Paradoxical facilitatory effect of low-dose alcohol consumption on memory mediated by NMDA receptors

Nutrient effects on working memory across the adult lifespan

OBJECTIVE

To identify the nutrients that influence the performance of working memory, which is greatly affected as age progresses.

METHOD

A total of 1646 healthy adults between 21 and 80 years old participated in the study. The daily consumption of 64 nutrients was examined using a food frequency questionnaire that assessed food intake during the previous year. Working memory was measured in the verbal and spatial domains using a computerized task. We examined which nutrients influence working memory across the entire adult lifespan and whether the influence of any of these nutrients on working memory is moderated by individuals' ages.

RESULTS

Working memory, across the entire adult lifespan, benefits from the intake of cholesterol, alcohol, gamma- and delta-tocopherol, vitamin B6, and palmitoleic, oleic, alpha linoleic and linoleic acids. Moderator analyses revealed that fats, energy, lactose and sodium negatively influenced working memory in middle-aged and older adults, whereas vitamin D and vitamin C had positive effects on memory beyond 70 years of age.

CONCLUSION

Nutrients have the ability to positively or negatively affect working memory, which varies as a function of age.

Animal models for studies of alcohol effects on the trajectory of age-related cognitive decline

There is growing interest in understanding how ethanol use interacts with advancing age to influence the brain and cognition. Animal models are employed to investigate the cellular and molecular mechanisms of brain aging and age-related neurodegenerative diseases that underlie cognitive decline. However, all too often research on problems and diseases of the elderly are conducted in healthy young animals, providing little clinical relevance. The validity of animal models is discussed, and confounds due to age-related differences in anxiety, sensory-motor function, and procedural learning are highlighted in order to enhance the successful translation of preclinical results into clinical settings. The mechanism of action of ethanol on brain aging will depend on the dose, acute or chronic treatment, or withdrawal from treatment and the age examined. Due to the fact that humans experience alcohol use throughout life, important questions concern the effects of the dose and duration of ethanol treatment on the trajectory of cognitive function. Central to this research will be questions of the specificity of alcohol effects on cognitive functions and related brain regions that decline with age, as well as the interaction of alcohol with mechanisms or biomarkers of brain aging. Alternatively, moderate alcohol use may provide a source of reserve and resilience against brain aging. Longitudinal studies have the advantage of being sensitive to detecting the effects of treatment on the emergence of cognitive impairment in middle age and can minimize effects of stress/anxiety associated with the novelty of alcohol exposure and behavioral testing, which disproportionately influence aged animals. Finally, the effect of alcohol on senescent neurophysiology and biomarkers of brain aging are discussed. In particular, the interaction of age and effects of alcohol on inflammation, oxidative stress, N-methyl-d-aspartate receptor function, and the balance of excitatory and inhibitory synaptic transmission are highlighted.

Paternal alcohol exposures program intergenerational hormetic effects on offspring fetoplacental growth

Hormesis refers to graded adaptive responses to harmful environmental stimuli where low-level toxicant exposures stimulate tissue growth and responsiveness while, in contrast, higher-level exposures induce toxicity. Although the intergenerational inheritance of programmed hormetic growth responses is described in plants and insects, researchers have yet to observe this phenomenon in mammals. Using a physiologically relevant mouse model, we demonstrate that chronic preconception paternal alcohol exposures program nonlinear, dose-dependent changes in offspring fetoplacental growth. Our studies identify an inverse j-shaped curve with a threshold of 2.4 g/Kg per day; below this threshold, paternal ethanol exposures induce programmed increases in placental growth, while doses exceeding this point yield comparative decreases in placental growth. In male offspring, higher paternal exposures induce dose-dependent increases in the placental labyrinth layer but do not impact fetal growth. In contrast, the placental hypertrophy induced by low-level paternal ethanol exposures associate with increased offspring crown-rump length, particularly in male offspring. Finally, alterations in placental physiology correlate with disruptions in both mitochondrial-encoded and imprinted gene expression. Understanding the influence of ethanol on the paternally-inherited epigenetic program and downstream hormetic responses in offspring growth may help explain the enormous variation observed in fetal alcohol spectrum disorder (FASD) phenotypes and incidence.

Alcohol consumption before pregnancy causes detrimental fetal development and maternal metabolic disorders

Alcohol consumption before or during pregnancy poses serious health risks to the fetus; however, the underlying mechanisms involved remain obscure. Here, we investigated whether ethanol consumption before pregnancy affects maternal or fetal health and whether pharmacological inhibition of CYP2E1, a major ethanol oxidation enzyme, by 4-methylpyrazole (4-MP) has therapeutic effects. We found that ethanol consumption (5%) 2 weeks before pregnancy resulted in a decrease in the number of viable fetuses and abnormal fetal development, and these effects were accompanied by impaired maternal glucose homeostasis and hepatic steatosis during pregnancy. Neonates of ethanol-fed mice had postnatal macrosomia and significantly decreased growth rates during the lactation period. However, treatment with 4-MP, a CYP2E1 inhibitor, markedly ameliorated the reduction in insulin action and glucose disposal responsiveness in the livers of ethanol-fed mice. Blockage of CYP2E1 significantly reduced the alteration in hepatic lipid deposition, fatty acid oxidation, mitochondrial energy status, and macrophage infiltration observed in ethanol-fed mice. Finally, there was a positive correlation between postnatal macrosomia or growth retardation and increased inflammatory responses. Collectively, our study suggests that even moderate ethanol intake may be detrimental to fetal development and may cause growth retardation through maternal metabolic disorders.

Predictors of Working Memory Maintenance and Decline in Older Adults

The aging process is associated with the gradual decline of several cognitive functions, and working memory is particularly affected. Although the majority of older adults experience a deterioration of their working memory, some individuals maintain their working memory in older age, and some suffer an extreme deterioration of their working memory. The purpose of the present study was to identify, among a total of 120 potential predictors, those that significantly contributed to these two extreme outcomes in working memory. A sample of 588 healthy adults was examined with the n-back task in the spatial and verbal domains using a 2-back level of difficulty. Individuals were classified as working memory maintainers or decliners if their discrimination level in the two domains was superior to the 80th percentile or inferior to the 20th percentile, respectively. Logistic regression identified eight and six significant predictors of working memory maintenance and decline, respectively. High vocabulary scores and smoking more were significant predictors of working memory maintenance; however, in the opposite direction, these same variables predicted working memory decline. Several consumption habits that influenced cerebrovascular function were found in both models. Psychological traits and everyday activities were present in both models. We identified specific predictors that contribute to extremely high or low working memory performance in older age.

A secret that underlies Parkinson's disease: The damaging cycle

Parkinson's disease (PD) is a movement disorder, and its common characteristics include the loss of dopaminergic neurons and the accumulation of a special type of cytoplasmic inclusions called Lewy bodies in the substantia nigra pars compacta, which are more prevalent in the elderly. However, the pathophysiology of PD is still elusive. In this review, we summarized five common factors involved in PD, namely, (i) oxidative stress, (ii) mitochondrial dysfunction, (iii) inflammation, (iv) abnormal α-synuclein, and (v) endogenous neurotoxins, and proposed a hypothesis involving a damaging cycle. Oxidative stress-triggered aldehydes react with biogenic amines to produce endogenous neurotoxins. They cause mitochondrial dysfunction and the formation of inflammasomes, which induce the activation of neuroglial cells and the infiltration of T lymphocytes. The synergistic effect of these processes fosters chronic inflammation and α-synuclein aggregation and further exacerbates the impact of oxidative stress to establish a damaging cycle that eventually results in the degeneration of dopaminergic neurons. This damaging cycle provides an explanation of progressive neuronal death during the pathogenesis of PD and provides new potential targets beneficial for developing new drugs and approaches for clinical neuroprotection.

Low-dose ethanol ameliorates amnesia induced by a brief seizure model: the role of NMDA signaling

Objective: The present study aimed to evaluate the ameliorative effect of low-dose ethanol (Eth) on amnesia induced by a brief seizure model and the role of N-methyl D-aspartate (NMDA) signaling in this event. Materials and Methods: Four groups of rats (total number = 36; n = 9, each group) were used: control, Eth (0.5 g/kg/i.p.), pentylenetetrazole (PTZ) (60 mg/kg/i.p.), and Eth+PTZ. Eth was administered for 6 days before the single injection of PTZ, at minute dose that cannot induce memory impairment. The consequences of Eth pretreatment, coadministered with PTZ, were studied in an inhibitory avoidance (IA) memory model. The PTZ was injected 30 min prior to the IA memory test. Thereafter, locomotion, liver enzymes, and the Real-time PCR for NR1 subunit of NMDA receptor were studied. The statistical analyses were performed using the parametric/nonparametric ANOVA and the post-hoc tests. Results: Our findings revealed that Eth pretreatment significantly improved the IA memory impairment induced by PTZ (P < 0.001), and indicated no change in locomotion and serum ALT, but significantly differed for AST between the PTZ and PTZ groups (P = < 0.05). The Real-time PCR results indicate the decreased NR1 mRNA expression in Eth and PTZ groups and the increased NR1 mRNA expression in Eth+PTZ group, compared to the control group (P < 0.001); however, the NR1 mRNA expression was increased in the Eth+PTZ group, compared to PTZ group (P < 0.001). Conclusion: The present study provides evidence that the low-dose Eth can improve the amnesia induced by a brief seizure model presumably via NMDA signaling in a rat.

Factors that positively or negatively mediate the effects of age on working memory across the adult life span

Working memory abilities significantly decrease with advancing age; hence, the search for factors that may increase or mitigate this decline is critical. Several factors have been identified that influence working memory; however, their effects have been mainly assessed separately and rarely together with other factors in the same sample. We examined 120 variables to search for factors that jointly act as mediators of working memory decay across the adult life span. A sample of 1652 healthy adults was assessed in spatial and verbal working memory domains. Structural equation modeling analyses were conducted to search for potential mediators that intervened between age and working memory. Only 14 and 10 variables reliably mediated spatial and verbal working memory, respectively. Factors from several domains remained in the models, such as individual characteristics, physiological traits, consumption habits, and regular activities. These factors are sufficiently powerful to influence working memory decline when they jointly interact, as in everyday living.

GABA and Glutamate Synaptic Coadaptations to Chronic Ethanol in the Striatum

Alcohol (ethanol) is a widely used and abused drug with approximately 90% of adults over the age of 18 consuming alcohol at some point in their lifetime. Alcohol exerts its actions through multiple neurotransmitter systems within the brain, most notably the GABAergic and glutamatergic systems. Alcohol's actions on GABAergic and glutamatergic neurotransmission have been suggested to underlie the acute behavioral effects of ethanol. The striatum is the primary input nucleus of the basal ganglia that plays a role in motor and reward systems. The effect of ethanol on GABAergic and glutamatergic neurotransmission within striatal circuitry has been thought to underlie ethanol taking, seeking, withdrawal and relapse. This chapter reviews the effects of ethanol on GABAergic and glutamatergic transmission, highlighting the dynamic changes in striatal circuitry from acute to chronic exposure and withdrawal.

The Association Between Alcohol Use and the Progression of Alzheimer's Disease

OBJECTIVE

To examine the relationship between alcohol, both the amount and type, and cognitive decline in a cohort of Alzheimer's disease (AD) patients.

METHODS

A cohort of 360 patients with early AD in New York, Boston, Baltimore and Paris were followed-up biannually for up to 19.28 years. At each visit, the cognitive profile of the patients was assessed using the modified Mini-Mental State Examination (mMMSE), and patients' alcohol intake, including beverage type, was reported by patients' primary caregivers. General estimating equation analysis was used to determine whether baseline alcohol use was associated with the rate of cognitive decline.

RESULTS

Heavy drinkers (8 or more alcoholic drinks/week) had a faster cognitive decline, deteriorating 1.849 more points on their mMMSE score annually compared to abstainers (P = 0.001), or 2.444 more points compared to mild-moderate drinkers (1-7 alcoholic drinks/week) (P = 0.008). There was no significant difference when comparing mild-moderate drinkers to abstainers. Increasing standard drinks of hard liquor, but not beer or wine, was also associated with a faster rate of cognitive decline (β = -0.117 P = 0.001).

CONCLUSION

Heavy alcohol consumption and more hard liquor are associated with a faster rate of cognitive decline in AD patients, suggesting that they may hasten progression of AD. Our results suggest that alcohol drinking habits might alter the course of AD.

Metabotropic and ionotropic glutamate receptors as potential targets for the treatment of alcohol use disorder

Emerging evidence indicates that dysfunctional glutamate neurotransmission is critical in the initiation and development of alcohol and drug dependence. Alcohol consumption induced downregulation of glutamate transporter 1 (GLT-1) as reported in previous studies from our laboratory. Glutamate is the major excitatory neurotransmitter in the brain, which acts via interactions with several glutamate receptors. Alcohol consumption interferes with the glutamatergic signal transmission by altering the functions of these receptors. Among the glutamate receptors involved in alcohol-drinking behavior are the metabotropic receptors such as mGluR1/5, mGluR2/3, and mGluR7, as well as the ionotropic receptors, NMDA and AMPA. Preclinical studies using agonists and antagonists implicate these glutamatergic receptors in the development of alcohol use disorder (AUD). Therefore, the purpose of this review is to discuss the neurocircuitry involving glutamate transmission in animals exposed to alcohol and further outline the role of metabotropic and ionotropic receptors in the regulation of alcohol-drinking behavior. This review provides ample information about the potential therapeutic role of glutamatergic receptors for the treatment of AUD.

Colour Vision Impairment in Young Alcohol Consumers

Alcohol consumption among young adults is widely accepted in modern society and may be the starting point for abusive use of alcohol at later stages of life. Chronic alcohol exposure can lead to visual function impairment. In the present study, we investigated the spatial luminance contrast sensitivity, colour arrangement ability, and colour discrimination thresholds on young adults that weekly consume alcoholic beverages without clinical concerns. Twenty-four young adults were evaluated by an ophthalmologist and performed three psychophysical tests to evaluate their vision functions. We estimated the spatial luminance contrast sensitivity function at 11 spatial frequencies ranging from 0.1 to 30 cycles/degree. No difference in contrast sensitivity was observed comparing alcohol consumers and control subjects. For the evaluation of colour vision, we used the Farnsworth-Munsell 100 hue test (FM 100 test) to test subject’s ability to perform a colour arrangement task and the Mollon-Reffin test (MR test) to measure subject’s colour discrimination thresholds. Alcohol consumers made more mistakes than controls in the FM100 test, and their mistakes were diffusely distributed in the FM colour space without any colour axis preference. Alcohol consumers also performed worse than controls in the MR test and had higher colour discrimination thresholds compared to controls around three different reference points of a perceptually homogeneous colour space, the CIE 1976 chromaticity diagram. There was no colour axis preference in the threshold elevation observed among alcoholic subjects. Young adult weekly alcohol consumers showed subclinical colour vision losses with preservation of spatial luminance contrast sensitivity. Adolescence and young adult age are periods of important neurological development and alcohol exposure during this period of life might be responsible for deficits in visual functions, especially colour vision that is very sensitive to neurotoxicants.

Optimization of AAV expression cassettes to improve packaging capacity and transgene expression in neurons

Adeno-associated virus (AAV) vectors can deliver transgenes to diverse cell types and are therefore useful for basic research and gene therapy. Although AAV has many advantages over other viral vectors, its relatively small packaging capacity limits its use for delivering large genes. The available transgene size is further limited by the existence of additional elements in the expression cassette without which the gene expression level becomes much lower. By using alternative combinations of shorter elements, we generated a series of AAV expression cassettes and systematically evaluated their expression efficiency in neurons to maximize the transgene size available within the AAV packaging capacity while not compromising the transgene expression. We found that the newly developed smaller expression cassette shows comparable expression efficiency with an efficient vector generally used for strong gene expression. This new expression cassette will allow us to package larger transgenes without compromising expression efficiency.

Differential phosphorylation of GluN1-MAPKs in rat brain reward circuits following long-term alcohol exposure

The effects of long-term alcohol consumption on the mitogen-activated protein kinases (MAPKs) pathway and N-methyl-D-aspartate-type glutamate receptor 1 (GluN1) subunits in the mesocorticolimbic system remain unclear. In the present study, rats were allowed to consume 6% (v/v) alcohol solution for 28 consecutive days. Locomotor activity and behavioral signs of withdrawal were observed. Phosphorylation and expression of extracellular signal-regulated protein kinase (ERK), c-Jun N-terminal kinase (JNK), p38 protein kinase and GluN1 in the nucleus accumbens, caudate putamen, amygdala, hippocampus and prefrontal cortex of these rats were also measured. Phosphorylation of ERK, but not JNK or p38, was decreased in all five brain regions studied in alcohol-drinking rats. The ratio of phospho/total-GluN1 subunit was reduced in all five brain regions studied. Those results suggest that the long-term alcohol consumption can inhibits GluN1 and ERK phosphorylation, but not JNK or p38 in the mesocorticolimbic system, and these changes may be relevant to alcohol dependence. To differentiate alcohol-induced changes in ERK and GluN1 between acute and chronic alcohol exposure, we have determined levels of phospho-ERK, phospho-GluN1 and total levels of GluN1 after acute alcohol exposure. Our data show that 30 min following a 2.5 g/kg dose of alcohol (administered intragastrically), levels of phospho-ERK are decreased while those of phospho-GluN1 are elevated with no change in total GluN1 levels. At 24 h following the single alcohol dose, levels of phospho-ERK are elevated in several brain regions while there are no differences between controls and alcohol treated animals in phospho-GluN1 or total GluN1. Those results suggest that alcohol may differentially regulate GluN1 function and ERK activation depending on alcohol dose and exposure time in the central nervous system.

Chronic alcohol exposure alters behavioral and synaptic plasticity of the rodent prefrontal cortex

In the present study, we used a mouse model of chronic intermittent ethanol (CIE) exposure to examine how CIE alters the plasticity of the medial prefrontal cortex (mPFC). In acute slices obtained either immediately or 1-week after the last episode of alcohol exposure, voltage-clamp recording of excitatory post-synaptic currents (EPSCs) in mPFC layer V pyramidal neurons revealed that CIE exposure resulted in an increase in the NMDA/AMPA current ratio. This increase appeared to result from a selective increase in the NMDA component of the EPSC. Consistent with this, Western blot analysis of the postsynaptic density fraction showed that while there was no change in expression of the AMPA GluR1 subunit, NMDA NR1 and NRB subunits were significantly increased in CIE exposed mice when examined immediately after the last episode of alcohol exposure. Unexpectedly, this increase in NR1 and NR2B was no longer observed after 1-week of withdrawal in spite of a persistent increase in synaptic NMDA currents. Analysis of spines on the basal dendrites of layer V neurons revealed that while the total density of spines was not altered, there was a selective increase in the density of mushroom-type spines following CIE exposure. Examination of NMDA-receptor mediated spike-timing-dependent plasticity (STDP) showed that CIE exposure was associated with altered expression of long-term potentiation (LTP). Lastly, behavioral studies using an attentional set-shifting task that depends upon the mPFC for optimal performance revealed deficits in cognitive flexibility in CIE exposed mice when tested up to 1-week after the last episode of alcohol exposure. Taken together, these observations are consistent with those in human alcoholics showing protracted deficits in executive function, and suggest these deficits may be associated with alterations in synaptic plasticity in the mPFC.

Heterozygous deletion of NR1 subunit of the NMDA receptor alters ethanol-related behaviors and regional expression of NR2 subunits in the brain

NMDA receptors have been hypothesized to play a role in various aspects of ethanol-related phenotypes, notably in ethanol withdrawal. However, the role of each of the specific subunits remains unclear. To address this issue, mice that are heterozygous for the NR1 deletion, and thus have a reduction in functional NMDA receptors, were examined for ethanol consumption and acute ethanol withdrawal. Additionally, mice were examined for the level of vocalization following footshock, and behavior in an elevated plus maze, to determine their responses to stress. In these behavioral tests, NR1 heterozygous mice were shown to consume significantly higher levels of ethanol in the two bottle-choice test showing a possible role for this receptor in ethanol consumption. Analysis of acute withdrawal found that the heterozygous mice exhibit lower levels of handling-induced convulsions consistent with a role in ethanol sensitivity or withdrawal. In contrast, no effects on stress-related phenotypes were detected. Levels of NR2A-NR2D subunits of the NMDA receptor in specific brain regions were compared between NR1+/- mice and wild-type controls to assess whether the behavioral responses were specific to the diminution in NR1 expression or whether these changes could be due to secondary changes in expression of other NMDA subunits. Real-time quantitative PCR, Western blot and immunohistochemistry were used to examine expression levels in the hippocampus, neocortex, striatum and cerebellum. For the majority of the subunits, no differences were found between the wild-type and heterozygous mice in any of the brain regions. However, the NR2B subunit exhibited differences in expression of RNA in the hippocampus and protein levels in multiple brain regions, between wild-type and NR1+/- mice. These results show that NR1 plays a role, through mechanisms as yet unknown, in the expression of NR2 subunits in a region and subtype specific manner. This provides evidence of the effects of altered levels of NR1 expression on ethanol withdrawal and consumption, and suggests that concomitant changes in the levels of NR2B may contribute to that effect.

Changes in expression of NMDA-NR1 receptor subunits in the rostral ventromedial medulla modulate pain behaviors

NMDA receptors have an important role in pain facilitation in rostral ventromedial medulla (RVM) and the NR1 subunit is essential for its function. Studies suggest that the NMDA receptors in RVM are critical to modulate both cutaneous and muscle hypersensitivity induced by repeated intramuscular acid injections. We propose that increased expression of the NR1 subunit in the RVM is critical for the full development of hypersensitivity. To test this we used recombinant lentiviruses to over-express the NR1 subunit in the RVM and measured nociceptive sensitivity to cutaneous and muscle stimuli. We also downregulated the expression of NR1 in the RVM and measured the hyperalgesia produced by repeated-acid injections. Increasing the expression of NR1 in the RVM reduces cutaneous and muscle withdrawal threshold, and decreasing the expression of NR1 in the RVM increases the muscle withdrawal threshold and prevents the development of hyperalgesia in an animal model of muscle pain. These results suggest that the NR1 subunits in the RVM are critical for modulating NMDA receptor function, which in turn sets the 'tone' of the nervous system's response to noxious stimuli and tissue injury.

Ethanol increases TIEG2-MAO B cell death cascade in the prefrontal cortex of ethanol-preferring rats

Brain cell loss has been reported in subjects with alcoholism. However, the molecular mechanisms are unclear. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and monoamine oxidase B (MAO B) reportedly play a role in cellular dysfunction with regards to ethanol exposure. We have recently reported that GAPDH protein expression was increased in the brains of rats fed with ethanol. Furthermore, GAPDH interacts with the transcriptional activator, transforming growth factor-beta-inducible early gene 2 (TIEG2), to augment TIEG2-mediated MAO B activation, resulting in neuronal cell damage due to ethanol exposure. The current study investigates whether the TIEG2-MAO B cascade is also active in the brains of rats fed with ethanol. Ten ethanol-preferring rats were fed with a liquid diet containing ethanol, with increasing amounts of ethanol up to a final concentration of 6.4% representing a final diet containing 36% of calories for 28 days. Ten control rats were fed the liquid diet without ethanol. The expression of TIEG2 protein, MAO B mRNA levels, MAO B catalytic activity, and the levels of anti-apoptotic protein Bcl 2 and apoptotic protein caspase 3 were determined in the prefrontal cortex of the rats. Ethanol significantly increased protein levels of TIEG2, active caspase 3, MAO B mRNA and enzyme activity, but significantly decreased Bcl 2 protein expression compared to control rats. In summary, ethanol increases the TIEG2-MAO B brain cell death cascade in rat brains, suggesting that the TIEG2-MAO B pathway is a novel pathway for brain cell damage resulting from ethanol exposure, and may contribute to chronic alcohol-induced brain damage.

Essential involvement of the NMDA receptor in ethanol preconditioning-dependent neuroprotection from amyloid-betain vitro

In several epidemiological studies, moderate ethanol consumption has been associated with reduced risks of cognitive decline or Alzheimer's dementia. Of potential relevance is that brain cultures preconditioned with moderate ethanol concentrations are resistant to neurotoxic Alzheimer's amyloid-beta (Abeta) peptides. Using rat cerebellar mixed cultures we investigated whether certain membrane receptors were early 'sensors' in moderate ethanol preconditioning (MEP). In a 6-day MEP protocol (30 mM ethanol), neuroprotection from Abeta25-35 was undiminished by antagonism during the first 3 days of either adenosine A(1) or Galpha(i/o) protein-coupled receptors. However, similar cotreatment with memantine or DL-2-amino-5-phosphono-pentanoic acid (AP-5), antagonists of NMDA receptors (NMDAR), abolished neuroprotection, indicating key early involvement of this ionotropic glutamate receptor. Also in these cultures, directly activating NMDAR using subexcitotoxic NMDA preconditioning prevented Abeta neurotoxicity. By day 2 of MEP, we observed increased levels of NMDAR subunits NR1, NR2B, and NR2C that persisted through day 6. Interestingly, memantine co-exposure blocked elevations in the obligatory NR1 subunit. Furthermore, 2 days of MEP significantly increased two indicators of synaptic NMDAR localization, NR2B phospho-Tyr1472, and post-synaptic density 95 scaffolding protein. The results indicate that ethanol preconditioning-dependent neuroprotection is associated with early increases in NR subunits concomitant with enhancement of synaptic localization and activity of NMDAR.

Alcohol consumption as a risk factor for dementia and cognitive decline: meta-analysis of prospective studies

The relationships between alcohol consumption and dementia and cognitive decline were investigated in a systematic review including meta-analyses of 15 prospective studies. Follow-ups ranged from 2 to 8 years. Meta-analyses were conducted on samples including 14,646 participants evaluated for Alzheimer disease (AD), 10,225 participants evaluated for vascular dementia (VaD), and 11,875 followed for any type of dementia (Any dementia). The pooled relative risks (RRs) of AD, VaD, and Any dementia for light to moderate drinkers compared with nondrinkers were 0.72 (95% CI = 0.61-0.86), 0.75 (95% CI = 0.57-0.98), and 0.74 (95% CI = 0.61-0.91), respectively. When the more generally classified "drinkers," were compared with "nondrinkers," they had a reduced risk of AD (RR = 0.66, 95% CI = 0.47-0.94) and Any dementia (RR = 0.53, 95% CI = 0.53-0.82) but not cognitive decline. There were not enough data to examine VaD risk among "drinkers." Those classified as heavy drinkers did not have an increased risk of Any dementia compared with nondrinkers, but this may reflect sampling bias. Our results suggest that alcohol drinkers in late life have reduced risk of dementia. It is unclear whether this reflects selection effects in cohort studies commencing in late life, a protective effect of alcohol consumption throughout adulthood, or a specific benefit of alcohol in late life.

Knockdown and overexpression of NR1 modulates NMDA receptor function

The N-methyl-d-aspartate receptor (NMDAR) is critically involved in learning and memory, neuronal survival, as well as neuroexcitotoxicity and seizures. We hypothesize that even mild reductions in the numbers of hippocampal NMDARs could impair learning and memory, whereas increasing receptor activity would facilitate learning but reduce seizure threshold. We developed novel gene transfer strategies assisted by an adeno-associated viral vector 1/2 to bi-directionally modulate expression levels of the NR1 protein in rat hippocampus. Functional consequences of the altered NR1 expression were examined in the acute seizure model, and on normal processes of fear memory and neurogenesis. We found that knocking down NR1 protected against seizures at the expense of impaired learning, as predicted. Paradoxically, NR1 overexpression not only increased fear memory and neurogenesis, but also delayed onset of more severe seizures. In conclusion, the observed consequences of NR1 knockdown and overexpression underscore NMDAR requirement for neuronal plasticity, and are in agreement with its dichotomous functions.

The expression of NMDA receptor subunit mRNA in human chronic alcoholics

Ethanol is a modulator at the N-methyl-d-aspartate class of glutamate receptors in the brain. In animal studies the receptor adapts to sustained ethanol exposure through altered expression of the subunits that make up the receptor complex. We used real-time RT-PCR normalized to GAPDH to assay NR1, NR2A, and NR2B subunit mRNA in superior frontal and primary motor cortex tissue obtained at autopsy from chronic alcoholics with and without co-morbid cirrhosis of the liver, and from matched controls. The expression of all three subunits was significantly lower in both areas of cirrhotic alcoholics than in the corresponding areas in both controls and alcoholics without co-morbid disease, who did not differ significantly from each other. The decrease was area-dependent when cases were partitioned by the 5-HTTLPR allele. Thus, polymorphisms in one gene can have a significant effect on the expression of a second, unrelated, gene. The expression of the N-methyl-d-aspartate glutamate receptor complex is under multifactorial control.

Surface trafficking of N-methyl-D-aspartate receptors: physiological and pathological perspectives

The N-methyl-D-aspartate receptor (NMDAR) plays a crucial role in shaping the strength of synaptic connections. Over the last decades, extensive studies have defined the cellular and molecular mechanisms by which synaptic NMDARs control the maturation and plasticity of synaptic transmission, and how altered synaptic NMDAR signaling is implicated in neurodegenerative and psychiatric disorders. It is now clear that activation of synaptic or extrasynaptic NMDARs produces different signaling cascades and thus neuronal functions. Our current understanding of NMDAR surface distribution and trafficking is only emerging. Exchange of NMDARs between synaptic and extrasynaptic areas through surface diffusion is a highly dynamic and regulated process. The aim of this review is to describe the identified mechanisms that regulate surface NMDAR behaviors and discuss the impact of this new trafficking pathway on the well-established NMDAR-dependent physiological and pathophysiological processes.

Hepatic insulin resistance induced by prenatal alcohol exposure is associated with reduced PTEN and TRB3 acetylation in adult rat offspring

Prenatal alcohol exposure (EtOH) results in insulin resistance in rats of both sexes with increased expression of hepatic gluconeogenic genes and glucose production. To investigate whether hepatic insulin signaling is defective, we studied 3-mo-old female offspring of dams that were given EtOH during pregnancy compared with those from pair-fed and control dams. We performed an intraperitoneal pyruvate tolerance test, determined the phosphorylation status of hepatic phosphoinositide-dependent protein kinase-1 (PDK1), Akt, and PKCζ before and after intravenous insulin bolus, and measured mRNA and in vivo acetylation of TRB3 (tribbles 3) and PTEN (phosphatase and tensin homolog deleted on chromosome ten) as well as the expression of the histone acetylase (HAT) PCAF (p300/CREB-binding protein-associated factor), histone deacetylase-1 (HDAC1), and HAT and HDAC activities. In EtOH compared with pair-fed and control offspring, basal and pyruvate-induced blood glucose was increased, insulin-induced PDK1, Akt, and PKCζ phosphorylation was reduced, and expression of PTEN and TRB3 was increased while their acetylation status was decreased in association with increased HDAC and decreased HAT activities. Thus female adult rats prenatally exposed to EtOH have increased gluconeogenesis, reduced insulin signaling, and increased PTEN and TRB3 expression in the liver. In addition, PTEN and TRB3 are hypoacetylated, which can contribute to Akt-inhibiting activity. These results suggest that hepatic insulin resistance in rats prenatally exposed to EtOH is explained, at least in part, by increased PTEN and TRB3 activity due to both increased gene expression and reduced acetylation.

Ethanol induces glutamate secretion by Ca2+ mobilization and ROS generation in rat hippocampal astrocytes

In this study we have investigated the effect of ethanol on [Ca2+]c by microfluorimetry and glutamate secretion using an enzyme-linked system, in rat hippocampal astrocytes in culture. Our results show that ethanol (1-200 mM) evoked a dose-dependent increase in glutamate secretion. 50 mM ethanol, a concentration within the range of blood alcohol levels in intoxicated humans, induced a release of Ca2+ from intracellular stores in the form of oscillations. Ca2+-mobilizing effect of ethanol was not prevented by preincubation of cells in the presence of 2 mM of the antioxidant dithiothreitol. Ethanol-evoked glutamate secretion was reduced when extracellular Ca2+ was omitted (medium containing 0.5 mM EGTA) and following preincubation of astrocytes in the presence of the intracellular Ca2+ chelator 1,2-bis-(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid tetraacetoxy-methyl ester (10 microM). Preincubation of astrocytes in the presence of 2 mM of the antioxidant dithiothreitol significantly reduced ethanol-evoked glutamate secretion. Finally, preincubation of astrocytes in the presence of bafilomycin (50 nM) significantly reduced ethanol-induced neurotransmitter release, indicating that exocytosis is involved in glutamate secretion. In conclusion, our results suggest that ethanol mobilizes Ca2+ from intracellular stores, and stimulates a Ca2+-dependent glutamate secretion, probably involving reactive oxygen species production, and therefore creating a situation potentially leading to neurotoxicity in the hippocampus.