Glutamatergic plasticity and alcohol dependence-induced alterations in reward, affect and cognition

Pre- and postsynaptic signatures in the prelimbic cortex associated with "alcohol use disorder" in the rat

The transition to alcohol use disorder (AUD) involves persistent neuroadaptations in executive control functions primarily regulated by the medial prefrontal cortex. However, the neurophysiological correlates to behavioral manifestations of AUD are not fully defined. The association between cortical neuroadaptations and behavioral manifestations of addiction was studied using a multi-symptomatic operant model based on the DSM-5 diagnostic criteria for AUD. This model aimed to characterize an AUD-vulnerable and AUD-resistant subpopulation of outbred male Wistar rats and was combined with electrophysiological measurements in the prelimbic cortex (PL). Mirroring clinical observations, rats exhibited individual variability in their vulnerability to develop AUD-like behavior, including motivation to seek for alcohol (crit 1), increased effort to obtain the substance (crit 2), and continued drinking despite negative consequences (crit 3). Only a small subset of rats met all the aforementioned AUD criteria (3 crit, AUD-vulnerable), while a larger fraction was considered AUD-resilient (0 crit). The development of AUD-like behavior was characterized by disruptions in glutamatergic synaptic activity, involving decreased frequency of spontaneous excitatory postsynaptic currents (sEPSCs) and heightened intrinsic excitability in layers 2/3 PL pyramidal neurons. These alterations were concomitant with a significant impairment in the ability of mGlu2/3 receptors to negatively regulate glutamate release in the PL but not in downstream regions like the basolateral amygdala or nucleus accumbens core. In conclusion alterations in PL synaptic activity were strongly associated with individual addiction scores, indicating their role as potential markers of the behavioral manifestations linked to AUD psychopathology.

Probiotics-role in alleviating the impact of alcohol liver disease and alcohol deaddiction: a systematic review

Background

There are few efficient treatment options for alcohol addiction, which continues to be a serious public health concern. The possible contribution of gut microbiota to the onset and progression of alcohol addiction has been brought to light by recent studies. Probiotics have become a cutting-edge intervention in the treatment of alcohol consumption disorder because of its favorable effects on gut health. The purpose of this systematic review is to assess the body of research on the advantages of probiotics in treating alcoholism and associated neuroinflammatory conditions.

Methods

To find pertinent research published from January 2012 to 2023, a thorough search of electronic databases, including PubMed, Scopus, Google Scholar and Web of Science, was carried out. Included were studies looking at how probiotics affect neuroinflammation, gut- brain axis regulation, alcohol addiction, and related behaviors.

Findings

Several investigations have shown how beneficial probiotics are in reducing systemic inflammation and alcoholic liver disease (ALD). Probiotic treatments successfully corrected the imbalance of microbiota, decreased intestinal permeability, and stopped the passage of bacterial constituents such lipopolysaccharides (LPS) into the bloodstream. Additionally, probiotics helped to regulate neurotransmitter pathways, especially those connected to GABA, glutamate, and dopamine, which are intimately linked to behaviors related to addiction. Furthermore, it was shown that probiotics altered the expression of neurotransmitter signaling and dopamine receptors.

Conclusion

There is strong evidence from this systematic study that probiotics have potential advantages in treating alcohol addiction. The potential of probiotic therapies is demonstrated by the way they modulate important neurotransmitter pathways implicated in addiction, decrease neuroinflammation, and restore the balance of gut flora. To fully investigate the therapeutic potential of probiotics in treating alcohol addiction and enhancing the general wellbeing of those afflicted by this condition, more research is necessary.

Alcohol withdrawal and amphetamine co-use in an animal model for attention deficit hyperactivity disorder

Background: Non-medical use of amphetamine and other stimulants prescribed for treatment of attention deficit/hyperactivity disorder (ADHD) is of special concern when combined with alcohol consumption. In a previous study, we modeled chronic ethanol-amphetamine co-use in adolescent Long-Evans (LE) rats and provided evidence that amphetamine attenuates alcohol withdrawal symptoms.Objectives: This project modeled co-use of amphetamine with alcohol in adolescents with ADHD-like symptoms by examining ethanol-amphetamine administration in adolescent Spontaneously Hypertensive Rats (SHR), an experimental model for the study of ADHD. Withdrawal symptoms were compared among SHR and two control rat strains, LE and Wistar Kyoto (WKY).Methods: At postnatal day 32, parallel groups of 12-24 male SHR, WKY and LE rats were administered a liquid diet containing ethanol (3.6%) and/or amphetamine (20 mg/L). Following administration periods up to 26 days, rats were withdrawn from their treatment and tested for overall severity of alcohol withdrawal symptoms, general locomotor activity, and anxiety-like behavior.Results: Overall withdrawal severity was lower for SHR than for LE (p < .001) or WKY (p = .027). Co-consumption of amphetamine decreased withdrawal severity for LE (p = .033) and WKY (p = .011) but not SHR (p = .600). Only WKY showed increased anxiety-like behavior during withdrawal (p = .031), but not after amphetamine co-administration (p = .832).Conclusion: Alcohol withdrawal severity may be attenuated when co-used with amphetamine. However, as a model for ADHD, SHR adolescents appeared resistant to developing significant signs of alcohol withdrawal following alcohol consumption. Whether alcohol withdrawal symptoms are attenuated or absent, potential consequences could include a decreased awareness of an emerging problem with alcohol use.

Upregulated GIRK2 Counteracts Ethanol-Induced Changes in Excitability and Respiration in Human Neurons

Genome-wide association studies (GWAS) of electroencephalographic endophenotypes for alcohol use disorder (AUD) has identified noncoding polymorphisms within the KCNJ6 gene. KCNJ6 encodes GIRK2, a subunit of a G-protein-coupled inwardly rectifying potassium channel that regulates neuronal excitability. We studied the effect of upregulating KCNJ6 using an isogenic approach with human glutamatergic neurons derived from induced pluripotent stem cells (male and female donors). Using multielectrode arrays, population calcium imaging, single-cell patch-clamp electrophysiology, and mitochondrial stress tests, we find that elevated GIRK2 acts in concert with 7-21 d of ethanol exposure to inhibit neuronal activity, to counteract ethanol-induced increases in glutamate response, and to promote an increase intrinsic excitability. Furthermore, elevated GIRK2 prevented ethanol-induced changes in basal and activity-dependent mitochondrial respiration. These data support a role for GIRK2 in mitigating the effects of ethanol and a previously unknown connection to mitochondrial function in human glutamatergic neurons.

Alcohol sensitivity and tolerance encoding in sleep regulatory circadian neurons in Drosophila

Alcohol tolerance is a simple form of behavioural and neural plasticity that occurs with the first drink. Neural plasticity in tolerance is likely a substrate for longer term adaptations that can lead to alcohol use disorder. Drosophila develop tolerance with characteristics similar to vertebrates, and it is a useful model for determining the molecular and circuit encoding mechanisms in detail. Rapid tolerance, measured after the first alcohol exposure is completely metabolized, is localized to specific brain regions that are not interconnected in an obvious way. We used a forward neuroanatomical screen to identify three new neural sites for rapid tolerance encoding. One of these was composed of two groups of neurons, the DN1a and DN1p glutamatergic neurons, that are part of the Drosophila circadian clock. We localized rapid tolerance to the two DN1a neurons that regulate arousal by light at night, temperature-dependent sleep timing, and night-time sleep. Two clock neurons that regulate evening activity, LNd6 and the 5th LNv, are postsynaptic to the DN1as, and they promote rapid tolerance via the metabotropic glutamate receptor. Thus, rapid tolerance to alcohol overlaps with sleep regulatory neural circuitry, suggesting a mechanistic link.

Alcohol tolerance encoding in sleep regulatory circadian neurons in Drosophila

Alcohol tolerance is a simple form of behavioral and neural plasticity that occurs with the first drink. Neural plasticity in tolerance is likely a substrate for longer term adaptations that can lead to alcohol use disorder. Drosophila develop tolerance with characteristics similar to vertebrates, and it is useful model for determining the molecular and circuit encoding mechanisms in detail. Rapid tolerance, measured after the first alcohol exposure is completely metabolized, is localized to specific brain regions that are not interconnected in an obvious way. We used a forward neuroanatomical screen to identify three new neural sites for rapid tolerance encoding. One of these was comprised of two groups of neurons, the DN1a and DN1p glutamatergic neurons, that are part of the Drosophila circadian clock. We localized rapid tolerance to the two DN1a neurons that regulate arousal by light at night, temperature-dependent sleep timing, and night-time sleep. Two clock neurons that regulate evening activity, LNd6 and the 5th LNv, are postsynaptic to the DN1as and they promote rapid tolerance via the metabotropic glutamate receptor. Thus, rapid tolerance to alcohol overlaps with sleep regulatory neural circuitry, suggesting a mechanistic link.

Imidacloprid Impairs Glutamatergic Synaptic Plasticity and Desensitizes Mechanosensitive, Nociceptive, and Photogenic Response of Drosophila melanogaster by Mediating Oxidative Stress, Which Could Be Rescued by Osthole

Background: Imidacloprid (IMD) is a widely used neonicotinoid-targeting insect nicotine acetylcholine receptors (nAChRs). However, off-target effects raise environmental concerns, including the IMD’s impairment of the memory of honeybees and rodents. Although the down-regulation of inotropic glutamate receptor (iGluR) was proposed as the cause, whether IMD directly manipulates the activation or inhibition of iGluR is unknown. Using electrophysiological recording on fruit fly neuromuscular junction (NMJ), we found that IMD of 0.125 and 12.5 mg/L did not activate glutamate receptors nor inhibit the glutamate-triggered depolarization of the glutamatergic synapse. However, chronic IMD treatment attenuated short-term facilitation (STF) of NMJ by more than 20%. Moreover, by behavioral assays, we found that IMD desensitized the fruit flies’ response to mechanosensitive, nociceptive, and photogenic stimuli. Finally, the treatment of the antioxidant osthole rescued the chronic IMD-induced phenotypes. We clarified that IMD is neither agonist nor antagonist of glutamate receptors, but chronic treatment with environmental-relevant concentrations impairs glutamatergic plasticity of the NMJ of fruit flies and interferes with the sensory response by mediating oxidative stress.

Tryptophan-kynurenine metabolism during acute alcohol withdrawal in patients with alcohol use disorder: The role of immune activation

BACKGROUND

Recent research has suggested that excessive alcohol consumption in patients with alcohol use disorder (AUD) is associated with chronic immune activation, which affects the metabolism of the neurotransmitter precursor amino acid tryptophan (TRP) and contributes to the complex pathophysiology of AUD. Our study investigated possible immune-associated alterations of TRP to kynurenine (KYN) metabolism in patients with AUD during acute alcohol withdrawal.

METHODS

We measured serum concentrations of TRP, KYN, quinolinic (QUIN), kynurenic acid (KYNA), and the immune activation marker neopterin (NEO) at the first, fifth and 10th day of alcohol withdrawal in patients with AUD, who attended a standardized in-patient treatment program and underwent a detailed clinical assessment.

RESULTS

Data from these individuals were compared to data from a reference control group (RCG). The primary outcome measures were the differences in serum concentrations of metabolites between AUD patients and RCG and correlations between NEO and metabolites of the tryptophan-kynurenine pathway. r = 0.695, p < 0.001) in the AUD group. Mixed models analysis showed that NEO concentrations were positively associated with QUIN but not with KYNA concentrations. Several behavioral symptoms correlated positively with QUIN concentrations and negatively with the KYNA/QUIN ratio.

CONCLUSIONS

Our findings demonstrate that the changes in TRP catabolism in acute alcohol withdrawal resulting in increased KYN production could reflect the involvement of immune-associated activation of the enzyme indoleamine 2,3-dioxygenase, as NEO concentrations correlated with the KYN/TRP ratio. In addition, our data show that this low-grade immune activation may cause an imbalance in the production of neurotoxic and neuroprotective kynurenine metabolites in AUD.

A review of functional brain differences predicting relapse in substance use disorder: Actionable targets for new methods of noninvasive brain stimulation

Neuroimaging studies have identified a variety of brain regions whose activity predicts substance use (i.e., relapse) in patients with substance use disorder (SUD), suggesting that malfunctioning brain networks may exacerbate relapse. However, this knowledge has not yet led to a marked improvement in treatment outcomes. Noninvasive brain stimulation (NIBS) has shown some potential for treating SUDs, and a new generation of NIBS technologies offers the possibility of selectively altering activity in both superficial and deep brain structures implicated in SUDs. The goal of the current review was to identify deeper brain structures involved in relapse to SUD and give an account of innovative methods of NIBS that might be used to target them. Included studies measured fMRI in currently abstinent SUD patients and tracked treatment outcomes, and fMRI results were organized with the framework of the Addictions Neuroclinical Assessment (ANA). Four brain structures were consistently implicated: the anterior and posterior cingulate cortices, ventral striatum and insula. These four deeper brain structures may be appropriate future targets for the treatment of SUD using these innovative NIBS technologies.

Cortical GABA levels are reduced in young adult binge drinkers: Association with recent alcohol consumption and sex

Binge drinking refers to a pattern of alcohol intake that raises blood alcohol concentration to or above legal intoxication levels. It is common among young adults and is associated with health risks that scale up with alcohol intake. Acute intoxication depresses neural activity via complex signaling mechanisms by enhancing inhibition mediated by gamma-amino butyric acid (GABA), and by decreasing excitatory glutamatergic effects. Evidence primarily rooted in animal research indicates that the brain compensates for the acute depressant effects under the conditions of habitual heavy use. These neuroadaptive changes are reflected in neural hyperexcitability via downregulated inhibitory signaling, which becomes apparent as withdrawal symptoms. However, human evidence on the compensatory reduction in GABA signaling is scant. The neurochemical aspect of this mechanistic model was evaluated in the present study with proton magnetic resonance spectroscopy (¹H-MRS) which is sensitive to GABA plus macromolecule signal (GABA + ). Furthermore, we examined sex differences in GABA + levels as a function of a recent history of binge drinking, given interactions between endogenous neurosteroids, GABA signaling, and alcohol. The study recruited young adult women and men (22.2 ± 2.8 years of age) who were classified as binge drinkers (BDs, N = 52) if they reported ≥ 5 binge episodes in the previous six months. Light drinkers (LDs, N = 49) reported drinking regularly, but not exceeding ≤ 2 binge episodes in the past six months. GABA-edited ¹H-MR spectra were acquired from the occipital cortex at 3 T with the MEGA-PRESS sequence. GABA + signal was analyzed relative to water and total creatine (Cr) levels as a function of binge drinking history and sex. Controlling for within-voxel tissue composition, both GABA + indices showed decreased GABA + levels in BDs relative to LDs. The reduced GABA + concentration was associated with occasional high-intensity drinking in the BD group. This evidence is consistent with compensatory GABA downregulation that accompanies alcohol misuse, tipping the excitation/inhibition balance towards hyperexcitability. Analysis of the time course of GABA + neuroplasticity indicated that GABA + was lowest when measured one day after the last drinking occasion in BDs. While the BD vs LD differences were primarily driven by LD women, there was no interaction between Sex and a history of binge drinking. GABA + was higher in LD women compared to LD men. Aligned with the allostasis model, the mechanistic compensatory GABA downregulation observed in young emerging adults engaging in occasional binge drinking complements direct neural measures of hyperexcitability in BDs. Notably, these results suggest that neuroadaptation to alcohol is detectable at the levels of consumption that are within a normative range, and may contribute to adverse health outcomes.

Neuroligin Plays a Role in Ethanol-Induced Disruption of Memory and Corresponding Modulation of Glutamate Receptor Expression

Exposure to alcohol causes deficits in long-term memory formation across species. Using a long-term habituation memory assay in Caenorhabditis elegans, the effects of ethanol on long-term memory (&gt; 24 h) for habituation were investigated. An impairment in long-term memory was observed when animals were trained in the presence of ethanol. Cues of internal state or training context during testing did not restore memory. Ethanol exposure during training also interfered with the downregulation of AMPA/KA-type glutamate receptor subunit (GLR-1) punctal expression previously associated with long-term memory for habituation in C. elegans. Interestingly, ethanol exposure alone had the opposite effect, increasing GLR-1::GFP punctal expression. Worms with a mutation in the C. elegans ortholog of vertebrate neuroligins (nlg-1) were resistant to the effects of ethanol on memory, as they displayed both GLR-1::GFP downregulation and long-term memory for habituation after training in the presence of ethanol. These findings provide insights into the molecular mechanisms through which alcohol consumption impacts memory.

The Effects of Enriched Rehabilitation on Cognitive Function and Serum Glutamate Levels Post-stroke

Aim

This study aimed to explore the effect of enriched rehabilitation (ER) on cognitive function and serum glutamate levels in patients with stroke.

Methods

Forty patients diagnosed with post-stroke cognitive impairment (PSCI), according to the inclusion criteria, and undergoing inpatient rehabilitation were enrolled in the study. Patients were randomly assigned to receive 8 weeks of ER treatment (ER group; n = 20) or conventional medical treatment (CM group; n = 20). In addition, 20 age-matched healthy subjects who were outpatients in our hospital during the same period formed the healthy control (HC) group. In- and between-group differences in cognitive function were assessed during pre-intervention and post-intervention based on the Montreal Cognitive Assessment (MoCA), the Symbol Digit Modalities Test (SDMT), and the Trail Making Test (TMT). The serum levels of glutamate, tumor necrosis factor (TNF), and malondialdehyde (MDA) levels were also detected pre-intervention and post-intervention.

Results

Pre-intervention cognitive function and the levels of all the serum parameters assessed significant difference between the HC group and the PSCI group (both ER and CM groups) (p < 0.05), but not between the two groups of patients with PSCI (p > 0.05). Significant improvements were observed in cognitive function in both the ER and the CM groups post-intervention compared with pre-intervention, as evidenced by the measured improvement in MoCA, SDMT, and TMT scores. Similar improvements were seen for serum glutamate, the degree of oxidative damage, and the level of inflammation in both the treatment groups (p < 0.05). More enhancements in cognitive function, including MoCA, SDMT, TMT scores, and the serum levels of glutamate, the degree of oxidative damage, and the level of inflammation were shown in the ER group compared with the CM group post-intervention (p < 0.05).

Conclusions

ER can improve cognitive function in patients with PSCI. The associated mechanism may be related to the negative regulatory effect of ER on serum glutamate, TNF, and MDA levels, which is likely to enhance synaptic plasticity and alleviate oxidative stress- and inflammation-related damage, at least to some extent.

Substance abuse and neurotransmission

The number of people who suffer from a substance abuse disorder has continued to rise over the last decade; particularly, the number of drug-related overdose deaths has sharply increased during the COVID-19 pandemic. Converging lines of clinical observations, supported by imaging and neuropsychological performance testing, have demonstrated that substance abuse-induced dysregulation of neurotransmissions in the brain is critical for development and expression of the addictive properties of abused substances. Recent scientific advances have allowed for better understanding of the neurobiological processes that mediates drugs of abuse and addiction. This chapter presents the past classic concepts and the recent advances in our knowledge about how cocaine, amphetamines, opioids, alcohol, and nicotine alter multiple neurotransmitter systems, which contribute to the behaviors associated with each drug. Additionally, we discuss the interactive effects of HIV-1 or COVID-19 and substance abuse on neurotransmission and neurobiological pathways. Finally, we introduce therapeutic strategies for development of pharmacotherapies for substance abuse disorders.

Neurobiology of alcohol seeking behavior

Alcohol addiction is a chronic relapsing brain disease characterized by an impaired ability to stop or control alcohol use despite adverse consequences. A main challenge of addiction treatment is to prevent relapse, which occurs in more than >50% of newly abstinent patients with alcohol disorder within 3 months. In people suffering from alcohol addiction, stressful events, drug-associated cues and contexts, or re-exposure to a small amount of alcohol trigger a chain of behaviors that frequently culminates in relapse. In this review, we first present the preclinical models that were developed for the study of alcohol seeking behavior, namely the reinstatement model of alcohol relapse and compulsive alcohol seeking under a chained schedule of reinforcement. We then provide an overview of the neurobiological findings obtained using these animal models, focusing on the role of opioids systems, corticotropin-release hormone and neurokinins, followed by dopaminergic, glutamatergic, and GABAergic neurotransmissions in alcohol seeking behavior.

Role of heat shock transcription factor 2 in the NMDA-dependent neuroplasticity induced by chronic ethanol intake in mouse hippocampus

Ethanol consumption impairs learning and memory through disturbances of NMDA-type glutamate receptor-dependent synaptic plasticity (long-term depression [LTD] and long-term potentiation [LTP]) in the hippocampus. Recently, we demonstrated that two ethanol binge-like episodes in young adult rats selectively blocked NMDA-LTD in hippocampal slices, increased NMDA receptor sensitivity to a GluN2B subunit antagonist, and induced cognitive deficits. Here, using knockout adult mice, we show that a stress-responsive transcription factor of the heat shock factor family, HSF2, which is involved in the perturbation of brain development induced by ethanol, participates in these processes. In the absence of ethanol, hsf2^-/- mice show a selective loss of LTD in the hippocampus, which is associated with an increased sensitivity of NMDA-field excitatory postsynaptic potentials (fEPSPs) to a GluN2B antagonist, compared with wild-type (WT) mice. These results suggest that HSF2 is required for proper glutamatergic synaptic transmission and LTD plasticity. After 1 month of chronic ethanol consumption in a two-bottle choice paradigm, WT mice showed an increase in hippocampal synaptic transmission, an enhanced sensitivity to GluN2B antagonist, and a blockade of LTD. In contrast, such modulation of synaptic transmission and plasticity were absent in hsf2^-/- mice. We conclude that HSF2 is an important mediator of both glutamatergic neurotransmission and synaptic plasticity in basal conditions and also mediates ethanol-induced neuroadaptations of the hippocampus network after chronic ethanol intake.

Activation of proline biosynthesis is critical to maintain glutamate homeostasis during acute methamphetamine exposure

Methamphetamine (METH) is a highly addictive psychostimulant that causes long-lasting effects in the brain and increases the risk of developing neurodegenerative diseases. The cellular and molecular effects of METH in the brain are functionally linked to alterations in glutamate levels. Despite the well-documented effects of METH on glutamate neurotransmission, the underlying mechanism by which METH alters glutamate levels is not clearly understood. In this study, we report an essential role of proline biosynthesis in maintaining METH-induced glutamate homeostasis. We observed that acute METH exposure resulted in the induction of proline biosynthetic enzymes in both undifferentiated and differentiated neuronal cells. Proline level was also increased in these cells after METH exposure. Surprisingly, METH treatment did not increase glutamate levels nor caused neuronal excitotoxicity. However, METH exposure resulted in a significant upregulation of pyrroline-5-carboxylate synthase (P5CS), the key enzyme that catalyzes synthesis of proline from glutamate. Interestingly, depletion of P5CS by CRISPR/Cas9 resulted in a significant increase in glutamate levels upon METH exposure. METH exposure also increased glutamate levels in P5CS-deficient proline-auxotropic cells. Conversely, restoration of P5CS expression in P5CS-deficient cells abrogated the effect of METH on glutamate levels. Consistent with these findings, P5CS expression was significantly enhanced in the cortical brain region of mice administered with METH and in the slices of cortical brain tissues treated with METH. Collectively, these results uncover a key role of P5CS for the molecular effects of METH and highlight that excess glutamate can be sequestered for proline biosynthesis as a protective mechanism to maintain glutamate homeostasis during drug exposure.

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 Drugs of Abuse on the Blood-Brain Barrier: A Brief Overview

The use of psychostimulants and alcohol disrupts blood-brain barrier (BBB) integrity, resulting in alterations to cellular function, and contributes to neurotoxicity. The BBB is the critical boundary of the central nervous system (CNS) where it maintains intracellular homeostasis and facilitates communication with the peripheral circulation. The BBB is regulated by tight junction (TJ) proteins that closely interact with endothelial cells (EC). The complex TJ protein network consists of transmembrane proteins, including claudins, occludins, and junction adhesion molecules (JAM), as well as cytoskeleton connected scaffolding proteins, zonula occludentes (ZO-1, 2, and 3). The use of psychostimulants and alcohol is known to affect the CNS and is implicated in various neurological disorders through neurotoxicity that partly results from increased BBB permeability. The present mini review primarily focuses on BBB structure and permeability. Moreover, we assess TJ protein and cytoskeletal changes induced by cocaine, methamphetamine, morphine, heroin, nicotine, and alcohol. These changes promote glial activation, enzyme potentiation, and BBB remodeling, which affect neuroinflammatory pathways. Although the effect of drugs of abuse on BBB integrity and the underlying mechanisms are well studied, the present review enhances the understanding of the underlying mechanisms through which substance abuse disorders cause BBB dysfunction.

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.

Prefrontal GABA and glutamate levels correlate with impulsivity and cognitive function of prescription opioid addicts: A 1 H-magnetic resonance spectroscopy study

AIM

Prescription opioids are psychoactive substances that can elicit many neuropsychological effects. There are no studies that directly demonstrate the effects of prescription opioid addiction (POA) on the human brain. This study aimed to quantify γ-aminobutyric acid (GABA) and glutamate (Glu) levels in the prefrontal cortex (PFC) of POA patients using proton magnetic resonance spectroscopy (¹ H-MRS), and to explore their association with impulsive behavior and cognitive impairment.

METHODS

Thirty-five patients with a definitive clinical diagnosis of codeine-containing cough syrup dependence and 35 matched healthy controls underwent neuropsychological assessments, namely the Barratt Impulsiveness Scale (BIS-11) and the Montreal Cognitive Assessment Scale (MoCA). Point-resolved spectroscopy was performed to detect GABA and glutamate within the medial PFC, and the corresponding levels were estimated using jMRUI and corrected for fraction of cerebrospinal fluid in the ¹ H-MRS voxel. The difference in metabolite levels between groups and the correlation between metabolite levels and psychometric scores in patients were analyzed statistically.

RESULTS

The peak level predominantly consisting of GABA with a relatively small influence of other chemicals (GABA+) was lower and that of glutamate was higher in the PFC of POA patients than in healthy controls. GABA+ levels correlated negatively with BIS-11 scores but correlated positively with MoCA scores. In contrast, glutamate levels showed a positive correlation with BIS-11 scores but no significant correlation with MoCA scores.

CONCLUSION

The quantitative in vivo measurement of GABA and glutamate levels in the PFC by ¹ H-MRS could be a reliable way to evaluate impulsivity and cognitive function of POA.

Withdrawal effects following repeated ethanol exposure are prevented by N-acetylcysteine in zebrafish

Alcohol abuse is a highly prevalent condition that substantially contributes to global morbidity and mortality. Most available pharmacological treatments offer little efficacy as relapse rates are high, due in part to the symptoms experienced during abstinence. The roles of oxidative stress and glutamatergic transmission in alcohol withdrawal have been demonstrated in several studies, suggesting that restoration of oxidative status and glutamatergic function may represent a new pharmacological target to prevent the behavioral and biochemical alterations observed during withdrawal. A well-known antioxidant and glutamatergic modulator, N-acetylcysteine (NAC), has shown promise in treating a variety of psychiatric conditions, including substance use disorders, and is a promising molecule in the management of alcohol withdrawal syndrome. Thus, the aim of this study was to investigate whether NAC is able to prevent the expression of behavioral and biochemical alterations induced by ethanol withdrawal in chronically exposed zebrafish. Animals were exposed to ethanol (1% v/v, 20 min) or control water, followed by treatment with NAC (1 mg/L, 10 min) or control water daily for 8 days; 24 h later, experimental animals were submitted to the novel tank test (NTT). Ethanol withdrawal decreased the distance traveled and increased the number of immobile episodes, indicating locomotor deficits; moreover, withdrawal decreased the number of entries and time spent in the top area, while increasing time spent in the bottom area, indicating anxiety-like behavior. Alcohol withdrawal also increased lipid peroxidation (TBARS) and decreased non-protein reduced sulfhydryl (NPSH) and superoxide dismutase (SOD) and catalase (CAT) activities. NAC attenuated these locomotor deficits and prevented the manifestation of anxiety-like behavior as well as the oxidative damage observed following ethanol withdrawal. Given its favorable safety profile, additional clinical and preclinical studies are warranted to unravel the long-term effects of NAC in the context of alcohol abuse and the exact mechanisms involved. Nevertheless, our study adds to the existing body of evidence supporting the clinical evaluation of NAC in substance abuse disorders.

Dropout from Court-Mandated Intervention Programs for Intimate Partner Violence Offenders: The Relevance of Alcohol Misuse and Cognitive Impairments

There is considerable interest in offering insight into the mechanisms that might explain why certain perpetrators of intimate partner violence against women (IPVAW) drop out of interventions. Although several socio-demographic variables and attitudes towards IPVAW have been proposed as risk factors for IPVAW perpetrators' dropout, less attention has been paid to alcohol misuse, and its interactions with empathic and cognitive deficits, in the discontinuation of the treatment. Therefore, the main aim of this study was to compare the profile of a carefully selected sample of IPVAW perpetrators, divided into four groups: those who completed the intervention with low (n = 267) and high alcohol consumption (n = 67); and those who dropped out before the intervention ended with low (n = 62).and high alcohol consumption (n = 27). Furthermore, we also studied the initial risk before the intervention started and the official IPVAW recidivism during the first year after the intervention ended. Our results revealed that IPVAW perpetrators, especially those who did not complete the intervention and had high alcohol consumption/alcohol misuse, were less accurate in decoding emotional facial signals and presented more errors and perseverative errors than those who completed the intervention. These differences were particularly marked in comparison with those who showed less alcohol consumption. Furthermore, the first group also presented the highest risk (assessed by therapists) and official recidivism rate (official records). Conversely, the lowest rate of IPVAW reoffending was presented by IPVAW treatment completers with low alcohol consumption. Hence, our study identifies different targets that should be addressed during the initial stages of interventions in order to prevent or reduce IPVAW dropout, which in turn might reduce violence recidivism in the long term through their effects on emotional information processing and behavioural regulation.

Alcohol in the Aging Brain - The Interplay Between Alcohol Consumption, Cognitive Decline and the Cardiovascular System

As our society grows older new challenges for medicine and healthcare emerge. Age-related changes of the body have been observed in essential body functions, particularly in the loco-motor system, in the cardiovascular system and in cognitive functions concerning both brain plasticity and changes in behavior. Nutrition and lifestyle, such as nicotine intake and chronic alcohol consumption, also contribute to biological changes in the brain. This review addresses the effect of alcohol consumption on cognitive decline, changes in brain plasticity in the aging brain and on cardiovascular health in aging. Thus, studies on the interplay of chronic alcohol intake and either cognitive decline or cognitive preservation are outlined. Because of the inconsistency in the literature of whether alcohol consumption preserves cognitive functions in the aging brain or whether it accelerates cognitive decline, it is crucial to consider individual contributing factors such as culture, health and lifestyle in future studies.

Alcohol withdrawal drives depressive behaviors by activating neurons in the rostromedial tegmental nucleus

Rostromedial tegmental nucleus (RMTg) GABA neurons exert a primary inhibitory drive onto midbrain dopamine neurons and are excited by a variety of aversive stimuli. There is, however, little evidence that the RMTg-ventral tegmental area (VTA)-nucleus accumbens shell (Acb) circuit plays a role in the aversive consequences of alcohol withdrawal. This study was performed in adult male Long-Evans rats at 48-h withdrawal from chronic alcohol drinking in the intermittent schedule. These rats displayed clear anhedonia and depression-like behaviors, as measured with the sucrose preference, and forced swimming tests. These aberrant behaviors were accompanied by a substantial increase in cFos expression in the VTA-projecting RMTg neurons, identified by a combination of immunohistochemistry and retrograde-tracing techniques. Pharmacological or chemogenetic inhibition of RMTg neurons mitigated the anhedonia and depression-like behaviors. Ex vivo electrophysiological data showed that chemogenetic inactivation of RMTg neurons reduced GABA release and accelerated spontaneous firings of VTA dopamine neurons. Finally, using a functional hemispheric disconnection procedure, we demonstrated that inhibition of unilateral RMTg, when combined with activation of D1 and D2 dopamine receptors in the contralateral (but not ipsilateral) Acb, mitigated the anhedonia and depression-like behaviors in alcohol-withdrawal rats. These data show that the integrity in the RMTg-VTA-Acb pathway in a single hemisphere is sufficient to elicit depression-like behavior during ethanol-withdrawal. Overall, the present results reveal that the RMTg-VTA-Acb pathway plays a crucial role in the depression-like behavior in animals undergoing alcohol withdrawal, further advocating the RMTg as a potential therapeutic target for alcoholism.

The lack of conditioned place preference, but unaltered stimulatory and ataxic effects of alcohol in mGluR3-KO mice

BACKGROUND

Alcohol use associates with environmental cues that can later reinstate drinking patterns without any alcohol exposure. Alcohol-induced reward, when combined with contextual signals of various sensory modalities in the central synapses of mesolimbic reward circuitries, can lead to the formation of conditioned responses.

AIMS

As the activation of glutamatergic synapses is pivotal in such processes, we aimed to investigate whether the metabotropic glutamate receptor subtype 3 plays a role in alcohol-induced behaviours including place preference.

METHODS

The metabotropic glutamate receptor subtype 3 knockout (mGluR3-KO) mouse line was used to study alcohol-induced place preference, locomotor activating and ataxic effects, limited access alcohol drinking, and preference for sucrose and saccharin.

RESULTS

Alcohol-induced horizontal locomotor stimulation and reduced rearing behaviour remained unchanged in the mGluR3-KO mice. However, alcohol-induced place conditioning in an unbiased paradigm setup was lacking in the mGluR3-KO mice, but clearly present in wildtype mice. Locomotor activity was not different between the mGluR3-KO and wildtype mice during the acquisition and expression trials. Alcohol consumption, studied through the 'drinking in the dark' model, remained unchanged in the mGluR3-KO mice, although low consumption in both wildtype and knockout mice hampers interpretation. The mGluR3-KO mice also showed normal sucrose and saccharin preference.

CONCLUSIONS

These studies indicate a role for metabotropic glutamate receptor subtype 3 in the conditioned contextual alcohol responses, but not in stimulatory, and ataxic alcohol effects.

Sequential Changes in Brain Glutamate and Adenosine A1 Receptors May Explain Severity of Adolescent Alcohol Withdrawal after Consumption of High Levels of Alcohol

There is an excellent correlation between the age when alcohol consumption begins and the likelihood of lifelong problems with alcohol abuse. Alcohol use often begins in adolescence, a time marked by brain development and maturation of numerous brain systems. Rats are an important model, wherein the emergence of alcohol withdrawal symptoms serves as a gauge of dependency following chronic alcohol consumption. Previous work has shown that adolescent Long-Evans rats consume high levels of alcohol and develop a severe alcohol withdrawal syndrome when fed alcohol as part of a liquid diet. Acutely, alcohol inhibits two important excitatory receptors for glutamate (NMDA and AMPA) and may further decrease glutamate activity through modulatory adenosine receptors. The present study focuses on potential adaptive changes in expression of these receptors that may create a receptor imbalance during chronic alcohol consumption and lead to severe overexcitation of the adolescent brain during alcohol withdrawal. Levels of brain expression of NMDA, AMPA, and adenosine A1 and A2a receptors were determined by Western blotting after adolescent rats consumed an alcohol-containing liquid diet for 4, 11, or 18 days. Severity of alcohol withdrawal was also assessed at these time points. Levels increased for both AMPA and NMDA receptors, significant and approaching maximal by day 11. In contrast, A1 receptor density showed a slow decline reaching significance at 18 days. There were no changes in expression of adenosine A2a receptor. The most severe withdrawal symptoms appear to coincide with the later downregulation of adenosine A1 receptors coming on top of maximal upregulation of excitatory AMPA and NMDA glutamate receptors. Thus, loss of adenosine "brakes" on glutamate excitation may punctuate receptor imbalance in alcohol-consuming adolescents by allowing the upregulation of the excitatory receptors to have full impact during early alcohol withdrawal.

Association between increased retinal background noise and co-occurrent regular cannabis and alcohol use

BACKGROUND

Cannabis consumption is widespread across the world, and the co-occurrence of cannabis use and alcohol consumption is common. The study of background noise - resting-state neural activity, in the absence of stimulation - is an approach that could enable the neurotoxicity of these substances to be explored. Preliminary results have shown that delta-9-tetrahydrocannabinol (Δ9-THC) causes an increase in neural noise in the brain. Neurons in the brain and the retina share a neurotransmission system and have similar anatomical and functional properties. Retinal function, evaluated using an electroretinogram (ERG), may therefore reflect central neurochemistry. This study analyses retinal background noise in a population of regular co-occurrent cannabis and alcohol consumers.

METHODS

We recorded the flash ERGs of 26 healthy controls and 45 regular cannabis consumers, separated into two groups based on their alcohol consumption: less than or equal to 4 glasses per week (CU ≤ 4) or strictly >4 glasses per week (CU >4). In order to extract the background noise, the Fourier transform of the pseudo-periodic and sinusoidal signals of the 3.0 flicker-response sequence was calculated. This sequence represents the vertical transmission of the signal from cones to bipolar cells. The magnitude of the background noise is defined as the average of the magnitudes of the two neighbouring harmonics: harmonic -1 (low frequency noise) and harmonic +1 (high frequency noise).

RESULTS

The magnitude of harmonic -1 was significantly increased between the groups CU > 4 (6.78 (±1.24)) and CU ≤ 4 (5.69 (±1.80)) among regular users of cannabis and alcohol. A significant increase in the average magnitude of the two harmonics was found between the groups CU > 4 (5.12 (±0.92)) and CU ≤ 4 (4.36 (±1.14)). No significant difference was observed with regard to the magnitude of the harmonic +1.

CONCLUSIONS

The increase in background noise may reflect the neurotoxicity of cannabis, potentiated by alcohol consumption, on retinal neurons dynamic. This neural disruption of the response generated by retinal stimulation may be attributable to altered neurotransmitter release.

Improving empathy with motivational strategies in batterer intervention programmes: Results of a randomized controlled trial

OBJECTIVES

Empathy (i.e., the ability to decode emotions, as well as cognitive and emotional empathy) is involved in moral reasoning, prosocial behaviour, social and emotional adequacy, mood and behaviour regulation. Hence, alterations in these functions could reduce behaviour control and the adoption of specific types of violence such as intimate partner violence (IPV). Although interventions for IPV perpetrators focus on reducing IPV risk factors and increasing protective factors to prevent this kind of violence, the study of the effectiveness of these programmes in promoting changes in empathy (cognitive and emotional) has been neglected.

DESIGN

Hence, the main aim of this study was to compare the effectiveness of two different modalities of IPV intervention programmes (Standard Batterer Intervention Programs [SBIP] vs. SBIP + Individualized Motivational Plan [IMP]) in promoting empathic improvements after both interventions.

METHOD

Participants were randomly assigned to receive SBIP (n = 40) or SBIP + IMP (n = 53). The effectiveness of the intervention in the total sample and the group effects were evaluated with general linear model repeated-measures ANOVA.

RESULTS

Results revealed that only the IPV perpetrators who received the SBIP + IMP were more accurate in decoding emotional facial signals and presented better cognitive empathy (perspective taking) after the intervention programme.

CONCLUSIONS

Our study reinforces the view that different modalities of IPV intervention might lead to different cognitive outcomes after the intervention. Thus, these results may help professionals to develop specific intervention programmes focused on improving cognitive abilities in order to reduce IPV recidivism.

PRACTITIONER POINTS

Interventions for batterers' neglected empathic changes after these programmes. Not enough randomized controlled trials for these kinds of interventions. An improvement in the ability to decode emotions after the intervention programme. An improvement in cognitive empathy (perspective taking) after the intervention programme. Different modalities of IPV intervention might lead to different cognitive outcomes after the intervention.

Rat 50-kHz ultrasonic vocalizations as a tool in studying neurochemical mechanisms that regulate positive emotional states

BACKGROUND

Adolescent and adult rats emit 50-kHz ultrasonic vocalizations (USVs) to communicate the appetitive arousal and the presence of positive emotional states to conspecifics.

NEW METHOD

Based on its communicative function, emission of 50-kHz USVs is increasingly being evaluated in preclinical studies of affective behavior, motivation and social behavior.

RESULTS

Emission of 50-kHz USVs is initiated by the activation of dopamine receptors in the shell subregion of the nucleus accumbens. However, several lines of evidence show that non-dopaminergic receptors may influence the numbers of 50-kHz USVs that are emitted, as well as the acoustic parameters of calls.

COMPARISON WITH EXISTING METHODS

Emission of 50-kHz USVs is a non-invasive method that may be used to study reward and motivation without the need for extensive training and complex animal manipulations. Moreover, emission of 50-kHz USVs can be used alone or combined with other well-standardized behavioral paradigms (e.g., conditioned place preference, self-administration).

CONCLUSIONS

This review summarizes the current evidence concerning molecular mechanisms that regulate the emission of 50-kHz USVs. Moreover, the review discusses the usefulness of 50-kHz USVs as an experimental tool to investigate how different neurotransmitter systems regulate the manifestations of positive emotional states, and also use of this tool in preclinical modeling of psychiatric diseases.

The endocannabinoid-alcohol crosstalk: Recent advances on a bi-faceted target

Increasing evidence has focusesed on the endocannabinoid system as a relevant player in the induction of aberrant synaptic plasticity and related addictive phenotype following chronic excessive alcohol drinking. In addition, the endocannabinoid system is implicated in the pathogenesis of alcoholic liver disease. Interestingly, whereas the involvement of CB1 receptors in alcohol rewarding properties is established, the central and peripheral action of CB2 signalling is still to be elucidated. This review aims at giving the input to deepen knowledge on the role of the endocannabinoid system, highlighting the advancing evidence that suggests that CB1 and CB2 receptors may play opposite roles in the regulation of both the reinforcing properties of alcohol in the brain and the mechanisms responsible for cell injury and inflammation in the hepatic tissue. The manipulation of the endocannabinoid system could represent a bi-faceted strategy to counteract alcohol-related dysfunction in central transmission and liver structural and functional disarrangement.

Morphological and functional evidence of increased excitatory signaling in the prelimbic cortex during ethanol withdrawal

Excessive alcohol consumption in humans induces deficits in decision making and emotional processing, which indicates a dysfunction of the prefrontal cortex (PFC). The present study aimed to determine the impact of chronic intermittent ethanol (CIE) inhalation on mouse medial PFC pyramidal neurons. Data were collected 6-8 days into withdrawal from 7 weeks of CIE exposure, a time point when mice exhibit behavioral symptoms of withdrawal. We found that spine maturity in prelimbic (PL) layer 2/3 neurons was increased, while dendritic spines in PL layer 5 neurons or infralimbic (IL) neurons were not affected. Corroborating these morphological observations, CIE enhanced glutamatergic transmission in PL layer 2/3 pyramidal neurons, but not IL layer 2/3 neurons. Contrary to our predictions, these cellular alterations were associated with improved, rather than impaired, performance in reversal learning and strategy switching tasks in the Barnes maze at an earlier stage of chronic ethanol exposure (5-7 days withdrawal from 3 to 4 weeks of CIE), which could result from the anxiety-like behavior associated with ethanol withdrawal. Altogether, this study adds to a growing body of literature indicating that glutamatergic activity in the PFC is upregulated following chronic ethanol exposure, and identifies PL layer 2/3 pyramidal neurons as a sensitive target of synaptic remodeling. It also indicates that the Barnes maze is not suitable to detect deficits in cognitive flexibility in CIE-withdrawn mice.

Trauma exposure and heavy drinking and drug use among college students: Identifying the roles of negative and positive affect lability in a daily diary study

Trauma exposure is linked to heavy drinking and drug use among college students. Extant research reveals positive associations between negative affect lability and both trauma exposure and alcohol use. This study aimed to extend past research by using daily diary methods to test whether (a) individuals with (versus without) trauma exposure experience greater negative and positive affect lability, (b) negative and positive affect lability are associated with heavy drinking and drug use, and (c) negative and positive affect lability mediate the relations between trauma exposure and heavy drinking and drug use. Participants were 1640 college students (M age=19.2, 54% female, 80% European American) who provided daily diary data for 30days via online surveys. Daily diaries assessed negative and positive affect and substance use (i.e., percent days of heavy drinking, percent days of drug use, total number of drugs used). Individuals with (versus without) a history of trauma exposure demonstrated higher levels of negative and positive affect lability. Negative, but not positive, affect lability was associated with percent days of heavy drinking, percent days of drug use, and total number of drugs used, and mediated the associations between trauma exposure and heavy drinking and drug use outcomes. Findings provide support for the underlying role of negative affect lability in the relations between trauma exposure and heavy drinking and drug use among college students, suggesting that treatments targeting negative affect lability may potentially serve to reduce heavy drinking and drug use among trauma-exposed college students.

Effect of N-acetylcysteine on motivation, seeking and relapse to ethanol self-administration

Alcohol use disorder is a chronic and highly relapsing disorder, characterized by a loss of control over alcohol consumption and craving. Several studies suggest a key role of glutamate in this disorder. In recent years, the modulation of cystine/glutamate exchange via the x_c^- system has emerged as a new therapeutic alternative for reducing the excitatory glutamatergic transmission observed after ethanol self-administration in both rats and humans. The objective of this study was to determine whether a treatment with N-acetylcysteine (NAC), a cystine prodrug, could reduce ethanol self-administration, ethanol-seeking behavior and reacquisition of ethanol self-administration. Male Long Evans rats were trained to self-administer 20 percent ethanol in operant cages for several weeks. Once the consumption surpassed 1 g of ethanol/kg body weight/15 minutes, the effect of an acute intraperitoneal injection of NAC (0, 25, 50 or 100 mg/kg) 1 hour before the beginning of each test was evaluated on different aspects of the operant self-administration behavior. We demonstrated antimotivational properties of NAC (100 mg/kg), as ethanol-reinforced responding was reduced in a fixed ratio (-35 percent) and in a progressive ratio schedule (-81 percent). NAC also reduced ethanol-seeking behavior (-77 percent) evaluated as extinction responding in a single extinction session. NAC was able to reduce reacquisition in rats that were abstinent for 17 days, while NAC had no effect on ethanol relapse in rats previously exposed to six extinction sessions. Overall, our results demonstrate that NAC limits motivation, seeking behavior and reacquisition in rats, making it a potential new treatment for the maintenance of abstinence.

Behavioral and Brain Activity Indices of Cognitive Control Deficits in Binge Drinkers

Heavy episodic drinking is prevalent among young adults and is a public issue of increasing importance. Its initiation and maintenance are associated with deficits in the capacity to inhibit automatic processing in favor of non-habitual responses. This study used functional magnetic resonance imaging (fMRI) to examine behavioral and brain activity indices of cognitive control during the Stroop task as a function of binge drinking. Heavy episodic drinkers (HED) reported consuming 5+/6+ drinks in two hours at least five times in the past six months and were compared to light drinkers (LED) who reported two or fewer binge episodes but were matched on demographics, intelligence and family history of alcoholism. Greater conflict-induced activity in the ventrolateral prefrontal cortex (VLPFC) and thalamus was observed in HED participants and it was positively correlated with alcohol intake and alcohol-related harmful consequences. HEDs maintained intact accuracy but at a cost of prolonged reaction times to high-conflict trials and increased ratings of task difficulty. Greater activation of the areas implicated in cognitive control is consistent with compensatory network expansion to meet higher cognitive demands. These results provide further insight into degradation of cognitive control in HEDs which may benefit development of detection and prevention strategies.

Increased Absolute Glutamate Concentrations and Glutamate-to-Creatine Ratios in Patients With Methamphetamine Use Disorders

Introduction: Previous studies have indicated that changes in the concentration of glutamate and related metabolites may mediate the progression of addiction in patients with methamphetamine (MA) use disorders. In the present study, we utilized magnetic resonance spectroscopy (MRS) to investigate absolute glutamate concentrations and metabolite ratios in patients with MA addiction. We further analyzed the association between glutamate concentration and various clinical indicators. Methods: The present study included 31 unmedicated patients with clinically diagnosed MA dependence (mean age: 30.5 ± 8.0 years) and 32 age-matched healthy controls (mean age: 32.9 ± 8.2 years). Patients were evaluated using the Barratt Impulsiveness Scale (BIS-11). We also collected general information regarding the duration and dosage of drug use. Point-resolved spectroscopy was used to quantify the absolute concentrations of metabolites (glutamate, choline, N-acetylaspartate, glutamine, and creatine), as well as the ratio of metabolites to total creatine, using LCModel software. We then compared differences in glutamate levels and psychometric scores between the two groups. Results: Glutamate-to-creatine ratios in the brainstem were significantly higher in the MA group than in the control group (t = 2.764, p = 0.008). Glutamate concentrations in the brainstem were also significantly higher in the MA group than in the control group (t = 2.390, p = 0.020). However, no significant differences in the concentrations or ratios of other metabolites were observed between the two groups (all p > 0.05). Glutamate concentration was positively correlated with the duration of drug use (r = 0.401, p = 0.035) and the total dose of regular addiction (duration of addiction × regular addiction dose; r = 0.207, p = .040), but not with BIS-11 scores. Conclusions: Our findings indicated that glutamate levels in the brainstem are significantly elevated in patients with MA use disorders, and that these levels are significantly associated with the duration and dose of drug use.Such findings suggest that glutamate concentration can be used as an objective biological marker for evaluating/monitoring disease status and treatment efficacy in patients with MA dependence.

Rat animal models for screening medications to treat alcohol use disorders

The purpose of this review is to present animal research models that can be used to screen and/or repurpose medications for the treatment of alcohol abuse and dependence. The focus will be on rats and in particular selectively bred rats. Brief introductions discuss various aspects of the clinical picture, which provide characteristics of individuals with alcohol use disorders (AUDs) to model in animals. Following this, multiple selectively bred rat lines will be described and evaluated in the context of animal models used to screen medications to treat AUDs. Next, common behavioral tests for drug efficacy will be discussed particularly as they relate to stages in the addiction cycle. Tables highlighting studies that have tested the effects of compounds using the respective techniques are included. Wherever possible the Tables are organized chronologically in ascending order to describe changes in the focus of research on AUDs over time. In general, high ethanol-consuming selectively bred rats have been used to test a wide range of compounds. Older studies usually followed neurobiological findings in the selected lines that supported an association with a propensity for high ethanol intake. Most of these tests evaluated the compound's effects on the maintenance of ethanol drinking. Very few compounds have been tested during ethanol-seeking and/or relapse and fewer still have assessed their effects during the acquisition of AUDs. Overall, while a substantial number of neurotransmitter and neuromodulatory system targets have been assessed; the roles of sex- and age-of-animal, as well as the acquisition of AUDs, ethanol-seeking and relapse continue to be factors and behaviors needing further study. This article is part of the Special Issue entitled "Alcoholism".

Homer2 and Alcohol: A Mutual Interaction

The past two decades of data derived from addicted individuals and preclinical animal models of addiction implicate a role for the excitatory glutamatergic transmission within the mesolimbic structures in alcoholism. The cellular localization of the glutamatergic receptor subtypes, as well as their signaling efficiency and function, are highly dependent upon discrete functional constituents of the postsynaptic density, including the Homer family of scaffolding proteins. The consequences of repeated alcohol administration on the expression of the Homer family proteins demonstrate a crucial and active role, particularly for the expression of Homer2 isoform, in regulating alcohol-induced behavioral and cellular neuroplasticity. The interaction between Homer2 and alcohol can be defined as a mutual relation: alcohol consumption enhances the expression of Homer2 protein isoform within the nucleus accumbens and the extended amygdala, cerebral areas where, in turn, Homer2 is able to mediate the development of the "pro-alcoholic" behavioral phenotype, as a consequence of the morpho-functional synaptic adaptations. Such findings are relevant for the detection of the strategic molecular components that prompt alcohol-induced functional and behavioral disarrangement as targets for future innovative treatment options.

Do specific NMDA receptor subunits act as gateways for addictive behaviors?

Addiction to alcohol and drugs is a major social and economic problem, and there is considerable interest in understanding the molecular mechanisms that promote addictive drives. A number of proteins have been identified that contribute to expression of addictive behaviors. NMDA receptors (NMDARs), a subclass of ionotropic glutamate receptors, have been of particular interest because their physiological properties make them an attractive candidate for gating induction of synaptic plasticity, a molecular change thought to mediate learning and memory. NMDARs are generally inactive at the hyperpolarized resting potentials of many neurons. However, given sufficient depolarization, NMDARs are activated and exhibit long-lasting currents with significant calcium permeability. Also, in addition to stimulating neurons by direct depolarization, NMDARs and their calcium signaling can allow strong and/or synchronized inputs to produce long-term changes in other molecules (such as AMPA-type glutamate receptors) which can last from days to years, binding internal and external stimuli in a long-term memory trace. Such memories could allow salient drug-related stimuli to exert strong control over future behaviors and thus promote addictive drives. Finally, NMDARs may themselves undergo plasticity, which can alter subsequent neuronal stimulation and/or the ability to induce plasticity. This review will address recent and past findings suggesting that NMDAR activity promotes drug- and alcohol-related behaviors, with a particular focus on GluN2B subunits as possible central regulators of many addictive behaviors, as well as newer studies examining the importance of non-canonical NMDAR subunits and endogenous NMDAR cofactors.

Neuroimaging markers of glutamatergic and GABAergic systems in drug addiction: Relationships to resting-state functional connectivity

Drug addiction is characterized by widespread abnormalities in brain function and neurochemistry, including drug-associated effects on concentrations of the excitatory and inhibitory neurotransmitters glutamate and gamma-aminobutyric acid (GABA), respectively. In healthy individuals, these neurotransmitters drive the resting state, a default condition of brain function also disrupted in addiction. Here, our primary goal was to review in vivo magnetic resonance spectroscopy and positron emission tomography studies that examined markers of glutamate and GABA abnormalities in human drug addiction. Addicted individuals tended to show decreases in these markers compared with healthy controls, but findings also varied by individual characteristics (e.g., abstinence length). Interestingly, select corticolimbic brain regions showing glutamatergic and/or GABAergic abnormalities have been similarly implicated in resting-state functional connectivity deficits in drug addiction. Thus, our secondary goals were to provide a brief review of this resting-state literature, and an initial rationale for the hypothesis that abnormalities in glutamatergic and/or GABAergic neurotransmission may underlie resting-state functional deficits in drug addiction. In doing so, we suggest future research directions and possible treatment implications.