New perspective for an old drug: Can naloxone be considered an antioxidant agent?

Background: Experimental evidence indicates that Naloxone (NLX) holds antioxidant properties. The present study aims at verifying the hypothesis that NLX could prevent oxidative stress induced by hydrogen peroxide (H2O2) in PC12 cells. Methods: To investigate the antioxidant effect of NLX, initially, we performed electrochemical experiments by means of platinum-based sensors in a cell-free system. Subsequently, NLX was tested in PC12 cells on H2O2-induced overproduction of intracellular levels of reactive-oxygen-species (ROS), apoptosis, modification of cells' cycle distribution and damage of cells' plasma membrane. Results: This study reveals that NLX counteracts intracellular ROS production, reduces H2O2-induced apoptosis levels, and prevents the oxidative damage-dependent increases of the percentage of cells in G2/M phase. Likewise, NLX protects PC12 cells from H2O2- induced oxidative damage, by preventing the lactate dehydrogenase (LDH) release. Moreover, electrochemical experiments confirmed the antioxidant properties of NLX. Conclusion: Overall, these findings provide a starting point for studying further the protective effects of NLX on oxidative stress.

Ethanol-Dependent Synthesis of Salsolinol in the Posterior Ventral Tegmental Area as Key Mechanism of Ethanol's Action on Mesolimbic Dopamine.

Abnormal consumption of ethanol, the ingredient responsible for alcoholic drinks' addictive liability, causes millions of deaths yearly. Ethanol's addictive potential is triggered through activation, by a still unknown mechanism, of the mesolimbic dopamine (DA) system, part of a key motivation circuit, DA neurons in the posterior ventral tegmental area (pVTA) projecting to the ipsilateral nucleus accumbens shell (AcbSh). The present in vivo brain microdialysis study, in dually-implanted rats with one probe in the pVTA and another in the ipsilateral or contralateral AcbSh, demonstrates this mechanism. As a consequence of the oral administration of a pharmacologically relevant dose of ethanol, we simultaneously detect a) in the pVTA, a substance, 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (salsolinol), untraceable under control conditions, product of condensation between DA and ethanol's first by-product, acetaldehyde; and b) in the AcbSh, a significant increase of DA release. Moreover, such newly generated salsolinol in the pVTA is responsible for increasing AcbSh DA release via µ opioid receptor (µOR) stimulation. In fact, inhibition of salsolinol's generation in the pVTA or blockade of pVTA µORs prevents ethanol-increased ipsilateral, but not contralateral, AcbSh DA release. This evidence discloses the long-sought key mechanism of ethanol's addictive potential and suggests the grounds for developing preventive and therapeutic strategies against abnormal consumption.

Effects of caffeine on ethanol-elicited place preference, place aversion and ERK phosphorylation in CD-1 mice.

BACKGROUND: Epidemiological studies indicate a rise in the combined consumption of caffeinated and alcoholic beverages, which can lead to increased risk of alcoholic-beverage overconsumption. However, the effects of the combination of caffeine and ethanol in animal models related to aspects of drug addiction are still underexplored. AIMS: To characterize the pharmacological interaction between caffeine and ethanol and establish if caffeine can affect the ability of ethanol (2 g/kg) to elicit conditioned place preference and conditioned place aversion, we administered caffeine (3 or 15 mg/kg) to male CD-1 mice before saline or ethanol. Moreover, we determined if these doses of caffeine could affect ethanol (2 g/kg) elicited extracellular signal-regulated kinase phosphorylation in brain areas, nucleus accumbens, bed nucleus of stria terminalis, central nucleus of the amygdala, and basolateral amygdala, previously associated with this type of associative learning. RESULTS: In the place-conditioning paradigm, caffeine did not have an effect on its own, whereas ethanol elicited significant conditioned-place preference and conditioned-place aversion. Caffeine (15 mg/kg) significantly prevented the acquisition of ethanol-elicited conditioned-place preference and, at both doses, also prevented the acquisition of ethanol-elicited conditioned-place aversion. Moreover, both doses of caffeine also prevented ethanol-elicited extracellular signal-regulated kinase phosphorylation expression in all brain areas examined. CONCLUSIONS: The present data indicate a functional antagonistic action of caffeine and ethanol on associative learning and extracellular signal-regulated kinase phosphorylation after an acute interaction. These results could provide exciting grounds for further studies, also in a translational perspective, of their pharmacological interaction modulating other processes involved in drug consumption and addiction.

Sleep and the Pharmacotherapy of Alcohol Use Disorder: Unfortunate Bedfellows. A Systematic Review With Meta-Analysis.

Background: Sleep disorders are commonly associated with acute and chronic use of alcohol and with abstinence. To date, there are four approved drugs to treat alcohol use disorder (AUD): disulfiram, acamprosate, naltrexone, and nalmefene. These AUD therapies reduce the craving and risk of relapse into heavy drinking, but little is known about their effect on sleep. As recent evidences indicate a crucial role of sleep disorders in AUD, claiming that sleep problems may trigger alcohol abuse and relapses, it is fundamental to clarify the impact of those drugs on the sleep quality of AUD patients. This systematic review aims to answer the question: how does the pharmacotherapy for AUD affect sleep? Methods: We searched PubMed, Embase, CINAHL Plus, Cochrane, and Scopus using sleep- and AUD pharmacotherapy-related keywords. The articles included were appraised using the CASP checklists, and the risk of bias was assessed following the Cochrane risk-of-bias assessment tool. Finally, we pooled sleep outcomes in a meta-analysis to measure the overall effect. Results and Conclusion: We included 26 studies: only three studies focused on sleep as a main outcome, two with polysomnography (objective measurement), and one with subjective self-reported sleep, while all the other studies reported sleep problems among the adverse effects (subjective report). The only study available on disulfiram showed reduced REM sleep. Acamprosate showed no/little effect on self-reported sleep but improved sleep continuity and architecture measured by polysomnography. The two opioidergic drugs naltrexone and nalmefene had mainly detrimental effect on sleep, giving increased insomnia and/or somnolence compared with placebo, although not always significant. The meta-analysis confirmed significantly increased somnolence and insomnia in the naltrexone group, compared with the placebo. Overall, the currently available evidences show more sleep problems with the opioidergic drugs (especially naltrexone), while acamprosate seems to be well tolerated or even beneficial. Acamprosate might be a more suitable choice when patients with AUD report sleep problems. Due to the paucity of information available, and with the majority of results being subjective, more research on this topic is needed to further inform the clinical practice, ideally with more objective measurements such as polysomnography.

Inhibition of Morphine- and Ethanol-Mediated Stimulation of Mesolimbic Dopamine Neurons by Withania somnifera.

Morphine- and ethanol-induced stimulation of neuronal firing of ventral tegmental area (VTA) dopaminergic neurons and of dopamine (DA) transmission in the shell of the nucleus accumbens (AcbSh) represents a crucial electrophysiological and neurochemical response underlying the ability of these compounds to elicit motivated behaviors and trigger a cascade of plasticity-related biochemical events. Previous studies indicate that the standardized methanolic extract of Withania somnifera roots (WSE) prevents morphine- and ethanol-elicited conditioned place preference and oral ethanol self-administration. Aim of the present research was to investigate whether WSE may also interfere with the ability of morphine and ethanol to stimulate VTA dopaminergic neurons and thus AcbSh DA transmission as assessed in male Sprague-Dawley rats by means of patch-clamp recordings in mesencephalic slices and in vivo brain microdialysis, respectively. Morphine and ethanol significantly stimulated spontaneous firing rate of VTA neurons and DA transmission in the AcbSh. WSE, at concentrations (200-400 µg/ml) that significantly reduce spontaneous neuronal firing of VTA DA neurons via a GABAA- but not GABAB-mediated mechanism, suppressed the stimulatory actions of both morphine and ethanol. Moreover, in vivo administration of WSE at a dose (75 mg/kg) that fails to affect basal DA transmission, significantly prevented both morphine- and ethanol-elicited increases of DA in the AcbSh. Overall, these results highlight the ability of WSE to interfere with morphine- and ethanol-mediated central effects and suggest a mechanistic interpretation of the efficacy of this extract to prevent the motivational properties of these compounds.

Not Just from Ethanol. Tetrahydroisoquinolinic (TIQ) Derivatives: from Neurotoxicity to Neuroprotection.

The 1,2,3,4-tetrahydroisoquinolines (TIQs) are compounds frequently described as alkaloids that can be found in the human body fluids and/or tissues including the brain. In most circumstances, TIQs may be originated as a consequence of reactions, known as Pictet-Spengler condensations, between biogenic amines and electrophilic carbonyl compounds, including ethanol's main metabolite, acetaldehyde. Several TIQs may also be synthesized enzymatically whilst others may be formed in the body as by-products of other compounds including TIQs themselves. The biological actions of TIQs appear critically dependent on their metabolism, and nowadays, among TIQs, 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (salsolinol), N-methyl-1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (N-methyl-(R)-salsolinol), 1-[(3,4-dihydroxyphenyl)methyl]-1,2,3,4-tetrahydroisoquinoline-6,7-diol (norlaudanosoline or tetrahydropapaveroline or THP) and 1-benzyl-1,2,3,4-tetrahydroisoquinoline (1BnTIQ) are considered as those endowed with the most potent neurotoxic actions. However, it remains to be established whether a continuous exposure to TIQs or to their metabolites might carry toxicological consequences in the short- or long-term period. Remarkably, recent findings suggest that some TIQs such as (1-[(4-hydroxyphenyl)methyl]-1,2,3,4-tetrahydroisoquinoline-6,7-diol) (higenamine) and 1-methyl-1,2,3,4-tetrahydroisoquinoline (1-MeTIQ) as well as N-methyl-tetrahydroisoquinoline (N-methyl-TIQ) exert unique neuroprotective and neurorestorative actions. The present review article provides an overview on these aspects of TIQs and summarizes those that presently appear the most significant highlights on this puzzling topic.

Is catalase involved in the effects of systemic and pVTA administration of 4-methylpyrazole on ethanol self-administration?

The oxidative metabolism of ethanol into acetaldehyde involves several enzymes, including alcohol dehydrogenase (ADH) and catalase-hydrogen peroxide (H2O2). In this regard, while it is well known that 4-methylpyrazole (4-MP) acts by inhibiting ADH in the liver, little attention has been placed on its ability to interfere with fatty acid oxidation-mediated generation of H2O2, a mechanism that may indirectly affect catalase whose enzymatic activity requires H2O2. The aim of our investigation was twofold: 1) to evaluate the effect of systemic (i.p. [intraperitoneal]) and local (into the posterior ventral tegmental area, pVTA) administration of 4-MP on oral ethanol self-administration, and 2) to assess ex vivo whether or not systemic 4-MP affects liver and brain H2O2 availability. The results show that systemic 4-MP reduced ethanol but not acetaldehyde or saccharin self-administration, and decreased the ethanol deprivation effect. Moreover, local intra-pVTA administration of 4-MP reduced ethanol but not saccharin self-administration. In addition, although unable to affect basal catalase activity, systemic administration of 4-MP decreased H2O2 availability both in liver and in brain. Overall, these results indicate that 4-MP interferes with ethanol self-administration and suggest that its behavioral effects could be due to a decline in catalase-H2O2 system activity as a result of a reduction of H2O2 availability, thus highlighting the role of central catalase-mediated metabolism of ethanol and further supporting the key role of acetaldehyde in the reinforcing properties of ethanol.

Mystic Acetaldehyde: The Never-Ending Story on Alcoholism.

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

Differential effects of the MEK inhibitor SL327 on the acquisition and expression of ethanol-elicited conditioned place preference and aversion in mice.

The involvement of mitogen-activating extracellular kinase (MEK) in place conditioning may vary depending on the motivational sign (positive or negative) and nature (pharmacological or nociceptive) of the unconditioned stimulus (US) and on the phase (acquisition or expression) of the learning process. This study investigated the role of MEK on the acquisition and expression of ethanol-elicited (given 2 g/kg) backward (preference, CPP) and forward (aversion, CPA) place conditioning. The MEK inhibitor SL327 (50 mg/kg for CPP, and 50 and 100 mg/kg for CPA) was administered to CD-1 mice 60 minutes before an ethanol dose (acquisition) or 60 minutes before the post-conditioning tests (expression). Ethanol significantly elicited CPP and CPA; SL327 (50 mg/kg) significantly blocked the acquisition of ethanol-elicited CPP, but not that of CPA. Moreover, SL327 (50 and 100 mg/kg) significantly reduced the expression of ethanol-elicited CPP, but not that of CPA. Finally, SL327 also prevented ethanol-elicited (given 2 g/kg) increases of phosphorylated extracellular signal regulated kinase (pERK)-positive neurons in the nucleus accumbens and other nuclei of the extended amygdala. Overall, these results confirmed the differential involvement of MEK in the acquisition and expression of drug-elicited place conditioning and suggested its differential involvement in distinct behavioral outcomes, depending on the motivational sign of the (same) US and on the significance of the experimental phase of the learning process.

From Ethanol to Salsolinol: Role of Ethanol Metabolites in the Effects of Ethanol.

In spite of the global reputation of ethanol as the psychopharmacologically active ingredient of alcoholic drinks, the neurobiological basis of the central effects of ethanol still presents some dark sides due to a number of unanswered questions related to both its precise mechanism of action and its metabolism. Accordingly, ethanol represents the interesting example of a compound whose actions cannot be explained as simply due to the involvement of a single receptor/neurotransmitter, a scenario further complicated by the robust evidence that two main metabolites, acetaldehyde and salsolinol, exert many effects similar to those of their parent compound. The present review recapitulates, in a perspective manner, the major and most recent advances that in the last decades boosted a significant growth in the understanding on the role of ethanol metabolism, in particular, in the neurobiological basis of its central effects.

Role of nucleus accumbens µ opioid receptors in the effects of morphine on ERK1/2 phosphorylation.

RATIONALE: Despite the critical role attributed to phosphorylated extracellular signal regulated kinase (pERK1/2) in the nucleus accumbens (Acb) in the actions of addictive drugs, the effects of morphine on ERK1/2 phosphorylation in this area are still controversial. OBJECTIVES: In order to investigate further this issue, we studied (1) the ability of morphine to affect ERK1/2 phosphorylation in the shell (AcbSh) and core (AcbC) of Sprague-Dawley and Wistar rats and of CD-1 and C57BL/6J mice and (2) the role of dopamine D1 and µ-opioid receptors in Sprague-Dawley rats and CD-1 mice. METHODS: The pERK1/2 expression was assessed by immunohistochemistry. RESULTS: In rats, morphine decreased AcbSh and AcbC pERK1/2 expression, whereas in mice, increased it preferentially in the AcbSh compared with the AcbC. Systemic SCH 39166 decreased pERK1/2 expression on its own in the AcbSh and AcbC of Sprague-Dawley rats and CD-1 mice; furthermore, in rats, SCH 39166 disclosed the ability of morphine to stimulate pERK1/2 expression. Systemic (rats and mice) and intra-Acb (rats) naltrexone prevented both decreases, in rats, and increases, in mice. CONCLUSIONS: These findings confirm the differential effects of morphine in rats and mice Acb and that D1 receptors exert a facilitatory role on ERK1/2 phosphorylation; furthermore, they indicate that, in rats, removal of the D1-dependent pERK1/2 expression discloses the stimulatory influence of morphine on ERK1/2 phosphorylation and that the morphine's ability to decrease pERK1/2 expression is mediated by Acb µ-opioid receptors. Future experiments may disentangle the psychopharmacological significance of the effects of morphine on pERK1/2 in the Acb.

Withania somnifera Dunal (Indian ginseng) impairs acquisition and expression of ethanol-elicited conditioned place preference and conditioned place aversion.

Withania somnifera Dunal (Indian Ginseng) has recently been shown to impair ethanol self-administration. In order to gain further insights on the ability of the Withania somnifera standardised root extract (WSE) to affect the motivational properties of ethanol, this study investigated whether WSE may also affect ethanol (2 g/kg)-elicited conditioned place preference (CPP) and aversion (CPA). To this end male CD-1 mice were conditioned under two distinct schedules: in backward conditioning experiments ethanol was administered before mice were placed in the conditioning apparatus (CPP) while, in forward conditioning experiments, ethanol was administered immediately after removing mice from the apparatus (CPA). Following these schedules, mice developed significant CPP and CPA, respectively. Administration of WSE significantly impaired both the acquisition (50 and 100 mg/kg) and the expression (50 mg/kg) of CPP and CPA without affecting spatial memory (50 mg/kg), as determined by a two-trial memory recognition task. Overall, the study highlights the ability of WSE to interfere with both positive and negative motivational properties of ethanol and suggests that the effects of WSE may target both ethanol's motivational properties and underpinning associative learning mechanisms. In conclusion, these results cast new light on Withania somnifera as an agent potentially useful to counteract distinct aspects of ethanol effects.

Role of ethanol-derived acetaldehyde in operant oral self-administration of ethanol in rats.

RATIONALE: The role of ethanol-derived acetaldehyde has not been examined yet on performance in a model of operant oral self-administration. However, previous studies reported that an acetaldehyde-sequestering agent, D-penicillamine (DP) and an inhibitor of catalase-mediated acetaldehyde production, 3-amino-1,2,4-triazole (3-AT) reduce voluntary ethanol consumption. OBJECTIVES: The aim of our investigation was to evaluate the effects of DP and 3-AT on acquisition and maintenance of oral operant ethanol self-administration. METHODS: Using operant chambers, rats learned to nose poke in order to receive ethanol solution (5-10 % v/v) under an FR1 schedule of reinforcement in which discrete light and tone cues were presented during ethanol delivery. RESULTS: DP and 3-AT impair the acquisition of ethanol self-administration, whereas its maintenance is not affected neither by drug given alone for both 10 or 5 % ethanol nor by drugs association for 5 % ethanol. Moreover, when the concentration of ethanol was diminished from 10 to 5 %, rats increased the rate of self-administration behaviour. CONCLUSIONS: These findings suggest that brain acetaldehyde plays a critical role during acquisition of operant self-administration in ethanol-naïve rats. In contrast, during the maintenance phase, acetaldehyde could contribute to ethanol self-administration by a combined mechanism: On one hand, its lack (by DP or 3-AT) might result in further ethanol-seeking and taking and, on the other, inhibition of ethanol metabolism (by 3-AT) might release an action of the un-metabolised fraction of ethanol that does not overall result in compromising maintenance of ethanol self-administration.

Change of cystine/glutamate antiporter expression in ethanol-dependent rats.

BACKGROUND: Some drugs of abuse down regulate the expression of cystine/glutamate (xCT) antiporter in the nucleus accumbens (Acb) after extinction or withdrawal. The altered level of xCT exchanger in Acb, a structure involved in ethanol reinforcement, may contribute to the pathological glutamatergic signaling, linked to addiction. We hypothesized that the expression of xCT may be changed in Acb and whole brain also in non-dependent (occasional drinkers), ethanol-dependent rats, as well as, during ethanol withdrawal. METHODS: Wistar rats were made ethanol-dependent by chronic exposure to an alcoholic milk beverage (from 2.4 to 7.2% v/v ethanol). Ethanol non-dependent rats were exposed to a similar, but non-alcoholic liquid diet and self-administered ethanol (10%) twice a week. Withdrawal in ethanol-dependent rats was studied at 12 h after the last ethanol-enriched diet exposure. Immediately after the measurement of somatic signs of withdrawal, Western blot analysis with a polyclonal antibody against xCT was carried out in a naïve control group, non-dependent and ethanol-dependent rats as well as withdrawal rats, in order to study the level of xCT expression in Acb and whole brain. RESULTS: Non-dependent rats self-administered an average dose of 1.21 ± 0.02 g/kg per session (30 min). Daily ethanol consumption during chronic exposure to the alcoholic beverage ranged from 6.30 ± 0.16 to 13.99 ± 0.66 g/kg. Ethanol dependent rats after suspension of the ethanol-enriched diet have shown significant somatic signs of withdrawal. Western blotting analysis of Acb lysates revealed that xCT was over expressed in ethanol-dependent rats whereas in whole brain preparations xCT was over expressed in both non-dependent and ethanol-dependent rats compared to control group. On the contrary, xCT expression during withdrawal was down regulated in Acb and restored to control level in whole brain preparations. CONCLUSIONS: The changes of xCT expression in both Acb and whole brain following ethanol dependence and withdrawal indicate that xCT might represent a novel therapeutic target for the treatment of ethanol addiction.

Effects of Withania somnifera on oral ethanol self-administration in rats.

Recent evidence has shown that Withania somnifera Dunal (Ashwagandha or Indian ginseng), a herbal remedy used in traditional medicine, impairs morphine-elicited place conditioning. Here, we investigated the effect of W. somnifera roots extract (WSE) on motivation for drinking ethanol using operant self-administration paradigms. Wistar rats were trained to self-administer ethanol (10%) by nose-poking. The effects of WSE (25-75 mg/kg) were evaluated on acquisition and maintenance, on ethanol breakpoint under a progressive-ratio schedule of reinforcement and on the deprivation effect and reinstatement of seeking behaviours. Moreover, on the basis of the recent suggestion of an involvement of GABAB receptors in WSE central effects, we studied the interaction between WSE and GABAB ligands. The effect of WSE on saccharin (0.05%) oral self-administration was also tested. The results show that WSE reduced the acquisition, maintenance and breakpoint of ethanol self-administration. WSE also reduced the deprivation effect, reinstatement of ethanol-seeking behaviours and saccharin reinforcement. Furthermore, the GABAB receptor antagonist, phaclofen, counteracted the ability of WSE to impair the maintenance of ethanol self-administration. These findings show that WSE, by an action that may involve GABAB receptors, impairs motivation for drinking ethanol and suggest that further investigations should be performed to determine whether W. somnifera may represent a new approach for the management of alcohol abuse.

Behavioral and biochemical evidence of the role of acetaldehyde in the motivational effects of ethanol.

Since Chevens' report, in the early 50's that his patients under treatment with the aldehyde dehydrogenase inhibitor, antabuse, could experience beneficial effects when drinking small volumes of alcoholic beverages, the role of acetaldehyde (ACD) in the effects of ethanol has been thoroughly investigated on pre-clinical grounds. Thus, after more than 25 years of intense research, a large number of studies have been published on the motivational properties of ACD itself as well as on the role that ethanol-derived ACD plays in the effects of ethanol. Accordingly, in particular with respect to the motivational properties of ethanol, these studies were developed following two main strategies: on one hand, were aimed to challenge the suggestion that also ACD may exert motivational properties on its own, while, on the other, with the aid of enzymatic manipulations or ACD inactivation, were aimed to test the hypothesis that ethanol-derived ACD might have a role in ethanol motivational effects. Furthermore, recent evidence significantly contributed to highlight, as possible mechanisms of action of ACD, its ability to commit either dopaminergic and opioidergic transmission as well as to activate the Extracellular signal Regulated Kinase cascade transduction pathway in reward-related brain structures. In conclusion, and despite the observation that ACD seems also to have inherited the elusive nature of its parent compound, the behavioral and biochemical evidence reviewed points to ACD as a neuroactive molecule able, on its own and as ethanol metabolite, to exert motivational effects.

Alpha-lipoic acid reduces ethanol self-administration in rats.

BACKGROUND: The main system of central ethanol (EtOH) oxidation is mediated by the enzyme catalase. By reacting with H2 O2 , brain catalase forms compound I (the catalase-H2 O2 system), which is able to oxidize EtOH to acetaldehyde (ACD) in the brain. We have previously shown that ACD regulates EtOH motivational properties and possesses reinforcing effects by itself. In this study, we investigate the effects of alpha-lipoic acid (ALA), a scavenging agent for H2 O2 , on oral EtOH self-administration. METHODS: To this end, we trained Wistar rats to orally self-administer EtOH (10%) by nose poking. The effect of intraperitoneal pretreatment with ALA was evaluated during (i) maintenance of EtOH self-administration, (ii) EtOH self-administration under a progressive ratio (PR) schedule of reinforcement, and (iii) oral EtOH priming to induce reinstatement of EtOH seeking behavior. Moreover, we tested the effect of ALA on saccharin (0.05%) reinforcement, as assessed by oral self-administration. RESULTS: The results indicate that ALA dose-dependently reduced the maintenance, the break point of EtOH self-administration under a PR and the reinstatement of EtOH seeking behavior without suppressing saccharin self-administration. CONCLUSIONS: These results support that ALA may have a potential use in alcoholism treatment.

Effects of L-cysteine on reinstatement of ethanol-seeking behavior and on reinstatement-elicited extracellular signal-regulated kinase phosphorylation in the rat nucleus accumbens shell.

BACKGROUND: Alcoholism is a neuroadaptive disorder, and the understanding of the mechanisms of the high rates of relapse, which characterize it, represents one of the most demanding challenges in alcoholism and addiction research. The extracellular signal-regulated kinase (ERK) is an intracellular kinase, critical for neuroplasticity in the adult brain that is suggested to play a fundamental role in the molecular mechanisms underlying drug addiction and relapse. We previously observed that a nonessential amino acid, L-cysteine, significantly decreases oral ethanol (EtOH) self-administration, reinstatement of EtOH-drinking behavior, and EtOH self-administration break point. METHODS: Here, we tested whether L-cysteine can affect the ability of EtOH priming to induce reinstatement of EtOH-seeking behavior. In addition, we determined the ability of EtOH priming to induce ERK phosphorylation as well as the ability of L-cysteine to affect reinstatement-elicited ERK activation. To these purposes, Wistar rats were trained to nose-poke for a 10% v/v EtOH solution. After stable drug-taking behavior was obtained, nose-poking for EtOH was extinguished, and reinstatement of drug seeking, as well as reinstatement-elicited pERK, was determined after an oral, noncontingent, priming of EtOH (0.08 g/kg). Rats were pretreated with either saline or L-cysteine (80 to 120 mg/kg) 30 minutes before testing for reinstatement. RESULTS: The findings of this study confirm that the noncontingent delivery of a nonpharmacologically active dose of EtOH to rats, whose previous self-administration behavior had been extinguished, results in significant reinstatement into EtOH-seeking behavior. In addition, the results indicate that reinstatement selectively activates ERK phosphorylation in the shell of the nucleus accumbens (Acb) and that pretreatment with L-cysteine reduces either reinstatement of EtOH seeking and reinstatement-elicited pERK in the AcbSh. CONCLUSIONS: Altogether, these results indicate that L-cysteine could be an effective pharmacological agent for the prevention of behavioral and molecular correlates of EtOH-primed reinstatement of EtOH seeking and that the shell of the Acb represents a critical neural substrate for priming-elicited reinstatement mechanisms involving ERK phosphorylation.

Effect of (L)-cysteine on acetaldehyde self-administration.

Acetaldehyde (ACD), the first metabolite of ethanol, has been implicated in several behavioural actions of alcohol, including its reinforcing effects. Recently, we reported that l-cysteine, a sequestrating agent of ACD, reduced oral ethanol self-administration and that ACD was orally self-administered. This study examined the effects of l-cysteine pre-treatment during the acquisition and maintenance phases of ACD (0.2%) self-administration as well as on the deprivation effect after ACD extinction and on a progressive ratio (PR) schedule of reinforcement. In a separate PR schedule of reinforcement, the effect of l-cysteine was assessed on the break-point produced by ethanol (10%). Furthermore, we tested the effect of l-cysteine on saccharin (0.2%) reinforcement. Wistar rats were trained to self-administer ACD by nose poking on a fixed ratio (FR1) schedule in 30-min daily sessions. Responses on an active nose-poke caused delivery of ACD solution, whereas responses on an inactive nose-poke had no consequences. l-cysteine reduced the acquisition (40 mg/kg), the maintenance and the deprivation effect (100 mg/kg) of ACD self-administration. Furthermore, at the same dose, l-cysteine (120 mg/kg) decreased both ACD and ethanol break point. In addition, l-cysteine was unable to suppress the different responses for saccharin, suggesting that its effect did not relate to an unspecific decrease in a general motivational state. Compared to saline, l-cysteine did not modify responses on inactive nose-pokes, suggesting an absence of a non-specific behavioural activation. Taken together, these results could support the hypotheses that ACD possesses reinforcing properties and l-cysteine reduces motivation to self-administer ACD.

Piecing together the puzzle of acetaldehyde as a neuroactive agent.

Mainly known for its more famous parent compound, ethanol, acetaldehyde was first studied in the 1940s, but then research interest in this compound waned. However, in the last two decades, research on acetaldehyde has seen a revitalized and uninterrupted interest. Acetaldehyde, per se, and as a product of ethanol metabolism, is responsible for many pharmacological effects which are not clearly distinguishable from those of its parent compound, ethanol. Consequently, the most recent advances in acetaldehyde's psychopharmacology have been inspired by the experimental approach to test the hypothesis that some of the effects of ethanol are mediated by acetaldehyde and, in this regard, the characterization of metabolic pathways for ethanol and the localization within discrete brain regions of these effects have revitalized the interest on the role of acetaldehyde in ethanol's central effects. Here we present and discuss a wealth of experimental evidence that converges to suggest that acetaldehyde is an intrinsically active compound, is metabolically generated in the brain and, finally, mediates many of the psychopharmacological properties of ethanol.