Ketamine and Ketamine Metabolite Pharmacology: Insights into Therapeutic Mechanisms

Chronic exposure to (2 R,6 R)-hydroxynorketamine induces developmental neurotoxicity in hESC-derived cerebral organoids

(R,S)-ketamine (ketamine) has been increasingly used recreationally and medicinally worldwide; however, it cannot be removed by conventional wastewater treatment plants. Both ketamine and its metabolite norketamine have been frequently detected to a significant degree in effluents, aquatic, and even atmospheric environments, which may pose risks to organisms and humans via drinking water and aerosols. Ketamine has been shown to affect the brain development of unborn babies, while it is still elusive whether (2 R,6 R)-hydroxynorketamine (HNK) induces similar neurotoxicity. Here, we investigated the neurotoxic effect of (2 R,6 R)-HNK exposure at the early stages of gestation by applying human cerebral organoids derived from human embryonic stem cells (hESCs). Short-term (2 R,6 R)-HNK exposure did not significantly affect the development of cerebral organoids, but chronic high-concentration (2 R,6 R)-HNK exposure at day 16 inhibited the expansion of organoids by suppressing the proliferation and augmentation of neural precursor cells (NPCs). Notably, the division mode of apical radial glia was unexpectedly switched from vertical to horizontal division planes following chronic (2 R,6 R)-HNK exposure in cerebral organoids. Chronic (2 R,6 R)-HNK exposure at day 44 mainly inhibited the differentiation but not the proliferation of NPCs. Overall, our findings indicate that (2 R,6 R)-HNK administration leads to the abnormal development of cortical organoids, which may be mediated by inhibiting HDAC2. Future clinical studies are needed to explore the neurotoxic effects of (2 R,6 R)-HNK on the early development of the human brain.

A Randomized Controlled Trial of Repeated Ketamine Administration for Chronic Posttraumatic Stress Disorder

Objective

Posttraumatic stress disorder (PTSD) is a chronic and disabling disorder, for which available pharmacotherapies have limited efficacy. The authors' previous proof-of-concept randomized controlled trial of single-dose intravenous ketamine infusion in individuals with PTSD showed significant and rapid PTSD symptom reduction 24 hours postinfusion. The present study is the first randomized controlled trial to test the efficacy and safety of repeated intravenous ketamine infusions for the treatment of chronic PTSD.

Methods

Individuals with chronic PTSD (N=30) were randomly assigned (1:1) to receive six infusions of ketamine (0.5 mg/kg) or midazolam (0.045 mg/kg) (psychoactive placebo control) over 2 consecutive weeks. Clinician-rated and self-report assessments were administered 24 hours after the first infusion and at weekly visits. The primary outcome measure was change in PTSD symptom severity, as assessed with the Clinician-Administered PTSD Scale for DSM-5 (CAPS-5), from baseline to 2 weeks (after completion of all infusions). Secondary outcome measures included the Impact of Event Scale-Revised, the Montgomery-Åsberg Depression Rating Scale (MADRS), and side effect measures.

Results

The ketamine group showed a significantly greater improvement in CAPS-5 and MADRS total scores than the midazolam group from baseline to week 2. At week 2, the mean CAPS-5 total score was 11.88 points (SE=3.96) lower in the ketamine group than in the midazolam group (d=1.13, 95% CI=0.36, 1.91). Sixty-seven percent of participants in the ketamine group were treatment responders, compared with 20% in the midazolam group. Among ketamine responders, the median time to loss of response was 27.5 days following the 2-week course of infusions. Ketamine infusions were well tolerated overall, without serious adverse events.

Conclusions

This randomized controlled trial provides the first evidence of efficacy of repeated ketamine infusions in reducing symptom severity in individuals with chronic PTSD. Further studies are warranted to understand ketamine's full potential as a treatment for chronic PTSD.Reprinted from Am J Psychiatry 2021; 178:193-202, with permission from American Psychiatric Association Publishing. Copyright © 2021.

Safety and efficacy of the combination of esketamine and propofol in procedural sedation/analgesia: a systematic review and meta-analysis

INTRODUCTION

This review and meta-analysis of randomized controlled trials (RCTs) assessed the side effects and efficacy of esketamine combined with propofol in procedural sedation and analgesia.

EVIDENCE ACQUISITION

The PubMed, MEDLINE, Embase and Cochrane Library databases were searched for relevant studies occurring between their inceptions and September 2022. The primary outcome was the incidence of sedation-related adverse events. Secondary outcomes included recovery time, total consumption of propofol and body movement.

EVIDENCE SYNTHESIS

Data from a total of seven RCTs enrolling 808 patients were included in the meta-analysis. Pooling of data showed that compared with other drug regimens, the esketamine and propofol combination was associated with a reduction in the risk of hypotension (relative risk [RR]: 0.37, 95% confidence interval [CI]: 0.25 to 0.56) and bradycardia (RR: 0.34, 95% CI: 0.15 to 0.80) as well as an increase in the risk of agitation (RR: 6.29, 95% CI: 1.15 to 34.32). The results also indicated a decrease in propofol consumption (standardized mean difference: -1.45, 95% CI: -2.39 to -0.50) with the use of the esketamine and propofol combination. No significant difference was observed between the two groups in respiratory depression, nausea/vomiting, recovery time or body movement.

CONCLUSIONS

Esketamine combined with propofol has an advantage in reducing the incidence of hypotension and bradycardia during procedural sedation and analgesia, but it may increase the risk of agitation in the recovery phase. More studies of high quality are needed before the widespread adoption of the combination of esketamine and propofol.

Perfusion index for early identification of regional anesthesia effectiveness: a narrative review

Regional anesthesia (RA) is a common and irreplaceable technique in clinical, which can be used in different surgery sites and control of acute and chronic pain, especially for outpatients, pediatrics and the elderly. RA demands are increasing during COVID-19 pandemic because many surgeries could be performed under RA to reduce the risk of cross-infection between patients and health care workers. Early and accurate identification of the effects of RA can help physicians make timely decisions about whether to supplement analgesics or switch to general anesthesia, which will save time and improve patient satisfaction in a busy operating room. Perfusion index (PI) is a parameter derived from photoplethysmography (PPG) and represents the ratio of pulsatile and non-pulsatile blood flow at monitoring sites. It reflects local perfusion and is mainly affected by stroke volume and vascular tone. With characteristics of non-invasive, rapid, simple, and objective, PI is widely used in clinical practice, such as fluid responsiveness prediction, nociceptive assessment, etc. Recently, many studies have assessed the accuracy of PI in early prediction of RA success, including brachial plexus block, sciatic nerve block, neuraxial anesthesia, paravertebral block, caudal block and stellate ganglion block. Successful RA often parallels increased PI. In this narrative review, we describe the principles and influencing factors of PI, and introduce the effects of PI on early identification of RA effectiveness.

Suicide prevention and ketamine: insights from computational modeling

Suicide is a pressing public health issue, with over 700,000 individuals dying each year. Ketamine has emerged as a promising treatment for suicidal thoughts and behaviors (STBs), yet the complex mechanisms underlying ketamine's anti-suicidal effect are not fully understood. Computational psychiatry provides a promising framework for exploring the dynamic interactions underlying suicidality and ketamine's therapeutic action, offering insight into potential biomarkers, treatment targets, and the underlying mechanisms of both. This paper provides an overview of current computational theories of suicidality and ketamine's mechanism of action, and discusses various computational modeling approaches that attempt to explain ketamine's anti-suicidal effect. More specifically, the therapeutic potential of ketamine is explored in the context of the mismatch negativity and the predictive coding framework, by considering neurocircuits involved in learning and decision-making, and investigating altered connectivity strengths and receptor densities targeted by ketamine. Theory-driven computational models offer a promising approach to integrate existing knowledge of suicidality and ketamine, and for the extraction of model-derived mechanistic parameters that can be used to identify patient subgroups and personalized treatment approaches. Future computational studies on ketamine's mechanism of action should optimize task design and modeling approaches to ensure parameter reliability, and external factors such as set and setting, as well as psychedelic-assisted therapy should be evaluated for their additional therapeutic value.

Functional and Molecular Changes in the Prefrontal Cortex of the Chronic Mild Stress Rat Model of Depression and Modulation by Acute Ketamine

Stress is a primary risk factor in the onset of neuropsychiatric disorders, including major depressive disorder (MDD). We have previously used the chronic mild stress (CMS) model of depression in male rats to show that CMS induces morphological, functional, and molecular changes in the hippocampus of vulnerable animals, the majority of which were recovered using acute subanesthetic ketamine in just 24 h. Here, we focused our attention on the medial prefrontal cortex (mPFC), a brain area regulating emotional and cognitive functions, and asked whether vulnerability/resilience to CMS and ketamine antidepressant effects were associated with molecular and functional changes in the mPFC of rats. We found that most alterations induced by CMS in the mPFC were selectively observed in stress-vulnerable animals and were rescued by acute subanesthetic ketamine, while others were found only in resilient animals or were induced by ketamine treatment. Importantly, only a few of these modifications were also previously demonstrated in the hippocampus, while most are specific to mPFC. Overall, our results suggest that acute antidepressant ketamine rescues brain-area-specific glutamatergic changes induced by chronic stress.

Efficacy and safety comparison of esketamine-propofol with nalbuphine-propofol for upper gastrointestinal endoscopy in children: a multi-center randomized controlled trial

Background and Aims

Anesthetics such as propofol, esketamine and nalbuphine are used during the upper gastrointestinal endoscopy to achieve and maintain the desired sedation level. The aim of the study was to evaluate the effectiveness and safety of propofol-nalbuphine and propofol-esketamine in children.

Methods

A multi-centered study was performed at three tertiary class-A hospitals. Children between 3 and 12 years old undergoing diagnostic painless upper gastrointestinal endoscopy were included and randomly divided into esketamine or nalbuphine group to estimate the primary outcome of successful endoscope insertion. The patients were given esketamine 0.5 mg/kg and propofol 2 mg/kg intravenously in esketamine group, with nalbuphine 0.2 mg/kg and propofol 2 mg/kg in the nalbuphine group. The primary outcome was success rate for the first attempt of endoscope insertion in each group. Secondary outcomes included the safety of both anesthesia regimens and gastroenterologist's satisfaction. We used the Face, Leg, Activity, Cry and Consolability (FLACC) scale to evaluate the level of pain before and during the procedure and the Pediatric Anesthesia Emergence Delirium (PAED) scale to assess the level of agitation and delirium after awakening from anesthesia.

Results

Among 246 patients, 200 were randomly included in the final intention-to-treat analysis, with 100 patients in each group. The success rate for the first attempt of endoscope insertion in the esketamine group was higher than the nalbuphine group (97% vs. 66%; P < 0.01). The heart rate and mean arterial pressure after intraoperative administration in the esketamine group were higher than those in the nalbuphine group, while the delirium incidence during awakening was higher in esketamine group (all P < 0.05).

Conclusion

The success rate for the first attempt of endoscope insertion of children undergoing upper gastrointestinal endoscopy in the esketamine group was higher than the nalbuphine group, propofol-related hemodynamic changes were reduced accordingly, while the incidence of esketamine-related adverse effects could be high.

Clinical Trial Registration

Chinese Clinical Trial Registry: ChiCTR2000040500.

Effect of Ketamine on Postoperative Neurocognitive Disorders: A Systematic Review and Meta-Analysis

BACKGROUND

Neurocognitive alterations in the perioperative period might be caused by a wide variety of factors including pain, blood loss, hypotension, hypoxia, micro- and macroemboli, cardiopulmonary bypass (CPB), reperfusion damage, and surgery itself, and all are risk factors for developing postoperative delirium (POD) and postoperative cognitive dysfunction (POCD). The objective of this study was to evaluate the effect of ketamine on neurocognitive dysfunction after anesthesia.

METHODS

We conducted a meta-analysis of randomized controlled trials (RCTs) comparing ketamine use (experimental group) with placebo (controls).

RESULTS

The model favors the control group over the experimental group in terms of frequency of hallucinations (the risk ratio with 95% CI is 1.54 [1.09, 2.19], p-value = 0.02), the number of patients readmitted within 30 days (RR with 95% CI is 0.25 [0.09, 0.70]), and the number of adverse events (overall RR with 95% CI is 1.31 [1.06, 1.62]). In terms of morphine consumption, the model favors the experimental group.

CONCLUSION

There was no statistically significant difference in incidences of postoperative delirium, vasopressor requirement, and fentanyl consumption between the ketamine and control groups. However, hallucinations were more frequently reported in the ketamine group.

Changes in synaptic markers after administration of ketamine or psychedelics: a systematic scoping review

Background

Ketamine and psychedelics have abuse liability. They can also induce "transformative experiences" where individuals experience enhanced states of awareness. This enhanced awareness can lead to changes in preexisting behavioral patterns which could be beneficial in the treatment of substance use disorders (SUDs). Preclinical and clinical studies suggest that ketamine and psychedelics may alter markers associated with synaptic density, and that these changes may underlie effects such as sensitization, conditioned place preference, drug self-administration, and verbal memory performance. In this scoping review, we examined studies that measured synaptic markers in animals and humans after exposure to ketamine and/or psychedelics.

Methods

A systematic search was conducted following PRISMA guidelines, through PubMed, EBSCO, Scopus, and Web of Science, based on a published protocol (Open Science Framework, DOI: 10.17605/OSF.IO/43FQ9). Both in vivo and in vitro studies were included. Studies on the following synaptic markers were included: dendritic structural changes, PSD-95, synapsin-1, synaptophysin-1, synaptotagmin-1, and SV2A.

Results

Eighty-four studies were included in the final analyses. Seventy-one studies examined synaptic markers following ketamine treatment, nine examined psychedelics, and four examined both. Psychedelics included psilocybin/psilocin, lysergic acid diethylamide, N,N-dimethyltryptamine, 2,5-dimethoxy-4-iodoamphetamine, and ibogaine/noribogaine. Mixed findings regarding synaptic changes in the hippocampus and prefrontal cortex (PFC) have been reported when ketamine was administered in a single dose under basal conditions. Similar mixed findings were seen under basal conditions in studies that used repeated administration of ketamine. However, studies that examined animals during stressful conditions found that a single dose of ketamine counteracted stress-related reductions in synaptic markers in the hippocampus and PFC. Repeated administration of ketamine also counteracted stress effects in the hippocampus. Psychedelics generally increased synaptic markers, but results were more consistently positive for certain agents.

Conclusion

Ketamine and psychedelics can increase synaptic markers under certain conditions. Heterogeneous findings may relate to methodological differences, agents administered (or different formulations of the same agent), sex, and type of markers. Future studies could address seemingly mixed results by using meta-analytical approaches or study designs that more fully consider individual differences.

A systematic review of the efficacy of ketamine for craniofacial pain

Background

Craniofacial pain (CFP) poses a burden on patients and health care systems. It is hypothesized that ketamine, an N-methyl-d-aspartate (NMDA) receptor antagonist, can reverse central sensitization associated with causation and propagation of CFP. This systematic review aims to assess the role of ketamine for CFP.

Methods

Databases were searched for studies published up to September 26, 2022, investigating the efficacy of ketamine for adults with CFP. Primary outcome was the change in pain intensity at 60 min postintervention. Two reviewers screened and extracted data. Registration with PROSPERO was performed (CRD42020178649).

Results

Twenty papers (six randomized controlled trials [RCTs], 14 observational studies) including 670 patients were identified. Substantial heterogeneity in terms of study design, population, dose, route of administration, treatment duration, and follow-up was noted. Bolus dose ranged from 0.2-0.3 mg/kg (intravenous) to 0.4 mg/kg (intramuscular) to 0.25-0.75 mg/kg (intranasal). Ketamine infusions (0.1-1 mg/kg/h) were given over various durations. Follow-up was short in RCTs (from 60 min to 72 h) but longer in observational studies (up to 18 months). Ketamine by bolus treatment failed to reduce migraine intensity but had an effect by reducing intensity of aura, cluster headache (CH), and trigeminal neuralgia. Prolonged ketamine infusions showed sustainable reduction of migraine intensity and frequency of CH attacks, but the quality of the evidence is low.

Conclusion

Current evidence remains conflicting on the efficacy of ketamine for CFP owing to low quality and heterogeneity across studies. Ketamine infusions are suggested to provide sustained improvement, possibly because of prolonged duration and higher dosage of administration. RCTs should focus on the dose-response relationship of prolonged ketamine infusions on CFP.

Migraine and treatment-resistant depression

Migraine and major depressive disorders (MDD) or treatment resistant depression (TRD) represent a significant global burden and are often comorbid, further complicating diagnosis and treatment. Epidemiological studies have demonstrated a bidirectional relationship between migraine and MDD/TRD, with patients suffering from one disorder exhibiting a heightened risk of developing the other. This association is believed to result from shared genetic factors, neurotransmitter dysregulation, inflammation, hormonal alteration, and other conditions comorbid with both disorders. Emerging evidence suggests that therapeutics targeting common pathways in both disorders may be beneficial for comorbid patients. Novel therapeutics for migraine or MDD/TRD, such as calcitonin gene-related peptide (CGRP)-targeting therapy, onabotulinumtoxinA, ketamine/esketamine, vagus nerve stimulation or transcranial magnetic stimulation, may be helpful in selected patients with comorbid migraine-MDD/TRD. Nevertheless, continued efforts are needed to improve early detection and intervention, to better understand the complex interplay between genetic, environmental, and psychosocial factors contributing to this comorbidity, to identify novel therapeutic targets, and ultimately, to alleviate the disease burden caused by this comorbidity.

Effects of intra-operative administration of subanesthetic s-ketamine on emergence from sevoflurane anesthesia: a randomized double-blind placebo-controlled study

BACKGROUND

Ketamine is administered in the perioperative period for its benefits in analgesia, anti-agitation and anti-depression when administered at a small dose. However, it is not clear whether the intra-operative administration of ketamine would affect emergence under sevoflurane anesthesia. To investigate this effect, we designed this trial.

METHODS

In this randomized, double-blind, placebo-controlled study, we enrolled 44 female patients aged 18-60 who were scheduled to elective laparoscopic gynecological surgeries. All patients were randomly assigned to saline or s-ketamine group. In s-ketamine group, patients received 0.125 mg/kg s-ketamine 30 min after the start of surgery. In saline group, patients were administered the same volume of saline. Sevoflurane and remifentanil were used to maintain general anesthesia. The primary outcome was emergence time. We also assessed postoperative agitation, cognitive function, and delirium. In addition, we collected and analyzed prefrontal electroencephalogram (EEG) during and after general anesthesia.

RESULTS

There were no significant differences in emergence time between s-ketamine group and saline group (10.80 ± 3.77 min vs. 10.00 ± 2.78 min, P = 0.457). Neither postoperative agitation (4 [3, 4] vs. 4 [3, 4], P = 0.835) nor cognitive function (25.84 ± 2.69 vs. 25.55 ± 2.19, P = 0.412) differed between groups. No postoperative delirium was observed in either group. Subanesthetic s-ketamine resulted in active EEG with decreased power of slow (-0.35 ± 1.13 dB vs. -1.63 ± 1.03 dB, P = 0.003), delta (-0.22 ± 1.11 dB vs. -1.32 ± 1.09 dB, P = 0.011) and alpha (-0.31 ± 0.71 dB vs. -1.71 ± 1.34 dB, P = 0.0003) waves and increased power of beta-gamma bands (-0.30 ± 0.89 dB vs. 4.20 ± 2.08 dB, P < 0.0001) during sevoflurane anesthesia, as well as an increased alpha peak frequency (-0.16 ± 0.48 Hz vs. 0.31 ± 0.73 Hz, P = 0.026). EEG patterns did not differ during the recovery period after emergence between groups.

CONCLUSION

Ketamine administered during sevoflurane anesthesia had no apparent influence on emergence time in young and middle-aged female patients undergoing laparoscopic surgery. Subanesthetic s-ketamine induced an active prefrontal EEG pattern during sevoflurane anesthesia but did not raise neurological side effects after surgery.

TRIAL REGISTRATION

Chinese Clinical Trial Registry, ChiCTR2100046479 (date: 16/05/2021).

Brain stimulation for treatment-resistant depression

Depression is one of the main public health problems in the world, having a high prevalence and being considered the main cause of disability. An important portion of patients does not respond to treatment with the initial trial of conventional antidepressants in the current depressive episode of moderate to severe intensity, which characterizes treatment-resistant depression. In this context, non-invasive neuromodulation procedures use an electric current or magnetic field to modulate the central nervous system, and they represent a new option for patients with treatment-resistant depression.

Explainable drug side effect prediction via biologically informed graph neural network

Early detection of potential side effects (SE) is a critical and challenging task for drug discovery and patient care. In-vitro or in-vivo approach to detect potential SEs is not scalable for many drug candidates during the preclinical stage. Recent advances in explainable machine learning may facilitate detecting potential SEs of new drugs before market release and elucidating the critical mechanism of biological actions. Here, we leverage multi-modal interactions among molecules to develop a biologically informed graph-based SE prediction model, called HHAN-DSI. HHAN-DSI predicted frequent and even uncommon SEs of the unseen drug with higher or comparable accuracy against benchmark methods. When applying HHAN-DSI to the central nervous system, the organs with the largest number of SEs, the model revealed diverse psychiatric medications' previously unknown but probable SEs, together with the potential mechanisms of actions through a network of genes, biological functions, drugs, and SEs.

The clinical toxicology of ketamine

INTRODUCTION

Ketamine is a pharmaceutical drug possessing both analgesic and anaesthetic properties. As an anaesthetic, it induces anaesthesia by producing analgesia with a state of altered consciousness while maintaining airway tone, respiratory drive, and hemodynamic stability. At lower doses, it has psychoactive properties and has gained popularity as a recreational drug.

OBJECTIVES

To review the epidemiology, mechanisms of toxicity, pharmacokinetics, clinical features, diagnosis and management of ketamine toxicity.

METHODS

Both OVID MEDLINE (January 1950-April 2023) and Web of Science (1900-April 2023) databases were searched using the term "ketamine" in combination with the keywords "pharmacokinetics", "kinetics", "poisoning", "poison", "toxicity", "ingestion", "adverse effects", "overdose", and "intoxication". Furthermore, bibliographies of identified articles were screened for additional relevant studies. These searches produced 5,268 non-duplicate citations; 185 articles (case reports, case series, pharmacokinetic studies, animal studies pertinent to pharmacology, and reviews) were considered relevant. Those excluded were other animal investigations, therapeutic human clinical investigations, commentaries, editorials, cases with no clinical relevance and post-mortem investigations.

EPIDEMIOLOGY

Following its introduction into medical practice in the early 1970s, ketamine has become a popular recreational drug. Its use has become associated with the dance culture, electronic and dubstep dance events.

MECHANISM OF ACTION

Ketamine acts primarily as a non-competitive antagonist on the glutamate N-methyl-D-aspartate receptor, causing the loss of responsiveness that is associated with clinical ketamine dissociative anaesthesia.

PHARMACOKINETICS

Absorption of ketamine is rapid though the rate of uptake and bioavailability is determined by the route of exposure. Ketamine is metabolized extensively in the liver. Initially, both isomers are metabolized to their major active metabolite, norketamine, by CYP2B6, CYP3A4 and CYP2C9 isoforms. The hydroxylation of the cyclohexan-1-one ring of norketamine to the three positional isomers of hydroxynorketamine occurs by CYP2B6 and CYP2A6. The dehydronorketamine metabolite occurs either by direct dehydrogenation from norketamine via CYP2B6 metabolism or non-enzymatic dehydration of hydroxynorketamine. Norketamine, the dehydronorketamine isomers, and hydroxynorketamine have pharmacological activity. The elimination of ketamine is primarily by the kidneys, though unchanged ketamine accounts for only a small percentage in the urine. The half-life of ketamine in humans is between 1.5 and 5 h.

CLINICAL FEATURES

Acute adverse effects following recreational use are diverse and can include impaired consciousness, dizziness, irrational behaviour, hallucinations, abdominal pain and vomiting. Chronic use can result in impaired verbal information processing, cystitis and cholangiopathy.

DIAGNOSIS

The diagnosis of acute ketamine intoxication is typically made on the basis of the patient's history, clinical features, such as vomiting, sialorrhea, or laryngospasm, along with neuropsychiatric features. Chronic effects of ketamine toxicity can result in cholangiopathy and cystitis, which can be confirmed by endoscopic retrograde cholangiopancreatography and cystoscopy, respectively.

MANAGEMENT

Treatment of acute clinical toxicity is predominantly supportive with empiric management of specific adverse effects. Benzodiazepines are recommended as initial treatment to reduce agitation, excess neuromuscular activity and blood pressure. Management of cystitis is multidisciplinary and multi-tiered, following a stepwise approach of pharmacotherapy and surgery. Management of cholangiopathy may require pain management and, where necessary, biliary stenting to alleviate obstructions. Chronic effects of ketamine toxicity are typically reversible, with management focusing on abstinence.

CONCLUSIONS

Ketamine is a dissociative drug employed predominantly in emergency medicine; it has also become popular as a recreational drug. Its recreational use can result in acute neuropsychiatric effects, whereas chronic use can result in cystitis and cholangiopathy.

Pharmacotherapy: Ketamine and Esketamine

Ketamine and esketamine have rapid-onset antidepressant effects and may be considered for the management of treatment-resistant depression. Intranasal esketamine has regulatory approval in the United States and European Union. Intravenous ketamine is often administered off-label as an antidepressant, though no standard operating procedures exist. Repeated administrations and the use of a concurrent standard antidepressant may maintain antidepressant effects of ketamine/esketamine. Possible adverse effects of ketamine and esketamine include psychiatric, cardiovascular, neurologic and genitourinary effects, and the potential for abuse. The long-term safety and efficacy of ketamine/esketamine as antidepressants require further study.

The effects of ketamine on viability, primary DNA damage, and oxidative stress parameters in HepG2 and SH-SY5Y cells

Ketamine is a dissociative anaesthetic used to induce general anaesthesia in humans and laboratory animals. Due to its hallucinogenic and dissociative effects, it is also used as a recreational drug. Anaesthetic agents can cause toxic effects at the cellular level and affect cell survival, induce DNA damage, and cause oxidant/antioxidant imbalance. The aim of this study was to explore these possible adverse effects of ketamine on hepatocellular HepG2 and neuroblastoma SH-SY5Y cells after 24-hour exposure to a concentration range covering concentrations used in analgesia, drug abuse, and anaesthesia (0.39, 1.56, and 6.25 µmol/L, respectively). At these concentrations ketamine had relatively low toxic outcomes, as it lowered HepG2 and SH-SY5Y cell viability up to 30 %, and low, potentially repairable DNA damage. Interestingly, the levels of reactive oxygen species (ROS), malondialdehyde (MDA), and glutathione (GSH) remained unchanged in both cell lines. On the other hand, oxidative stress markers [superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase (CAT)] pointed to ketamine-induced oxidant/antioxidant imbalance.

The antidepressant actions of ketamine and its enantiomers

Ketamine, an N-methyl-d-aspartate receptor (NMDAR) antagonist first developed as an anesthetic, has shown significant promise as a medication with rapid antidepressant properties in treatment-resistant depression. However, concerns such as adverse side effects and potential misuse liability have limited its widespread use. Racemic ketamine has two enantiomers-(S)- and (R)-ketamine-that appear to have disparate underlying mechanisms. This brief review summarizes some of the most recent preclinical and clinical research regarding the convergent and divergent prophylactic, immediate, and sustained antidepressant effects of (S)- and (R)-ketamine while addressing potential differences in their side effect and misuse liability profiles. Preclinical research suggests divergent mechanisms underlying (S)- and (R)-ketamine, with (S)-ketamine more directly affecting mechanistic target of rapamycin complex 1 (mTORC1) signaling and (R)-ketamine more directly affecting extracellular signal-related kinase (ERK) signaling. Clinical research suggests that (R)-ketamine has a milder side effect profile than (S)-ketamine and decreases depression rating scale scores, but recent randomized, controlled trials found that it had no significant antidepressant efficacy compared to placebo, suggesting that caution is warranted in interpreting its therapeutic potential. Future preclinical and clinical research is needed to maximize the efficacy of each enantiomer, either by optimizing dose, route of administration, or administration paradigm.

Contribution of the opioid system to depression and to the therapeutic effects of classical antidepressants and ketamine

Major depressive disorder (MDD) afflicts approximately 5 % of the world population, and about 30-50 % of patients who receive classical antidepressant medications do not achieve complete remission (treatment resistant depressive patients). Emerging evidence suggests that targeting opioid receptors mu (MOP), kappa (KOP), delta (DOP), and the nociceptin/orphanin FQ receptor (NOP) may yield effective therapeutics for stress-related psychiatric disorders. As depression and pain exhibit significant overlap in their clinical manifestations and molecular mechanisms involved, it is not a surprise that opioids, historically used to alleviate pain, emerged as promising and effective therapeutic options in the treatment of depression. The opioid signaling is dysregulated in depression and numerous preclinical studies and clinical trials strongly suggest that opioid modulation can serve as either an adjuvant or even an alternative to classical monoaminergic antidepressants. Importantly, some classical antidepressants require the opioid receptor modulation to exert their antidepressant effects. Finally, ketamine, a well-known anesthetic whose extremely efficient antidepressant effects were recently discovered, was shown to mediate its antidepressant effects via the endogenous opioid system. Thus, although opioid system modulation is a promising therapeutical venue in the treatment of depression further research is warranted to fully understand the benefits and weaknesses of such approach.

Effects of Pregnanolone Glutamate and Its Metabolites on GABAA and NMDA Receptors and Zebrafish Behavior

Multiple molecular targets have been identified to mediate membrane-delimited and nongenomic effects of natural and synthetic steroids, but the influence of steroid metabolism on neuroactive steroid signaling is not well understood. To begin to address this question, we set out to identify major metabolites of a neuroprotective synthetic steroid 20-oxo-5β-pregnan-3α-yl l-glutamyl 1-ester (pregnanolone glutamate, PAG) and characterize their effects on GABAA and NMDA receptors (GABARs, NMDARs) and their influence on zebrafish behavior. Gas chromatography-mass spectrometry was used to assess concentrations of PAG and its metabolites in the hippocampal tissue of juvenile rats following intraperitoneal PAG injection. PAG is metabolized in the peripheral organs and nervous tissue to 20-oxo-17α-hydroxy-5β-pregnan-3α-yl l-glutamyl 1-ester (17-hydroxypregnanolone glutamate, 17-OH-PAG), 3α-hydroxy-5β-pregnan-20-one (pregnanolone, PA), and 3α,17α-dihydroxy-5β-pregnan-20-one (17-hydroxypregnanolone, 17-OH-PA). Patch-clamp electrophysiology experiments in cultured hippocampal neurons demonstrate that PA and 17-OH-PA are potent positive modulators of GABARs, while PAG and 17-OH-PA have a moderate inhibitory effect at NMDARs. PAG, 17-OH-PA, and PA diminished the locomotor activity of zebrafish larvae in a dose-dependent manner. Our results show that PAG and its metabolites are potent modulators of neurotransmitter receptors with behavioral consequences and indicate that neurosteroid-based ligands may have therapeutic potential.

Ketamine reduces electrophysiological network activity in cortical neuron cultures already at sub-micromolar concentrations - Impact on TrkB-ERK1/2 signaling

The dissociative anesthetic ketamine regulates cortical activity in a dose-dependent manner. Subanesthetic-dose ketamine has paradoxical excitatory effects which is proposed to facilitate brain-derived neurotrophic factor (BDNF) (a ligand of tropomyosin receptor kinase B, TrkB) signaling, and activation of extracellular signal-regulated kinase 1/2 (ERK1/2). Previous data suggests that ketamine, at sub-micromolar concentrations, induces glutamatergic activity, BDNF release, and activation of ERK1/2 also on primary cortical neurons. We combined western blot analysis with multiwell-microelectrode array (mw-MEA) measurements to examine ketamine's concentration-dependent effects on network-level electrophysiological responses and TrkB-ERK1/2 phosphorylation in rat cortical cultures at 14 days in vitro. Ketamine did not cause an increase in neuronal network activity at sub-micromolar concentrations, but instead a decrease in spiking that was evident already at 500 nM concentration. TrkB phosphorylation was unaffected by the low concentrations, although BDNF elicited prominent phosphorylation response. High concentration of ketamine (10 μM) strongly reduced spiking, bursting and burst duration, which was accompanied with decreased phosphorylation of ERK1/2 but not TrkB. Notably, robust increases in spiking and bursting activity could be produced with carbachol, while it did not affect phosphorylation of TrkB or ERK1/2. Diazepam abolished neuronal activity, which was accompanied by reduced ERK1/2 phosphorylation without change on TrkB. In conclusion, sub-micromolar ketamine concentrations did not cause an increase in neuronal network activity or TrkB-ERK1/2 phosphorylation in cortical neuron cultures that readily respond to exogenously applied BDNF. Instead, pharmacological inhibition of network activity can be readily observed with high concentration of ketamine and it is associated with reduced ERK1/2 phosphorylation.

Pharmacotherapy optimization for rapid sequence intubation in the emergency department

PURPOSE

Rapid-sequence intubation (RSI) is the process of administering a sedative and neuromuscular blocking agent (NMBA) in rapid succession to facilitate endotracheal intubation. It is the most common and preferred method for intubation of patients presenting to the emergency department (ED). The selection and use of medications to facilitate RSI is critical for success. The purpose of this review is to describe pharmacotherapies used during the RSI process, discuss current clinical controversies in RSI medication selection, and review pharmacotherapy considerations for alternative intubation methods.

SUMMARY

There are several steps to the intubation process requiring medication considerations, including pretreatment, induction, paralysis, and post-intubation sedation and analgesia. Pretreatment medications include atropine, lidocaine, and fentanyl; but use of these agents in clinical practice has fallen out of favor as there is limited evidence for their use outside of select clinical scenarios. There are several options for induction agents, though etomidate and ketamine are the most used due to their more favorable hemodynamic profiles. Currently there is retrospective evidence that etomidate may produce less hypotension than ketamine in patients presenting with shock or sepsis. Succinylcholine and rocuronium are the preferred neuromuscular blocking agents, and the literature suggests minimal differences between succinylcholine and high dose rocuronium in first-pass success rates. Selection between the two is based on patient specific factors, half-life and adverse effect profiles. Finally, medication-assisted preoxygenation and awake intubation are less common methods for intubation in the ED but require different considerations for medication use.

AREAS FOR FUTURE RESEARCH

The optimal selection, dosing, and administration of RSI medications is complicated, and further research is needed in several areas. Additional prospective studies are needed to determine optimal induction agent selection and dosing in patients presenting with shock or sepsis. Controversy exists over optimal medication administration order (paralytic first vs induction first) and medication dosing in obese patients, but there is insufficient evidence to significantly alter current practices regarding medication dosing and administration. Further research examining awareness with paralysis during RSI is needed before definitive and widespread practice changes to medication use during RSI can be made.

The Pain Management of Trauma Patients in the Emergency Department

The vast majority of injured patients suffer from pain. Systematic assessment of pain on admission to the emergency department (ED) is a cornerstone of translating the best treatment strategies for patient care into practice. Pain must be measured with severity scales that are validated in clinical practice, including for specific populations (such as children and older adults). Although primary care ED of trauma patients focuses on resuscitation, diagnosis and treatment, pain assessment and management remains a critical element as professionals are not prepared to provide effective and early therapy. To date, most EDs have pain assessment and management protocols that take into account the patient's hemodynamic status and clinical condition and give preference to non-pharmacological approaches where possible. When selecting medications, the focus is on those that are least disruptive to hemodynamic status. Pain relief may still be necessary in hemodynamically unstable patients, but caution should be exercised, especially when using opioids, as absorption may be impaired or shock may be exacerbated. The analgesic dose of ketamine is certainly an attractive option. Fentanyl is clearly superior to other opioids in initial resuscitation and treatment as it has minimal effects on hemodynamic status and does not cause central nervous system depression. Inhaled analgesia techniques and ultrasound-guided nerve blocks are also increasingly effective solutions. A multimodal pain approach, which involves the use of two or more drugs with different mechanisms of action, plays an important role in the relief of trauma pain. All EDs must have policies and promote the adoption of procedures that use multimodal strategies for effective pain management in all injured patients.

Ketamine supresses REM sleep and markedly increases EEG gamma oscillations in the Wistar Kyoto rat model of treatment-resistant depression

Wistar-Kyoto (WKY) rats exhibit depression-like characteristics and decreased sensitivity to monoamine-based antidepressants, making them a suitable model of treatment-resistant depression (TRD). Ketamine has emerged recently as a rapidly acting antidepressant with high efficacy in TRD. Our aim was to determine whether subanaesthetic doses of ketamine can correct sleep and electroencephalogram (EEG) alterations in WKY rats and whether any ketamine-induced changes differentially affect WKY rats compared to Sprague-Dawley (SD) rats. Thus, we surgically implanted 8SD and 8 WKY adult male rats with telemetry transmitters and recorded their EEG, electromyogram, and locomotor activity after vehicle or ketamine (3, 5 or 10mg/kg, s.c.) treatment. We also monitored the plasma concentration of ketamine and its metabolites, norketamine and hydroxynorketamine in satellite animals. We found that WKY rats, have an increased amount of rapid eye movement (REM) sleep, fragmented sleep-wake pattern, and increased EEG delta power during non-REM sleep compared to SD rats. Ketamine suppressed REM sleep and increased EEG gamma power during wakefulness in both strains, but the gamma increase was almost twice as large in WKY rats than in SD rats. Ketamine also increased beta oscillations, but only in WKY rats. These differences in sleep and EEG are unlikely to be caused by dissimilarities in ketamine metabolism as the plasma concentrations of ketamine and its metabolites were similar in both strains. Our data suggest an enhanced antidepressant-like response to ketamine in WKY rats, and further support the predictive validity of acute REM sleep suppression as a measure of antidepressant responsiveness.

Narrative Review: Low-Dose Ketamine for Pain Management

Pain is the leading cause of medical consultations and occurs in 50-70% of emergency department visits. To date, several drugs have been used to manage pain. The clinical use of ketamine began in the 1960s and it immediately emerged as a manageable and safe drug for sedation and anesthesia. The analgesic properties of this drug were first reported shortly after its use; however, its psychomimetic effects have limited its use in emergency departments. Owing to the misuse and abuse of opioids in some countries worldwide, ketamine has become a versatile tool for sedation and analgesia. In this narrative review, ketamine's role as an analgesic is discussed, with both known and new applications in various contexts (acute, chronic, and neuropathic pain), along with its strengths and weaknesses, especially in terms of psychomimetic, cardiovascular, and hepatic effects. Moreover, new scientific evidence has been reviewed on the use of additional drugs with ketamine, such as magnesium infusion for improving analgesia and clonidine for treating psychomimetic symptoms. Finally, this narrative review was refined by the experience of the Pain Group of the Italian Society of Emergency Medicine (SIMEU) in treating acute and chronic pain with acute manifestations in Italian Emergency Departments.

Treatment of cholinergic-induced status epilepticus with polytherapy targeting GABA and glutamate receptors

Despite new antiseizure medications, the development of cholinergic-induced refractory status epilepticus (RSE) continues to be a therapeutic challenge as pharmacoresistance to benzodiazepines and other antiseizure medications quickly develops. Studies conducted by Epilepsia. 2005;46:142 demonstrated that the initiation and maintenance of cholinergic-induced RSE are associated with trafficking and inactivation of gamma-aminobutyric acid A receptors (GABAA R) thought to contribute to the development of benzodiazepine pharmacoresistance. In addition, Dr. Wasterlain's laboratory reported that increased N-methyl-d-aspartate receptors (NMDAR) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPAR) contribute to enhanced glutamatergic excitation (Neurobiol Dis. 2013;54:225; Epilepsia. 2013;54:78). Thus, Dr. Wasterlain postulated that targeting both maladaptive responses of reduced inhibition and increased excitation that is associated with cholinergic-induced RSE should improve therapeutic outcome. We currently review studies in several animal models of cholinergic-induced RSE that demonstrate that benzodiazepine monotherapy has reduced efficacy when treatment is delayed and that polytherapy with drugs that include a benzodiazepine (eg midazolam and diazepam) to counter loss of inhibition, concurrent with an NMDA antagonist (eg ketamine) to reduce excitation provide improved efficacy. Improved efficacy with polytherapy against cholinergic-induced seizure is demonstrated by reduction in (1) seizure severity, (2) epileptogenesis, and (3) neurodegeneration compared with monotherapy. Animal models reviewed include pilocarpine-induced seizure in rats, organophosphorus nerve agent (OPNA)-induced seizure in rats, and OPNA-induced seizure in two mouse models: (1) carboxylesterase knockout (Es1-/- ) mice which, similarly to humans, lack plasma carboxylesterase and (2) human acetylcholinesterase knock-in carboxylesterase knockout (KIKO) mice. We also review studies showing that supplementing midazolam and ketamine with a third antiseizure medication (valproate or phenobarbital) that targets a nonbenzodiazepine site rapidly terminates RSE and provides further protection against cholinergic-induced SE. Finally, we review studies on the benefits of simultaneous compared with sequential drug treatments and the clinical implications that lead us to predict improved efficacy of early combination drug therapies. The data generated from seminal rodent studies of efficacious treatment of cholinergic-induced RSE conducted under Dr. Wasterlain's guidance suggest that future clinical trials should treat the inadequate inhibition and temper the excess excitation that characterize RSE and that early combination therapies may provide improved outcome over benzodiazepine monotherapy.

Chronic oral ketamine prevents anhedonia and alters neuronal activation in the lateral habenula and nucleus accumbens in rats under chronic unpredictable mild stress

Acute injections of ketamine lead to rapid but transient antidepressant effects. Chronic oral treatment at low doses, a promising non-invasive alternative, may prolong this therapeutic effect. Here, we examine the antidepressant effects of chronic oral ketamine in rats under chronic unpredictable mild stress (CUMS), and reveal their neuronal correlates. Male Wistar rats were divided into control, ketamine, CUMS, and CUMS-ketamine groups. The CUMS protocol was applied to the latter two groups for 9 weeks, and ketamine (0.013 mg/ml) was provided ad libitum to the ketamine and CUMS-ketamine groups for 5 weeks. The sucrose consumption test, forced swim test, open field test, elevated plus maze, and Morris water maze were respectively used to assess anhedonia, behavioral despair, general locomotor activity, anxiety-like behavior and spatial reference memory. CUMS caused a reduction of sucrose consumption and impaired spatial memory, accompanied by increased neuronal activation in the lateral habenula (LHb) and paraventricular thalamic nucleus (PVT). Oral ketamine prevented behavioral despair and CUMS-induced anhedonia. Reward-triggered c-Fos immunoreactivity was decreased in the LHb and increased in the nucleus accumbens shell (NAcSh) in the CUMS-ketamine group compared to the CUMS group. Ketamine did not produce a differential effect in the OFT, EPM and MWM. These results show that chronic oral ketamine at low doses prevents anhedonia without impairing spatial reference memory. The observed neuronal activation changes in the LHb and NAcSh may be involved in the preventive effects of ketamine on anhedonia. This article is part of the Special Issue on "Ketamine and its Metabolites".

Effect of chromosomal integration on catalytic performance of a multi-component P450 system in Escherichia coli

Cytochromes P450 are useful biocatalysts in synthetic chemistry and important bio-bricks in synthetic biology. Almost all bacterial P450s require separate redox partners for their activity, which are often expressed in recombinant Escherichia coli using multiple plasmids. However, the application of CRISPR/Cas recombineering facilitated chromosomal integration of heterologous genes which enables more stable and tunable expression of multi-component P450 systems for whole-cell biotransformations. Herein, we compared three E. coli strains W3110, JM109, and BL21(DE3) harboring three heterologous genes encoding a P450 and two redox partners either on plasmids or after chromosomal integration in two genomic loci. Both loci proved to be reliable and comparable for the model regio- and stereoselective two-step oxidation of (S)-ketamine. Furthermore, the CRISPR/Cas-assisted integration of the T7 RNA polymerase gene enabled an easy extension of T7 expression strains. Higher titers of soluble active P450 were achieved in E. coli harboring a single chromosomal copy of the P450 gene compared to E. coli carrying a medium copy pET plasmid. In addition, improved expression of both redox partners after chromosomal integration resulted in up to 80% higher (S)-ketamine conversion and more than fourfold increase in total turnover numbers.

Provider-directed analgesia for dental pain

INTRODUCTION

Extraction of impacted molar teeth is a common procedure performed by oral surgeons and general dentists, with postoperative pain being a significant adverse event post-surgery. If mismanaged, pain can lead to complications that impact oral and systemic health. The current scourge of the opioid epidemic has ushered in a new era of provider-directed analgesic (PDA) therapy in dentistry.

AREAS COVERED

This article provides an in-depth review on the major pharmacological and therapeutic properties of established and alternative analgesics used to manage dental pain.

EXPERT OPINION

Substantial evidence-based literature shows combination of a non-steroidal anti-inflammatory drug (NSAID; e.g. ibuprofen) and acetaminophen provides superior pain relief than single-agent or combination opioid regimens. However, there are clinical scenarios (e.g. severe pain) when short-course opioid prescription is appropriate in select patients, in which a 2-3-day treatment duration is typically sufficient. Alternative agents (e.g. caffeine, gabapentin, phytotherapies), typically in combination with established agents, can mitigate postoperative dental pain. Some evidence suggests preemptive therapies (e.g. corticosteroids, NSAIDs) reduce amounts of postsurgical analgesic consumption and might lessen opioid prescription burden. In summary, this comprehensive review provides an opportune update on the evolving landscape of pharmacotherapy for acute postsurgical dental pain, informing best practices for PDA in the dental setting.

Electrophysiological phenotypes of suicidality predict prolonged response to oral ketamine treatment

Oral ketamine has shown to be a rapid-acting antidepressant and a potential treatment option for suicidality, however, repeated doses are often required. Objective markers of prolonged treatment response are needed to help individuals and clinicians make informed treatment decisions. This secondary analysis sought to identify objective electrophysiological predictors of both prolonged response and dose sensitivity to low-dose oral ketamine in people with chronic suicidality. Individuals with a Beck Scale for Suicide Ideation total score (BSS) ≥ 6 (N = 29) completed a six-week ketamine treatment, pre-treatment electroencephalography and follow-up assessment of suicidality (four weeks from the final ketamine dose). Prolonged response was observed in 52% of participants (follow-up BSS reduced by 50% or ≤6); nearly half were prolonged non-responders. There was decisive evidence for a predictive Bayesian linear regression model with follow-up BSS score as the response variable and pre-treatment auditory evoked power bands as predictors (theta, alpha and beta frequencies, BF₁₀ = 17,948, R² = 0.70). A Bayesian one-way ANOVA indicated strong evidence for a model of positive association between auditory evoked power and ketamine dose sensitivity (theta-alpha BF₊₀ = 108, effect size δ = 1.3, 95% CI 0.5-2.1; high-beta BF₊₀ = 7.4, δ = 0.8, 95% CI 0.1-1.6). Given auditory evoked power may index serotonin neurotransmission, these results suggest that a prolonged response to ketamine may, in part, be mediated by pre-treatment serotonergic functioning. In addition, the observed beta power differences may arise from GABAergic functioning. These suicidality phenotypes, identifiable by pre-treatment electrophysiology, may aid diagnosis, treatment selection and prediction of prolonged treatment outcome.

Kynurenine pathway of tryptophan metabolism in pathophysiology and therapy of major depressive disorder

Serotonin deficiency in major depressive disorder (MDD) has formed the basis of antidepressant drug development and was originally attributed to induction of the major tryptophan (Trp)-degrading enzyme, liver Trp 2,3-dioxygenase (TDO), by cortisol, leading to decreased Trp availability to the brain for serotonin synthesis. Subsequently, the serotonin deficiency was proposed to involve induction of the extrahepatic Trp-degrading enzyme indoleamine 2,3-dioxygenase (IDO) by proinflammatory cytokines, with inflammation being the underlying cause. Recent evidence, however, challenges this latter concept, as not all MDD patients are immune-activated and, when present, inflammation is mild and/or transient. A wide range of antidepressant drugs inhibit the activity of liver TDO and bind specifically to the enzyme, but not to IDO. IDO induction is not a major event in MDD, but, when it occurs, its metabolic consequences may be masked and overridden by upregulation of kynurenine monooxygenase (KMO), the gateway to production of modulators of immune and neuronal functions. KMO appears to be activated in MDD by certain proinflammatory cytokines and antidepressants with anti-inflammatory properties may block this activation. We demonstrate the ability of the antidepressant ketamine to dock (bind) to KMO. The pathophysiology of MDD may be underpinned by both the serotonin deficiency and glutamatergic activation mediated respectively by TDO induction and N-methyl-D-aspartate receptor activation. Inhibition of TDO and KMO should be the focus of MDD pharmacotherapy.

Whole-brain mapping reveals the divergent impact of ketamine on the dopamine system

Ketamine is a multifunctional drug with clinical applications as an anesthetic, as a pain management medication and as a transformative fast-acting antidepressant. It is also abused as a recreational drug due to its dissociative property. Recent studies in rodents are revealing the neuronal mechanisms that mediate the complex actions of ketamine, however, its long-term impact due to prolonged exposure remains much less understood with profound scientific and clinical implications. Here, we develop and utilize a high-resolution whole-brain phenotyping approach to show that repeated ketamine administration leads to a dosage-dependent decrease of dopamine (DA) neurons in the behavior state-related midbrain regions and, conversely, an increase within the hypothalamus. Congruently, we show divergently altered innervations of prefrontal cortex, striatum, and sensory areas. Further, we present supporting data for the post-transcriptional regulation of ketamine-induced structural plasticity. Overall, through an unbiased whole-brain analysis, we reveal the divergent brain-wide impact of chronic ketamine exposure on the association and sensory pathways.

"Anti-cancer" effect of ketamine in comparison with MK801 on neuroglioma and lung cancer cells

Ketamine, a N-methyl-D-aspartate (NMDA) receptor antagonist, is commonly used to induce anaesthesia during cancer surgery and relieve neuropathic and cancer pain. This study was conducted to assess whether ketamine has any inhibiting effects on neuroglioma (H4) and lung cancer cells (A549) in vitro. The cultured H4 and A549 cells were treated with ketamine and MK801 (0.1, 1, 10, 100, or 1000 μM) for 24 h. The expressions of glutamate receptors on both types of cancer cells were assessed with qRT-PCR. In addition, cell proliferation and migration were assessed with cell counting Kit-8 and wound healing assays. Cyclin D1, matrix metalloproteinase 9 (MMP9), phosphorylation of extracellular signal-regulated kinase (pERK), and cleaved-caspase-3 expression together with reactive oxygen species (ROS) were also assessed with Western blot, immunostaining, and/or flowcytometry. NMDA and α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors were expressed on both H4 and A549 cells. Ketamine inhibited cancer cell proliferation and migration in a dose-dependent manner by suppressing the cell cycle and inducing apoptosis. Ketamine decreased cyclin D1, pERK, and MMP9 expression. In addition, ketamine increased ROS and cleaved caspase-3 expression and induced apoptosis. The anti-cancer effect of ketamine was more pronounced in A549 cells when compared with H4 cells. MK801 showed similar effects to those of ketamine. Ketamine suppressed cell proliferation and migration in both neuroglioma and lung cancer cells, likely through the antagonization of NMDA receptors.

Effects of ketamine-induced H3K9 hypoacetylation during pregnancy on cardiogenesis of mouse offspring

BACKGROUND

Prenatal exposure to adverse factors can cause congenital heart defects. Ketamine, a widely used anesthetic drug, produces several adverse reactions such as tachycardia, hypertension, and laryngospasm, especially in pediatric patients. This study aimed to detect the effects of ketamine exposure during pregnancy on the cardiogenesis of mouse offspring and the potential mechanisms.

METHODS

In this study, ketamine at an addictive dose (5 mg/kg) was administered to mice during early gestation to explore the epigenetic mechanism of its causing cardiac dysplasia. The cardiac morphology of the mouse offspring was observed through hematoxylin-eosin staining and transmission electron microscopy. The heart function of one-month-old neonates was detected by echocardiography. The expression of cardiomyogenesis-related genes was detected by western blot and RT-qPCR. The acetylation level of histone H3K9 at the Mlc2 promoter and its deacetylase level and activity were detected by CHIP-qPCR, RT-qPCR, and ELISA, respectively.

RESULTS

Our data revealed that ketamine exposure during pregnancy could cause cardiac enlargement, myocardial sarcomere disorganization, and decreased cardiac contractile function in mouse offspring. Moreover, ketamine reduced the expression of Myh6, Myh7, Mlc2, Mef2c, and cTnI. The histone H3K9 acetylation level at the Mlc2 promoter was down-regulated by increasing the histone deacetylase activity and HDAC3 level upon ketamine administration.

CONCLUSIONS

Our work indicates that H3K9 acetylation is a vital player in cardiac dysplasia in offspring caused by prenatal ketamine exposure and HDAC3 is a key regulatory factor.

Ketamine as an alternative to ECT in catatonia in elderly women with bipolar disorder: A case report

The following paper described two cases of patients with catatonic depression in bipolar disorder (BD) referred to our electroconvulsive therapy (ECT) service. Both were deemed not medically fit for ECT, and were, instead, treated with intravenous (IV) ketamine. Both responded with a resolution of symptoms, returning to baseline level of functioning. During the COVID-19 pandemic, given the risks associated with providing ECT (an aerosol generating procedure) and, in the context of limited resources, ketamine therapy for catatonia is a potentially beneficial alternative or supportive treatment to ECT that merits additional research.

Efficacy of ketamine mouthwash in the management of oral and pharyngeal toxicity associated with head and neck chemoradiotherapy: protocol for a phase II, Simon's two-stage trial

INTRODUCTION

Curative intent treatment of head and neck cancer (HNC) is frequently radiation therapy over 7 weeks with concurrent chemotherapy. This regimen is effective but carries a burden of toxicity leading to severe pain and treatment breaks portending inferior outcomes. Conventional palliation methods include opioids, anticonvulsants and local anaesthetics. Breakthrough toxicities are nevertheless ubiquitous and present an urgent unmet need. Ketamine is an inexpensive drug with mechanisms of analgesia outside the opioid pathway including N-methyl-D-aspartate (NMDA) receptor antagonism and a pharmacologically unique property of opioid desensitisation. Systemic ketamine is validated in randomised controlled trials for efficacy in reducing pain and/or opioid burden in the oncologic setting. Literature supports peripherally administered ketamine for pain control without systemic toxicity. These data support our rationale of using ketamine mouthwash to decrease acute toxicity of curative treatment of HNC, the efficacy of which is our aim to elucidate.

METHODS AND ANALYSIS

This is a phase II, Simon's two-stage trial. Patients have pathologically confirmed HNC and an intended regimen of 70 Gy of radiation with concurrent cisplatin. The protocol is initiated on diagnosis of grade 3 mucositis and consists of 2 weeks of 4 times daily (QID) ketamine mouthwash use. The primary endpoint is pain response defined as a combination of pain score and opioid use. 23 subjects will be enrolled in stage 1. If statistical criteria are met, 33 subjects will be enrolled in stage 2. Secondary endpoints include daily pain, daily opioid use, dysphagia at baseline and completion, nightly sleep quality, feeding tube placement and any unscheduled treatment breaks.

ETHICS AND DISSEMINATION

All trial data will be stored in an Institutional Review Board (IRB) approved database. The protocol is registered under Northwell IRB registration number #22-0292 and U.S. Food and Drug Administration (FDA) Investigational New Drug (IND) approval has been granted under IND number 161609. Results are intended to be published in an open-source journal and further data, statistics and source documents are available on request.

TRIAL REGISTRATION NUMBER

NCT05331131.

The Acute Effects and Mechanism of Ketamine on Nicotine-Induced Neurogenic Relaxation of the Corpus Cavernosum in Mice

The present study aimed to investigate the acute effects and the mechanism of ketamine on nicotine-induced relaxation of the corpus cavernosum (CC) in mice. This study measured the intra-cavernosal pressure (ICP) of male C57BL/6 mice and the CC muscle activities using an organ bath wire myograph. Various drugs were used to investigate the mechanism of ketamine on nicotine-induced relaxation. Direct ketamine injection into the major pelvic ganglion (MPG) inhibited MPG-induced increases in ICP. D-serine/L-glutamate-induced relaxation of the CC was inhibited by MK-801 (N-methyl-D-aspartate (NMDA) receptor inhibitor), and nicotine-induced relaxation was enhanced by D-serine/L-glutamate. NMDA had no effect on CC relaxation. Nicotine-induced relaxation of the CC was suppressed by mecamylamine (a non-selective nicotinic acetylcholine receptor antagonist), lidocaine, guanethidine (an adrenergic neuronal blocker), N^w-nitro-L-arginine (a non-selective nitric oxide synthase inhibitor), MK-801, and ketamine. This relaxation was almost completely inhibited in CC strips pretreated with 6-hydroxydopamine (a neurotoxic synthetic organic compound). Ketamine inhibited cavernosal nerve neurotransmission via direct action on the ganglion and impaired nicotine-induced CC relaxation. The relaxation of the CC was dependent on the interaction of the sympathetic and parasympathetic nerves, which may be mediated by the NMDA receptor.

Effect of subanesthetic dose of esketamine on postoperative rehabilitation in elderly patients undergoing hip arthroplasty

OBJECTIVE

The majority of individuals with femoral neck fractures opt for total hip replacement to enhance their quality of life. However, this group frequently exhibits perioperative symptoms of pain, anxiety, and sadness, which extends recovery time to some extent. Esketamine, the right-handed monomer of ketamine, is more popular these days due to its sedative, analgesic, and antidepressant properties. There are currently few domestic and international research on the use of esketamine in elderly individuals who have undergone surgery for a femoral neck fracture. In order to further cut the length of the hospital stay and hasten postoperative recovery, this study investigates whether esketamine postoperative analgesia can lessen postoperative pain, anxiety, and depression in older patients having hip replacement.

METHODS

150 patients, ASA physical status I-II, aged ≥ 60 years, no limitation in gender, BMI 18-25 kg/cm², who underwent selective total hip arthroplasty, according to random number table method, esketamine group (group A) and sufentanil group (group B) were randomized, 75 patients in each group. The two groups received general anesthesia method. At the end of the operation, PCIA was connected for analgesia. In group A, esketamine 2.5 mg/kg was mixed with normal saline to 100 ml. In group B, sufentanil 2.5 ug/kg was mixed with normal saline to 100 ml. Record the VAS scores after operation. Record the first ambulation time, ambulation distance and Patient-controlled Analgesia compression times after operation. The incidence of postoperative adverse reactions such as drowsiness, dizziness, nausea and vomiting, multilingual were recorded. ELISA was used to detect IL-6 and CRP in the morning, 24 h and 72 h after operation. The Hospital Anxiety and Depression Scale (HAD) score and Harris score at 3 days, 1 week and 1 month after operation were followed up.

RESULTS

There was no significant difference in VAS score and PCA compression times (P > 0.05), but the incidence of nausea, vomiting and dizziness in group B was higher than that in group A (P < 0.05). Compared with group B, the levels of IL-6 and CRP in group A at 24 h and 72 h after operation were significantly decreased (P < 0.05). Postoperative ambulation time and ambulation distance in group A were better than those in group B (P < 0.05). The HAD score of group A was lower than that of group B at 3 days and 1 week after operation (P < 0.05). However, there was no significant difference between the two groups at 1 month after operation (P > 0.05). The Harris score of group A was higher than that of group B at 3 days, 1 week and 1 month after operation (P < 0.05).

CONCLUSIONS

Esketamine can reduce short-term postoperative anxiety and depression, relieve postoperative pain and stress response, shorten bed rest time after total hip replacement, and accelerate postoperative recovery.

Understanding the habenula: A major node in circuits regulating emotion and motivation

Over the last decade, the understanding of the habenula has rapidly advanced from being an understudied brain area with the Latin name 'habena" meaning "little rein", to being considered a "major rein" in the control of key monoaminergic brain centers. This ancient brain structure is a strategic node in the information flow from fronto-limbic brain areas to brainstem nuclei. As such, it plays a crucial role in regulating emotional, motivational, and cognitive behaviors and has been implicated in several neuropsychiatric disorders, including depression and addiction. This review will summarize recent findings on the medial (MHb) and lateral (LHb) habenula, their topographical projections, cell types, and functions. Additionally, we will discuss contemporary efforts that have uncovered novel molecular pathways and synaptic mechanisms with a focus on MHb-Interpeduncular nucleus (IPN) synapses. Finally, we will explore the potential interplay between the habenula's cholinergic and non-cholinergic components in coordinating related emotional and motivational behaviors, raising the possibility that these two pathways work together to provide balanced roles in reward prediction and aversion, rather than functioning independently.

Acute oral toxicity, cognitive-enhancing and anti-lipid peroxidation efficacy, and qualitative phytochemistry of the aqueous aerial part extract of Launaea cornuta (Hochst. ex. Oliv. &Hiern) C. Jeffrey

At present, there is no cure for dementia or its related cognitive impairments. Available treatments only provide symptomatic relief and do not alter the disease's progression and they suffer serious drawbacks limiting their clinical use, hence the need for alternative therapies. Although Launaea cornuta has been used traditionally to treat cognitive deficits, its pharmacological efficacy and safety have not been empirically validated, prompting this study. Acute oral toxicity of the extract was examined in Swiss albino mice using the up-and-down procedure described by the Organisation for Economic Cooperation and Development guideline number 425. The Morris water maze technique was adopted in assessing cognitive-enhancing effects of the extract in ketamine-induced cognitive-impaired mice. The malondialdehyde concentrations in the whole brain of experimental mice involved in the MWM experiment were measured to determine the extract's anti-lipid peroxidation efficacy. Qualitative phytochemical screening of the extract was performed using standard procedures. Our results showed that the test extract was safe and did not cause any clinical signs of acute oral toxicity in mice at all doses (LD50 > 2000 mg/kg BW). Moreover, the extract significantly improved cognitive function in ketamine-induced cognitive-impaired mice in a dose-dependent manner, as indicated by reduced escape latency, navigation distance, and longer latency in the target quadrant during the probe trial. The extract also significantly reduced malondialdehyde concentrations in mice in a dose-dependent manner, demonstrating its antioxidative stress efficacy. The studied extract contained various phytochemicals associated with cognitive enhancement and antioxidant efficacy, among other pharmacologic effects. Further empirical studies are needed to determine and characterise the extract's specific cognitive-enhancing compounds, specific mechanisms of action, and complete toxicity profiles.

Clinical pharmacological innovation in the treatment of depression

INTRODUCTION

Deficiencies in standard of care antidepressants are driving novel drug discovery. A new age of antidepressant medications has emerged with the introduction of rapid-acting antidepressants with efficacy in treatment-resistant patients.

AREAS COVERED

The newly approved medicines and those in clinical development for major depressive disorder (MDD) are documented in this scoping review of newly approved and emerging antidepressants. Compounds are evaluated for clinical efficacy, tolerability, and safety and compared to those of standard of care medicines.

EXPERT OPINION

A new age of antidepressant discovery relies heavily on glutamatergic mechanisms. New medicines based upon the model of ketamine have been delivered and are in clinical development. Rapid onset and the ability to impact treatment-resistant depression, raises the question of the best first-line medicines for patients. Drugs with improvements in tolerability are being investigated (e.g. mGlu_2/3 receptor antagonists, AMPA receptor potentiators, and novel NMDA receptor modulators). Multiple companies are working toward the identification of novel psychedelic drugs where the requirement for psychedelic activity is not fully known. Gaps still exist - methods for matching patients with specific medicines are needed, and medicines for the prevention of MDD and its disease progression need research attention.

(2R,6R)-Hydroxynorketamine Treatment of Rats Exposed to Repetitive Low-Level Blast Injury

Many military veterans who experienced blast-related traumatic brain injuries (TBIs) in the conflicts in Iraq and Afghanistan suffer from chronic cognitive and mental health problems, including post-traumatic stress disorder (PTSD). Male rats subjected to repetitive low-level blast exposure develop chronic cognitive and PTSD-related traits that develop in a delayed manner. Ketamine has received attention as a treatment for refractory depression and PTSD. (2R,6R)-hydroxynorketamine [(2R,6R)-HNK] is a ketamine metabolite that exerts rapid antidepressant actions. (2R,6R)-HNK has become of clinical interest because of its favorable side-effect profile, low abuse potential, and oral route of administration. We treated three cohorts of blast-exposed rats with (2R,6R)-HNK, beginning 7-11 months after blast exposure, a time when the behavioral phenotype is established. Each cohort consisted of groups (n = 10-13/group) as follows: 1) Sham-exposed treated with saline, 2) blast-exposed treated with saline, and 3) blast-exposed treated with a single dose of 20 mg/kg of (2R,6R)-HNK. (2R,6R)-HNK rescued blast-induced deficits in novel object recognition (NOR) and anxiety-related features in the elevated zero maze (EZM) in all three cohorts. Exaggerated acoustic startle was reversed in cohort 1, but not in cohort 3. (2R,6R)-HNK effects were still present in the EZM 12 days after administration in cohort 1 and 27 days after administration in NOR testing of cohorts 2 and 3. (2R,6R)-HNK may be beneficial for the neurobehavioral syndromes that follow blast exposure in military veterans. Additional studies will be needed to determine whether higher doses or more extended treatment regimens may be more effective.

Dynamic 3D imaging of cerebral blood flow in awake mice using self-supervised-learning-enhanced optical coherence Doppler tomography

Cerebral blood flow (CBF) is widely used to assess brain function. However, most preclinical CBF studies have been performed under anesthesia, which confounds findings. High spatiotemporal-resolution CBF imaging of awake animals is challenging due to motion artifacts and background noise, particularly for Doppler-based flow imaging. Here, we report ultrahigh-resolution optical coherence Doppler tomography (µODT) for 3D imaging of CBF velocity (CBFv) dynamics in awake mice by developing self-supervised deep-learning for effective image denoising and motion-artifact removal. We compare cortical CBFv in awake vs. anesthetized mice and their dynamic responses in arteriolar, venular and capillary networks to acute cocaine (1 mg/kg, i.v.), a highly addictive drug associated with neurovascular toxicity. Compared with awake, isoflurane (2-2.5%) induces vasodilation and increases CBFv within 2-4 min, whereas dexmedetomidine (0.025 mg/kg, i.p.) does not change vessel diameters nor flow. Acute cocaine decreases CBFv to the same extent in dexmedetomidine and awake states, whereas decreases are larger under isoflurane, suggesting that isoflurane-induced vasodilation might have facilitated detection of cocaine-induced vasoconstriction. Awake mice after chronic cocaine show severe vasoconstriction, CBFv decreases and vascular adaptations with extended diving arteriolar/venular vessels that prioritize blood supply to deeper cortical capillaries. The 3D imaging platform we present provides a powerful tool to study dynamic changes in vessel diameters and morphology alongside CBFv networks in the brain of awake animals that can advance our understanding of the effects of drugs and disease conditions (ischemia, tumors, wound healing).

Characterization of 3-Hydroxyeticyclidine (3-HO-PCE) Metabolism in Human Liver Microsomes and Biological Samples Using High-Resolution Mass Spectrometry

3-Hydroxyeticyclidine (3-HO-PCE) is a ketamine derivative that produces dissociative, hallucinogenic, and euphoric effects when consumed, but little is known about its pharmacological properties, metabolism, and toxicity compared to other designer ketamine analogs. To address this gap in knowledge, this study explored for the first time the metabolism of 3-HO-PCE. Based on this investigation, it is hypothesized that combining the use of Human Liver Microsomes (HLM) as an In vitro model with urine and hair samples from drug users may enable the identification of key analytes that can extend the detection window of 3-HO-PCE, particularly in cases of overdose. The analysis identified 15 putative metabolites, 12 of which are produced through phase I metabolism involving N-dealkylation, deamination, and oxidation, and 3 through phase II O-glucuronidation. The metabolism of 3-HO-PCE is similar to that of O-PCE, another designer ketamine of the eticyclidine family. The study identified M2a and hydroxy-PCA as reliable biomarkers for untargeted screening of the eticyclidine family in urine and hair, respectively. For targeted screening of 3-HO-PCE, M10 is recommended as the target analyte in urine, and M5 shows promise for long-term monitoring of 3-HO-PCE using hair analysis.

Ketamine and serotonergic psychedelics: An update on the mechanisms and biosignatures underlying rapid-acting antidepressant treatment

The discovery of ketamine as a rapid-acting antidepressant spurred significant research to understand its underlying mechanisms of action and to identify other novel compounds that may act similarly. Serotonergic psychedelics (SPs) have shown initial promise in treating depression, though the challenge of conducting randomized controlled trials with SPs and the necessity of long-term clinical observation are important limitations. This review summarizes the similarities and differences between the psychoactive effects associated with both ketamine and SPs and the mechanisms of action of these compounds, with a focus on the monoaminergic, glutamatergic, gamma-aminobutyric acid (GABA)-ergic, opioid, and inflammatory systems. Both molecular and neuroimaging aspects are considered. While their main mechanisms of action differ-SPs increase serotonergic signaling while ketamine is a glutamatergic modulator-evidence suggests that the downstream mechanisms of action of both ketamine and SPs include mechanistic target of rapamycin complex 1 (mTORC1) signaling and downstream GABAA receptor activity. The similarities in downstream mechanisms may explain why ketamine, and potentially SPs, exert rapid-acting antidepressant effects. However, research on SPs is still in its infancy compared to the ongoing research that has been conducted with ketamine. For both therapeutics, issues with regulation and proper controls should be addressed before more widespread implementation. This article is part of the Special Issue on "Ketamine and its Metabolites".

Can Opioid-Free Anaesthesia Be Personalised? A Narrative Review

Background: A significant amount of evidence suggests that Opioid-Free Anaesthesia (OFA) may provide better outcomes for patients undergoing surgery, sparing patients who are particularly vulnerable to adverse side effects of opioids. However, to what extent personalizing OFA is feasible and beneficial has not been adequately described. Methods: We conducted a narrative literature review aiming to provide a comprehensive understanding of nociception and pain and its context within the field of OFA. Physiological (including monitoring), pharmacological, procedural (type of surgery), genetical and phenotypical (including patients’ conditions) were considered. Results: We did not find any monitoring robustly associated with improved outcomes. However, we found evidence supporting particular OFA indications, such as bariatric and cancer surgery. We found that vulnerable patients may benefit more from OFA, with an interesting field of research in patients suffering from vascular disease. We found a variety of techniques and medications making it impossible to consider OFA as a single technique. Our findings suggest that a vast field of research remains unexplored. In particular, a deeper understanding of nociception with an interest in its genetic and acquired contributors would be an excellent starting point paving the way for personalised OFA. Conclusion: Recent developments in OFA may present a more holistic approach, challenging the use of opioids. Understanding better nociception, given the variety of OFA techniques, may help to maximize their potential in different contexts and potential indications.

The NMDA receptor antagonists memantine and ketamine as anti-migraine agents

Migraine is a debilitating disorder affecting females more frequently than males. There is some evidence that drugs targeting glutamate receptors: memantine and ketamine might be beneficial in the therapy of this entity. Therefore, the purpose of this work is to present NMDA receptor antagonists, memantine and ketamine, as potential anti-migraine agents. We searched PubMed/MEDLINE, Embase, and clinical trials submitted to ClinicalTrials.gov to find publications describing eligible trials published between database inception and December 31, 2021. This comprehensive literature review summarizes data on the use of the NMDA receptor antagonists memantine and ketamine in the pharmacotherapy of migraine. Results from 20 previous and recent preclinical experiments are discussed and correlated with 19 clinical trials (including case series, open-label, and randomized placebo-controlled trials). For the purposes of this review, the authors hypothesized that the propagation of SD is a major mechanism in the pathophysiology of migraine. In several animal studies and in vitro studies, memantine and ketamine inhibited or reduced propagation of the SD. In addition, the results of clinical trials suggest that memantine or ketamine may be an effective treatment option for migraine. However, most studies on these agents lack control group. Although further clinical trials are needed, the results suggest that ketamine or memantine may be promising molecules for the treatment of severe migraine. Particular attention should be paid to people who have a treatment-resistant form of migraine with aura or have exhausted existing treatment options. For them, the drugs under discussion could represent an interesting alternative in the future.

Point-of-care electrochemical sensor for selective determination of date rape drug "ketamine" based on core-shell molecularly imprinted polymer

Misuse of illicit drugs is a serious problem that became the primary concern for many authorities worldwide. Point-of-care (POC) diagnostic tools can provide accurate and fast screening information that helps to detect illicit drugs in a short time. A portable, disposable and reproducible core-shell molecularly imprinted polymer (MIP) screen-printed sensor was synthesized as a POC analyzer for the assay of the date rape drug "ketamine hydrochloride" in different matrices. Firstly, the screen-printed electrode substrate was modified electrochemically with polyaniline (PANI) as an ion-to-electron transducer interlayer to improve the potential signal stability. Secondly, core-shell MIP was prepared, the core consisting of silica nanoparticles prepared by Stober's method, while the MIP shell was synthesized onto silica nanoparticles surface by copolymerizing methacrylic acid functional monomer and the crossing agent; ethylene glycol dimethacrylate in the presence of ketamine as a template molecule. Finally, the core-shell MIP was incorporated into the PVC membrane as an ionophore and drop-casted over PANI modified screen-printed carbon electrode. The imprinting process and the morphology of MIP were examined using scanning electron microscopy, Fourier-transform infrared and X-ray photoelectron spectroscopic methods. The sensor exhibited a short response time within 3-5 s in a pH range (2.0-5.0). The potential profile indicated a linear relationship in a dynamic concentration range of 1.0 × 10^-6 M to 1.0 × 10^-2 M with a slope of 54.7 mV/decade. The sensor was employed to determine ketamine in biological matrices and beverages.

Ketamine and its metabolite 2R,6R-hydroxynorketamine promote ocular dominance plasticity and release tropomyosin-related kinase B from inhibitory control without reducing perineuronal nets enwrapping parvalbumin interneurons

Ketamine has been described as a fast-acting antidepressant, exerting effects in depressed patients and in preclinical models with a rapid onset of action. The typical antidepressant fluoxetine is known to induce plasticity in the adult rodent visual cortex, as assessed by a shift in ocular dominance, a classical model of brain plasticity, and a similar effect has been described for ketamine and its metabolite 2R,6R-hydroxynorketamine (R,R-HNK). Here, we demonstrate that ketamine (at 3 or 20 mg/kg) and R,R-HNK facilitated the shift in ocular dominance in monocularly deprived mice, after three injections, throughout the 7-day monocular deprivation regimen. Notably, the comparison between the treatments indicates a higher effect size of R,R-HNK compared with ketamine. Treatment with ketamine or R,R-HNK failed to influence the levels of perineuronal nets (PNNs) surrounding parvalbumin-positive interneurons. However, we observed in vitro that both ketamine and R,R-HNK are able to disrupt the tropomyosin-related kinase B (TRKB) interaction with the protein tyrosine phosphatase sigma (PTPσ), which upon binding to PNNs dephosphorylates TRKB. These results support a model where diverse drugs promote the reinstatement of juvenile-like plasticity by directly binding TRKB and releasing it from PTPσ regulation, without necessarily reducing PNNs deposits.

Ketamine preservative benzethonium chloride potentiates hippocampal synaptic transmission and binds neurotransmitter receptors and transporters

Benzethonium chloride (BZT) is an excipient used in numerous products including (R,S)-ketamine (ketamine) drug formulations for human and veterinary use. Emerging evidence indicates BZT is pharmacologically active. BZT may therefore contribute to some of the clinical or preclinical effects observed with ketamine. In the present study, we evaluated: (i) the affinity of BZT for neurotransmitter receptors and transporters, (ii) the effects of BZT on hippocampal synaptic transmission in vitro, and (iii) plasma and brain concentrations of BZT following its intraperitoneal administration to male CD1 mice. Radioligand binding assays determined the affinity of BZT for neurotransmitter targets. Effects of BZT on field excitatory postsynaptic potentials (fEPSPs) were established via electrophysiological recordings from slices collected from male C57BL/6J mice. The binding assays revealed that BZT binds to numerous receptors (e.g., σ2 Ki = 7 nM) and transporters (e.g., dopamine transporter Ki = 545 nM). Bath application of BZT potentiated hippocampal fEPSPs in mouse hippocampal slices with an EC50 of 2.03 nM. Following intraperitoneal administration, BZT was detected in the plasma, but not in the brain of mice. These data highlight that studies measuring peripheral endpoints or directly exposing systems, in vitro, intracerebroventricularly, or intracortically, to BZT-containing formulations should account for the direct effects of BZT. Our findings also suggest that earlier data attributing pharmacological effects to ketamine may be confounded by BZT and that additional investigation into the functional impact of BZT is warranted. This article is part of the Special Issue on 'Ketamine and its Metabolites'.