Attenuation of ketamine effects by nimodipine pretreatment in recovering ethanol dependent men: psychopharmacologic implications of the interaction of NMDA and L-type calcium channel antagonists

The Role of Ketamine as a Component of Multimodal Analgesia in Burns: A Retrospective Observational Study

Background: Burn wound dressing and debridement are excruciatingly painful procedures that call for appropriate analgesia-typically multimodal. Better post-procedural pain management, less opioid use, and consequently fewer side effects, which could prolong recovery and increase morbidity, are all benefits of this type of analgesia. Intravenously administered ketamine can be effective as monotherapy or in combination with opioids, especially with procedural sedation such as in burn wound dressing. Methods: This observational study investigated the effect of ketamine administered in subanesthetic doses combined with opioids during burn wound dressing. The study was conducted from October 2018 to October 2021. A total of 165 patients met the inclusion criteria. A total of 82 patients were in the ketamine group, while 83 patients were dressed without ketamine. The main outcome was the effect of ketamine on intraprocedural opioid consumption. The secondary outcome included the effect of ketamine on postprocedural pain control. Results: Patients dressed with ketamine were significantly older (p = 0.001), while the mean doses of intraoperatively administered propofol and fentanyl were significantly lower than in patients dressed without ketamine (150 vs. 220 mg, p < 0.001; and 0.075 vs. 0.150 mg, p < 0.001; respectively). Conclusions: Ketamine was an independent predictor of lower intraoperative fentanyl consumption, according to the multivariate regression analysis (p = 0.015). Contrarily, both groups of patients required postoperative tramadol treatment, while intraoperative ketamine administration had no beneficial effects on postoperative pain management.

Ketamine and the neurobiology of depression: Toward next-generation rapid-acting antidepressant treatments

Ketamine has emerged as a transformative and mechanistically novel pharmacotherapy for depression. Its rapid onset of action, efficacy for treatment-resistant symptoms, and protection against relapse distinguish it from prior antidepressants. Its discovery emerged from a reconceptualization of the neurobiology of depression and, in turn, insights from the elaboration of its mechanisms of action inform studies of the pathophysiology of depression and related disorders. It has been 25 y since we first presented our ketamine findings in depression. Thus, it is timely for this review to consider what we have learned from studies of ketamine and to suggest future directions for the optimization of rapid-acting antidepressant treatment.

Recent advances in the study of anesthesia-and analgesia-related mechanisms of S-ketamine

Ketamine is a racemic mixture of equal amounts of R-ketamine and S-ketamine and is well known to anesthesiologists for its unique dissociative anesthetic properties. The pharmacological properties of ketamine, namely, its sympathetic excitation, mild respiratory depression, and potent analgesia, are still highly valued in its use as an anesthetic for some patients. In particular, since its advent, S-ketamine has been widely used as an anesthetic in many countries due to its increased affinity for NMDA receptors and its enhanced anesthetic and analgesic effects. However, the anesthetic and analgesic mechanisms of S-ketamine are not fully understood. In addition to antagonizing NMDA receptors, a variety of other receptors or channels may be involved, but there are no relevant mechanistic summaries in the literature. Therefore, the purpose of this paper is to review the mechanisms of action of S-ketamine on relevant receptors and systems in the body that result in its pharmacological properties, such as anesthesia and analgesia, with the aim of providing a reference for its clinical applications and research.

L-Type Calcium Channel Blockers: A Potential Novel Therapeutic Approach to Drug Dependence

This review describes interactions between compounds, primarily dihydropyridines, that block L-type calcium channels and drugs that cause dependence, and the potential importance of these interactions. The main dependence-inducing drugs covered are alcohol, psychostimulants, opioids, and nicotine. In preclinical studies, L-type calcium channel blockers prevent or reduce important components of dependence on these drugs, particularly their reinforcing actions and the withdrawal syndromes. The channel blockers also reduce the development of tolerance and/or sensitization, and they have no intrinsic dependence liability. In some instances, their effects include reversal of brain changes established during drug dependence. Prolonged treatment with alcohol, opioids, psychostimulant drugs, or nicotine causes upregulation of dihydropyridine binding sites. Few clinical studies have been carried out so far, and reports are conflicting, although there is some evidence of effectiveness of L-channel blockers in opioid withdrawal. However, the doses of L-type channel blockers used clinically so far have necessarily been limited by potential cardiovascular problems and may not have provided sufficient central levels of the drugs to affect neuronal dihydropyridine binding sites. New L-type calcium channel blocking compounds are being developed with more selective actions on subtypes of L-channel. The preclinical evidence suggests that L-type calcium channels may play a crucial role in the development of dependence to different types of drugs. Mechanisms for this are proposed, including changes in the activity of mesolimbic dopamine neurons, genomic effects, and alterations in synaptic plasticity. Newly developed, more selective L-type calcium channel blockers could be of considerable value in the treatment of drug dependence. SIGNIFICANCE STATEMENT: Dependence on drugs is a very serious health problem with little effective treatment. Preclinical evidence shows drugs that block particular calcium channels, the L-type, reduce dependence-related effects of alcohol, opioids, psychostimulants, and nicotine. Clinical studies have been restricted by potential cardiovascular side effects, but new, more selective L-channel blockers are becoming available. L-channel blockers have no intrinsic dependence liability, and laboratory evidence suggests they reverse previously developed effects of dependence-inducing drugs. They could provide a novel approach to addiction treatment.

Antidepressant Actions of Ketamine: Potential Role of L-Type Calcium Channels

Recently, the United States Food and Drug Administration approved esketamine, the S-enantiomer of ketamine, as a fast-acting therapeutic drug for treatment-resistant depression. Although ketamine is known as an N-methyl-d-aspartate (NMDA) receptor antagonist, the underlying mechanisms of how it elicits an antidepressant effect, specifically at subanesthetic doses, are not clear and remain an advancing field of research interest. On the other hand, high-dose (more than the anesthetic dose) ketamine-induced neurotoxicity in animal models has been reported. There has been progress in understanding the potential pathways involved in ketamine-induced antidepressant effects, some of which include NMDA-receptor antagonism, modulation of voltage-gated calcium channels, and brain-derived neurotrophic factor (BDNF) signaling. Often these pathways have been shown to be linked. Voltage-gated L-type calcium channels have been shown to mediate the rapid-acting antidepressant effects of ketamine, especially involving induction of BDNF synthesis downstream, while BDNF deficiency decreases the expression of L-type calcium channels. This review focuses on the reported studies linking ketamine's rapid-acting antidepressant actions to L-type calcium channels with an objective to present a perspective on the importance of the modulation of intracellular calcium in mediating the effects of subanesthetic (antidepressant) versus high-dose ketamine (anesthetic and potential neurotoxicant), the latter having the ability to reduce intracellular calcium by blocking the calcium-permeable NMDA receptors, which is implicated in potential neurotoxicity.

A molecular approach to treating cognition in schizophrenia by calcium channel blockade: An open-label pilot study of the calcium-channel antagonist isradipine

Cognitive impairment is a prominent and difficult to treat symptom in schizophrenia (SZ), which is directly related to functional disability. A variant in the gene coding for the alpha 1C subunit of L-type voltage gated calcium channel (CACNA1C) has been shown to negatively affect several neurocognitive domains. We conducted a 4-week, open label, pilot study of isradipine, a calcium channel blocker, to determine its feasibility, safety, and efficacy in improving cognition in SZ patients.

Ten adults with stable SZ were started on a flexible dose of isradipine 5 mg/day (up to 10 mg/day) for 4 weeks. Weekly in-person visits tracked side effects and symptoms while neurocognition and functional capacity were assessed at baseline and week 4.

There were no serious adverse events reported. Newly emergent side effects were dizziness (1 new incidence at week 4); difficulty sleeping (2 new incidences at week 4); and decreased energy (3 new incidences at week 4). 1 patient discontinued medication and was withdrawn. Treatment did not exacerbate clinical symptoms. Although power is limited, results indicate no clear benefit on neurocognition but a positive effect (baseline mean = 6.8 ± 1.3 to week 4 mean = 7.9 ± 1.1; t = 2.91, p = 0.017) on functional capacity was noted.

This open label, pilot study provides preliminary evidence that isradipine is a relatively safe medication when used adjunctively in SZ patients. This study suggests that isradipine offers no clear cognitive and only minimal functional benefit; however, additional studies may be warranted in symptomatic patients, or those with specific CACNA1C genotypes.

Efficacy of single and repeated administration of ketamine in unipolar and bipolar depression: a meta-analysis of randomized clinical trials

BACKGROUND

Due to unmet clinical needs for efficient drugs with a rapid onset of antidepressant effects, we aimed to evaluate the efficacy of single-dose ketamine in different subgroups of patients with major depression and establish whether repeated ketamine administration could be a viable strategy to maintain treatment gains.

METHODS

Electronic databases (Medline via PubMed, Embase, Cochrane Library, Trip Database) were systematically searched until February 22, 2019, for published peer-reviewed randomized controlled trials (RCTs) concerning a single and repeated administration of ketamine in patients with major depression. All relevant RCTs were selected and critically appraised, and a meta-analysis of eligible studies was performed.

RESULTS

A total of 20 studies were included in the meta-analysis. The largest effect of ketamine vs. controls in reducing depressive symptoms was observed at 24 h (SMD = - 0.89; 95% CI - 1.24; - 0.53; p < 0.00001); however, a significant difference was shown for up to 7 days after a single dose. Significant differences compared with controls were observed for up to 7 days in treatment-resistant patients and when ketamine was added to ongoing antidepressant treatment, while there were no significant differences at 7 days when ketamine was used as monotherapy. In patients with major depression, initial antidepressant effects of ketamine were maintained during repeated dosing. At 2-3 weeks of repeated ketamine treatment, significant reduction of depression severity scores was observed: SMD = - 0.70; 95% CI - 1.15; - 0.25 or SMD = - 0.81; 95% CI - 1.41; - 0.20 (depending on the dosing regimen used); p ≤ 0.009 vs placebo.

CONCLUSIONS

Our meta-analysis revealed rapid and robust antidepressant effects of single-dose ketamine in patients with treatment-resistant depression (TRD). By pooling data from RCTs, we showed for the first time that repeated ketamine administration is effective in sustaining initial antidepressant effects observed after single dosing.

Overlap in the neural circuitry and molecular mechanisms underlying ketamine abuse and its use as an antidepressant

Ketamine, a dissociative anesthetic and psychedelic compound, has revolutionized the field of psychopharmacology by showing robust, and rapid-acting antidepressant activity in patients suffering from major depressive disorder (MDD), suicidal tendencies, and treatment-resistant depression (TRD). Ketamine's efficacy, however, is transient, and patients must return to the clinic for repeated treatment as they experience relapse. This is cause for concern because ketamine is known for its abuse liability, and repeated exposure to drugs of abuse often leads to drug abuse/dependence. Though the mechanism(s) underlying its antidepressant activity is an area of current intense research, both clinical and preclinical evidence shows that ketamine's effects are mediated, at least in part, by molecular adaptations resulting in long-lasting synaptic changes in mesolimbic brain regions known to regulate natural and drug reward. This review outlines our limited knowledge of ketamine's neurobiological and biochemical underpinnings mediating its antidepressant effects and correlates them to its abuse potential. Depression and addiction share overlapping neural circuitry and molecular mechanisms, and though speculative, repeated use of ketamine for the treatment of depression could lead to the development of substance use disorder/addiction, and thus should be tempered with caution. There is much that remains to be known about the long-term effects of ketamine, and our lack of understanding of neurobiological mechanisms underlying its antidepressant effects is a clear limiting factor that needs to be addressed systematically before using repeated ketamine in the treatment of depressed patients.

Anticonvulsive effects of protodioscin against pilocarpine-induced epilepsy

Epilepsy is associated with increased morbidity and mortality together and places a large financial burden on individuals and society. To evaluate the anticonvulsant action of protodioscin (PDSN) in experiments with animals with pilocarpine-induced convulsions. We assessed the activity of PDSN in pilocarpine induced seizures in combination with different agents which are acting via diverse receptors, such as atropine, memantine, nimodipine, diazepam, and flumazenil, to determine the exact receptors responsible for the action of PDSN. Furthermore, the level of antioxidant markers was investigated in the cerebellum and cerebral cortex in mice to define the antioxidant action of PDSN. The effects of PDSN on proapoptotic markers (i.e., Bcl-2, Bax, and caspase-3) was investigated via western blot analysis. PDSN significantly enhanced latency to the first convulsion and survival compared to the group treated with pilocarpine alone. Moreover, PDSN improved animal survival, and subjects experiencing no convulsions. Striatal glutamate and aspartate levels were not modified, and gamma amino butyric acid (GABA) levels increased, as a result of treatment with PDSN. The results suggest that the anticonvulsive action of PDSN is dependent on inhibitory amino acids. PDSN treatment also significantly decreased nitrite levels in the blood and brain cortex compared to the normal control. In the western blot analysis, PDSN exerted its neuroprotective effect via the upregulation of Bcl-2 and downregulation of Bax and caspase-3. The results of this study suggest that PDSN exerts neuroprotective effects via multiple mechanisms.

1,2-Diarylethylamine- and Ketamine-Based New Psychoactive Substances

While phencyclidine (PCP) and ketamine remain the most well-studied and widely known dissociative drugs, a number of other agents have appeared since the late 1950s and early 1960s, when the pharmacological potential of this class was first realized. For example, hundreds of compounds have been pursued as part of legitimate research efforts to explore these agents. Some of these found their way out of the research labs and onto illicit markets of the 1960s and following decades as PCP analogs. Other "illicit analogs" apparently never appeared in the scientific literature prior to their existence on clandestine markets, thus originating as novel innovations in the minds of clandestine chemists and their colleagues. Like so much else in this world, new technologies changed this dynamic. In the 1990s individuals separated by vast geographical distances could now communicate nearly instantaneously with ease through the Internet. Some individuals used this newly found opportunity to discuss the chemistry and psychoactive effects of dissociative drugs as well as to collaborate on the design and development of novel dissociative compounds. Similar to modern pharmaceutical companies and academic researchers, these seekers tinkered with the structure of their leads pursuing goals such as improved duration of action, analgesic effects, and reduced toxicity. Whether all these goals were achieved for any individual compound remains to be seen, but their creations have been let out of the bag and are now materialized as defined compositions of matter. Moreover, these creations now exist not only in and of themselves but live on further as permutations into various novel analogs and derivatives. In some cases these compounds have made their way to academic labs where potential clinical applications have been identified. These compounds reached wider distribution when other individuals picked up on these discussions and began to market them as "research chemicals" or "legal highs". The result is a continuously evolving game that is being played between legislatures, law enforcement, and research chemical market players. Two structurally distinct classes that have appeared as dissociative-based new psychoactive substances (NPS) are the 1,2-diarylethylamines and β-keto-arylcyclohexylamines. Examples of the former include diphenidine and various analogs such as fluorolintane and N-ethyl-lanicemine, and examples of the latter are analogs of ketamine such as methoxetamine, deschloroketamine, and 2-fluoro-2-deschloroketamine. The subject of this chapter is the introduction to some of the dissociative NPS from these classes and their known pharmacology that have emerged on the market in recent years.

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.

Ketamine in adult cardiac surgery and the cardiac surgery Intensive Care Unit: an evidence-based clinical review

Ketamine is a unique anesthetic drug that provides analgesia, hypnosis, and amnesia with minimal respiratory and cardiovascular depression. Because of its sympathomimetic properties it would seem to be an excellent choice for patients with depressed ventricular function in cardiac surgery. However, its use has not gained widespread acceptance in adult cardiac surgery patients, perhaps due to its perceived negative psychotropic effects. Despite this limitation, it is receiving renewed interest in the United States as a sedative and analgesic drug for critically ill-patients. In this manuscript, the authors provide an evidence-based clinical review of ketamine use in cardiac surgery patients for intensive care physicians, cardio-thoracic anesthesiologists, and cardio-thoracic surgeons. All MEDLINE indexed clinical trials performed during the last 20 years in adult cardiac surgery patients were included in the review.

Memories reactivated under ketamine are subsequently stronger: A potential pre-clinical behavioral model of psychosis

BACKGROUND

Sub-anesthetic doses of the NMDA antagonist ketamine have been shown to model the formation and stability of delusion in human subjects. The latter has been predicted to be due to aberrant prediction error resulting in enhanced destabilization of beliefs. To extend the scope of this model, we investigated the effect of administration of low dose systemic ketamine on memory in a rodent model of memory reconsolidation.

METHODS

Systemic ketamine was administered either prior to or immediately following auditory fear memory reactivation in rats. Memory strength was assessed by measuring freezing behavior 24h later. Follow up experiments were designed to investigate an effect of pre-reactivation ketamine on short-term memory (STM), closely related memories, and basolateral amygdala (BLA) specific destabilization mechanisms.

RESULTS

Rats given pre-reactivation, but not post-reactivation, ketamine showed larger freezing responses 24h later compared to vehicle. This enhancement was not observed 3h after the memory reactivation, nor was it seen in a closely related contextual memory. Prior inhibition of a known destabilization mechanism in the BLA blocked the effect of pre-reactivation ketamine.

CONCLUSIONS

Pre- but not post-reactivation ketamine enhances fear memory. These data together with recent data in human subjects supports a model of delusion fixity that proposes that aberrant prediction errors result in enhanced destabilization and strengthening of delusional belief.

Enhanced dopamine-dependent hippocampal plasticity after single MK-801 application

Dopaminergic hyperfunction and N-methyl-D-aspartate receptor (NMDAR) hypofunction have both been implicated in psychosis. Dopamine-releasing drugs and NMDAR antagonists replicate symptoms associated with psychosis in healthy humans and exacerbate symptoms in patients with schizophrenia. Though hippocampal dysfunction contributes to psychosis, the impact of NMDAR hypofunction on hippocampal plasticity remains poorly understood. Here, we used an NMDAR antagonist rodent model of psychosis to investigate hippocampal long-term potentiation (LTP). We found that single systemic NMDAR antagonism results in a region-specific, presynaptic LTP at hippocampal CA1-subiculum synapses that is induced by activation of D1/D5 dopamine receptors and modulated by L-type voltage-gated Ca(2+) channels. Thereby, our findings may provide a cellular mechanism how NMDAR antagonism can lead to an enhanced hippocampal output causing activation of the hippocampus-ventral tegmental area-loop and overdrive of the dopamine system.

The neurobiology of bipolar disorder: identifying targets for specific agents and synergies for combination treatment

Bipolar disorder (BD) is a chronic psychiatric illness described by severe changes in mood. Extensive research has been carried out to understand the aetiology and pathophysiology of BD. Several hypotheses have been postulated, including alteration in genetic factors, protein expression, calcium signalling, neuropathological alteration, mitochondrial dysfunction and oxidative stress in BD. In the following paper, we will attempt to integrate these data in a manner which is to understand targets of treatment and how they may be, in particular, relevant to combination treatment. In summary, the data suggested that BD might be associated with neuronal and glial cellular impairment in specific brain areas, including the prefrontal cortex. From molecular and genetics: (1) alterations in dopaminergic system, through catechol-O-aminotransferase; (2) decreased expression and polymorphism on brain-derived neurotrophic factor; (3) alterations cyclic-AMP responsive element binding; (4) dysregulation of calcium signalling, including genome-wide finding for voltage-dependent calcium channel α-1 subunit are relevant findings in BD. Future studies are now necessary to understand how these molecular pathways interact and their connection to the complex clinical manifestations observed in BD.

Ketamine pharmacology: an update (pharmacodynamics and molecular aspects, recent findings)

For more than 50 years, ketamine has proven to be a safe anesthetic drug with potent analgesic properties. The active enantiomer is S(+)-ketamine. Ketamine is mostly metabolized in norketamine, an active metabolite. During "dissociative anesthesia", sensory inputs may reach cortical receiving areas, but fail to be perceived in some association areas. Ketamine also enhances the descending inhibiting serotoninergic pathway and exerts antidepressive effects. Analgesic effects persist for plasma concentrations ten times lower than hypnotic concentrations. Activation of the (N-Methyl-D-Aspartate [NMDA]) receptor plays a fundamental role in long-term potentiation but also in hyperalgesia and opioid-induced hyperalgesia. The antagonism of NMDA receptor is responsible for ketamine's more specific properties. Ketamine decreases the "wind up" phenomenon, and the antagonism is more important if the NMDA channel has been previously opened by the glutamate binding ("use dependence"). Experimentally, ketamine may promote neuronal apoptotic lesions but, in usual clinical practice, it does not induce neurotoxicity. The consequences of high doses, repeatedly administered, are not known. Cognitive disturbances are frequent in chronic users of ketamine, as well as frontal white matter abnormalities. Animal studies suggest that neurodegeneration is a potential long-term risk of anesthetics in neonatal and young pediatric patients.

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.

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.

Separate and combined effects of low dose ketamine and nicotine on behavioural and neural correlates of sustained attention

Given the cognitive-promoting properties of the nicotinic acetylcholinergic receptor (nAChR) agonist, nicotine, the increased prevalence of smoke-inhaled nicotine in schizophrenia has been interpreted as an attempt to self-correct cognitive deficits, which have been particularly pronounced in the attentional domain. As glutamatergic abnormalities have been implicated in these attentional deficiencies, this study attempted to shed light on the separate and interactive roles of the N-methyl-d-aspartate receptor (NMDAR) and nAChR systems in the modulation of attention by investigating, in healthy volunteers, the separate and combined effects of nicotine and the NMDAR antagonist ketamine on neural and behavioural responses in a sustained attention task. In a randomized, double-blind, placebo controlled study, performance and the P300 event-related brain potential (ERP) in a visual information processing (RVIP) task were examined in 20 smokers and 20 non-smokers (both male and female). Assessment involved intravenous injection of a low subperceptual bolus dose (.04mg/kg) of ketamine or placebo, which was accompanied by acute treatment with nicotine (4mg) or placebo gum. Nicotine-enhanced attentional processing was most evident in nonsmokers, with both performance accuracy and P300 amplitude measures. Ketamine's detrimental effects on these behavioural and electrophysiologic measures were negatively moderated by acute nicotine, the synergistic effects being expressed differently in smokers and nonsmokers. These findings support the view that acute alterations and individual differences in nAChR function can moderate even subtle glutamatergic-driven cognitive deficiencies in schizophrenia and can be important therapeutic targets for treating cognitive impairments in schizophrenia.

Participation of L-type calcium channels in ethanol-induced behavioral stimulation and motor incoordination: effects of diltiazem and verapamil

Calcium flux through voltage gate calcium channels (VGCC) is involved in many neuronal processes such as membrane depolarization, gene expression, hormone secretion, and neurotransmitter release. Several studies have shown that either acute or chronic exposure to ethanol modifies calcium influx through high voltage activated channels. Of special relevance is the L-type VGCC. Pharmacological manipulation of L-type calcium channels affects ethanol intake, ethanol discrimination and manifestations of withdrawal syndrome. The present study investigates the role of L-type channels on the psychomotor effects (stimulation and sedation/ataxia) of ethanol by testing the effects of different L-type calcium channel blockers (CCB) on such behaviors. Mice were pretreated intraperitoneally with the CCB, diltiazem (0-40 mg/kg) or verapamil (0-30 mg/kg) 30 min before ethanol (0-3.5 g/kg). Locomotion was measured in an open field chamber for 20 min immediately after ethanol. The two CCB tested prevented locomotor stimulation, but not locomotor suppression produced by ethanol. Doses of the two CCB which reduced ethanol stimulation, did not alter spontaneous locomotion. The ataxic effects of ethanol (1.25 g/kg), measured with an accelerating rotarod task, were not affected by diltiazem (20mg/kg) or verapamil (15 mg/kg). In addition, our results indicated that ethanol is more sensitive to the antagonism of L-type calcium channels than other drugs with stimulant properties; doses of the two CCB that reduced ethanol stimulation did not reduce the psychomotor effects of amphetamine, caffeine or cocaine. In conclusion, these data provide further evidence of the important involvement of L-type calcium channels in the behavioral effects produced by ethanol.

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'.

[Prevention of psychedelic side effects associated with low dose continuous intravenous ketamine infusion]

OBJECTIVE

Continuous low dose infusion of intravenous ketamine for postoperative analgesia was often associated with frightening acute psychodysleptic experiences in our patients. We hypothesized they were due to boluses of ketamine accumulated in the infusion line. We evaluated on two successive groups the impact of perfusion line modifications on psychodysleptic side effects occurrence.

METHODS

We compared a reference historic group (in which ketamine line was connected to perfusion line) to a second prospective group (in which ketamine line was connected to the venous catheter via an unidirectional valve).

RESULTS

Psychodysleptic experiences occurrence decreased from 4 patients of 26 (15%) to 2 of 116 (2%, p = 0.01). Moreover, these experiences were no longer associated with severe anxious symptoms like near death experiences.

CONCLUSION

An unidirectional valve must be considered to limit the occurrence of low dose intravenous ketamine infusion associated psychedelic side effects, during postoperative analgesia.

Schizophrenia, ketamine and cannabis: evidence of overlapping memory deficits

Drug models of mental illness are considered useful if they provoke its characteristic symptoms. In this respect, ketamine and tetrahydrocannabinol (cannabis) are coming under increasing scrutiny as models for schizophrenia. However, although both undoubtedly produce psychotic symptoms characteristic of the disorder, we argue here that, because schizophrenia is also accompanied by cognitive deficits, a full understanding of the impact of these drugs on cognition will be crucial in taking these models further. Memory deficits are pronounced in schizophrenia and we focus upon patterns of working and episodic memory impairment produced by ketamine and cannabis, identifying overlaps between drug and illness. We suggest that close attention to these deficits can offer insights into core pathophysiology of schizophrenia.

The potential role of lamotrigine in schizophrenia

RATIONALE

Atypical antipsychotic drugs are the drugs of choice for the treatment of schizophrenia. However, despite advances, no treatments have been established for patients who fail to improve with the most effective of these, clozapine. The inhibition of dopamine transmission through blockade of dopamine D2 receptors is considered to be essential for antipsychotic efficacy, but it is postulated that modulation of glutamate transmission may be equally important. In support of this, symptoms similar to schizophrenia can be induced in healthy volunteers using N-methyl-D-aspartate (NMDA) antagonist drugs that are also known to enhance glutamate transmission. Furthermore, lamotrigine, which can modulate glutamate release, may add to or synergise with atypical antipsychotic drugs, some of which may themselves modulate glutamate transmission.

OBJECTIVES

We examine the evidence for the efficacy of lamotrigine. We consider how this fits with a glutamate neuron dysregulation hypothesis of the disorder. We discuss mechanisms by which lamotrigine might influence neuronal activity and glutamate transmission, and possible ways in which the drug might interact with antipsychotic medications.

RESULTS

Data from four clinical studies support the efficacy of adjunctive lamotrigine in the treatment of schizophrenia. In addition, and consistent with a glutamate neuron dysregulation hypothesis of schizophrenia, lamotrigine can prevent the psychotic symptoms or behavioural disruption induced by NMDA receptor antagonists in healthy volunteers or rodents.

CONCLUSIONS

The efficacy of lamotrigine is most likely explained within the framework of a glutamate neuron dysregulation hypothesis, and may arise primarily through the drugs ability to influence glutamate transmission and neural activity in the cortex. The drug is likely to act through inhibition of voltage-gated sodium channels, though other molecular interactions cannot be ruled out. Lamotrigine may add to or synergise with some atypical antipsychotic drugs acting on glutamate transmission; alternatively, they may act independently on glutamate and dopamine systems to bring about a combined therapeutic effect. We propose new strategies for the treatment of schizophrenia using a combination of anti-dopaminergic and anti-glutamatergic drugs.

Preliminary evidence of attenuation of the disruptive effects of the NMDA glutamate receptor antagonist, ketamine, on working memory by pretreatment with the group II metabotropic glutamate receptor agonist, LY354740, in healthy human subjects

RATIONALE

Some of the behavioral consequences of deficits in N-methyl-D-aspartate (NMDA) glutamate receptor function are thought to arise from the disinhibition of cortical glutamatergic circuitry.

OBJECTIVE

This study evaluated whether pretreatment with a drug that reduces glutamatergic activation, the group II metabotropic glutamate receptor (mGluR) agonist, LY354740, reduced the cognitive effects of the NMDA glutamate receptor antagonist, ketamine, in healthy human subjects.

METHODS

Nineteen healthy human subjects completed 3 test days during which LY354740 (matched placebo, 100 mg, 400 mg) was administered under double-blind conditions 4 h prior to the single-blind intravenous administration of saline and 5.7 h prior to ketamine administration (bolus of 0.26 mg/kg over 1 min, infusion of 0.65 mg/kg per hour for 100 min). Thus on each test day each subject received a single dose of LY354740 (or its matched placebo) and both saline and ketamine infusions.

RESULTS

Ketamine impaired attention, working memory, and delayed recall. It also produced positive and negative symptoms, perceptual changes, and dysphoric mood. LY354740 did not have a significant effect on working memory on the placebo day; however, it produced a significant dose-related improvement in working memory during ketamine infusion.

CONCLUSIONS

These data provide preliminary and suggestive evidence that LY354740 or other group II mGluR agonists might play a role in treating working memory impairment related to deficits in NMDA receptor function.

Altered NMDA glutamate receptor antagonist response in recovering ethanol-dependent patients

Ethanol is an antagonist of the N-methyl-D-aspartate (NMDA) glutamate receptor. Ethanol dependence upregulates NMDA receptors and contributes to crosstolerance with selective NMDA receptor antagonists in animals. This study evaluated whether recovering ethanol-dependent patients show evidence of a reduced level of response to the effects of the NMDA receptor antagonist, ketamine. In this double-blind study, 34 recently detoxified alcohol-dependent patients and 26 healthy comparison subjects completed 3 test days involving a 40-min infusion of saline, ketamine 0.1 mg/kg, or ketamine 0.5 mg/kg in a randomized order. Recovering ethanol-dependent patients showed reduced perceptual alterations, dysphoric mood, and impairments in executive cognitive functions during ketamine infusion relative to the healthy comparison group. No attenuation of ketamine-induced amnestic effects, euphoria, or activation was observed. The alterations in NMDA receptor function observed in recovering ethanol-dependent patients may have important implications for ethanol tolerance, ethanol dependence, and the treatment of alcoholism.

NMDA Receptor Antagonism and the Ethanol Intoxication Signal

This paper reviews clinical evidence suggesting that antagonism of the N-methyl-D-aspartate subtype of glutamate receptors by ethanol may convey an important component of the ethanol intoxication signal, that is, subjective and objective responses associated with the consumption of a large amount of ethanol. It will then review recent evidence that two phenotypes associated with increased risk for heavy alcohol consumption, recovering ethanol-dependent patients, and healthy individuals with a family history of alcohol dependence, exhibit reduced sensitivity to the dysphoric consequences of administration of the NMDA receptor antagonist, ketamine. Each of these groups displays reduced sensitivity to a potentially important response that might normally trigger the cessation of ethanol consumption. These data raise the possibility that alterations in NMDA receptor function that reduce the response to the NMDA antagonist component of ethanol may increase the risk for heavy drinking. This hypothesis is consistent with growing evidence that NMDA receptor antagonists may play a role in the treatment of alcoholism by suppressing alcohol withdrawal, reducing the development or expression of alcohol tolerance, or preventing or reversing the sensitiziation to ethanol effects.

NMDA receptor antagonist effects, cortical glutamatergic function, and schizophrenia: toward a paradigm shift in medication development

There is an urgent need to improve the pharmacotherapy of schizophrenia despite the introduction of important new medications. New treatment insights may come from appreciating the therapeutic implications of model psychoses. In particular, basic and clinical studies have employed the N-methyl-D-aspartate (NMDA) glutamate receptor antagonist, ketamine, as a probe of NMDA receptor contributions to cognition and behavior. These studies illustrate a translational neuroscience approach for probing mechanistic hypotheses related to the neurobiology and treatment of schizophrenia and other disorders. Two particular pathophysiologic themes associated with schizophrenia, the disturbance of cortical connectivity and the disinhibition of glutamatergic activity may be modeled by the administration of NMDA receptor antagonists. The purpose of this review is to consider the possibility that agents that attenuate these two components of NMDA receptor antagonist response may play complementary roles in the treatment of schizophrenia.

N-methyl-D-aspartate glutamate receptors and alcoholism: reward, dependence, treatment, and vulnerability

This review takes a translational neuroscience perspective on the role of glutamate systems in human ethanol abuse and dependence. Ethanol is a simple molecule with profound effects on many chemical systems in the brain. Glutamate is the primary excitatory neurotransmitter in the brain. Glutamatergic systems are targets for the actions of ethanol via its antagonism of the N-methyl-D-aspartate (NMDA) subtype of the glutamate receptor and other mechanisms. The modulation of glutamatergic function by ethanol contributes to both euphoric and dysphoric consequences of ethanol intoxication. Adaptations within glutamatergic systems appear to contribute to ethanol tolerance and dependence and to both acute and protracted features of ethanol withdrawal. Perhaps because of the important glutamatergic mediation of the behavioral effects of ethanol, glutamatergic systems appear to contribute to the vulnerability to alcoholism, and novel glutamatergic agents may play a role in the treatment of ethanol abuse and dependence.

Glutamate and GABA systems as targets for novel antidepressant and mood-stabilizing treatments

Glutamate and gamma-amino butyric acid (GABA) systems are emerging as targets for development of medications for mood disorders. There is increasing preclinical and clinical evidence that antidepressant drugs directly or indirectly reduce N-methyl-D-aspartate glutamate receptor function. Drugs that reduce glutamatergic activity or glutamate receptor-related signal transduction may also have antimanic effects. Recent studies employing magnetic resonance spectroscopy also suggest that unipolar, but not bipolar, depression is associated with reductions in cortical GABA levels. Antidepressant and mood-stabilizing treatments also appear to raise cortical GABA levels and to ameliorate GABA deficits in patients with mood disorders. The preponderance of available evidence suggests that glutamatergic and GABAergic modulation may be an important property of available antidepressant and mood-stabilizing agents. Future research will be needed to develop and evaluate new agents with specific glutamate and GABA receptor targets in the treatment of mood disorders.