Ethanol exposure decreases glutamate uptake in the nucleus accumbens

β_lactam antibiotics against drug addiction: A novel therapeutic option

Drug addiction as a problem for the health of the individual and the society is the result of a complex process in which there is an interaction between brain nuclei and neurotransmitters (such as glutamate). β-lactam antibiotics, due to their enhancing properties on the glutamate transporter glutamate transporter-1, can affect and counteract the addictive mechanisms of drugs through the regulation of extracellular glutamate. Since glutamate is a key neurotransmitter in the development of drug addiction, it seems that β-lactams can be considered as a promising treatment for addiction. However, more research in this field is necessary to identify other mechanisms involved in their effectiveness. This article is a review of the studies conducted on the effect of β-lactam administration in preventing the development of drug addiction, as well as their possible cellular and molecular mechanisms. This review suggests the clinical use of β-lactam antibiotics that have weak antimicrobial properties (such as clavulanic acid) in the treatment of drug dependence.

Clavulanic Acid Improves Memory Dysfunction and Anxiety Behaviors through Upregulating Glutamatergic Transporters in the Nucleus Accumbens of Mice Repeatedly Exposed to Khat Extract

Khat (Catha edulis) is an evergreen shrub whose buds and leaves give a state of delight and euphoria when chewed. Cathinone, an amphetamine-like stimulant that is among the active ingredients in khat, is able to downregulate glutamate transporter subtype I (GLT-1). Neurobehavioral dysfunctions such as altered locomotor activity, anorexia, and nociception have been observed in animals exposed to cathinone. Interestingly, treatment with a β-lactam antibiotic such as ceftriaxone, which upregulates GLT-1, normalizes cathinone-induced conditioned place preference, and alters repetitive movements in rats. However, little is known about the role of the glutamatergic system in memory dysfunction and anxiety-like behaviors in mice exposed to khat. We found here that clavulanic acid, a β-lactam-containing compound and GLT-1 upregulator, would modulate the neurobehavioral changes, including memory impairment and anxiety-like behaviors, associated with repeated exposure of mice to khat. Our data supported that clavulanic acid could improve memory impairment and anxiety-like behaviors through upregulating GLT-1 in the nucleus accumbens (NAc), an effect abolished with a selective GLT-1 blocker. This upregulation was associated with restored glutamate/cystine antiporter expression in the NAc using a Western blotting assay. Cathine and cathinone were identified in khat extract using the gas chromatography technique. Our work provides preclinical insight into the efficacy of β-lactam-containing compounds for the attenuation of neurobehavioral changes induced by khat exposure.

A novel monobactam lacking antimicrobial activity, MC-100093, reduces sex-specific ethanol preference and depressive-like behaviors in mice

Several β-lactam derivatives upregulate astrocytic glutamate transporter type 1expression and are known to improve measures in models of mood and alcohol use disorders (AUD) through normalizing glutamatergic states. However, long-term, and high doses of β-lactams may cause adverse side effects for treating mood disorders and AUD. Studies suggest that MC-100093, a novel β-lactam lacking antimicrobial activity, rescues GLT1 expression. Thus, we sought to investigate whether MC-100093 improves affective behaviors and reduces voluntary ethanol drinking. We intraperitoneally administered MC-100093 (50 mg/kg) or vehicle once per day to C57BL/6J male and female mice (8-10 weeks old) over 6 days. We employed the open field test and the elevated plus maze to examine the effect of MC-100093 on anxiety-like behaviors. We assayed MC-100093's effects on depressive-like behaviors using the tail suspension and forced swim tests. Next, utilizing a separate cohort of male and female C57BL6 mice, we assessed the effects MC100093 treatment on voluntary ethanol drinking utilizing the 2-bottle choice continuous access drinking paradigm. After screening and selecting high-drinking mice, we systematically administered MC-100093 (50 mg/kg) or vehicle to the high-drinking mice over 6 days. Overall, we found that MC-100093 treatment resulted in sex-specific pharmacological effects with female mice displaying reduced innate depressive-like behaviors during the tail suspension and force swim testing juxtaposed with male treated mice who displayed no changes in tail suspension and a paradoxical increased depressive-like behavior during the forced swim testing. Additionally, we found that MC100093 treatment reduced female preference for 10% EtOH during the 2-bottle choice continuous access drinking with no effects of MC100093 treatment detected in male mice. Overall, this data suggests sex-specific regulation of innate depressive-like behavior and voluntary EtOH drinking by MC100093 treatment. Western blot analysis of the medial prefrontal cortex and hippocampus revealed no changes in male or female GLT1 protein abundance relative to GAPDH.

The administration of Alda-1, an activator of ALDH2, inhibits relapse-like ethanol intake in female alcohol-preferring UChB rats

AIMS

Alcohol relapse is a main limitation for the treatment of alcohol use disorders. Previous studies have shown that Alda-1, a pharmacological activator of ALDH2, inhibits both acquisition and chronic ethanol intake in rats; however, its effects on relapse-like ethanol intake are unknown. The aim of this study was to assess the effect of Alda-1 on post-deprivation and reaccess relapse-like ethanol intake in alcohol-preferring UChB rats. We also aimed to assess the possible mechanisms associated with the effects of Alda-1 by measuring the levels of glutamate transporter (GLT-1), oxidative stress and neuroinflammation markers in different regions of the mesocorticolimbic system.

MAIN METHODS

In Experiment I, UChB female rats were exposed for 100 days to voluntary ethanol intake followed by 2-weeks of ethanol withdrawal and 1 week of ethanol reaccess. Alda-1 (25 mg/kg, intragastric, i.g) or vehicle was administered daily for 14 days during the withdrawal/re-access period. Experiment II was similar to Experiment I, but after the withdrawal period, ethanol re-access was not allowed, and Alda-1 was administered during the last week of withdrawal. At the end of both experiments, the levels of GLT-1, oxidative stress (GSH, MDA), and neuroinflammation markers (GFAP, Iba-1) were assessed in nucleus accumbens and/or hippocampus.

KEY FINDINGS

The results showed that Alda-1 administration markedly blocked (90 %, p < 0.001) relapse-like ethanol intake in UChB rats. Alda-1 increased Iba-1 reactivity (microglial marker) in the NAc of ethanol-deprived rats. Alda-1 administration did not influence the levels of GLT-1, oxidative stress markers (MDA, GSH) or GFAP reactivity in the mesocorticolimbic system.

SIGNIFICANCE

These preclinical findings support the use of activators of ALDH2, such as Alda-1, as a potential pharmacological strategy in the treatment of alcohol relapse.

N-Acetylcysteine normalizes brain oxidative stress and neuroinflammation observed after protracted ethanol abstinence: a preclinical study in long-term ethanol-experienced male rats

RATIONALE

Using a preclinical model based on the Alcohol Deprivation Effect (ADE), we have reported that N-Acetylcysteine (NAC) can prevent the relapse-like drinking behaviour in long-term ethanol-experienced male rats.

OBJECTIVES

To investigate if chronic ethanol intake and protracted abstinence affect several glutamate transporters and whether NAC, administered during the withdrawal period, could restore the ethanol-induced brain potential dysfunctions. Furthermore, the antioxidant and anti-inflammatory effects of NAC during abstinence in rats under the ADE paradigm were also explored.

METHODS

The expression of GLT1, GLAST and xCT in nucleus accumbens (Nacc) and dorsal striatum (DS) of male Wistar was analysed after water and chronic ethanol intake. We used the model based on the ADE within another cohort of male Wistar rats. During the fourth abstinence period, rats were treated for 9 days with vehicle or NAC (60, 100 mg/kg; s.c.). The effects of NAC treatment on (i) glutamate transporters expression in the Nacc and DS, (ii) the oxidative status in the hippocampus (Hip) and amygdala (AMG) and (iii) some neuroinflammatory markers in prefrontal cortex (PFC) were tested.

RESULTS

NAC chronic administration during protracted abstinence restored oxidative stress markers (GSSG and GGSH/GSH) in the Hip. Furthermore, NAC was able to normalize some neuroinflammation markers in PFC without normalizing the observed downregulation of GLT1 and GLAST in Nacc.

CONCLUSIONS

NAC restores brain oxidative stress and neuroinflammation that we previously observed after protracted ethanol abstinence in long-term ethanol-experienced male rats. This NAC effect could be a plausible mechanism for its anti-relapse effect. Also, brain oxidative stress and neuroinflammation could represent and identify plausible targets for searching new anti-relapse pharmacotherapies.

Ceftriaxone as a Novel Therapeutic Agent for Hyperglutamatergic States: Bridging the Gap Between Preclinical Results and Clinical Translation

Dysregulation of glutamate homeostasis is a well-established core feature of neuropsychiatric disorders. Extracellular glutamate concentration is regulated by glutamate transporter 1 (GLT-1). The discovery of a beta-lactam antibiotic, ceftriaxone (CEF), as a safe compound with unique ability to upregulate GLT-1 sparked the interest in testing its efficacy as a novel therapeutic agent in animal models of neuropsychiatric disorders with hyperglutamatergic states. Indeed, more than 100 preclinical studies have shown the efficacy of CEF in attenuating the behavioral manifestations of various hyperglutamatergic brain disorders such as ischemic stroke, amyotrophic lateral sclerosis (ALS), seizure, Huntington’s disease, and various aspects of drug use disorders. However, despite rich and promising preclinical data, only one large-scale clinical trial testing the efficacy of CEF in patients with ALS is reported. Unfortunately, in that study, there was no significant difference in survival between placebo- and CEF-treated patients. In this review, we discussed the translational potential of preclinical efficacy of CEF based on four different parameters: (1) initiation of CEF treatment in relation to induction of the hyperglutamatergic state, (2) onset of response in preclinical models in relation to onset of GLT-1 upregulation, (3) mechanisms of action of CEF on GLT-1 expression and function, and (4) non-GLT-1-mediated mechanisms for CEF. Our detailed review of the literature brings new insights into underlying molecular mechanisms correlating the preclinical efficacy of CEF. We concluded here that CEF may be clinically effective in selected cases in acute and transient hyperglutamatergic states such as early drug withdrawal conditions.

Astroglia in the Vulnerability and Maintenance of Alcohol Use Disorders

Changes induced in the morphology and the multiplicity of functional roles played by astrocytes in brain regions critical to the establishment and maintenance of alcohol abuse suggest that they make an important contribution to the vulnerability to alcohol use disorders. The understanding of the relevant mechanisms accounting for that contribution is complicated by the fact that alcohol itself acts directly on astrocytes altering their metabolism, gene expression, and plasticity, so that the ultimate result is a complex interaction of various cellular pathways, including intracellular calcium regulation, neuroimmune responses, and regulation of neurotransmitter and gliotransmitter release and uptake. The recent years have seen a steady increase in the characterization of several of the relevant mechanisms, but much remains to be done for a full understanding of the astrocytes' contribution to the vulnerability to alcohol dependence and abuse and for using that knowledge in designing effective therapies for AUDs.

Effects of ceftriaxone on ethanol drinking and GLT-1 expression in ethanol dependence and relapse drinking

Repeated cycles of chronic intermittent ethanol (CIE) exposure increase voluntary consumption of alcohol (ethanol) in mice. Previous reports from our laboratory show that CIE increases extracellular glutamate in the nucleus accumbens (NAc) and that manipulating accumbal glutamate concentrations will alter ethanol drinking, indicating that glutamate homeostasis plays a crucial role in ethanol drinking in this model. A number of studies have shown that ceftriaxone increases GLT-1 expression, the major glutamate transporter, and that treatment with this antibiotic reduces ethanol drinking. The present studies examined the effects of ceftriaxone on ethanol drinking and GLT-1 in a mouse model of ethanol dependence and relapse drinking. The results show that ceftriaxone did not influence drinking at any dose in either ethanol-dependent or non-dependent mice. Further, ceftriaxone did not increase GLT-1 expression in the accumbens core or shell, with the exception of the ethanol-dependent mice receiving the highest dose of ceftriaxone. Interestingly, ethanol-dependent mice treated with only vehicle displayed reduced expression of GLT-1 in the accumbens shell and of the presynaptic mGlu2 receptor in the accumbens core. The reduced expression of the major glutamate transporter (GLT-1), as well as a receptor that regulates glutamate release (mGlu2), may help explain, at least in part, increased glutamatergic transmission in this model of ethanol dependence and relapse drinking.

Effect of Modulation of the Astrocytic Glutamate Transporters' Expression on Cocaine-Induced Reinstatement in Male P Rats Exposed to Ethanol

AIM

Reinforcing properties of ethanol and cocaine are mediated in part through the glutamatergic system. Extracellular glutamate concentration is strictly maintained through several glutamate transporters, such as glutamate transporter 1 (GLT-1), cystine/glutamate transporter (xCT) and glutamate aspartate transporter (GLAST). Previous findings revealed that cocaine and ethanol exposure downregulated GLT-1 and xCT, and that β-lactam antibiotics restored their expression.

METHODS

In this study, we investigated the effect of ampicillin/sulbactam (AMP/SUL) (200 mg/kg, i.p.), a β-lactam antibiotic, on cocaine-induced reinstatement and locomotor activity in male alcohol preferring (P) rats using free choice ethanol (15 and 30%, v/v) and water. We also investigated the effect of co-exposure to ethanol and cocaine (20 mg/kg, i.p.) on GLT-1, xCT and GLAST expression in the nucleus accumbens (NAc) core, NAc shell and dorsomedial prefrontal cortex (dmPFC).

RESULTS

Cocaine exposure decreased ethanol intake and preference. Cocaine and ethanol co-exposure acquired place preference and increased locomotor activity compared to ethanol-exposed rats. GLT-1 and xCT expression were downregulated after cocaine and ethanol co-exposure in the NAc core and shell, but not in dmPFC. AMP/SUL attenuated reinstatement to cocaine as well attenuated the decrease in locomotor activity and ethanol intake and preference. These effects were associated with upregulation of GLT-1 and xCT expression in the NAc core/shell and dmPFC. GLAST expression was not affected after ethanol and cocaine co-exposure or AMP/SUL treatment.

CONCLUSION

Our findings demonstrate that astrocytic glutamate transporters within the mesocorticolimbic area are critical targets in modulating cocaine-seeking behavior while being consuming ethanol.

Effects of N-acetylcysteine treatment on ethanol's rewarding properties and dopaminergic alterations in mesocorticolimbic and nigrostriatal pathways

Recent reports have shown that N-acetylcysteine (N-AC) has beneficial effects in the treatment of cocaine and nicotine abuse. Considering the similar neurobiologic mechanisms involved in the development of addiction to different drugs, N-AC treatment could be useful in the treatment of ethanol abuse. The rewarding properties of the drugs of abuse plays an important role in the development of addiction and can be studied using the conditioned place preference (CPP) paradigm. Thus, to study the effects of N-AC treatment in the rewarding effects of ethanol, we investigated the effects of N-AC administration in the ethanol-induced CPP and neurochemical alterations within the mesocorticolimbic and the nigrostriatal dopaminergic pathways. Adult male Swiss mice were pretreated with N-AC (60 or 120 mg/kg intraperitoneal) and tested for the development, expression, or extinction of the ethanol-induced CPP. Another cohort of animals received N-AC (60 or 120 mg/kg intraperitoneal) 2-h before an acute administration of ethanol and had their brains removed for dopamine and its metabolites quantification in the mesocorticolimbic and nigrostriatal pathways. Pretreatment with N-AC (120 mg/kg) blocked the development of ethanol-induced CPP. On the other hand, N-AC at both doses did not alter the expression nor the extinction of ethanol-induced CPP. N-AC increased 3,4-dihydroxyphenylacetic acid content in the medial prefrontal cortex and dopaminergic turnover within the substantia nigra. Besides that, there was an increase in dopamine content in the nucleus accumbens of ethanol-treated animals. In summary, N-AC treatment blocked the development of ethanol CPP, without altering ethanol effects on dopaminergic neurotransmission.

Enduring dysregulation of nucleus accumbens catecholamine and glutamate transmission by developmental exposure to phenylpropanolamine

For over 50 years, the sympathomimetic phenylpropanolamine (PPA; ±-norephedrine) was a primary active ingredient in over-the-counter nasal decongestants for both children and adults and continues to be prevalent in the vast majority of countries today. Previously, we reported that juvenile PPA exposure alters the developmental trajectory of catecholamine and amino acid neurotransmitter systems in the nucleus accumbens (NAC), impacting the motivational valence of cocaine in later life. The present study employed a combination of in vivo microdialysis and immunoblotting approaches to better understand how juvenile PPA exposure impacts catecholamine and glutamate function within the NAC. For this, C57BL/6J mice were pretreated repeatedly with PPA (0 or 40 mg/kg) during postnatal days 21-33. Starting at 70 days of age, the function and expression of receptors and transporters regulating extracellular dopamine and glutamate were determined. Juvenile PPA pretreatment completely abolished the capacity of selective dopamine and epinephrine reuptake inhibitors to increase NAC levels of both catecholamines, without impacting D2 or α2 receptor regulation of catecholamine release. Juvenile PPA pretreatment facilitated the rise in NAC glutamate elicited by dopamine, norepinephrine and glutamate transporter inhibitors and blunted mGlu2/3 inhibition of glutamate release in this region. These data confirm that juvenile exposure to PPA produces protracted perturbations in the regulation of extracellular catecholamine and glutamate levels within the NAC and further the hypothesis that early exposure to sympathomimetic drugs found in cough, cold and allergy medicines, have long-lasting effects upon neurotransmission within brain regions gating motivation.

E-cigarette aerosols containing nicotine modulate nicotinic acetylcholine receptors and astroglial glutamate transporters in mesocorticolimbic brain regions of chronically exposed mice

Nicotine exposure increases the release of glutamate in part through stimulatory effects on pre-synaptic nicotinic acetylcholine receptors (nAChRs). To assess the impact of chronic electronic (e)-cigarette use on these drug dependence pathways, we exposed C57BL/6 mice to three types of inhalant exposures for 3 months; 1) e-cigarette aerosol generated from liquids containing nicotine (ECN), 2) e-cigarette aerosol generated from liquids containing vehicle chemicals without nicotine (Veh), and 3) air only (AC). We investigated the effects of daily e-cigarette exposure on protein levels of α7 nAChR and α4/β2 nAChR, gene expression and protein levels of astroglial glutamate transporters, including glutamate transporter-1 (GLT-1) and cystine/glutamate antiporter (xCT), in the frontal cortex (FC), striatum (STR) and hippocampus (HIP). We found that chronic inhalation of ECN increased α4/β2 nAChR in all brain regions, and increased α7 nAChR expression in the FC and STR. The total GLT-1 relative mRNA and protein expression were decreased in the STR. Moreover, GLT-1 isoforms (GLT-1a and GLT-1b) were downregulated in the STR in ECN group. However, inhalation of e-cigarette aerosol downregulated xCT expression in STR and HIP compared to AC and Veh groups. ECN group had increased brain-derived neurotrophic factor in the STR compared to control groups. Finally, mass spectrometry detected high concentrations of the nicotine metabolite, cotinine, in the FC and STR in ECN group. This work demonstrates that chronic inhalation of nicotine within e-cigarette aerosols significantly alters the expression of nAChRs and astroglial glutamate transporters in specific mesocorticolimbic brain regions.

Influence of n-acetylcysteine maintenance on the pharmacodynamic effects of oral ethanol

RATIONALE

Glutamate systems play an important role in the abuse related effects of alcohol. n-Acetylcysteine, a drug that promotes glutamate homeostasis, attenuates a range of alcohol effects in preclinical models.

OBJECTIVES

This human laboratory study determined the influence of n-acetylcysteine maintenance on alcohol self-administration using a model predictive of treatment effectiveness, along with the subjective, performance and physiological effects of alcohol. We hypothesized that n-acetylcysteine would attenuate alcohol self-administration, as well as positive subjective effects of alcohol.

METHODS

Nine subjects with alcohol use disorder completed this within-subjects study. Subjects were maintained on placebo, 1.2 and 2.4 g n-acetylcysteine in random order on an outpatient basis. After five days of maintenance on the target dose, subjects completed overnight inpatient experimental sessions in which the pharmacodynamic effects of alcohol were determined.

RESULTS

Alcohol produced prototypic effects (e.g., increased breath alcohol concentration, increased ratings of Feel Drink). n-Acetylcysteine did not alter the effects of alcohol.

CONCLUSIONS

These results indicate that although n-acetylcysteine can safely be combined with alcohol, it does not attenuate the abuse related effects of alcohol and is unlikely to be an effective standalone alcohol use disorder treatment. However, considering study limitations, future work is needed to further understand whether and how n-acetylcysteine might be used as a treatment for alcohol use disorder (e.g., in combination with a behavioral treatment or another pharmacological agent).

Effects of chronic ethanol consumption on the expression of GLT-1 and neuroplasticity-related proteins in the nucleus accumbens of alcohol-preferring rats

Chronic ethanol exposure induces impairments in CNS excitatory and inhibitory activity. These impairments are associated with glutamatergic dysfunction, including altered neuroplasticity. This study examined the effects of 6-week ethanol (15% and 30% v/v) consumption, by male alcohol-preferring P rats, on protein expression associated with neuroplasticity and glutamate transporter-1 (GLT-1) function. The latter regulates intra- and extra-synaptic glutamate levels. We focused on the shell and core subregions of the nucleus accumbens (Acb); i.e., shell (AcbSh) and core (AcbCo), for these measures. Chronic ethanol exposure increased the expression of BDNF, Arc and phosphorylated (p)-post-synaptic density protein-95 (p-PSD-95) in the AcbSh of P rats. Moreover, the ratio of phospho-neuronal nitric oxide synthase (p-nNOS) to total nNOS was also increased in the AcbSh. These changes in BDNF, Arc and p-nNOS/nNOS ratio were not observed in the AcbCo. Furthermore, chronic ethanol consumption reduced GLT-1 expression in the AcbSh. Alternatively, treatment with ceftriaxone (CEF), a known GLT-1 upregulator, abolished the effect of chronic ethanol consumption on BDNF expression in the AcbSh. Overall, the present findings confirm that chronic ethanol consumption modulates activity-associated synaptic proteins, including BDNF, Arc and nNOS in a subregion-specific (i.e., in the AcbSh but not AcbCo) manner. Thus, alterations in mesocorticolimbic glutamatergic homeostasis and neuroplasticity are possible functional targets for the treatment of alcohol use disorders.

Roles of dopamine and glutamate co-release in the nucleus accumbens in mediating the actions of drugs of abuse

Projections of ventral tegmental area dopamine (DA) neurons to the medial shell of the nucleus accumbens have been increasingly implicated as integral to the behavioral and physiological changes involved in the development of substance use disorders (SUDs). Recently, many of these nucleus accumbens-projecting DA neurons were found to also release the neurotransmitter glutamate. This glutamate co-release from DA neurons is critical in mediating the effect of drugs of abuse on addiction-related behaviors. Potential mechanisms underlying the role(s) of dopamine/glutamate co-release in contributing to SUDs are unclear. Nevertheless, an important clue may relate to glutamate's ability to potentiate loading of DA into synaptic vesicles within terminals in the nucleus accumbens in response to drug-induced elevations in neuronal activity, enabling a more robust release of DA after stimulation. Here, we summarize how drugs of abuse, particularly cocaine, opioids, and alcohol, alter DA release in the nucleus accumbens medial shell, examine the potential role of DA/glutamate co-release in mediating these effects, and discuss future directions for further investigating these mechanisms.

Behavioral, neurobiological, and neurochemical mechanisms of ethanol self-administration: A translational review

Alcohol use disorder has multiple characteristics including excessive ethanol consumption, impaired control over drinking behaviors, craving and withdrawal symptoms, compulsive seeking behaviors, and is considered a chronic condition. Relapse is common. Determining the neurobiological targets of ethanol and the adaptations induced by chronic ethanol exposure is critical to understanding the clinical manifestation of alcohol use disorders, the mechanisms underlying the various features of the disorder, and for informing medication development. In the present review, we discuss ethanol's interactions with a variety of neurotransmitter systems, summarizing findings from preclinical and translational studies to highlight recent progress in the field. We then describe animal models of ethanol self-administration, emphasizing the value, limitations, and validity of commonly used models. Lastly, we summarize the behavioral changes induced by chronic ethanol self-administration, with an emphasis on cue-elicited behavior, the role of ethanol-related memories, and the emergence of habitual ethanol seeking behavior.

Ampicillin/Sulbactam Treatment Modulates NMDA Receptor NR2B Subunit and Attenuates Neuroinflammation and Alcohol Intake in Male High Alcohol Drinking Rats

Exposure to ethanol commonly manifests neuroinflammation. Beta (β)-lactam antibiotics attenuate ethanol drinking through upregulation of astroglial glutamate transporters, especially glutamate transporter-1 (GLT-1), in the mesocorticolimbic brain regions, including the nucleus accumbens (Acb). However, the effect of β-lactam antibiotics on neuroinflammation in animals chronically exposed to ethanol has not been fully investigated. In this study, we evaluated the effects of ampicillin/sulbactam (AMP/SUL, 100 and 200 mg/kg, i.p.) on ethanol consumption in high alcohol drinking (HAD1) rats. Additionally, we investigated the effects of AMP/SUL on GLT-1 and N-methyl-d-aspartate (NMDA) receptor subtypes (NR2A and NR2B) in the Acb core (AcbCo) and Acb shell (AcbSh). We found that AMP/SUL at both doses attenuated ethanol consumption and restored ethanol-decreased GLT-1 and NR2B expression in the AcbSh and AcbCo, respectively. Moreover, AMP/SUL (200 mg/kg, i.p.) reduced ethanol-increased high mobility group box 1 (HMGB1) and receptor for advanced glycation end-products (RAGE) expression in the AcbSh. Moreover, both doses of AMP/SUL attenuated ethanol-elevated tumor necrosis factor-alpha (TNF-α) in the AcbSh. Our results suggest that AMP/SUL attenuates ethanol drinking and modulates NMDA receptor NR2B subunits and HMGB1-associated pathways.

Susceptibility to extinction and reinstatement of ethanol-induced conditioned place preference is related to differences in astrocyte cystine-glutamate antiporter content

Individual susceptibility to alcohol effects plays an important role in the development of alcohol addiction and studies have shown that glutamate release is altered after chronic ethanol consumption. The cystine-glutamate antiporter (xCT) is a protein that regulates glutamate release. However, little is known about the relationship between xCT levels and this individual susceptibility. Thus, this study aimed to evaluate the relationship between the extinction and stress-induced reinstatement of ethanol conditioned place preference (CPP) and xCT levels in the medial prefrontal cortex (mPFC), nucleus accumbens (NAcc) and amygdala (Amy). Male Swiss mice were submitted to a CPP procedure followed by an extinction protocol and then identified as those which extinguished the CPP and those that did not. In another cohort, mice that extinguished the CPP were submitted to a protocol of stress-induced reinstatement. Immediately after the tests, brains were removed for xCT quantification. The xCT levels were significantly lower in the mPFC and NAcc of mice that did not extinguish CPP. Moreover, mice that were susceptible to stress-induced reinstatement of CPP had lower levels of xCT in the NAcc. Our results suggest that individual susceptibility to the extinction and reinstatement of ethanol CPP is related to alterations in xCT levels.

Alcohol and IL-6 Alter Expression of Synaptic Proteins in Cerebellum of Transgenic Mice with Increased Astrocyte Expression of IL-6

Recent studies indicate that neuroimmune factors, including the cytokine interleukin-6 (IL-6), play a role in the CNS actions of alcohol. The cerebellum is a sensitive target of alcohol, but few studies have examined a potential role for neuroimmune factors in the actions of alcohol on this brain region. A number of studies have shown that synaptic transmission, and in particular inhibitory synaptic transmission, is an important cerebellar target of alcohol. IL-6 also alters synaptic transmission, although it is unknown if IL-6 targets are also targets of alcohol. This is an important issue because alcohol induces glial production of IL-6, which could then covertly influence the actions of alcohol. The persistent cerebellar effects of both IL-6 and alcohol typically involve chronic exposure and, presumably, altered gene and protein expression. Thus, in the current studies we tested the possibility that proteins involved in inhibitory and excitatory synaptic transmission in the cerebellum are common targets of alcohol and IL-6. We used transgenic mice that express elevated levels of astrocyte produced IL-6 to model persistently elevated expression of IL-6, as would occur in alcohol use disorders, and a chronic intermittent alcohol exposure/withdrawal paradigm (CIE/withdrawal) that is known to produce alcohol dependence. Multiple cerebellar synaptic proteins were assessed by Western blot. Results show that IL-6 and CIE/withdrawal have both unique and common actions that affect synaptic protein expression. These common targets could provide sites for IL-6/alcohol exposure/withdrawal interactions and play an important role in cerebellar symptoms of alcohol use such as ataxia.

Ethanol-Induced Changes in Brain of Transgenic Mice Overexpressing DYRK1A

Alcoholism is a chronic relapsing disorder defined by loss of control over excessive consumption of ethanol despite damaging effects on the liver and brain. We previously showed that the overexpression in mice of Dyrk1A (TgDyrk1A, for dual-specificity tyrosine (Y) phosphorylation-regulated kinase 1A) reduces the severity of alcohol mediated liver injury. Ethanol consumption has also been associated with increased brain glutamate concentration that led to therapies targeting glutamatergic receptors and normalization of glutamatergic neurotransmission. Interestingly, mice overexpressing Dyrk1A (TgDyrk1A mice) present a reduction of glutamatergic brain transmission, which we propose could be protective against alcohol intake. To answer this question, we investigated the ethanol preference in TgDyrk1A mice using a two-bottle choice paradigm. TgDyrk1A mice showed a non-significant decrease of voluntary ethanol intake and ethanol preference compared with wild-type mice. At the peripheral level, mice overexpressing Dyrk1A show lower ethanol plasma levels, indicating a faster ethanol metabolism. At the end of the protocol, lasting 21 days, brains were extracted for protein analysis. Ethanol reduced levels of the synaptic protein PSD-95 and increased the glutamate decarboxylase GAD65, specifically in the cortex of TgDyrk1A mice. Our results suggest that overexpression of DYRK1A may cause different ethanol-induced changes in the brain.

Molecular changes evoked by the beta-lactam antibiotic ceftriaxone across rodent models of substance use disorder and neurological disease

Ceftriaxone is a beta-lactam antibiotic that increases the expression of the major glutamate transporter, GLT-1. As such, ceftriaxone ameliorates symptoms across multiple rodent models of neurological diseases and substance use disorders. However, the mechanism behind GLT-1 upregulation is unknown. The present review synthesizes this literature in order to identify commonalities in molecular changes. We find that ceftriaxone (200 mg/kg for at least two days) consistently restores GLT-1 expression in multiple rodent models of neurological disease, especially when GLT-1 is decreased in the disease model. The same dose given to healthy/drug-naive rodents does not reliably upregulate GLT-1 in any brain region except the hippocampus. Increased GLT-1 expression does not consistently arise from transcriptional regulation, and is likely to be due to trafficking changes. In addition to altered transporter expression, ceftriaxone ameliorates neuropathologies (e.g. tau, amyloid beta, cell death) and aberrant protein expression associated with a number of neurological disease models. Taken together, these results indicate that ceftriaxone remains a strong candidate for treatment of multiple disorders in the clinic.

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.

Ethanol-induced changes in synaptic amino acid neurotransmitter levels in the nucleus accumbens of differentially sensitized mice

RATIONALE

Ethanol-induced behavioural sensitization (EBS) does not occur uniformly in mice exposed to the sensitization paradigm. This suggests innate differential responses to ethanol (EtOH) in the reward circuitry of individual animals.

OBJECTIVES

To better characterize the adaptive differences between low-sensitized (LS) and high-sensitized (HS) mice, we examined excitatory amino acid (EAA) and inhibitory amino acid (IAA) neurotransmitter levels in the nucleus accumbens (NAc) during EBS expression.

METHODS

Male DBA/2J mice received five ethanol (EtOH) (2.2 g/kg) or saline injections, and locomotor activity (LMA) was assessed during EBS induction. EtOH mice were classified as LS or HS on the basis of final LMA scores. Following an EtOH challenge (1.8 g/kg) 2 weeks later, LMA was re-evaluated and in vivo microdialysis samples were collected from the NAc.

RESULTS

Most differences in amino acid levels were observed within the first 20 min after EtOH challenge. LS mice exhibited similar glutamate levels compared with acutely treated (previously EtOH naïve) mice, and generally increased levels of the IAAs GABA, glycine, and taurine. By contrast, HS mice exhibited increased glutamate and attenuated levels of GABA, glycine, and taurine.

CONCLUSION

These data suggest that the profile of amino acid neurotransmitters in the NAc of LS and HS mice significantly differs. Elucidating these adaptive differences contributes to our understanding of factors that confer susceptibility/resilience to alcohol use disorder.

Comorbid HIV infection and alcohol use disorders: Converging glutamatergic and dopaminergic mechanisms underlying neurocognitive dysfunction

Alcohol use disorders (AUDs) are highly comorbid with human immunodeficiency virus (HIV) infection, occurring at nearly twice the rate in HIV positive individuals as in the general population. Individuals with HIV who consume alcohol show worse long-term prognoses and may be at elevated risk for the development of HIV-associated neurocognitive disorders. The direction of this relationship is unclear, and likely multifactorial. Chronic alcohol exposure and HIV infection independently promote cognitive dysfunction and further may interact to exacerbate neurocognitive deficits through effects on common targets, including corticostriatal glutamate and dopamine neurotransmission. Additionally, drug and alcohol use is likely to reduce treatment adherence, potentially resulting in accelerated disease progression and subsequent neurocognitive impairment. The development of neurocognitive impairments may further reduce cognitive control over behavior, resulting in escalating alcohol use. This review will examine the complex relationship between HIV infection and alcohol use, highlighting impacts on dopamine and glutamate systems by which alcohol use and HIV act independently and in tandem to alter corticostriatal circuit structure and function to dysregulate cognitive function.

Ethanol-induced alterations in endocannabinoids and relevant neurotransmitters in the nucleus accumbens of fatty acid amide hydrolase knockout mice

Deletion of fatty acid amide hydrolase (FAAH), enzyme responsible for degrading endocannabinoids, increases alcohol consumption and preference. However, there is a lack of data on neurochemical events in mice exposed to alcohol in the absence of FAAH. Extracellular levels of endocannabinoids and relevant neurotransmitters were measured by in vivo microdialysis in the nucleus accumbens (NAc) of FAAH knockout (KO) and wild-type (WT) mice during an ethanol (EtOH; 2 g/kg, ip) challenge in EtOH-naive and repeated (r) EtOH-treated mice. In both genotypes, EtOH treatment caused no changes in baseline endocannabinoid levels, although FAAH KO mice displayed higher baseline N-arachidonoylethanolamine levels than WT mice. EtOH challenge caused a sustained increase in 2-arachidonoylglycerol (2-AG) levels in EtOH-naive WT mice but not in FAAH KO mice. In contrast, 2-AG levels were decreased following EtOH challenge in (r)EtOH-treated mice in both genotypes. Whereas (r)EtOH-treated mice showed higher baseline dopamine and serotonin levels than EtOH-naive mice in WT mice, these differences were attenuated in FAAH KO mice. Significant differences in baseline γ-aminobutyric acid (GABA) and glutamate levels by EtOH history were observed in WT mice but not in FAAH KO mice. Moreover, opposed effects on glutamate response were observed after EtOH challenge in EtOH-naive and (r)EtOH-treated FAAH KO mice. Finally, FAAH deletion failed to show EtOH-induced locomotion sensitivity. These data provide evidence of a potential influence of 2-AG in the neurochemical response to EtOH exposure in the NAc.

Pregabalin: Potential for Addiction and a Possible Glutamatergic Mechanism

Drug addiction remains a prevalent and fatal disease worldwide that carries significant social and economic impacts. Recent reports suggest illicit pregabalin (Lyrica) use may be increasing among youth, however the addictive potential of pregabalin has not been well established. Drug seeking behavior and chronic drug use are associated with deficits in glutamate clearance and activation of postsynaptic glutamatergic receptors. In the current study, we investigated the abuse potential of pregabalin using conditioned place preference (CPP) paradigm. Different doses of pregabalin (30, 60, 90, and 120 mg/kg) were used to assess the seeking behavior in mice. Glutamate homeostasis is maintained by glutamate transporter type-1 (GLT-1), which plays a vital role in clearing the released glutamate from synapses and drug seeking behavior. Therefore, we investigated the role of glutamate in pregabalin-seeking behavior with ceftriaxone (CEF), a potent GLT-1 upregulator. Mice treated with pregabalin 60 and 90 mg/kg doses demonstrated drug seeking-like behavior, which was significantly blocked by CEF pretreatment. These results suggest that pregabalin-induced CPP was successfully modulated by CEF which could serve as a lead compound for developing treatment for pregabalin abuse.

Serial exposure to ethanol drinking and methamphetamine enhances glutamate excitotoxicity

A significant comorbidity exists between alcohol and methamphetamine (Meth) abuse but the neurochemical consequences of this co-abuse are unknown. Alcohol and Meth independently and differentially affect glutamatergic transmission but the unique effects of their serial exposure on glutamate signaling in mediating damage to dopamine neurons are unknown. Sprague-Dawley rats had intermittent voluntary access to 10% ethanol (EtOH) every other day and water over 28 days and were then administered a binge injection regimen of Meth or saline. EtOH drinking decreased the glutamate aspartate transporter and increased basal extracellular concentrations of glutamate within the striatum when measured after the last day of drinking. Ceftriaxone is known to increase the expression and/or activity of glutamate transporters in the brain and prevented both the decreases in glutamate aspartate transporter and the increases in basal extracellular glutamate when administered during EtOH drinking. EtOH drinking also exacerbated the acute increases in extracellular glutamate observed upon Meth exposure, the subsequent increases in spectrin proteolysis, and the long-term decreases in dopamine content in the striatum, all of which were attenuated by ceftriaxone administration during EtOH drinking only. These results implicate EtOH-induced increases in extracellular glutamate and corresponding decreases in glutamate uptake as mechanisms that contribute to the vulnerability produced by EtOH drinking and the unique neurotoxicity observed after serial exposure to Meth that is not observed with either drug alone. Open Science: This manuscript was awarded with the Open Materials Badge For more information see: https://cos.io/our-services/open-science-badges/.

Simultaneous wireless and high-resolution detection of nucleus accumbens shell ethanol concentrations and free motion of rats upon voluntary ethanol intake

Highly sensitive detection of ethanol concentrations in discrete brain regions of rats voluntarily accessing ethanol, with high temporal resolution, would represent a source of greatly desirable data in studies devoted to understanding the kinetics of the neurobiological basis of ethanol's ability to impact behavior. In the present study, we present a series of experiments aiming to validate and apply an original high-tech implantable device, consisting of the coupling, for the first time, of an amperometric biosensor for brain ethanol detection, with a sensor for detecting the microvibrations of the animal. This device allows the real-time comparison between the ethanol intake, its cerebral concentrations, and their effect on the motion when the animal is in the condition of voluntary drinking. To this end, we assessed in vitro the efficiency of three different biosensor designs loading diverse alcohol oxidase enzymes (AOx) obtained from three different AOx-donor strains: Hansenula polymorpha, Candida boidinii, and Pichia pastoris. In vitro data disclosed that the devices loading H. polymorpha and C. boidinii were similarly efficient (respectively, linear region slope [LRS]: 1.98 ± 0.07 and 1.38 ± 0.04 nA/mM) but significantly less than the P. pastoris-loaded one (LRS: 7.57 ± 0.12 nA/mM). The in vivo results indicate that this last biosensor design detected the rise of ethanol in the nucleus accumbens shell (AcbSh) after 15 minutes of voluntary 10% ethanol solution intake. At the same time, the microvibration sensor detected a significant increase in the rat's motion signal. Notably, both the biosensor and microvibration sensor described similar and parallel time-dependent U-shaped curves, thus providing a highly sensitive and time-locked high-resolution detection of the neurochemical and behavioral kinetics upon voluntary ethanol intake. The results overall indicate that such a dual telemetry unit represents a powerful device which, implanted in different brain areas, may boost further investigations on the neurobiological mechanisms that underlie ethanol-induced motor activity and reward.

Presynaptic Ethanol Actions: Potential Roles in Ethanol Seeking

Ethanol produces intoxication through actions on numerous molecular and cellular targets. Adaptations involving these and other targets contribute to chronic drug actions that underlie continued and problematic drinking. Among the mechanisms involved in these ethanol actions are alterations in presynaptic mechanisms of synaptic transmission, including presynaptic protein function and excitation-secretion coupling. At synapses in the central nervous system (CNS), excitation-secretion coupling involves ion channel activation followed by vesicle fusion and neurotransmitter release. These mechanisms are altered by presynaptic neurotransmitter receptors and prominently by G protein-coupled receptors (GPCRs). Studies over the last 20-25 years have revealed that acute ethanol exposure alters neurotransmitter secretion, with especially robust effects on synapses that use the neurotransmitter gamma-aminobutyric acid (GABA). Intracellular signaling pathways involving second messengers such as cyclic AMP and calcium are implicated in these acute ethanol actions. Ethanol-induced release of neuropeptides and small molecule neurotransmitters that act on presynaptic GPCRs also contribute to presynaptic potentiation at synapses in the amygdala and hippocampus and inhibition of GABA release in the striatum. Prolonged exposure to ethanol alters neurotransmitter release at many CNS GABAergic and glutamatergic synapses, and changes in GPCR function are implicated in many of these neuroadaptations. These presynaptic neuroadaptations appear to involve compensation for acute drug effects at some synapses, but "allostatic" effects that result in long-term resetting of synaptic efficacy occur at others. Current investigations are determining how presynaptic neuroadaptations contribute to behavioral changes at different stages of alcohol drinking, with increasing focus on circuit adaptations underlying these behaviors. This chapter will discuss the acute and chronic presynaptic effects of ethanol in the CNS, as well as some of the consequences of these effects in amygdala and corticostriatal circuits that are related to excessive seeking/drinking and ethanol abuse.

GLAST (GLutamate and ASpartate Transporter) in human prefrontal cortex; interactome in healthy brains and the expression of GLAST in brains of chronic alcoholics

We have analysed post-mortem samples of prefrontal cortex from control and alcoholic human brains by the technique of Western blotting to estimate and compare the expressions of glutamate transporter GLAST (Excitatory Amino Acid Transporter One; EAAT1). Furthermore, using the non-alcoholic prefrontal cortex and custom-made GLAST (EAAT1) antibody we determined GLAST (EAAT1) "interactome" i.e. the set of proteins selectively bound by GLAST (EAAT1). We found that GLAST (EAAT1) was significantly more abundant (about 1.6-fold) in the cortical tissue from alcoholic brains compared to that from non-alcoholic controls. The greatest increase in the level of GLAST (EAAT1) was found in plasma membrane fraction (2.2-fold). Additionally, using the prefrontal cortical tissue from control brains, we identified 38 proteins specifically interacting with GLAST (EAAT1). These can be classified as contributing to the cell structure (6 proteins; 16%), energy and general metabolism (18 proteins; 47%), neurotransmitter metabolism (three proteins; 8%), signalling (6 proteins: 16%), neurotransmitter storage/release at synapses (three proteins; 8%) and calcium buffering (two proteins; 5%). We discuss possible consequences of the increased expression of GLAST (EAAT1) in alcoholic brain tissue and whether or how this could disturb the function of the proteins potentially interacting with GLAST (EAAT1) in vivo. The data represent an extension of our previous proteomic and metabolomic studies of human alcoholism revealing another aspect of the complexity of changes imposed on brain by chronic long-term consumption of ethanol.

β-lactams modulate astroglial glutamate transporters and attenuate dependence to CP 55,940, a CB1 receptor agonist, in rat model

Studies on cannabinoids have reported contradictory findings, showing both aversion and rewarding outcomes in conditioned place preference (CPP). Various possibilities have been suggested to explain the aversive properties of cannabinoids, including the pharmacokinetics profile and dose selection. In this study, we have established a CPP method to investigate the effects of modulating astroglial glutamate transporters in cannabinoid dependence using a cannabinoid receptor 1 (CB1R) agonist, CP 55,940 (CP). Previous reports using CPP paradigm demonstrated the involvement of glutamatergic system in seeking behavior of several drugs of abuse such as cocaine, heroin and nicotine. Glutamate homeostasis is maintained by several astroglial glutamate transporters, such as glutamate transporter 1 (GLT-1), cystine/glutamate transporter (xCT) and glutamate aspartate transporter (GLAST). In this study, we investigated the effects of Ampicillin/Sulbactam, β-lactam compounds known to upregulate GLT-1 and xCT, on cannabinoid seeking behavior using CP. We found first that one prime dose of CP induced CP reinstatement; this effect was associated, in part, with significant downregulation of xCT expression in the nucleus accumbens, dorsomedial prefrontal cortex and amygdala. Moreover, GLT-1 expression was downregulated in the amygdala. Importantly, Ampicillin/Sulbactam treatment during the extinction phase attenuated CP-induced reinstatement and restored the expression of GLT-1 and xCT in mesocorticolimbic brain regions. These findings suggest that β-lactams may play a potential therapeutic role in attenuating dependence to cannabinoids, in part, through upregulation of GLT-1 and xCT.

Effects of Clavulanic Acid Treatment on Reinstatement to Methamphetamine, Glial Glutamate Transporters, and mGluR 2/3 Expression in P Rats Exposed to Ethanol

Evidence demonstrated that the glutamatergic system is implicated in mediating relapse to several drugs of abuse, including methamphetamine (METH). Glutamate homeostasis is maintained by a number of glutamate transporters, such as glutamate transporter type 1 (GLT-1), cystine/glutamate transporter (xCT), and glutamate aspartate transporter (GLAST). In addition, group II metabotropic glutamate receptors (mGluR2/3) were found to be implicated in relapse-seeking behavior. Ample evidence showed that β-lactam antibiotics are effective in upregulating GLT-1 and xCT expression, thus improving glutamate homeostasis and attenuating relapse to drugs of abuse. In this study, we investigated the reinstatement of METH using conditioned place preference (CPP) in male alcohol-preferring (P) rats exposed to home-cage free choice ethanol drinking. Here, we tested the effect of clavulanic acid (CA), a β-lactam, on the reinstatement of METH-seeking and ethanol drinking. In addition, we examined the expression of GLT-1, xCT, and GLAST as well as metabotropic glutamate receptor (mGluR2/3) in the nucleus accumbens (NAc) shell, NAc core, and dorsomedial prefrontal cortex (dmPFC). A priming i.p. injection of METH reinstated preference in METH-paired chamber following extinction. Chronic exposure to ethanol decreased the expression of GLT-1 and xCT in the NAc shell, but not in the NAc core or dmPFC. CA treatment blocked the reinstatement of METH-seeking, decreased ethanol intake, and restored the expression of GLT-1 and xCT in the NAc shell. In addition, the expression of mGluR2/3 was increased by CA treatment in the NAc shell and dmPFC. These findings suggest that these glutamate transporters and mGluR2/3 might be potential therapeutic targets for the attenuation of reinstatement to METH-seeking.

Role of glutamatergic system and mesocorticolimbic circuits in alcohol dependence

Emerging evidence demonstrates that alcohol dependence is associated with dysregulation of several neurotransmitters. Alterations in dopamine, glutamate and gamma-aminobutyric acid release are linked to chronic alcohol exposure. The effects of alcohol on the glutamatergic system in the mesocorticolimbic areas have been investigated extensively. Several studies have demonstrated dysregulation in the glutamatergic systems in animal models exposed to alcohol. Alcohol exposure can lead to an increase in extracellular glutamate concentrations in mesocorticolimbic brain regions. In addition, alcohol exposure affects the expression and functions of several glutamate receptors and glutamate transporters in these brain regions. In this review, we discussed the effects of alcohol exposure on glutamate receptors, glutamate transporters and glutamate homeostasis in each area of the mesocorticolimbic system. In addition, we discussed the genetic aspect of alcohol associated with glutamate and reward circuitry. We also discussed the potential therapeutic role of glutamate receptors and glutamate transporters in each brain region for the treatment of alcohol dependence. Finally, we provided some limitations on targeting the glutamatergic system for potential therapeutic options for the treatment alcohol use disorders.

Altered glutamate clearance in ascorbate deficient mice increases seizure susceptibility and contributes to cognitive impairment in APP/PSEN1 mice

Ascorbate (vitamin C) is critical as a first line of defense antioxidant within the brain, and specifically within the synapse. Ascorbate is released by astrocytes during glutamate clearance and disruption of this exchange mechanism may be critical in mediating glutamate toxicity within the synapse. This is likely even more critical in neurodegenerative disorders with associated excitotoxicity and seizures, in particular Alzheimer's disease, in which ascorbate levels are often low. Using Gulo^-/- mice that are dependent on dietary ascorbate, we established that low brain ascorbate increased sensitivity to kainic acid as measured via behavioral observations, electroencephalography (EEG) measurements, and altered regulation of several glutamatergic system genes. Kainic acid-induced immobility was improved in wild-type mice following treatment with ceftriaxone, which upregulates glutamate transporter GLT-1. The same effect was not observed in ascorbate-deficient mice in which sufficient ascorbate is not available for release. A single, mild seizure event was sufficient to disrupt performance in the water maze in low-ascorbate mice and in APP_SWE/PSEN1_dE9 mice. Together, the data support the critical role of brain ascorbate in maintaining protection during glutamatergic hyperexcitation events, including seizures. The study further supports a role for mild, subclinical seizures in cognitive decline in Alzheimer's disease.

Involvement of NMDA Receptors, Nitric Oxide, and GABA in Rostral Ventrolateral Medulla in Acute Ethanol-Induced Cardiovascular Responses in Rats

BACKGROUND

Consumption of ethanol (EtOH) (alcohol) has many effects on physiological functions, particularly those in the central nervous system (CNS) and cardiovascular system. Acute excessive intake of EtOH (alcohol intoxication) may cause hypotension and tachycardia. In this study, we examined the mechanistic involvement of glutamatergic N-methyl-d-aspartate (NMDA) receptors, nitric oxide (NO), and γ-aminobutyric acid (GABA) pathways in the CNS in acute EtOH-induced cardiovascular effects.

METHODS

EtOH was administered by intraperitoneal (IP) injection in Sprague-Dawley rats. The blood pressure (BP) and heart rate (HR) were measured in conscious and in urethane-anesthetized rats. Inhibitors were applied by intracerebroventricular (ICV) injection or by microinjection into rostral ventrolateral medulla (RVLM). Microdialysis was used to determine the level of glutamate, NO, and GABA in the RVLM.

RESULTS

IP injection of EtOH (3.2 g/kg) caused a significant decrease in BP in conscious and anesthetized rats and a late increase in HR in conscious rats. The cardiovascular effects of EtOH were significantly attenuated by ICV or by RVLM post treatment with ketamine (an NMDA receptor antagonist), N5-(nitroamidino)-L-2,5-diaminopentanoic acid (L-NNA; a NO synthase inhibitor), or bicuculline (a GABA receptor antagonist). EtOH caused an increase in the level of glutamate, NO, and GABA in the RVLM during the hypotensive responses. RVLM posttreatment with ketamine blocked the increase in NO and GABA levels; post treatment with L-NNA blocked the increase in GABA level.

CONCLUSIONS

Our results indicate that EtOH augmentation of glutamatergic NMDA receptors/NO/GABA pathways in the RVLM may participate in the hypotensive effects induced by acute administration of EtOH.

Molecular Neuropathology of Astrocytes and Oligodendrocytes in Alcohol Use Disorders

Postmortem studies reveal structural and molecular alterations of astrocytes and oligodendrocytes in both the gray and white matter (GM and WM) of the prefrontal cortex (PFC) in human subjects with chronic alcohol abuse or dependence. These glial cellular changes appear to parallel and may largely explain structural and functional alterations detected using neuroimaging techniques in subjects with alcohol use disorders (AUDs). Moreover, due to the crucial roles of astrocytes and oligodendrocytes in neurotransmission and signal conduction, these cells are very likely major players in the molecular mechanisms underpinning alcoholism-related connectivity disturbances between the PFC and relevant interconnecting brain regions. The glia-mediated etiology of alcohol-related brain damage is likely multifactorial since metabolic, hormonal, hepatic and hemodynamic factors as well as direct actions of ethanol or its metabolites have the potential to disrupt distinct aspects of glial neurobiology. Studies in animal models of alcoholism and postmortem human brains have identified astrocyte markers altered in response to significant exposures to ethanol or during alcohol withdrawal, such as gap-junction proteins, glutamate transporters or enzymes related to glutamate and gamma-aminobutyric acid (GABA) metabolism. Changes in these proteins and their regulatory pathways would not only cause GM neuronal dysfunction, but also disturbances in the ability of WM axons to convey impulses. In addition, alcoholism alters the expression of astrocyte and myelin proteins and of oligodendrocyte transcription factors important for the maintenance and plasticity of myelin sheaths in WM and GM. These changes are concomitant with epigenetic DNA and histone modifications as well as alterations in regulatory microRNAs (miRNAs) that likely cause profound disturbances of gene expression and protein translation. Knowledge is also available about interactions between astrocytes and oligodendrocytes not only at the Nodes of Ranvier (NR), but also in gap junction-based astrocyte-oligodendrocyte contacts and other forms of cell-to-cell communication now understood to be critical for the maintenance and formation of myelin. Close interactions between astrocytes and oligodendrocytes also suggest that therapies for alcoholism based on a specific glial cell type pathology will require a better understanding of molecular interactions between different cell types, as well as considering the possibility of using combined molecular approaches for more effective therapies.

Long-term subregion-specific encoding of enhanced ethanol intake by D1DR medium spiny neurons of the nucleus accumbens

The nucleus accumbens (NAc) is a critical component of the mesocorticolimbic system and is involved in mediating the motivational and reinforcing aspects of ethanol consumption. Chronic intermittent ethanol (CIE) exposure is a reliable model to induce ethanol dependence and increase volitional ethanol consumption in mice. Following a CIE-induced escalation of ethanol consumption, NMDAR (N-methyl-D-aspartate receptor)-dependent long-term depression in D1 dopamine receptor expressing medium spiny neurons of the NAc shell was markedly altered with no changes in plasticity in D1 dopamine receptor medium spiny neurons from the NAc core. This disruption of plasticity persisted for up to 2 weeks after cessation of ethanol access. To determine if changes in AMPA receptor (AMPAR) composition contribute to this ethanol-induced neuroadaptation, we monitored the rectification of AMPAR excitatory postsynaptic currents (EPSCs). We observed a marked decrease in the rectification index in the NAc shell, suggesting the presence of GluA2-lacking AMPARs. There was no change in the amplitude of spontaneous EPSCs (sEPSCs), but there was a transient increase in sEPSC frequency in the NAc shell. Using the paired pulse ratio, we detected a similar transient increase in the probability of neurotransmitter release. With no change in sEPSC amplitude, the change in the rectification index suggests that GluA2-containing AMPARs are removed and replaced with GluA2-lacking AMPARs in the NAc shell. This CIE-induced alteration in AMPAR subunit composition may contribute to the loss of NMDAR-dependent long-term depression in the NAc shell and therefore may constitute a critical neuroadaptive response underlying the escalation of ethanol intake in the CIE model.

Effects of group II metabotropic glutamate receptor modulation on ethanol- and sucrose-seeking and consumption in the rat

Previous studies suggest that group II metabotropic glutamate receptors (mGluR2/3) are involved in regulating ethanol-seeking and consumption. The mGluR2/3 agonist LY379268 (LY37) and selective mGluR2 positive allosteric modulator biphenyl‑indanone A (BINA) were used to investigate the relative contribution of mGlu2 and mGlu3 receptors on ethanol- and sucrose-seeking and consumption. A microinjection study was then performed to examine the role of nucleus accumbens (NAc) core mGluR2/3 on ethanol-seeking. For the systemic experiments, separate groups of male Wistar rats [LY37 (0-2.0 mg/kg); BINA (0-20 mg/kg)] were trained to complete a response requirement (RR) resulting in access to 10% ethanol or 2% sucrose (in separate groups) for a 20‑min drinking period. Animals then underwent consummatory testing (weekly drug injections with RR1) followed by appetitive testing (weekly drug injections followed by extinction session). A separate group of male Wistar rats was surgically implanted with bilateral guide cannulae directed toward the NAc core and had weekly microinjections followed by an extinction session. Systemic administration of the mGluR2/3 agonist LY37 significantly reduced ethanol- and sucrose-seeking. The same treatment also reduced sucrose consumption and body weight (24‑h post injection). Systemic administration of the selective mGluR2 PAM BINA, however, had no effect on either seeking or consumption of ethanol or sucrose. Intra-accumbens core LY37 significantly reduced ethanol-seeking. These findings suggest that systemic mGluR2/3 agonism, but not allosteric modulation of mGluR2, reduces reinforcer-seeking. In particular, NAc core group II mGluR may be involved in regulating ethanol-seeking.

GABA and Glutamate Synaptic Coadaptations to Chronic Ethanol in the Striatum

Alcohol (ethanol) is a widely used and abused drug with approximately 90% of adults over the age of 18 consuming alcohol at some point in their lifetime. Alcohol exerts its actions through multiple neurotransmitter systems within the brain, most notably the GABAergic and glutamatergic systems. Alcohol's actions on GABAergic and glutamatergic neurotransmission have been suggested to underlie the acute behavioral effects of ethanol. The striatum is the primary input nucleus of the basal ganglia that plays a role in motor and reward systems. The effect of ethanol on GABAergic and glutamatergic neurotransmission within striatal circuitry has been thought to underlie ethanol taking, seeking, withdrawal and relapse. This chapter reviews the effects of ethanol on GABAergic and glutamatergic transmission, highlighting the dynamic changes in striatal circuitry from acute to chronic exposure and withdrawal.

Effects of sequential ethanol exposure and repeated high-dose methamphetamine on striatal and hippocampal dopamine, serotonin and glutamate tissue content in Wistar rats

Alcohol (ethanol) and methamphetamine (METH) co-abuse is a major public health issue. Ethanol or METH exposure has been associated with changes in neurotransmitter levels in several central brain regions. However, little is known about the effect of sequential exposure to ethanol and METH on glutamate, dopamine and serotonin tissue content in striatum and hippocampus. In this study, we investigated the effects of sequential exposure to ethanol and METH on tissue content of these neurotransmitters. Male Wistar rats were orally gavaged with either ethanol (6g/kg) or water for seven days. Rats were administered with high dose of METH (10mg/kg, i.p. every 2h×4) or saline on Day 8 and euthanized 48h of last METH or saline i.p. injection. In the striatum, sequential exposure to ethanol and METH increased glutamate tissue content while reducing dopamine and serotonin tissue content as compared to the group exposed to ethanol alone. In the hippocampus, sequential exposure to ethanol and METH decreased serotonin tissue content as compared to the group that was exposed to ethanol alone. However, this study showed that ethanol has no additive effect to METH on tissue content of dopamine and serotonin as compared to METH in the striatum and hippocampus. This study demonstrated that sequential exposure of ethanol and METH has an additive effect on tissue content of certain neurotransmitters in the brain.

GABA Uptake Inhibition Reduces In Vivo Extraction Fraction in the Ventral Tegmental Area of Long Evans Rats Measured by Quantitative Microdialysis Under Transient Conditions

Inhibitory signaling in the ventral tegmental area (VTA) is involved in the mechanism of action for many drugs of abuse. Although drugs of abuse have been shown to alter extracellular γ-aminobutyric acid (GABA) concentration in the VTA, knowledge on how uptake mechanisms are regulated in vivo is limited. Quantitative (no-net-flux) microdialysis is commonly used to examine the extracellular concentration and clearance of monoamine neurotransmitters, however it is unclear whether this method is sensitive to changes in clearance for amino acid neurotransmitters such as GABA. The purpose of this study was to determine whether changes in GABA uptake are reflected by in vivo extraction fraction within the VTA. Using quantitative (no-net-flux) microdialysis adapted for transient conditions, we examined the effects of local perfusion with the GABA uptake inhibitor, nipecotic acid, in the VTA of Long Evans rats. Basal extracellular GABA concentration and in vivo extraction fraction were 44.4 ± 1.9 nM (x-intercepts from 4 baseline regressions using a total of 24 rats) and 0.19 ± 0.01 (slopes from 4 baseline regressions using a total of 24 rats), respectively. Nipecotic acid (50 μM) significantly increased extracellular GABA concentration to 170 ± 4 nM and reduced in vivo extraction fraction to 0.112 ± 0.003. Extraction fraction returned to baseline following removal of nipecotic acid from the perfusate. Conventional microdialysis substantially underestimated the increase of extracellular GABA concentration due to nipecotic acid perfusion compared with that obtained from the quantitative analysis. Together, these results show that inhibiting GABA uptake mechanisms within the VTA alters in vivo extraction fraction measured using microdialysis and that in vivo extraction fraction may be an indirect measure of GABA clearance.

Glial and neuroinflammatory targets for treating substance use disorders

BACKGROUND

The plenary session at the 2016 Behavior, Biology and Chemistry: Translational Research in Addiction Conference focused on glia as potential players in the development, persistence and treatment of substance use disorders. Glia partake in various functions that are important for healthy brain activity. Drugs of abuse alter glial cell activity producing several perturbations in brain function that are thought to contribute to behavioral changes associated with substance use disorders. Consequently, drug-induced changes in glia-driven processes in the brain represent potential targets for pharmacotherapeutics treating substance use disorders.

METHODS

Four speakers presented preclinical and clinical research illustrating the effects that glial modulators have on abuse-related behavioral effects of psychostimulants and opioids. This review highlights some of these findings and expands its focus to include other research focused on drug-induced glia abnormalities and glia-focused treatment approaches in substance use disorders.

RESULTS

Preclinical findings show that drugs of abuse induce neuroinflammatory signals and disrupt glutamate homeostasis through their interaction with microglia and astrocytes. Preclinical and clinical studies testing the effects of glial modulators show general effectiveness in reducing behaviors associated with substance use disorders.

CONCLUSIONS

The contribution of drug-induced glial activity continues to emerge as an intriguing target for substance use disorder treatments. Clinical investigations of glial modulators have yielded promising results on substance use measures and indicate that they are generally safe and well-tolerated. However, results have not been entirely positive and more questions remain for continued exploration in the development and testing of glial-directed treatments for substance use disorders.

Convergent Neuronal Plasticity and Metaplasticity Mechanisms of Stress, Nicotine, and Alcohol

Stress and tobacco smoking are risk factors for alcoholism, but the underlying neural mechanisms are not well understood. Although stress, nicotine, and alcohol have broad, individual effects in the brain, some of their actions converge onto the same mechanisms and circuits. Stress and nicotine augment alcohol-related behaviors, in part via modulation of alcohol-evoked neuronal plasticity and metaplasticity mechanisms. Stress modulates alcohol-evoked plasticity via the release of signaling molecules that influence synaptic transmission. Nicotine also activates some of the same signaling molecules, cells, and circuits, producing a convergence of both stress and nicotine onto common plasticity mechanisms that influence alcohol self-administration. We describe several forms of alcohol-induced plasticity, including classic Hebbian plasticity at glutamatergic synapses, and we highlight less appreciated forms, such as non-Hebbian and GABAergic synaptic plasticity. Risk factors such as stress and nicotine initiate lasting neural changes that modify subsequent alcohol-induced synaptic plasticity and increase the vulnerability to alcohol addiction.

A role for nucleus accumbens glutamate in the expression but not the induction of behavioural sensitization to ethanol

Mechanisms underlying differential sensitivity to behavioural sensitization to ethanol (EtOH) remain poorly understood, although accumulating evidence suggests a role for glutamatergic processes in the ventral striatum. Efforts to address this issue can benefit from the well-documented fact that in any given cohort, some of the mice (High sensitized; HS) show robust sensitization, while others (Low sensitized; LS) show little, if any, sensitization. Here, we examined whether this variability might be differentially associated with nucleus accumbens (NAc) glutamate processes. Male DBA mice received 5 EtOH (2.2g/kg) or saline injections twice a week and were challenged with EtOH (1.8g/kg) 2 weeks after injection 5. When an EtOH challenge was administered 2 weeks following the induction of sensitization, HS, but not LS, mice showed a robust increase in glutamate levels (67%, P<0.01) as measured by in vivo microdialysis. In a separate cohort, the mGlu2/3 agonist LY354740 (10mg/kg), given prior to the EtOH challenge, abolished the expression of sensitization. To ascertain whether enhanced release could also be observed during the induction of sensitization, glutamate levels were measured after the 1st and 5th EtOH injection and were found to be unchanged in HS mice, although briefly elevated in LS mice at injection 5. To further assess possible glutamate involvement during the induction of sensitization, sensitizing EtOH injections were co-administered with NMDAR antagonists. At the doses used, MK-801 (0.25mg/kg) and CGS 19755 (10mg/kg) blocked the expression of sensitization, but did not significantly interfere with the development of EtOH sensitization. Within the limitations of the present design, the results suggest an important role for EtOH-induced glutamate release in the NAc when sensitization is well established, but not necessarily during the development of sensitization.

β-Lactamase inhibitor, clavulanic acid, attenuates ethanol intake and increases glial glutamate transporters expression in alcohol preferring rats

Studies from our laboratory showed that upregulation of glutamate transporter 1 (GLT-1) and cystine-glutamate exchanger (xCT) expression with ceftriaxone, β-lactam antibiotic, in the brain was associated with attenuation of ethanol consumption. In this study, we tested clavulanic acid, which is another β-lactam compound with negligible antimicrobial activity, on ethanol consumption and expression of GLT-1, xCT and glutamate aspartate transporter (GLAST) in male alcohol-preferring (P) rats. Clavulanic acid has the central β-lactam pharmacophore that is critical for the upregulation of GLT-1 and xCT expression. We found that clavulanic acid, at 5mg/kg (i.p.) dose, significantly attenuated ethanol consumption and ethanol preference in P rats as compared to vehicle-treated group. This effect was associated with a significant increase in water intake in clavulanic acid treated group. Importantly, we found that clavulanic acid increased the expression of GLT-1 and xCT in nucleus accumbens. However, there was no effect of clavulanic acid on GLAST expression in the nucleus accumbens. Clavulanic acid treatment did not upregulate the expression of GLT-1, xCT and GLAST in prefrontal cortex. These findings revealed that clavulanic acid at 20-40 fold lower dose than ceftriaxone can attenuate ethanol consumption, in part through upregulation of GLT-1 and xCT expression in the nucleus accumbens. Thus, we suggest that clavulanic acid might be used as an alternative option to ceftriaxone to attenuate ethanol drinking behavior.

Ceftriaxone reduces alcohol intake in outbred rats while upregulating xCT in the nucleus accumbens core

Alcohol addiction is a chronic disease characterized by an inability to regulate drinking. A critical brain region involved in alcohol consumption is the nucleus accumbens (NA). Glutamate transmission in this region regulates alcohol consumption and relapse to alcohol-seeking. Across multiple alcohol-administration rodent models, basal extracellular glutamate levels are increased in the NA during early withdrawal. Glutamate transporter 1 (GLT-1) and system x_C-, containing the subunit xCT, regulate NA glutamate levels. Ceftriaxone (Cef) increases expression and function of both transporters following extinction from cocaine self-administration and here we sought to determine if Cef would similarly decrease alcohol consumption while increasing xCT and GLT-1 in the NA core. We used the intermittent access to alcohol (IAA) paradigm to induce drinking in outbred Sprague-Dawley rats; this paradigm permits rats access to alcohol (20%v/v) for 24-h without water deprivation, followed by 24-h of abstinence. Following 17 24-h drinking sessions, Cef treatment (200mg/kg IP) was initiated and continued for 5days while a control group received vehicle (0.9% saline IP). Alcohol consumption was assessed for two 24-h periods during Cef and two 24-h periods after cessation of Cef treatment. In a separate cohort of rats, Cef's ability to alter blood alcohol levels (BALs) after a non-contingent alcohol injection (1g/kg) was assessed. We found that Cef decreased alcohol consumption during the period of Cef treatment and on the two days following injections, and this was accompanied by an increase in NA core xCT expression. Furthermore, a history of alcohol consumption did not alter xCT and GLT-1 expression relative to alcohol-naïve controls. Cef did not alter BALs, indicating that the reduction in alcohol consumption was not caused by altered alcohol clearance. These results indicate that while Cef reduces alcohol consumption in outbred rats, its ability to do so is not associated with an increase in GLT-1 expression.

Effects of chronic inhalation of electronic cigarettes containing nicotine on glial glutamate transporters and α-7 nicotinic acetylcholine receptor in female CD-1 mice

Alteration in glutamate neurotransmission has been found to mediate the development of drug dependence, including nicotine. We and others, through using western blotting, have reported that exposure to drugs of abuse reduced the expression of glutamate transporter-1 (GLT-1) as well as cystine/glutamate antiporter (xCT), which consequently increased extracellular glutamate concentrations in the mesocorticolimbic area. However, our previous studies did not reveal any changes in glutamate/aspartate transporter (GLAST) following exposure to drugs of abuse. In the present study, for the first time, we investigated the effect of chronic exposure to electronic (e)-cigarette vapor containing nicotine, for one hour daily for six months, on GLT-1, xCT, and GLAST expression in frontal cortex (FC), striatum (STR), and hippocampus (HIP) in outbred female CD1 mice. In this study, we also investigated the expression of alpha-7 nicotinic acetylcholine receptor (α-7 nAChR), a major pre-synaptic nicotinic receptor in the glutamatergic neurons, which regulates glutamate release. We found that inhalation of e-cigarette vapor for six months increased α-7 nAChR expression in both FC and STR, but not in the HIP. In addition, chronic e-cigarette exposure reduced GLT-1 expression only in STR. Moreover, e-cigarette vapor inhalation induced downregulation of xCT in both the STR and HIP. We did not find any significant changes in GLAST expression in any brain region. Finally, using liquid chromatography-tandem mass spectrometry (LC-MS/MS) techniques, we detected high concentrations of nicotine and cotinine, a major metabolite of nicotine, in the FC tissues of e-cigarette exposed mice. These data provide novel evidence about the effects of chronic nicotine inhalation on the expression of key glial glutamate transporters as well as α-7 nAChR. Our work may suggest that nicotine exposure via chronic inhalation of e-cigarette vapor may be mediated in part by alterations in the glutamatergic system.

Modulatory effects of Ampicillin/Sulbactam on glial glutamate transporters and metabotropic glutamate receptor 1 as well as reinstatement to cocaine-seeking behavior

Glutamatergic system has an important role in cocaine-seeking behavior. Studies have reported that chronic exposure to cocaine induces downregulation of glutamate transporter-1 (GLT-1) and cystine/glutamate exchanger (xCT) in the central reward brain regions. Ceftriaxone, a β-lactam antibiotic, restored GLT-1 expression and consequently reduced cue-induced reinstatement of cocaine-seeking behavior. In this study, we investigated the reinstatement to cocaine (20mg/kg, i.p.) seeking behavior using a conditioned place preference (CPP) paradigm in male alcohol-preferring (P) rats. In addition, we investigated the effects of Ampicillin/Sulbactam (AMP/SUL) (200mg/kg, i.p.), a β-lactam antibiotic, on cocaine-induced reinstatement. We also investigated the effects of AMP/SUL on the expression of glial glutamate transporters and metabotropic glutamate receptor 1 (mGluR1) in the nucleus accumbens (NAc) core and shell and the dorsomedial prefrontal cortex (dmPFC). We found that AMP/SUL treatment reduced cocaine-triggered reinstatement. This effect was associated with a decrease in locomotor activity. Moreover, GLT-1 and xCT were downregulated in the NAc core and shell, but not in the dmPFC, following cocaine-primed reinstatement. However, cocaine exposure increased the expression of mGluR1 in the NAc core, but not in the NAc shell or dmPFC. Importantly, AMP/SUL treatment normalized GLT-1 and xCT expression in the NAc core and shell; however, the drug normalized mGluR1 expression in the NAc core only. Additionally, AMP/SUL increased the expression of GLT-1 and xCT in the dmPFC as compared to the water naïve group. These findings demonstrated that glial glutamate transporters and mGluR1 in the mesocorticolimbic area could be potential therapeutic targets for the attenuation of reinstatement to cocaine-seeking behavior.

Glutamate Transport: A New Bench to Bedside Mechanism for Treating Drug Abuse

Drug addiction has often been described as a "hijacking" of the brain circuits involved in learning and memory. Glutamate is the principal excitatory neurotransmitter in the brain, and its contribution to synaptic plasticity and learning processes is well established in animal models. Likewise, over the past 20 years the addiction field has ascribed a critical role for glutamatergic transmission in the development of addiction. Chronic drug use produces enduring neuroadaptations in corticostriatal projections that are believed to contribute to a maladaptive deficit in inhibitory control over behavior. Much of this research focuses on the role played by ionotropic glutamate receptors directly involved in long-term potentiation and depression or metabotropic receptors indirectly modulating synaptic plasticity. Importantly, the balance between glutamate release and clearance tightly regulates the patterned activation of these glutamate receptors, emphasizing an important role for glutamate transporters in maintaining extracellular glutamate levels. Five excitatory amino acid transporters participate in active glutamate reuptake. Recent evidence suggests that these glutamate transporters can be modulated by chronic drug use at a variety of levels. In this review, we synopsize the evidence and mechanisms associated with drug-induced dysregulation of glutamate transport. We then summarize the preclinical and clinical data suggesting that glutamate transporters offer an effective target for the treatment of drug addiction. In particular, we focus on the role that altered glutamate transporters have in causing drug cues and contexts to develop an intrusive quality that guides maladaptive drug seeking behaviors.