in neuroimmune genes, regardless of brain region. Intermittent "binge-type" ethanol during the adolescent period established an intermediate neuroinflammatory response in the hippocampus and frontal cortex, that can persist into adulthood. Chronic excessive drinking throughout adulthood, adolescent intermittent ethanol exposure, and thiamine deficiency all led to a loss of the cholinergic neuronal phenotype within the basal forebrain, reduced hippocampal neurogenesis, and alterations in the frontal cortex. Only thiamine deficiency results in gross pathological lesions of the thalamus. The behavioral impairment following these types of treatments is hierarchical: Thiamine deficiency produces the greatest impairment of hippocampal- and prefrontal-dependent behaviors, chronic ethanol drinking ensues mild impairments on both types of tasks and adolescent intermittent ethanol exposure leads to impairments on frontocortical tasks, with sparing on most hippocampal-dependent tasks. However, our preliminary data suggest that as rodents age following adolescent intermittent ethanol exposure, hippocampal functional deficits began to emerge. A necessary requirement for the advancement of understanding the neural consequences of alcoholism is a more comprehensive assessment and understanding of how excessive alcohol drinking at different development periods (adolescence, early adulthood, middle-aged and aged) influences the trajectory of the aging process, including pathological aging and disease.

Its complicated: The relationship between alcohol and microglia in the search for novel pharmacotherapeutic targets for alcohol use disorders

Alcohol use disorder (AUD) is a chronic relapsing disorder with wide-ranging health consequences. Alcohol targets the central nervous system producing neurodegeneration and subsequent cognitive and behavioral deficits, but the mechanisms behind these effects remain unclear. Recently, evidence has been mounting for the role of neuroimmune activation in the pathogenesis of AUDs, but our nascent state of knowledge about the interaction of alcohol with the neuroimmune system supports that the relationship is complicated. As the resident macrophage of the central nervous system, microglia are a central focus. Human and animal research on the interplay between microglia and alcohol in AUDs has proven to be complex, and though early research focused on a pro-inflammatory phenotype of microglia, the anti-inflammatory and homeostatic roles of microglia must be considered. How these new roles for microglia should be incorporated into our thinking about the neuroimmune system in AUDs is discussed in the context of developing novel pharmacotherapies for AUDs.

Intranasal mesenchymal stem cell secretome administration markedly inhibits alcohol and nicotine self-administration and blocks relapse-intake: mechanism and translational options

BACKGROUND

Chronic consumption of most drugs of abuse leads to brain oxidative stress and neuroinflammation, which inhibit the glutamate transporter GLT-1, proposed to perpetuate drug intake. The present study aimed at inhibiting chronic ethanol and nicotine self-administration and relapse by the non-invasive intranasal administration of antioxidant and anti-inflammatory secretome generated by adipose tissue-derived activated mesenchymal stem cells. The anti-addiction mechanism of stem cell secretome is also addressed.

METHODS

Rats bred for their alcohol preference ingested alcohol chronically or were trained to self-administer nicotine. Secretome of human adipose tissue-derived activated mesenchymal stem cells was administered intranasally to animals, both (i) chronically consuming alcohol or nicotine and (ii) during a protracted deprivation before a drug re-access leading to relapse intake.

RESULTS

The intranasal administration of secretome derived from activated mesenchymal stem cells inhibited chronic self-administration of ethanol or nicotine by 85% and 75%, respectively. Secretome administration further inhibited by 85-90% the relapse "binge" intake that occurs after a protracted drug deprivation followed by a 60-min drug re-access. Secretome administration fully abolished the oxidative stress induced by chronic ethanol or nicotine self-administration, shown by the normalization of the hippocampal oxidized/reduced glutathione ratio, and the neuroinflammation determined by astrocyte and microglial immunofluorescence. Knockdown of the glutamate transporter GLT-1 by the intracerebral administration of an antisense oligonucleotide fully abolished the inhibitory effect of the secretome on ethanol and nicotine intake.

CONCLUSIONS

The non-invasive intranasal administration of secretome generated by human adipose tissue-derived activated mesenchymal stem cells markedly inhibits alcohol and nicotine self-administration, an effect mediated by the glutamate GLT-1 transporter. Translational implications are envisioned.

Comparative study on the effects of cigarette smoke exposure, ethanol consumption and association: Behavioral parameters, apoptosis, glial fibrillary acid protein and S100β immunoreactivity in different regions of the rat hippocampus

Exposure to cigarette smoke and ethanol are proposed to trigger neurotoxicity, apoptosis, and to impair neuronal signaling. However, it is little known how the combination of both might trigger astrogliosis and the morphological changes capable of affecting a differential susceptibility of hippocampal regions to these licit drugs. The present study investigated the chronic effects of exposure to cigarette smoke and/or ethanol on behavioral parameters, apoptosis, and alteration in immunoreactivity of glial fibrillary acid protein (GFAP) and S100β in the CA1, CA3, and dentate gyrus (DG) of the rat hippocampus. Adult male Wistar rats (n = 32) were divided into four groups: vehicle (VE, glucose 3% in water, 10 mL/kg), cigarette smoke (TOB, total 12 cigarettes per day), ethanol (ethanol, 2 g/kg), and cigarette smoke plus ethanol (TOB plus ethanol, total 12 cigarettes per day plus ethanol 2 g/kg) for 54 days. The groups were submitted to tail-flick, open-field, and inhibitory avoidance tasks. The results showed that ethanol per se worsened the short-term memory. The association between TOB and ethanol increased the immunoreactivity of cleaved caspase-3 in the CA3 and DG regions. The TOB plus ethanol group showed a lower immunoreactivity to GFAP in all regions of the hippocampus. In addition, ethanol and TOB per se also reduced the immunoreactivity for GFAP in the DG. Ethanol increased S100β immunoreactivity only in the DG. In conclusion, this study showed that only ethanol worsened short-term memory, and the DG became more susceptible to changes in the markers investigated. This evidence suggests that DG is more sensitive to neurotoxicity induced by cigarette smoke and ethanol.

Recurrent binge ethanol is associated with significant loss of dentate gyrus granule neurons in female rats despite concomitant increase in neurogenesis

Binge drinking is becoming increasingly common among American women and girls. We have previously shown significant cell loss, downregulation of neurotrophins and microgliosis in female rats after a single 4-day ethanol exposure. To determine whether recurrent binge exposure would produce similar effects, we administered ethanol (5 g/kg) or iso-caloric control diet once-weekly for 11 weeks to adult female rats. As we have previously shown exercise neuroprotection against binge-induced damage, half the rats were given access to exercise wheels. Blood ethanol concentration (BEC) did not differ between sedentary and exercised groups, nor did it change across time. Using stereology, we quantified the number and/or size of neurons in the medial prefrontal cortex (mPFC) and hippocampal dentate gyrus (DG), as well as the number and activation state of microglia. Binged sedentary rats had significant cell loss in the dentate gyrus, but exercise eliminated this effect. Compared to sedentary controls, sedentary binged rats and all exercised rats showed increased neurogenesis in the DG. Number and nuclear volume of neurons in the mPFC were not changed. In the hippocampus and mPFC, the number of microglia with morphology indicative of partial activation was increased by recurrent binge ethanol and decreased by exercise. In summary, we show significant binge-induced loss of DG granule neurons despite increased neurogenesis, suggesting an unsuccessful compensatory response. Although exercise eliminated cell loss, our results indicate that infrequent, but recurrent exposure to clinically relevant BEC is neurotoxic.

Activated mesenchymal stem cell administration inhibits chronic alcohol drinking and suppresses relapse-like drinking in high-alcohol drinker rats

Neuroinflammation has been reported to follow chronic ethanol intake and may perpetuate alcohol consumption. Present studies determined the effect of human mesenchymal stem cells (hMSCs), known for their anti-inflammatory action, on chronic ethanol intake and relapse-like ethanol intake in a post-deprivation condition. Rats were allowed 12-17 weeks of chronic voluntary ethanol (10% and 20% v/v) intake, after which a single dose of activated hMSCs (5 × 10⁵ ) was injected into a brain lateral ventricle. Control animals were administered vehicle. After assessing the effect of hMSCs on chronic ethanol intake for 1 week, animals were deprived of ethanol for 2 weeks and thereafter an ethanol re-access of 60 min was allowed to determine relapse-like intake. A single administration of activated hMSCs inhibited chronic alcohol consumption by 70% (P < 0.001), an effect seen within the first 24 hours of hMSCs administration, and reduced relapse-like drinking by 80% (P < 0.001). In the relapse-like condition, control animals attain blood ethanol ('binge-like') levels >80 mg/dl. The single hMSC administration reduced relapse-like blood ethanol levels to 20 mg/dl. Chronic ethanol intake increased by 250% (P < 0.001) the levels of reactive oxygen species in hippocampus, which were markedly reduced by hMSC administration. Astrocyte glial acidic fibrillary protein immunoreactivity, a hallmark of neuroinflammation, was increased by 60-80% (P < 0.001) by chronic ethanol intake, an effect that was fully abolished by the administration of hMSCs. This study supports the neuroinflammation-chronic ethanol intake hypothesis and suggest that mesenchymal stem cell administration may be considered in the treatment of alcohol use disorders.

Hippocampal granule cell loss in human chronic alcohol abusers

Chronic alcohol abuse causes cognitive impairments associated with neurodegeneration and volume loss in the human hippocampus. Here, we hypothesize that alcohol reduces the number of granule cells in the human dentate gyrus and consequently contribute to the observed volume loss. Hippocampal samples were isolated from deceased donors with a history of chronic alcohol abuse and from controls with no alcohol overconsumption. From each case, a sample from the mid-portion of hippocampus was sectioned, immunostained for the neuronal nuclear marker NeuN, and counter stained with hematoxylin. Granule cell number and volume of granular cell layer in the dentate gyrus were estimated using stereology. We found a substantial reduction in granule cell number and also a significantly reduced volume of the granular cell layer of chronic alcohol abusers as compared to controls. In controls there was a slight age-related decline in the number of granule cells and volume of granular cell layer in line with previous studies. This was not observed among the alcoholics, possibly due to a larger impact of alcohol abuse than age on the degenerative changes in the dentate gyrus. Loss of neurons in the alcoholic group could either be explained by an increase of cell death or a reduced number of new cells added to the granular cell layer. However, there is no firm evidence for an increased neuronal death by chronic alcohol exposure, whereas a growing body of experimental data indicates that neurogenesis is impaired by alcohol. In a recent study, we reported that alcoholics show a reduced number of stem/progenitor cells and immature neurons in the dentate gyrus, hence that alcohol negatively affects hippocampal neurogenesis. The present results further suggest that such impairment of neurogenesis by chronic alcohol abuse also results in a net loss of granule cells in the dentate gyrus of hippocampus.

The SERCA2: A Gatekeeper of Neuronal Calcium Homeostasis in the Brain

Calcium (Ca2+) ions are prominent cell signaling regulators that carry information for a variety of cellular processes and are critical for neuronal survival and function. Furthermore, Ca2+ acts as a prominent second messenger that modulates divergent intracellular cascades in the nerve cells. Therefore, nerve cells have developed intricate Ca2+ signaling pathways to couple the Ca2+ signal to their biochemical machinery. Notably, intracellular Ca2+ homeostasis greatly relies on the rapid redistribution of Ca2+ ions into the diverse subcellular organelles which serve as Ca2+ stores, including the endoplasmic reticulum (ER). It is well established that Ca2+ released into the neuronal cytoplasm is pumped back into the ER by the sarco-/ER Ca2+ ATPase 2 (SERCA2), a P-type ion-motive ATPase that resides on the ER membrane. Even though the SERCA2 is constitutively expressed in nerve cells, its precise role in brain physiology and pathophysiology is not well-characterized. Intriguingly, SERCA2-dependent Ca2+ dysregulation has been implicated in several disorders that affect cognitive function, including Darier's disease, schizophrenia, Alzheimer's disease, and cerebral ischemia. The current review summarizes knowledge on the expression pattern of the different SERCA2 isoforms in the nervous system, and further discusses evidence of SERCA2 dysregulation in various neuropsychiatric disorders. To the best of our knowledge, this is the first literature review that specifically highlights the critical role of the SERCA2 in the brain. Advancing knowledge on the role of SERCA2 in maintaining neuronal Ca2+ homeostasis may ultimately lead to the development of safer and more effective pharmacotherapies to combat debilitating neuropsychiatric disorders.

Intravenous administration of anti-inflammatory mesenchymal stem cell spheroids reduces chronic alcohol intake and abolishes binge-drinking

Chronic alcohol intake leads to neuroinflammation and astrocyte dysfunction, proposed to perpetuate alcohol consumption and to promote conditioned relapse-like binge drinking. In the present study, human mesenchymal stem cells (MSCs) were cultured in 3D-conditions to generate MSC-spheroids, which greatly increased MSCs anti-inflammatory ability and reduced cell volume by 90% versus conventionally 2D-cultured MSCs, enabling their intravenous administration and access to the brain. It is shown, in an animal model of chronic ethanol intake and relapse-drinking, that both the intravenous and intra-cerebroventricular administration of a single dose of MSC-spheroids inhibited chronic ethanol intake and relapse-like drinking by 80–90%, displaying significant effects over 3–5 weeks. The MSC-spheroid administration fully normalized alcohol-induced neuroinflammation, as shown by a reduced astrocyte activation, and markedly increased the levels of the astrocyte Na-glutamate (GLT-1) transporter. This research suggests that the intravenous administration of MSC-spheroids may constitute an effective new approach for the treatment of alcohol-use disorders.

Apolipoprotein E4 exacerbates ethanol-induced neurotoxicity through augmentation of oxidative stress and apoptosis in N2a-APP cells

Neuronal loss is a prominent phenomenon in Alzheimer's disease (AD) and alcohol-induced brain damage. Alcohol abuse is associated with an increased risk of AD, regardless of the type of alcoholic beverage. Furthermore, the detrimental effect of excessive alcohol consumption on the risk of AD is exacerbated among people carrying apolipoprotein E (APOE) ε4 allele, the major genetic risk factor for AD. However, how APOE ε4 and alcohol abuse synergistically enhance the possibility of AD is unclear. Here we show that in N2a cells stably expressing human APP695 (N2a-APP), high-concentration ethanol-induced neurotoxicity was significantly augmented in the presence of apoE4 protein, compared with apoE3 protein. Early and late apoptotic cells were apparently more in cells treated with the combination of apoE4 and ethanol, compared with that of apoE3 and ethanol. Inhibition of apoptosis using a pan-caspase inhibitor z-vad resulted in abolishment of the apoE isoform-specific effect on high-concentration ethanol-induced neurotoxicity. Moreover, compared with apoE3, apoE4 augmented ethanol-induced cellular oxidative stress, and pre-incubation with a reactive oxygen species (ROS) scavenger NAC abrogated the specific effect of apoE4 on ethanol-induced neurotoxicity. Taken together, our results for the first time demonstrate that apoE4 and high-concentration ethanol synergistically enhance neurotoxicity through elevating cellular oxidative stress and increasing neuronal apoptosis, and support the notion that avoiding excessive alcohol consumption can help to prevent AD especially in APOE ε4 carriers.

Myths and truths about the cellular composition of the human brain: A review of influential concepts

Over the last 50 years, quantitative methodology has made important contributions to our understanding of the cellular composition of the human brain. Not all of the concepts that emerged from quantitative studies have turned out to be true. Here, I examine the history and current status of some of the most influential notions. This includes claims of how many cells compose the human brain, and how different cell types contribute and in what ratios. Additional concepts entail whether we lose significant numbers of neurons with normal aging, whether chronic alcohol abuse contributes to cortical neuron loss, whether there are significant differences in the quantitative composition of cerebral cortex between male and female brains, whether superior intelligence in humans correlates with larger numbers of brain cells, and whether there are secular (generational) changes in neuron number. Do changes in cell number or changes in ratios of cell types accompany certain diseases, and should all counting methods, even the theoretically unbiased ones, be validated and calibrated? I here examine the origin and the current status of major influential concepts, and I review the evidence and arguments that have led to either confirmation or refutation of such concepts. I discuss the circumstances, assumptions and mindsets that perpetuated erroneous views, and the types of technological advances that have, in some cases, challenged longstanding ideas. I will acknowledge the roles of key proponents of influential concepts in the sometimes convoluted path towards recognition of the true cellular composition of the human brain.

Acquisition, Maintenance and Relapse-Like Alcohol Drinking: Lessons from the UChB Rat Line

This review article addresses the biological factors that influence: (i) the acquisition of alcohol intake; (ii) the maintenance of chronic alcohol intake; and (iii) alcohol relapse-like drinking behavior in animals bred for their high-ethanol intake. Data from several rat strains/lines strongly suggest that catalase-mediated brain oxidation of ethanol into acetaldehyde is an absolute requirement (up 80%–95%) for rats to display ethanol’s reinforcing effects and to initiate chronic ethanol intake. Acetaldehyde binds non-enzymatically to dopamine forming salsolinol, a compound that is self-administered. In UChB rats, salsolinol: (a) generates marked sensitization to the motivational effects of ethanol; and (b) strongly promotes binge-like drinking. The specificity of salsolinol actions is shown by the finding that only the R-salsolinol enantiomer but not S-salsolinol accounted for the latter effects. Inhibition of brain acetaldehyde synthesis does not influence the maintenance of chronic ethanol intake. However, a prolonged ethanol withdrawal partly returns the requirement for acetaldehyde synthesis/levels both on chronic ethanol intake and on alcohol relapse-like drinking. Chronic ethanol intake, involving the action of lipopolysaccharide diffusing from the gut, and likely oxygen radical generated upon catechol/salsolinol oxidation, leads to oxidative stress and neuro-inflammation, known to potentiate each other. Data show that the administration of N-acetyl cysteine (NAC) a strong antioxidant inhibits chronic ethanol maintenance by 60%–70%, without inhibiting its initial intake. Intra-cerebroventricular administration of mesenchymal stem cells (MSCs), known to release anti-inflammatory cytokines, to elevate superoxide dismutase levels and to reverse ethanol-induced hippocampal injury and cognitive deficits, also inhibited chronic ethanol maintenance; further, relapse-like ethanol drinking was inhibited up to 85% for 40 days following intracerebral stem cell administration. Thus: (i) ethanol must be metabolized intracerebrally into acetaldehyde, and further into salsolinol, which appear responsible for promoting the acquisition of the early reinforcing effects of ethanol; (ii) acetaldehyde is not responsible for the maintenance of chronic ethanol intake, while other mechanisms are indicated; (iii) the systemic administration of NAC, a strong antioxidant markedly inhibits the maintenance of chronic ethanol intake; and (iv) the intra-cerebroventricular administration of anti-inflammatory and antioxidant MSCs inhibit both the maintenance of chronic ethanol intake and relapse-like drinking.

Quantitative analysis of nanoscale intranuclear structural alterations in hippocampal cells in chronic alcoholism via transmission electron microscopy imaging

Chronic alcoholism is known to alter the morphology of the hippocampus, an important region of cognitive function in the brain. Therefore, to understand the effect of chronic alcoholism on hippocampal neural cells, we employed a mouse model of chronic alcoholism and quantified intranuclear nanoscale structural alterations in these cells. Transmission electron microscopy (TEM) images of hippocampal neurons were obtained, and the degree of structural alteration in terms of mass density fluctuation was determined using the light-localization properties of optical media generated from TEM imaging. The results, which were obtained at length scales ranging from ~30 to 200 nm, show that 10-12 week-old mice fed a Lieber-DeCarli liquid (alcoholic) diet had a higher degree of structural alteration than control mice fed a normal diet without alcohol. The degree of structural alteration became significantly distinguishable at a sample length of ~100 nm, which is the typical length scale of the building blocks of cells, such as DNA, RNA, proteins and lipids. Interestingly, different degrees of structural alteration at such length scales suggest possible structural rearrangement of chromatin inside the nuclei in chronic alcoholism.

REVIEW ■ : Long-lasting Effects of Recreational Drugs of Abuse on the Central Nervous System

Although a wealth of knowledge exists regarding the acute pharmacological effects of recreational drugs on the CNS, much less is known about the long-term toxic effects of recreational drugs on the CNS. Recent findings in nonhuman primates treated with amphetamine analogs, such as ±3,4-methylenedioxymetham phetamine (MDMA), indicate that these drugs can produce long-lasting, probably permanent, changes in brain serotonin innervation. Similarly, animals treated with phencyclidine (PCP) and related drugs develop neurodegenerative changes in selected brain regions. It seems clear, then, that some psychoactive drugs have the potential to produce persistent changes in CNS structure and, possibly, function. The goal of this article is to summarize current knowledge regarding the long-term effects of several popular recreational drugs, including MDMA and related amphetamine analogs, cocaine, marijuana, alcohol, PCP, lysergic acid (LSD), and opiates. Gaps in the current knowledge base are identified, and areas ripe for future research efforts are suggested. NEUROSCIENTIST 3:399-411, 1997

Adolescent Intermittent Alcohol Exposure: Deficits in Object Recognition Memory and Forebrain Cholinergic Markers

The long-term effects of intermittent ethanol exposure during adolescence (AIE) are of intensive interest and investigation. The effects of AIE on learning and memory and the neural functions that drive them are of particular interest as clinical findings suggest enduring deficits in those cognitive domains in humans after ethanol abuse during adolescence. Although studies of such deficits after AIE hold much promise for identifying mechanisms and therapeutic interventions, the findings are sparse and inconclusive. The present results identify a specific deficit in memory function after AIE and establish a possible neural mechanism of that deficit that may be of translational significance. Male rats (starting at PND-30) received exposure to AIE (5g/kg, i.g.) or vehicle and were allowed to mature into adulthood. At PND-71, one group of animals was assessed using the spatial-temporal object recognition (stOR) test to evaluate memory function. A separate group of animals was used to assess the density of cholinergic neurons in forebrain areas Ch1-4 using immunohistochemistry. AIE exposed animals manifested deficits in the temporal component of the stOR task relative to controls, and a significant decrease in the number of ChAT labeled neurons in forebrain areas Ch1-4. These findings add to the growing literature indicating long-lasting neural and behavioral effects of AIE that persist into adulthood and indicate that memory-related deficits after AIE depend upon the tasks employed, and possibly their degree of complexity. Finally, the parallel finding of diminished cholinergic neuron density suggests a possible mechanism underlying the effects of AIE on memory and hippocampal function as well as possible therapeutic or preventive strategies for AIE.

Interactions between chronic ethanol consumption and thiamine deficiency on neural plasticity, spatial memory, and cognitive flexibility

BACKGROUND

Many alcoholics display moderate to severe cognitive dysfunction accompanied by brain pathology. A factor confounded with prolonged heavy alcohol consumption is poor nutrition, and many alcoholics are thiamine deficient. Thus, thiamine deficiency (TD) has emerged as a key factor underlying alcohol-related brain damage (ARBD). TD in humans can lead to Wernicke Encephalitis that can progress into Wernicke-Korsakoff syndrome and these disorders have a high prevalence among alcoholics. Animal models are critical for determining the exact contributions of ethanol (EtOH)- and TD-induced neurotoxicity, as well as the interactions of those factors to brain and cognitive dysfunction.

METHODS

Adult rats were randomly assigned to 1 of 6 treatment conditions: chronic EtOH treatment (CET) where rats consumed a 20% v/v solution of EtOH over 6 months; severe pyrithiamine-induced TD (PTD-moderate acute stage); moderate PTD (PTD-early acute stage); moderate PTD followed by CET (PTD-CET); moderate PTD during CET (CET-PTD); and pair-fed (PF) control. After recovery from treatment, all rats were tested on spontaneous alternation and attentional set-shifting. After behavioral testing, brains were harvested for determination of mature brain-derived neurotrophic factor (BDNF) and thalamic pathology.

RESULTS

Moderate TD combined with CET, regardless of treatment order, produced significant impairments in spatial memory, cognitive flexibility, and reductions in brain plasticity as measured by BDNF levels in the frontal cortex and hippocampus. These alterations are greater than those seen in moderate TD alone, and the synergistic effects of moderate TD with CET lead to a unique cognitive profile. However, CET did not exacerbate thalamic pathology seen after moderate TD.

CONCLUSIONS

These data support the emerging theory that subclinical TD during chronic heavy alcohol consumption is critical for the development of significant cognitive impairment associated with ARBD.

Adolescent alcohol exposure alters GABAA receptor subunit expression in adult hippocampus

BACKGROUND

The long-term consequences of adolescent alcohol abuse that persist into adulthood are poorly understood and have not been widely investigated. We have shown that intermittent exposure to alcohol during adolescence decreased the amplitude of GABAA receptor (GABAA R)-mediated tonic currents in hippocampal dentate granule cells in adulthood. The aim of this study was to investigate the enduring effects of chronic intermittent alcohol exposure during adolescence or adulthood on the expression of hippocampal GABAA Rs.

METHODS

We used a previously characterized tissue fractionation method to isolate detergent resistant membranes and soluble fractions, followed by Western blots to measure GABAA R protein expression. We also measured mRNA levels of GABAA R subunits using quantitative real-time polymerase chain reaction.

RESULTS

Although the protein levels of α1-, α4-, and δ-GABAA R subunits remained stable between postnatal day (PD) 30 (early adolescence) and PD71 (adulthood), the α5-GABAA R subunit was reduced across that period. In rats that were subjected to adolescent intermittent ethanol (AIE) exposure between PD30 and PD46, there was a significant reduction in the protein levels of the δ-GABAA R, in the absence of any changes in mRNA levels, at 48 hours and 26 days after the last ethanol (EtOH) exposure. Protein levels of the α4-GABAA R subunit were significantly reduced, but mRNA levels were increased, 26 days (but not 48 hours) after the last AIE exposure. Protein levels of α5-GABAA R were not changed by AIE, but mRNA levels were reduced at 48 hours but normalized 26 days after AIE. In contrast to the effects of AIE, chronic intermittent ethanol (CIE) exposure during adulthood had no effect on expression of any of the GABAA R subunits examined.

CONCLUSIONS

AIE produced both short- and long-term alterations of GABAA R subunits mRNA and protein expression in the hippocampus, whereas CIE produced no long-lasting effects on those measures. The observed reduction of protein levels of the δ-GABAA R, specifically, is consistent with previously reported altered hippocampal GABAA R-mediated electrophysiological responses after AIE. The absence of effects of CIE underscores the emerging view of adolescence as a time of distinctive vulnerability to the enduring effects of repeated EtOH exposure.

Changes in expression of BDNF and its receptors TrkB and p75NTR in the hippocampus of a dog model of chronic alcoholism and abstinence

Chronic ethanol consumption can produce learning and memory deficits. Brain-derived neurotrophic factor (BDNF) and its receptors affect the pathogenesis of alcoholism. In this study, we examined the expression of BDNF, tropomyosin receptor kinase B (TrkB) and p75 neurotrophin receptor (p75NTR) in the hippocampus of a dog model of chronic alcoholism and abstinence. Twenty domestic dogs (9-10 months old, 15-20 kg; 10 males and 10 females) were obtained from Harbin Medical University. A stable alcoholism model was established through ad libitum feeding, and anti-alcohol drug treatment (Zhong Yao Jie Jiu Ling, the main ingredient was the stems of watermelon; developed in our laboratory), at low- and high-doses, was carried out. The Zhong Yao Jie Jiu Ling was effective for the alcoholism in dogs. The morphology of hippocampal neurons was evaluated using hematoxylin-eosin staining. The number and morphological features of BDNF, TrkB and p75NTR-positive neurons in the dentate gyrus (DG), and the CA1, CA3 and CA4 regions of the hippocampus were observed using immunohistochemistry. One-way ANOVA was used to determine differences in BDNF, TrkB and p75NTR expression. BDNF, TrkB and p75NTR-positive cells were mainly localized in the granular cell layer of the DG and in the pyramidal cell layer of the CA1, CA3 and CA4 regions (DG>CA1>CA3>CA4). Expression levels of both BDNF and TrkB were decreased in chronic alcoholism, and increased after abstinence. The CA4 region appeared to show the greatest differences. Changes in p75NTR expression were the opposite of those of BDNF and TrkB, with the greatest differences observed in the DG and CA4 regions.

Alcohol use across the lifespan: An analysis of adolescent and aged rodents and humans

Adolescence and old age are unique periods of the lifespan characterized by differential sensitivity to the effects of alcohol. Adolescents and the elderly appear to be more vulnerable to many of alcohol's physiological and behavioral effects compared to adults. The current review explores the differential effects of acute alcohol, predominantly in terms of motor function and cognition, in adolescent and aged humans and rodents. Adolescents are less sensitive to the sedative-hypnotic, anxiolytic, and motor-impairing effects of acute alcohol, but research results are less consistent as it relates to alcohol's effects on cognition. Specifically, previous research has shown adolescents to be more, less, and similarly sensitive to alcohol-induced cognitive deficits compared to adults. These equivocal findings suggest that learning acquisition may be differentially affected by ethanol compared to memory, or that ethanol-induced cognitive deficits are task-dependent. Older rodents appear to be particularly vulnerable to the motor- and cognitive-impairing effects of acute alcohol relative to younger adults. Given that alcohol consumption and abuse is prevalent throughout the lifespan, it is important to recognize age-related differences in response to acute and long-term alcohol. Unfortunately, diagnostic measures and treatment options for alcohol dependence are rarely dedicated to adolescent and aging populations. As discussed, although much scientific advancement has been made regarding the differential effects of alcohol between adolescents and adults, research with the aged is underrepresented. Future researchers should be aware that adolescents and the aged are uniquely affected by alcohol and should continue to investigate alcohol's effects at different stages of maturation.

Alcohol and adult hippocampal neurogenesis: promiscuous drug, wanton effects

Adult neurogenesis is now widely accepted as an important contributor to hippocampal integrity and function but also dysfunction when adult neurogenesis is affected in neuropsychiatric diseases such as alcohol use disorders. Excessive alcohol consumption, the defining characteristic of alcohol use disorders, results in a variety of cognitive and behavioral impairments related wholly or in part to hippocampal structure and function. Recent preclinical work has shown that adult neurogenesis may be one route by which alcohol produces hippocampal neuropathology. Alcohol is a pharmacologically promiscuous drug capable of interfering with adult neurogenesis through multiple mechanisms. This review will discuss the primary mechanisms underlying alcohol-induced changes in adult hippocampal neurogenesis including alcohol's effects on neurotransmitters, CREB and its downstream effectors, and the neurogenic niche.

Acute and chronic effects of ethanol on learning-related synaptic plasticity

Alcoholism is associated with acute and long-term cognitive dysfunction including memory impairment, resulting in substantial disability and cost to society. Thus, understanding how ethanol impairs cognition is essential for developing treatment strategies to dampen its adverse impact. Memory processing is thought to involve persistent, use-dependent changes in synaptic transmission, and ethanol alters the activity of multiple signaling molecules involved in synaptic processing, including modulation of the glutamate and gamma-aminobutyric acid (GABA) transmitter systems that mediate most fast excitatory and inhibitory transmission in the brain. Effects on glutamate and GABA receptors contribute to ethanol-induced changes in long-term potentiation (LTP) and long-term depression (LTD), forms of synaptic plasticity thought to underlie memory acquisition. In this paper, we review the effects of ethanol on learning-related forms of synaptic plasticity with emphasis on changes observed in the hippocampus, a brain region that is critical for encoding contextual and episodic memories. We also include studies in other brain regions as they pertain to altered cognitive and mental function. Comparison of effects in the hippocampus to other brain regions is instructive for understanding the complexities of ethanol's acute and long-term pharmacological consequences.

Effects of ethanol exposure on nervous system development in zebrafish

Alcohol (ethanol) is a teratogen that adversely affects nervous system development in a wide range of animal species. In humans numerous congenital abnormalities arise as a result of fetal alcohol exposure, leading to a spectrum of disorders referred to as fetal alcohol spectrum disorder (FASD). These abnormalities include craniofacial defects as well as neurological defects that affect a variety of behaviors. These human FASD phenotypes are reproduced in the rodent central nervous system (CNS) following prenatal ethanol exposure. While the study of ethanol effects on zebrafish development has been more limited, several studies have shown that different strains of zebrafish exhibit differential susceptibility to ethanol-induced cyclopia, as well as behavioral deficits. Molecular mechanisms underlying the effects of ethanol on CNS development also appear to be shared between rodent and zebrafish. Thus, zebrafish appear to recapitulate the observed effects of ethanol on human and mouse CNS development, indicating that zebrafish can serve as a complimentary developmental model system to study the molecular basis of FASD. Recent studies examining the effect of ethanol exposure on zebrafish nervous system development are reviewed, with an emphasis on attempts to elucidate possible molecular pathways that may be impacted by developmental ethanol exposure. Recent work from our laboratories supports a role for perturbed extracellular matrix function in the pathology of ethanol exposure during zebrafish CNS development. The use of the zebrafish model to assess the effects of ethanol exposure on adult nervous system function as manifested by changes in zebrafish behavior is also discussed.

Determining the threshold for alcohol-induced brain damage: new evidence with gliosis markers

BACKGROUND

Chronic intake of ethanol (EtOH) has been linked to serious health consequences such as cardiac and liver problems, cognitive impairments, and brain damage. Alcohol's detrimental effects depend upon the dose, duration, and pattern of exposure with binge drinking as one of the most common, but most damaging, patterns of intake. Little is known about the threshold of the damaging effects of alcohol. Therefore, these experiments sought to determine a threshold for brain damage using various markers of neurodegeneration.

METHODS

Adult male Sprague-Dawley rats were administered nutritionally complete liquid diet containing either EtOH (25% w/v) or isocaloric dextrose every 8 hours for either 1 (mean dose, 13.4 ± 0.3 g/kg/d; mean blood EtOH concentration (BEC), 336.2 ± 18.8 mg/dl) or 2 days (mean dose, 10.9 ± 0.3 g/kg/d; mean BEC, 369.8 ± 18.1 mg/dl). On the basis of a known time course of various neurodegeneration-associated events, rats were perfused transcardially immediately following, 2 days after, or 7 days post EtOH exposure. To label actively dividing cells, some animals were injected with BromodeoxyUridine (BrdU) 2 hours prior to perfusion. Tissue was then analyzed for the presence of BrdU (cell proliferation), FluoroJade B (degenerative neurons), and vimentin (reactive astrogliosis) immunoreactivity.

RESULTS

One or 2 days of EtOH exposure failed to alter cell proliferation at any of the time points analyzed. However, significant 2- to 9-fold increases in neuronal degeneration in limbic cortex and clear evidence of reactive gliosis as indicated by a 2- to 8-fold upregulation in vimentin immunoreactivity in the hippocampus were observed following as little as 1 day of binge EtOH exposure.

CONCLUSIONS

These results indicate that as little as 1 day (24 hours) of high BEC, binge-like EtOH exposure is enough to elicit signs of alcohol-induced brain damage in adult rats. Further, reactive gliosis may be a more sensitive marker of alcohol-induced damage in the hippocampus.

Susceptibility to ethanol sensitization is differentially associated with changes in pCREB, trkB and BDNF mRNA expression in the mouse brain

Repeated exposure to ethanol in mice induces behavioural sensitization, a progressive increase in locomotor activity that is common to drugs of abuse. Not all mice however show sensitization to ethanol. The goal of the present study was to examine whether variability in the sensitization response to ethanol (EtOH) is differentially associated with regional brain changes in specific molecular markers associated with neuroplasticity, namely BDNF and its receptor trkB, and levels of phosphorylated cyclic AMP-regulated element-binding protein (pCREB), 14 days after withdrawal from chronic, intermittent EtOH exposure. Male DBA/2NCrl mice received 7 biweekly EtOH (2.2g/kg, i.p.) or saline (SAL) injections and were classified as Sensitized or Non-sensitized on the basis of final locomotor activity (LMA) scores. Brains were removed two weeks later for immunohistochemical and in situ hybridization analyses. Compared to SAL-treated and Non-sensitized mice, Sensitized animals showed a higher number of pCREB-immunoreactive cells in the nucleus accumbens shell (+68% and +50%, respectively) and in the bed nucleus of the stria terminalis (+61% and 46%, respectively), whereas SAL and Non-sensitized groups did not differ from each other. A different pattern was seen when BDNF and trkB mRNA levels were analyzed in the same groups. Non-sensitized mice displayed lower BDNF mRNA in several brain areas and significantly lower trkB levels throughout the brain when compared to either the Sensitized or to SAL groups, which did not differ from each other. These results indicate that sensitization to EtOH is differentially associated with increased pCREB levels in specific brain areas. The observed decrease in BDNF and trkB mRNA in the Non-sensitized group suggests the possibility that EtOH may have neurotoxic effects in a subpopulation of mice, which might in turn prevent the development of behavioural sensitization. The lack of a difference in BDNF and trkB mRNA expression between Sensitized and SAL mice suggests that EtOH sensitization may be mediated by mechanisms different from those mediating sensitization to other psychostimulants.

Theta event-related synchronization is a biomarker for a morbid effect of alcoholism on the brain that may partially resolve with extended abstinence

Analyzing the induced (non-stimulus-phase-locked) EEG activity elicited by targets in a three-condition visual oddball task, Fein and colleagues have shown increased theta band event-related synchronization (ERS) in two different samples of long-term abstinent alcoholics (LTAA) compared with age- and gender-comparable controls. The theta ERS effect in alcoholics was also shown to be independent of, and opposite in direction to, the reduced amplitude evoked (stimulus-phase-locked) activity typically found in alcoholics and those at genetic risk of developing alcoholism. This study extends these findings by applying time-frequency analysis to target stimulus event-related EEG to compare evoked and induced theta activity in 43 LTAA and 72 nonalcoholic controls with a group of 31 alcoholics who just recently initiated abstinence from alcohol (between 6- and 15-week abstinent; referred to as short-term abstinent alcoholics, STAA). Results demonstrated that (1) evoked theta power was reduced to the same degree in STAA and LTAA compared with nonalcoholic control participants, while (2) induced theta activity, measured by theta ERS, was increased in both STAA and LTAA relative to controls, but was also increased in STAA relative to LTAA. The STAA and LTAA groups did not differ on measures of alcohol use severity or family history of alcohol problems. These results, coupled with previous findings that show a relationship between stronger theta ERS and increased memory load and attention allocation, suggest that increased theta ERS may be a biomarker for a detrimental effect of chronic alcohol abuse on the brain - a detriment that may recover, at least partially, with extended abstinence.

A Pilot Study for the Neuroprotective Effect of Gongjin-dan on Transient Middle Cerebral Artery Occlusion-Induced Ischemic Rat Brain

In this study, we investigated whether gongjin-dan improves functional recovery and has neuroprotective effects on reducing the infarct volume after transient middle cerebral artery occlusion (MCAo). Infarct volume was measured using TTC staining and glucose utilization by F-18 FDG PET. Functional improvement was evaluated with the Rota-rod, treadmill, Garcia score test, and adhesive removal test. At 14 days after MCAo, neuronal cell survival, astrocytes expansion, and apoptosis were assessed by immunohistofluorescence staining in the peri-infarct region. Also, the expression of neurotrophic factors and inflammatory cytokines such as VEGF, BDNF, Cox-2, TNF-α, IL-1β, and IL-1α was measured in ischemic hemisphere regions. The gongjin-dan-treated group showed both reduced infarct volume and increased glucose utilization. Behavior tests demonstrated a significant improvement compared to the control. Also in the gongjin-dan treated group, NeuN-positive cells were increased and number of astrocytes, microglia, and apoptotic cells was significantly decreased compared with the control group in the ischemic peri-infarct area. Furthermore, the expression of VEGF and BDNF was increased and level of Cox-2, TNF-α, IL-1β, and IL-1α was decreased. These results suggest that gongjin-dan may improve functional outcome through the rapid restoration of metabolism and can be considered as a potential neuroprotective agent.

Alcohol-related amnesia and dementia: animal models have revealed the contributions of different etiological factors on neuropathology, neurochemical dysfunction and cognitive impairment

Chronic alcoholism is associated with impaired cognitive functioning. Over 75% of autopsied chronic alcoholics have significant brain damage and over 50% of detoxified alcoholics display some degree of learning and memory impairment. However, the relative contributions of different etiological factors to the development of alcohol-related neuropathology and cognitive impairment are questioned. One reason for this quandary is that both alcohol toxicity and thiamine deficiency result in brain damage and cognitive problems. Two alcohol-related neurological disorders, alcohol-associated dementia and Wernicke-Korsakoff syndrome have been modeled in rodents. These pre-clinical models have elucidated the relative contributions of ethanol toxicity and thiamine deficiency to the development of dementia and amnesia. What is observed in these models--from repeated and chronic ethanol exposure to thiamine deficiency--is a progression of both neural and cognitive dysregulation. Repeated binge exposure to ethanol leads to changes in neural plasticity by reducing GABAergic inhibition and facilitating glutamatergic excitation, long-term chronic ethanol exposure results in hippocampal and cortical cell loss as well as reduced hippocampal neurotrophin protein content critical for neural survival, and thiamine deficiency results in gross pathological lesions in the diencephalon, reduced neurotrophic protein levels, and neurotransmitters levels in the hippocampus and cortex. Behaviorally, after recovery from repeated or chronic ethanol exposure there is impairment in working or episodic memory that can recover with prolonged abstinence. In contrast, after thiamine deficiency there is severe and persistent spatial memory impairments and increased perseverative behavior. The interaction between ethanol and thiamine deficiency does not produce more behavioral or neural pathology, with the exception of reduction of white matter, than long-term thiamine deficiency alone.

Ex vivo detection for chronic ethanol consumption-induced neurochemical changes in rats

The aim of this study was to quantitatively investigate the chronic ethanol-induced cerebral metabolic changes in various regions of the rat brain, using the proton high resolution magic angle spinning spectroscopy technique. The rats were divided into two groups (control group: N=11, ethanol-treated group: N=11) and fed with the liquid diets for 10 weeks. In each week, the mean intake volumes of liquid diet were measured. The brain tissues, including cerebellum (Cere), frontal cortex (FC), hippocampus (Hip), occipital cortex (OC) and thalamus (Thal), were harvested immediately after the end of experiments. The ex vivo proton spectra for the five brain regions were acquired with the Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence at 500-MHz NMR spectrometer. All of the spectra were processed using the LCModel software, with simulated basis-set file, and the metabolite levels were referenced to total creatine. In the ethanol liquid diet group, there were significant increases in the metabolites ratio levels, as compared to control (Cere: alanine, glutathione, and N-acetlyaspartate; FC: phosphocholine and taurine; Hip: alanine, glutamine, and N-acetylaspartate; OC: glutamine; Thal: alanine, γ-aminobutyric acid, glutamate, glycerophosphocholine, phosphocholine, taurine, and free choline). However, in the ethanol liquid diet group, the myo-inositol levels of the OC were significantly lower. The present study demonstrates how chronic ethanol consumption affects cerebral metabolites in the chronic ethanol-treated rat. Therefore, this result could be useful to pursue clinical applications for quantitative diagnosis in human alcoholism.

Upregulated vimentin suggests new areas of neurodegeneration in a model of an alcohol use disorder

Excessive alcohol intake, characteristic of an alcohol use disorder (AUD), results in neurodegeneration as well as cognitive deficits that may recover in abstinence. Neurodegeneration in psychiatric disorders such as AUDs is due to various effects on tissue integrity. Several groups report that alcohol-induced neurodegeneration and recovery include a role for adult neurogenesis. Therefore, the initial purpose of this study was to investigate the effect of alcohol on the temporal profile of neural progenitor cells using the radial glia marker, vimentin, in a model of an AUD. However, striking vimentin expression throughout corticolimbic regions led, instead, to the discovery of a significant gliosis response in this model. Adult male rats were subjected to a 4-day binge model of an AUD and brains harvested for immunohistochemistry at 0, 2, 4, 7, 14, and 28 days following the last dose of ethanol. A prominent increase in vimentin immunoreactivity was apparent at 4 and 7 days post binge that returned to control levels by 14 days in the corticolimbic regions examined. Vimentin-positive cells co-labeled with glial fibrillary acidic protein (GFAP), which suggested that cells were reactive astrocytes. A second experiment supported that increased vimentin was not primarily due to alcohol withdrawal seizures and is more likely due to alcohol-induced cell death. As this gliosis was remarkably distinct in regions where cell death had not previously been reported in this model, adjacent tissue sections were processed for FluoroJade B staining for cell death. FluoroJade B-positive cells were evident immediately following the last ethanol dose as expected, but were significantly elevated in the hippocampal dentate gyrus and CA3 regions and corticolimbic regions from 2 to 7 days post binge. Intriguingly, vimentin labeling of astrogliosis is more widespread than FluoroJade B labeling of cell death, which suggests that 4-day binge ethanol consumption is more damaging than originally realized.

Ethanol down regulates the expression of myelin proteolipid protein in the rat hippocampus

It is well known that chronic ethanol treatment affects the synthesis of RNA and protein in the brain and the maintenance and function of nervous system. The changes in myelination-related genes are most prominent in human alcoholics. Previously, our cDNA microarray study showed altered Proteolipid protein (PLP), a major protein of central myelin. The present study aimed to gain more understanding of the expression of PLP after chronic ethanol treatment. Male Sprague-Dawley rats were daily treated with ethanol (15% in saline, 3 g/kg, i.p.) or saline for 14 days. Messenger RNAs from hippocampus of each group were subjected to cDNA expression array hybridization to determine the differential gene expressions. Among many ethanol responsive genes, PLP was negatively regulated by ethanol treatment, which is one of the most abundant proteins in the CNS and has an important role in the stabilization of myelin sheath. Using northern blot and immunohistochemical analysis, we showed the change in expression level of PLP mRNA and protein after ethanol treatment. PLP mRNA and protein were decreased in hippocampus of rat with chronic ethanol exposure, suggesting that ethanol may affect the stabilization of myelin sheath through the modulation of PLP expression and induce the pathophysiology of alcoholic brain.

Reversibility of object recognition but not spatial memory impairment following binge-like alcohol exposure in rats

Excessive alcohol use leads to neurodegeneration in several brain structures including the hippocampal dentate gyrus and the entorhinal cortex. Cognitive deficits that result are among the most insidious and debilitating consequences of alcoholism. The object exploration task (OET) provides a sensitive measurement of spatial memory impairment induced by hippocampal and cortical damage. In this study, we examine whether the observed neurotoxicity produced by a 4-day binge ethanol treatment results in long-term memory impairment by observing the time course of reactions to spatial change (object configuration) and non-spatial change (object recognition). Wistar rats were assessed for their abilities to detect spatial configuration in the OET at 1 week and 10 weeks following the ethanol treatment, in which ethanol groups received 9-15 g/kg/day and achieved blood alcohol levels over 300 mg/dl. At 1 week, results indicated that the binge alcohol treatment produced impairment in both spatial memory and non-spatial object recognition performance. Unlike the controls, ethanol treated rats did not increase the duration or number of contacts with the displaced object in the spatial memory task, nor did they increase the duration of contacts with the novel object in the object recognition task. After 10 weeks, spatial memory remained impaired in the ethanol treated rats but object recognition ability was recovered. Our data suggest that episodes of binge-like alcohol exposure result in long-term and possibly permanent impairments in memory for the configuration of objects during exploration, whereas the ability to detect non-spatial changes is only temporarily affected.

Alcohol inhibition of neurogenesis: a mechanism of hippocampal neurodegeneration in an adolescent alcohol abuse model

Adolescents diagnosed with an alcohol use disorder show neurodegeneration in the hippocampus, a region important for learning, memory, and mood regulation. This study examines a potential mechanism by which excessive alcohol intake, characteristic of an alcohol use disorder, produces neurodegeneration. As hippocampal neural stem cells underlie ongoing neurogenesis, a phenomenon that contributes to hippocampal structure and function, we investigated aspects of cell death and cell birth in an adolescent rat model of an alcohol use disorder. Immunohistochemistry of various markers along with Bromo-deoxy-Uridine (BrdU) injections were used to examine different aspects of neurogenesis. After 4 days of binge alcohol exposure, neurogenesis was decreased by 33 and 28% at 0 and 2 days after the last dose according to doublecortin expression. To determine whether this decrease in neurogenesis was due to effects on neural stem cell proliferation, quantification of BrdU-labeled cells revealed a 21% decrease in the dentate gyrus of alcohol-exposed brains. Cell survival and phenotype of BrdU-labeled cells were assessed 28 days after alcohol exposure and revealed a significant, 50% decrease in the number of surviving cells in the alcohol-exposed group. Reduced survival was supported by significant increases in the number of pyknotic-, FluoroJade B positive-, and TUNEL-positive cells. However, so few cells were TUNEL-positive that cell death is likely necrotic in this model. Although alcohol decreased the number of newborn cells, it did not affect the percentage of cells that matured into neurons (differentiation). Thus, our data support that in a model of an adolescent alcohol use disorder, neurogenesis is impaired by two mechanisms: alcohol-inhibition of neural stem cell proliferation and alcohol effects on new cell survival. Remarkably, alcohol inhibition of neurogenesis may outweigh the few dying cells per section, which implies that alcohol inhibition of neurogenesis contributes to hippocampal neurodegeneration in alcohol use disorders.