Brain and liver aldehyde dehydrogenase activity and voluntary ethanol consumption by rats: relations to strain, sex, and age

Hepatic injury and inflammation alter ethanol metabolism and drinking behavior

While liver injury is commonly associated with excessive alcohol consumption, how liver injury affects alcohol metabolism and drinking preference remains unclear. To answer these questions, we measured the expression and activity of alcohol dehydrogenase 1 (ADH1) and acetaldehyde dehydrogenase 2 (ALDH2) enzymes, ethanol and acetaldehyde levels in vivo, and binge-like and preferential drinking behaviors with drinking in the dark and two-bottle choice in animal models with liver injury. Acute and chronic carbon tetrachloride (CCl4), and acute LPS-induced liver injury repressed hepatic ALDH2 activity and expression and consequently, blood and liver acetaldehyde concentrations were increased in these models. In addition, chronic CCl4 and acute LPS treatment inhibited hepatic ADH1 expression and activity, leading to increases in blood and liver ethanol concentrations. Consistent with the increase in acetaldehyde levels, alcohol drinking behaviors were reduced in mice with acute or chronic liver injury. Furthermore, oxidative stress induced by hydrogen peroxide attenuated ADH1 and ALDH2 activity post-transcriptionally, while proinflammatory cytokines led to transcriptional repression of ADH1 and ALDH2 in cultured hepatocytes, which correlated with the repression of transcription factor HNF4α. Collectively, our data suggest that alcohol metabolism is suppressed by inflammation and oxidative stress, which is correlated with decreased drinking behavior.

Increased ethanol drinking in "humanized" mice expressing the mu opioid receptor A118G polymorphism are mediated through sex-specific mechanisms

The A118G single nucleotide polymorphism (SNP) of the mu-opioid receptor gene (Oprm1) has been implicated in mediating the rewarding effects of alcohol. Clinical and preclinical studies suggest that the G allele may confer a genetic vulnerability to alcohol dependence, though it remains unknown whether these effects are sex-specific. We used male and female mice homozygous for the "humanized" 118AA or 118GG alleles to determine whether the A118G SNP potentiates ethanol consumption in a sex-specific manner in both the two-bottle choice and drinking-in-the-dark (DID) paradigms. Mice were also assessed for differences in naltrexone sensitivity, ethanol reward assessed via conditioned place preference (CPP), and sensitivity to the sedative/ataxic effects of ethanol using the rota-rod and loss of righting reflex (LORR) assays. We found that male and female 118GG mice drank significantly more ethanol than 118AA littermates using a continuous access, two-bottle choice paradigm. In the limited-access DID drinking model, (i) female (but not male) 118GG mice consumed more ethanol than 118AA mice and (ii) naltrexone pretreatment was equally efficacious at attenuating ethanol intake in both 118AA and 118GG female mice while having no effect in males. Male and female 118GG and female 118AA mice developed a robust conditioned place preference (CPP) for ethanol. Female 118GG mice displayed less sensitivity to the sedative/ataxic effects of ethanol compared to female 118AA mice on both the rota-rod and the LORR assays while male mice did not differ in their responses on either assay. Our findings suggest that increased ethanol consumption in male 118GG mice may be due to increased ethanol reward, while increased drinking in female 118GG mice might be due to decreased sensitivity to the sedative/ataxic effects of ethanol. Collectively, these data might be used to help identify sex-specific pharmacotherapies to combat alcohol use disorders.

Altering ethanol pharmacokinetics to treat alcohol use disorder: Can you teach an old dog new tricks?

Disulfiram was the first pharmacotherapy approved to treat alcohol use disorder in the 1950s. Disulfiram alters ethanol pharmacokinetics and causes uncomfortable reactions (e.g. headache, tachycardia, nausea, flushing and hypotension) when alcohol is consumed. Subsequently, a better understanding of the neurobiological pathways involved in alcohol use disorder led to the development of other medications (e.g. naltrexone and acamprosate). These neurobiological-based medications act on alcohol use disorder-related phenotypes including craving, stress, and/or withdrawal. The original approach to treat alcohol use disorder, by altering ethanol pharmacokinetics has been much less investigated. Recent research on ethanol pharmacokinetics has shed light on the mechanisms of action underlying alcohol use disorder and how some medications that alter ethanol pharmacokinetics may be helpful in treating alcohol use disorder. This review summarizes and discusses the complex pharmacokinetics of ethanol, and proposes that altering ethanol pharmacokinetics via novel pharmacological approaches may be a viable approach to treat alcohol use disorder.

Ethanol Sensitization during Adolescence or Adulthood Induces Different Patterns of Ethanol Consumption without Affecting Ethanol Metabolism

In previous study, we demonstrated that ethanol preexposure may increase ethanol consumption in both adolescent and adult mice, in a two-bottle choice model. We now questioned if ethanol exposure during adolescence results in changes of consumption pattern using a three-bottle choice procedure, considering drinking-in-the-dark and alcohol deprivation effect as strategies for ethanol consumption escalation. We also analyzed aldehyde dehydrogenase (ALDH) activity as a measurement of ethanol metabolism. Adolescent and adult Swiss mice were treated with saline (SAL) or 2.0 g/kg ethanol (EtOH) during 15 days (groups: Adolescent-SAL, Adolescent-EtOH, Adult-SAL and Adult-EtOH). Five days after the last injection, mice were exposed to the three-bottle choice protocol using sucrose fading procedure (4% + sucrose vs. 8%–15% ethanol + sucrose vs. water + sucrose) for 2 h during the dark phase. Sucrose was faded out from 8% to 0%. The protocol was composed of a 6-week acquisition period, followed by four withdrawals and reexposures. Both adolescent and adult mice exhibited ethanol behavioral sensitization, although the magnitude of sensitization in adolescents was lower than in adults. Adolescent-EtOH displayed an escalation of 4% ethanol consumption during acquisition that was not observed in Adult-EtOH. Moreover, Adult-EtOH consumed less 4% ethanol throughout all the experiment and less 15% ethanol in the last reexposure period than Adolescent-EtOH. ALDH activity varied with age, in which older mice showed higher ALDH than younger ones. Ethanol pretreatment or the pattern of consumption did not have influence on ALDH activity. Our data suggest that ethanol pretreatment during adolescence but not adulthood may influence the pattern of ethanol consumption toward an escalation in ethanol consumption at low dose, without exerting an impact on ALDH activity.

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.

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.

Enhanced 5-HT(2A) receptors in brain stem and ALDH activity in brain stem and liver: 5-HT(2A) regulation on ALDH in primary hepatocytes cultures in vitro

Brain serotonin (5-HT) modulates the neural effects of ethanol. In the present study, we investigated the changes in 5-HT level, 5-HT(2A) receptor binding and aldehyde dehydrogenase (ALDH) activity in brain stem and liver of ethanol treated rats and 5-HT(2A) regulation on ALDH in hepatocyte cultures in vitro. The 5-HT content in the brain stem and liver significantly decreased with an increased 5-HIAA/5-HT ratio in the ethanol treated rats compared to control. Scatchard analysis of [(3)H] (+/-)2,3-dimethoxyphenyl-1-[2-(-4-piperidine)-methanol] [(3)H] MDL 100907 against ketanserin in brain stem of ethanol treated rats showed a significant increase in B (max) without any change in K (d) compared to control. The competition curve for [(3)H] MDL 100907 against ketanserin fitted one-site model in both control and ethanol treated rats with unity as Hill slope value. A significant increase in V (max) of ALDH activity in liver and a significant decrease in K (m) in liver and brain stem of ethanol treated rats compared to control was observed. In 24 h culture studies, an increase in enzyme activity was observed in cells in medium with 10% ethanol. The elevated ALDH activity in ethanol treated cells was reversed to control level in presence of 10(-5) and 10(-7) M 5-HT. Ketanserin, an antagonist of 5-HT(2A), reversed the effect of 5HT on 10% ethanol induced ALDH activity in hepatocytes. Our results showed that there was a decreased 5-HT content with an enhanced 5-HT(2A) receptor and aldehyde dehydrogenase activity in the brain stem of alcohol treated rats and in vitro hepatocyte cultures. The enhanced ALDH activity in ethanol supplemented hepatocytes was reversed to control level in presence of 10(-5) and 10(-7) M 5-HT.

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.

Voluntary alcohol drinking and acetaldehyde metabolism in F2 hybrid crosses of AA and ANA rat lines

Alcohol-preferring AA and alcohol-avoiding ANA rat lines differ in their acetaldehyde metabolism and this has been suggested to be one reason for their different ethanol drinking behavior. To study whether acetaldehyde accumulation is indeed associated with alcohol drinking behavior and to evaluate which enzymatic differences previously observed in these rat lines are of importance in this regard, we produced an F2 generation from them. ADH and ALDH activities, and ALDH patterns were then assessed from these hybrids and correlated with their voluntary ethanol drinking and blood acetaldehyde concentrations measured during ethanol metabolism. A significant negative correlation between voluntary ethanol intake and blood acetaldehyde concentration was observed in F2 females drinking less than 17% of the total fluid as ethanol. In F2 males, hepatic microsomal high Km ALDH activities correlated negatively with blood acetaldehyde concentrations, indicating that low activity of this isoenzyme in ANA rats could be at least in part responsible for the accumulation of acetaldehyde in their blood. Finally, F2 rats that possessed the cytosolic ALDH isoenzyme pattern most frequently found in the AA rat line drank significantly more ethanol than the animals with typical ANA pattern, suggesting that this polymorphism might also be relevant in the regulation of voluntary ethanol drinking although it is probably not associated with acetaldehyde metabolism.

The regulation of alcohol consumption in rats: the role of alcohol-metabolizing enzymes-catalase and aldehyde dehydrogenase

Aldehyde dehydrogenase (ALDH) and catalase enzymatic activities in brain were assayed and compared to measures of alcohol consumption in two groups of animals screened and maintained on free-choice alcohol access under different conditions. In the first group of Long-Evans rats screened and maintained in home cages, mean alcohol intake was 3.49 g/kg/day with a range of 1.69-5.33 g/kg/day. When alcohol intake (g/kg), total ALDH, low K(m) ALDH, and catalase activities were entered in a multiple regression, a significant correlation of r = 0.51 (p < 0.05) was obtained. In the second group of rats consisting of Long-Evans, P, and NP rats screened using a drinkometer procedure, a multiple correlation between ALDH and catalase enzyme activities and alcohol intake of r = 0.42 (p < 0.05) was obtained. There was a strong relationship between the frequency of alcohol drinking bouts and the activities of catalase and ALDH (r = 0.68, p < 0.0001). The P rats had significantly higher catalase activities than either the NP or Long-Evans rats. The results of the present study confirmed earlier reports on the role of alcohol-metabolizing enzymes in the regulation of alcohol intake. The results also highlighted the fact that the activity of these alcohol-metabolizing enzymes may play a mediating role in patterns of alcohol intake displayed by animals selected for high and low alcohol drinking and also unselected animals.

Acetaldehyde metabolism by brain mitochondria from UChA and UChB rats

The acetaldehyde (AcH) oxidizing capacity of total brain homogenates from the genetically high-ethanol consumer (UChB) appeared to be greater than that of the low-ethanol consumer (UChA) rats. To gain further information about this strain difference, the activity of aldehyde dehydrogenase (AIDH) in different subcellular fractions of whole brain homogenates from naive UChA and UChB rat strains of both sexes has been studied by measuring the rate of AcH disappearance and by following the reduction of NAD to NADH. The results demonstrated that the higher capacity of brain homogenates from UChB rats to oxidize AcH when compared to UChA ones was because the UChB mitochondrial low Km AIDH exhibits a much greater affinity for NAD than that of the UChA rats, as evidenced by four-to fivefold differences in the Km values for NAD. But the dehydrogenases from both strains exhibited a similar maximum rate at saturating NAD concentrations. Because intact brain mitochondria isolated from UChB rats oxidized AcH at a higher rate than did mitochondria from UChA rats only in state 4, but not in state 3, this strain difference in AIDH activity might be restricted in vivo to NAD disposition.

Mitochondrial aldehyde dehydrogenase (ALDH2) polymorphism in AA and ANA rats: lack of genotype and phenotype line differences

Polymorphism of the gene coding for mitochondrial ALDH2 in humans is known to be associated with differences in alcohol drinking behavior. Recently, two different alleles of the ALDH2 gene, ALDH2R and ALDH2Q, have been found in rats also and a possible relationship between the frequencies of the two alleles and drinking behavior has been proposed. In this study, we examined whether this polymorphism of ALDH2 was the underlying cause for the previously reported acetaldehyde accumulation in the alcohol-avoiding ANA rat line and, thus, could be one of the factors explaining the differences in alcohol drinking behavior between the ANA and the alcohol-preferring AA rat lines. The experimental animals were genotyped and their mitochondrial ALDH activities and blood acetaldehyde concentrations after ethanol injection were measured. The two lines did not differ in their frequencies of ALDH2R and ALDH2Q alleles. Thus, the polymorphism in the ALDH2 gene does not explain the acetaldehyde accumulation in ANA rats and it does not seem to be associated with differences in the alcohol drinking behavior in these rat lines.

Age dependent development of ethanol drinking in rats after inhibition of aldehyde dehydrogenase

The purpose of this experiment was to determine the temporal characteristics associated with the age-related development of volitional consumption of ethanol induced by the pharmacological inhibition of aldehyde dehydrogenase (AlDH). To induce preference for ethanol, the AlDH inhibitor, cyanamide, was administered to male Sprague-Dawley rats which were 30 days of age. Cyanamide (n = 8) was injected subcutaneously twice daily in a dose of 10 mg/kg over a period of 3 days while the control group (n = 6) received the saline vehicle solution according to the same schedule. Then at 50, 70, 90, and 110 days of age, both groups of rats were given a standard 11-day test of preference for water versus ethanol offered in concentrations ranging from 3% through 30%. The results showed that at 70 days of age the preference for ethanol increased above the level of the 50-day test in terms of absolute g/kg intakes and proportion of ethanol to water consumed over the lower range of 3% through 15% concentrations. During the tests at 90 and 110 days of age, the cyanamide-treated rats further increased their preference for ethanol significantly over the levels at the 70-day test in terms of both g/kg and proportional intakes. The pattern of drinking of ethanol offered in the higher concentrations of 25% and 30% was unrelated to the age of the rats and the overall intakes were significantly higher than those of the lower concentrations. These findings demonstrate that the enzymatic inhibition of AlDH systematically acts in a delayed fashion to shift the pattern of preference for ethanol which is contingent on the maturation of the animal. In this instance, the volitional intake of ethanol in the cyanamide-treated rats reached its maximal level by 90-110 days of age. It is proposed that an endocrine mechanism involved in gonadal maturation may function in the intense shift in alcohol drinking.

Differential ethanol intake in Tryon maze-bright and Tryon maze-dull rats: implications for the validity of the animal model of selectively bred rats for high ethanol consumption

The search for a genetically based "animal model of alcoholism" has led to the creation of extensive research programs using various combinations of initial ethanol preference screening techniques and breeding methods to yield rodents with primary genetic differences that contribute to high or low ethanol preference. The present experiment examined the ethanol intake of the Tryon rat strain, which were bred for high and low maze learning scores. It was observed that the Tryon Maze Bright rats displayed an unprecedented affinity for ethanol with stable intakes between 12.7 and 13.7 g/kg per day and preference ratios exceeding 0.75 for ethanol concentrations ranging between 15 and 29%. The pattern of ethanol intake of the Tryon Maze Dull rats resembled the ethanol intake pattern of other, non-selectively bred strains of rats, approximately 2-3 g/kg of absolute ethanol at preference ratios between 0.11 and 0.28. The affinity for ethanol observed for the Tryon Maze Bright rats seems to exceed the reported consumption patterns of rat strains specifically bred for high ethanol consumption although the Tryon rats were selectively bred for variables that were seemingly unrelated to ethanol intake.

Opposite effects of naltrexone on ETOH intake by Syracuse high and low avoidance rats

Rats which were selectively bred for good (Syracuse High Avoidance: SHA) and poor (Syracuse Low Avoidance: SLA) shuttle-box avoidance learning were used to assess the effects of naltrexone on ethanol ingestion. Male rats from both strains were offered a free choice of water and ethanol (10%, v/v) for two 8-day periods between which was inserted a 4-day period of forced ethanol consumption. The net ethanol consumption and ethanol preference ratio were significantly greater in control SHA rats than in control SLA rats in the first choice period, but they did not differ in the forced and the second choice periods. Chronic naltrexone administration from an implanted 30-mg pellet showed bidirectional effects, i.e., suppression of ethanol consumption in SLA animals and enhancement in SHA rats.

Histochemical study of aldehyde dehydrogenase in the rat CNS

A quantitative histochemical method was developed to determine aldehyde dehydrogenase (EC 1.2.1.3; ALDH) activity in the CNS. The distribution of ALDH activity in all rat brain and spinal cord regions is described. Among the CNS neuron structures, high enzyme activity was found in receptor and effector neurons, whereas low activity was noted in perikarya of the majority of intermediate neurons, including all aminergic neurons. A positive correlation was demonstrated between the distribution of ALDH activity among rat CNS microregions (our own data) and the density of dopaminergic terminals, dopamine content, and monoamine oxidase activity (literature data) among the same microregions. They may reflect a spatial linkage between ALDH and the predicted sites of natural aldehyde production. Lower enzyme activity was found in phylogenetically younger brain structures. It may explain the differential resistance of CNS structures to ethanol (acetaldehyde). Among the barrier CNS structures, moderate ALDH activity was found in capillaries and surrounding astrocytes and high activity was noted in ependimocytes covering the brain cavities and those of the vascular plexus. This provides realization of the function of ALDH as a brain metabolic barrier for aldehydes.

A histochemical study of the distribution of aldehyde dehydrogenase activity in brain structures of rats with genetically different alcohol-related behaviour

Brain samples from rats genetically selected for high or low voluntary alcohol intake (AA and ANA strains) or for differences in alcohol-induced motor incoordination (AT and ANT strains) were analyzed by histochemistry for aldehyde dehydrogenase (EC 1.2.1.3; ALDH) activity in various CNS structures. All strains exhibited the highest ALDH activities in neurons of the mesencephalic tract of trigeminal nerve nucleus and in spinal cord motoneurons, while the lowest activities were observed in the somatosensory cortex. Although the general distribution pattern of ALDH activity was similar in the genetically selected strains, some potentially important differences were observed. AA rats with high voluntary alcohol consumption had lower ALDH activity (with acetaldehyde as substrate) in the neuropil of the olfactory tubercle but higher activity (with benzaldehyde as substrate) in the spinal cord motoneurons, Purkinje cells and capillary endothelium of the cerebellum as compared to the corresponding structures from the alcohol avoiding ANA rats. Alcohol-resistant AT rats had higher ALDH activity, with benzaldehyde, in most CNS structures than did the alcohol-sensitive ANT's, significantly so in the lamina II of the somatosensory cortex and the neurons of the lateral hypothalamic area. This relationship was also found with acetaldehyde as substrate in the neurons of the hypothalamic arcuate nuclei and in cerebellar capillaries, but the ANT's had the higher activity in the neurons of the cerebral cortex V lamina. We suggest that some of the differences observed may relate to the differences between the rat strains with respect to voluntary alcohol intake and alcohol-induced motor incoordination.

Cyanamide given ICV or systemically to the rat alters subsequent alcohol drinking

Cyanamide or disulfiram serves to suppress volitional intake of alcohol presumably because of the toxic build-up of acetaldehyde dehydrogenase (AIDH). However, the presence of acetaldehyde systemically favors the in vivo synthesis of addictive-like metabolites in the brain which in turn enhance alcohol drinking. The purpose of this investigation, therefore, was to determine whether cyanamide administered to the rat, which did not have access to alcohol during treatment, would nevertheless affect the subsequent preference for alcohol. In the first experiment, cannulae were implanted bilaterally above the cerebral ventricle of 33 adult male Sprague-Dawley rats so that an artificial CSF or a solution of cyanamide could be infused intracerebroventricularly (ICV). Following post-operative recovery, each rat was tested for its alcohol preference by offering it water and a solution of ethyl alcohol which was increased over 8 days from 3-20%. After a single test concentration of alcohol (range of 5-9%) was selected for each individual animal presented with water over a 5-day interval, cyanamide was infused in a volume of 2.5 microliters per side three times daily for 4 days in one of the following total doses: 0.03, 0.1, 0.3, 0.5 or 1.0 mg. A second five-day preference test was run, and 6 weeks following cyanamide infusions a final 3-20% alcohol preference screen was run over 8 days. The results showed that a long-term, dose-dependent increase or decrease in alcohol intake occurred in those rats reactive to the drug.(ABSTRACT TRUNCATED AT 250 WORDS)

A correlation between voluntary ethanol consumption and brain catalase activity in the rat

The relationship between voluntary ethanol consumption and brain catalase activity was investigated in male Long Evans rats. In the first study, rats which were voluntarily consuming alcohol or water for 25 days were sacrificed by decapitation immediately (group A) or 15 days (group B) following withdrawal of alcohol and their brains analysed for catalase activity. Mean brain catalase activity did not differ among the two groups of rats exposed to ethanol and the ones exposed to water only. Furthermore, there were significant positive correlations between individual voluntary ethanol intake and catalase activity in both groups, (group A:r = .69, p less than or equal to 0.05; group B:r = .54, p less than or equal to 0.05). In the second study, rats were forced to drink high levels of ethanol presented as the only source of fluid for 25 days. Rats were sacrificed and brain, liver, muscle and heart tissue were extracted and analysed for catalase activity. There were no differences in mean brain catalase activity between water and forced ethanol drinking rats indicating that the enzyme was not inducible by high volume ethanol consumption. The results suggest that inherent differences in brain catalase activity may be one of the factors in determining an animal's propensity to voluntarily consume ethanol.

A two dimensional model of alcohol consumption: possible interaction of brain catalase and aldehyde dehydrogenase

The possible existence of a biological marker system mediating voluntary consumption of ethanol in rats has been examined in a series of studies. The working hypothesis underlying this research was that acetaldehyde, the primary metabolite of ethanol, mediates the positive reinforcing properties of ethanol and thus underlies the voluntary consumption of ethanol in both animals and humans. We further hypothesized that brain catalase and aldehyde dehydrogenase, the enzymes controlling the production and elimination of acetaldehyde in the brain, may represent a biological marker system underlying the affinity of the animals to consume ethanol. Data demonstrating that the activity levels of these enzymes are positively correlated with alcohol ingestion seems to suggest that it is likely that the enzyme activity can serve as a predictor of the propensity to drink alcohol. A predictive model is proposed which describes the modulation of voluntary ethanol intake through the activity of these enzymes and their role in determining rates of formation and degradation of acetaldehyde in the brain.

Brain ALDH as a possible modulator of voluntary ethanol intake

The relationship between voluntary ethanol intake and brain aldehyde dehydrogenase (ALDH) activity was investigated in the laboratory rat. Voluntary ethanol intake was compared to subcellular forms of brain ALDH. Mitochondrial, microsomal and cytosolic fractions were prepared and recovered ALDH activity of each form was compared to voluntary ethanol intake in Long Evans rats. Strong correlations were found between both mitochondrial and microsomal ALDH fractions and ethanol intake. No activity was observed in cytosolic fraction as measured with aromatic or aliphatic aldehydes. In addition, microsomal activity was detected with aromatic aldehydes only, whereas the mitochondrial form would oxidize both aromatic and aliphatic aldehydes.

Higher correlation of ethanol consumption with brain than liver aldehyde dehydrogenase in three strains of rats

Voluntary ethanol consumption and high Km (mM range) brain and liver aldehyde dehydrogenase (ALDH) activity were measured in male rats of the Long-Evans, Wistar and Sprague-Dawley strains. The total amounts of ethanol consumed by the three strains did not differ significantly, nor did the levels of cerebral ALDH activity. Levels of brain ALDH did not differ as a function of ethanol exposure and across strains. Levels of ethanol consumption correlated better with levels of brain than liver aldehyde-oxidizing capacity, which were tested separately for each strain and also combining all the animals. Inherent variation in brain ALDH may be a biochemical counterpart of observed differences in voluntary ethanol intake within strains.

Suppression of alcohol drinking with brain aldehyde dehydrogenase inhibition

Calcium cyanamide, an aldehyde dehydrogenase (ALDH) inhibitor used in the treatment of alcoholism, strongly suppressed voluntary ethanol drinking by rats. Such inhibitors have generally been believed to act primarily by limiting drinking through acetaldehyde accumulation after ethanol consumption. Administration of a low dose of 4-methylpyrazole (4-MP) that abolished acetaldehyde accumulation did not, however, remove the suppression produced by cyanamide. 4-MP alone did not affect the unsuppressed alcohol intake by Long Evans rats or the drinking by rats of the ANA strain developed for low levels of ethanol consumption. When given from the start with cyanamide, 4-MP did affect the development of the suppression, but probably by its effect in lessening the degree of brain ALDH inhibition: a high correlation (r = +0.825, p less than 0.001) was found between brain ALDH activity and ethanol consumption. The results suggest that cyanamide suppresses alcohol drinking also in the absence of acetaldehyde accumulation probably by some action related to its direct inhibition of brain ALDH.

Brain aldehyde dehydrogenase activity in rat strains with high and low ethanol preferences

The activity of aldehyde dehydrogenase in subcellular fractions of whole brain homogenates from the AA and ANA rat strains developed respectively for high and low ethanol preferences has been studied. No significant strain or sex differences between naive AA and ANA rats were found. In ethanol-experienced rats some strain and sex differences were found, the most consistent being higher enzyme activity in AA females than in males both with aliphatic and aromatic aldehyde substrates. However, contrary to previous findings no relation between brain aldehyde dehydrogenase activity and drinking behavior was found in the AA and ANA rat strains.

The aversive effect of acetaldehyde on alcohol drinking behavior in the rat

There are a number of indications suggesting that acetaldehyde (AcH) is one factor affecting the alcohol drinking behavior in laboratory animals. In the present study, the voluntary alcohol consumption in a free-choice situation was recorded in 17 females Sprague-Dawley rats fed with two different diets. The first diet (commercial Astra-Ewos, Sweden) caused significantly (p less than 0.001) higher blood AcH concentrations after oral alcohol administration and lower alcohol preferences (alcohol intake as percentage of total fluid intake) than the other diet (prepared at the Alko laboratories). With the Alko diet, the individual preference values correlated negatively with the blood AcH concentrations (p less than 0.01) and positively with the liver aldehyde dehydrogenase activities (p less than 0.05). Hepatic alcohol oxidation rate was found to correlate positively with the AcH concentrations from perfused livers (p less than 0.05) and negatively with the alcohol preferences (p less than 0.05), Alko diet). The results are discussed considering a possible biphasic relation between the AcH metabolism and alcohol drinking behavior.

Aversive factors in alcohol drinking in humans and animals

In human subjects there is a wide range of response to the taste of alcohol in varying concentrations. What some people find totally aversive may be accepted with relish by others. Both individual and racial responses to ingested or injected alcohol can be aversive, since markedly dysphoric experiences can occur. Human studies also suggest that the euphorigenic properties of alcohol are very variable between subjects and that this correlates with characteristics of biogenic amines present in the body. Except for relatively low concentrations, the laboratory rat, used commonly in alcohol drinking experiments, avoids the selection of alcohol. Paralleling human studies are animal investigations that manipulate the levels of chemical substances in the brain and demonstrate effects of this upon alcohol self-selection. When certain tetrahydroisoquinolines or beta-carboline substances are infused into the brain of the rat or monkey, the aversive nature of orally ingested alcohol, particularly in very high concentrations, is overcome. In contrast, however, when a high dose of a tetrahydropapaveroline is infused, the animal's volitional intake of alcohol is inhibited and even weak concentrations of alcohol are rejected. The possible mechanisms for this phenomenon and the recent investigations of agents acting on CNS opiate receptors in reinstating alcohol aversion are considered.

Ethanol consumption and hepatic enzyme activity

Enzyme activity and ethanol consumption were measured in an F2 generation derived from the C57BL and C3H inbred mouse strains. A significant correlation (0.25) was found between alcohol dehydrogenase activity and ethanol acceptance in the F2 generation. Mass selection from a genetically heterogenous mouse stock, HS/Ibg, has yielded high ethanol acceptance (HEA) and low ethanol acceptance (LEA) lines of mice. The mean ethanol acceptance scores for the fifth generation of these lines are 1.008 and 0.606, respectively. The total liver alcohol dehydrogenase activity was found to be 24% higher in the HEA line than in the LEA line after five generations of selective breeding. No association between cytosolic aldehyde dehydrogenase activity and ethanol acceptance was found in either the F2 generation or the fifth generation of the selectively bred lines.