Ethanol and amino acids in the central nervous system: assessment of the pharmacological actions of acamprosate

Preclinical and clinical pharmacology of alcohol dependence

In recent years, advances in neuroscience led to the development of new medications to treat alcohol dependence and especially to prevent alcohol relapse after detoxification. Whereas the earliest medications against alcohol dependence were fortuitously discovered, recently developed drugs are increasingly based on alcohol's neurobiological mechanisms of action. This review discusses the most recent developments in alcohol pharmacotherapy and emphasizes the neurobiological basis of anti-alcohol medications. There are currently three approved drugs for the treatment of alcohol dependence with quite different mechanisms of action. Disulfiram is an inhibitor of the enzyme aldehyde dehydrogenase and acts as an alcohol-deterrent drug. Naltrexone, an opiate antagonist, reduces alcohol craving and relapse in heavy drinking, probably via a modulation of the mesolimbic dopamine activity. Finally, acamprosate helps maintaining alcohol abstinence, probably through a normalization of the chronic alcohol-induced hyperglutamatergic state. In addition to these approved medications, many other drugs have been suggested for preventing alcohol consumption on the basis of preclinical studies. Some of these drugs remain promising, whereas others have produced disappointing results in preliminary clinical studies. These new drugs in the field of alcohol pharmacotherapy are also discussed, together with their mechanisms of action.

Acamprosate: a new tool in the battle against alcohol dependence

Acamprosate, a medication that has been used in Europe for years, is the newest drug to be approved by the US Federal Drug Administration for the treatment of alcohol dependence. It has been shown to assist in the maintenance of abstinence in recently detoxified alcohol-dependent individuals. The following review delineates the proposed mechanism of action and pharmacokinetics of the drug. Findings of clinical trials are outlined and topics such as cost effectiveness, comparison with other medications used for the treatment of alcohol dependences as well as combination pharmacotherapy are discussed. In combination with psychosocial treatment, acamprosate is a promising tool for the maintenance of abstinence in alcohol-dependent patients after alcohol withdrawal. This review also illustrates the continued need to search for more effective treatments, as the overall effectiveness of our currently available pharmacotherapies remains limited in the long-term maintenance of recovery from alcohol dependence.

Drugs, their targets and the nature and number of drug targets

What is a drug target? And how many such targets are there? Here, we consider the nature of drug targets, and by classifying known drug substances on the basis of the discussed principles we provide an estimation of the total number of current drug targets.

Alcohol, Neurotransmitter Systems, and Behavior

Alcohol affects several neurotransmitter systems within the brain. In this article, the author describes its effects on 5 major ones: glutamate, gamma-amino-butyric acid (GABA), dopamine, serotonin, and opioid systems. The author also notes the interactions and interdependencies of these transmitters, and provides details on both immediate effects and long-term adaptations. Last, the author explains several psychopharmacological treatments for alcoholism and the effects of these treatments on transmitters, and draws conclusions.

Nicotine-induced changes of glutamate and arginine in naive and chronically alcoholized rats: An in vivo microdialysis study

The effects of nicotine, when administered either acutely or chronically, at doses of 0.15, 0.3 or 0.6 mg/kg, on the release of glutamate and arginine in the rat nucleus accumbens have been studied in microdialysis experiments. Glutamate release significantly increased after acute nicotine injection, 0.3 mg/kg, which was accentuated if there was a priming regime of saline for the previous 27 days. This is possibly related to the rewarding effects of nicotine. Five hours after cessation of chronic oral nicotine administration, there were significant increases in glutamate content, which was possibly reflective of a withdrawal process. Significant decreases in nucleus accumbens arginine release were evident, between 1 and 2 h, after chronic nicotine administration. When nicotine was co-administered to rats during chronic ethanol intoxication, at either 0.15 mg/kg or 0.3 mg/kg doses, glutamate release did not increase during the first 12 h of withdrawal. However, a decrease in arginine microdialysate content was still observed with all nicotine doses. The nicotine-induced changes in glutamate and arginine release in nucleus accumbens highlights the complex neuropharmacological interactions evoked by this compound and also identified its possible modulating effect on glutamate release during the initial stages of chronic ethanol withdrawal.

Behavioral effects of aminoadamantane class NMDA receptor antagonists on schedule-induced alcohol and self-administration of water in mice

RATIONALE

Aminoadamantanes represent a class of NMDA glutamate receptor antagonists that reduce alcohol consumption and may prevent alcohol-induced neuronal adaptations and side effects.

OBJECTIVE

Behavioral specificity of memantine and amantadine on alcohol drinking in a schedule-induced polydipsia (SIP) task was investigated in mice.

METHODS

Male C57BL/6J mice were food-deprived and divided into four groups: 5% alcohol SIP, water SIP, 1 h limited access regulatory water drinking, and a control group to determine if either drug altered ethanol drinking. Behavioral specificity of memantine (5, 10, and 25 mg/kg, ip) and amantadine (20, 40, and 60 mg/kg, ip) was determined by comparing alterations in alcohol or water consumption in SIP and regulatory water drinking. Drug effects on SIP drinking-specific measures (grams per kilogram consumption) were also compared to nondrinking measures (locomotion, head-entries for food, and lick efficiency).

RESULTS

Compared to saline, memantine reduced alcohol SIP drinking (10 and 25 mg/kg). Memantine increased locomotion during alcohol SIP (25 mg/kg) and during water SIP (5 and 25 mg/kg). In contrast, amantadine reduced both alcohol SIP (40 mg/kg) and water SIP (40 and 60 mg/kg). Both drugs reduced regulatory water consumption over the entire dose range tested. Blood alcohol concentrations indicated consumption of physiologically meaningful amounts of alcohol during SIP, and that changes in alcohol metabolism did not account for drug-induced reductions in alcohol drinking.

CONCLUSIONS

In addition to reducing alcohol drinking, both drugs had other behavioral effects that included reductions in regulatory drinking. These results suggest that the therapeutic utility of these drugs for ameliorating human alcohol addiction remains questionable.

GLUTAMIC ACID IN WITHDRAWAL AND WEANING IN PATIENTS CLASSIFIED ACCORDING TO CLONINGER'S AND LESCH'S TYPOLOGIES

AIMS

Though glutamic acid is well known as a working excitatory in the CNS, its impact on the modulation of alcohol withdrawal symptoms and withdrawal fits are not yet clear. The study has been undertaken to examine the levels of glutamic acid in chronic alcohol-dependent patients at different stages of alcohol withdrawal and weaning and to examine any existence of any differences according to Cloninger's and Lesch's typologies.

PATIENTS AND METHODS

One hundred and fifty-nine alcohol-dependent patients were assessed according to Cloninger's and Lesch's typologies and related to abstinence duration, age, and gender. Blood samples were taken for mean corpuscular volume (MCV), gamma-glutamyltransferase (GGT) and glutamic acid, in order to find primarily any differences in glutamic acid according to the typologies, age, abstinence duration, and liver damage.

RESULTS

There was no significant association between Cloninger's and Lesch's typologies. Cloninger's types 1 and 2 had an equal distribution of GGT and duration of abstinence, while Lesch's type I had more patients with high GGT, and more patients who were sober for a maximum of 2 days. Unlike in Lesch's types, glutamic acid levels did not differ according to Cloninger's types, as significantly higher glutamic acid values were found in Lesch's types I and IV. Glutamic acid values did not differ significantly in different age groups.

CONCLUSIONS

Our study findings of varying glutamic acid levels seen in Lesch's typology, higher in types I and IV than in types II and III, are of significant clinical value and can be interpreted differently, as in type I high levels of glutamic acid is seen as a kindling phenomenon, while in type IV elevated levels might be related to either compulsivity of frequent repetition of drinking or withdrawal.

Attenuation of cocaine-induced reinstatement of cocaine conditioned place preference by acamprosate

Acamprosate (calcium acetylhomotaurinate) is a glutamatergic neuromodulator efficacious at reducing relapse in alcoholic patients. The effect of acamprosate on relapse to other drugs of abuse has received little attention, however, and given increasing evidence that glutamatergic transmission mediates relapse to cocaine-seeking behavior, the purpose of this study was to assess the effects of acamprosate on the reinstatement of a conditioned place preference for cocaine. Mice were conditioned daily with cocaine (15 mg/kg), tested for the establishment of cocaine conditioned place preference, and then retested once weekly to monitor the extinction of the place preference. Following extinction of cocaine conditioned place preference, animals were treated daily with saline or acamprosate (30 or 100 mg/kg) for 3 days, followed by a single injection of cocaine (15 mg/kg) to reinstate conditioned place preference. In mice treated with saline or the low (30 mg/kg) dose of acamprosate, cocaine induced a significant reinstatement of the previously extinguished conditioned place preference; however, this reinstatement was not observed in mice treated with the high (100 mg/kg) dose of acamprosate. These results indicate that acamprosate can attenuate relapse-like behavior in mice and suggest that this compound may be potentially useful in the treatment for cocaine addiction.

Acamprosate for the treatment of alcohol dependence

BACKGROUND

Both inpatient and outpatient treatment centers that focus solely on psychosocial therapies for the treatment of alcohol dependence have high relapse rates. Thus, extensive research has focused on the development of pharmacologic moieties to attenuate the craving for alcohol after acute alcohol detoxification. Three drug therapies are currently approved by the US Food and Drug Administration (FDA) for this purpose: disulfiram, naltrexone, and acamprosate. The latter was approved by the FDA in 2004.

OBJECTIVE

This article describes the pharmacologic properties and clinical usefulness of acamprosate for the treatment of alcohol dependence.

METHODS

Relevant information was identified through searches of MEDLINE (1966 to March 2005), International Pharmaceutical Abstracts (1970-2005), Current Contents (1996-2005), and Cumulative Index to Nursing and Allied Health Literature (1982-Week 2, 2004) using the key words acamprosate, alcohol dependence, and alcoholism (MeSH).

RESULTS

Acamprosate limited to randomized, controlled clinical trials yielded 33 hits in MEDLINE. Twenty-two articles were reviewed for efficacy end points, and 10 were reviewed for pharmacology and pharmacokinetics data. Acamprosate plus pharmacokinetics and pharmacodynamics yielded 19 hits, some of which were duplicates from the previously described search. Acamprosate plus meta-analysis (MeSH) yielded 5 hits, naltrexone plus meta-analysis (MeSH) yielded 9 hits, and disulfiram plus meta-analysis yielded 3 hits. The most recent review articles and their reference lists were assessed to ensure completeness of literature searches. Based on these searches, acamprosate is known to be an analogue of taurine and gamma-aminobutyric acid (GABA), 2 central nervous system neuromodulators. Acamprosate is thought to share some of the cellular actions of taurine affecting GABA and glutaminergic receptors in the nucleus accumbens, a brain region that may be responsible for the reinforcing effects received after alcohol consumption. Acamprosate is thought to also suppress excitation-induced calcium entry that results from chronic alcohol exposure, thereby altering the conformation of the N-methyl-d-aspartate receptors. The percentage of patients taking acamprosate who were completely abstinent throughout the different durations of the studies varied from approximately 18% to 61%, compared with 4% to 45% with placebo. Diarrhea was the most common adverse effect accompanying acamprosate therapy, and this was generally described as dose related and transient.

CONCLUSIONS

Acamprosate is associated with modest treatment effects. Its efficacy is similar to naltrexone, and the combination of acamprosate and naltrexone appears to be more efficacious than acamprosate alone, when combined with psychosocial interventions.

Acamprosate in the treatment of alcoholism: mechanisms and perspectives

Acamprosate, calcium acetyl homotaurinate, was first developed and tested in the early 1980s in France and has been available in the USA since 2004. Its major mechanism of action is the reduction of cerebral hyperexcitability by interacting with glutamate receptors. More than 20 randomized, placebo-controlled trials have been conducted. With very few exceptions, these studies have demonstrated a significant benefit of acamprosate over placebo. Side effects of acamprosate, such as diarrhoea, are benign and transient. Studies in which acamprosate was given in combination with disulfiram or naltrexone also showed promising results. Further studies are underway to identify potential acamprosate responders on a neurobiological basis. If successful, this would allow an individually targeted prescription of acamprosate that would then further improve its efficacy and cost–effectiveness.

Microdialysis as a tool in local pharmacodynamics

In many cases the clinical outcome of therapy needs to be determined by the drug concentration in the tissue compartment in which the pharmacological effect occurs rather than in the plasma. Microdialysis is an in vivo technique that allows direct measurement of unbound tissue concentrations and permits monitoring of the biochemical and physiological effects of drugs throughout the body. Microdialysis was first used in pharmacodynamic research to study neurotransmission, and this remains its most common application in the field. In this review, we give an overview of the principles, techniques, and applications of microdialysis in pharmacodynamic studies of local physiological events, including measurement of endogenous substances such as acetylcholine, catecholamines, serotonin, amino acids, peptides, glucose, lactate, glycerol, and hormones. Microdialysis coupled with systemic drug administration also permits the more intensive examination of the pharmacotherapeutic effect of drugs on extracellular levels of endogenous substances in peripheral compartments and blood. Selected examples of the physiological effects and mechanisms of action of drugs are also discussed, as are the advantages and limitations of this method. It is concluded that microdialysis is a reliable technique for the measurement of local events, which makes it an attractive tool for local pharmacodynamic research.

Involvement of the AMPA receptor GluR-C subunit in alcohol-seeking behavior and relapse

Craving and relapse are core symptoms of drug addiction and alcoholism. It is suggested that, after chronic drug consumption, long-lasting neuroplastic changes within the glutamatergic system are important determinants of addictive behavior. Here, we show that the AMPA type glutamate receptor plays a crucial role in alcohol craving and relapse. We observed, in two animal models of alcohol craving and relapse, that the AMPA antagonist GYKI 52466 [1-(4-aminophenyl)-4-methyl-7, 8-methylenedioxy-5H-2, 3-benzodiazepine] dose-dependently reduced cue-induced reinstatement of alcohol-seeking behavior and the alcohol deprivation effect. The involvement of the AMPA receptor in these phenomena was further studied using mice deficient for the GluR-C AMPA subunit [GluR-C knock-out (KO)]. GluR-C KOs displayed a blunted, cue-induced reinstatement response and alcohol deprivation effect, when compared with wild-type controls; however, no differences between genotypes could be observed regarding ethanol self-administration under operant or home cage drinking conditions. These results imply a role for GluR-C in alcohol relapse, although this phenotype could also be attributable to a reduction in the total number of AMPA receptors in specific brain areas. In conclusion, AMPA receptors seem to be involved in the neuroplastic changes underlying alcohol seeking behavior and relapse. Thus, AMPA receptors represent a novel therapeutic target in preventing relapse.

Binge drinking in midlife and dementia risk

BACKGROUND

Studies examining the long-term effects of alcohol consumption on cognitive functioning have produced conflicting results. Our goal was to determine whether a long follow-up period combined with information about drinking patterns, in addition to total alcohol consumption, would provide new insights about the relationship of alcohol use with dementia risk.

METHODS

A population-based cohort of 554 Finnish twins, who had provided data on alcohol consumption in questionnaires in 1975 and 1981, was followed for 25 years. Subjects were age 65 years or older at the time of dementia assessment in 1999-2001. Dementia risk was analyzed with respect to varying patterns of alcohol use by log-linear modeling, adjusted for age, sex, and education.

RESULTS

By the end of follow-up, 103 participants had developed dementia. Binge drinking (ie, alcohol exceeding the amount of 5 bottles of beer or a bottle of wine on 1 occasion at least monthly), as reported in 1975, was associated with a relative risk of 3.2 (95% confidence interval=1.2-8.6) for dementia. Passing out at least twice as a result of excessive alcohol use during the previous year, as reported in 1981, was associated with a relative risk of 10.5 (2.4-46) for dementia in drinkers.

CONCLUSIONS

Binge drinking in midlife is associated with an increased risk of dementia.

Memantine inhibits ethanol-induced NMDA receptor up-regulation in rat hippocampal neurons

The present study examined the effect of memantine, an uncompetitive NMDA receptor antagonist, on ethanol-induced NMDA receptor up-regulation. Primary glutamatergic rat hippocampal neurons were exposed to ethanol and memantine for 5 days. The ethanol-sensitive NMDA receptor subunits NR1, NR2A and NR2B were quantified by Western immunoblot analysis. Exposure to ethanol (50 mM) caused an increase in the levels of NR1 (137 +/- 11% of untreated control, P = 0.009), NR2A (128 +/- 14%, P = 0.022) and NR2B (136 +/- 19%, P = 0.012). Coincubation with memantine (10 microM) completely blocked the ethanol-induced up-regulation of NR1 (102 +/- 4%), NR2A (95 +/- 7%) and NR2B (105 +/- 13%). No effect of memantine on NR subunit expression was observable, except for NR2A, where a decrease (79 +/- 6%, P = 0.034) was noted. Neither ethanol nor memantine alone or in combination were toxic in the concentrations tested. These results may provide a molecular explanation for beneficial effects of memantine on ethanol-induced glutamatergic hyperexcitability reflected in the ethanol withdrawal syndrome and on the development of ethanol dependence.

RECURRENT DETOXIFICATIONS ARE ASSOCIATED WITH CRAVING IN PATIENTS CLASSIFIED AS TYPE 1 ACCORDING TO LESCH'S TYPOLOGY

AIMS

Recurrent detoxifications have been suggested to be associated with elevated alcohol craving. The aim of this investigation was to study the influence of preceding detoxifications on craving in patients with alcoholism classified according to Lesch's typology.

METHODS

We examined 192 patients (154 men, 38 women) after admission for detoxification treatment. Craving was assessed using the Obsessive Compulsive Drinking Scale, and patients were classified into one of the four subgroups of Lesch's typology. The number of preceding detoxifications was assessed with a structured interview.

RESULTS

Lesch's typology type 4 patients showed significantly higher craving scores than type 1-3 patients (Mann-Whitney U-Test; P < 0.05). With respect to the influence of recurrent detoxifications, we found a significant correlation between the number of preceding detoxifications and the extent of craving for the whole population (Spearman's rho r = 0.241, P = 0.001, N = 192), particularly for patients of Lesch's type 1 (Spearman's rho r = 0.534, P = 0.001, N = 37). No significant association was found for patients of the other subgroups (Lesch's type 2-4).

CONCLUSION

The influence of recurrent detoxifications on craving is especially important in patients with Lesch's type 1. Our results underline the importance of the kindling effect particularly in this group of patients, possibly mediated by an increase of glutamatergic neurotransmission. Furthermore, our results emphasize the need to classify patients with alcohol-dependency in addiction research.

Neuroprotective and abstinence-promoting effects of acamprosate: elucidating the mechanism of action

Acamprosate is an abstinence-promoting drug widely used in the treatment of alcohol dependence but which has a mechanism of action that has remained obscure for many years. Recently, evidence has emerged that this drug may interact with excitatory glutamatergic neurotransmission in general and as an antagonist of the metabotropic glutamate receptor subtype 5 (mGluR5) in particular. These findings provide, for the first time, a satisfactory, unifying hypothesis that can bring together and explain the diverse neurochemical effects of acamprosate. Glutamic acid is involved in several aspects of alcohol dependence and withdrawal, many of which can be modified by acamprosate. For example, during chronic exposure to alcohol, the glutamatergic system becomes upregulated, leaving the brain exposed to excessive glutamatergic activity when alcohol is abruptly withdrawn. The surge in glutamic acid release that occurs following alcohol withdrawal can be attenuated by acamprosate. The elevated extracellular levels of glutamic acid observed in withdrawal, together with supersensitivity of NMDA receptors, may expose vulnerable neurons to excitotoxicity, possibly contributing to the neuronal loss sometimes observed in chronic alcohol dependence. In vitro studies suggest that the excitotoxicity produced by ethanol can effectively be blocked by acamprosate. Moreover, glutamatergic neurotransmission plays an important role in the acquisition of cue-elicited drinking behaviours, which again can be modulated by acamprosate. In conclusion, the glutamatergic hypothesis of the mechanism of action of acamprosate helps explain many of its effects in human alcohol dependence and points the way to potential new activities, such as neuroprotection, that merit exploration in the clinic.

Differential effects of ethanol ingestion on somatostatin content, somatostatin receptors and adenylyl cyclase activity in the frontoparietal cortex of virgin and parturient rats

Chronic ethanol ingestion decreases the number of somatostatin (SRIF) receptors in the rat frontoparietal cortex and female sex hormones modulate the effects of ethanol in the brain. Therefore, we investigated the differential effects of ethanol consumption on the SRIFergic system in the frontoparietal cortex of virgin and parturient rats given ethanol in their drinking water before and during gestation. In parturient rats, ethanol consumption decreased the density of SRIF receptors (25%, p<0.01 vs control parturient group) whereas the SRIF-like immunoreactivity (SRIF-LI) content was increased (140%, p<0.01). In virgin rats, ethanol ingestion decreased the density of SRIF receptors (42%, p<0.01) more than in alcoholic parturient rats. SRIF-LI levels were unaffected. The inhibitory effect of SRIF on basal and forskolin-stimulated adenylyl cyclase was significantly lower in alcoholic virgin rats as compared to alcoholic parturient rats. No differences in the levels of the G inhibitory (Gi) alpha1 and Gialpha2 proteins were observed among the experimental groups. These results suggest that gestation may confer partial resistance to the ethanol-induced effect on the SRIFergic system.

The effects of acamprosate and neramexane on cue-induced reinstatement of ethanol-seeking behavior in rat

This study examines, for the first time, the effects of acamprosate and the non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist neramexane on ethanol-seeking induced by alcohol-related environmental stimuli in an animal model of relapse. Wistar rats were trained to operantly self-administer ethanol (10% w/v) or water on a fixed-ratio 1 schedule in a 30-min daily session. Ethanol availability was signaled by an olfactory discriminative stimulus of orange extract (S+). In addition, each lever press was accompanied by a 5-s illumination of the operant chamber's house light (CS+). Water availability was signaled by anise odor (S-) and 5-s white noise stimulus (CS-). After completion of the conditioning phase, indicated by stable levels of responding, operant behaviors were extinguished. Prior to reinstatement tests, animals were divided into groups according to either treatment with acamprosate (100, 200 mg/kg given twice), neramexane (1.0, 2.0, 4.0 mg/kg), or vehicle. In vehicle-treated rats, re-exposure to the S+/CS+ in the absence of further ethanol availability elicited strong recovery of responding. No effect was observed following presentation of water-paired cues (S-/CS-). Acamprosate dose-dependently attenuated recovery of responding elicited by ethanol-paired cues (S+/CS+), whereas responding under S-/CS- was not modified by drug administration. Treatment with 1.0 and 2.0 mg/kg of neramexane did not significantly modify responding under both S+/CS+ and S-/CS- conditions. However, a slight reduction of cue-induced reinstatement of alcohol seeking was observed. At the dose of 4.0 mg/kg, neramexane elicited a marked inhibition of responding following presentation of both ethanol- and water-paired cues. In conclusion, acamprosate significantly and selectively reduced alcohol-seeking elicited by environmental stimuli predictive of alcohol availability. Treatment with neramexane that shares part of the pharmacological effects of acamprosate on NMDA receptors, however, resulted in a nonselective reduction of lever responding.

Effect of acamprosate on neonatal excitotoxic cortical lesions in in utero alcohol-exposed hamsters

Alcohol exposition during pregnancy has irreversible effects on the fetus brain. In hamsters, intrapallial injection of the glutamate receptor agonist ibotenic acid (100ng) on the day of birth (P0) induced neuronal migration disorders. In utero alcohol (7%) exposure from day 5 of gestation to P5, enhanced lesions size measured in pups' brain at P5. The administration for the same period of the taurine derivative acamprosate together with alcohol or in water to pregnant females reduced the rate of occurrence of nodular heterotopia, sub-pial ectopia and microgyria in non-alcohol-exposed pups. In addition acamprosate diminished lesion size in alcohol-exposed and non-exposed pups. A significant dose-related effect of acamprosate was observed. In addition, acamprosate rescued 27% of the pups injected with 10 microg ibotenic acid, a lethal dose in alcohol-exposed animals.

Differential increase in taurine levels by low-dose ethanol in the dorsal and ventral striatum revealed by microdialysis with on-line capillary electrophoresis

Ethanol increases taurine efflux in the nucleus accumbens or ventral striatum (VS), a dopaminergic terminal region involved in positive reinforcement. However, this has been found only at ethanol doses above 1 g/kg intraperitoneally, which is higher than what most rats will self-administer. We used a sensitive on-line assay of microdialysate content to test whether lower doses of ethanol selectively increase taurine efflux in VS as opposed to other dopaminergic regions not involved in reinforcement (e.g., dorsal striatum; DS). Adult male rats with microdialysis probes in VS or DS were injected with ethanol (0, 0.5, 1, and 2 g/kg intraperitoneally), and the amino acid content of the dialysate was measured every 11 sec using capillary electrophoresis and laser-induced fluorescence detection. In VS, 0.5 g/kg ethanol significantly increased taurine levels by 20% for 10 min. A similar increase was seen after 1 g/kg ethanol, which lasted for about 20 min after injection. A two-phased taurine efflux was observed with the 2.0 g/kg dose, where taurine was increased by 2-fold after 5 min but it remained elevated by 30% for at least 60 min. In contrast, DS exhibited much smaller dose-related increases in taurine. Glycine, glutamate, serine, and gamma-aminobutyric acid were not systematically affected by lower doses of ethanol; however, 2 g/kg slowly decreased these amino acids in both brain regions during the hour after injection. These data implicate a possible role of taurine in the mechanism of action of ethanol in the VS. The high sensitivity and time resolution afforded by capillary electrophoresis and laser-induced fluorescence detection will be useful for detecting subtle changes of neuronally active amino acids levels due to low doses of ethanol.

Influence of ethanol on the threshold for electroshock-induced seizures and electrically-evoked hippocampal afterdischarges

The anticonvulsant activity of ethanol was investigated in two representative models of experimental epilepsy. In the maximal electroshock seizure threshold test in mice, ethanol (0.5-2 g/kg i.p.) dose-dependently raised the electroconvulsive threshold for tonic seizures. In co-medication with valproate and carbamazepine, ethanol significantly increased the anticonvulsant effectiveness of both antiepileptic drugs. Subchronic premedication of ethanol did not reveal marked decrease of its additive anticonvulsant action and only tended to reduce the effectiveness of valproate and carbamazepine. No changes of the plasma levels of both antiepileptics could be detected. Furthermore, in the hippocampal afterdischarge model in rats, ethanol dose-dependently raised the focal stimulation threshold and significantly increased the anticonvulsant efficacy of co-administered carbamazepine after acute application. Subchronic premedication of ethanol tended to reduce the effectiveness of the latter. In conclusion, the present results indicated pronounced anticonvulsant effects of ethanol against generalized tonic-clonic as well as complex partial seizures which did not reveal strong tolerance after subchronic administration.

The clock gene Per2 influences the glutamatergic system and modulates alcohol consumption

Period (Per) genes are involved in regulation of the circadian clock and are thought to modulate several brain functions. We demonstrate that Per2(Brdm1) mutant mice, which have a deletion in the PAS domain of the Per2 protein, show alterations in the glutamatergic system. Lowered expression of the glutamate transporter Eaat1 is observed in these animals, leading to reduced uptake of glutamate by astrocytes. As a consequence, glutamate levels increase in the extracellular space of Per2(Brdm1) mutant mouse brains. This is accompanied by increased alcohol intake in these animals. In humans, variations of the PER2 gene are associated with regulation of alcohol consumption. Acamprosate, a drug used to prevent craving and relapse in alcoholic patients is thought to act by dampening a hyper-glutamatergic state. This drug reduced augmented glutamate levels and normalized increased alcohol consumption in Per2(Brdm1) mutant mice. Collectively, these data establish glutamate as a link between dysfunction of the circadian clock gene Per2 and enhanced alcohol intake.

Alcoholism: genes and mechanisms

Alcoholism is a chronic relapsing/remitting disease that is frequently unrecognized and untreated, in part because of the partial efficacy of treatment. Only approximately one-third of patients remain abstinent and one-third have fully relapsed 1 year after withdrawal from alcohol, with treated patients doing substantially better than untreated [1]. The partial effectiveness of strategies for prevention and treatment, and variation in clinical course and side effects, represent a challenge and an opportunity to better understand the neurobiology of addiction. The strong heritability of alcoholism suggests the existence of inherited functional variants of genes that alter the metabolism of alcohol and variants of other genes that alter the neurobiologies of reward, executive cognitive function, anxiety/dysphoria, and neuronal plasticity. Each of these neurobiologies has been identified as a critical domain in the addictions. Functional alleles that alter alcoholism-related intermediate phenotypes include common alcohol dehydrogenase 1B and aldehyde dehydrogenase 2 variants that cause the aversive flushing reaction; catechol-O-methyltransferase (COMT) Val158Met leading to differences in three aspects of neurobiology: executive cognitive function, stress/anxiety response, and opioid function; opioid receptor μ1 (OPRM1) Asn40Asp, which may serve as a gatekeeper molecule in the action of naltrexone, a drug used in alcoholism treatment; and HTTLPR, which alters serotonin transporter function and appears to affect stress response and anxiety/dysphoria, which are factors relevant to initial vulnerability, the process of addiction, and relapse.

Acamprosate Calcium Delayed-Release Tablets

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In vivo monitoring of amino acids by microdialysis sampling with on-line derivatization by naphthalene-2,3-dicarboxyaldehyde and rapid micellar electrokinetic capillary chromatography

An analytical method was developed to monitor amino acids collected by in vivo microdialysis. Microdialysate was continuously derivatized on-line by mixing 6 mM naphthalene-2,3-dicarboxyaldehyde (NDA) and 10 mM potassium cyanide with the dialysate stream in a fused silica capillary to form fluorescent products. Reaction time, determined by the flow rate and volume of reaction capillary, was 3 min. Derivatized amino acids were continuously delivered into a flow-gated interface and periodically injected onto a capillary electrophoresis unit equipped with a laser-induced fluorescence detection based on a commercial microscope. Separation was performed in the micellar electrokinetic chromatography mode using 30 mM sodium dodecyl sulfate in 15 mM phosphate buffer at pH 8.0 as the separation media. An electric field of 1.3 kV/cm was applied across a 10 cm long, 10 microm internal diameter separation capillary. These conditions allowed 17 amino acid derivatives to be resolved in less than 30 s. On-line injections could be performed at 30 s intervals for in vivo samples. Detection limits were from 10 to 30 nM for the amino acids. The method was applied to monitor the acute ethanol-induced amino acid level changes in freely moving rats. The results demonstrate the utility of the method to reveal dynamics of amino acid concentration in vivo.

Pharmacotherapy of alcohol dependence: a review of the clinical data

Over the last 20 years, the role of adjuvant pharmacotherapy in optimising outcome in rehabilitation programmes for alcohol-dependent patients has become increasingly evident. New avenues for rational drug treatment have arisen from better understanding of the neurobiological substrates of alcohol dependence, including adaptive changes in amino acid neurotransmitter systems, stimulation of dopamine and opioid peptide systems, and, possibly, changes in serotonergic activity. Disulfiram, naltrexone and acamprosate are currently the only treatments approved for the management of alcohol dependence. However, there is still no unequivocal evidence from randomised controlled clinical trials that disulfiram improves abstinence rates over the long term. Aversive therapy with disulfiram is not without risk for certain patients, and should be closely supervised. Both naltrexone and acamprosate improve outcome in rehabilitation of alcohol-dependent patients, but seem to act on different aspects of drinking pathology. Naltrexone is thought to decrease relapse to heavy drinking by attenuating the rewarding effects of alcohol. However, data from the naltrexone clinical trial programme are somewhat inconsistent, with several large studies being negative. Acamprosate is believed to maintain abstinence by blocking the negative craving that alcohol-dependent patients experience in the absence of alcohol. The clinical development programme has involved a large number of patients and studies, of which the vast majority have shown a beneficial effect of acamprosate on increasing abstinence rates. Both drugs are generally well tolerated; nausea is reported by around 10% of patients treated with naltrexone, while the most frequent adverse effect reported with acamprosate is diarrhoea. Another opioid receptor antagonist, nalmefene, has shown promising activity in pilot studies, and may have a similar profile to naltrexone. Data from studies of SSRIs in alcohol dependence are somewhat heterogeneous, but it appears that these drugs may indirectly improve outcome by treating underlying depression rather than affecting drinking behaviour per se. Similarly, the anxiolytic buspirone may act by ameliorating underlying psychiatric pathology. Dopaminergic neuroleptics, benzodiazepines and antimanic drugs have not yet demonstrated evidence of activity in large controlled clinical trials. Trials with drugs acting at serotonin receptors have yielded disappointing results, with the possible exception of ondansetron. Because the biological basis of alcohol dependence appears to be multifactorial, the future of management of alcoholism may be combination therapy, using drugs acting on different neuronal pathways, such as acamprosate and naltrexone. Pharmacotherapy should be used in association with appropriate psychosocial support and specific treatment provided for any underlying psychiatric comorbidities.

Ethanol modulates neuropeptide-degrading aminopeptidases at synapse level in calcium-dependent conditions

AIMS

To investigate the role of aminopeptidases in the pathways to peptides neurotransmission/neuromodulation ending in the actions of ethanol (EtOH) on the brain.

METHODS

The effects of EtOH on alanyl-, arginyl-, cystyl-, leucyl- and tyrosyl-aminopeptidase activities were studied under basal/resting and K+-stimulated conditions at the synapse level, using mouse frontal cortex synaptosomes and their incubation supernatant in a Ca2+-containing or Ca2+-free medium.

RESULTS

Under basal conditions, synaptosome aminopeptidase activities showed an inhibitory or biphasic response depending on the concentration of EtOH used and the aminopeptidase assayed, whereas supernatant activities showed a more complex response. Under K+-stimulated conditions, EtOH inhibited all synaptosome aminopeptidases assayed in presence of Ca2+. However, in absence of Ca2+, different responses were obtained depending on the concentration of EtOH used. In the supernatant, the highest concentration of EtOH inhibited the K+-stimulated increase on aminopeptidase activities, although the lowest concentration enhanced the release in presence of Ca2+. In absence of it, EtOH blocked the K+-stimulated decrease or increased the activity depending on the concentration of EtOH used.

CONCLUSIONS

The changes on aminopeptidase activities induced by EtOH may reflect the functional status of their corresponding endogenous substrates. EtOH may influence opioid peptides, oxytocin, vasopressin and the brain renin-angiotensin system through their degrading enzymes.

Pharmacological mechanisms of naltrexone and acamprosate in the prevention of relapse in alcohol dependence

Naltrexone and acamprosate may ultimately prove to be useful additions to pharmacotherapy for alcoholism by reducing relapse. Naltrexone is a relatively selective competitive antagonist at mu-opioid receptors, and this activity may explain its anti-relapse action either because endogenous opioids are involved in the positively reinforcing effects of alcohol and/or because these same transmitters are involved in the conditioned anticipation of these effects. In contrast, the pharmacology of acamprosate is still poorly understood. This is not surprising because it is a small flexible molecule with similarities to several neuro-active amino acids and is used in high doses. All these factors suggest that it may have multiple actions. Currently, the best explanation for the effects of acamprosate seems to be that it inhibits the glutamatergic transmitter system involved in both the negative reinforcing effects of alcohol and the conditioned "pseudo-withdrawal" that may be important in cue-induced relapse.

Pharmacodynamic effects of acamprosate on markers of cerebral function in alcohol-dependent subjects administered as pretreatment and during alcohol abstinence

Animal studies suggested that acamprosate modulates neuronal hyperexcitability of acute alcohol withdrawal, acting through the glutamatergic neurotransmission. In the present study, we further investigated whether treatment with acamprosate could attenuate the post-alcohol withdrawal hyperexcitability or hyperarousal in humans using brain magnetoencephalography mapping of spontaneous fields. A double-blind, randomised, placebo-controlled study with a parallel group design comparing 2,000 mg/day of acamprosate versus placebo was conducted in alcohol-dependent subjects meeting DSM-IV criteria for alcohol dependence. Treatments were initiated 8 days before alcohol withdrawal and prolonged during the 15 following (abstinence) days. The study demonstrated that during alcohol withdrawal, acamprosate decreased the arousal level as reflected by alpha slow-wave index (ASI) measurement. This effect was mostly evidenced in left parietotemporal regions and, to a lesser extent, in the contiguous anterior, posterior and right-sided regions. In the placebo group, on the contrary, ASI measures increased between day 2 (acute withdrawal) and day 14 (prolonged withdrawal). The present results suggest a sustained effect of acamprosate on the hyperexcitability state due to alcohol withdrawal in alcohol-dependent patients and that acamprosate may have a protective effect when administered 8 days before alcohol withdrawal.

Synthesis and assessment of [11C]acetylhomotaurine as an imaging agent for the study of the pharmacodynamic properties of acamprosate by positron emission tomography

Acetylhomotaurine was labeled with (11)C via N-acetylation with [(11)C]acetyl chloride. The synthesis yielded 48.2+/-3.8%, decay corrected to end of bombardment. The specific activity of the (radio)chemically pure product was 20.8+/-2.0 GBq/micromol at EOS. In vivo studies revealed a very fast clearance of the tracer from the blood and a uniform distribution in the different brain regions. Unfortunately, the poor passage through the blood brain barrier makes the tracer not suitable for PET studies.

Effect of the combination of naltrexone and acamprosate on alcohol intake in mice

Both naltrexone and acamprosate have been utilized clinically in recovering alcoholics with varying success. In the experiment reported here the combination of naltrexone and acamprosate was examined in a limited access alcohol model using C57BL/6 mice to determine if there was evidence of additive or synergistic effects. The results of this experiment demonstrate that naltrexone, at the higher dose but not the lower dose, significantly reduced alcohol consumption. When combined with naltrexone, acamprosate reduced alcohol consumption across both doses of naltrexone. This effect was sensitive to both dose and number of days of exposure to the naltrexone/acamprosate combination.

Taurine activates strychnine-sensitive glycine receptors in neurons freshly isolated from nucleus accumbens of young rats

Although functional glycine receptors (GlyRs) are present in the mature nucleus accumbens (NAcc), an important area of the mesolimbic dopamine system involved in drug addiction, their role has been unclear because the NAcc contains little glycine. However, taurine, an agonist of GlyRs, is abundant throughout the brain, especially during early development. In the present study on freshly dissociated NAcc neurons from young Sprague-Dawley rats (12- to 21-day old), we found that both glycine and taurine can strongly depolarize NAcc neurons and modulate their excitability. In voltage-clamped NAcc neurons, glycine and taurine elicited chloride currents (IGly and ITau) with an EC50 of 0.12 and 1.25 mM, respectively. The reversal potential of IGly or ITau was 0 mV in conventional whole cell mode and -30 mV in gramicidin-perforated mode. At concentrations <1 mM, both glycine and taurine were very effectively antagonized by strychnine and by picrotoxin (with an IC50 of 60 nM and 36.5 microM for IGly, and 40 nM and 42.2 microM for ITau) but were insensitive to 10 microM bicuculline. The currents elicited by taurine (< or =1 mM) showed complete cross-desensitization with IGly, but none with gamma-aminobutyric acid (GABA)-induced currents (IGABA). However, ITau elicited by very concentrated taurine (10 mM) showed partial cross-desensitization with IGABA, and it was substantially antagonized by 10 microM bicuculline. These results indicate that taurine binds mainly to GlyRs in NAcc, but it could be a partial agonist of GABAA receptors. By activating GlyRs, taurine may play an important physiological role in the control of NAcc function, especially during development.

Does acamprosate improve reduction of drinking as well as aiding abstinence?

The study aimed to discover whether acamprosate reduces the severity of relapse for those patients undergoing abstinence-orientated treatment who are unable to abstain completely. Data on patients' alcohol consumption from 15 placebo-controlled treatment studies (n = 3309) were examined to test whether, at a given time point, patients who have taken one or more drinks since the last assessment ('relapsers', n = 1010) take alcohol on fewer days, report lower average number of drinks per day, and consume less alcohol in total with acamprosate compared to placebo. These studies had varying duration (90 days, 180 days and 360 days). There were four dates that were common to some studies (days 30, 90, 180 and 360). Among relapsers, acamprosate was significantly associated with less quantity (Q) and frequency (F) of drinking compared to placebo in each of the four follow-up periods (p < 0.001). The differences were most marked for the product Q x F (overall weekly consumption). For each period, there were fewer who were drinking an average of five or more drinks per day in the acamprosate compared to the placebo groups. Acamprosate helps reduce the severity of relapse in patients undergoing abstinence-orientated treatment.

Future directions in substance dependence research

Substance dependence is a major health problem but increasing understanding of its neurobiology is likely to lead to improved prevention and treatment. Fundamental aspects of dependence include tolerance and withdrawal and the fact that the drug becomes the centre of the addict's world. Neuroimaging has been key in defining underlying neurobiological mechanisms. The activity in particular brain regions has been shown to be altered in addiction. These include the anterior cingulate which is involved in emotional salience and the orbitofrontal cortex, involved in impulse control. Dopamine is the key neurotransmitter since most abused drugs increase its levels, and many pharmacotherapies have targeted this system. The opiate system is also key in mediating the pleasurable effects of some drugs such as alcohol by increasing dopamine levels. The GABA and glutamate systems mediate many of the other effects of alcohol. As the neurobiology of different components of addiction become evident, pharmacological approaches involve exploiting our new understanding which will likely lead to improved treatments.

Effects of naltrexone alone and in combination with acamprosate on the alcohol deprivation effect in rats

Previous research in our laboratory has shown that responding for ethanol increases after a period of imposed deprivation during which no ethanol is available (the alcohol deprivation effect). This selective increase in responding for ethanol was blocked by chronic administration of acamprosate. In the present study the effects of naltrexone and the combination of naltrexone+acamprosate on oral ethanol self-administration were examined following an imposed period of abstinence. Male Wistar rats were trained to respond for ethanol (10% w/v) or water in a two-lever free-choice condition. After training, separate groups of rats received chronic injections (2 x /day) of saline, naltrexone, or naltrexone+acamprosate during a 5-day period of abstinence. Ethanol self-administration was tested in all groups of rats on the last day of abstinence, 30 min after the last drug injection. Responding for ethanol increased significantly following the deprivation period in animals treated with saline. Chronic administration of naltrexone and the combination naltrexone+acamprosate blocked the increased ethanol consumption following the imposed abstinence period on post-deprivation Day 1. On post-deprivation Day 2, the combination of acamprosate with naltrexone blocked the rebound increase in ethanol consumption observed in animals treated with a low dose of naltrexone. These results support the hypothesis that naltrexone and acamprosate are effective in modulating aspects of alcohol-seeking behavior, and under certain situations may be more effective in combination.

Colocalization of taurine and glial fibrillary acidic protein immunoreactivity in mouse hippocampus induced by short-term ethanol exposure

Morphological changes of the hippocampus were investigated in mice exhibiting signs of intoxication following short-term exposure to 6% ethanol. These alterations were examined by a double immunofluorescent study using antibodies to taurine and anti-glial fibrillary acidic protein (GFAP) antibody. Antibody-labeled taurine was localized mainly in the astrocytes and endothelial cells of control mice. Ethanol administration resulted in a significant increase in the accumulation of taurine and GFAP immunoreactivity (IR) in the stratum lacunosum-moleculare (sl-m) of the hippocampus. Specifically, the cell bodies of taurine-positive astrocytes were hypertrophied, their processes were elongated in the pericapillary region, and some colocalized with GFAP-IR cells. Furthermore, quantitative analysis revealed that the merged area in ethanol-treated mice was twice that (71.6% vs. 35.8%) of control mice. Since taurine is involved in various neuroprotective functions, the present observations suggest that the expression of taurine IR in reactive astrocytes after ethanol exposure might play an important role in neuroprotective processes.

The anti-relapse compound acamprosate inhibits the development of a conditioned place preference to ethanol and cocaine but not morphine

The effects of the anti-relapse compound acamprosate (calcium acetylhomotaurinate) on the conditioned rewarding effects of ethanol, cocaine and morphine were studied using the conditioned place preference (CPP) paradigm. During 3 days of drug conditioning, mice were pretreated with saline or acamprosate (30, 100 or 300 mg kg(-1) i.p.) 10 min prior to the administration of ethanol (2 g kg(-1) i.p.), cocaine (15 mg kg(-1) i.p.) or morphine (10 mg kg(-1) i.p.), and subsequently confined to one of two distinct conditioning chambers. On the following day, mice were tested for the expression of CPP. Acamprosate dose-dependently reduced the development of CPP to ethanol and cocaine but not morphine. When tested as the conditioning drug, acamprosate alone produced neither a conditioned place preference nor aversion. These data suggest that acamprosate can suppress the conditioned rewarding effects of ethanol and certain classes of abused substances.

Systemic osmotic manipulations modulate ethanol-induced taurine release: a brain microdialysis study

In recent microdialysis studies, increased extracellular concentrations of taurine after high ethanol dose administration were identified in various rat brain regions. The mechanisms by which ethanol caused these increases in extracellular taurine concentration remained unclear but could be related to ethanol-induced cell swelling. The aim of the current study was to investigate whether changes in the body osmotic state modulate the effects of ethanol on brain extracellular taurine concentrations. In several groups of rats, brain hypoosmotic or hyperosmotic states were superimposed on acute ethanol (2.0-g/kg) injections, and extracellular taurine concentrations within the nucleus accumbens were assessed by using an intracerebral microdialysis procedure. A hypoosmotic state was obtained by systemic administration of water while hyperosmotic states were induced by intraperitoneal injections of hypertonic saline solutions (1.8% or 3.6% saline). In isoosmotic conditions, ethanol induced an immediate and significant increase in taurine microdialysate content, confirming results of previous studies. However, the effects of ethanol on taurine concentrations were modulated by osmotic manipulations. Hypoosmotic conditions significantly potentiated ethanol-induced taurine release. In contrast, ethanol-induced increases in extracellular taurine levels were attenuated by 1.8% saline injection and totally prevented by 3.6% saline administration. These results strongly argue in favor of a primary role of osmoregulation in ethanol-induced taurine release. Ethanol-induced cell swelling probably activates volume-sensitive channels, and taurine passively diffuses outside the cells along its concentration gradient.

Differential taurine responsiveness to ethanol in high- and low-alcohol sensitive rats: a brain microdialysis study

Several microdialysis studies have investigated the effects of acute ethanol on extracellular amino acids in various rat brain regions. However, these studies led to conflicting results, suggesting that individual differences between rat strains and lines may play an important role. In the present study, high-alcohol sensitive (HAS) and low-alcohol sensitive (LAS) rats were used to investigate the possible relationship between ethanol sensitivity and the concentrations of extracellular amino acids in the nucleus accumbens. Several groups of HAS and LAS rats were injected with either saline or ethanol (1.0, 2.0 or 3.0 g/kg, i.p.) and the concentrations of amino acids in the nucleus accumbens microdialysates were assayed by electrochemical detection. Acute ethanol induced a dose-dependent increase in extracellular taurine concentrations. However, this increase was significantly reduced at 2.0 and 3.0 g/kg ethanol in HAS rats relative to LAS rats. Since the biological functions of taurine suggest its implication in the reduction of ethanol adverse effects, a higher increase in taurine concentrations may contribute to the lower ethanol sensitivity of LAS rats. Although 2.0 and 3.0 g/kg ethanol did not affect extracellular glutamate concentrations, a significant increase in glutamate was observed after 1.0 g/kg ethanol to HAS rats but not to LAS rats. Such an effect remains unexplained but suggests that discrepancies between the results of previous microdialysate studies may be related to differences in the ethanol sensitivities of various rat strains.

Effects of acamprosate and some polyamine site ligands of NMDA receptor on short-term memory in rats

The aim of this study was to evaluate the effect of multiple acamprosate (500.0 mg/kg, p.o.) administration on short-term memory, using the social recognition test in rats. Ifenprodil (1.0 mg/kg, i.p.), arcaine (5.0 mg/kg, i.p.) and spermidine (20.0 mg/kg, i.p.) were chosen as polyamine ligands and their action or interaction with acamprosate was also studied. The doses used did not show any sedative activity, which was assessed by measuring locomotor activity and the hypnotic effect of ethanol. The findings suggest that acute acamprosate treatment did not impair short-term memory. Multiple acamprosate and a single spermidine or arcaine administration led to better performance in the memory test, whereas no significant difference was observed in ifenprodil-treated rats. Co-administration of a single arcaine or spermidine dose with multiple acamprosate produced worse results. This means that the effect of repeated acamprosate administration can be changed by the co-administration of other polyamine ligands, so that care should be taken in interpreting.

Effects of acamprosate and scopolamine on the working memory of rats in a three-panel runway task

The aim of this study was to evaluate the effect of treatment with single (1x) and multiple (10x) doses of the anti-craving compound acamprosate (AC, calcium acetyl homotaurinate) on working memory in rats, using in a three-panel runway test. We measured tasks after the animals were treated with AC (500 mg/kg/d, i.p.); scopolamine (SC, 0.5 mg/kg/d, i.p.), a cholinergic muscarinic receptor antagonist; or both drugs concomitantly (ACSC), either for 1 day (1x) or daily for 10 consecutive days (10x). Neither 1x not 10x AC alone had a significant effect on working memory task performance, whereas treatment with SC alone had a significantly negative effect on the ability of the rats to complete the tasks. Rats receiving ACSC performed better than those receiving SC alone, making fewer errors and displaying shorter latency, similar to the performance of the control group. These observations support the hypothesis of an indirect involvement of AC in the cholinergic system.

Behavioral consequences of the hypotaurine-ethanol interaction

In order to evaluate the effect of hypotaurine on ethanol-induced locomotion, different groups of mice received an injection of saline or 5.62, 8.45, 11.25, 16.87 or 33.75 mg/kg of hypotaurine 30 min prior to administering ethanol (2.4 g/kg). The duration of the effect of hypotaurine was explored by treating animals with ethanol 0, 30, 60 and 90 min after hypotaurine pretreatment. The effect of hypotaurine on acute stimulating ethanol locomotion was evaluated by pretreating animals with saline or 11.25 mg/kg of hypotaurine 30 or 60 min before ethanol (1.6, 2.4, 3.2 g/kg) or saline injections. Hypotaurine (11.25 mg/kg) required 30 min to boost, specifically ethanol-stimulated locomotion (2.4 g/kg). These results suggest a central locus for the interaction, firstly, because blood ethanol levels were not different between hypotaurine and saline pretreated mice, and, secondly, because a cotreatment with beta-alanine (22 mg/kg), a beta-amino acid that counteracts the transfer of hypotaurine across the blood-brain barrier (BBB), prevented the enhancement in ethanol-induced locomotion produced by hypotaurine.

Ethanol decreases the expression of mitochondrial cytochrome c oxidase mRNA in the rat

To evaluate the molecular and cellular bases of effects of ethanol on the brain, we utilized a differential display-polymerase chain reaction. Several cDNA fragments were differentially expressed in the hippocampus of control vs. ethanol-treated rats. One of these genes was homologous to the rat mitochondrial cytochrome c oxidase mRNA. Northern blot analysis revealed that the expression of this message in the whole hippocampus was clearly lower after ethanol treatment. Using in situ hybridization, we also found that cytochrome c oxidase mRNA expression, especially in the CA1 and CA3 of the hippocampal regions, was significantly decreased by ethanol treatment. As cytochrome c oxidase is related to oxidative stress, the present study suggests that ethanol might affect the brain through modulation of an oxidative stress reaction.

The anti-craving compound acamprosate acts as a weak NMDA-receptor antagonist, but modulates NMDA-receptor subunit expression similar to memantine and MK-801

NMDA-receptor-mediated mechanisms may be crucial in addictive states, e.g. alcoholism, and provide a target for the novel anti-craving compound acamprosate. Here, the pharmacological effects of acamprosate on NMDA-receptors were studied using electrophysiological techniques in different cell lines in vitro. Additionally, a possible modulation of brain NMDA-receptor subunit expression was examined in vivo in rats, and compared to two effective non-competitive NMDA-receptor antagonists, memantine and MK-801. Electrophysiology in cultured hippocampal neurons (IC(50) approx. 5.5mM) and Xenopus oocytes (NR1-1a/NR2A assemblies: IC(50) approx. 350 microM, NR1-1a/NR2B: IC(50) approx. 250 microM) consistently revealed only a weak antagonism of acamprosate on native or recombinant NMDA-receptors. In HEK-293 cells, acamprosate showed almost no effect on NR1-1a/NR2A or NR1-1a/NR2B recombinants (IC(50)s not calculated). Protein blotting demonstrated an up-regulation of NMDA-receptor subunits after acamprosate as well as after memantine or MK-801, in comparison to controls. After acamprosate, protein levels were increased in the cortex (NR1-3/1-4: 190+/-11% of controls) and hippocampus (NR1-1/1-2: 163+/-11%). The up-regulations observed after memantine (cortex, NR2B: 172+/-17%; hippocampus, NR1-1/1-2: 156+/-8%) or MK-801 (cortex, NR2B: 174+/-22%; hippocampus, NR1-1/1-2: 140+/-3%) were almost identical. No changes were detected in the brainstem. The present data indicate an extremely weak antagonism of NMDA-receptors by acamprosate. However, its ability to modulate the expression of NMDA-receptor subunits in specific brain regions - shared with the well established NMDA-antagonists memantine and MK-801 - may be of relevance for its therapeutic profile, especially considering the growing importance of NMDA-receptor plasticity in the research of ethanol addiction.