Ketamine: 50 Years of Modulating the Mind

NMDAR Hypofunction Animal Models of Schizophrenia

The N-methyl-d-aspartate receptor (NMDAR) hypofunction hypothesis has been proposed to help understand the etiology and pathophysiology of schizophrenia. This hypothesis was based on early observations that NMDAR antagonists could induce a full range of symptoms of schizophrenia in normal human subjects. Accumulating evidence in humans and animal studies points to NMDAR hypofunctionality as a convergence point for various symptoms of schizophrenia. Here we review animal models of NMDAR hypofunction generated by pharmacological and genetic approaches, and how they relate to the pathophysiology of schizophrenia. In addition, we discuss the limitations of animal models of NMDAR hypofunction and their potential utility for therapeutic applications.

Esketamine for treatment resistant depression

Introduction: Treatment Resistant Depression (TRD) is a common and burdensome condition with poor outcomes and few treatment options. Esketamine is the S-enantiomer of ketamine and has recently been FDA approved in the United States for treating depression that has failed to respond to trials of two or more antidepressants. Areas covered: This review will briefly discuss current treatment options for TRD, then review esketamine. Relevant literature was identified through online database searches, and clinical trial data were provided by Janssen Pharmaceuticals. Pharmacology, including kinetics and dynamics, is discussed, then clinical data regarding efficacy and safety for esketamine from Phase 2-3 trials are reviewed. Expert opinion: In the expert opinion, the authors discuss multiple factors including patient, physician, and social factors that will influence the use of esketamine. While the efficacy of esketamine compared to off-label use of racemic ketamine remains unclear, both esketamine's approval for use in TRD and longer-term safety data may position it preferentially above racemic ketamine, although factors such as cost and monitoring requirements may limit its use. While questions remain regarding duration and frequency of treatment, as well as addictive potential, esketamine is a novel treatment option offering new hope for TRD.

Subanesthetic Dose Ketamine in Posttraumatic Stress Disorder: A Role for Reconsolidation During Trauma-Focused Psychotherapy?

Despite efforts to develop more effective therapies, PTSD remains a difficult disorder to treat. Insight into the dynamic nature of memory formation and its required molecular machinery can provide an opportunity to target pathological memories for emotionally arousing events. As memories become labile upon retrieval, novel information can update the strength and course of these consolidated memories. Targeting the process of reconsolidation may offer a relevant approach to attenuate fearful and traumatic memories. Specific molecular mechanisms that are required for reconsolidation of arousing information include an intact functioning of the glutamatergic signaling pathways and, more specifically, the integrity of NMDA receptors. Ketamine, a noncompetitive NMDA-receptor antagonist, is receiving increasing interest for a variety of psychiatric indications. This compound can also be an interesting candidate for targeting emotional memories. We explore whether single intravenous infusion of a subanesthetic dose of ketamine can be considered as a viable augmentation strategy for trauma-focused psychotherapy in patients with PTSD. As a consequence, a systematic approach is needed to assess the pharmacodynamic effects of ketamine in relation to both psychotherapy and its pharmacokinetics prior to its application in patient populations. By using a "question-based drug development plan," we can explore such aspects for novel drugs, and we formulated five additional topics that need to be addressed concerning the psychotherapeutic approach and phase orientation of pharmacological assisted psychotherapy.

Comparison of antidepressant and side effects in mice after intranasal administration of (R,S)-ketamine, (R)-ketamine, and (S)-ketamine

The N-methyl-d-aspartate receptor (NMDAR) antagonist (R,S)-ketamine produces rapid and sustained antidepressant effects in treatment-resistant patients with depression although intranasal use of (R,S)-ketamine in ketamine abusers is popular. In March 5, 2019, nasal spray of (S)-ketamine for treatment-resistant depression was approved as a new antidepressant by the US Food Drug Administration. Clinical study of (R)-ketamine is underway. In a chronic social defeat stress (CSDS) model, we compared the antidepressant effects of (R,S)-ketamine, (R)-ketamine, and (S)-ketamine after a single intranasal administration. Furthermore, we also compared the side effects (i.e., locomotion, prepulse inhibition (PPI), abuse liability) of these three compounds in mice. The order of potency of antidepressant effects after a single intranasal administration was (R)-ketamine > (R,S)-ketamine > (S)-ketamine. In contrast, the order of locomotor activity and prepulse inhibition (PPI) deficits after a single intranasal administration was (S)-ketamine > (R,S)-ketamine > (R)-ketamine. In the conditioned place preference (CPP) test, both (S)-ketamine and (R,S)-ketamine increased CPP scores in mice after repeated intranasal administration, in a dose dependent manner. In contrast, (R)-ketamine did not increase CPP scores in mice. These findings suggest that intranasal administration of (R)-ketamine would be a safer antidepressant than (R,S)-ketamine and (S)-ketamine.

[Ketamine in the therapy of chronic pain and depression]

Although ketamine has been known and clinically applied for a long time, questions still arise around the many possible indications in which the anesthetic and analgesic substance could be used. In particular, these questions relate to new indications in which ketamine is used in low subanesthetic doses.The mechanism of action at the NMDA receptor clearly distinguishes ketamine from all other analgesics. Possible applications include the prevention of chronic postoperative pain as well as the treatment of neuropathic pain. With the treatment of refractory depression completely new therapeutic areas for ketamine could be established.

Is Ketamine Suitable for Use in Glutamate Toxicity Conditions?: An In Vitro Study

Ketamine is an anesthetic agent with sedative and analgesic properties frequently used in surgery. However, particular anesthetic substances need to be applied for different diseases and surgical procedures. Can ketamine be used in all operations and in all patients with an additional disease? The purpose of this study was to determine the neurotoxic or neuroprotective effects of different dosages of ketamine in a glutamate-derived toxicity model in olfactory, cortex and cerebellum cell cultures. Glutamate 10^-5mM was added to all culture groups with the exception of the negative control group. Cells were exposed to four different dosages of ketamine for 24 h. At the end of the experiment, analyses were conducted using MTT, total antioxidant capacity (TAC), total oxidant status (TOS) and flow cytometry (annexin V apoptosis marker) tests. The highest viability rate was obtained at the lowest ketamine dosage, at approximately 80% in cerebellum cells, but less than 75% in cortex and olfactory culture cells. Based on our study findings, although ketamine is an NMDA antagonist, it causes an increase in toxicity levels and a decrease in cell viability. Ketamine use should therefore be avoided in neurological events in which glutamate levels increase significantly.

Acute Ketamine Infusion in Rat Does Not Affect In Vivo [11C]ABP688 Binding to Metabotropic Glutamate Receptor Subtype 5

Detecting changes in metabotropic glutamate receptor 5 (mGluR5) availability through molecular imaging with the positron emission tomography (PET) tracer [¹¹C]ABP688 is valuable for studying dysfunctional glutamate transmission associated with neuropsychiatric disorders. Using an infusion protocol in rats, we visualized the acute effect of subanesthetic doses of ketamine on mGluR5 in rat brain. Ketamine is an N-methyl-D-aspartate (NMDA) receptor antagonist known to increase glutamate release. Imaging was performed with a high-affinity PET ligand [¹¹C]ABP688, a negative allosteric modulator of mGluR5. Binding did not change significantly from baseline to ketamine in any region, thereby confirming previous literature with other NMDA receptor antagonists in rodents. Hence, in rats, we could not reproduce the findings in a human setup showing significant decreases in the [¹¹C]ABP688 binding after a ketamine bolus followed by ketamine infusion. Species differences may have contributed to the different findings in the present study of rats. In conclusion, we could not confirm in rats that endogenous glutamate increases by ketamine infusion are reflected in [¹¹C]ABP688 binding decreases as was previously shown for humans.

Ketamine induces central antinociception mediated by endogenous cannabinoids and activation of CB1 receptors

The participation of endocannabinoids in central and peripheral antinociception induced by several compounds has been shown by our group. In this study, we investigated the effect of endocannabinoids on the central antinociception induced by ketamine. The nociceptive threshold for thermal stimulation was measured using the tail-flick test in Swiss mice. The drugs were administered intracerebroventricularly. Probabilities less than 5% (p < 0.05) were considered to be statistically significant (Two-way ANOVA/Bonferroni's test). The CB₁-selective cannabinoid receptor antagonist AM251 (2 and 4 μg) completely reversed the central antinociception induced by ketamine (4 μg) in a dose-dependent manner. In contrast, the CB₂-selective cannabinoid receptor antagonist AM630 (2 and 4 μg) did not antagonize this effect. Additionally, the administration of the anandamide amidase inhibitor MAFP (0.2 μg) and anandamide uptake inhibitor VDM11 (4 μg) significantly enhanced the antinociception induced by a low dose of ketamine (2 μg). It was concluded that central antinociception induced by ketamine involves the activation of CB₁ cannabinoid receptors. Mobilization of cannabinoids might be required for the activation of those receptors, since inhibitors of the endogenous cannabinoids potentiate the effect of Ketamine.

Ketamine for Treatment-Resistant Mood Disorders

Strong evidence supports the rapid, although temporary, antidepressant effects of a single intravenous ketamine infusion for treatment-resistant major depressive disorder (MDD) and bipolar depression. Although ketamine has diverse effects on brain neurotransmitters, current theories have implicated N-methyl-d-aspartate antagonist effects at the presynaptic interneuron in mediating its antidepressant effects. Intravenous ketamine administration for treatment-resistant depression (TRD) is generally safe and well tolerated when administered by trained professionals. Repeated intravenous ketamine infusions as an off-label treatment for TRD are increasingly available for clinical use, although their safety and effectiveness are not well characterized. Intranasal administration of esketamine-the (S)-enantiomer of racemic ketamine-recently completed phase 3 multicenter trials; a Food and Drug Administration application for its use in TRD is expected. Relatively little is known about the longer term side effects of ketamine for TRD. Concerns have been raised about its dissociative side effects, risk of abuse, and potential excitotoxic neuronal injury at higher doses and with repeated use. Treatment guidelines are needed to standardize ketamine use in psychiatric disorders. Ketamine research is transforming our understanding of the pathophysiology of mood disorders and leading the way toward developing new, rapid-acting interventions for TRD.

Ketamine and selective activation of parvalbumin interneurons inhibit stress-induced dendritic spine elimination

Stress is a major risk factor for the onset of many psychiatric diseases. In rodent models, chronic stress induces depression and impairs excitatory neurotransmission. However, little is known about the effect of stress on synaptic circuitry during the development of behavioral symptoms. Using two-photon transcranial imaging, we studied the effect of repeated restraint stress on dendritic spine plasticity in the frontal cortex in vivo. We found that restraint stress induced dendritic spine loss by decreasing the rate of spine formation and increasing the rate of spine elimination. The N-methyl-D-aspartate receptor antagonist ketamine inhibited stress-induced spine loss mainly by protecting mushroom spines from elimination. Ketamine also induced re-formation of spines in close proximity to previously stress-eliminated spines. Electrophysiological and in vivo imaging experiments showed that ketamine enhanced activity of parvalbumin (PV) interneurons under stress and counterbalanced the stress-induced net loss of PV axonal boutons. In addition, selective chemogenetic excitation of PV interneurons mimicked the protective effects of ketamine on dendritic spines against stress. Collectively, our data provide new insights on the effects of ketamine on synaptic circuitry under stress and a possible mechanism to counteract stress-induced synaptic impairments through PV interneuron activation.

An update on ketamine and its two enantiomers as rapid-acting antidepressants

Introduction: Depression is one of the most disabling diseases worldwide. Approximately one-third of depressed patients are treatment-resistant to the currently available antidepressants and there is a significant therapeutic time lag of weeks to months. There is a clear unmet need for rapid-acting and more efficacious treatments. (R,S)-ketamine, an old anesthetic drug, appears now to be going through a renaissance. Areas covered: This paper reviews recent literature describing the antidepressant effects of ketamine and its enantiomer (S)-ketamine in patients with major depressive disorder (MDD) and bipolar disorder (BD). Furthermore, the authors discuss the therapeutic potential of (R)-ketamine, another enantiomer of (R,S)-ketamine, and (S)-norketamine. Expert commentary: A number of clinical studies have demonstrated that (R,S)-ketamine has rapid-acting and sustained antidepressant activity in treatment-resistant patients with MDD, BD, and other psychiatric disorders. Off-label use of ketamine for mood disorders is proving popular in the United States. Meanwhile, preclinical data suggests that (R)-ketamine can exert longer-lasting antidepressant effects than (S)-ketamine in animal models of depression, and (R)-ketamine may have less detrimental side effects than (R,S)-ketamine and (S)-ketamine. Additionally, (S)-norketamine exhibits rapid and sustained antidepressant effects, with a potency similar to that of (S)-ketamine. Unlike (S)-ketamine, (S)-norketamine does not cause behavioral and biochemical abnormalities and could be a safer than (S)-ketamine too.

Faster emergence behavior from ketamine/xylazine anesthesia with atipamezole versus yohimbine

Recent interest in reversal of the hypnotic effects of anesthesia has mainly focused on overcoming a surge in GABA-mediated inhibitory signaling through activation of subcortical arousal circuits or antagonizing GABA receptors. Here we examine the reversal of anesthesia produced from non-GABA agents ketamine/xylazine and the effects of antagonists of adrenoreceptors. These antagonists vary in selectivity and produce temporally unique waking behavior post-anesthesia. We compared two antagonists with differential selectivity for α₁- vs. α₂-receptors, yohimbine (YOH, 1:40 selectivity) and atipamezole (ATI, 1:8500). Adult mice received intraperitoneal injections of either YOH (4.3 mg/kg), ATI (0.4 mg/kg), or saline after achieving sustained loss of righting following injection of ketamine/xylazine (ketamine: 65.0 mg/kg; xylazine: 9.9 mg/kg). Behaviors indicative of the post-anesthesia, re-animation sequence were carefully monitored and the timing of each behavior relative to anesthesia induction was compared. Both YOH and ATI hastened behaviors indicative of emergence, but ATI was faster than YOH to produce certain behaviors, including whisker movement (YOH: 21.9±1.5 min, ATI: 17.5±0.5 min, p = 0.004) and return of righting reflex (RORR) (YOH: 40.6±8.8 min, ATI: 26.0±1.2 min, p<0.001). Interestingly, although YOH administration hastened early behavioral markers of emergence relative to saline (whisking), the completion of the emergence sequence (time from first marker to appearance of RORR) was delayed with YOH. We attribute this effect to antagonism of α₁ receptors by yohimbine. Also notable was the failure of either antagonist to hasten the re-establishment of coordinated motor behavior (e.g., attempts to remove adhesive tape on the forepaw placed during anesthesia) relative to the end of emergence (RORR). In total, our work suggests that in addition to pharmacokinetic effects, re-establishment of normal waking behaviors after anesthesia involves neuronal circuits dependent on time and/or activity.

Influence of mTOR signaling pathway on ketamine-induced injuries in the hippocampal neurons of rats

OBJECTIVE

To explore the influences of mammalian target of rapamycin (mTOR) signaling pathway on ketamine-induced apoptosis, oxidative stress and Ca²⁺ concentration in the hippocampal neurons of rats.

METHODS

The primary hippocampal neurons isolated from fetal Sprague Dawley rats were treated with ketamine (0, 50, 100 and 500 μM) for 4 days to observe its effect on mTOR signaling pathway and apoptosis of rat hippocampal neurons. Then, the hippocampal neurons were divided into C (Control), R (Rapamycin, an inhibitor of mTOR signaling pathway), K (Ketamine) and R + K (Rapamycin + Ketamine) groups to detect the apoptosis, reactive oxygen species (ROS) production, and Ca²⁺ concentration via the terminal transferase uridyl nick end labelling (TUNEL) assay, dichloro-dihydro-fluorescein diacetate (DCFH-DA) method and Fluo-3 acetoxymethyl ester (Fluo-3AM) staining, respectively. The expressions of mTOR signaling pathway and apoptosis-related proteins in hippocampal neurons were examined by qRT-PCR and Western blot.

RESULTS

Ketamine could dose-dependently promote the apoptosis of rat hippocampal neurons with upregulation of p-mTOR and its downstream regulators (p-4E-BP-1 and p-p70S6K). However, ketamine-induced apoptosis in hippocampal neurons was reversed significantly by the administration of rapamycin, as evident by the decrease in expressions of pro-apoptotic proteins (Bax and cleaved Caspase-3) and the increase in anti-apoptotic protein (Bcl-2). Meanwhile, the ROS generation and Ca²⁺ concentration was inhibited accompanied with reduced malonildialdehyde levels but elevated superoxide and glutathione peroxidase activities.

CONCLUSION

Inhibition of mTOR signaling pathway protected rat hippocampal neurons from ketamine-induced injuries via reducing apoptosis, oxidative stress, as well as Ca²⁺ concentration.

ABBREVIATIONS

mTOR: mammalian target of rapamycin; SD: Sprague-Dawley; SPF: Specific-pathogen free; ROS: reactive oxygen species; TUNEL: terminal transferase uridyl nick end labelling; DCFH-DA: Dichloro-dihydro-fluorescein diacetate; Fluo-3A: Fluo-3 acetoxymethyl ester; NMDAR: non-competitive N-methyl-D-aspartame glutamate receptor; 4E-BP1: 4E binding protein 1; p70S6K: p70 S6 Kinase; PCR: Polymerase chain reaction; MDA: malonildialdehyde; GSH-PX: glutathione peroxidase; ANOVA: One-way Analysis of Variance.

Default Mode Connectivity in Major Depressive Disorder Measured Up to 10 Days After Ketamine Administration

BACKGROUND

The symptoms of major depressive disorder (MDD) are rapidly alleviated by administration of a single dose of the glutamatergic modulator ketamine. However, few studies have investigated the potential sustained neural effects of this agent beyond immediate infusion. This study used functional magnetic resonance imaging to examine the effect of a single ketamine infusion on the resting state default mode network (DMN) at 2 and 10 days after a single ketamine infusion in unmedicated subjects with MDD as well as healthy control subjects (HCs).

METHODS

Data were drawn from a double-blind, placebo-controlled crossover study of 58 participants (33 with MDD and 25 HCs) who received an intravenous infusion of either ketamine hydrochloride (0.5 mg/kg) or placebo on 2 separate test days spaced 2 weeks apart. Eight minutes of functional magnetic resonance imaging resting state data was acquired at baseline and at about 2 and 10 days after both infusions. The DMN was defined using seed-based correlation and was compared across groups and scans.

RESULTS

In subjects with MDD, connectivity between the insula and the DMN was normalized compared with HCs 2 days postketamine infusion. This change was reversed after 10 days and did not appear in either of the placebo scans. Group-specific connectivity differences in drug response were observed, most notably in the insula in subjects with MDD and in the thalamus in HCs.

CONCLUSIONS

Connectivity changes in the insula in subjects with MDD suggest that ketamine may normalize the interaction between the DMN and salience networks, supporting the triple network dysfunction model of MDD.

Fighting against depression with TREK-1 blockers: Past and future. A focus on spadin

Depression is a devastating mood disorder and a leading cause of disability worldwide. Depression affects approximately one in five individuals in the world and represents heavy economic and social burdens. The neurobiological mechanisms of depression are not fully understood, but evidence highlights the role of monoamine neurotransmitter balance. Several antidepressants (ADs) are marketed to treat depression and related mood disorders. However, despite their efficacy, they remain nonspecific and unsafe because they trigger serious adverse effects. Therefore, developing new molecules for new targets in depression has become a real necessity. Eight years ago, spadin was described as a natural peptide with AD properties. This 17-amino acid peptide blocks TREK-1 channels, an original target in depression. Compared to the classical AD drugs such as fluoxetine, which requires 3-4 weeks for the AD effect to manifest, spadin acts rapidly within only 4 days of treatment. The AD properties are associated with increased neurogenesis and synaptogenesis in the brain. Despite the advantages of this fast-acting AD, the in vivo stability is weak and does not last for >7 h. The present review summarizes different strategies such as retro-inverso strategy, cyclization, and shortening the spadin sequence that has led to the development and optimization of spadin as an AD. Shortened spadin analogs present increased inhibition potency for TREK-1, an improved AD activity, and prolonged in vivo bioavailability. Finally, we also discuss about other inhibitors of TREK-1 channels with a proven efficacy in treating depression in the clinic, such as fluoxetine.

Intraoperative ketamine administration to prevent delirium or postoperative cognitive dysfunction: A systematic review and meta-analysis

BACKGROUND

Postoperative cognitive complications are associated with substantial morbidity and mortality. Ketamine has been suggested to have neuroprotective effects in various settings. This systematic review evaluates the effects of intraoperative ketamine administration on postoperative delirium and postoperative cognitive dysfunction (POCD).

METHODS

Medline, Embase and Central were searched to 4 March 2018 without date or language restrictions. We considered randomised controlled trials (RCTs) comparing intraoperative ketamine administration versus no intervention in adults undergoing surgery under general anaesthesia. Primary outcomes were postoperative delirium and POCD. Non-cognitive adverse events, mortality and length of stay were considered as secondary outcomes. Data were independently extracted. The quality of the evidence (GRADE approach) was assessed following recommendations from the Cochrane collaboration. Risk ratios were calculated for binary outcomes, mean differences for continuous outcomes. We planned to explore the effects of age, specific anaesthesia regimen, depth of anaesthesia and intraoperative haemodynamic events through subgroup analyses.

RESULTS

Six RCTs were included. The incidence of postoperative delirium did not differ between groups (4 trials, 557 patients, RR 0.83, 95% CI [0.25, 2.80]), but patients receiving ketamine seemed at lower risk of POCD (3 trials, 163 patients, RR 0.34, 95% CI [0.15, 0.73]). However, both analyses presented limitations. Therefore, the quality of the evidence (GRADE) was deemed low (postoperative delirium) and very low (POCD).

CONCLUSION

The effect of ketamine on postoperative delirium remains unclear but its administration may offer some protection towards POCD. Large, well-designed randomised trials are urgently needed to further clarify the efficacy of ketamine on neurocognitive outcomes.

Aquaporin-4 knockout mice exhibit increased hypnotic susceptibility to ketamine

PURPOSE

This study examines anesthetic/hypnotic effects of ketamine in AQP4 knockout (KO) and wild-type (WT) mice with the particular focus on neurotransmission.

MATERIALS AND METHODS

Ketamine (100 mg/kg) was intraperitoneally injected in 16 WT and 16 KO mice. The hypnotic potencies were evaluated by the loss of the righting reflex (LORR). The amino acids neurotransmitter levels in prefrontal cortex were measured by microdialysis.

RESULTS

This study demonstrated that AQP4 knockout significantly shortened the latency compared with WT mice (98.0 ± 4.2 vs. 138.1 ± 15.0 s, p < .05) and prolonged duration of LORR (884.7 ± 58.6 vs. 562.0 ± 51.7 s, p < .05) compared with WT mice in LORR induced by ketamine. Microdialysis showed that lack of AQP4 markedly decreased glutamate level within 20 min (p < .05) and increased γ-aminobutyric acid (GABA) level within 30-40 min (p < .05) after use of ketamine. Moreover, the levels of taurine were remarkably higher in KO mice than in WT mice, but no obvious differences in aspartate were observed between two genotypes.

CONCLUSION

AQP4 deficiency led to more susceptibility of mice to ketamine, which is probably due to the modulation of specific neurotransmitters, hinting an essential maintenance of synaptic activity mediated by AQP4 in the action of ketamine.

Circulating microRNAs as biomarkers for depression: Many candidates, few finalists

BACKGROUND

Recent research has highlighted the potential of microRNAs to serve as physiological indicators of disease process among clinically depressed patients.

METHODS

In a comprehensive literature search through PubMed, we identified 23 articles comparing circulating (blood, plasma, or serum) microRNA expression levels in depressed versus healthy human subjects. Six studies examining circulatory microRNA expression through animal models of depression were also identified through the search and details of each study were outlined. A meta-analytic evaluation of these studies was not considered feasible, given the absence of concordance in the literature to date.

RESULTS

A total of 178 specific microRNA candidates were identified in the human studies as significantly expressed among depressed samples. Ninety-seven of these microRNAs were upregulated, 75 were downregulated, and 6 showed mixed expression in depressed samples. Few microRNAs were consistently expressed across studies; the most consistent evidence was for microRNA-132, with replication in 4 different studies. Among animal studies, 2 studies investigated microRNA-16 through distinct stress-induced depression models.

LIMITATIONS

Structural variations in microRNA sequences, methodological inconsistencies in technology used among studies to measure microRNA expression levels, differences in the clinical severity and forms of depression among subjects, and the overall paucity of studies make it difficult to ascertain any robust, preliminary targets deserving of biomarker potential.

CONCLUSIONS

Ongoing research needs to address this high rate of non-replication as well as the methodological and reporting challenges of microRNA experimentation in order to determine valid effect sizes for the more proliferative candidates associated with depression.

An Evidence-Based Opioid-Free Anesthetic Technique to Manage Perioperative and Periprocedural Pain

Background

The epidemic of opioid abuse is increasing, and the number of deaths secondary to opioid overdose is also increasing. Recent attention has focused on opioid prescribing and management of chronic pain. However, opioid use in perioperative and periprocedural patients, whether they have chronic pain or exhibit new persistent opioid abuse after a procedure, has received little attention.

Methods

We present an evidence-based technique that combines subanesthetic infusions of lidocaine and dexmedetomidine supplemented with other intravenous agents and a low dose of inhaled anesthetic.

Results

Based on evidence of drug action and interaction, an opioid-free anesthetic can be delivered successfully. We present the cases of 2 patients in whom the opioid-free anesthetic technique was used with a successful outcome, adequate pain management, and avoidance of opioid drugs.

Conclusion

This anesthetic prescription can be useful for opioid-naïve patients as well as for patients with chronic pain that is managed with opioids.

S(+)-ketamine : Current trends in emergency and intensive care medicine

S(+)-ketamine, the pure dextrorotatory enantiomer of ketamine has been available for clinical use in analgesia and anesthesia for more than 25 years. The main effects are mediated by non-competitive inhibition of the N-methyl-D-aspartate (NMDA) receptor but S(+)-ketamine also interacts with opioid receptors, monoamine receptors, adenosine receptors and other purinergic receptors. Effects on α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, metabotropic glutamate receptors (mGluR) and L‑type calcium chanels have also been described. S(+)-ketamine stimulates the sympathetic nerve system, making it an ideal drug for analgosedation or induction of anesthesia in instable patients. In addition, the neuroprotective properties, bronchodilatory, antihyperalgesic or antiepileptic effects provide interesting therapeutic options. In this article we discuss the numerous effects of S(+)-ketamine under pharmacological and clinical aspects especially for typical indications in emergency medicine as well as intensive care.

Antidepressant Efficacy and Tolerability of Ketamine and Esketamine: A Critical Review

Ketamine and its enantiomer S-ketamine (esketamine) are promising candidates to produce a rapid-onset antidepressant effect in treatment-resistant depression. Ketamine causes continued blockade of the glutamate N-methyl-D-aspartate (NMDA) receptor, though this might not primarily mediate the antidepressant effect. Alternative hypotheses include selectivity for the NMDA receptor subtype containing the NMDA receptor subunit 2B (NR2B), inhibition of the phosphorylation of the eukaryotic elongation factor 2 (eEF2) kinase, increased expression of brain-derived neurotrophic factor (BDNF) and tropomyosin receptor kinase B (TrKB), and activation of the mammalian target of rapamycin (mTOR) signaling pathway, alongside other independent actions attributed to the ketamine metabolism to R-hydroxynorketamine (R-HNK). The enantiomer S-ketamine (esketamine) displays approximately fourfold greater affinity for the glutamate NMDA receptor in vitro than R-ketamine. Proof-of-concept single-dose and repeat-dose studies with intravenous ketamine show a significant antidepressant and probably antisuicidal effect in the short term, with response rates over 60% as early as 4.5 h after a single dose, with a sustained effect after 24 h, and over 40% after 7 days. This response can be further sustained over several weeks with repeated doses (two to three doses per week). Tolerability seems acceptable in the short term, with transient elevation of blood pressure and mild and transient dissociative and psychotomimetic effects. Intranasal esketamine has shown a comparable antidepressant effect, which has resulted in the US FDA granting the drug a "breakthrough therapy" designation, and theoretically it may offer an improved tolerability profile. However, major concerns remain regarding an effective protocol to maintain the clinical antidepressant effect of ketamine seen with acute administration and the safety of ketamine and esketamine in the long term, specifically related to potential neurocognitive and urologic toxicity, together with the potential induction of substance use disorders. Ketamine and esketamine are not currently approved treatments for depression, but the clinical use of ketamine is increasing in a variety of practice settings internationally.

Subanaesthetic ketamine and altered states of consciousness in humans

BACKGROUND

Despite its designation as a 'dissociative anaesthetic,' the dissociative and psychoactive effects of ketamine remain incompletely understood. The goal of this study was to characterise the subjective experiences and accompanying EEG changes with subanaesthetic doses of ketamine.

METHODS

High-density EEG was recorded in 15 human volunteers before, during, and after subanaesthetic ketamine infusion (0.5 mg kg^-1 over 40 min), with self-reported measures of altered states of consciousness obtained after ketamine exposure. Sensor- and source-level EEG changes were analysed with a focus on spectral power and regional changes.

RESULTS

Ketamine-induced altered states were characterised predominantly by dissociative experiences such as disembodiment and ego transcendence; sensory disturbances were also common. Ketamine broadly decreased low-frequency power, with mean reductions largest at alpha (8-12 Hz) in parietal (-0.94 dB, P<0.001) and occipital (-1.8 dB, P<0.001) channel clusters. Significant decreases in alpha were identified in the precuneus and temporal-parietal junction.

CONCLUSIONS

Ketamine induces altered states of consciousness during periods of reduced alpha power in the precuneus and temporal-parietal junction. Modulation of these temporal-parietal loci are candidate mechanisms of the psychoactive effects of ketamine, given that this region is involved in multisensory integration, body representation, and consciousness.

The role of glutamatergic modulation in the mechanism of action of ketamine, a prototype rapid-acting antidepressant drug

Over the past decade, ketamine has been one of the most commonly studied potential antidepressants. This is because it produces a spectacularly rapid and persistent therapeutic effect in people suffering from severe treatment-resistant depression (TRD), for which classical drugs are ineffective. Similar efficacy was demonstrated for scopolamine, a drug belonging to a completely different pharmacological group. This interesting coincidence piqued the interest of psychopharmacologists and prompted them to search for a possible common mechanism of these rapid acting antidepressant drugs (RAADs). A thorough explanation of this mechanism is also important because each of these substances induces serious side effects. Knowing the mechanism responsible for the therapeutic efficacy of RAADs could lead to minimizing, or even avoiding certain undesirable effects. This review provides an overview of the mechanism of action of a prototype RAAD, ketamine, in animal models, with a particular focus on the roles of NMDA receptors, AMPA receptors, synaptogenesis, and modulation of glutamate transmission by other modulators of this system, such as mGlu receptor ligands. Recently studied roles for ketamine enantiomers and metabolites in its rapid antidepressant effect are also considered. Finally, the results of multiple clinical trials are reported and discussed in relation to basic research. This review concludes that success in introducing novel therapeutic RAADs will depend on better cooperation and integration of neuroscience research and clinical practice.

Hydroxynorketamine: Implications for the NMDA Receptor Hypothesis of Ketamine's Antidepressant Action

The prevailing hypothesis of ketamine’s unique antidepressant effects implicates N-methyl-d-aspartate receptor (NMDAR) inhibition-dependent enhancement of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor-mediated transmission, activation of intracellular signalling pathways and increased synaptogenesis. Recently, however, a seminal study by Zanos et al. directly challenged the NMDAR hypothesis of ketamine with the claim that an active ketamine metabolite, (2R,6R)-hydroxynorketamine, devoid of NMDAR binding properties or key side effects of its parent compound, is both necessary and sufficient for ketamine’s antidepressant effects in rodents. However, following these encouraging initial findings, one preclinical study failed to replicate the antidepressant effects of (2R,6R)-hydroxynorketamine (HNK), while others have questioned the metabolite’s contribution to ketamine’s therapeutic effects or argued against rejecting the NMDAR hypothesis of ketamine action. In light of these potentially paradigm-shifting, but highly controversial, findings, this review will summarise and critically evaluate the evidence for and against the NMDA receptor hypothesis of ketamine action, with a particular focus on (2R,6R)-HNK and the implications of its discovery for understanding ketamine’s mechanism of action in depression. Ultimately, uncovering the molecular mechanisms underlying the therapeutic effects of ketamine and possibly (2R,6R)-HNK, will aid the development of novel and more efficacious antidepressant agents so urgently needed to address a major public health concern, and could hold potential for the treatment of other stress-related psychopathologies, including bipolar disorder, post-traumatic stress disorder and suicidality.

Randomized Controlled Feasibility Trial of Intranasal Ketamine Compared to Intranasal Fentanyl for Analgesia in Children with Suspected Extremity Fractures

OBJECTIVES

We compared the tolerability and efficacy of intranasal subdissociative ketamine to intranasal fentanyl for analgesia of children with acute traumatic pain and investigated the feasibility of a larger noninferiority trial that could investigate the potential opioid-sparing effects of intranasal ketamine.

METHODS

This randomized controlled trial compared 1 mg/kg intranasal ketamine to 1.5 μg/kg intranasal fentanyl in children 4 to 17 years old with acute pain from suspected isolated extremity fractures presenting to an urban Level II pediatric trauma center from December 2015 to November 2016. Patients, parents, treating physicians, and outcome assessors were blinded to group allocation. The primary outcome, a tolerability measure, was the frequency of cumulative side effects and adverse events within 60 minutes of drug administration. The secondary outcomes included the difference in mean pain score reduction at 20 minutes, the proportion of patients achieving a clinically significant reduction in pain in 20 minutes, total dose of opioid pain medication in morphine equivalents/kg/hour (excluding study drug) required during the emergency department (ED) stay, and the feasibility of enrolling children presenting to the ED in acute pain into a randomized trial conducted under U.S. regulations. All patients were monitored until 6 hours after their last dose of study drug or until admission to the hospital ward or operating room.

RESULTS

Of 629 patients screened, 87 received the study drug and 82 had complete data for the primary outcome (41 patients in each group). The median (interquartile range) age was 8 (6-11) years and 62% were male. Baseline pain scores were similar among patients randomized to receive ketamine (73 ± 26) and fentanyl (69 ± 26; mean difference [95% CI] = 4 [-7 to 15]). The cumulative number of side effects was 2.2 times higher in the ketamine group, but there were no serious adverse events and no patients in either group required intervention. The most common side effects of ketamine were bad taste in the mouth (37; 90.2%), dizziness (30; 73.2%), and sleepiness (19; 46.3%). The most common side effects of fentanyl were sleepiness (15; 36.6%), bad taste in the mouth (9; 22%), and itchy nose (9; 22%). No patients experienced respiratory side effects. At 20 minutes, the mean pain scale score reduction was 44 ± 36 for ketamine and 35 ± 29 for fentanyl (mean difference = 9 [95% CI = -4 to 23]). Procedural sedation with ketamine occurred in 28 ketamine patients (65%) and 25 fentanyl patients (57%) prior to completing the study.

CONCLUSIONS

Intranasal ketamine was associated with more minor side effects than intranasal fentanyl. Pain relief at 20 minutes was similar between groups. Our data support the feasibility of a larger, noninferiority trial to more rigorously evaluate the safety, efficacy, and potential opioid-sparing benefits of intranasal ketamine analgesia for children with acute pain.

Depression in chronic ketamine users: Sex differences and neural bases

Chronic ketamine use leads to cognitive and affective deficits including depression. Here, we examined sex differences and neural bases of depression in chronic ketamine users. Compared to non-drug using healthy controls (HC), ketamine-using females but not males showed increased depression score as assessed by the Center of Epidemiological Studies Depression Scale (CES-D). We evaluated resting state functional connectivity (rsFC) of the subgenual anterior cingulate cortex (sgACC), a prefrontal structure consistently implicated in the pathogenesis of depression. Compared to HC, ketamine users (KU) did not demonstrate significant changes in sgACC connectivities at a corrected threshold. However, in KU, a linear regression against CES-D score showed less sgACC connectivity to the orbitofrontal cortex (OFC) with increasing depression severity. Examined separately, male and female KU showed higher sgACC connectivity to bilateral superior temporal gyrus and dorsomedial prefrontal cortex (dmPFC), respectively, in correlation with depression. The linear correlation of sgACC-OFC and sgACC-dmPFC connectivity with depression was significantly different in slope between KU and HC. These findings highlighted changes in rsFC of the sgACC as associated with depression and sex differences in these changes in chronic ketamine users.

Ketamine for pain

The efficacy of the N-methyl-D-aspartate receptor antagonist ketamine as an analgesic agent is still under debate, especially for indications such as chronic pain. To understand the efficacy of ketamine for relief of pain, we performed a literature search for relevant narrative and systematic reviews and meta-analyses. We retrieved 189 unique articles, of which 29 were deemed appropriate for use in this review. Ketamine treatment is most effective for relief of postoperative pain, causing reduced opioid consumption. In contrast, for most other indications (that is, acute pain in the emergency department, prevention of persistent postoperative pain, cancer pain, and chronic non-cancer pain), the efficacy of ketamine is limited. Ketamine's lack of analgesic effect was associated with an increase in side effects, including schizotypical effects.

Intraoperative ketamine for prevention of postoperative delirium or pain after major surgery in older adults: an international, multicentre, double-blind, randomised clinical trial

BACKGROUND

Delirium is a common and serious postoperative complication. Subanaesthetic ketamine is often administered intraoperatively for postoperative analgesia, and some evidence suggests that ketamine prevents delirium. The primary purpose of this trial was to assess the effectiveness of ketamine for prevention of postoperative delirium in older adults.

METHODS

The Prevention of Delirium and Complications Associated with Surgical Treatments [PODCAST] study is a multicentre, international randomised trial that enrolled adults older than 60 years undergoing major cardiac and non-cardiac surgery under general anaesthesia. Using a computer-generated randomisation sequence we randomly assigned patients to one of three groups in blocks of 15 to receive placebo (normal saline), low-dose ketamine (0·5 mg/kg), or high dose ketamine (1·0 mg/kg) after induction of anaesthesia, before surgical incision. Participants, clinicians, and investigators were blinded to group assignment. Delirium was assessed twice daily in the first 3 postoperative days using the Confusion Assessment Method. We did analyses by intention-to-treat and assessed adverse events. This trial is registered with clinicaltrials.gov, number NCT01690988.

FINDINGS

Between Feb 6, 2014, and June 26, 2016, 1360 patients were assessed, and 672 were randomly assigned, with 222 in the placebo group, 227 in the 0·5 mg/kg ketamine group, and 223 in the 1·0 mg/kg ketamine group. There was no difference in delirium incidence between patients in the combined ketamine groups and the placebo group (19·45% vs 19·82%, respectively; absolute difference 0·36%, 95% CI -6·07 to 7·38, p=0·92). There were more postoperative hallucinations (p=0·01) and nightmares (p=0·03) with increasing ketamine doses compared with placebo. Adverse events (cardiovascular, renal, infectious, gastrointestinal, and bleeding), whether viewed individually (p value for each >0·40) or collectively (36·9% in placebo, 39·6% in 0·5 mg/kg ketamine, and 40·8% in 1·0 mg/kg ketamine groups, p=0·69), did not differ significantly across groups.

INTERPRETATION

A single subanaesthetic dose of ketamine did not decrease delirium in older adults after major surgery, and might cause harm by inducing negative experiences.

FUNDING

National Institutes of Health and Cancer Center Support.

Bottom-Up and Top-Down Mechanisms of General Anesthetics Modulate Different Dimensions of Consciousness

There has been controversy regarding the precise mechanisms of anesthetic-induced unconsciousness, with two salient approaches that have emerged within systems neuroscience. One prominent approach is the “bottom up” paradigm, which argues that anesthetics suppress consciousness by modulating sleep-wake nuclei and neural circuits in the brainstem and diencephalon that have evolved to control arousal states. Another approach is the “top-down” paradigm, which argues that anesthetics suppress consciousness by modulating the cortical and thalamocortical circuits involved in the integration of neural information. In this article, we synthesize these approaches by mapping bottom-up and top-down mechanisms of general anesthetics to two distinct but inter-related dimensions of consciousness: level and content. We show how this explains certain empirical observations regarding the diversity of anesthetic drug effects. We conclude with a more nuanced discussion of how levels and contents of consciousness interact to generate subjective experience and what this implies for the mechanisms of anesthetic-induced unconsciousness.

Propofol, Sevoflurane, and Ketamine Induce a Reversible Increase in Delta-Gamma and Theta-Gamma Phase-Amplitude Coupling in Frontal Cortex of Rat

Studies from human and non-human species have demonstrated a breakdown of functional corticocortical connectivity during general anesthesia induced by anesthetics with diverse molecular, neurophysiological, and pharmacological profiles. Recent studies have demonstrated that changes in long-range neural communication, and by corollary, functional connectivity, might be influenced by cross-frequency coupling (CFC) between the phase of slow oscillations and the amplitude of local fast oscillations. Phase-amplitude coupling (PAC) between slow oscillations and alpha rhythm during general anesthesia reveal distinct patterns depending on the anesthetic. In this study, we analyzed the effect of three clinically used anesthetics (propofol: n = 6, sevoflurane: n = 10, and ketamine: n = 8) with distinct molecular mechanisms on changes in PAC in the frontal cortex of rat. The loss of righting reflex was used as a surrogate for unconsciousness. PAC was calculated using the modulation index (MI) algorithm between delta (1–4 Hz), theta (4–10 Hz), low gamma (25–55 Hz), and high gamma (65–125 Hz) bands. A linear mixed model with fixed effects was used for statistical comparisons between waking, anesthetized, and post-anesthesia recovery epochs. All three anesthetics increased the coupling between delta and low gamma (p < 0.0001) as well as between theta and low gamma (p < 0.0001) oscillations, which returned to baseline waking levels during the post-anesthetic recovery period. In addition, a reversible reduction in high gamma power (p < 0.0001) was a consistent change during anesthesia induced by all three agents. The changes in delta-high gamma and theta-high gamma PAC as well as power spectral changes in delta, theta, and low gamma bandwidths did not show a uniform response across the three anesthetics. These results encourage the study of alternative PAC patterns as drug-invariant markers of general anesthesia in humans.

Common general anesthetic propofol impairs kinesin processivity

Propofol is the most widely used i.v. general anesthetic to induce and maintain anesthesia. It is now recognized that this small molecule influences ligand-gated channels, including the GABA_A receptor and others. Specific propofol binding sites have been mapped using photoaffinity ligands and mutagenesis; however, their precise target interaction profiles fail to provide complete mechanistic underpinnings for the anesthetic state. These results suggest that propofol and other common anesthetics, such as etomidate and ketamine, may target additional protein networks of the CNS to contribute to the desired and undesired anesthesia end points. Some evidence for anesthetic interactions with the cytoskeleton exists, but the molecular motors have received no attention as anesthetic targets. We have recently discovered that propofol inhibits conventional kinesin-1 KIF5B and kinesin-2 KIF3AB and KIF3AC, causing a significant reduction in the distances that these processive kinesins can travel. These microtubule-based motors are highly expressed in the CNS and the major anterograde transporters of cargos, such as mitochondria, synaptic vesicle precursors, neurotransmitter receptors, cell signaling and adhesion molecules, and ciliary intraflagellar transport particles. The single-molecule results presented show that the kinesin processive stepping distance decreases 40-60% with EC₅₀ values <100 nM propofol without an effect on velocity. The lack of a velocity effect suggests that propofol is not binding at the ATP site or allosteric sites that modulate microtubule-activated ATP turnover. Rather, we propose that a transient propofol allosteric site forms when the motor head binds to the microtubule during stepping.