Dose-related ethanol-like effects of the NMDA antagonist, ketamine, in recently detoxified alcoholics

Substitution therapy for patients with alcohol dependence: Mechanisms of action and efficacy

New approaches for the treatment of alcohol dependence (AD) may improve patient outcomes. Substitution maintenance therapy is one of the most effective treatment options for opioid and nicotine use disorders. So far, there has been little attention to substitution therapy for the treatment of AD. Here, we explain the mechanistic foundations of alcohol substitution maintenance therapy. Alcohol has many primary targets in the brain (and other organs) and the physical interaction of ethanol molecules with these specific ethanol-sensitive sites on a variety of ionotropic receptors (e.g. GABA-A, NMDA, and nicotinic acetylcholine (nACh) receptors) and ion channels provides the rationale for substitution. As such, a variety of compounds can interact with those ethanol-sensitive sites and can thus substitute for some of the effects of alcohol. For some of these compounds, alcohol discrimination studies have shown their substitution potential. Accordingly, potential substitution treatments include agonists acting at GABA receptors such as sodium oxybate, baclofen and benzodiazepines, NMDA receptor antagonists such as ketamine and memantine, or nAChRs agonists such as varenicline. All these compounds are already approved for other indications and we present clinical evidence for these drugs in the treatment of alcohol withdrawal syndrome (AWS) and in the long-term treatment of AD, and outline future steps for their acceptance as substitution treatment in AD. Finally, we discuss the substitution approach of managed alcohol programs for the most severely affected homeless populations. Results showed that sodium oxybate is probably the closest to a substitution therapy for AD and is already approved for the treatment of AWS and in the long-term treatment of AD in some countries. In conclusion, we argue that better AD treatment can be provided if substitution maintenance treatments for alcohol are implemented at a similar scale as for opioid and nicotine use disorder.

Ketamine and rapid antidepressant action: new treatments and novel synaptic signaling mechanisms

Ketamine is an open channel blocker of ionotropic glutamatergic N-Methyl-D-Aspartate (NMDA) receptors. The discovery of its rapid antidepressant effects in patients with depression and treatment-resistant depression fostered novel effective treatments for mood disorders. This discovery not only provided new insight into the neurobiology of mood disorders but also uncovered fundamental synaptic plasticity mechanisms that underlie its treatment. In this review, we discuss key clinical aspects of ketamine's effect as a rapidly acting antidepressant, synaptic and circuit mechanisms underlying its action, as well as how these novel perspectives in clinical practice and synapse biology form a road map for future studies aimed at more effective treatments for neuropsychiatric disorders.

Post-Partum Depression Lactating Rat Model for Evaluating Ketamine’s Safety as a Pharmacotherapeutic Treatment: Roles in Cardiac and Urinary Function

Depression is one of the world’s most common and mentally disabling illnesses. Post-partum depression is a subtype of depression that affects one in seven women worldwide. Successful pharmacological treatment must consider the consequences for both, since the mother–child bond is fundamental for the well-being of both mother and infant as well as the general development of the newborn. Changes in maternal physiology and/or behavior can significantly influence the development of breastfed infants. Ketamine has been extensively studied for use as an antidepressant due to its mixed mechanisms of action. Safety and efficacy studies in the cardiovascular and urinary systems of a lactating postpartum depression animal model are essential for contributing toward ketamine’s clinical use in the respective patient population. Thus, this project aimed to study the implications of postpartum maternal exposure to ketamine during lactation on the cardiovascular system of female rats submitted to the depression induction model by maternal separation. This model promotes depressive effects through stress caused by the interruption of mother–infant bond early in the offspring’s life. To achieve depression, each dam was separated from her offspring for 3 h per day, from post-natal day 2 (PND2) to PND12. Experimental groups received daily treatment with either 5, 10, or 20 mg/kg of ketamine intraperitoneally during the lactation period, from PND2 to PND21. Behavioral tests consisted of the maternal and aggressive maternal behavior tests, the olfactory preference test, and the forced swim test. A technique for the detection of catecholamines and indoleamines in the heart muscle was developed for the experimental model groups. The histopathological evaluation was performed on these animals’ cardiac muscles and urinary bladders. Our findings suggest that ketamine is safe for use in postpartum depression and does not induce cardiovascular and/or urinary systems toxicity.

Interoception and alcohol: Mechanisms, networks, and implications

Interoception refers to the perception of the internal state of the body and is increasingly being recognized as an important factor in mental health disorders. Drugs of abuse produce powerful interoceptive states that are upstream of behaviors that drive and influence drug intake, and addiction pathology is impacted by interoceptive processes. The goal of the present review is to discuss interoceptive processes related to alcohol. We will cover physiological responses to alcohol, how interoceptive states can impact drinking, and the recruitment of brain networks as informed by clinical research. We also review the molecular and brain circuitry mechanisms of alcohol interoceptive effects as informed by preclinical studies. Finally, we will discuss emerging treatments with consideration of interoception processes. As our understanding of the role of interoception in drug and alcohol use grows, we suggest that the convergence of information provided by clinical and preclinical studies will be increasingly important. Given the complexity of interoceptive processing and the multitude of brain regions involved, an overarching network-based framework can provide context for how focused manipulations modulate interoceptive processing as a whole. In turn, preclinical studies can systematically determine the roles of individual nodes and their molecular underpinnings in a given network, potentially suggesting new therapeutic targets and directions. As interoceptive processing drives and influences motivation, emotion, and subsequent behavior, consideration of interoception is important for our understanding of processes that drive ongoing drinking and relapse.

TSPAN5 influences serotonin and kynurenine: pharmacogenomic mechanisms related to alcohol use disorder and acamprosate treatment response

We previously reported that SNPs near TSPAN5 were associated with plasma serotonin (5-HT) concentrations which were themselves associated with selective serotonin reuptake inhibitor treatment outcomes in patients with major depressive disorder (MDD). TSPAN5 SNPs were also associated with alcohol consumption and alcohol use disorder (AUD) risk. The present study was designed to explore the biological function of TSPAN5 with a focus on 5-HT and kynurenine concentrations in the tryptophan pathway. Ethanol treatment resulted in decreased 5-HT concentrations in human induced pluripotent stem cell (iPSC)-derived neuron culture media, and the downregulation of gene expression of TSPAN5, DDC, MAOA, MAOB, TPH1, and TPH2 in those cells. Strikingly, similar observations were made when the cells were treated with acamprosate-an FDA approved drug for AUD therapy. These results were replicated in iPSC-derived astrocytes. Furthermore, TSPAN5 interacted physically with proteins related to clathrin and other vesicle-related proteins, raising the possibility that TSPAN5 might play a role in vesicular function in addition to regulating expression of genes associated with 5-HT biosynthesis and metabolism. Downregulation of TSPAN5 expression by ethanol or acamprosate treatment was also associated with decreased concentrations of kynurenine, a major metabolite of tryptophan that plays a role in neuroinflammation. Knockdown of TSPAN5 also influenced the expression of genes associated with interferon signaling pathways. Finally, we determined that TSPAN5 SNPs were associated with acamprosate treatment outcomes in AUD patients. In conclusion, TSPAN5 can modulate the concentrations of 5-HT and kynurenine. Our data also highlight a potentially novel pharmacogenomic mechanism related to response to acamprosate.

Rewarding Subjective Effects of the NMDAR Antagonist Nitrous Oxide (Laughing Gas) Are Moderated by Impulsivity and Depressive Symptoms in Healthy Volunteers

BACKGROUND

Nitrous oxide (N2O) is an anesthetic gas with both therapeutic and abuse potential. Because N2O is an NMDA receptor (NMDAR) antagonist, its effects are expected to resemble those of the prototypical NMDAR antagonist, ketamine. In this study, we examined the subjective rewarding effects of N2O using measures previously employed in studies of ketamine. We also tested for moderation of these effects by bipolar phenotype, depressive symptoms, and impulsivity.

METHODS

Healthy volunteers were randomly assigned to either 50% N2O (n = 40) or medical air (n = 40). Self-reported rewarding (liking and wanting), and alcohol-like effects were assessed pre-, peri- and post inhalation.

RESULTS

Effect sizes for the various rewarding/alcohol-like effects of N2O were generally similar to those reported in studies of moderate-dose ketamine. Impulsivity moderated the subjective reinforcing (liking) effects of inhaled gas, while depressive symptoms moderated motivational (wanting [more]) effects. However, depression and impulsivity had opposite directional influences, such that higher impulsivity was associated with higher N2O liking, and higher depression, with lower N2O wanting.

CONCLUSION

To the extent that static (versus longitudinal) subjective rewarding effects are a reliable indicator of future problematic drug use, our findings suggests that impulsivity and depression may predispose and protect, respectively, against N2O abuse. Future studies should examine if these moderators are relevant for other NMDAR antagonists, including ketamine, and novel ketamine-like therapeutic and recreational drugs. Similarities between moderate-dose N2O and moderate-dose ketamine in the intensity of certain subjective effects suggest that N2O may, at least to some extent, serve as substitute for ketamine as a safe and easily implemented experimental tool for probing reward-related NMDAR function and dysfunction in humans.

Adolescent intermittent ethanol exposure does not alter responsiveness to ifenprodil or expression of vesicular GABA and glutamate transporters

Adolescent intermittent ethanol (AIE) exposure in the rat results in a retention of adolescent-like responsiveness to ethanol into adulthood characterized by enhanced sensitivity to socially facilitating and decreased sensitivity to socially suppressing and aversive effects. Similar pattern of responsiveness to social and aversive effects of the selective glutamate NMDA NR2B receptor antagonist ifenprodil is evident in adolescent rats, suggesting that AIE would also retain this pattern of ifenprodil sensitivity into adulthood. Social (Experiment 1) and aversive (measured via conditioned taste aversion; Experiment 2) effects of ifenprodil were assessed in adult male and female rats following AIE exposure. Sensitivity to the social and aversive effects of ifenprodil was not affected by AIE exposure. Experiment 3 assessed protein expression of vesicular transporters of GABA (vGAT) and glutamate (vGlut2) within the prelimbic cortex and nucleus accumbens in adolescents versus adults and in AIE adults versus controls. vGlut2 expression was higher in adolescents relative to adults within the PrL, but lower in the NAc. AIE adults did not retain these adolescent-typical ratios. These findings suggest that AIE is not associated with the retention of adolescent-typical sensitivity to NR2B receptor antagonism, along with no AIE-induced shift in vGlut2 to vGAT ratios.

A Pilot Randomized, Placebo-Controlled Trial of Glycine for Treatment of Schizophrenia and Alcohol Dependence

Objectives: The hypofunctioning of N-methyl-D-aspartate (NMDA) receptors are thought to play an important role in the pathophysiology of schizophrenia. The augmentation of the glutamatergic system through the NMDA receptor may attenuate alcohol craving and use. This study was designed to evaluate the efficacy of glycine, an agonist of the glycine B co-agonist site of the NMDA receptor on alcohol consumption and cravings as well as on negative symptoms in schizophrenia. Methods: Participants (N = 20) were given 0.8 g/kg glycine or matching placebo (provided in bottles with mixed in solution) each week for the duration of the 12-week trial. Primary outcome measures included drinking, craving for alcohol, and symptoms of schizophrenia. Cognitive functioning (attention, concentration, and memory) was also evaluated. Results: Glycine showed no benefit over placebo in the reduction of heavy drinking days or craving for alcohol over a 12-week treatment period. Nor was there an effect on negative symptoms of schizophrenia or on cognitive functioning. Conclusions: Although our study showed no beneficial effect of glycine over placebo, our results are consistent with the largest trial of glycine treatment in schizophrenia. Diagnosed schizophrenia and alcohol dependence might be more difficult to treat because of more severe psychopathology. This is the first study to date to examine an innovative treatment approach with an amino acid, glycine, as potentially acting on both alcohol intake and negative symptoms of schizophrenia.

Prelimbic NMDA receptors stimulation mimics the attenuating effects of clozapine on the auditory electrophysiological rebound induced by ketamine withdrawal

Ketamine (KET) is a non-competitive N-Methyl-d-aspartate (NMDA) receptors antagonist that intensifies sensory experiences, prompts hallucinations and delusions, exacerbates previously installed psychosis and disrupts physiological evoked potentials (AEPs). Pharmacologically, KET stimulates glutamate efflux in the medial prefrontal cortex, mainly in the prelimbic (PrL) sub-region. Efferences from this region exert a top-down regulatory control of bottom-up sensory processes either directly or indirectly. In the midbrain, the central nucleus of the inferior colliculus (CIC) plays a fundamental role in the processing of auditory ascending information related to sound localization, sensorimotor gating, and preattentive event-related potentials. Auditory hallucinations elicited during a psychotic outbreak are accompanied by CIC neural activation. Thus, it is possible that NMDA-mediated glutamate neurotransmission in the PrL indirectly modulates CIC neuronal firing. The aim of the present study was to assess the effects of KET on the latency and amplitude of AEPs elicited in the CIC of rats tested during KET effects and following withdrawal from the chronic administration. Changes on emotionally induced by KET treatment were evaluated with the use of the elevated zero maze (EZM). Unlike typical neuroleptics, the atypical antipsychotic clozapine (CLZ) potently blocks the disruption of the sensorimotor gating induced by NMDA antagonists. Therefore, the effects of KET withdrawal on AEPs were challenged with a systemic injection of CLZ. In addition, we further investigated the role of NMDA receptors of the PrL on the AEPs expression recorded in the CIC through intra-PrL infusions of NMDA itself. Our results showed that the processing of sensory information in the CIC is under indirect control of PrL. These data suggest that the long-term KET treatment disrupts the collicular auditory field potentials, possibly through influencing PrL glutamate activity on intrinsic 5-HT mechanisms in the dorsal raphe and CIC.

Cerebral dopaminergic and glutamatergic transmission relate to different subjective responses of acute alcohol intake: an in vivo multimodal imaging study

Converging preclinical evidence links extrastriatal dopamine release and glutamatergic transmission via the metabotropic glutamate receptor 5 (mGluR5) to the rewarding properties of alcohol. To date, human evidence is lacking on how and where in the brain these processes occur. Mesocorticolimbic dopamine release upon intravenous alcohol administration and mGluR5 availability were measured in 11 moderate social drinkers by single-session [¹⁸ F]fallypride and [¹⁸ F]FPEB positron emission tomography, respectively. Additionally, baseline and postalcohol glutamate and glutamine levels in the anterior cingulate cortex (ACC) were measured by using proton-magnetic resonance spectroscopy. To investigate differences in reward domains linked to both neurotransmitters, regional imaging data were related to subjective alcohol responses. Alcohol induced significant [¹⁸ F]fallypride displacement in the prefrontal cortex (PFC), temporal and parietal cortices and thalamus (P < 0.05, corrected for multiple comparisons). Dopamine release in the ACC and orbitofrontal and ventromedial PFCs were correlated with subjective 'liking' and 'wanting' effects (P < 0.05). In contrast, baseline mGluR5 availability was positively correlated with the 'high' effect of alcohol in dorsolateral, ventrolateral and ventromedial PFCs and in the medial temporal lobe, thalamus and caudate nucleus (P < 0.05). Although neither proton-magnetic resonance spectroscopy glutamate nor glutamine levels were affected by alcohol, baseline ACC glutamate levels were negatively associated with the alcohol 'liking' effect (P < 0.003). These data reveal new mechanistic understanding and differential neurobiological underpinnings of the effects of acute alcohol consumption on human behavior. Specifically, prefrontal dopamine release may encode alcohol 'liking' and 'wanting' effects in specific areas underlying value processing and motivation, whereas mGluR5 availability in distinct prefrontal-temporal-subcortical regions is more related to the alcohol 'high' effect.

A proof-of-concept investigation into ketamine as a pharmacological treatment for alcohol dependence: study protocol for a randomised controlled trial

Background

Worldwide, alcohol abuse is a burgeoning problem. Abstinence is key to allow recovery of physical and mental health as well as quality of life, but treatment for alcohol dependence is associated with high relapse rates. Preliminary data have suggested that a combined repeated ketamine and psychological therapy programme may be effective in reducing relapse in severe alcohol use disorder. This non-commercial proof-of-concept trial is aimed at making a preliminary assessment of the effectiveness of this combined treatment in this patient group.

Methods/design

This is a phase II, randomised, double-blind, placebo-controlled, parallel-group clinical trial taking place in two sites in the UK: the South West of England and London. Ninety-six recently detoxified alcoholics, with comorbid depressive symptoms, will be randomised to one of four treatment arms. Patients will receive either three sessions of ketamine (0.8 mg/kg administered intravenously (IV) over 40 minutes) or placebo (50 ml saline 0.9% IV over 40 minutes) plus either seven sessions of manualised psychological therapy or an alcohol education control. Patients will be assessed at 3 and 6 months on a range of psychological and biological variables. The primary endpoints are (1) relapse rates at 6 months and (2) percentage days abstinent at 6 months. Secondary endpoints include 3 and 6 month percentage days abstinence, tolerability (indicated by dropout), adverse events, depressive symptoms, craving and quality of life.

Discussion

This study will provide important information on a new combined psychological and pharmacological intervention aimed at reducing relapse rates in alcoholics. The findings would have broad application given the worldwide prevalence of alcoholism and its associated medical, psychological and social problems.

Trial registration

ClinicalTrials.gov, NCT02649231. Registered on 5 January 2016.

Electronic supplementary material

The online version of this article (doi:10.1186/s13063-017-1895-6) contains supplementary material, which is available to authorized users.

Glutamate plasticity woven through the progression to alcohol use disorder: a multi-circuit perspective

Glutamate signaling in the brain is one of the most studied targets in the alcohol research field. Here, we report the current understanding of how the excitatory neurotransmitter glutamate, its receptors, and its transporters are involved in low, episodic, and heavy alcohol use. Specific animal behavior protocols can be used to assess these different drinking levels, including two-bottle choice, operant self-administration, drinking in the dark, the alcohol deprivation effect, intermittent access to alcohol, and chronic intermittent ethanol vapor inhalation. Importantly, these methods are not limited to a specific category, since they can be interchanged to assess different states in the development from low to heavy drinking. We encourage a circuit-based perspective beyond the classic mesolimbic-centric view, as multiple structures are dynamically engaged during the transition from positive- to negative-related reinforcement to drive alcohol drinking. During this shift from lower-level alcohol drinking to heavy alcohol use, there appears to be a shift from metabotropic glutamate receptor-dependent behaviors to N-methyl-D-aspartate receptor-related processes. Despite high efficacy of the glutamate-related pharmaceutical acamprosate in animal models of drinking, it is ineffective as treatment in the clinic. Therefore, research needs to focus on other promising glutamatergic compounds to reduce heavy drinking or mediate withdrawal symptoms or both.

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.

Ketamine and MAG Lipase Inhibitor-Dependent Reversal of Evolving Depressive-Like Behavior During Forced Abstinence From Alcohol Drinking

Although alcoholism and depression are highly comorbid, treatment options that take this into account are lacking, and mouse models of alcohol (ethanol (EtOH)) intake-induced depressive-like behavior have not been well established. Recent studies utilizing contingent EtOH administration through prolonged two-bottle choice access have demonstrated depression-like behavior following EtOH abstinence in singly housed female C57BL/6J mice. In the present study, we found that depression-like behavior in the forced swim test (FST) is revealed only after a protracted (2 weeks), but not acute (24 h), abstinence period. No effect on anxiety-like behavior in the EPM was observed. Further, we found that, once established, the affective disturbance is long-lasting, as we observed significantly enhanced latencies to approach food even 35 days after ethanol withdrawal in the novelty-suppressed feeding test (NSFT). We were able to reverse affective disturbances measured in the NSFT following EtOH abstinence utilizing the N-methyl D-aspartate receptor (NMDAR) antagonist and antidepressant ketamine but not memantine, another NMDAR antagonist. Pretreatment with the monoacylglycerol (MAG) lipase inhibitor JZL-184 also reduced affective disturbances in the NSFT in ethanol withdrawn mice, and this effect was prevented by co-administration of the CB1 inverse agonist rimonabant. Endocannabinoid levels were decreased within the BLA during abstinence compared with during drinking. Finally, we demonstrate that the depressive behaviors observed do not require a sucrose fade and that this drinking paradigm may favor the development of habit-like EtOH consumption. These data could set the stage for developing novel treatment approaches for alcohol-withdrawal-induced mood and anxiety disorders.

Intersubunit interactions at putative sites of ethanol action in the M3 and M4 domains of the NMDA receptor GluN1 and GluN2B subunits

BACKGROUND AND PURPOSE

The NMDA receptor is an important target of alcohol action in the brain. Recent studies in this laboratory have demonstrated that alcohol-sensitive positions in the intersubunit interfaces of the M3 and M4 domains of GluN1 and GluN2A subunits interact with respect to ethanol sensitivity and receptor kinetics and that alcohol-sensitive positions in the M domains of GluN2A and GluN2B subunits differ. In this study, we tested for interactions among alcohol-sensitive positions at the M domain intersubunit interfaces in GluN1/GluN2B NMDA receptors.

EXPERIMENTAL APPROACH

We used whole-cell patch-clamp recording in tsA201 cells expressing tryptophan substitution mutants at ethanol-sensitive positions in the GluN1 and GluN2B NMDA receptor subunits to test for interactions among positions.

KEY RESULTS

Six pairs of positions in GluN1/GluN2B significantly interacted to regulate ethanol inhibition: Gly(638) /Met(824) , Gly(638) /Leu(825) , Phe(639) /Leu(825) , Phe(639) /Gly(826) , Met(818) /Phe(637) and Val(820) /Phe(637) . Tryptophan substitution at Met(824) or Leu(825) in GluN2B did not alter ethanol sensitivity but interacted with positions in the GluN1 M3 domain to regulate ethanol action, whereas tryptophan substitution at Gly(638) , which is the cognate of an ethanol-sensitive position in GluN2A, did not alter ethanol sensitivity or interact with positions in GluN1. Two and three pairs of positions interacted to regulate glutamate steady-state and peak current EC50 , respectively, and one pair interacted with respect to macroscopic desensitization.

CONCLUSIONS

Despite highly-conserved M domain sequences and similar ethanol sensitivity in the GluN2A and GluN2B subunits, the manner in which these subunits interact with the GluN1 subunit to regulate ethanol sensitivity and receptor kinetics differs.

Chronic intermittent ethanol exposure produces persistent anxiety in adolescent and adult rats

BACKGROUND

Ethanol (EtOH) dependence and tolerance in the adult are marked by increased function of NMDA receptors and decreased function of GABAA receptors, which coincide with altered receptor subunit expression in specific brain regions. Adolescents often use EtOH at levels greater than adults, yet the receptor subunit expression profiles following chronic intermittent EtOH (CIE) exposure in adolescents are not known. Persistent age-dependent changes in receptor subunit alterations coupled with withdrawal-related anxiety may help explain the increase in alcohol abuse following adolescent experimentation with the drug.

METHODS

Adolescent and adult rats received 10 intraperitoneal administrations of 4.0 g/kg EtOH or saline every 48 hours. At either 24 hours or 12 days after the final exposure, anxiety-like behavior was assessed on the elevated plus maze and tissue was collected. Western blotting was used to assess changes in selected NMDA and GABAA receptor subunits in whole cortex and bilateral hippocampus.

RESULTS

CIE exposure yields a persistent increase in anxiety-like behavior in both age groups. However, selected NMDA and GABAA receptor subunits were not differentially altered by this CIE exposure paradigm in adolescents or adults.

CONCLUSIONS

CIE exposure produced persistent anxiety-like behavior, which has important implications for alcohol cessation. Given the reported behavioral and neuropeptide expression changes in response to this dose of EtOH, it is important for future work to consider the circumstances under which these measures are altered by EtOH exposure.

Treatment-Resistant Major Depression: Rationale for NMDA Receptors as Targets and Nitrous Oxide as Therapy

Major depressive disorder (MDD) remains a huge personal and societal encumbrance. Particularly burdensome is a virulent subtype of MDD, treatment resistant major depression (TMRD), which afflicts 15-30% of MDD patients. There has been recent interest in N-methyl-d-aspartate receptors (NMDARs) as targets for treatment of MDD and perhaps TMRD. To date, most pre-clinical and clinical studies have focused on ketamine, although psychotomimetic and other side effects may limit ketamine's utility. These considerations prompted a recent promising pilot clinical trial of nitrous oxide, an NMDAR antagonist that acts through a mechanism distinct from that of ketamine, in patients with severe TRMD. In this paper, we review the clinical picture of TRMD as a subtype of MDD, the evolution of ketamine as a fast-acting antidepressant, and clinical and basic science studies supporting the possible use of nitrous oxide as a rapid antidepressant.

Evaluation of adjunctive ketamine to benzodiazepines for management of alcohol withdrawal syndrome

BACKGROUND

Adjunctive medications to manage alcohol withdrawal syndrome (AWS) in patients not adequately responding to escalating doses of benzodiazepines (BZDs) are limited. The use of the N-methyl-d-aspartate antagonist ketamine, may serve as an effective adjunct agent; however, no published data currently exist for this practice.

OBJECTIVE

To determine the safety and efficacy of adjunct ketamine for management of AWS.

METHODS

The study was a retrospective review of adult patients from April 2011 to March 2014 who were administered ketamine specifically for management of AWS. Outcomes included changes in BZD requirements and ketamine-related adverse reactions.

RESULTS

Of 235 patients screened, 23 patients met study eligibility. Ketamine was initiated primarily with toxicology consultation for significant BZD requirements or delirium tremens. The mean time to initiation of ketamine from first treatment of AWS, and total duration of therapy were 33.6 and 55.8 hours, respectively. Mean initial infusion dose and median total infusion rate during therapy were 0.21 and 0.20 mg/kg/h, respectively. There was no change in sedation or alcohol withdrawal scores in patients within 6 hours of ketamine initiation. The median change in BZD requirements at 12 and 24 hours post-ketamine initiation were -40.0 and -13.3 mg, respectively. The mean time to AWS resolution was 5.6 days. There was one documented adverse reaction of oversedation, requiring dose reduction.

CONCLUSIONS

Ketamine appears to reduce BZD requirements and is well tolerated at low doses. Prospective dose range evaluations in the management of AWS would be helpful in determining its place as an adjunctive agent.

Repeated ketamine administration alters N-methyl-D-aspartic acid receptor subunit gene expression: implication of genetic vulnerability for ketamine abuse and ketamine psychosis in humans

For more than 40 years following its approval by the Food and Drug Administration (FDA) as an anesthetic, ketamine, a non-competitive N-methyl-D-aspartic acid (NMDA) receptor antagonist, has been used as a tool of psychiatric research. As a psychedelic drug, ketamine induces psychotic symptoms, cognitive impairment, and mood elevation, which resemble some symptoms of schizophrenia. Recreational use of ketamine has been increasing in recent years. However, little is known of the underlying molecular mechanisms responsible for ketamine-associated psychosis. Recent animal studies have shown that repeated ketamine administration significantly increases NMDA receptor subunit gene expression, in particular subunit 1 (NR1 or GluN1) levels. This results in neurodegeneration, supporting a potential mechanism where up-regulation of NMDA receptors could produce cognitive deficits in chronic ketamine abuse patients. In other studies, NMDA receptor gene variants are associated with addictive behavior. Here, we focus on the roles of NMDA receptor gene subunits in ketamine abuse and ketamine psychosis and propose that full sequencing of NMDA receptor genes may help explain individual vulnerability to ketamine abuse and ketamine-associated psychosis.

Metaplastic effects of subanesthetic ketamine on CA1 hippocampal function

Ketamine is a non-competitive N-methyl-d-aspartate receptor (NMDAR) antagonist of interest in neuropsychiatry. In the present studies, we examined the effects of subanesthetic, low micromolar ketamine on excitatory postsynaptic potentials (EPSPs), population spikes (PSs) and synaptic plasticity in the CA1 region of rat hippocampal slices. Ketamine acutely inhibited NMDAR-mediated synaptic responses with half-maximal effects near 10 μM. When administered for 15-30 min at 1-10 μM, ketamine had no effect on baseline dendritic AMPA receptor-mediated EPSPs, but persistently enhanced somatic EPSPs in the pyramidal cell body layer and augmented PS firing. Acute low micromolar ketamine also had no effect on the induction of long-term potentiation (LTP) but blocked long-term depression (LTD). Following 30 min administration of 1-10 μM ketamine, however, a slowly developing and persistent form of LTP inhibition was observed that took two hours following ketamine washout to become manifest. This LTP inhibition did not result from prolonged or enhanced NMDAR inhibition during drug washout. Effects of low ketamine on somatic EPSPs and LTP were not mimicked by a high ketamine concentration that completely inhibited NMDARs, and both of these effects were blocked by co-administration of low ketamine with a low concentration of the competitive NMDAR antagonist, 2-amino-5-phosphonovalerate or inhibitors of nitric oxide synthase. These results indicate that concentrations of ketamine relevant to psychotropic and psychotomimetic effects have complex metaplastic effects on hippocampal function that involve activation of unblocked NMDARs during ketamine exposure.

Use of naltrexone in ketamine dependence

Ketamine is used as a cheap alternative to anaesthetic agents in developing countries. It is also misused as a rave drug because of its psychedelic effect. There are no guidelines for effective management of ketamine withdrawal effects or dependence. Herein we report a case of ketamine dependence and its successful treatment with opioid receptor antagonist naltrexone.

Clinical predictors of ketamine response in treatment-resistant major depression

OBJECTIVE

The N-methyl-D-aspartate receptor antagonist ketamine has rapid antidepressant effects in treatment-resistant major depressive disorder (MDD) and bipolar depression. Clinical predictors may identify those more likely to benefit from ketamine within clinically heterogeneous populations.

METHOD

Data were analyzed from 4 studies of treatment-resistant inpatients with DSM-IV-TR-diagnosed MDD or bipolar I or II depression. Patients who were currently experiencing a moderate-to-severe major depressive episode were enrolled between November 2004 and March 2013. All subjects received a single subanesthetic (0.5 mg/kg) ketamine infusion over 40 minutes. Patients were analyzed at the 230-minute postinfusion time point (n = 108), at day 1 (n = 82), and at day 7 (n = 71). Univariate Pearson correlations were performed for each variable with percent change from baseline in the 17-item Hamilton Depression Rating Scale (HDRS). Multivariate linear regression was then conducted for statistically significant predictors (P ≤ .05, 2-tailed).

RESULTS

Higher body mass index correlated with greater HDRS improvement at 230 minutes (standardized β = -0.30, P = .004) and at day 1 (standardized β = -0.37, P = .001), but not at day 7 (standardized β = -0.18, P = .10). Family history of an alcohol use disorder in a first-degree relative was associated with greater HDRS improvement at day 1 (standardized β = -0.27, P = .014) and day 7 (standardized β = -0.41, P < .001). No prior history of suicide attempt(s) was associated with greater improvement only at day 7 (standardized β = 0.28, P = .01). The overall statistical model explained 13%, 23%, and 36% of HDRS percent change variance at 230 minutes, day 1, and day 7, respectively.

CONCLUSIONS

Despite its post hoc nature, this study identified several clinical correlates of ketamine's rapid and durable antidepressant effects. Further investigation of these relationships is critical for individualized treatment of depression.

Pharmacological approaches to reducing craving in patients with alcohol use disorders

Research on the concept of craving may lead to better understanding of the biobehavioural circuitries that contribute to the complexity of alcohol use disorders (AUDs). The experiences described as craving or desire to drink are often associated with physical responses such as increased salivation and heart rate, and alteration of stress hormones, as well as psychological responses such as anxiety and depression. Greater craving has been associated with an increased probability of alcohol relapse. Reversal of craving, which is understood as a symptom of protracted abstinence, offers the possibility of preventing relapses and treating alcoholism. Various medications have been studied to establish whether they are able to reduce craving; however, the results obtained from clinical studies have been inconsistent. Here, we review the interdisciplinary models developed to evaluate craving, then the different approaches used to assess and measure craving and, finally, the medications utilized and tested to lessen craving in patients suffering from AUDs.

Lack of efficacy of dextromethorphan in managing alcohol withdrawal: a preliminary report of a randomized, double-blind, placebo-controlled trial

Alcohol withdrawal syndrome is associated with increased central N-methyl-D-aspartate (NMDA) glutamate transmission. Medications that reduce glutamate release or block NMDA overactivation have shown efficacy for treating alcohol withdrawal syndrome. Dextromethorphan (DXM), a widely used antitussive drug, is a low-affinity, noncompetitive NMDA antagonist with potential neuroprotective properties. This study, using a randomized, double-blind, placebo-controlled study design, examined the benefit of DXM in the management of acute alcohol withdrawal. Alcohol-dependent patients admitted for detoxification treatment and experiencing moderate alcohol withdrawal, as measured by a score greater than 10 on the revised Clinical Institute Withdrawal Assessment for Alcohol (CIWA-Ar), were randomly assigned to receive either DXM 360 mg/d or an identical placebo for 7 days in a double-blind manner. All subjects received a concurrent dose of lorazepam 2 mg along with the initial administration of DXM or placebo and were given additional lorazepam (1 mg) as a rescue medication according to the symptom-triggered detoxification protocol. Outcome measures consisted of the mean total dose of lorazepam received, the sequential scores on the CIWA-Ar, and craving assessed by the Obsessive-Compulsive Drinking Scale. Forty subjects completed the study, 18 in the DXM group and 22 in the placebo group. We found that compared with placebo, DXM use was not associated with lower lorazepam doses to control alcohol withdrawal symptoms. The progression in CIWA-Ar and Obsessive-Compulsive Drinking Scale scores was also comparable between the 2 groups. Our preliminary results do not support the efficacy of high-dose DXM in reducing the need of benzodiazepines to treat withdrawal symptoms in alcohol-dependent patients.

Molecular basis of alcoholism

Acute alcohol intoxication causes cellular changes in the brain that last for hours, while chronic alcohol use induces widespread neuroadaptations in the nervous system that can last a lifetime. Chronic alcohol use and the progression into dependence involve the remodeling of synapses caused by changes in gene expression produced by alcohol. The progression of alcohol use, abuse, and dependence can be divided into stages, which include intoxication, withdrawal, and craving. Each stage is associated with specific changes in gene expression, cellular function, brain circuits, and ultimately behavior. What are the molecular mechanisms underlying the transition from recreational use (acute) to dependence (chronic)? What cellular adaptations result in drug memory retention, leading to the persistence of addictive behaviors, even after prolonged drug abstinence? Research into the neurobiology of alcoholism aims to answer these questions. This chapter will describe the molecular adaptations caused by alcohol use and dependence, and will outline key neurochemical participants in alcoholism at the molecular level, which are also potential targets for therapy.

Glial abnormalities in substance use disorders and depression: does shared glutamatergic dysfunction contribute to comorbidity?

OBJECTIVES

Preclinical and clinical research in neuropsychiatric disorders, particularly mood and substance use disorders, have historically focused on neurons; however, glial cells-astrocytes, microglia, and oligodendrocytes - also play key roles in these disorders.

METHODS

Peer-reviewed PubMed/Medline articles published through December 2012 were identified using the following keyword combinations: glia, astrocytes, oligodendrocytes/glia, microglia, substance use, substance abuse, substance dependence, alcohol, opiate, opioid, cocaine, psychostimulants, stimulants, and glutamate.

RESULTS

Depressive and substance use disorders are highly comorbid, suggesting a common or overlapping aetiology and pathophysiology. Reduced astrocyte cell number occurs in both disorders. Altered glutamate neurotransmission and metabolism - specifically changes in the levels/activity of transporters, receptors, and synaptic proteins potentially related to synaptic physiology - appear to be salient features of both disorders. Glial cell pathology may also underlie the pathophysiology of both disorders via impaired astrocytic production of neurotrophic factors. Microglial/neuroinflammatory pathology is also evident in both depressive and substance use disorders. Finally, oligodendrocyte impairment decreases myelination and impairs expression of myelin-related genes in both substance use and depressive disorders.

CONCLUSIONS

Glial-mediated glutamatergic dysfunction is a common neuropathological pathway in both substance use and depression. Therefore, glutamatergic neuromodulation is a rational drug target in this comorbidity.

Alterations in ethanol-induced behaviors and consumption in knock-in mice expressing ethanol-resistant NMDA receptors

Ethanol's action on the brain likely reflects altered function of key ion channels such as glutamatergic N-methyl-D-aspartate receptors (NMDARs). In this study, we determined how expression of a mutant GluN1 subunit (F639A) that reduces ethanol inhibition of NMDARs affects ethanol-induced behaviors in mice. Mice homozygous for the F639A allele died prematurely while heterozygous knock-in mice grew and bred normally. Ethanol (44 mM; ∼0.2 g/dl) significantly inhibited NMDA-mediated EPSCs in wild-type mice but had little effect on responses in knock-in mice. Knock-in mice had normal expression of GluN1 and GluN2B protein across different brain regions and a small reduction in levels of GluN2A in medial prefrontal cortex. Ethanol (0.75-2.0 g/kg; i.p.) increased locomotor activity in wild-type mice but had no effect on knock-in mice while MK-801 enhanced activity to the same extent in both groups. Ethanol (2.0 g/kg) reduced rotarod performance equally in both groups but knock-in mice recovered faster following a higher dose (2.5 g/kg). In the elevated zero maze, knock-in mice had a blunted anxiolytic response to ethanol (1.25 g/kg) as compared to wild-type animals. No differences were noted between wild-type and knock-in mice for ethanol-induced loss of righting reflex, sleep time, hypothermia or ethanol metabolism. Knock-in mice consumed less ethanol than wild-type mice during daily limited-access sessions but drank more in an intermittent 24 h access paradigm with no change in taste reactivity or conditioned taste aversion. Overall, these data support the hypothesis that NMDA receptors are important in regulating a specific constellation of effects following exposure to ethanol.

Glutamatergic targets for new alcohol medications

RATIONALE

An increasingly compelling literature points to a major role for the glutamate system in mediating the effects of alcohol on behavior and the pathophysiology of alcoholism. Preclinical studies indicate that glutamate signaling mediates certain aspects of ethanol's intoxicating and rewarding effects, and undergoes adaptations following chronic alcohol exposure that may contribute to the withdrawal, craving and compulsive drug-seeking that drive alcohol abuse and alcoholism.

OBJECTIVES

We discuss the potential for targeting the glutamate system as a novel pharmacotherapeutic approach to treating alcohol use disorders, focusing on five major components of the glutamate system: the N-methyl-D-aspartate (NMDA) receptor and specific NMDA subunits, the glycineB site on the NMDA receptors (NMDAR), L-alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid ionotropic (AMPA) and kainate (KAR) receptors, metabotropic receptors (mGluR), and glutamate transporters.

RESULTS

Chronic alcohol abuse produces a hyperglutamatergic state, characterized by elevated extracellular glutamate and altered glutamate receptors and transporters. Pharmacologically manipulating glutamatergic neurotransmission alters alcohol-related behaviors including intoxication, withdrawal, and alcohol-seeking, in rodents and human subjects. Blocking NMDA and AMPA receptors reduces alcohol consumption in rodents, but side-effects may limit this as a therapeutic approach. Selectively targeting NMDA and AMPA receptor subunits (e.g., GluN2B, GluA3), or the NMDAR glycineB site offers an alternative approach. Blocking mGluR5 potently affects various alcohol-related behaviors in rodents, and mGluR2/3 agonism also suppresses alcohol consumption. Finally, glutamate transporter upregulation may mitigate behavioral and neurotoxic sequelae of excess glutamate caused by alcohol.

CONCLUSIONS

Despite the many challenges that remain, targeting the glutamate system offers genuine promise for developing new treatments for alcoholism.

D-amino acid aberrations in cerebrospinal fluid and plasma of smokers

The glutamatergic neurotransmission system and the N-methyl-D-aspartate receptor (NMDAR) have been implicated in smoking and alcohol consumption behavior. Preclinical studies have demonstrated that nicotine and ethanol influence NMDAR functionality, which may have a role in tendencies to consume these substances. Nonetheless, little is known about concentrations of NMDAR coagonists in the cerebrospinal fluid (CSF) and plasma of individuals who smoke or consume alcohol. Glycine and L- and D-stereoisomers of alanine, serine, and proline were therefore measured using ultra-high-performance liquid chromatography-tandem mass spectrometry in 403 healthy subjects. Nicotine and alcohol consumption were quantified using questionnaires. Possible differences in NMDAR coagonist concentrations in plasma and CSF were investigated using ANCOVA with age, body mass index, and storage duration as covariates. The significance threshold was Bonferroni corrected (α=0.00625). Compared with non-smokers, smokers displayed lower levels of D-proline in plasma (p=0.0027, Cohen's d=-0.41) and D-proline in CSF (p=0.0026, Cohen's d=-0.43). D-Serine in CSF was higher in smokers than in non-smokers (p=0.0052, Cohen's d=0.41). After subdividing participants based on smoking quantity, dose-dependent decreases were demonstrated in smokers for D-proline in plasma (F=5.65, p=0.0039) and D-proline in CSF (F=5.20, p=0.0060). No differences in NMDAR coagonist levels between alcohol consumption groups were detected. To our knowledge, this is the first report to implicate D-amino acids in smoking behavior of humans. Whether such concentration differences lie at the root of or result from smoking habits may be addressed in prospective studies.

Pre-exposure to ethanol, but not to caffeine and nicotine, induced place preference and self-administration of the NMDA receptor antagonist-benzodiazepine combination, Zoletil®

Zoletil® is an equal amount combination of the NMDA receptor antagonist, tiletamine, and the benzodiazepine, zolazepam, usually used as a veterinary anesthetic. Previous studies have shown that pre-exposure to Zoletil® and other psychoactive drugs (e.g. ketamine, diazepam) plays a significant role in the abuse liability of the compound. However, these studies were only focused on illicit psychoactive drugs and not on the more widely used licit psychoactive substances. Thus, the goal of the present work is to investigate whether pre-exposure to the three most commonly used licit psychoactive substances (caffeine, nicotine, and ethanol) affects the rewarding and reinforcing effects of Zoletil®. Rats were pretreated with caffeine (1.25 or 2.5 mg/kg), nicotine (125 or 250 μg/kg), ethanol (0.5, 2, or 4 g/kg), or saline (1 ml/kg) for 14 days, and evaluated for subsequent Zoletil® place preference (2.5 mg/kg) and self-administration (250 μg/kg). Zoletil® produced neither place preference nor self-administration in saline-pretreated rats. Pre-exposure to caffeine or nicotine does not have significant effects on Zoletil®'s abuse potential. However, pretreatment of ethanol significantly produced Zoletil® place preference and self-administration. These results suggest that individuals who are exposed to ethanol may have a high propensity to use/abuse Zoletil®. More importantly, the present result advocates the careful monitoring on the use and dispensation of Zoletil® or related substances.

mTOR activation is required for the anti-alcohol effect of ketamine, but not memantine, in alcohol-preferring rats

Glutamate NMDA receptors mediate many molecular and behavioral effects of alcohol, and they play a key role in the development of excessive drinking. Uncompetitive NMDA receptor antagonists may, therefore, have therapeutic potential for alcoholism. The first aim was to compare the effects of the NMDA antagonists memantine and ketamine on ethanol and saccharin drinking in alcohol-preferring rats. The second aim was to determine whether the effects of the two NMDA receptor antagonists were mediated by the mammalian target of rapamycin (mTOR). TSRI Sardinian alcohol-preferring rats were allowed to self-administer either 10% w/v ethanol or 0.08% w/v saccharin, and water. Operant responding and motor activity were assessed following administration of either memantine (0-10mg/kg) or ketamine (0-20mg/kg). Finally, ethanol self-administration was assessed in rats administered with either memantine or ketamine but pretreated with the mTOR inhibitor rapamycin (2.5mg/kg). The uncompetitive NMDA receptor antagonists memantine and ketamine dose-dependently reduced ethanol drinking in alcohol-preferring rats; while memantine had a preferential effect on alcohol over saccharin, ketamine reduced responding for both solutions. Neither antagonist induced malaise, as shown by the lack of effect on water intake and motor activity. The mTOR inhibitor rapamycin blocked the effects of ketamine, but not those of memantine. Memantine and ketamine both reduce alcohol drinking in alcohol-preferring rats, but only memantine is selective for alcohol. The effects of ketamine, but not memantine, are mediated by mTOR. The results support the therapeutic potential of uncompetitive NMDA receptor antagonists, especially memantine, in alcohol addiction.

Family history of alcohol dependence and antidepressant response to an N-methyl-D-aspartate antagonist in bipolar depression

OBJECTIVES

Both ketamine and ethanol are N-methyl-d-aspartate (NMDA) receptor antagonists. Ketamine has rapid antidepressant properties in major depressive disorder (MDD) as well as bipolar depression. In individuals with MDD, a positive family history of alcohol dependence (FHP) was associated with greater improvement in depressive symptoms after ketamine administration compared to individuals whose family history of alcohol dependence was negative (FHN). This study investigated whether FHP influences ketamine's antidepressant and perceptual effects in individuals with bipolar depression.

METHODS

A post hoc analysis was conducted on 33 subjects with DSM-IV bipolar disorder (BD) type I or II depression pooled from two previously published studies. All subjects had undergone a double-blind, randomized, crossover trial of a single intravenous infusion of ketamine (0.5 mg/kg) combined with lithium or valproate therapy. Subjects were rated at baseline; at 40, 80, 120, and 230 min; and at days 1, 2, 3, 7, 10, and 14 post-infusion. The primary outcome measure was Montgomery-Åsberg Depression Rating Scale (MADRS) scores. Patients were categorized as FHP when they reported at least one first-degree relative with alcohol dependence. Measures of psychosis, dissociation, and dysphoria were also collected.

RESULTS

After ketamine infusion, subjects with FHP showed significantly greater improvement on MADRS scores than FHN subjects. In addition, patients with FHP had attenuated psychotomimetic and dissociative scores compared to FHN patients.

CONCLUSIONS

FHP appears to predict a more sustained antidepressant response to ketamine in individuals with BD. Family history of alcoholism may be an important consideration in the development of glutamatergic-based therapies for depression.

NMDA receptor antagonism: escalation of aggressive behavior in alcohol-drinking mice

RATIONALE

Memantine is a potential treatment for alcoholic patients, yet few studies investigate the effect of concurrent treatment with memantine and ethanol on aggression. We evaluated aggressive behavior following ethanol consumption and treatment with glutamatergic drugs to characterize interactions between these compounds.

OBJECTIVE

This study aimed to use rodent models of aggression to examine interactions between glutamatergic compounds and ethanol.

MATERIALS AND METHODS

Once male CFW mice reliably self-administered 1 g/kg ethanol or water, they were assessed for aggression in resident-intruder confrontations. Alternatively, aggression was evaluated following a social-instigation procedure. Animals were then injected with memantine, ketamine, neramexane, MTEP, or LY379268 before aggressive confrontations. Effects of the pharmacological manipulations on salient aggressive and non-aggressive behaviors were analyzed.

RESULTS

Moderate doses of memantine, neramexane, and MTEP interacted with ethanol to increase the frequency of attack bites while ketamine did not. The highest dose of LY379268, an mGluR(2/3) agonist, reduced both aggressive and non-aggressive behaviors after water and ethanol self-administration. Attack bites increased with social instigation and decreased with administration of high doses of MTEP and LY379268. Memantine and MTEP both reduced attack bite frequency in the instigation condition without reducing locomotor behavior.

CONCLUSIONS

Memantine and neramexane interacted with ethanol to heighten aggression. The binding characteristics of these compounds allow for 'partial trapping' by which some NMDARs are unblocked between depolarizations. We propose that this feature may contribute to the differential aggression-heightening interactions between these compounds and ethanol. MTEP also interacted with ethanol to escalate aggression, possibly through inhibition of mGluR(5) modulation of NMDARs.

Interactions among positions in the third and fourth membrane-associated domains at the intersubunit interface of the N-methyl-D-aspartate receptor forming sites of alcohol action

The N-methyl-D-aspartate (NMDA) glutamate receptor is a major target of ethanol in the brain. Previous studies have identified positions in the third and fourth membrane-associated (M) domains of the NMDA receptor GluN1 and GluN2A subunits that influence alcohol sensitivity. The predicted structure of the NMDA receptor, based on that of the related GluA2 subunit, indicates a close apposition of the alcohol-sensitive positions in M3 and M4 between the two subunit types. We tested the hypothesis that these positions interact to regulate receptor kinetics and ethanol sensitivity by using dual substitution mutants. In single-substitution mutants, we found that a position in both subunits adjacent to one previously identified, GluN1(Gly-638) and GluN2A(Phe-636), can strongly regulate ethanol sensitivity. Significant interactions affecting ethanol inhibition and receptor deactivation were observed at four pairs of positions in GluN1/GluN2A: Gly-638/Met-823, Phe-639/Leu-824, Met-818/Phe-636, and Leu-819/Phe-637; the latter pair also interacted with respect to desensitization. Two interactions involved a position in M4 of both subunits, GluN1(Met-818) and GluN2A(Leu-824), that does not by itself alter ethanol sensitivity, whereas a previously identified ethanol-sensitive position, GluN2A(Ala-825), did not unequivocally interact with any other position tested. These results also indicate a shift by one position of the predicted alignment of the GluN1 M4 domain. These findings have allowed for the refinement of the NMDA receptor M domain structure, demonstrate that this region can influence apparent agonist affinity, and support the existence of four sites of alcohol action on the NMDA receptor, each consisting of five amino acids at the M3-M4 domain intersubunit interfaces.

Glycine transporter inhibitor attenuates the psychotomimetic effects of ketamine in healthy males: preliminary evidence

Enhancing glutamate function by stimulating the glycine site of the NMDA receptor with glycine, D-serine, or with drugs that inhibit glycine reuptake may have therapeutic potential in schizophrenia. The effects of a single oral dose of cis-N-methyl-N-(6-methoxy-1-phenyl-1,2,3,4-tetrahydronaphthalen-2-ylmethyl) amino-methylcarboxylic acid hydrochloride (Org 25935), a glycine transporter-1 (GlyT1) inhibitor, and placebo pretreatment on ketamine-induced schizophrenia-like psychotic symptoms, perceptual alterations, and subjective effects were evaluated in 12 healthy male subjects in a randomized, counter-balanced, within-subjects, crossover design. At 2.5 h after administration of the Org 25935 or placebo, subjects received a ketamine bolus and constant infusion lasting 100 min. Psychotic symptoms, perceptual, and a number of subjective effects were assessed repeatedly before, several times during, and after completion of ketamine administration. A cognitive battery was administered once per test day. Ketamine produced behavioral, subjective, and cognitive effects consistent with its known effects. Org 25935 reduced the ketamine-induced increases in measures of psychosis (Positive and Negative Syndrome Scale (PANSS)) and perceptual alterations (Clinician Administered Dissociative Symptoms Scale (CADSS)). The magnitude of the effect of Org 25935 on ketamine-induced increases in Total PANSS and CADSS Clinician-rated scores was 0.71 and 0.98 (SD units), respectively. None of the behavioral effects of ketamine were increased by Org 25935 pretreatment. Org 25935 worsened some aspects of learning and delayed recall, and trended to improve choice reaction time. This study demonstrates for the first time in humans that a GlyT1 inhibitor reduces the effects induced by NMDA receptor antagonism. These findings provide preliminary support for further study of the antipsychotic potential of GlyT1 inhibitors.

The safety of studies with intravenous Δ⁹-tetrahydrocannabinol in humans, with case histories

RATIONALE

Delta-9-tetrahydrocannabinol (THC) is one of the few cannabinoid receptor ligands that can be used to probe the cannabinoid system in humans. Despite increasing interest in the cannabinoid receptor system, use of intravenous THC as a research tool has been limited by concerns about its abuse liability and psychoactive effects.

OBJECTIVES

This study aims to evaluate the safety of all intravenous THC studies conducted at this center for the past 13 years.

METHODS

Included were 11 studies with 266 subjects (14 schizophrenia patients and 252 healthy subjects, of whom 76 were frequent cannabis users), 351 active THC infusions, and 226 placebo infusions. Subjects were monitored for subjective and physical adverse events and followed up to 12 months beyond study participation.

RESULTS

There was one serious and 70 minor adverse events in 9.7% of subjects and 7.4% of infusions, with 8.5% occurring after the end of the test day. Nausea and dizziness were the most frequent side effects. Adverse events were more likely to be associated with faster infusion rates (2-5 min) and higher doses (>2.1 mg/70 kg). Of 149 subjects on whom long-term follow-up data were gathered, 94% reported either no change or a reduction in their desire to use cannabis in the post-study period, 18% stated that their cannabis use decreased, and 3% stated that it increased in the post-study period.

CONCLUSIONS

With careful subject selection and screening, risk to subjects is relatively low. Safeguards are generally sufficient and effective, reducing both the duration and severity of adverse events.

Intravenous ethanol infusion decreases human cortical γ-aminobutyric acid and N-acetylaspartate as measured with proton magnetic resonance spectroscopy at 4 tesla

BACKGROUND

Ethanol modulates glutamate and γ-aminobutyric (GABA) function. However, little is known about the acute pharmacologic effects of ethanol on levels of GABA, glutamate, and other metabolites measurable in the human cortex in vivo with proton magnetic resonance spectroscopy ((1)H-MRS).

METHODS

Eleven healthy social drinkers received two intravenous ethanol infusions that raised breath alcohol levels to a clamped plateau of 60 mg/dL over 60-70 min. The first infusion established tolerability of the procedure, and the second procedure, conducted 15 ± 12 days later, was performed during (1)H-MRS of occipital GABA, glutamate, and other metabolites.

RESULTS

The time course of brain ethanol approximated that of breath ethanol, but venous ethanol lagged by approximately 7 min. The GABA fell 13 ± 8% after 5 min of the ethanol infusion and remained reduced (p = .003) throughout the measurement. The combination of N-acetylaspartate and N-acetylaspartyl glutamate (summed as NAA) fell steadily during the infusion by 8 ± 3% (p = .0036).

CONCLUSIONS

Ethanol reduced cortical GABA and NAA levels in humans. Reductions in GABA levels are consistent with facilitation of GABA(A) receptor function by ethanol. The gradual decline in NAA levels suggests inhibition of neural or metabolic activity in the brain.

Ketamine use: a review

AIMS

Ketamine remains an important medicine in both specialist anaesthesia and aspects of pain management. At the same time, its use as a recreational drug has spread in many parts of the world during the past few years. There are now increasing concerns about the harmful physical and psychological consequences of repeated misuse of this drug. The aim of this review was to survey and integrate the research literature on physical, psychological and social harms of both acute and chronic ketamine use.

METHOD

The literature on ketamine was systematically searched and findings were classified into the matrix of Nutt et al.'s (2007) rational scale for assessing the harms of psychoactive substances.

RESULTS

A major physical harm is ketamine induced ulcerative cystitis which, although its aetiology is unclear, seems particularly associated with chronic, frequent use of the drug. Frequent, daily use is also associated with neurocognitive impairment and, most robustly, deficits in working and episodic memory. Recent studies suggest certain neurological abnormalities which may underpin these cognitive effects. Many frequent users are concerned about addiction and report trying but failing to stop using ketamine.

CONCLUSIONS

The implications of these findings are drawn out for treatment of ketamine-induced ulcerative cystitis in which interventions from urologists and from addiction specialists should be coordinated. Neurocognitive impairment in frequent users can impact negatively upon achievement in education and at work, and also compound addiction problems. Prevention and harm minimization campaigns are needed to alert young people to these harmful and potentially chronic effects of ketamine.

Characterization of the interactive effects of glycine and D-cycloserine in men: further evidence for enhanced NMDA receptor function associated with human alcohol dependence

Reduced responses to N-methyl-D-aspartate (NMDA) glutamate receptor antagonists in alcohol-dependent animals and humans provided evidence that chronic alcohol consumption increased NMDA receptor function. To further probe alterations in NMDA glutamate receptor function associated with human alcohol dependence, this study examined the interactive effects of agents acting at the glycine(B) coagonist site of the NMDA receptor. In doing so, it tested the hypothesis that raising brain glycine concentrations would accentuate the antagonist-like effects of the glycine(B) partial agonist, D-cycloserine (DCS). Twenty-two alcohol-dependent men and 22 healthy individuals completed 4 test days, during which glycine 0.3 g/kg or saline were administered intravenously and DCS 1000 mg or placebo were administered orally. The study was conducted under double-blind conditions with randomized test day assignment. In this study, DCS produced alcohol-like effects in healthy subjects that were deemed similar to a single standard alcohol drink. The alcohol-like effects of DCS were blunted in alcohol-dependent patients, providing additional evidence of increased NMDA receptor function in this group. Although glycine administration reduced DCS plasma levels, glycine accentuated DCS effects previously associated with the NMDA receptor antagonists, ketamine and ethanol. Thus, this study provided evidence that raising glycine levels accentuated the NMDA receptor antagonist-like effects of DCS and that alcohol-dependent patients showed tolerance to these DCS effects.

Subjective responses to alcohol consumption as endophenotypes: advancing behavioral genetics in etiological and treatment models of alcoholism

Individual differences in subjective responses to alcohol consumption represent genetically mediated biobehavioral mechanisms of alcoholism risk (i.e., endophenotype). The objective of this review is three-fold: (1) to provide a critical review the literature on subjective response to alcohol and to discuss the rationale for its conceptualization as an endophenotype for alcoholism; (2) to examine the literature on the neurobiological substrates and associated genetic factors subserving individual differences in subjective response to alcohol; and (3) to discuss the treatment implications of this approach and to propose a framework for conceptualizing, and systematically integrating, endophenotypes into alcoholism treatment.

N-methyl-D-aspartate receptor subunit expression in adult and adolescent brain following chronic ethanol exposure

Substantial evidence suggests that glutamatergic neurotransmission is a critical mediator of the experience-dependent synaptic plasticity that may underlie alcohol dependence. Substance abuse typically begins in adolescence; therefore, the impact of alcohol on glutamatergic systems during this critical time in brain development is of particular importance. The N-methyl-d-aspartate receptor (NMDAR) is involved in developmental mechanisms underlying neuronal differentiation and synaptogenesis and as such may be a target system for alcohol effects during adolescence. In the present study quantitative biochemical determinations were made of the relative abundance of different protein expressions of NMDAR subunits in adolescents and adults after 2 weeks of ethanol vapor exposure, and 24 h and 2 weeks following withdrawal. After 2 weeks of ethanol vapor exposure N-methyl-d-aspartate receptor NR1 subunit (NR1), N-methyl-d-aspartate receptor NR2A subunit (NR2A), and N-methyl-d-aspartate receptor NR2B subunit (NR2B) subunit expression was found to be increased in hippocampus of the adults. In contrast, 2 weeks of ethanol exposure resulted in no significant changes in NR1 and NR2B subunits and a reduction NR2A subunit expression in hippocampus in adolescents. Twenty-four h and 2 weeks following withdrawal from ethanol vapor NR1 and NR2A subunit expression in hippocampus was decreased in adolescents, whereas in adults it had returned to control levels. In frontal cortex, 2 weeks of chronic ethanol exposure produced decreases in NR1 subunit expression in both adults and adolescents but also produced decreases in NR2A and NR2B subunit expression in adults that returned or exceeded control levels by 2 weeks following withdrawal from ethanol vapor. These results demonstrate that NMDAR subunit composition can be modulated differentially between adolescents and adults by chronic ethanol exposure and withdrawal. These developmental differences in NMDAR subunits composition may also be associated with the enhanced vulnerability of the adolescent brain to ethanol dependence.

Riluzole for relapse prevention following intravenous ketamine in treatment-resistant depression: a pilot randomized, placebo-controlled continuation trial

The N-methyl-D-aspartate (NMDA) glutamate receptor antagonist ketamine may have rapid, albeit transient, antidepressant properties. This study in patients with treatment-resistant major depression (TRD) aimed to (1) replicate the acute efficacy of single-dose intravenous (i.v.) ketamine; (2) test the efficacy of the glutamate-modulating agent riluzole in preventing post-ketamine relapse; and (3) examine whether pretreatment with lamotrigine would attenuate ketamine's psychotomimetic effects and enhance its antidepressant activity. Twenty-six medication-free patients received open-label i.v. ketamine (0.5 mg/kg over 40 min). Two hours prior to infusion, patients were randomized to lamotrigine (300 mg) or placebo. Seventeen patients (65%) met response criterion (50% reduction from baseline on the Montgomery-Asberg Depression Rating Scale) 24 h following ketamine. Lamotrigine failed to attenuate the mild, transient side-effects associated with ketamine and did not enhance its antidepressant effects. Fourteen patients (54%) met response criterion 72 h following ketamine and proceeded to participate in a 32-d, randomized, double-blind, placebo-controlled, flexible-dose continuation trial of riluzole (100-200 mg/d). The main outcome measure was time-to-relapse. An interim analysis found no significant differences in time-to-relapse between riluzole and placebo groups [log-rank chi(2) = 0.17, d.f. = 1, p = 0.68], with 80% of patients relapsing on riluzole vs. 50% on placebo. The trial was thus stopped for futility. This pilot study showed that a sub-anaesthetic dose of i.v. ketamine is well-tolerated in TRD, and may have rapid and sustained antidepressant properties. Riluzole did not prevent relapse in the first month following ketamine. Further investigation of relapse prevention strategies post-ketamine is necessary.

Ethanol-like effects of thiopental and ketamine in healthy humans

The gamma-aminobutyric acid-A (GABA(A)) and N-methyl-D-aspartate (NMDA) receptors mediate aspects of the behavioural effects of alcohol. Prior studies reported drugs that block NMDA receptors or facilitate GABA(A) receptor function produce ethanol-like effects in humans. The purpose of this study was to compare the ethanol-related effects of two pharmacological agents with known NMDA and GABA(A) receptor activity. As part of an ongoing, larger study, 28 subjects (age, 21-30) with no personal or family histories of alcoholism were administered subanesthetic doses of the GABA(A) receptor agonist thiopental, the NMDA receptor antagonist, ketamine and placebo on three separate test days. Various ethanol-related measures were administered. At doses of thiopental and ketamine that produced similar levels of sedation and cognitive effects, both agents produced significant ethanol-like effects and subjective intoxication. However, the intensity of the ethanol-like effects of ketamine was greater than that of thiopental. In addition, ketamine produced alterations in perception that were not produced by thiopental. These data provide further support for a model where GABA(A) receptor facilitation may contribute significantly to ethanol effects associated with social drinking, whereas NMDA receptor antagonism may contribute to relatively greater extent to features of ethanol 'intoxication'.