Potentiation of low dose ketamine effects by naltrexone: potential implications for the pharmacotherapy of alcoholism

Activity-State Dependent Reversal of Ketamine-Induced Resting State EEG Effects by Clozapine and Naltrexone in the Freely Moving Rat

Ketamine is a non-competitive N-Methyl-D-aspartate receptor (NMDAR) antagonist used in the clinic to initiate and maintain anaesthesia; it induces dissociative states and has emerged as a breakthrough therapy for major depressive disorder. Using local field potential recordings in freely moving rats, we studied resting state EEG profiles induced by co-administering ketamine with either: clozapine, a highly efficacious antipsychotic; or naltrexone, an opioid receptor antagonist reported to block the acute antidepressant effects of ketamine. As human electroencephalography (EEG) is predominantly recorded in a passive state, head-mounted accelerometers were used with rats to determine active and passive states at a high temporal resolution to offer the highest translatability. In general, pharmacological effects for the three drugs were more pronounced in (or restricted to) the passive state. Specifically, during inactive periods clozapine induced increases in delta (0.1-4 Hz), gamma (30-60 Hz) and higher frequencies (>100 Hz). Importantly, it reversed the ketamine-induced reduction in low beta power (10-20 Hz) and potentiated ketamine-induced increases in gamma and high frequency oscillations (130-160 Hz). Naltrexone inhibited frequencies above 50 Hz and significantly reduced the ketamine-induced increase in high frequency oscillations. However, some frequency band changes, such as clozapine-induced decreases in delta power, were only seen in locomoting rats. These results emphasise the potential in differentiating between activity states to capture drug effects and translate to human resting state EEG. Furthermore, the differential reversal of ketamine-induced EEG effects by clozapine and naltrexone may have implications for the understanding of psychotomimetic as well as rapid antidepressant effects of ketamine.

Classic serotonergic psychedelics for mood and depressive symptoms: a meta-analysis of mood disorder patients and healthy participants

RATIONALE

Major depressive disorder is one of the leading global causes of disability, for which the classic serotonergic psychedelics have recently reemerged as a potential therapeutic treatment option.

OBJECTIVE

We present the first meta-analytic review evaluating the clinical effects of classic serotonergic psychedelics vs placebo for mood state and symptoms of depression in both healthy and clinical populations (separately).

RESULTS

Our search revealed 12 eligible studies (n = 257; 124 healthy participants, and 133 patients with mood disorders), with data from randomized controlled trials involving psilocybin (n = 8), lysergic acid diethylamide ([LSD]; n = 3), and ayahuasca (n = 1). The meta-analyses of acute mood outcomes (3 h to 1 day after treatment) for healthy volunteers and patients revealed improvements with moderate significant effect sizes in favor of psychedelics, as well as for the longer-term (16 to 60 days after treatments) mood state of patients. For patients with mood disorder, significant effect sizes were detected on the acute, medium (2-7 days after treatment), and longer-term outcomes favoring psychedelics on the reduction of depressive symptoms.

CONCLUSION

Despite the concerns over unblinding and expectancy, the strength of the effect sizes, fast onset, and enduring therapeutic effects of these psychotherapeutic agents encourage further double-blind, placebo-controlled clinical trials assessing them for management of negative mood and depressive symptoms.

Ketamine: A tale of two enantiomers

The discovery of the rapid antidepressant effects of the dissociative anaesthetic ketamine, an uncompetitive N-Methyl-D-Aspartate receptor antagonist, is arguably the most important breakthrough in depression research in the last 50 years. Ketamine remains an off-label treatment for treatment-resistant depression with factors that limit widespread use including its dissociative effects and abuse potential. Ketamine is a racemic mixture, composed of equal amounts of (S)-ketamine and (R)-ketamine. An (S)-ketamine nasal spray has been developed and approved for use in treatment-resistant depression in the United States and Europe; however, some concerns regarding efficacy and side effects remain. Although (R)-ketamine is a less potent N-Methyl-D-Aspartate receptor antagonist than (S)-ketamine, increasing preclinical evidence suggests (R)-ketamine may have more potent and longer lasting antidepressant effects than (S)-ketamine, alongside fewer side effects. Furthermore, a recent pilot trial of (R)-ketamine has demonstrated rapid-acting and sustained antidepressant effects in individuals with treatment-resistant depression. Research is ongoing to determine the specific cellular and molecular mechanisms underlying the antidepressant actions of ketamine and its component enantiomers in an effort to develop future rapid-acting antidepressants that lack undesirable effects. Here, we briefly review findings regarding the antidepressant effects of ketamine and its enantiomers before considering underlying mechanisms including N-Methyl-D-Aspartate receptor antagonism, γ-aminobutyric acid-ergic interneuron inhibition, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic receptor activation, brain-derived neurotrophic factor and tropomyosin kinase B signalling, mammalian target of rapamycin complex 1 and extracellular signal-regulated kinase signalling, inhibition of glycogen synthase kinase-3 and inhibition of lateral habenula bursting, alongside potential roles of the monoaminergic and opioid receptor systems.

Association of Ketamine With Psychiatric Symptoms and Implications for Its Therapeutic Use and for Understanding Schizophrenia: A Systematic Review and Meta-analysis

Importance

Ketamine hydrochloride is increasingly used to treat depression and other psychiatric disorders but can induce schizophrenia-like or psychotomimetic symptoms. Despite this risk, the consistency and magnitude of symptoms induced by ketamine or what factors are associated with these symptoms remain unknown.

Objective

To conduct a meta-analysis of the psychopathological outcomes associated with ketamine in healthy volunteers and patients with schizophrenia and the experimental factors associated with these outcomes.

Data Sources

MEDLINE, Embase, and PsychINFO databases were searched for within-participant, placebo-controlled studies reporting symptoms using the Brief Psychiatric Rating Scale (BPRS) or the Positive and Negative Syndrome Scale (PANSS) in response to an acute ketamine challenge in healthy participants or patients with schizophrenia.

Study Selection

Of 8464 citations retrieved, 36 studies involving healthy participants were included. Inclusion criteria were studies (1) including healthy participants; (2) reporting symptoms occurring in response to acute administration of subanesthetic doses of ketamine (racemic ketamine, s-ketamine, r-ketamine) intravenously; (3) containing a placebo condition with a within-subject, crossover design; (4) measuring total positive or negative symptoms using BPRS or PANSS; and (5) providing data allowing the estimation of the mean difference and deviation between the ketamine and placebo condition.

Data Extraction and Synthesis

Two independent investigators extracted study-level data for a random-effects meta-analysis. Total, positive, and negative BPRS and PANSS scores were extracted. Subgroup analyses were conducted examining the effects of blinding status, ketamine preparation, infusion method, and time between ketamine and placebo conditions. The Meta-analysis of Observational Studies in Epidemiology (MOOSE) and Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines were followed.

Main Outcomes and Measures

Standardized mean differences (SMDs) were used as effect sizes for individual studies. Standardized mean differences between ketamine and placebo conditions were calculated for total, positive, and negative BPRS and PANSS scores.

Results

The overall sample included 725 healthy volunteers (mean [SD] age, 28.3 [3.6] years; 533 [73.6%] male) exposed to the ketamine and placebo conditions. Racemic ketamine or S-ketamine was associated with a statistically significant increase in transient psychopathology in healthy participants for total (SMD = 1.50 [95% CI, 1.23-1.77]; P < .001), positive (SMD = 1.55 [95% CI, 1.29-1.81]; P < .001), and negative (SMD = 1.16 [95% CI, 0.96-1.35]; P < .001) symptom ratings relative to the placebo condition. The effect size for this association was significantly greater for positive than negative symptoms of psychosis (estimate, 0.36 [95% CI, 0.12-0.61]; P = .004). There was significant inconsistency in outcomes between studies (I2 range, 77%-83%). Bolus followed by constant infusion increased ketamine's association with positive symptoms relative to infusion alone (effect size, 1.63 [95% CI, 1.36-1.90] vs 0.84 [95% CI, 0.35-1.33]; P = .006). Single-day study design increased ketamine's ability to generate total symptoms (effect size, 2.29 [95% CI, 1.69-2.89] vs 1.39 [95% CI, 1.12-1.66]; P = .007), but age and sex did not moderate outcomes. Insufficient studies were available for meta-analysis of studies in schizophrenia. Of these studies, 2 found a statistically significant increase in symptoms with ketamine administration in total and positive symptoms. Only 1 study found an increase in negative symptom severity with ketamine.

Conclusions and Relevance

This study found that acute ketamine administration was associated with schizophrenia-like or psychotomimetic symptoms with large effect sizes, but there was a greater increase in positive than negative symptoms and when a bolus was used. These findings suggest that bolus doses should be avoided in the therapeutic use of ketamine to minimize the risk of inducing transient positive (psychotic) symptoms.

Ketamine: The final frontier or another depressing end?

Two decades ago, the observation of a rapid and sustained antidepressant response after ketamine administration provided an exciting new avenue in the search for more effective therapeutics for the treatment of clinical depression. Research elucidating the mechanism(s) underlying ketamine's antidepressant properties has led to the development of several hypotheses, including that of disinhibition of excitatory glutamate neurons via blockade of N-methyl-d-aspartate (NMDA) receptors. Although the prominent understanding has been that ketamine's mode of action is mediated solely via the NMDA receptor, this view has been challenged by reports implicating other glutamate receptors such as AMPA, and other neurotransmitter systems such as serotonin and opioids in the antidepressant response. The recent approval of esketamine (Spravato™) for the treatment of depression has sparked a resurgence of interest for a deeper understanding of the mechanism(s) underlying ketamine's actions and safe therapeutic use. This review aims to present our current knowledge on both NMDA and non-NMDA mechanisms implicated in ketamine's response, and addresses the controversy surrounding the antidepressant role and potency of its stereoisomers and metabolites. There is much that remains to be known about our understanding of ketamine's antidepressant properties; and although the arrival of esketamine has been received with great enthusiasm, it is now more important than ever that its mechanisms of action be fully delineated, and both the short- and long-term neurobiological/functional consequences of its treatment be thoroughly characterized.

[A double blind placebo controlled randomized clinical trial of the efficacy and safety of pregabalin in induction of remission in patients with alcohol dependence]

AIM

To study the efficacy of pregabalin for relapse prevention and reduction of drinking in patients with alcohol dependence.

MATERIAL AND METHODS

One hundred recently detoxified out-patients with alcohol dependence were randomly assigned to one of two treatment groups. Patients of the first group (n=50; 38 men, 12 women, age 43.0±1.27) received pregabalin (150 mg once a day at night time) for 3 months, while patients of the second group (n=50; 45 men, 5 women, age 45.92±1.4) received identically looking placebo. All patients received standardized manualized weekly counseling (medical management). Drinking was measured on the weekly basis with Time Line Follow Back technique and GGT enzyme activity. Also, craving for alcohol, depression, and anxiety were measured weekly with the number of scales.

RESULTS

Kaplan-Meier survival analysis demonstrated significantly higher retention in treatment and in remission in the pregabalin group (lower drop out and relapse rate) mediana (CL)-12 (10.4-13.6) weeks in the pregabalin group vs. 6 (4.5-7.5) in the placebo group, Log Rank Mantel-Cox test = 0.005). Proportion of patients, who completed treatment in the pregabalin group, was significantly higher compared to the placebo group: 50% vs. 24%. Mean duration of participation in the treatment program was also higher in the pregabalin group: 9.1±0.5 weeks vs. 7.1±0.5 in the placebo group. General linear model demonstrated the significant treatment group effect on: (1) total alcohol consumption (TAC) (mean grams of alcohol per day) with lower TAC in the pregabalin group and (2) on the number of heavy drinking days (NHDD) with lower NHDD in the pregabalin group. Mean NHDD per patient for the period of participation in the study was lower in the pregabalin group (3.6±0.7 vs. 6.4±0.8; p=0.009), while the mean number of abstinent (sober) days was higher (55.9±3.6 vs. 40.0±3.3; p=0.001). No significant differences between the two groups were found in the scores on craving for alcohol, depression and anxiety scales. GGT activity was also similar in both groups throughout the study with no significant between group differences. The rate of adverse events (sleepiness, dizziness, and headache) was insignificantly higher in the pregabalin group compared with the placebo group. All adverse events were mild, gradually disappeared, and did not require any medication.

CONCLUSION

Results of this study provide evidence that pregabalin in a low dose of 150 mg per day is an effective and safe medication for relapse prevention and reduction of drinking in patients with alcohol dependence.

Urothelial toxicity of esketamine in the treatment of depression

RATIONALE

Ketamine is the first widely used substance with rapid-onset antidepressant action. However, there are uncertainties regarding its potential urothelial toxicity, particularly after repeated application. In the context of rising recreational ketamine use, severe side effects affecting the human urinary tract have been reported. It is assumed that ketamine interacts with bladder urothelial cells and induces apoptosis.

OBJECTIVES

This study aimed to assess whether single or repeated doses of esketamine used in an antidepressant indication are associated with urinary toxicity.

METHODS

We included male and female inpatients with a current episode of depression and a diagnosis of recurrent depressive disorder, bipolar disorder or schizoaffective disorder according to ICD-10 criteria (n = 25). The esketamine treatment schedule involved a maximum of 3× weekly dosing at 0.25-0.5 mg/kg i.v. or s.c. The primary outcome was the change in urine toxicity markers (leukocytes, erythrocytes, protein and free haemoglobin). Description of demographic, clinical and laboratory data was conducted using means, standard deviations, frequencies and percentages. Changes in urinary toxicity markers over time were evaluated using linear mixed models with gender as a covariate.

RESULTS

The participants received an average of 11.4 (SD 8) esketamine treatments, and an average number of 11.2 (SD 8) urine samples were analysed over the course of treatment. Neither urinary leukocyte concentration (F(20; 3.0) = 3.1; p = 0.2) nor erythrocyte concentration (F(20;2.2) = 4.1; p = 0.2) showed a significant trend towards increase during the course of esketamine treatment. Similarly, free haemoglobin and protein concentrations, which were analysed descriptively, did not display a rise during treatment. There was a significant improvement in depression ratings after esketamine treatment (p < 0.001).

CONCLUSIONS

This study is, to the best of our knowledge, the first to focus on urothelial toxicity of esketamine used in antidepressant indication and dose. The results indicate that the use of single or repeated doses of esketamine is unlikely to cause urothelial toxicity. The results are in need of confirmation as sample size was small.

Influence of combined treatment with naltrexone and memantine on alcohol drinking behaviors: a phase II randomized crossover trial

Glutamate and opioid systems play important roles in alcohol drinking behaviors. We examined if combined treatment with the NMDA antagonist memantine and the opioid antagonist naltrexone, when compared with naltrexone alone, would have a greater influence on alcohol drinking behaviors. Fifty-six, non-treatment-seeking heavy drinkers, with alcohol dependence and a positive family history (FHP) of alcoholism, participated in a randomized, double-blind, crossover trial, including two 6-8 days treatment periods, separated by a 6-day washout, and 3 alcohol drinking paradigm (ADP) sessions. After the first baseline (BAS) ADP1 session, participants were randomized to receive either naltrexone (NTX; 50 mg/day) + placebo memantine, or NTX (50 mg/day) + memantine (MEM; 20 mg/day), during the first treatment period, following which they completed ADP2. After a 6-day washout, participants were crossed over to the treatment they did not receive during the first treatment period, following which they completed ADP3. During each ADP, participants received a priming drink of alcohol followed by 3 1-hour, self-administration periods during which they had ad-lib access to 12 drinks. Individually, both NTX and NTX + MEM, when compared to BAS ADP1, significantly reduced the number of drinks consumed (p's < 0.001) and craving (p's < 0.001). When comparing NTX + MEM vs. NTX on number of drinks consumed, there was a significant treatment* sequence interaction (p = 0.004). Specifically, when NTX + MEM followed NTX alone, NTX + MEM resulted in a further reduction in drinking (mean: -1.94; 95% CI: -2.6, -0.8, p = 0.0005). However, when NTX alone followed NTX + MEM, NTX alone did not lead to further reduction in drinking (mean: 0.59; 95% CI: -0.67, 1.43, p = 0.47). Similar patterns were observed for alcohol craving; specifically, a significant reduction in craving was observed when NTX + MEM followed NTX alone (p = 0.009), but craving reduction was maintained when NTX + MEM was followed by NTX alone. Neither treatment condition significantly influenced alcohol-induced stimulation or sedation. Memantine (at a dose of 20 mg/day) enhances the efficacy of naltrexone (50 mg/day) in reducing alcohol drinking and craving among FHP drinkers with beneficial effects that appear to carryover after discontinuation of memantine treatment.

Ketamine Assisted Psychotherapy (KAP): Patient Demographics, Clinical Data and Outcomes in Three Large Practices Administering Ketamine with Psychotherapy

Currently, ketamine is the only legal psychedelic medicine available to mental health providers for the treatment of emotional suffering. Over the past several years, ketamine has come into psychiatric use as an intervention for treatment resistant depression (TRD), administered intravenously without a psychotherapeutic component. In these settings, ketamine's psychedelic effects are viewed as undesirable "side effects." In contrast, we believe ketamine can benefit patients with a wide variety of diagnoses when administered with psychotherapy and using its psychedelic properties without need for intravenous (IV) access. Its proven safety over decades of use makes it ideal for office and supervised at-home use. The unique experience that ketamine facilitates with its biological, experiential, and psychological impacts has been tailored to optimize office-based treatment evolving into a method that we call Ketamine Assisted Psychotherapy (KAP). This article is the first to explore KAP within an analytical framework examining three distinct practices that use similar methods. Here, we present demographic and outcome data from 235 patients. Our findings suggest that KAP is an effective method for decreasing depression and anxiety in a private practice setting, especially for older patients and those with severe symptom burden.

Association of Combined Naltrexone and Ketamine With Depressive Symptoms in a Case series of Patients With Depression and Alcohol Use Disorder

This study examines whether naltrexone pretreatment interferes with the antidepressant effects of ketamine.

Potential Anti-Depressive Treatment Maneuvers from Bench to Bedside

Numerous antidepressants are available for the treatment of the major depressive disorder (MDD). Unfortunately, the disadvantages of these antidepressive medications, including inadequate treatment response, the therapeutic lag between drug administration and the onset of symptoms alleviation, and the safety consideration limit their clinical use and accelerate the exploration of advanced antidepressants with novel action mechanisms/newer targets, with fewer side effects. In this chapter, a series of compounds showing clinical potent in the treatment of MDD has been reviewed based on their reported results from different phase clinical trials. Although the majority of these strategies currently only lead to a systematic approach in the aspects of treatment resistant depression, some of them would be a routine clinical practice which is usable in the treatment of MDD, such as ketamine. Additionally, beyond the mechanism of action for novel therapeutic molecules involving glutamatergic, opiate, cholinergic receptors, and neuroplasticity, some supplemental procedures such as polyunsaturated fatty acids were also included in this chapter due to their solid property against MDD.

Attenuation of Antidepressant Effects of Ketamine by Opioid Receptor Antagonism

OBJECTIVE

In addition to N-methyl-d-aspartate receptor antagonism, ketamine produces opioid system activation. The objective of this study was to determine whether opioid receptor antagonism prior to administration of intravenous ketamine attenuates its acute antidepressant or dissociative effects.

METHOD

In a proposed double-blind crossover study of 30 adults with treatment-resistant depression, the authors performed a planned interim analysis after studying 14 participants, 12 of whom completed both conditions in randomized order: placebo or 50 mg of naltrexone preceding intravenous infusion of 0.5 mg/kg of ketamine. Response was defined as a reduction ≥50% in score on the 17-item Hamilton Depression Rating Scale (HAM-D) score on postinfusion day 1.

RESULTS

In the interim analysis, seven of 12 adults with treatment-resistant depression met the response criterion during the ketamine plus placebo condition. Reductions in 6-item and 17-item HAM-D scores among participants in the ketamine plus naltrexone condition were significantly lower than those of participants in the ketamine plus placebo condition on postinfusion days 1 and 3. Secondary analysis of all participants who completed the placebo and naltrexone conditions, regardless of the robustness of response to ketamine, showed similar results. There were no differences in ketamine-induced dissociation between conditions. Because naltrexone dramatically blocked the antidepressant but not the dissociative effects of ketamine, the trial was halted at the interim analysis.

CONCLUSIONS

The findings suggest that ketamine's acute antidepressant effect requires opioid system activation. The dissociative effects of ketamine are not mediated by the opioid system, and they do not appear sufficient without the opioid effect to produce the acute antidepressant effects of ketamine in adults with treatment-resistant depression.

Ketamine and Ketamine Metabolite Pharmacology: Insights into Therapeutic Mechanisms

Ketamine, a racemic mixture consisting of (S)- and (R)-ketamine, has been in clinical use since 1970. Although best characterized for its dissociative anesthetic properties, ketamine also exerts analgesic, anti-inflammatory, and antidepressant actions. We provide a comprehensive review of these therapeutic uses, emphasizing drug dose, route of administration, and the time course of these effects. Dissociative, psychotomimetic, cognitive, and peripheral side effects associated with short-term or prolonged exposure, as well as recreational ketamine use, are also discussed. We further describe ketamine's pharmacokinetics, including its rapid and extensive metabolism to norketamine, dehydronorketamine, hydroxyketamine, and hydroxynorketamine (HNK) metabolites. Whereas the anesthetic and analgesic properties of ketamine are generally attributed to direct ketamine-induced inhibition of N-methyl-D-aspartate receptors, other putative lower-affinity pharmacological targets of ketamine include, but are not limited to, γ-amynobutyric acid (GABA), dopamine, serotonin, sigma, opioid, and cholinergic receptors, as well as voltage-gated sodium and hyperpolarization-activated cyclic nucleotide-gated channels. We examine the evidence supporting the relevance of these targets of ketamine and its metabolites to the clinical effects of the drug. Ketamine metabolites may have broader clinical relevance than was previously considered, given that HNK metabolites have antidepressant efficacy in preclinical studies. Overall, pharmacological target deconvolution of ketamine and its metabolites will provide insight critical to the development of new pharmacotherapies that possess the desirable clinical effects of ketamine, but limit undesirable side effects.

Interactive effects of an N-methyl-d-aspartate receptor antagonist and a nicotinic acetylcholine receptor agonist on mismatch negativity: Implications for schizophrenia

N-methyl-d-aspartate glutamate receptor (NMDAR) hypofunction has been implicated in the pathophysiology of schizophrenia, including auditory processing abnormalities reflected by the mismatch negativity (MMN) event-related potential component. Evidence suggesting cognitive benefits from nicotine administration, together with the high rate of cigarette use in patients with schizophrenia, has stimulated interest in whether nicotine modulates NMDAR hypofunction. We examined the interactive effects of ketamine, an NMDAR antagonist that produces transient schizophrenia-like neurophysiological effects, and nicotine, a nicotinic acetylcholine receptor (nAChR) agonist, in 30 healthy volunteers to determine whether nicotine prevents or attenuates MMN abnormalities. Secondary analyses compared the profile of ketamine and schizophrenia effects on MMN using previously reported data from 24 schizophrenia patients (Hay et al. 2015). Healthy volunteers completed four test days, during which they received ketamine/placebo and nicotine/placebo in a double-blind, counterbalanced design. MMN to intensity, frequency, duration, and frequency+duration double deviant sounds was assessed each day. Ketamine decreased intensity, frequency, and double deviant MMN amplitudes, whereas nicotine increased intensity and double deviant MMN amplitudes. A ketamine×nicotine interaction indicated, however, that nicotine failed to attenuate the decrease in MMN associated with ketamine. Although the present dose of ketamine produced smaller decrements in MMN than those associated with schizophrenia, the profile of effects across deviant types did not differ between ketamine and schizophrenia. Results suggest that while ketamine and schizophrenia produce similar profiles of MMN effects across deviant types, nicotinic agonists may have limited potential to improve these putative NMDAR hypofunction-mediated impairments in schizophrenia.

Classics in Chemical Neuroscience: Ketamine

Ketamine, a molecule of many faces, has contributed immeasurably to numerous realms of clinical practice and scientific inquiry. From anesthesia and analgesia to depression and schizophrenia, it continues to shed light on the molecular underpinnings of pain, consciousness, and the pathophysiology of neuropsychiatric disorders. In particular, research on ketamine's mechanism of action is providing new hope in the search for therapies for treatment-resistant depression and affords insights into disorders of glutamatergic dysfunction. In this Review, we will cover aspects of ketamine's synthesis, manufacturing, metabolism, pharmacology, approved and off-label indications, and adverse effects. We will also discuss the captivating history of this molecule, its influence on neuropsychiatry, and its potential to advance the fields of chemical neuroscience and neuropharmacology.

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.

Are Alcohol Anti-relapsing and Alcohol Withdrawal Drugs Useful in Cannabinoid Users?

Cannabinoids are still classified as illegal psychoactive drugs despite their broad and increasingly acknowledged therapeutic potential. These substances are most famous for their wide recreational use, particularly among young adults to either alter the state of consciousness, intensify pleasure induced by other psychoactive substances or as an alternative to the previously abused drugs. It is important to emphasize that cannabinoids are often taken together with a variety of medications intended for the treatment of alcohol use disorder (AUD) or alcohol withdrawal syndrome (AWS). These medications include disulfiram, acamprosate, and naltrexone. In this paper, we summarize recent advances in the knowledge of possible beneficial effects and interactions between cannabinoids and drugs commonly used for treatment of AUD and AWS either comorbid or existing as a separate disorder.

Role of ketamine in acute postoperative pain management: a narrative review

OBJECTIVES

The objective of this narrative review was to examine the usage of ketamine as a postoperative analgesic agent across a wide variety of surgeries.

DESIGN

A literature search was performed using the phrases "ketamine" and "postoperative pain." The authors analyzed the studies that involved testing ketamine's effectiveness at controlling postoperative pain. Effectiveness was assessed through various outcomes such as the amount of opiate consumption, visual analog scale (VAS) pain scores, and persistent postoperative pain at long-term follow-up.

RESULTS

While many different administration protocols were evaluated, delivering ketamine both as a pre- or perioperative bolus and postoperative infusion for up to 48 hours appeared to be the most effective. These effects are dose-dependent. However, a number of studies analyzed showed no benefit in using ketamine versus placebo for controlling postoperative pain. While ketamine is a safe and well-tolerated drug, it does have adverse effects, and there are concerns for possible neurotoxicity and effects on memory.

CONCLUSIONS

In a number of limited situations, ketamine has shown some efficacy in controlling postoperative pain and decreasing opioid consumption. More randomized controlled trials are necessary to determine the surgical procedures and administrations (i.e., intravenous, epidural) that ketamine is best suited for.

Relationship of resting brain hyperconnectivity and schizophrenia-like symptoms produced by the NMDA receptor antagonist ketamine in humans

N-methyl-D-aspartate glutamate receptor (NMDA-R) antagonists produce schizophrenia-like positive and negative symptoms in healthy human subjects. Preclinical research suggests that NMDA-R antagonists interfere with the function of gamma-aminobutyric acid (GABA) neurons and alter the brain oscillations. These changes have been hypothesized to contribute to psychosis. In this investigation, we evaluated the hypothesis that the NMDA-R antagonist ketamine produces alterations in cortical functional connectivity during rest that are related to symptoms. We administered ketamine to a primary sample of 22 subjects and to an additional, partially overlapping, sample of 12 subjects. Symptoms before and after the experimental session were rated with the Positive and Negative Syndrome Scale (PANSS). In the primary sample, functional connectivity was measured via functional magnetic resonance imaging almost immediately after infusion began. In the additional sample, this assessment was repeated after 45 min of continuous ketamine infusion. Global, enhanced functional connectivity was observed at both timepoints, and this hyperconnectivity was related to symptoms in a region-specific manner. This study supports the hypothesis that pathological increases in resting brain functional connectivity contribute to the emergence of positive and negative symptoms associated with schizophrenia.

Naltrexone does not attenuate the effects of intravenous Δ9-tetrahydrocannabinol in healthy humans

Although a wealth of preclinical evidence indicates an interplay between the μ-opioid (MOR) and cannabinoid 1 receptor (CB1R) systems, the precise nature of the cross modulation in humans is unclear. The objective of this study was to evaluate the effects of pretreatment with the MOR antagonist, naltrexone, on the subjective, behavioural and cognitive effects of the CB1R agonist, Δ9-tetrahydrocannabinol (THC), in healthy human subjects. Healthy human subjects, screened carefully for any medical or psychiatric illness, were administered either placebo or active naltrexone (25 mg) orally on each test day, followed 45 min later by placebo and 165 min later by active i.v. THC (0.025 mg/kg) in a randomized, fixed-order, double-blind manner. Subjective, behavioural and cognitive effects were assessed before and at several points after each drug administration. THC produced expected effects, including euphoria, anxiety, transient perceptual alterations, transient psychotomimetic effects and cognitive impairments. However, naltrexone did not produce any effects alone, nor did it attenuate any of THC's effects. Thus, in healthy human subjects who use cannabis intermittently, MOR antagonism does not modulate the common acute subjective, behavioural and cognitive effects of THC.

Pharmacogenetically driven treatments for alcoholism: are we there yet?

Pharmacogenetic analyses of treatments for alcohol dependence attempt to predict treatment response and side-effect risk for specific medications. We review the literature on pharmacogenetics relevant to alcohol dependence treatment, and describe state-of-the-art methods of pharmacogenetic research in this area. Two main pharmacogenetic study designs predominate: challenge studies and treatment-trial analyses. Medications studied include US FDA-approved naltrexone and acamprosate, both indicated for treating alcohol dependence, as well as several investigational (and off-label) treatments such as sertraline, olanzapine and ondansetron. The best-studied functional genetic variant relevant to alcoholism treatment is rs1799971, a single-nucleotide polymorphism in exon 1 of the OPRM1 gene that encodes the μ-opioid receptor. Evidence from clinical trials suggests that the presence of the variant G allele of rs1799971 may predict better treatment response to opioid receptor antagonists such as naltrexone. Evidence from clinical trials also suggests that several medications interact pharmacogenetically with variation in genes that encode proteins involved in dopaminergic and serotonergic neurotransmission. Variation in the DRD4 gene, which encodes the dopamine D(4) receptor, may predict better response to naltrexone and olanzapine. A polymorphism in the serotonin transporter gene SLC6A4 promoter region appears related to differential treatment response to sertraline depending on the subject's age of onset of alcoholism. Genetic variation in SLC6A4 may also be associated with better treatment response to ondansetron. Initial pharmacogenetic efforts in alcohol research have identified functional variants with potential clinical utility, but more research is needed to further elucidate the mechanism of these pharmacogenetic interactions and their moderators in order to translate them into clinical practice.

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.

Behavioral effects of gamma-hydroxybutyrate in humans

Despite the therapeutic use and abuse potential of gamma-hydroxybutyrate (GHB or Xyrem), relatively few studies have examined the behavioral effects of GHB in humans under controlled laboratory conditions. Thus, this eight-session study examined in 10 non-substance-abusing volunteers the behavioral effects of GHB at each of the following doses: 0, 0.32, 0.56, 0.75, 1.0, 1.8, 2.4, 3.2 g/70 kg, orally. Order of dose testing was random, except that the first two participants received active doses in ascending order and 2.4 g/70 kg was always tested before 3.2 g/70 kg. Before drug administration and at several postdrug time points, self-report, observer report, physiological, and psychomotor performance measures were obtained. Analyses based on area under the curve showed that GHB produced dose-related increases in subjective ratings of sedative-like, stimulant-like, positive mood, and dissociative effects, but no changes in psychomotor performance measures or blood pressure. Analyses based on peak effects generally showed dose-related increases in ratings indicating sedative-like, dissociative, and drug liking, although some measures showed U-shaped dose-related changes. These initial findings suggest that GHB at doses of 0.32-3.2 g/70 kg produces dissociative, sedating and some stimulant-like effects in humans without a history of sedative abuse.

Safety and efficacy of repeated-dose intravenous ketamine for treatment-resistant depression

BACKGROUND

A single subanesthetic (intravenous) IV dose of ketamine might have rapid but transient antidepressant effects in patients with treatment-resistant depression (TRD). Here we tested the tolerability, safety, and efficacy of repeated-dose open-label IV ketamine (six infusions over 12 days) in 10 medication-free symptomatic patients with TRD who had previously shown a meaningful antidepressant response to a single dose.

METHODS

On day 1, patients received a 40-min IV infusion of ketamine (.5 mg/kg) in an inpatient setting with continuous vital-sign monitoring. Psychotomimetic effects and adverse events were recorded repeatedly. The primary efficacy measure was change from baseline in the Montgomery-Asberg Depression Rating Scale (MADRS) score. If patients showed a > or =50% reduction in MADRS scores on day 2, they received five additional infusions on an outpatient basis (days 3, 5, 8, 10, and 12). Follow-up visits were conducted twice-weekly for > or =4 weeks or until relapse.

RESULTS

Ketamine elicited minimal positive psychotic symptoms. Three patients experienced significant but transient dissociative symptoms. Side effects during and after each ketamine infusion were generally mild. The response criterion was met by nine patients after the first infusion as well as after the sixth infusion. The mean (SD) reduction in MADRS scores after the sixth infusion was 85% (12%). Postketamine, eight of nine patients relapsed, on average, 19 days after the sixth infusion (range 6 days-45 days). One patient remained antidepressant-free with minimal depressive symptoms for >3 months.

CONCLUSIONS

These pilot findings suggest feasibility of repeated-dose IV ketamine for the acute treatment of TRD.

Effects of haloperidol on the behavioral, subjective, cognitive, motor, and neuroendocrine effects of Delta-9-tetrahydrocannabinol in humans

INTRODUCTION

Cannabinoids produce a spectrum of effects in humans including euphoria, cognitive impairments, psychotomimetic effects, and perceptual alterations. The extent to which dopaminergic systems contribute to the effects of Delta-9-tetrahydrocannabinol (Delta-9-THC) remains unclear. This study evaluated whether pretreatment with a dopamine receptor antagonist altered the effects of Delta-9-THC in humans.

MATERIALS AND METHODS

In a 2-test-day double-blind study, 28 subjects including healthy subjects (n = 17) and frequent users of cannabis (n = 11) were administered active (0.057 mg/kg) or placebo oral haloperidol in random order followed 90 and 215 min later by fixed order intravenous administration of placebo (vehicle) and active (0.0286 mg/kg) Delta-9-THC, respectively.

RESULTS

Consistent with previous reports, intravenous Delta-9-THC produced psychotomimetic effects, perceptual alterations, and subjective effects including "high." Delta-9-THC also impaired verbal recall and attention. Haloperidol pretreatment did not reduce any of the behavioral effects of Delta-9-THC. Haloperidol worsened the immediate free and delayed free and cued recall deficits produced by Delta-9-THC. Haloperidol and Delta-9-THC worsened distractibility and vigilance. Neither drug impaired performance on a motor screening task, the Stockings of Cambridge task, or the delayed match to sample task. Frequent users had lower baseline plasma prolactin levels and blunted Delta-9-THC induced memory impairments.

CONCLUSIONS

The deleterious effects of haloperidol pretreatment on the cognitive effects of Delta-9-THC are consistent with the preclinical literature in suggesting crosstalk between DAergic and CBergic systems. However, it is unlikely that DA D(2) receptor mechanisms play a major role in mediating the psychotomimetic and perceptual altering effects of Delta-9-THC. Further investigation is warranted to understand the basis of the psychotomimetic effects of Delta-9-THC and to better understand the crosstalk between DAergic and CBergic systems.

Endogenous opiates and behavior: 2006

This paper is the 29th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning 30 years of research. It summarizes papers published during 2006 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurological disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Update on neuropharmacological treatments for alcoholism: scientific basis and clinical findings

The past decade has seen an expansion of research and knowledge on pharmacotherapy for the treatment of alcohol dependence. The Food and Drug Administration (FDA)-approved medications naltrexone and acamprosate have shown mixed results in clinical trials. Oral naltrexone and naltrexone depot formulations have generally demonstrated efficacy at treating alcohol dependence, but their treatment effect size is small, and more research is needed to compare the effects of different doses on drinking outcome. Acamprosate has demonstrated efficacy for treating alcohol dependence in European trials, but with a small effect size. In U.S. trials, acamprosate has not proved to be efficacious. Research continues to explore which types of alcohol-dependent individual would benefit the most from treatment with naltrexone or acamprosate. The combination of the two medications demonstrated efficacy for treating alcohol dependence in one European study but not in a multi-site U.S. study. Another FDA-approved medication, disulfiram, is an aversive agent that does not diminish craving for alcohol. Disulfiram is most effective when given to those who are highly compliant or who are receiving their medication under supervision. Of the non-approved medications, topiramate is among the most promising, with a medium effect size in clinical trials. Another promising medication, baclofen, has shown efficacy in small trials. Serotonergic agents such as selective serotonin reuptake inhibitors and the serotonin-3 receptor antagonist, ondansetron, appear to be efficacious only among certain genetic subtypes of alcoholic. As neuroscientific research progresses, other promising medications, as well as medication combinations, for treating alcohol dependence continue to be explored.

Psychiatric safety of ketamine in psychopharmacology research

RATIONALE

A growing number of investigators are studying ketamine effects in healthy human subjects, but concerns remain about its safety as a research tool. Therefore, it is timely to revisit the safety of subanesthetic doses of ketamine in experimental psychopharmacology studies.

OBJECTIVE

To report on the safety of laboratory studies with subanesthetic doses of ketamine in healthy humans using an existing dataset.

MATERIALS AND METHODS

Medically healthy subjects with no personal or familial Axis I psychotic spectrum disorders were administered subanesthetic doses of ketamine by intravenous infusion in a series of clinical investigations from 1989 to 2005. The safety of ketamine administration was monitored in these subjects.

RESULTS

Four hundred and fifty subjects received at least one dose of active ketamine. Eight hundred and thirty three active ketamine and 621 placebo infusions were administered. Ten adverse mental status events were documented in nine subjects/infusions that were deemed related to ketamine administration (2% of subjects, 1.45% of infusions). All but one adverse reaction resolved by the end of the test session. The side effects in the remaining individual were no longer clinically significant within 4 days of the test session. No residual sequelae were observed.

CONCLUSION

Ketamine administration at subanesthetic doses appears to present an acceptable level of risk for carefully screened populations of healthy human subjects in the context of clinical research programs that intensively monitor subjects throughout their study participation.

Greater vulnerability to the amnestic effects of ketamine in males

RATIONALE

Gender differences both in response to ketamine in animals and general cognitive functioning in humans have been observed and suggested to be related to modulatory effects of sex hormones on N-methyl-D: -aspartate receptor (NMDA-R) functioning.

OBJECTIVES

The current study aimed to determine whether there were gender differences in response to ketamine in humans.

METHODS

Behavioral data including positive and negative symptoms (Brief Psychiatric Rating Scale), perceptual alterations (Clinician-Administered Dissociative States Scale, CADSS), and "high" and "anxiety" states (Visual Analog Scale) from 295 subjects who participated in a total of 11 placebo-controlled ketamine studies were analyzed. In a subset of subjects, memory (Hopkins Verbal Learning Task: HVLT, n=108) and attention (continuous performance task, n=177) data were also analyzed.

RESULTS

Male participants showed a greater performance decrement on the HVLT after ketamine administration compared to women. Men also reported a greater subjective sense of memory impairment on a CADSS subscale. No other gender differences in behavioral or cognitive measures were observed.

CONCLUSIONS

Men showed a greater vulnerability to the amnestic effects of ketamine than women. Possible explanations of these findings are neuroanatomical and cognitive differences in processing of words in men and women and interactions between sex hormones and NMDA-R function.