Brain acetaldehyde after ethanol administration

Coordinated action of a gut-liver pathway drives alcohol detoxification and consumption

Alcohol use disorder (AUD) affects millions of people worldwide, causing extensive morbidity and mortality with limited pharmacological treatments. The liver is considered as the principal site for the detoxification of ethanol metabolite, acetaldehyde (AcH), by aldehyde dehydrogenase 2 (ALDH2) and as a target for AUD treatment, however, our recent data indicate that the liver only plays a partial role in clearing systemic AcH. Here we show that a liver-gut axis, rather than liver alone, synergistically drives systemic AcH clearance and voluntary alcohol drinking. Mechanistically, we find that after ethanol intake, a substantial proportion of AcH generated in the liver is excreted via the bile into the gastrointestinal tract where AcH is further metabolized by gut ALDH2. Modulating bile flow significantly affects serum AcH level and drinking behaviour. Thus, combined targeting of liver and gut ALDH2, and manipulation of bile flow and secretion are potential therapeutic strategies to treat AUD.

Role of Metabolism on Alcohol Preference, Addiction, and Treatment

Studies presented in this chapter show that: (1) in the brain, ethanol is metabolized by catalase to acetaldehyde, which condenses with dopamine forming salsolinol; (2) acetaldehyde-derived salsolinol increases the release of dopamine mediating, via opioid receptors, the reinforcing effects of ethanol during the acquisition of ethanol consumption, while (3) brain acetaldehyde does not influence the maintenance of chronic ethanol intake, it is suggested that a learned cue-induced hyperglutamatergic system takes precedence over the dopaminergic system. However, (4) following a prolonged ethanol deprivation, the generation of acetaldehyde in the brain again plays a role, contributing to the increase in ethanol intake observed during ethanol re-access, called the alcohol deprivation effect (ADE), a model of relapse behavior; (5) naltrexone inhibits the high ethanol intake seen in the ADE condition, suggesting that acetaldehyde-derived salsolinol via opioid receptors also contributes to the relapse-like drinking behavior. The reader is referred to glutamate-mediated mechanisms that trigger the cue-associated alcohol-seeking and that also contribute to triggering relapse.

Alcohol, inflammation, and blood-brain barrier function in health and disease across development

Alcohol is the most commonly used drug of abuse in the world and binge drinking is especially harmful to the brain, though the mechanisms by which alcohol compromises overall brain health remain somewhat elusive. A number of brain diseases and pathological states are accompanied by perturbations in Blood-Brain Barrier (BBB) function, ultimately exacerbating disease progression. The BBB is critical for coordinating activity between the peripheral immune system and the brain. Importantly, BBB integrity is responsive to circulating cytokines and other immune-related signaling molecules, which are powerfully modulated by alcohol exposure. This review will highlight key cellular components of the BBB; discuss mechanisms by which permeability is achieved; offer insight into methodological approaches for assessing BBB integrity; and forecast how alcohol-induced changes in the peripheral and central immune systems might influence BBB function in individuals with a history of binge drinking and ultimately Alcohol Use Disorders (AUD).

Acetaldehyde Adsorption Characteristics of Ag/ACF Composite Prepared by Liquid Phase Plasma Method

Ag particles were precipitated on an activated carbon fiber (ACF) surface using a liquid phase plasma (LPP) method to prepare a Ag/ACF composite. The efficiency was examined by applying it as an adsorbent in the acetaldehyde adsorption experiment. Field-emission scanning electron microscopy and energy-dispersive X-ray spectrometry confirmed that Ag particles were distributed uniformly on an ACF surface. X-ray diffraction and X-ray photoelectron spectroscopy confirmed that metallic silver (Ag0) and silver oxide (Ag2O) precipitated simultaneously on the ACF surface. Although the precipitated Ag particles blocked the pores of the ACF, the specific surface area of the Ag/ACF composite material decreased, but the adsorption capacity of acetaldehyde was improved. The AA adsorption of ACF and Ag/ACF composites performed in this study was suitable for the Dose-Response model.

The Mechanism of Action of Salsolinol in Brain: Implications in Parkinson's Disease

1-Methyl-1,2,3,4-tetrahydroisoquinoline-6,7-diol, commonly known as salsolinol, is a compound derived from dopamine. It was first discovered in 1973 and has gained attention for its role in Parkinson's disease. Salsolinol and its derivatives were claimed to play a role in the pathogenesis of Parkinson's disease as a neurotoxin that induces apoptosis of dopaminergic neurons due to its structural similarity to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and its ability to induce Parkinsonism. In this article, we discussed the biosynthesis, distribution and blood-brain barrier permeability of salsolinol. The roles of salsolinol in a healthy brain, particularly the interactions with enzymes, hormone and catecholamine, were reviewed. Finally, we discussed the involvement of salsolinol and its derivatives in the pathogenesis of Parkinson's disease.

The Role of Alcohol Metabolism in the Pathology of Alcohol Hangover

The limited number of available studies that examined the pathology of alcohol hangover focused on biomarkers of alcohol metabolism, oxidative stress and the inflammatory response to alcohol as potentially important determinants of hangover severity. The available literature on alcohol metabolism and oxidative stress is reviewed in this article. The current body of evidence suggests a direct relationship between blood ethanol concentration and hangover severity, whereas this association is not significant for acetaldehyde. The rate of alcohol metabolism seems to be an important determinant of hangover severity. That is, fast elimination of ethanol is associated with experiencing less severe hangovers. An explanation for this observation may be the fact that ethanol-in contrast to acetaldehyde-is capable of crossing the blood-brain barrier. With slower ethanol metabolism, more ethanol is able to reach the brain and elicit hangover symptoms. Hangover severity was also significantly associated with biomarkers of oxidative stress. More oxidative stress in the first hours after alcohol consumption was associated with less severe next-day hangovers (i.e., a significant negative correlation was found between hangover severity and malondialdehyde). On the contrary, more oxidative stress at a later stage after alcohol consumption was associated with having more severe next-day hangovers (i.e., a significant positive correlation was found between hangover severity and 8-isoprostane). In conclusion, assessment of biomarkers of alcohol metabolism suggests that fast elimination of ethanol is associated with experiencing less severe hangovers. More research is needed to further examine the complex interrelationship between alcohol metabolism, the role of acetaldehyde and oxidative stress and antioxidants, and the pathology of the alcohol hangover.

Diffusion-weighted MRI in neurodegenerative and psychiatric animal models: Experimental strategies and main outcomes

Preclinical MRI approaches constitute a key tool to study a wide variety of neurological and psychiatric illnesses, allowing a more direct investigation of the disorder substrate and, at the same time, the possibility of back-translating such findings to human subjects. However, the lack of consensus on the optimal experimental scheme used to acquire the data has led to relatively high heterogeneity in the choice of protocols, which can potentially impact the comparison between results obtained by different groups, even using the same animal model. This is especially true for diffusion-weighted MRI data, where certain experimental choices can impact not only on the accuracy and precision of the extracted biomarkers, but also on their biological meaning. With this in mind, we extensively examined preclinical imaging studies that used diffusion-weighted MRI to investigate neurodegenerative, neurodevelopmental and psychiatric disorders in rodent models. In this review, we discuss the main findings for each preclinical model, with a special focus on the analysis and comparison of the different acquisition strategies used across studies and their impact on the heterogeneity of the findings.

Activation of mitochondrial aldehyde dehydrogenase (ALDH2) by ALDA-1 reduces both the acquisition and maintenance of ethanol intake in rats: A dual mechanism?

A number of pre-clinical studies have shown that brain-generated acetaldehyde, the first metabolite of ethanol, exerts reinforcing effects that promote the acquisition of ethanol intake, while chronic intake maintenance appears to be mediated by alcohol-induced brain neuroinflammation/oxidative stress. Recently, it was described that N-(1,3-benzodioxol-5-ylmethyl)-2,6-dichlorobenzamide (ALDA-1) activates aldehyde dehydrogenase-2 (ALDH2), enzyme that catalyzes the oxidation of ethanol-derived acetaldehyde to acetate. The aim of this study was to determine the effects of ALDA-1 on both the acquisition and the maintenance of alcohol intake in alcohol-preferring UChB rats. For ethanol acquisition studies, naïve UChB rats were treated with five daily doses of ALDA-1 (12.5, 25 or 50 mg/kg, i.p.) from one day before the start of ethanol exposure. For chronic intake studies, UChB rats exposed for 98 days to a free access to 10% ethanol and water were treated daily with ALDA-1 (12.5, 25 or 50 mg/kg, i.p.) for five days. The administration of ALDA-1 reduced by 72-90% (p < 0.001) the acquisition of ethanol consumption in naïve rats. At chronic ethanol consumption, ALDA-1 reduced ethanol intake by 61-82% (p < 0.001). ALDA-1 administration increased by 3- and 2.3-fold the activity of ALDH2 in brain and liver, respectively. ALDA-1 did not affect saccharin consumption, nor it modified the rate of ethanol elimination. The study shows that the activation of ALDH2 by ALDA-1 is effective for inhibiting both the acquisition and the maintenance of chronic ethanol intake by alcohol-preferring rats. Thus, the activation of brain ALDH2 may constitute a novel approach in the treatment of alcohol use disorders.

Salsolinol: an Unintelligible and Double-Faced Molecule-Lessons Learned from In Vivo and In Vitro Experiments

Salsolinol (1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline) is a tetrahydroisoquinoline derivative whose presence in humans was first detected in the urine of Parkinsonian patients on l-DOPA (l-dihydroxyphenylalanine) medication. Thus far, multiple hypotheses regarding its physiological/pathophysiological roles have been proposed, especially related to Parkinson’s disease or alcohol addiction. The aim of this review was to outline studies related to salsolinol, with special focus on in vivo and in vitro experimental models. To begin with, the chemical structure of salsolinol together with its biochemical implications and the role in neurotransmission are discussed. Numerous experimental studies are summarized in tables and the most relevant ones are stressed. Finally, the ability of salsolinol to cross the blood–brain barrier and its possible double-faced neurobiological potential are reviewed.

Mystic Acetaldehyde: The Never-Ending Story on Alcoholism

After decades of uncertainties and drawbacks, the study on the role and significance of acetaldehyde in the effects of ethanol seemed to have found its main paths. Accordingly, the effects of acetaldehyde, after its systemic or central administration and as obtained following ethanol metabolism, looked as they were extensively characterized. However, almost 5 years after this research appeared at its highest momentum, the investigations on this topic have been revitalized on at least three main directions: (1) the role and the behavioral significance of acetaldehyde in different phases of ethanol self-administration and in voluntary ethanol consumption; (2) the distinction, in the central effects of ethanol, between those arising from its non-metabolized fraction and those attributable to ethanol-derived acetaldehyde; and (3) the role of the acetaldehyde-dopamine condensation product, salsolinol. The present review article aims at presenting and discussing prospectively the most recent data accumulated following these three research pathways on this never-ending story in order to offer the most up-to-date synoptic critical view on such still unresolved and exciting topic.

Acetaldehyde, Motivation and Stress: Behavioral Evidence of an Addictive ménage à trois

Acetaldehyde (ACD) contributes to alcohol's psychoactive effects through its own rewarding properties. Recent studies shed light on the behavioral correlates of ACD administration and the possible interactions with key neurotransmitters for motivation, reward and stress-related response, such as dopamine and endocannabinoids. This mini review article critically examines ACD psychoactive properties, focusing on behavioral investigations able to unveil ACD motivational effects and their pharmacological modulation in vivo. Similarly to alcohol, rats spontaneously drink ACD, whose presence is detected in the brain following chronic self-administration paradigm. ACD motivational properties are demonstrated by operant paradigms tailored to model several drug-related behaviors, such as induction and maintenance of operant self-administration, extinction, relapse and punishment resistance. ACD-related addictive-like behaviors are sensitive to pharmacological manipulations of dopamine and endocannabinoid signaling. Interestingly, the ACD-dopamine-endocannabinoids relationship also contributes to neuroplastic alterations of the NPYergic system, a stress-related peptide critically involved in alcohol abuse. The understanding of the ménage-a-trois among ACD, reward- and stress-related circuits holds promising potential for the development of novel pharmacological approaches aimed at reducing alcohol abuse.

Developmental lead exposure induces opposite effects on ethanol intake and locomotion in response to central vs. systemic cyanamide administration

Lead (Pb) is a developmental neurotoxicant that elicits differential responses to drugs of abuse. Particularly, ethanol consumption has been demonstrated to be increased as a consequence of environmental Pb exposure, with catalase (CAT) and brain acetaldehyde (ACD, the first metabolite of ethanol) playing a role. The present study sought to interfere with ethanol metabolism by inhibiting ALDH2 (mitochondrial aldehyde dehydrogenase) activity in both liver and brain from control and Pb-exposed rats as a strategy to accumulate ACD, a substance that plays a major role in the drug's reinforcing and/or aversive effects. To evaluate the impact on a 2-h chronic voluntary ethanol intake test, developmentally Pb-exposed and control rats were administered with cyanamide (CY, an ALDH inhibitor) either systemically or intracerebroventricularly (i.c.v.) on the last 4 sessions of the experiment. Furthermore, on the last session and after locomotor activity was assessed, all animals were sacrificed to obtain brain and liver samples for ALDH2 and CAT activity determination. Systemic CY administration reduced the elevated ethanol intake already reported in the Pb-exposed animals (but not in the controls) accompanied by liver (but not brain) ALDH2 inactivation. On the other hand, a 0.3 mg i.c.v. CY administration enhanced both ethanol intake and locomotor activity accompanied by brain ALDH2 inactivation in control animals, while an increase in ethanol consumption was also observed in the Pb-exposed group, although in the absence of brain ALDH2 blockade. No changes were observed in CAT activity as a consequence of CY administration. These results support the participation of liver and brain ACD in ethanol intake and locomotor activity, responses that are modulated by developmental Pb exposure.

Diffusion Kurtosis Imaging Detects Microstructural Changes in the Brain after Acute Alcohol Intoxication in Rats

The aim of this study was to test the technical feasibility of diffusion kurtosis imaging (DKI) in the brain after acute alcohol intoxication. Diffusion tensor imaging (DTI) and DKI during 7.0 T MRI were performed in the frontal lobe and thalamus before and 30 min, 2 h, and 6 h after ethyl alcohol administration. Compared with controls, mean kurtosis values of the frontal lobe and thalamus first decreased by 44% and 38% within 30 min (p < 0.01 all) and then increased by 14% and 46% at 2 h (frontal lobe, p > 0.05; thalamus, p < 0.01) and by 29% and 68% at 6 h (frontal lobe, p < 0.05; thalamus, p < 0.01) after acute intake. Mean diffusivity decreased significantly in both the frontal lobe and the thalamus at various stages. However, fractional anisotropy decreased only in the frontal lobe, with no detectable change in the thalamus. This demonstrates that DKI possesses sufficient sensitivity for tracking pathophysiological changes at various stages associated with acute alcohol intoxication and may provide additional information that may be missed by conventional DTI parameters.

Quantification of Neural Ethanol and Acetaldehyde Using Headspace GC-MS

BACKGROUND

There is controversy regarding the active agent responsible for alcohol addiction. The theory that ethanol (EtOH) itself was the agent in alcohol drinking behavior was widely accepted until acetaldehyde (AcH) was found in the brain. The importance of AcH formation in the brain is still subject to speculation due to the lack of a method to accurately assay the AcH levels directly. A highly sensitive gas chromatography mass spectrometry (GC-MS) method to reliably determine AcH concentration with certainty is needed to address whether neural AcH is indeed responsible for increased alcohol consumption.

METHODS

A headspace gas chromatograph coupled to selected-ion monitoring MS was utilized to develop a quantitative assay for AcH and EtOH. Our GC-MS approach was carried out using a Bruker Scion 436-GC SQ MS.

RESULTS

Our approach yields limits of detection of AcH in the nanomolar range and limits of quantification in the low micromolar range. Our linear calibration includes 5 concentrations with a least-square regression greater than 0.99 for both AcH and EtOH. Tissue analyses using this method revealed the capacity to quantify EtOH and AcH in blood, brain, and liver tissue from mice.

CONCLUSIONS

By allowing quantification of very low concentrations, this method may be used to examine the formation of EtOH metabolites, specifically AcH, in murine brain tissue in alcohol research.

The "first hit" toward alcohol reinforcement: role of ethanol metabolites

This review analyzes literature that describes the behavioral effects of 2 metabolites of ethanol (EtOH): acetaldehyde and salsolinol (a condensation product of acetaldehyde and dopamine) generated in the brain. These metabolites are self-administered into specific brain areas by animals, showing strong reinforcing effects. A wealth of evidence shows that EtOH, a drug consumed to attain millimolar concentrations, generates brain metabolites that are reinforcing at micromolar and nanomolar concentrations. Salsolinol administration leads to marked increases in voluntary EtOH intake, an effect inhibited by mu-opioid receptor blockers. In animals that have ingested EtOH chronically, the maintenance of alcohol intake is no longer influenced by EtOH metabolites, as intake is taken over by other brain systems. However, after EtOH withdrawal brain acetaldehyde has a major role in promoting binge-like drinking in the condition known as the "alcohol deprivation effect"; a condition seen in animals that have ingested alcohol chronically, are deprived of EtOH for extended periods, and are allowed EtOH re-access. The review also analyzes the behavioral effects of acetate, a metabolite that enters the brain and is responsible for motor incoordination at low doses of EtOH. Also discussed are the paradoxical effects of systemic acetaldehyde. Overall, evidence strongly suggests that brain-generated EtOH metabolites play a major role in the early ("first-hit") development of alcohol reinforcement and in the generation of relapse-like drinking.

Chronic intermittent ethanol inhalation increases ethanol self-administration in both C57BL/6J and DBA/2J mice

Inbred mouse strains provide significant opportunities to understand the genetic mechanisms controlling ethanol-directed behaviors and neurobiology. They have been specifically employed to understand cellular mechanisms contributing to ethanol consumption, acute intoxication, and sensitivities to chronic effects. However, limited ethanol consumption by some strains has restricted our understanding of clinically relevant endpoints such as dependence-related ethanol intake. Previous work with a novel tastant-substitution procedure using monosodium glutamate (MSG or umami flavor) has shown that the procedure greatly enhances ethanol consumption by mouse strains that express limited drinking phenotypes using other methods. In the current study, we employ this MSG-substitution procedure to examine how ethanol dependence, induced with passive vapor inhalation, modifies ethanol drinking in C57BL/6J and DBA/2J mice. These strains represent 'high' and 'low' drinking phenotypes, respectively. We found that the MSG substitution greatly facilitates ethanol drinking in both strains, and likewise, ethanol dependence increased ethanol consumption regardless of strain. However, DBA/2J mice exhibited greater sensitivity dependence-enhanced drinking, as represented by consumption behaviors directed at lower ethanol concentrations and relative to baseline intake levels. DBA/2J mice also exhibited significant withdrawal-associated anxiety-like behavior while C57BL/6J mice did not. These findings suggest that the MSG-substitution procedure can be employed to examine dependence-enhanced ethanol consumption across a range of drinking phenotypes, and that C57BL/6J and DBA/2J mice may represent unique neurobehavioral pathways for developing dependence-enhanced ethanol consumption.

Long-term inhibition of ethanol intake by the administration of an aldehyde dehydrogenase-2 (ALDH2)-coding lentiviral vector into the ventral tegmental area of rats

Previous studies suggest that acetaldehyde generated from ethanol in the brain is reinforcing. The present studies tested the feasibility of achieving a long-term reduction of chronic and post-deprivation binge ethanol drinking by a single administration into the brain ventral tegmental area (VTA) of a lentiviral vector that codes for aldehyde dehydrogenase-2 (ALDH2), which degrades acetaldehyde. The ALDH2 gene coding vector or a control lentiviral vector were microinjected into the VTA of rats bred for their alcohol preference. In the chronic alcohol administration model, naïve animals administered the control vector and subsequently offered 10% ethanol and water ingested 8-9 g ethanol/kg body weight/day. The single administration of the ALDH2-coding vector prior to allowing ethanol availability reduced ethanol drinking by 85-90% (P < 0.001) for the 45 days tested. In the post-deprivation binge-drinking model, animals that had previously consumed ethanol chronically for 81 days were administered the lentiviral vector and were thereafter deprived of ethanol for three 7-day periods, each interrupted by a single 60-minute ethanol re-access after the last day of each deprivation period. Upon ethanol re-access, control vector-treated animals consumed intoxicating 'binge' amounts of ethanol, reaching intakes of 2.7 g ethanol/kg body weight in 60 minutes. The administration of the ALDH2-coding vector reduced re-access binge drinking by 75-80% (P < 0.001). This study shows that endowing the ventral tegmental with an increased ability to degrade acetaldehyde greatly reduces chronic alcohol consumption and post-deprivation binge drinking for prolonged periods and supports the hypothesis that brain-generated acetaldehyde promotes alcohol drinking.

Acetaldehyde, not ethanol, impairs myelin formation and viability in primary mouse oligodendrocytes

BACKGROUND

Excessive ethanol (EtOH) drinking is associated with white matter loss in the brain at all stages of life. Myelin-forming oligodendrocytes (OLs) are a major component of white matter, but their involvement in EtOH-mediated white matter loss is unclear. Myelination continues throughout the life with highest rates during fetal development and adolescence. However, little is known about the effects of EtOH and its principal metabolite acetaldehyde (ACD) on OLs at the cellular level.

METHODS

We compared the responses to different concentrations of EtOH or ACD by primary OLs in culture.

RESULTS

EtOH did not cause significant cell death at concentrations lower than 120 mM, even after 24 hours. In comparison, ACD was highly lethal at doses above 50 μM. High concentrations of EtOH (120 mM) and ACD (500 μM) for 24 hours did not reduce myelin in mature OLs. Myelin production and OL differentiation were significantly impaired by 7 days exposure to 500 or 50 μM ACD but not 120 mM EtOH.

CONCLUSIONS

This study shows that OLs are relatively resistant to EtOH, even at a concentration more than 4 times the typical blood EtOH concentrations associated with social drinking (10 to 30 mM). In contrast, OLs are much more sensitive to ACD than EtOH, particularly with long-term exposure. This suggests that part of white matter loss in response to EtOH, especially during high rates of myelin formation, may be due in part to the effects of its principal metabolite ACD.

Key role of salsolinol in ethanol actions on dopamine neuronal activity of the posterior ventral tegmental area

Ethanol excites dopamine (DA) neurons in the posterior ventral tegmental area (pVTA). This effect is responsible for ethanol's motivational properties and may contribute to alcoholism. Evidence indicates that catalase-mediated conversion of ethanol into acetaldehyde in pVTA plays a critical role in this effect. Acetaldehyde, in the presence of DA, condensates with it to generate salsolinol. Salsolinol, when administered in pVTA, excites pVTA DA cells, elicits DA transmission in nucleus accumbens and sustains its self-administration in pVTA. Here we show, by using ex vivo electrophysiology, that ethanol and acetaldehyde, but not salsolinol, failed to stimulate pVTA DA cell activity in mice administered α-methyl-p-tyrosine, a DA biosynthesis inhibitor that reduces somatodendritic DA release. This effect was specific for ethanol and acetaldehyde since morphine, similarly to salsolinol, was able to excite pVTA DA cells in α-methyl-p-tyrosine-treated mice. However, when DA was bath applied in slices from α-methyl-p-tyrosine-treated mice, ethanol-induced excitation of pVTA DA neurons was restored. This effect requires ethanol oxidation into acetaldehyde given that, when H2 O2 -catalase system was impaired by either 3-amino-1,2,4-triazole or in vivo administration of α-lipoic acid, ethanol did not enhance DA cell activity. Finally, high performance liquid chromatography-tandem mass spectrometry analysis of bath medium detected salsolinol only after co-application of ethanol and DA in α-methyl-p-tyrosine-treated mice. These results demonstrate the relationship between ethanol and salsolinol effects on pVTA DA neurons, help to untangle the mechanism(s) of action of ethanol in this area and contribute to an exciting research avenue prosperous of theoretical and practical consequences.

Fenofibrate--a lipid-lowering drug--reduces voluntary alcohol drinking in rats

The administration of disulfiram raises blood acetaldehyde levels when ethanol is ingested, leading to an aversion to alcohol. This study was aimed at assessing the effect of fenofibrate on voluntary ethanol ingestion in rats. Fenofibrate reduces blood triglyceride levels by increasing fatty acid oxidation by liver peroxisomes, along with an increase in the activity of catalase, which can oxidize ethanol to acetaldehyde. UChB drinker rats were allowed to consume alcohol 10% v/v freely for 60 days, until consumption stabilized at around 7 g ethanol/kg/24 h. About 1-1.2 g ethanol/kg of this intake is consumed in the first 2 h of darkness of the circadian cycle. Fenofibrate subsequently administered (50 mg/kg/day by mouth [p.o.]) for 14 days led to a 60-70% (p < 0.001) reduction of 24-h ethanol consumption. When ethanol intake was determined within the first 2 h of darkness, the reduction was 85-90% (p < 0.001). We determined whether animals chronically allowed access to ethanol and subsequently treated with fenofibrate, would a) increase liver catalase activity, and b) increase blood acetaldehyde levels after a 24-h ethanol deprivation and the subsequent administration of 1 g ethanol/kg. The oral administration of 1 g ethanol/kg produced a rapid increase in blood (arterial) acetaldehyde in fenofibrate-treated animals versus controls also administered 1 g/kg ethanol (70 μM vs. 7 μM; p < 0.001). Liver catalase activity following fenofibrate treatment was increased 3-fold (p < 0.01). Other hepatic enzymes responsible for the metabolism of ethanol (alcohol dehydrogenase and aldehyde dehydrogenase) remained unchanged. No liver damage was induced, as measured by serum glutamic-pyruvic transaminase (GPT) activity. The effect of fenofibrate in reducing alcohol intake was fully reversible. Overall, in rats allowed chronic ethanol intake, by mouth (p.o.), fenofibrate administration increased liver catalase activity and reduced voluntary ethanol intake. The administration of 1 g ethanol/kg (p.o.) to these animals increased blood acetaldehyde levels in fenofibrate-treated animals, suggesting the possible basis for the reduction in ethanol intake.

Elucidating the biological basis for the reinforcing actions of alcohol in the mesolimbic dopamine system: the role of active metabolites of alcohol

The development of successful pharmacotherapeutics for the treatment of alcoholism is predicated upon understanding the biological action of alcohol. A limitation of the alcohol research field has been examining the effects of alcohol only and ignoring the multiple biological active metabolites of alcohol. The concept that alcohol is a "pro-drug" is not new. Alcohol is readily metabolized to acetaldehyde within the brain. Acetaldehyde is a highly reactive compound that forms a number of condensation products, including salsolinol and iso-salsolinol (acetaldehyde and dopamine). Recent experiments have established that numerous metabolites of alcohol have direct CNS action, and could, in part or whole, mediate the reinforcing actions of alcohol within the mesolimbic dopamine system. The mesolimbic dopamine system originates in the ventral tegmental area (VTA) and projects to forebrain regions that include the nucleus accumbens (Acb) and the medial prefrontal cortex (mPFC) and is thought to be the neurocircuitry governing the rewarding properties of drugs of abuse. Within this neurocircuitry there is convincing evidence that; (1) biologically active metabolites of alcohol can directly or indirectly increase the activity of VTA dopamine neurons, (2) alcohol and alcohol metabolites are reinforcing within the mesolimbic dopamine system, (3) inhibiting the alcohol metabolic pathway inhibits the biological consequences of alcohol exposure, (4) alcohol consumption can be reduced by inhibiting/attenuating the alcohol metabolic pathway in the mesolimbic dopamine system, (5) alcohol metabolites can alter neurochemical levels within the mesolimbic dopamine system, and (6) alcohol interacts with alcohol metabolites to enhance the actions of both compounds. The data indicate that there is a positive relationship between alcohol and alcohol metabolites in regulating the biological consequences of consuming alcohol and the potential of alcohol use escalating to alcoholism.

Gene specific modifications unravel ethanol and acetaldehyde actions

Ethanol is metabolized into acetaldehyde mainly by the action of alcohol dehydrogenase in the liver, while mainly by the action of catalase in the brain. Aldehyde dehydrogenase-2 metabolizes acetaldehyde into acetate in both organs. Gene specific modifications reviewed here show that an increased liver generation of acetaldehyde (by transduction of a gene coding for a high-activity liver alcohol dehydrogenase ADH1^*B2) leads to increased blood acetaldehyde levels and aversion to ethanol in animals. Similarly aversive is an increased acetaldehyde level resulting from the inhibition of liver aldehyde dehydrogenase-2 (ALDH2) synthesis (by an antisense coding gene against aldh2 mRNA). The situation is diametrically different when acetaldehyde is generated in the brain. When the brain ventral tegmental area (VTA) is endowed with an increased ability to generate acetaldehyde (by transfection of liver rADH) the reinforcing effects of ethanol are increased, while a highly specific inhibition of catalase synthesis (by transduction of a shRNA anti catalase mRNA) virtually abolishes the reinforcing effects of ethanol as seen by a complete abolition of ethanol intake in rats bred for generations as high ethanol drinkers. Data shows two divergent effects of increases in acetaldehyde generation: aversive in the periphery but reinforcing in the brain.

The alcohol deprivation effect: marked inhibition by anticatalase gene administration into the ventral tegmental area in rats

BACKGROUND

Animals that have chronically consumed alcohol and are subsequently deprived of it markedly increase their intake above basal levels when access to alcohol is reinstated. Such an effect, termed the alcohol deprivation effect (ADE), has been proposed to reflect (i) an obsessive-compulsive behavior, (ii) craving, or (iii) an increased reinforcing value of ethanol (EtOH). It has been reported that acetaldehyde, a highly reinforcing metabolite of EtOH, is generated in the brain by the action of catalase. Recent studies show that the administration of an anticatalase (shRNA)-encoding lentiviral vector into the brain ventral tegmental area (VTA) of naïve rats virtually abolishes (85 to 95%) their EtOH intake. It is hypothesized that the antireinforcing effect of the anticatalase vector will also inhibit the ADE.

METHODS

Two-month-old Wistar-derived UChB alcohol drinker rats were offered free access to water and 10 and 20% EtOH for 67 days. Thereafter, the animals were deprived of EtOH for 15 days and were subsequently offered access to the EtOH solutions. At the start of the deprivation period, animals were microinjected a single dose of an anticatalase (or control) vector into the VTA. EtOH intake was measured on the first hour of EtOH re-exposure as well as on a 24-hour basis for 7 days.

RESULTS

A marked ADE was observed when EtOH intake was measured on the first hour or 24 hours following EtOH re-exposure, compared to the corresponding controls. The administration of the anticatalase vector reduced ADE by 60 to 80% (p < 0.001) on the first hour and by 63 to 80% (p < 0.001) on the initial 24 hours of EtOH re-exposure (first and second ADE, respectively) without changing the total fluid intake, indicating a specific effect on EtOH drinking.

CONCLUSIONS

Ethanol intake associated with ADE--a binge-like drinking behavior--is markedly inhibited by the administration of an anticatalase vector into the VTA, which blocks the conversion of EtOH into acetaldehyde, strongly suggesting that the marked increased EtOH intake that follows an alcohol deprivation period is mediated by acetaldehyde and its reinforcing metabolite.

The role of CYP2E1 in alcohol metabolism and sensitivity in the central nervous system

Ethanol consumption has effects on the central nervous system (CNS), manifesting as motor incoordination, sleep induction (hypnosis), anxiety, amnesia, and the reinforcement or aversion of alcohol consumption. Acetaldehyde (the direct metabolite of ethanol oxidation) contributes to many aspects of the behavioral effects of ethanol. Given acetaldehyde cannot pass through the blood brain barrier, its concentration in the CNS is primarily determined by local production from ethanol. Catalase and cytochrome P450 2E1 (CYP2E1) represent the major enzymes in the CNS that catalyze ethanol oxidation. CYP2E1 is expressed abundantly within the microsomes of certain brain cells and is localized to particular brain regions. This chapter focuses on the discussion of CYP2E1 in ethanol metabolism in the CNS, covering topics including how it is regulated, where it is expressed and how it influences sensitivity to ethanol in the brain.

Place conditioning with ethanol in rats bred for high (UChB) and low (UChA) voluntary alcohol drinking

The main goal of this study was to investigate the ability of an ethanol dose (1g/kg) administered intraperitoneally to induce conditioned place preference (CPP) and/or conditioned place aversion (CPA) in two lines of rats selectively bred for their high (UChB) or low (UChA) voluntary ethanol intake. It was found that five pairings with ethanol induced CPA in ethanol-naïve rats of both lines, but the magnitude of avoidance was lower in the UChB relative to the UChA rats, indicating that ethanol was less aversive to naïve rats bred for high alcohol drinking. After 2 months of high voluntary ethanol drinking (~6-7g/kg/day), in free choice between 10% ethanol and water, ethanol produced CPP in UChB rats, reflecting that ethanol had become rewarding to these rats. By contrast, the low voluntary ethanol intake (<1g/kg/day) displayed by UChA rats preexposed for 2 months in free choice did not change ethanol-induced CPA. However, preexposure of UChA rats to forced ethanol drinking (~5.7g/kg/day) and the later inhibition of ethanol-derived acetaldehyde by 4-methylpyrazole (10mg/kg intraperitoneal), an inhibitor of the enzyme alcohol dehydrogenase, not only increased their voluntary ethanol intake in free choice, but also had a facilitating effect on the development of CPP. Taken together, these results show that the expression of the reinforcing effects of ethanol required a period of voluntary ethanol intake in UChB rats, whereas in UChA rats, both prior exposure to forced ethanol drinking and reduction of high blood ethanol-derived acetaldehyde were required.

Ethanol as a prodrug: brain metabolism of ethanol mediates its reinforcing effects

BACKGROUND

 While the molecular entity responsible for the rewarding effects of virtually all drugs of abuse is known, that for ethanol remains uncertain. Some lines of evidence suggest that the rewarding effects of alcohol are mediated not by ethanol per se but by acetaldehyde generated by catalase in the brain. However, the lack of specific inhibitors of catalase has not allowed strong conclusions to be drawn about its role on the rewarding properties of ethanol. The present studies determined the effect on voluntary alcohol consumption of two gene vectors, one designed to inhibit catalase synthesis and one designed to synthesize alcohol dehydrogenase (ADH), to respectively inhibit or increase brain acetaldehyde synthesis.

METHODS

 The lentiviral vectors, which incorporate the genes they carry into the cell genome, were (i) one encoding a shRNA anticatalase synthesis and (ii) one encoding alcohol dehydrogenase (rADH1). These were stereotaxically microinjected into the brain ventral tegmental area (VTA) of Wistar-derived rats bred for generations for their high alcohol preference (UChB), which were allowed access to an ethanol solution and water.

RESULTS

 Microinjection into the VTA of the lentiviral vector encoding the anticatalase shRNA virtually abolished (-94% p < 0.001) the voluntary consumption of alcohol by the rats. Conversely, injection into the VTA of the lentiviral vector coding for ADH greatly stimulated (2 to 3 fold p < 0.001) their voluntary ethanol consumption.

CONCLUSIONS

The study strongly suggests that to generate reward and reinforcement, ethanol must be metabolized into acetaldehyde in the brain. Data suggest novel targets for interventions aimed at reducing chronic alcohol intake.

Ethanol as a prodrug: brain metabolism of ethanol mediates its reinforcing effects--a commentary

BACKGROUND

This commentary discusses a study by Karahanian and colleagues (2011) on the role of central nervous system acetaldehyde in the reinforcing effects of ethanol. The goal is to emphasize the importance of the study and to discuss future directions.

RESULTS

This important paper solidifies the idea that the levels of acetaldehyde in the central nervous system have profound effects in mediating the reinforcing actions of ethanol. This is accomplished by manipulating the brain levels of acetaldehyde produced from ethanol by the injection of lentivirus containing either an anti-catalase shRNA construct or a rat liver alcohol dehydrogenase into the central nervous system and observing the effects on alcohol preference by high ethanol-consuming rats. A factor not directly considered is that acetaldehyde is further metabolized to acetate, which also has some behavioral actions.

CONCLUSIONS

The efficacy of lentivirus injections of enzyme inhibitors or enzymes themselves to alter a behavioral response to ethanol is clearly demonstrated here. The many other actions of ethanol that are postulated to be a result of the production of acetaldehyde in the brain remain to be investigated by similar techniques. Possible "therapeutic avenues to reduce chronic alcohol use" are envisioned.

Phosphorylation regulates removal of synaptic N-methyl-D-aspartate receptors after withdrawal from chronic ethanol exposure

Alterations in N-methyl-d-aspartate receptor (NMDAR) protein levels or subcellular localization in brain after chronic ethanol exposure may contribute to withdrawal-associated seizures and neurotoxicity. We have investigated synaptic localization of NMDARs in cultured hippocampal pyramidal neurons after prolonged (7 days) exposure to, and acute withdrawal from, 80 mM ethanol using fluorescence immunocytochemistry techniques. After chronic ethanol exposure, there was a significant increase in the clustering of NR1 and NR2B subunits and their colocalization with the synaptic proteins synaptophysin and postsynaptic density protein 95, respectively. There was also increased expression of NR1 variants containing the C2' cassette after chronic ethanol exposure. The ethanol-induced synaptic clustering and colocalization were rapidly reversed within 4 h after ethanol withdrawal. Surface labeling of NR2B subunits suggested that this rapid reversal involved lateral receptor movement to extrasynaptic sites rather than internalization of receptors. Receptor removal from the synapse during ethanol withdrawal was associated with changes in the phosphorylation state of NR2B Ser1480, controlled by the protein kinase CK2. The redistribution of NMDAR to synapses produced by long-term ethanol exposure, as well as the rapid removal during withdrawal, may not only affect neuronal withdrawal hyperexcitability but also may sensitize the system to subsequent synaptic plasticity.

Genomic insights into acute alcohol tolerance

Alcohol "sensitivity" has been proposed as a predictive factor for development of alcohol dependence (Schuckit et al., 2005). Most measures of alcohol sensitivity in humans and animals include a component that can be ascribed to acute functional tolerance (AFT). AFT is a form of tolerance that develops within a single period of alcohol exposure and has a genetic component. We used microarray technology as well as quantitative trait locus analysis of phenotypic and gene expression data across 30 BXD recombinant inbred strains of mice, 20 inbred strains of mice, and two replicate lines of mice selectively bred for differences in AFT, to identify differentially expressed candidate genes that contribute to predisposition to AFT. Eight candidate genes were identified by our statistical and filtering methods. The location of brain expression of these genes was mapped using the Allen Brain Atlas (http://www.brain-map.org), and the transcript location and molecular pathway analysis indicated that brain structures and biochemical pathways implicated in long-term potentiation and memory might also participate in the generation of acute functional alcohol tolerance.

Acetaldehyde, a major constituent of tobacco smoke, enhances behavioral, endocrine, and neuronal responses to nicotine in adolescent and adult rats

We have previously shown that acetaldehyde, a constituent of tobacco smoke, increases nicotine self-administration in adolescent, but not adult, rats. The aim of this study was to determine whether acetaldehyde influences other behavioral, endocrine, or neuronal responses to nicotine at either age. Juvenile (postnatal day (P) 27) and adult (P90) male Sprague-Dawley rats were treated with saline, acetaldehyde (16 microg/kg/injection x 2, i.v.), nicotine (30 microg/kg/injection x 2, i.v.) or a combination of acetaldehyde and nicotine. Locomotion and center time were evaluated for 30 min in a novel open field, before measurement of plasma corticosterone levels and brain c-fos mRNA. Nicotine increased locomotor activity in juveniles but decreased it in adults; in contrast, center time was increased at both ages. Acetaldehyde potentiated nicotine's locomotor effects, but not center time. Nicotine induced c-fos expression in the bed nucleus of the stria terminalis, the central nucleus of the amygdala (CeA), nucleus accumbens, and the superior colliculus (SC) at both ages, whereas it activated the hypothalamic paraventricular nucleus (PVN) and consequent corticosterone secretion only in adults. Acetaldehyde potentiated nicotine-induced c-fos in CeA and SC, and activation of PVN c-fos expression/plasma corticosterone release; however, this drug interaction was only observed in behaviorally tested animals, not those that were minimally stressed. Thus, acetaldehyde may modulate the interaction of nicotine and stress. Although pharmacokinetic studies showed that acetaldehyde did not change nicotine levels in either brain or serum, nicotine penetration into the brain was slower in juveniles as compared to adults.

Ethanol-induced conditioned place preference, but not aversion, is blocked by treatment with D -penicillamine, an inactivation agent for acetaldehyde

RATIONALE

There is evidence to suggest that acetaldehyde is involved in the control of ethanol-seeking behavior and reward. D -penicillamine, a thiol amino acid, is a highly selective agent for the inactivation of acetaldehyde. Previous studies from our laboratory have demonstrated that D -penicillamine prevents both behavioral stimulation induced by ethanol and acetaldehyde-produced locomotor depression in mice.

OBJECTIVES

The contribution of ethanol-derived acetaldehyde to the affective effects of ethanol (preference and aversion) was assessed using an unbiased place conditioning design.

METHODS

Male mice received four pairings of a distinctive floor stimulus (CS+: GRID+ or HOLE+) with injections of saline and ethanol (2 g/kg) given before (preference) or after (aversion) the 5-min exposure to the place conditioning apparatus. A different floor stimulus (CS-: GRID- or HOLE-), associated with saline-saline injections on alternate days, was presented. For a different group of animals, the pairings with the CS+ were associated with saline and ethanol injections, but on alternate days, they received D -penicillamine (50 or 75 mg/kg) and ethanol injections paired with the CS-floor stimulus. A 60-min preference test was carried out 24 h after the last conditioning trial. A similar procedure was followed to test the effect of D -penicillamine on morphine (16 mg/kg) and cocaine-induced (20 mg/kg) conditioned place preference (CPP).

RESULTS

CPP and conditioned place aversion (CPA) were observed for ethanol, but D -penicillamine only blocked CPP. D -penicillamine, by itself, did not produce either rewarding or aversive effects. CPP observed for morphine and cocaine was unaffected by D -penicillamine pretreatment.

CONCLUSIONS

The results of the present study suggest that the selective inactivation of acetaldehyde blocked the rewarding, but not aversive, effects of ethanol and support the role of this ethanol metabolite in the affective properties of ethanol.

The role of acetaldehyde in the neurobehavioral effects of ethanol: A comprehensive review of animal studies

Acetaldehyde has long been suggested to be involved in a number of ethanol's pharmacological and behavioral effects, such as its reinforcing, aversive, sedative, amnesic and stimulant properties. However, the role of acetaldehyde in ethanol's effects has been an extremely controversial topic during the past two decades. Opinions ranged from those virtually denying any role for acetaldehyde in ethanol's effects to those who claimed that alcoholism is in fact "acetaldehydism". Considering the possible key role of acetaldehyde in alcohol addiction, it is critical to clarify the respective functions of acetaldehyde and ethanol molecules in the pharmacological and behavioral effects of alcohol consumption. In the present paper, we review the animal studies reporting evidence that acetaldehyde is involved in the pharmacological and behavioral effects of ethanol. A number of studies demonstrated that acetaldehyde administration induces a range of behavioral effects. Other pharmacological studies indicated that acetaldehyde might be critically involved in several effects of ethanol consumption, including its reinforcing consequences. However, conflicting evidence has also been published. Furthermore, it remains to be shown whether pharmacologically relevant concentrations of acetaldehyde are achieved in the brain after alcohol consumption in order to induce significant effects. Finally, we review current evidence about the central mechanisms of action of acetaldehyde.

Inhibition of acetaldehyde metabolism decreases acetylcholine release in medial frontal cortex of freely moving rats

The effect of high acetaldehyde (ACe) on acetylcholine (ACh) release was studied in vivo in the medial frontal cortex (mfc) of freely moving rats using brain microdialysis coupled with high performance liquid chromatography and an electrochemical detector. Ethanol (EtOH) and ACe concentrations were quantified simultaneously in the mfc of awake rats by in vivo microdialysis followed by head-space gas chromatography. Rats were treated intraperitoneally with saline, EtOH (1 and 2 g/kg) or cyanamide (CY, 50 mg/kg, a potent aldehyde dehydrogenase inhibitor) plus EtOH (1 and 2 g/kg). No significant effect on ACh levels was observed in saline groups, as compared to baseline value. The basal level of ACh in the dialysate was about 0.30 +/- 0.04 pmol/20 microl, and this value was reduced significantly in the EtOH (1 and 2 g/kg) and CY + EtOH (1 and 2 g/kg) groups for 240 min after EtOH administration. The time courses of ACh release continued to decrease significantly after EtOH administration in the CY + EtOH (1 and 2 g/kg) groups compared to the values in the saline and EtOH (1 and 2 g/kg) groups. A significant decrease in ACh release was observed from 140 to 240 min after EtOH dosing in the EtOH (1 and 2 g/kg) groups, as compared to saline groups. EtOH and ACe concentrations in the mfc were first determined at 15 min after a dose of EtOH, reached a peak at 30 min and then gradually decreased in the CY + EtOH (1 and 2 g/kg) groups. The present study suggests that both EtOH and ACe concentration in the brain can decrease in vivo ACh release in the mfc of free-moving rats, and the ACe-induced decrease in ACh levels was significantly higher than EtOH.

Microdialysis for the determination of acetaldehyde and ethanol concentrations in the striatum of freely moving rats

The subject of the present paper is the simultaneous determination of ethanol (EtOH) and acetaldehyde (AcH) concentrations in the striatum of freely moving rats using an in vivo microdialysis followed by head-space gas chromatography (GC). Major operation conditions of GC were as follows: column, injector and detector temperatures 90, 110 and 200 degrees C, respectively; Supelcowax wide bore capillary column (60 m length, 0.53 mm i.d., 2 microm film thickness); carrier gas, nitrogen; flow rate, 20 ml/min. The recovery of EtOH and AcH at a concentration 40 mM and 250 microM, respectively, by microdialysis showed a maximum of 83.8+/-12.2 and 51.2+/-6.5%, respectively, at a flow rate of 0.8 microl/min. A good linear calibration curve in the concentration range of 5-50 mM for EtOH (r=0.998), and 10-250 microM for AcH (r=0.988) was observed. Microdialysates were collected for 10 min each after insertion of probe into the striatum. Rats were treated with cyanamide (100mg/kg, a potent aldehyde dehydrogenase inhibitor) and 60 min later with EtOH (1g/kg) intraperitoneally. A 10 min sample was about 8 microl. This volume was mixed with 40 microl of 0.002% t-butanol as an internal standard in 0.6N perchloric acid, and then analyzed by head-space GC method. The peak EtOH and AcH concentrations in the striatal dialysates reached maximum at 30 min, and then gradually decreased. This method represents a reasonable tool to quantify in vivo both AcH and EtOH levels simultaneously in rat brain.

In vivo study of salsolinol produced by a high concentration of acetaldehyde in the striatum and nucleus accumbens of free-moving rats

BACKGROUND

Salsolinol, a neuropharmacologically active compound, is formed by the condensation of acetaldehyde (AcH) with dopamine (DA) in the brain. The aim of our study was to examine the effect of a high concentration of AcH on salsolinol formation and to compare the release of DA, serotonin (5-HT), and salsolinol in the striatum and nucleus accumbens (NAc) in free-moving rats.

METHODS

After the insertion of a microdialysis probe, male Wistar rats (250-300 g) were treated with cyanamide (CY, a potent aldehyde dehydrogenase inhibitor) + ethanol (EtOH), CY + 4-methylpyrazole (4-MP, a strong alcohol dehydrogenase inhibitor) + EtOH, 4-MP + EtOH, CY, and 4-MP. Simultaneous quantitation of DA, 5-HT, and salsolinol in dialysates was performed by using in vivo microdialysis coupled with high-performance liquid chromatography with an electrochemical detector and blood EtOH and AcH by using a head-space gas chromatographic method.

RESULTS

Salsolinol was detected only in the CY + EtOH groups in both the striatum and NAc, and we also detected a high AcH concentration in the blood in those groups. A correlation was found between the dialysate levels of salsolinol and blood concentrations of AcH. The striatal levels of DA and 5-HT were approximately two times higher, whereas salsolinol levels were approximately three times higher compared with the usual level in the NAc. No significant difference of DA and 5-HT levels in the dialysates was observed in either the control or the other study groups.

CONCLUSION

Our observation suggested that the brain salsolinol formation may depend on the concentrations of DA and AcH in freely moving rats, and there is no effect of a high concentration of AcH on DA and 5-HT levels in the striatum and NAc.

Acetaldehyde-reinforcing effects: differences in low-alcohol-drinking (UChA) and high-alcohol-drinking (UChB) rats

It has been suggested that acetaldehyde has a biphasic effect on voluntary alcohol consumption. At low brain concentration, it might exert reinforcing effects, whereas high acetaldehyde levels would be predominantly aversive. The objective of the current study was to compare the effect of an intraperitoneal dose of acetaldehyde (50 mg/kg) in high-alcohol-drinking (UChB) and low-alcohol-drinking (UChA) rat lines, which differ in the activity of the brain mitochondrial class 2 aldehyde dehydrogenase (ALDH2) as a consequence of differences in their ALDH2 genotypes. A classical place-conditioning procedure was used to determine the reinforcing or aversive (or both) effects of acetaldehyde in ethanol-naive UChB and UChA rats. Environmental cues were paired with an intraperitoneal 50-mg/kg injection of acetaldehyde. On 10 consecutive days, each rat received one place conditioning per day; the acetaldehyde-pairing was alternated with saline-pairing. Results showed that conditioning with the 50-mg/kg dose of acetaldehyde induced place preference in UChB rats and place aversion in UChA rats. In a second experiment, UChB and UChA rats, pretested for ethanol preference, were injected with one 50-mg/kg dose of acetaldehyde or saline and tested for their voluntary ethanol consumption during 4 weeks. Results showed that the acetaldehyde dose induced a persistent and long-lasting enhancement of ethanol intake in UChB rats, but not in UChA rats. These results, together with the finding that after administration of a 50-mg/kg dose of acetaldehyde cerebral venous blood acetaldehyde levels in UChA rats were consistently higher than levels in UChB rats, support the suggestion that differential acetaldehyde levels, differential brain ALDH2 activity, or both were responsible for the different effects of acetaldehyde in the two rat lines.

The effect of cyanamide and 4-methylpyrazole on the ethanol-induced locomotor activity in mice

To assess the role of cyanamide and 4-methylpyrazole (4-MP) in mediating ethanol-induced locomotor activity in mice, they were pretreated with cyanamide (12.5, 25, or 50 g/kg) prior to one ethanol injection (2.4 g/kg) and showed significantly depressed locomotor activity compared with control groups. Cyanamide (25 mg/kg) also cancelled out the biphasic action of ethanol (0, 0.8, 1.6, 2.4, 3.2, or 4 g/kg) on locomotor activity. The action of cyanamide and 4-MP in combined administration was also tested. Our data show that pretreatment with 4-MP alone does not change the spontaneous or ethanol-induced locomotor activity. Conversely, when mice were pretreated with cyanamide and 4-MP, the depressive effect of cyanamide on the locomotor activity induced by ethanol disappeared, and the locomotor activity rose to levels similar to those of the control group, recovering the biphasic ethanol effect. These effects cannot be attributed to peripheral elevated blood acetaldehyde levels, as pretreatment with 4-MP prevents accumulation of acetaldehyde. These data might suggest some influence of brain catalase and aldehyde dehydrogenase (ALDH) on the effects of ethanol.

L-cysteine, a thiol amino acid, increases the stimulating acute effect of ethanol on locomotion

The present study deals with the effect of L-cysteine on the acute stimulating effects of ethanol. Swiss albino mice were pretreated with 0.0, 18.75, 37.50, or 75.00 mg/kg of cysteine simultaneously, 30 or 60 min, before the administration of saline or 0.8, 1.6, 2.4, or 3.2 g/kg of ethanol at 20% vol./vol. After these treatments, mice were left in the open-field chamber for 20 min, and locomotor activity was evaluated for the last 10 min. The specificity of the effects of L-cysteine was analyzed with the use of two drugs that also induce locomotor activity--d-amphetamine and methanol. Mice received L-cysteine (37.5 mg/kg), and 30 min after this treatment d-amphetamine (2 mg/kg) or methanol (2.4 g/kg) was injected. Data showed that L-cysteine at 37.5 mg/kg was able to increase locomotion induced by 2.4 and 3.2 g/kg of ethanol when it was administered 30 min before ethanol injection. The effects of L-cysteine are specific for the stimulation of ethanol on locomotion, because L-cysteine does not alter d-amphetamine-induced locomotor activity or methanol-induced locomotion. Moreover, blood ethanol levels were not affected by L-cysteine pretreatment. Therefore, the present findings demonstrated that ethanol-induced locomotor effects are enhanced by L-cysteine, in a manner similar to that of other sulfur amino acids.

Chronic ethanol exposure delays the 'developmental switch' of the NMDA receptor 2A and 2B subunits in cultured cerebellar granule neurons

Chronic ethanol treatment of cultured neurons from various brain areas has been found to increase NMDA receptor function and to alter the levels of some NMDA receptor subunit proteins. Because the cultured neurons are exposed to ethanol during a period when the NMDA receptor is undergoing developmental changes in subunit expression, we wished to determine whether ethanol treatment alters this developmental pattern. We found that 3 days of treatment of cerebellar granule neurons with ethanol, which was previously reported to increase NMDA receptor function, resulted in a delay in the 'developmental switch' of the NR2A and NR2B subunits, i.e. the developmental decrease in NR2B and increase in NR2A protein expression. As a result, the level of NR2B was higher, and that of NR2A was lower, in the ethanol-treated cells than in control cells. Cross-linking experiments showed that the changes in total receptor subunit proteins levels were reflected in cell-surface expressed proteins, indicating changes in the amount of functional receptors. These results were confirmed by a higher potency of glycine at the NMDA receptor in the ethanol-treated cells, as determined by NMDA/glycine-induced increases in intracellular Ca(2+). The results suggest that the mechanism by which ethanol alters NMDA receptor expression in cultured neurons, where receptors are undergoing development, differs from the mechanism of ethanol's effect on NMDA receptors in adult brain. Changes in the proportion of NR2A and NR2B subunits may contribute to effects of ethanol on neuronal development.

Key role for the epsilon isoform of protein kinase C in painful alcoholic neuropathy in the rat

Chronic alcohol consumption produces a painful peripheral neuropathy for which there is no reliably successful therapy, attributable to, in great part, a lack of understanding of the underlying mechanisms. We tested the hypothesis that neuropathic pain associated with chronic alcohol consumption is a result of abnormal peripheral nociceptor function. In rats maintained on a diet to simulate chronic alcohol consumption in humans, mechanical hyperalgesia was present by the fourth week and maximal at 10 weeks. Thermal hyperalgesia and mechanical allodynia were also present. Mechanical threshold of C-fibers in ethanol fed rats was lowered, and the number of action potentials during sustained stimulation increased. The hyperalgesia was acutely attenuated by intradermal injection of nonselective protein kinase C (PKC) or selective PKCepsilon inhibitors injected at the site of nociceptive testing. Western immunoblot analysis indicated a higher level of PKCepsilon in dorsal root ganglia from alcohol-fed rats, supporting a role for enhanced PKCepsilon second-messenger signaling in nociceptors contributing to alcohol-induced hyperalgesia.

Chronic ethanol exposure attenuates the anti-apoptotic effect of NMDA in cerebellar granule neurons

Ethanol, added to primary cultures of cerebellar granule neurons simultaneously with NMDA, was previously shown to inhibit the anti-apoptotic effect of NMDA. The in vitro anti-apoptotic effect of NMDA is believed to mimic in vivo protection against apoptosis afforded by innervation of developing cerebellar granule neurons by glutamatergic mossy fibers. Therefore, the results suggested that the presence of ethanol in the brain at a critical period of development would promote apoptosis. In the present studies, we examined the effect of chronic ethanol exposure on the anti-apoptotic action of NMDA in cerebellar granule neurons. The neurons were treated with ethanol in vitro for 1-3 days in the absence of NMDA. Even after ethanol was removed from the culture medium, as ascertained by gas chromatography, the protective effect of added NMDA was significantly attenuated. The decreased anti-apoptotic effect of NMDA was associated with a change in the properties of the NMDA receptor, as indicated by a decrease in ligand binding, decreased expression of NMDA receptor subunit proteins, and decreased functional responses including stimulation of increases in intracellular Ca(2+) and induction of brain-derived neurotrophic factor expression. The latter effect may directly underlie the attenuated protective effect of NMDA in these neurons. The results suggest that ethanol exposure during development can have long-lasting effects on neuronal survival. The change in the NMDA receptor caused by chronic ethanol treatment may contribute to the loss of cerebellar granule neurons that is observed in animals and humans exposed to ethanol during gestation.