Local acamprosate modulates dopamine release in the rat nucleus accumbens through NMDA receptors: an in vivo microdialysis study

Acamprosate reduces ethanol intake in the rat by a combined action of different drug components

Alcohol misuse accounts for a sizeable proportion of the global burden of disease, and Campral® (acamprosate; calcium-bis-(N-acetylhomotaurinate)) is widely used as relapse prevention therapy. The mechanism underlying its effect has in some studies been attributed to the calcium moiety and not to the N-acetylhomotaurine part of the compound. We recently suggested that the dopamine elevating effect of acamprosate is mediated both by N-acetylhomotaurine and calcium in a glycine receptor dependent manner. Here we aimed to explore, by means of in vivo microdialysis, if our previous study using local administration was functionally relevant and if systemic administration of the sodium salt of N-acetylhomotaurine (sodium acamprosate; 200 mg/kg, i.p.) enhanced the effects of calcium chloride (CaCl2; 73.5 mg/kg, i.p.) on nucleus accumbens (nAc) dopamine and/or taurine levels in male Wistar rats. In addition, we investigated the impact of regular acamprosate and the combination of CaCl2 and N-acetylhomotaurine on the alcohol deprivation effect (ADE). Finally, we assessed if N-acetylhomotaurine potentiates the ethanol-intake reducing effect of CaCl2 in a two-bottle choice voluntary ethanol consumption model followed by an ADE paradigm. Systemic administration of regular acamprosate, sodium acamprosate and CaCl2 all trended to increase nAc dopamine whereas the combination of CaCl2 and sodium acamprosate produced a significant increase. Sodium acamprosate elevated extracellular taurine levels without additional effects of CaCl2. Ethanol intake was significantly reduced by systemic administration of CaCl2 without additional effects of the combination of CaCl2 and sodium acamprosate. Both acamprosate and CaCl2 combined with sodium acamprosate blocked the ADE following acute treatment. The data presented suggest that CaCl2 and N-acetylhomotaurine act in concert on a neurochemical level, but calcium appears to have the predominant effect on ethanol intake.

The Role of NMDA Receptor Partial Antagonist, Carbamathione, as a Therapeutic Agent for Transient Global Ischemia

Carbamathione (Carb), an NMDA glutamate receptor partial antagonist, has potent neuroprotective functions against hypoxia- or ischemia-induced neuronal injury in cell- or animal-based stroke models. We used PC-12 cell cultures as a cell-based model and bilateral carotid artery occlusion (BCAO) for stroke. Whole-cell patch clamp recording in the mouse retinal ganglion cells was performed. Key proteins involved in apoptosis, endoplasmic reticulum (ER) stress, and heat shock proteins were analyzed using immunoblotting. Carb is effective in protecting PC12 cells against glutamate- or hypoxia-induced cell injury. Electrophysiological results show that Carb attenuates NMDA-mediated glutamate currents in the retinal ganglion cells, which results in activation of the AKT signaling pathway and increased expression of pro-cell survival biomarkers, e.g., Hsp 27, P-AKT, and Bcl2 and decreased expression of pro-cell death markers, e.g., Beclin 1, Bax, and Cleaved caspase 3, and ER stress markers, e.g., CHOP, IRE1, XBP1, ATF 4, and eIF2α. Using the BCAO animal stroke model, we found that Carb reduced the brain infarct volume and decreased levels of ER stress markers, GRP 78, CHOP, and at the behavioral level, e.g., a decrease in asymmetric turns and an increase in locomotor activity. These findings for Carb provide promising and rational strategies for stroke therapy.

A Review of DNA Risk Alleles to Determine Epigenetic Repair of mRNA Expression to Prove Therapeutic Effectiveness in Reward Deficiency Syndrome (RDS): Embracing "Precision Behavioral Management"

This is a review of research on "Precision Behavioral Management" of substance use disorder (SUD). America is experiencing a high prevalence of substance use disorder, primarily involving legal and illegal opioid use. A 3000% increase in treatment for substance abuse has occurred between 2000 and 2016. Unfortunately, present day treatment of opioid abuse involves providing replacement therapy with powerful opioids to, at best, induce harm reduction, not prophylaxis. These interventions do not enhance gene expression and restore the balance of the brain reward system's neurotransmitters. We are proposing a generalized approach called "Precision Behavioral Management". This approach includes 1) using the Genetic Addiction Risk Severity (GARS, a 10 candidate polymorphic gene panel shown to predict ASI-alcohol and drug severity) to assess early pre-disposition to substance use disorder; 2) using a validated reward deficiency syndrome (RDS) questionnaire; 3) utilization of the Comprehensive Analysis of Reported Drugs (CARD™) to assess treatment compliance and abstinence from illicit drugs during treatment, and, importantly; 4) utilization of a "Pro-dopamine regulator (KB220)" (via IV or oral [KB220Z] delivery systems) to optimize gene expression, restore the balance of the Brain Reward Cascade's neurotransmitter systems and prevent relapse by induction of dopamine homeostasis, and; 5) utilization of targeted DNA polymorphic reward genes to direct mRNA genetic expression profiling during the treatment process. Incorporation of these events can be applied to not only the under-considered African-American RDS community, but all victims of RDS, as a demonstration of a paradigm shift that uniquely provides a novel putative "standard of care" based on DNA guided precision nutrition therapy to induce "dopamine homeostasis" and rebalance neurotransmitters in the Brain Reward Cascade. We are also developing a Reward Deficiency Syndrome Diagnostic Criteria (RDSDC) to assist in potential tertiary treatment.

Effects of low-dose alcohol exposure in adolescence on subsequent alcohol drinking in adulthood in a rat model of depression

OBJECTIVE

Adolescence drinking and subsequent development of alcohol use disorder (AUD) is a worldwide health concern. In particular, mood dysregulation or early alcohol exposure can be the cause of heavy drinking in some individuals or a consequence of heavy drinking in others.

METHODS

This study investigated the effects of voluntary alcohol intake during adolescence, i.e. continuous 10% alcohol access between postnatal days (PND) 29 to 43 and olfactory bulbectomy (OBX) model of depression (performed on PND 59) on alcohol drinking in Wistar rats during adulthood (PND 80-120, intermittent 20% alcohol access). In addition, the effect of NBQX, an AMPA/kainate receptor antagonist (5 mg/kg, IP) on spontaneous alcohol consumption was examined.

RESULTS

Rats exposed to 10% alcohol during adolescence exhibited a lower 20% alcohol intake in the intermittent paradigm during adulthood, while the OBX-induced phenotype did not exert a significant effect on the drinking behaviour. NBQX exerted a transient reduction on alcohol intake in the OBX rats.

CONCLUSIONS

Our results indicate that exposure to alcohol during adolescence can affect alcohol drinking in adulthood and that further exploration of AMPA and/or kainate receptor antagonists in co-morbid alcoholism-depression is warranted.

Pharmacotherapeutic management of co-morbid alcohol and opioid use

Opioid use disorder (OUD) and alcohol use disorder (AUD) are two highly prevalent substance-related disorders worldwide. Co-use of the substances is also quite prevalent, yet there are no pharmacological treatment approaches specifically designed to treat co-morbid OUD and AUD. Here, the authors critically summarize OUD, AUD and opioid/alcohol co-use and their current pharmacotherapies for treatment. They also review the mechanisms of action of opioids and alcohol within the brain reward circuitry and discuss potential combined mechanisms of action and resulting neuroadaptations. Pharmacotherapies that aim to treat AUD or OUD that may be beneficial in the treatment of co-use are also highlighted. Preclinical models assessing alcohol and opioid co-use remain sparse. Lasting neuroadaptations in brain reward circuits caused by co-use of alcohol and opioids remains largely understudied. In order to fully understand the neurobiological underpinnings of alcohol and opioid co-use and develop efficacious pharmacotherapies, the preclinical field must expand its current experimental paradigms of 'single drug' use to encompass polysubstance use. Such studies will provide insights on the neural alterations induced by opioid and alcohol co-use, and may help develop novel pharmacotherapies for individuals with co-occurring alcohol and opioid use disorders.

Acamprosate's ethanol intake-reducing effect is associated with its ability to increase dopamine

Previous studies indicate that the anti-craving substance acamprosate modulates nucleus accumbens (nAc) dopamine levels via a dopamine-controlling nAc-VTA-nAc neurocircuitry. It was demonstrated that glycine receptors in the nAc are involved both in the dopamine-elevating effect and the ethanol intake-reducing effect of the drug. Here we wanted to explore the interaction of ethanol and acamprosate on nAc dopamine and investigate whether dopaminergic transmission may be related to the ethanol intake-reducing effects. In three separate studies we investigated nAc extracellular dopamine levels by means of in vivo microdialysis after administration of acamprosate and ethanol in 1) naïve rats, 2) rats pre-treated with acamprosate for two days or 3) ethanol medium- and high-preferring rats receiving ten days of acamprosate pre-treatment. In the first two studies, acamprosate elevated dopamine and simultaneously prevented ethanol from further increasing dopamine output. In the third study, long-term acamprosate pre-treatment produced a loss of the ethanol intake-reducing as well as the dopamine-elevating effects of acamprosate, and the dopamine elevating property of ethanol was restored. We suggest that acamprosate may partly substitute for the dopamine-elevating effect of ethanol but once tolerance develops to this effect, the ability to decrease ethanol intake is lost.

The Glycine Receptor-A Functionally Important Primary Brain Target of Ethanol

Identification of ethanol's (EtOH) primary molecular brain targets and determination of their functional role is an ongoing, important quest. Pentameric ligand-gated ion channels, that is, the nicotinic acetylcholine receptor, the γ-aminobutyric acid type A receptor, the 5-hydroxytryptamine₃ , and the glycine receptor (GlyR), are such targets. Here, aspects of the structure and function of these receptors and EtOH's interaction with them are briefly reviewed, with special emphasis on the GlyR and the importance of this receptor and its ligands for EtOH pharmacology. It is suggested that GlyRs are involved in (i) the dopamine-activating effect of EtOH, (ii) regulating EtOH intake, and (iii) the relapse preventing effect of acamprosate. Exploration of the GlyR subtypes involved and efforts to develop subtype specific agonists or antagonists may offer new pharmacotherapies for alcohol use disorders.

Combination of acamprosate and baclofen as a promising therapeutic approach for Parkinson's disease

Parkinson’s disease (PD) is a progressive neurodegenerative disorder characterised by the loss of dopaminergic nigrostriatal neurons but which involves the loss of additional neurotransmitter pathways. Mono- or polytherapeutic interventions in PD patients have declining efficacy long-term and no influence on disease progression. The systematic analysis of available genetic and functional data as well as the substantial overlap between Alzheimer’s disease (AD) and PD features led us to repurpose and explore the effectiveness of a combination therapy (ABC) with two drugs – acamprosate and baclofen – that was already effective in AD animal models, for the treatment of PD. We showed in vitro that ABC strongly and synergistically protected neuronal cells from oxidative stress in the oxygen and glucose deprivation model, as well as dopaminergic neurons from cell death in the 6-hydroxydopamine (6-OHDA) rat model. Furthermore, we showed that ABC normalised altered motor symptoms in vivo in 6-OHDA-treated rats, acting by protecting dopaminergic cell bodies and their striatal terminals. Interestingly, ABC also restored a normal behaviour pattern in lesioned rats suggesting a symptomatic effect, and did not negatively interact with L-dopa. Our results demonstrate the potential value of combining repurposed drugs as a promising new strategy to treat this debilitating disease.

Assessing ethanol's actions in the suprachiasmatic circadian clock using in vivo and in vitro approaches

Research over the past decade has demonstrated substantial interactions between the circadian system and the processes through which alcohol affects behavior and physiology. Here we summarize the results of our collaborative efforts focused on this intersection. Using a combination of in vivo and in vitro approaches, we have shown that ethanol affects many aspects of the mammalian circadian system, both acutely as well as after chronic administration. Conversely, we have shown circadian influences on ethanol consumption. Importantly, we are beginning to delve into the cellular mechanisms associated with these effects. We are also starting to form a picture of the neuroanatomical bases for many of these actions. Finally, we put our current findings into perspective by suggesting new avenues of inquiry for our future efforts.

Clinically Combating Reward Deficiency Syndrome (RDS) with Dopamine Agonist Therapy as a Paradigm Shift: Dopamine for Dinner?

Everyday, there are several millions of people that are increasingly unable to combat their frustrating and even fatal romance with getting high and/or experiencing “normal” feelings of well-being. In the USA, the FDA has approved pharmaceuticals for drug and alcohol abuse: tobacco and nicotine replacement therapy. The National Institute on Drug Abuse (NIDA) and the National Institute on Alcohol Abuse and Alcoholism (NIAAA) remarkably continue to provide an increasing understanding of the intricate functions of brain reward circuitry through sophisticated neuroimaging and molecular genetic applied technology. Similar work is intensely investigated on a worldwide basis with enhanced clarity and increased interaction between not only individual scientists but across many disciplines. However, while it is universally agreed that dopamine is a major neurotransmitter in terms of reward dependence, there remains controversy regarding how to modulate its role clinically to treat and prevent relapse for both substance and non-substance-related addictive behaviors. While the existing FDA-approved medications promote blocking dopamine, we argue that a more prudent paradigm shift should be biphasic—short-term blockade and long-term upregulation, enhancing functional connectivity of brain reward circuits.

S-(N, N-diethylcarbamoyl)glutathione (carbamathione), a disulfiram metabolite and its effect on nucleus accumbens and prefrontal cortex dopamine, GABA, and glutamate: a microdialysis study

Disulfiram (DSF), used for the treatment of alcohol use disorders (AUDs) for over six decades, most recently has shown promise for treating cocaine dependence. Although DSF's mechanism of action in alcohol abuse is due to the inhibition of liver mitochondrial aldehyde dehydrogenase (ALDH2), its mechanism of action in the treatment of cocaine dependence is unknown. DSF is a pro-drug, forming a number of metabolites each with discrete pharmacological actions. One metabolite formed during DSF bioactivation is S-(N, N-diethylcarbamoyl) glutathione (carbamathione) (carb). We previously showed that carb affects glutamate binding. In the present studies, we employed microdialysis techniques to investigate the effect of carb administration on dopamine (DA), GABA, and glutamate (Glu) in the nucleus accumbens (NAc) and medial prefrontal cortex (mPFC), two brain regions implicated in substance abuse dependence. The effect of DSF on DA, GABA, and Glu in the NAc also was determined. Both studies were carried out in male rats. Carb (20, 50, 200 mg/kg i v) in a dose-dependent manner increased DA, decreased GABA, and had a biphasic effect on Glu, first increasing and then decreasing Glu in both the NAc and mPFC. These changes all occurred concurrently. After carb administration, NAc and mPFC carb, as well as carb in plasma, were rapidly eliminated with a half-life for each approximately 4 min, while the changes in DA, GABA, and GLu in the NAc and mPFC persisted for approximately two hours. The maximal increase in carb (Cmax) in the NAc and mPFC after carb administration was dose-dependent, as was the area under the curve (AUC). DSF (200 mg/kg i p) also increased DA, decreased GABA, and had a biphasic effect on Glu in the NAc similar to that observed in the NAc after carb administration. When the cytochrome P450 inhibitor N-benzylimidazole (NBI) (20 mg/kg i p) was administered before DSF dosing, no carb could be detected in the NAc and plasma and also no changes in NAc DA, GABA, and GLu occurred. Changes in these neurotransmitters occurred only if carb was formed from DSF. When NBI was administered prior to dosing with carb, the increase in DA, decrease in GABA, and biphasic effect on GLu was similar to that seen after dosing with carb only. The i p or i v administration of carb showed similar changes in DA, GABA, and GLu, except the time to reach Cmax for DA as well as the changes in GABA, and GLu after i p administration occurred later. The elimination half-life of carb and the area under the curve (AUC) were similar after both routes of administration. It is concluded that carb must be formed from DSF before any changes in DA, GABA, and GLu in the NAc and mPFC are observed. DSF and carb, when administered to rats, co-release DA, GABA, and GLu. Carb, once formed can cross the blood brain barrier and enter the brain. Although inhibition of liver ALDH2 is the accepted mechanism for DSF's action in treating AUDs, the concurrent changes in DA, GABA, and GLu in the NAc and mPFC after DSF administration suggest that changes in these neurotransmitters as a potential mechanism of action not only for AUDs, but also for cocaine dependence cannot be excluded.

Acamprosate in alcohol dependence: implications of a unique mechanism of action

Acamprosate, in combination with psychosocial therapy, has been shown to be clinically effective in maintaining abstinence in alcohol dependence. Current research suggests that its mechanism of action involves functional antagonism of the ionotropic glutamate N-methyl-d-aspartate (NMDA) receptor. However, direct interactions between acamprosate and the NMDA receptor are weak, and recent findings suggest that acamprosate may modulate NMDA receptors via regulatory polyamine sites, or that it may act directly on metabotropic glutamate receptors. All of these mechanisms are novel for the treatment of alcohol dependence and have far-reaching implications for understanding relapse, as well as for the discovery of drugs with greater efficacy. Understanding the mechanism of action of acamprosate may be an important stimulus for change in the perception and treatment of alcohol dependence.

Acamprosate-responsive brain sites for suppression of ethanol intake and preference

Acamprosate suppresses alcohol intake and craving in recovering alcoholics; however, the central sites of its action are unclear. To approach this question, brain regions responsive to acamprosate were mapped using acamprosate microimplants targeted to brain reward and circadian areas implicated in alcohol dependence. mPer2 mutant mice with nonfunctional mPer2, a circadian clock gene that gates endogenous timekeeping, were included, owing to their high levels of ethanol intake and preference. Male wild-type (WT) and mPer2 mutant mice received free-choice (15%) ethanol/water for 3 wk. The ethanol was withdrawn for 3 wk and then reintroduced to facilitate relapse. Four days before ethanol reintroduction, mice received bilateral blank or acamprosate-containing microimplants releasing ∼50 ng/day into reward [ventral tegmental (VTA), peduculopontine tegmentum (PPT), and nucleus accumbens (NA)] and circadian [intergeniculate leaflet (IGL) and suprachiasmatic nucleus (SCN)] areas. The hippocampus was also targeted. Circadian locomotor activity was measured throughout. Ethanol intake and preference were greater in mPer2 mutants than in wild-type (WT) mice (27 g·kg(-1)·day(-1) vs. 13 g·kg(-1)·day(-1) and 70% vs. 50%, respectively; both, P < 0.05). In WTs, acamprosate in all areas, except hippocampus, suppressed ethanol intake and preference (by 40-60%) during ethanol reintroduction. In mPer2 mutants, acamprosate in the VTA, PPT, and SCN suppressed ethanol intake and preference by 20-30%. These data are evidence that acamprosate's suppression of ethanol intake and preference are manifest through actions within major reward and circadian sites.

Acamprosate determinations in plasma and cerebrospinal fluid after multiple dosing measured by liquid chromatography-mass spectroscopy: a pharmacokinetic study in healthy volunteers

The central nervous system-active medication acamprosate has been shown to modulate alcohol-related behavior in both preclinical and clinical studies. Although commonly used in the treatment of alcohol dependence, there are still unanswered questions concerning the pharmacokinetic properties of acamprosate. The aims of the present study were to 1) to validate liquid chromatography-mass spectrometry as a method to study the presence of acamprosate in plasma and cerebrospinal fluid (CSF) in humans; and 2) validate previous results on clinically important pharmacokinetic data for acamprosate. In an open label, single-site design, 13 healthy males and females were recruited to 22 days of oral acamprosate treatment (1998 mg/day). Subjects provided in all 256 plasma samples for analysis at regular intervals at Day 1, 7, 14, and 22 of treatment. On Day 22, subjects also left a sample of CSF for measurement of acamprosate. The results showed that steady-state level of acamprosate was accomplished within 5 days after the start of treatment and remained fairly stable for 2 to 3 days after termination of treatment. Variations in plasma concentrations corresponded to earlier studies and did not exceed those for comparable pharmacotherapeutic agents. Acamprosate concentrations in the CSF were below the limit of quantification, ie, estimated concentrations between 9 and 33 ng/mL. Plasma concentrations were more than 25 times higher than in lumbar CSF. The low CSF levels seen after 3 weeks of treatment may provide an explanation to the delay in therapeutic effect noticed in treatment studies on acamprosate. A longer duration of treatment might be necessary to obtain clinically significant brain levels of acamprosate. In summary, the present study validated liquid chromatography-mass spectrometry as a method for assessment of compliance to acamprosate treatment. Furthermore, the results suggest that the mechanism of action of acamprosate needs to be further explored with regard to the peripheral actions of the drug.

Glycine receptors involved in acamprosate's modulation of accumbal dopamine levels: an in vivo microdialysis study

BACKGROUND

Glycine receptors (GlyRs) in the nucleus accumbens (nAc) and nicotinic acetylcholine receptors (nAChRs) in the ventral tegmental area (VTA) have been suggested to be involved in the positive reinforcing and dopamine elevating effects of ethanol. Recent studies have also shown that ethanol high-preferring rats substantially decrease their ethanol intake when treated with a glycine transporter 1 inhibitor (ORG 25935). Acamprosate, a drug used for relapse prevention in treatment of alcohol dependence, has also been demonstrated to elevate extracellular dopamine levels in the nAc. However, the underlying mechanism of action of acamprosate is not fully understood. Here we investigated whether acamprosate interferes with a neuronal circuitry that previously has been demonstrated to be involved in the dopamine elevating effects of ethanol and taurine.

METHODS

In vivo microdialysis in freely moving rats was used to assess accumbal dopamine levels before and during local (nAc) or systemic administration of acamprosate.

RESULTS

Perfusion of 0.5 mM acamprosate in the nAc significantly increased dopamine levels. Pretreatment either with 10 microM strychnine in the nAc or 100 microM mecamylamine in the VTA, completely antagonized the acamprosate-induced elevation of accumbal dopamine levels. Also, systemic acamprosate administration elevated accumbal dopamine output, an effect that was abolished by local (nAc) pretreatment with 10 microM strychnine.

CONCLUSIONS

These results suggest that both systemic and local application of acamprosate elevate extracellular dopamine levels in the nAc by activating accumbal GlyRs, and, secondarily, tegmental nAChRs.

The glycine reuptake inhibitor org 25935 interacts with basal and ethanol-induced dopamine release in rat nucleus accumbens

BACKGROUND

The mesolimbic dopamine (DA) projection from the ventral tegmental area to nucleus accumbens (nAc), a central part of the reward system, is activated by ethanol (EtOH) and other drugs of abuse. We have previously demonstrated that the glycine receptor in the nAc and its amino acid agonists may be implicated in the DA activation and reinforcing properties of EtOH. We have also reported that the glycine transporter 1 inhibitor, Org 25935, produces a robust and dose-dependent decrease in EtOH consumption in Wistar rats. The present study explores the interaction between EtOH and Org 25935 with respect to DA levels in the rat nAc.

METHODS

The effects of Org 25935 (6 mg/kg, i.p.) and/or EtOH (2.5 g/kg, i.p.) on accumbal DA levels were examined by means of in vivo microdialysis (coupled to HPLC-ED) in freely moving male Wistar rats. The effect of Org 25935 on accumbal glycine output was also investigated.

RESULTS

Systemic Org 25935 increased DA output in a subpopulation of rats (52% in Experiment 1 and 38% in Experiment 2). In Experiment 2, EtOH produced a significant increase in DA levels in vehicles (35%) and in Org 25935 nonresponders (19%), whereas EtOH did not further increase the DA level in rats responding to Org 25935 (2%). The same dose of Org 25935 increased glycine levels by 87% in nAc.

CONCLUSIONS

This study demonstrates that Org 25935, probably via increased glycine levels, (i) counteracts EtOH-induced increases of accumbal DA levels and (ii) increases basal DA levels in a subpopulation of rats. The results are in line with previous findings and it is suggested that the effects observed involve interference with accumbal GlyRs and are related to the alcohol consumption modulating effect of Org 25935.

Acamprosate: recent findings and future research directions

This article explores the mechanisms of action and the potential responder profile of acamprosate, a compound efficacious in relapse prevention of alcoholism. New evidence at the molecular and cellular level suggests that acamprosate attenuates hyper-glutamatergic states that occur during early abstinence and involves iono (NMDA)- and metabotrotropic (mGluR5) glutamate receptors along with augmented intracellular calcium release and electrophysiological changes. Thus mutant mice with enhanced glutamate levels exhibit higher alcohol consumption than wild type mice and respond better to acamprosate, demonstrating that acamprosate acts mainly on a hyper-glutamatergic system. This mode of action further suggests that acamprosate exhibits neuroprotective properties. In rats, cue-induced reinstatement behavior is significantly reduced by acamprosate treatment whereas cue-induced craving responses in alcohol-dependent patients seem not to be affected by this treatment. An ongoing study ("Project Predict") defines specific responder profiles for an individualized use of acamprosate and naltrexone. Neurophysiological as well as psychometric data are used to define 2 groups of patients: "reward cravers" and "relief cravers". While naltrexone should work better in the first group, acamprosate is hypothesized to be efficacious in the latter where withdrawal associated and/or cue induced hyper-glutamatergic states are thought to trigger relapse. Further research should target the definition of subgroups applying endophenotypic approaches, e.g. by detecting a hyperglutamatergic syndrome using MR spectroscopy.

Glutamate-dopamine-GABA interactions in the aging basal ganglia

The study of neurotransmitter interactions gives a better understanding of the physiology of specific circuits in the brain. In this review we focus mostly on our own results on the interaction of the neurotransmitters glutamate, dopamine and GABA in the basal ganglia during the normal process of aging. We review first the studies on the action of endogenous glutamate on the extracellular concentrations of dopamine and GABA in the neostriatum and nucleus accumbens during aging. It was found that there exists an age-related change in the interaction of glutamate, dopamine and GABA and that these effects of aging exhibit a dorsal-to-ventral pattern of effects with no changes in the dorsal parts (dorsal striatum) and changes in the most ventral parts (nucleus accumbens). Second we reviewed the data on the effects of different ionotropic and metabotropic glutamate receptor agonists on the extracellular concentrations of dopamine and GABA in the nucleus accumbens. The results obtained clearly show the different contribution of each glutamate receptor subtype in the age-related changes produced on the interaction of glutamate, dopamine and GABA in this area of the brain. Third the effects of an enriched environment on the action of AMPA and NMDA-receptor agonists in the nucleus accumbens of rats during aging are also evaluated. Finally, and since the nucleus accumbens has been suggested to play a role in emotion and motivation and also motor behaviour, we speculated on the possibility of a specific contribution for the different glutamatergic pathways terminating in the nucleus accumbens and their interaction with a decreased dopamine playing a relevant role in motor behaviour during aging.

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.

Substance use disorders and schizophrenia: A question of shared glutamatergic mechanisms

Schizophrenia is noted for the remarkably high prevalence of substance use disorders (SUDs) including nicotine (>85%), alcohol and stimulants. Mounting evidence supports the hypothesis that the endophenotype of schizophrenia involves hypofunction of a subpopulation of cortico-limbic NMDA receptors. Low doses of NMDA receptor antagonists such as ketamine replicate in normal volunteers positive, negative and cognitive symptoms of schizophrenia as well as associated physiologic abnormalities such as eye tracking and abnormal event related potentials. Genetic studies have identified putative risk genes that directly or indirectly affect NMDA receptors including D-amino acid oxidase, its modulator G72, proline oxidase, mGluR3 and neuregulin. Clinical trials have shown that agents that directly or indirectly enhance the function of the NMDA receptor at its glycine modulatory site (GMS) reduce negative symptoms and in the case of D-serine and sarcosine improve cognition and reduce positive symptoms in schizophrenic subjects receiving concurrent anti-psychotic medications. Notably, the GMS partial agonist D-cycloserine exacerbates negative symptoms in clozapine responders whereas full agonists, glycine and D-serine have no effects, suggesting clozapine may act indirectly as a full agonist at the GMS of the NMDA receptor. Clozapine treatment is uniquely associated with decreased substance use in patients with schizophrenia, even without psychologic intervention. Given the role of NMDA receptors in the reward circuitry and in substance dependence, it is reasonable to speculate that NMDA receptor dysfunction is a shared pathologic process in schizophrenia and co-morbid SUDs.

Effects of dorsal and ventral hippocampal NMDA stimulation on nucleus accumbens core and shell dopamine release

This study has analysed the effects of infusing N-methyl-D-aspartate (NMDA) into either the ventral or dorsal hippocampus on dopamine (DA) transmission in the nucleus accumbens (NAC) core or shell for the first time. Dopamine was measured using in vivo microdialysis with high performance liquid chromatography with electrochemical detection (HPLC-EC). Unilateral NMDA infusion (0.5 microg) into the ventral hippocampus (VH) increased extracellular DA levels in NAC shell during the first 30 min following infusion compared to saline (SAL) infused animals. In contrast, NAC core DA levels were unaffected. NMDA infusion into the dorsal hippocampus (DH) led to a decrease in NAC core DA levels; this effect was not observed in the SAL-infused group. DA levels in NAC shell remained unaltered. At the end of the experiments, we examined the response to a systemic amphetamine (AMPH) injection of 1mg/kg on extracellular DA levels of the NAC core and shell. Interestingly, on2ly animals previously infused with NMDA into the VH exhibited a sensitized DA response in the NAC shell in response to the AMPH injection. We can conclude that VH activation has an acute stimulatory effect on DA release in the shell and that DH activation has a suppressive effect on extracellular DA levels in the core.

Taurine elevates dopamine levels in the rat nucleus accumbens; antagonism by strychnine

The mesolimbic dopamine (DA) system, projecting from the ventral tegmental area (VTA) to the nucleus accumbens (nAcc), is involved in reward-related behaviours and addictive processes, such as alcoholism and drug addiction. It was recently suggested that strychnine-sensitive glycine receptors (GlyR) in the nAcc regulate both basal and ethanol-induced mesolimbic DA activity via a neuronal loop involving endogenous activation of nicotinic acetylcholine receptors (nAChR) in the VTA. However, as the nAcc appears to contain few glycine-immunoreactive cell bodies or fibres, the question as to what may be the endogenous ligand for GlyRs in this brain region remains open. Here we have investigated whether the amino acid taurine could serve this purpose using in vivo microdialysis in awake, freely moving male Wistar rats. Local perfusion of taurine (1, 10 or 100 mm in the perfusate) increased DA levels in the nAcc. The taurine (10 mm)-induced DA increase was, similarly to that previously observed after ethanol, completely blocked by (i) perfusion of the competitive GlyR antagonist strychnine in the nAcc, (ii) perfusion of the nAChR antagonist mecamylamine (100 microm) in the VTA, and (iii) systemic administration of the acetylcholine-depleting drug vesamicol (0.4 mg/kg, i.p). The present results suggest that taurine may be an endogenous ligand for GlyRs in the nAcc and that the taurine-induced elevation of DA levels in this area, similarly to that observed after local ethanol, is mediated via a neuronal loop involving endogenous activation of nAChRs in the VTA.

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.

The acute anti-craving effect of acamprosate in alcohol-preferring rats is associated with modulation of the mesolimbic dopamine system

Acamprosate (Campral) is a drug used clinically for the treatment of alcoholism. In order to examine further the time-course and mechanism of action of acamprosate, the effect of acute and repeated acamprosate administration was examined on (i) operant ethanol self-administration and (ii) voluntary home cage ethanol consumption by alcohol-preferring Fawn-Hooded, iP and Alko Alcohol (AA) rats. Acutely, acamprosate was shown to cause a significant decrease in operant ethanol self-administration by Fawn-Hooded and alcohol-preferring iP rats in part by decreasing the motivational relevance of a specific ethanol cue; however, repeated injection of acamprosate led to tolerance to this effect. Voluntary alcohol consumption in the home cage in Fawn-Hooded and AA rats was also reduced by an acute acamprosate injection; however, again tolerance developed to repeated injections. In a separate experiment, the effect of acamprosate on markers of the dopaminergic system was examined. Interestingly, acute acamprosate was also shown to cause increased dopamine transporter density and decreased dopamine D2-like receptor density within the nucleus accumbens but not in the caudate-putamen, suggesting a link between the decreased motivational salience of the ethanol cue and altered dopaminergic signalling within the nucleus accumbens. With repeated injections of acamprosate, markers of the dopaminergic system returned to steady state levels with a similar temporal profile to the development of tolerance in the behavioural studies. Along with previous studies, our findings indicate that acamprosate modulates the mesolimbic dopaminergic system and may thereby decrease ethanol reinforcement processes; however, these effects undergo tolerance in alcohol-preferring rats and may in part explain the fact why some subjects are non-responders to chronic acamprosate treatment.

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.

Dopaminergic Modulation of Neurosecretory Cells in the Crayfish

The main aims of this paper are (a) to locate possible dopaminergic neurons in the eyestalk with anti-tyrosine hydroxylase antibodies, (b) to search for the presence of dopamine (DA) in the nervous structures of the eyestalk, (c) to explore its release, and (d) to test the effect of DA on neurosecretory cells in the eyestalk. Experiments were performed in adult crayfishes Procambarus clarkii, in isolated optic peduncle. Immunocytochemistry was made with the antibody against its precursor synthesizing enzyme tyrosine-hydroxylase. The content and release studies of DA were made using high performance liquid chromatography (HPLC). Extracellular and intracellular recordings were conducted with conventional recording techniques. A large number (approximately 2000) of immunopositive somata of different sizes and shapes were identified in various regions of the eyestalk. The majority of somata are of the smallest size (5-25 microm diameter). DA content in the eyestalk was 5.6 +/- 0.1 pmol per structure; the greatest content is in the MT (over 60%). A basal level release of DA was observed. Incubation of eyestalks in solution containing a high K+ concentration increased the DA release (79%). Two effects of DA on the excitability of X-organ neurons were observed; an excitatory effect on neurons of approximately 25 microm somata diameter and another inhibitory effect in the group of approximately 35-microm somata diameter neurons. The excitation occurs with a depolarization and decrement of membrane conductance in the cell soma while the inhibition occurs with a hyperpolarization and increment of membrane conductance in soma. We concluded the following: (1) Dopamine is present in each optic ganglia of the crayfish eyestalk. (2) There is a basal release of DA from the isolated eyestalk. (3) DA release is enhanced threefold by eyestalk incubation in 40 mM [K+] solution. (4) DA selectively excites a population of neurons with low-speed conduction axons, and small somata in the X-organ-sinus gland system, while inhibiting another population characterized by higher axonal conduction speed and large somata. (5) These observations support a role for DA as a neurotransmitter or neuromodulator in the X-organ neurons of the crayfish eyestalk.

Acamprosate Calcium Delayed-Release Tablets

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Plasma homocysteine concentrations do not influence craving in alcohol withdrawal

Results of a number of studies indicate that the glutamate system, especially the N-methyl-D-aspartate (NMDA) receptor, has a major function in chronic alcoholism, including craving. Homocysteine and other excitatory amino acids, such as glutamate and aspartate, lead to an overstimulation of NMDA receptors. Because alcoholism is associated with elevated plasma homocysteine concentrations, we designed the current study to determine whether elevated plasma homocysteine concentrations have an influence on craving in alcohol withdrawal. Two groups of patients with an established diagnosis of alcohol dependence were compared. Group A comprised 50 consecutively admitted alcohol-dependent individuals who had been abstinent from alcohol between 24 and 72 h before hospitalization. Group B comprised 146 consecutively recruited alcohol-dependent individuals who were admitted, acutely intoxicated, for withdrawal treatment. All patients were assessed with the Obsessive Compulsive Drinking Scale (OCDS) on the day of admission and after 7 days of treatment. The mean (27.1, S.D. 18.4) plasma homocysteine concentration for group B was significantly higher than the mean (12.5, S.D. 5.3) plasma homocysteine concentration for group A (Mann-Whitney U test: P < .001). No significant influence of homocysteine concentration on the extent of craving was found for either group with the use of the Spearman correlation (day 0: group A, r = -.076, P = .601; group B, r = .120, P = .148) and logistic regression analysis. Although homocysteine is a potent modulator of glutamatergic neurotransmission, results of the current study provide no evidence for a pathophysiologic role of homocysteine in withdrawal craving. Therefore, further research about alcohol craving should focus on neurobiologic factors other than homocysteine.

Effects of NMDA receptor antagonists (MK-801 and memantine) on the acquisition of morphine-induced conditioned place preference in mice

Several studies have shown that the systemic administration of a variety of N-methyl-D-aspartate (NMDA) receptor antagonists can block the development or expression of conditioned place preference (CPP) induced by rewarding drugs such as morphine. In the present study, we examined the effects of different doses of two non-competitive NMDA receptor antagonists, MK-801 (0.1, 0.2 and 0.3 mg/kg) and memantine (2.5, 5, 10, 20 and 40 mg/kg), in CPP induced by 40 mg/kg of morphine in male mice. The CPP was carried out with an unbiased procedure in terms of initial spontaneous preference. Animals received the different doses of drugs in the conditioning sessions. MK-801 and memantine, at all doses used, produced neither place preference nor place aversion, but the higher doses of memantine (20 and 40 mg/kg) were able to completely block morphine-induced CPP. The present data show that the NMDA receptor antagonists MK-801 and memantine have no reinforcing properties but memantine is capable of preventing the acquisition of morphine-induced CPP. These results suggest that the development of morphine-induced CPP may be closely related to NMDA receptors and that the glutamatergic system can modulate opiate reward.

Ionotropic Glutamate Receptor Antagonists Modulate Cue-Induced Reinstatement of Ethanol-Seeking Behavior

BACKGROUND

Glutamatergic neurotransmission has been implicated in drug-environment conditioning, but little is known about the role of glutamate in alcohol seeking maintained by alcohol-associated cues. Therefore, we examined the effects of ionotropic glutamate receptor antagonists on cue-induced ethanol-seeking behavior in the extinction/reinstatement model.

METHODS

Rats were trained to orally self-administer ethanol (10% w/v) and a nonrewarding (80 microM) quinine solution on randomly alternating days. Ethanol and quinine availability were signaled by olfactory discriminative stimuli (S+/S-). In addition, ethanol delivery was accompanied by a light stimulus (CS+) and quinine delivery by an auditory stimulus (CS-). Thereafter, rats were subjected to extinction training during which responding had no programmed consequences. Reinstatement of responding was tested under three conditions: in the presence of the S-/CS-, S+/CS+, and S+/CS+ together with a small (0.2 ml) response-contingent oral ethanol dose at the beginning of the reinstatement session (S+/CS+/priming). We examined the effects of the noncompetitive NMDA receptor antagonist MK-801 (0, 0.05, 0.15 mg/kg intraperitoneally), the competitive NMDA antagonist CGP39551 (0, 5, 10 mg/kg intraperitoneally), the NMDA/glycine receptor antagonist L-701,324 (0, 2, 4 mg/kg intraperitoneally), the AMPA/kainate receptor antagonist CNQX (0, 0.5, 1.5 mg/kg intraperitoneally), and the opioid receptor antagonist naltrexone (0, 0.3, 1 mg/kg subcutaneously) on ethanol seeking under the S+/CS+/priming condition.

RESULTS

Presentation of the S+/CS+ stimulus condition reinstated extinguished responding, whereas presentation of the S-/CS- condition did not. Response-contingent ethanol priming enhanced reinstatement further. Under these reinstatement conditions, L-701,324, CNQX, and naltrexone inhibited ethanol-seeking behavior significantly. In contrast, MK-801 and CGP39551 failed to affect reinstated responding.

CONCLUSIONS

These results show that glutamate antagonism suppresses ethanol-seeking behavior induced by ethanol-paired stimuli. Furthermore, the data suggest that ionotropic glutamate receptors may have differential roles in mediation of this behavior.

Pharmacology of acamprosate: an overview

In the last years important advances have been made in the development of drugs for the treatment of alcohol addiction. Acamprosate (calcium bis-acetylhomotaurine) is one of the better established drugs in this field on the European market. This review focuses first on the pharmacokinetics of acamprosate. The published data and the recent advances in our knowledge on the mechanisms involved in the intestinal absorption and elimination of this drug are summarized. The importance of pharmacokinetics for the proper clinical use of acamprosate is highlighted. The anti-relapse as well as the well-known effects of acamprosate on ethanol intake are discussed. The recent experiments in animal models of conditioned withdrawal are reviewed. These experiments, explored for the first time the anticraving effect of the drug. Finally, the proposed hypotheses on the neuropharmacological mechanism of action of acamprosate are discussed. The discussion deals with the relative importance of various hypotheses as well as with the recent experiments that support them. It is pointed out that further research is necessary in order to clearly understand the mode of action of acamprosate as well as the neurobiological mechanisms involved in alcohol dependence.