Acute and chronic effects of ketamine upon human memory: a review

Abnormal resting-state functional connectivity of the right anterior cingulate cortex in chronic ketamine users and its correlation with cognitive impairments

BACKGROUND

Chronic ketamine use leads to cognitive impairments, however, the neural mechanisms underpinning these impairments are still unclear.

AIMS

Many studies showed Anterior cingulate cortex (ACC)is strongly involved in cognition and drug addiction, as supported by our previous studies. The objective of this study was to assess the variations in resting-state functional connectivity (FC) changes in the right anterior cingulate cortex (ACC) of chronic ketamine users (CKUs) and their relationship with cognitive performance.

METHODS

The study enrolled 28 chronic ketamine users (CKUs) and 30 healthy controls (HCs). Resting-state functional magnetic resonance imaging (fMRI) data were gathered from both groups. Cognitive functions were evaluated using the MATRICS Consensus Cognitive Battery (MCCB).

RESULTS

CKUs demonstrated significantly poorer cognitive performance than HCs in various cognitive domains, including Visual Learning, Speed of Processing, Working Memory, and the composite score of MCCB. Group-level comparisons revealed that CKUs exhibited enhanced functional connectivity between the right ACC and the right postcentral gyrus (PCG) compared to HCs. There was a positive relationship between the connectivity of right ACC-PCG and reasoning and problem-solving score, but there was no significant association with the characteristics of ketamine use.

CONCLUSION

CKUs showed enhanced connectivity between the right ACC and the right PCG. This enhanced functional connectivity may indicate functional compensation for cognitive deficits in CKUs, especially for reasoning and problem-solving impairments in CKUs.

No negative effects of intra-abdominal bio-logger implantation under general anaesthesia on spatial cognition learning in a hibernator the edible dormouse

The effect of hibernation on cognitive capacities of individuals is not fully understood, as studies provide conflicting results. Most studies focus on behavioural observations without taking the physiological state of individuals to account. To mechanistically understand the effect of hibernation on the brain, physiological parameters need to be included. The implantation of bio-loggers can provide insights on i.e. body temperature without further manipulation of the animals. Surgeries and anaesthesia, however, can harm animals' health and cause cognitive dysfunction, potentially biasing data collected through bio-loggers. We investigated the effects of bio-logger implantation surgery on cognitive performance and learning, controlling for animal and study design characteristics. First, juvenile dormice successfully learned to solve a spatial cognition task using a vertical maze. Distance, transitions, velocity, and duration were measured as indicators for performance. After training, bio-loggers were implanted intra-abdominally under general anaesthesia. Animals were re-tested in the maze two weeks after. We found no effect of bio-logger implantation and surgery on performance. This study is the first to show spatial cognition learning in edible dormice and provides a full description of the peri-anaesthetic management and a protocol for bio-logger implantation surgery in dormice. Importantly, measures were taken to mitigate common anaesthetic complications that could lead to post-operative cognitive dysfunction and influence animal behaviour. By pairing physiological measurements through bio-logger implantation with behaviour and cognition measurements, future research will significantly advance the understanding on mechanisms of learning and behaviour.

Research trends and hotspots of ketamine from 2014 to 2023: a bibliometric analysis

Background

Despite this growing interest, there remains a lack of comprehensive and systematic bibliometric analyses of ketamine research. This study aimed to summarize the progress in ketamine research through bibliometric analysis, providing insights into the development and direction of the field.

Methods

Publications related to ketamine were retrieved from the Web of Science Core Collection (WoSCC) database on February 15, 2024. In conducting a comprehensive bibliometric analysis, a variety of bibliographic elements were meticulously collected to map the landscape of research within a specific field.

Results

Between January 1, 2014, and December 31, 2023, a total of 10,328 articles on ketamine research were published across 1,752 academic journals by 45,891 authors from 8,914 institutions in 128 countries. The publication volume has shown a steady increase over this period. The United States of America (USA) and the People's Republic of China lead in both publication and citation counts. The National Institute of Mental Health (NIMH) and Yale University emerge as the most active institutions in this research domain. Carlos Zarate of the NIH National Institute of Mental Health was noted for the highest number of significant publications and received the most co-citations. The analysis revealed key research themes including mechanism of action, adverse events, psychiatric applications, and perioperative implications.

Conclusion

This study provided comprehensive bibliometric and knowledge mapping analysis of the global ketamine research landscape, offering valuable insights into the trends, key contributors, and thematic focus areas within the field. By delineating the evolution of ketamine research, this study aims to guide future scholarly endeavors and enhance our understanding of ketamine's therapeutic potential.

Change in neurocognitive functioning in patients with treatment-resistant depression with serial intravenous ketamine infusions: The Bio-K multicenter trial

This nonrandomized, multicenter, open-label clinical trial explored the impact of intravenous (IV) ketamine on cognitive function in adults (n = 74) with treatment-resistant depression (TRD). Patients received three IV ketamine infusions during the acute phase and, if remitted, four additional infusions in the continuation phase (Mayo site). Cognitive assessments using the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) were conducted at baseline, end of the acute phase, and end of the continuation phase (Mayo site). Results showed a significant 53 % (39/74) remission rate in depression symptoms after the acute phase. In adjusted models, baseline language domain score was associated with a higher odd of remission (Odds Ratio, 1.09, 95 % CI = 1.03-1.17, p = 0.004) and greater improvement in MADRS at the end of the acute phase (β =-0.97; 95 % CI, -1.74 to -0.20; P = 0.02). The likelihood of remission was not significantly associated with baseline immediate or delayed memory, visuospatial/constructional, or attention scores. In the continuation phase, improvements in immediate and delayed memory and attention persisted, with additional gains in visuospatial and language domains. Limitations included an open-label design, potential practice effects, and ongoing psychotropic medication use. Overall, the study suggests cognitive improvement, not deterioration, associated with serial IV ketamine administrations for TRD. These findings encourage future studies with larger sample sizes and longer follow-up periods to examine any potential for deleterious effect with recurrent ketamine use for TRD. Trial Registration: ClinicalTrials.gov: NCT03156504.

Psychedelic Therapy: A Primer for Primary Care Clinicians-Ketamine

BACKGROUND

Ketamine, an arylcyclohexylamine dissociative anesthetic agent, has evolved into a versatile therapeutic. It has a rapid-onset, well-understood cardiovascular effects and a favorable safety profile in clinical use. Its enantiomeric compound, esketamine, was approved by the Food and Drug Administration in 2019 for both treatment-resistant depression and major depressive disorder with suicidal ideation.

AREAS OF UNCERTAINTY

Research indicates dose-dependent impacts on cognition, particularly affecting episodic and working memory following both acute administration and chronic use, albeit temporarily for the former and potentially persistent for the latter. Alongside acute risks to cardiovascular stability, ketamine use poses potential liver toxicity concerns, especially with prolonged or repeated exposure within short time frames. The drug's association with "ketamine cystitis," characterized by bladder inflammation, adds to its profile of physiological risks.

THERAPEUTIC ADVANCES

Data demonstrate a single intravenous infusion of ketamine exhibits antidepressant effects within hours (weighted effect size averages of depression scores (N = 518) following a single 0.5 mg/kg infusion of ketamine is d = 0.96 at 24 hours). Ketamine is also effective at reducing posttraumatic stress disorder (PTSD) symptom severity following repeated infusions (Clinician-Administered PTSD Scale scores: -11.88 points compared with midazolam control). Ketamine also decreased suicidal ideation in emergency settings (Scale for Suicidal Ideation scores: -4.96 compared with midazolam control). Through its opioid-sparing effect, ketamine has revolutionized postoperative pain management by reducing analgesic consumption and enhancing recovery.

LIMITATIONS

Many studies indicate that ketamine's therapeutic effects may subside within weeks. Repeated administrations, given multiple times per week, are often required to sustain decreases in suicidality and depressive symptoms.

CONCLUSIONS

Ketamine's comprehensive clinical profile, combined with its robust effects on depression, suicidal ideation, PTSD, chronic pain, and other psychiatric conditions, positions it as a substantial contender for transformative therapeutic application.

The impact of depressive symptoms on cognitive impairments in chronic ketamine users

BACKGROUND

Chronic ketamine use has been associated with cognitive impairments, while depressive symptoms are commonly observed in individuals using ketamine. However, the influence of depressive symptoms on cognitive impairments in chronic ketamine users remains unclear. This study aimed to examine the impact of depressive symptoms on cognitive function in this population.

METHODS

A cross-sectional study was conducted with a sample of chronic ketamine users. Participants underwent comprehensive cognitive assessments, including measures of attention, executive function, working memory, verbal and visual memory. Depressive symptoms were assessed using Beck Depression Inventory (BDI) scores. Multivariate analyses were utilized to compare the cognitive performance of individuals who use ketamine, both with and without depressive symptoms, as well as a control group, while controlling for relevant covariates.

RESULTS

The results revealed a significant negative impact of depressive symptoms on cognitive impairments, particularly in the domains of memory and executive function, among chronic ketamine users. The analysis of partial correlations revealed that among individuals who use ketamine and have depressive symptoms, those with higher levels of depressive symptoms demonstrated poorer cognitive performance compared to individuals with lower levels of depressive symptoms, controlling for potential confounding factors.

CONCLUSIONS

The findings suggest that depressive symptoms contribute to cognitive impairments, specifically in memory and executive function, in chronic ketamine users. Therefore, it is crucial to evaluate depressive symptoms when considering cognitive enhancement treatment for this population.

Sex-Specific Alterations in Spatial Memory and Hippocampal AKT-mTOR Signaling in Adult Mice Pre-exposed to Ketamine and/or Psychological Stress During Adolescence

Background

Ketamine (KET) is administered to manage major depression in adolescent patients. However, the long-term effects of juvenile KET exposure on memory-related tasks have not been thoroughly assessed. We examined whether exposure to KET, psychological stress, or both results in long-lasting alterations in spatial memory in C57BL/6 mice. Furthermore, we evaluated how KET and/or psychological stress history influenced hippocampal protein kinase B-mechanistic target of rapamycin (AKT-mTOR)-related signaling.

Methods

On postnatal day 35, male and female mice underwent vicarious defeat stress (VDS), a form of psychological stress that reduces sociability in both sexes, with or without KET exposure (20 mg/kg/day, postnatal days 35-44). In adulthood (postnatal day 70), mice were assessed for spatial memory performance on a water maze task or euthanized for hippocampal tissue collection.

Results

Juvenile pre-exposure to KET or VDS individually increased the latency (seconds) to locate the escape platform in adult male, but not female, mice. However, juvenile history of concomitant KET and VDS prevented memory impairment. Furthermore, individual KET or VDS pre-exposure, unlike their combined history, decreased hippocampal AKT-mTOR signaling in adult male mice. Conversely, KET pre-exposure alone increased AKT-mTOR in the hippocampus of adult female mice. Lastly, rapamycin-induced decreases of mTOR in naïve adult female mice induced spatial memory retrieval deficits, mimicking adult male mice with a history of exposure to VDS or KET.

Conclusions

Our preclinical model shows how KET treatment for the management of adolescent psychological stress-induced sequelae does not impair spatial memory later in life. However, juvenile recreational KET misuse, like psychological stress history, results in long-term spatial memory deficits and hippocampal AKT-mTOR signaling changes in a sex-specific manner.

Sex-Dependent Attentional Impairments in a Subchronic Ketamine Mouse Model for Schizophrenia

Background

The development of more effective treatments for schizophrenia targeting cognitive and negative symptoms has been limited, partly due to a disconnect between rodent models and human illness. Ketamine administration is widely used to model symptoms of schizophrenia in both humans and rodents. In mice, subchronic ketamine treatment reproduces key dopamine and glutamate dysfunction; however, it is unclear how this translates into behavioral changes reflecting positive, negative, and cognitive symptoms.

Methods

In male and female mice treated with either subchronic ketamine or saline, we assessed spontaneous and amphetamine-induced locomotor activity to measure behaviors relevant to positive symptoms, and used a touchscreen-based progressive ratio task of motivation and the rodent continuous performance test of attention to capture specific negative and cognitive symptoms, respectively. To explore neuronal changes underlying the behavioral effects of subchronic ketamine treatment, we quantified expression of the immediate early gene product, c-Fos, in key corticostriatal regions using immunofluorescence.

Results

We showed that spontaneous locomotor activity was unchanged in male and female subchronic ketamine-treated animals, and amphetamine-induced locomotor response was reduced. Subchronic ketamine treatment did not alter motivation in either male or female mice. In contrast, we identified a sex-specific effect of subchronic ketamine on attentional processing wherein female mice performed worse than control mice due to increased nonselective responding. Finally, we showed that subchronic ketamine treatment increased c-Fos expression in prefrontal cortical and striatal regions, consistent with a mechanism of widespread disinhibition of neuronal activity.

Conclusions

Our results highlight that the subchronic ketamine mouse model reproduces a subset of behavioral symptoms that are relevant for schizophrenia.

Exploratory evidence for differences in GABAergic regulation of auditory processing in autism spectrum disorder

Altered reactivity and responses to auditory input are core to the diagnosis of autism spectrum disorder (ASD). Preclinical models implicate ϒ-aminobutyric acid (GABA) in this process. However, the link between GABA and auditory processing in humans (with or without ASD) is largely correlational. As part of a study of potential biosignatures of GABA function in ASD to inform future clinical trials, we evaluated the role of GABA in auditory repetition suppression in 66 adults (n = 28 with ASD). Neurophysiological responses (temporal and frequency domains) to repetitive standard tones and novel deviants presented in an oddball paradigm were compared after double-blind, randomized administration of placebo, 15 or 30 mg of arbaclofen (STX209), a GABA type B (GABAB) receptor agonist. We first established that temporal mismatch negativity was comparable between participants with ASD and those with typical development (TD). Next, we showed that temporal and spectral responses to repetitive standards were suppressed relative to responses to deviants in the two groups, but suppression was significantly weaker in individuals with ASD at baseline. Arbaclofen reversed weaker suppression of spectral responses in ASD but disrupted suppression in TD. A post hoc analysis showed that arbaclofen-elicited shift in suppression was correlated with autistic symptomatology measured using the Autism Quotient across the entire group, though not in the smaller sample of the ASD and TD group when examined separately. Thus, our results confirm: GABAergic dysfunction contributes to the neurophysiology of auditory sensory processing alterations in ASD, and can be modulated by targeting GABAB activity. These GABA-dependent sensory differences may be upstream of more complex autistic phenotypes.

Alterations of neural activity in the prefrontal cortex associated with deficits in working memory performance

Working memory (WM), a core cognitive function, enables the temporary holding and manipulation of information in mind to support ongoing behavior. Neurophysiological recordings conducted in nonhuman primates have revealed neural correlates of this process in a network of higher-order cortical regions, particularly the prefrontal cortex (PFC). Here, we review the circuit mechanisms and functional importance of WM-related activity in these areas. Recent neurophysiological data indicates that the absence of these neural correlates at different stages of WM is accompanied by distinct behavioral deficits, which are characteristic of various disease states/normal aging and which we review here. Finally, we discuss emerging evidence of electrical stimulation ameliorating these WM deficits in both humans and non-human primates. These results are important for a basic understanding of the neural mechanisms supporting WM, as well as for translational efforts to developing therapies capable of enhancing healthy WM ability or restoring WM from dysfunction.

Ketamine evoked disruption of entorhinal and hippocampal spatial maps

Ketamine, a rapid-acting anesthetic and acute antidepressant, carries undesirable spatial cognition side effects including out-of-body experiences and spatial memory impairments. The neural substrates that underlie these alterations in spatial cognition however, remain incompletely understood. Here, we used electrophysiology and calcium imaging to examine ketamine's impacts on the medial entorhinal cortex and hippocampus, which contain neurons that encode an animal's spatial position, as mice navigated virtual reality and real world environments. Ketamine acutely increased firing rates, degraded cell-pair temporal firing-rate relationships, and altered oscillations, leading to longer-term remapping of spatial representations. In the reciprocally connected hippocampus, the activity of neurons that encode the position of the animal was suppressed after ketamine administration. Together, these findings demonstrate ketamine-induced dysfunction of the MEC-hippocampal circuit at the single cell, local-circuit population, and network levels, connecting previously demonstrated physiological effects of ketamine on spatial cognition to alterations in the spatial navigation circuit.

Application of Ketamine in Pain Management and the Underlying Mechanism

Since ketamine was approved by the FDA as an intravenous anesthetic, it has been in clinical use for more than 50 years. Apart from its anesthetic effects, ketamine is one of the few intravenous anesthetics with potent analgesic properties. As part of the effort to develop pain management, renewed interest has focused on the use of ketamine for the treatment of acute and chronic pain. Ketamine is commonly used to treat various kinds of chronic pain syndromes and is also applied to control perioperative pain and reduce the consumption of postoperative analgesics. However, its precise mechanisms of action remain mysterious for a large part. Despite extensive research in the field, the mechanism of ketamine is still unclear. Its analgesic effect appears to be largely mediated by blockade of NMDARs, but opioid, GABA, and monoaminergic system seem to partly participate in the pain transmission procedure. Its metabolites also have an analgesic effect, which may prolong pain relief. More recently, the antidepressant effect of ketamine has been considered to reduce pain-related aversion to relieve chronic pain. Overall, the analgesic mechanism of ketamine seems to be a complex combination of multiple factors. Due to its potent analgesic properties, ketamine is an analgesic with great clinical application prospects. Exploring the precise mechanism of action of ketamine will help guide clinical medication and confirm indications for ketamine analgesia. This review aims to list the application of ketamine in pain management and discuss its analgesic mechanism.

The acute effects of psychoactive drugs on emotional episodic memory encoding, consolidation, and retrieval: A comprehensive review

Psychoactive drugs modulate learning and emotional processes in ways that could impact their recreational and medical use. Recent work has revealed how drugs impact different stages of processing emotional episodic memories, specifically encoding (forming memories), consolidation (stabilizing memories), and retrieval (accessing memories). Drugs administered before encoding may preferentially impair (e.g., GABAA sedatives including alcohol and benzodiazepines, Δ9-tetrahydrocannabinol or THC, ketamine), enhance (e.g., dextroamphetamine and dextromethamphetamine), or both impair and enhance (i.e., ± 3,4-methylenedioxymethylamphetamine or MDMA) emotionally negative and positive compared to neutral memories. GABAA sedatives administered immediately post-encoding (during consolidation) can preferentially enhance emotional memories, though this selectivity may decline or even reverse (i.e., preferential enhancement of neutral memories) as the delay between encoding and retrieval increases. Finally, retrieving memories under the effects of THC, dextroamphetamine, MDMA, and perhaps GABAA sedatives distorts memory, with potentially greater selectively for emotional (especially positive) memories. We review these effects, propose neural mechanisms, discuss methodological considerations for future work, and speculate how drug effects on emotional episodic memory may contribute to drug use and abuse.

Age, Dose, and Locomotion: Decoding Vulnerability to Ketamine in C57BL/6J and BALB/c Mice

Ketamine has been abused as a psychedelic agent and causes diverse neurobehavioral changes. Adolescence is a critical developmental stage but vulnerable to substances and environmental stimuli. Growing evidence shows that ketamine affects glutamatergic neurotransmission, which is important for memory storage, addiction, and psychosis. To explore diverse biological responses, this study was designed to assess ketamine sensitivity in mice of different ages and strains. Male C57BL/6J and BALB/c mice were studied in adolescence and adulthood separately. An open field test assessed motor behavioral changes. After a 30-min baseline habituation, mice were injected with ketamine (0, 25, and 50 mg/kg), and their locomotion was measured for 60 min. Following ketamine injection, the travelled distance and speed significantly increased in C57BL/6J mice between both age groups (p < 0.01), but not in BALB/c mice. The pattern of hyperlocomotion showed that mice were delayed at the higher dose (50 mg/kg) compared to the lower dose (25 mg/kg) of ketamine treatment. Ketamine accentuated locomotor activation in adolescent C57BL/6J mice compared to adults, but not in the BALB/c strain. Here, we show that ketamine-induced locomotor behavior is modulated by dose and age. The discrepancy of neurobehaviors in the two strains of mice indicates that sensitivity to ketamine is biologically determined. This study suggests that individual vulnerability to ketamine's pharmacological responses varies biologically.

The Effects of Acute and Repeated Administration of Ketamine on Memory, Behavior, and Plasma Corticosterone Levels in Female Mice

Ketamine is an anesthetic drug that has recently been approved for the treatment of treatment-resistant depression. Females are diagnosed with Major Depressive Disorder at higher rates than males, yet most of the pre-clinical research on ketamine has been conducted in male subjects. Additionally, the literature on the acute and long-term behavioral and cognitive effects of ketamine shows conflicting results. It is important to examine the acute and long-term cognitive and behavioral effects of ketamine exposure at lower sub-anesthetic doses, as the recreational use of the drug at higher doses is associated with cognitive and memory impairments. The current study examined the effects of acute and repeated ketamine exposure on anxiety-like behavior, novel object recognition memory, depression-like behavior, and plasma corticosterone levels in 20 adult female C57BL/6J mice. Mice were exposed acutely or repeatedly for 10 consecutive days to saline or 15 mg/kg ketamine and behavior was measured in the open field test, novel object recognition test, and the Porsolt forced swim test. Plasma corticosterone levels were measured following behavioral testing. Acute ketamine exposure decreased locomotor activity and increased anxiety-like behavior in the open field test compared to controls, while repeated ketamine exposure impaired memory in the novel object recognition test. There were no effects of acute or repeated ketamine exposure on depression-like behavior in the Porsolt forced swim test or on plasma corticosterone levels. These findings suggest that a subanesthetic dose of ketamine alters behavior and cognition in female mice and the effects are dependent on the duration of exposure.

Ketamine evoked disruption of entorhinal and hippocampal spatial maps

Ketamine, a rapid-acting anesthetic and acute antidepressant, carries undesirable spatial cognition side effects including out-of-body experiences and spatial memory impairments. The neural substrates that underlie these alterations in spatial cognition however, remain incompletely understood. Here, we used electrophysiology and calcium imaging to examine ketamine's impacts on the medial entorhinal cortex and hippocampus, which contain neurons that encode an animal's spatial position, as mice navigated virtual reality and real world environments. Ketamine induced an acute disruption and long-term re-organization of entorhinal spatial representations. This acute ketamine-induced disruption reflected increased excitatory neuron firing rates and degradation of cell-pair temporal firing rate relationships. In the reciprocally connected hippocampus, the activity of neurons that encode the position of the animal was suppressed after ketamine administration. Together, these findings point to disruption in the spatial coding properties of the entorhinal-hippocampal circuit as a potential neural substrate for ketamine-induced changes in spatial cognition.

Decrease in gamma-band auditory steady-state response in patients with treatment-resistant schizophrenia

BACKGROUND

Thirty percent of patients with schizophrenia do not respond to non-clozapine antipsychotics and are termed treatment-resistant schizophrenia (TRS). The 40-Hz auditory steady-state response (ASSR) is a well-known to be reduced in patients with schizophrenia compared to healthy controls (HCs), suggesting impaired gamma oscillation in schizophrenia. Given no ASSR study on TRS, we aimed to examine the neurophysiological basis of TRS employing 40-Hz ASSR paradigm.

METHOD

We compared ASSR measures among HCs, patients with non-TRS, and patients with TRS. TRS criteria were defined by a score of 4 or higher on two items of the Positive and Negative Syndrome Scale (PANSS) positive symptoms despite standard antipsychotic treatment. Participants were examined for ASSR with 40-Hz click-train stimulus, and then time-frequency analysis was performed to calculate evoked power and phase-locking factor (PLF) of 40-Hz ASSR.

RESULTS

A total of 79 participants were included: 27 patients with TRS (PANSS = 92.6 ± 15.8); 27 patients with non-TRS (PANSS = 63.3 ± 14.7); and 25 HCs. Evoked power in 40-Hz ASSR was lower in the TRS group than in the HC group (F_2,79 = 8.37, p = 0.015; TRS vs. HCs: p = 0.012, d = 1.1) while no differences in PLF were found between the groups.

CONCLUSION

These results suggest that glutamatergic and GABAergic neurophysiological dysfunctions are involved in the pathophysiology of TRS. Our findings warrant more comprehensive and longitudinal studies for deep phenotyping of TRS.

The thalamus in psychosis spectrum disorder

Psychosis spectrum disorder (PSD) affects 1% of the world population and results in a lifetime of chronic disability, causing devastating personal and economic consequences. Developing new treatments for PSD remains a challenge, particularly those that target its core cognitive deficits. A key barrier to progress is the tenuous link between the basic neurobiological understanding of PSD and its clinical phenomenology. In this perspective, we focus on a key opportunity that combines innovations in non-invasive human neuroimaging with basic insights into thalamic regulation of functional cortical connectivity. The thalamus is an evolutionary conserved region that forms forebrain-wide functional loops critical for the transmission of external inputs as well as the construction and update of internal models. We discuss our perspective across four lines of evidence: First, we articulate how PSD symptomatology may arise from a faulty network organization at the macroscopic circuit level with the thalamus playing a central coordinating role. Second, we discuss how recent animal work has mechanistically clarified the properties of thalamic circuits relevant to regulating cortical dynamics and cognitive function more generally. Third, we present human neuroimaging evidence in support of thalamic alterations in PSD, and propose that a similar "thalamocortical dysconnectivity" seen in pharmacological imaging (under ketamine, LSD and THC) in healthy individuals may link this circuit phenotype to the common set of symptoms in idiopathic and drug-induced psychosis. Lastly, we synthesize animal and human work, and lay out a translational path for biomarker and therapeutic development.

Ketamine Inhalation Alters Behavior and Lower Urinary Tract Function in Mice

We aimed to evaluate behavioral and lower urinary tract changes in mice using a novel ketamine inhalation model mimicking human ketamine abusers and compare the results to those obtained using a ketamine intraperitoneal injection model. C57BL/6N mice were placed in a transparent acrylic observation cage connected to an ultrasonic nebulizer producing ketamine (KI) or saline (SI) fog. The mice were given KI or SI fog twice a week for three months. In another experiment arm, the mice were given intraperitoneal ketamine injections (KP) or saline injections (SP) twice a week for three months. The presence of urine ketamine (>100 ng/mL) was determined using a quick test kit. Locomotor activity was recorded by video using the open field test. Lower urinary tract function was assessed using urine spots, cystometry and histology. KI and KP mice crossed the center more frequently and traveled farther than SI and SP mice. Only KI mice, however, demonstrated popcorn-like jumping, and frequent center crossing. Detrusor overactivity, reduced cystometric bladder capacity, and denuded mucosa were observed in both KI and KP mice. Ketamine inhalation induces behavioral and lower urinary tract changes in mice that are comparable to intraperitoneal ketamine injections.

Acute effects of ketamine and esketamine on cognition in healthy subjects: A meta-analysis

BACKGROUND

Impairment in cognition is frequently associated with acute ketamine administration. However, some questions remain unanswered as to which deficits are most prominent and what variables modulate these effects.

METHODS

A literature search yielded 56 experimental studies of acute ketamine administration that assessed cognition in 1041 healthy volunteers. A multivariate meta-analysis was performed, and effect sizes were estimated for eleven cognitive domains: attention, executive function, response inhibition, social cognition, speed of processing, verbal / language, verbal learning, verbal memory, visual learning & memory, visuospatial abilities, and working memory.

RESULTS

There were small-to-moderate impairments across all cognitive domains. Deficits in verbal learning / memory were most prominent, whereas response inhibition was the least affected. Meta-regression analysis revealed that the negative effects of ketamine on cognition are dependent on infusion dose and plasma level, but unaffected by enantiomer type, route of administration, sex or age. A publication bias was observed.

DISCUSSION

Acute ketamine broadly impairs cognition across all domains among healthy individuals. Verbal learning and memory figures most prominently in cognitive impairment elicited by acute ketamine administration.

Neurobiological, behavioral, and cognitive effects of ketamine in adolescents: A review of human and pre-clinical research

S-ketamine is approved for treatment-resistant patients with depression and adult patients with suicide behavior. While ketamine is therapeutically beneficial in adults, there is a dearth of research on the effects of ketamine on adolescent brain function and behavior. In this review we summarize the current literature on the neurobiological and behavioral effects of adolescent ketamine exposure in preclinical animal models and humans. A search of PubMed was conducted using pre-defined criteria, resulting in the evaluation of 406 articles. A total of 39 animal studies and 7 human studies met the selection criteria. The included studies examined the effects of ketamine exposure during adolescence and excluded studies on ketamine use for pain or anesthesia and ketamine as a model of schizophrenia. Pre-clinical animal models of adolescent ketamine exposure show ketamine-induced neurotoxicity and apoptosis, and changes in locomotor activity, social behaviors, anxiety- and depression-like behaviors, and memory. There is variability in the results, and differences in ketamine dose and length of exposure appears to influence the results. Ketamine reduces symptoms of depression and anxiety and improves mood in human adolescents. Much of the literature on adolescent ketamine exposure examines the effects in males, with more limited research in females. Relatively little research has focused on adolescent ketamine exposure. Despite its effectiveness for mitigating symptoms of depression, adolescent ketamine exposure can disrupt memory and other behaviors and have deleterious effects on brain function. Further research is warranted to better define doses and dosing paradigms that are beneficial without unintended side effects in adolescence.

Ketamine plus Alcohol: What We Know and What We Can Expect about This

Drug abuse has become a public health concern. The misuse of ketamine, a psychedelic substance, has increased worldwide. In addition, the co-abuse with alcohol is frequently identified among misusers. Considering that ketamine and alcohol share several pharmacological targets, we hypothesize that the consumption of both psychoactive substances may synergically intensify the toxicological consequences, both under the effect of drugs available in body systems and during withdrawal. The aim of this review is to examine the toxicological mechanisms related to ketamine plus ethanol co-abuse, as well the consequences on cardiorespiratory, digestive, urinary, and central nervous systems. Furthermore, we provide a comprehensive discussion about the probable sites of shared molecular mechanisms that may elicit additional hazardous effects. Finally, we highlight the gaps of knowledge in this area, which deserves further research.

Is Multimodal Anesthesia Effecting Postoperative Nausea and Vomiting in Laparoscopic Cholecystectomy?

Background: Multimodal anesthesia represents a technique that can improve analgesia and lower the occurrence of opioid side effects in the postoperative period, such as postoperative nausea and vomiting (PONV). It can be achieved by providing different types of medication during the intraoperative period which can decrease the need for opioids. PONV happens more often in patients who have received large amounts of opioids during laparoscopic cholecystectomy. In this study, our aim was to observe the occurrence of PONV between three different groups of patients who received lidocaine, ketamine and magnesium sulfate in combination with fentanyl in the intraoperative period. We also observed any additional nausea and vomiting in the three groups as well as the amount of fentanyl given to these groups during operation. Materials and methods: 120 patients aged 20-65 years old were included in this randomized and prospective study, ASA classification 1 and 2, scheduled for laparoscopic cholecystectomy. Patients were classified into three groups randomly: Group 1 (lidocaine group-LG), these patients received lidocaine at 1 mg/kg during induction to general anesthesia and 2 mg/kg/h after intubation in continuous intravenous infusion; Group 2 (ketamine group-KG) these patients received ketamine at 0.5 mg/kg during induction to general anesthesia; and Group 3 (magnesium group-MG) these patients received magnesium sulfate at 1.5 gr/hr as a continuous intravenous infusion after intubation. In all three groups, patients additionally received bolus doses of fentanyl. Postoperative nausea and vomiting were monitored in all three groups at 1, 4, 8, 12, and 24 hours after surgery as a primary objective, and if patients had complainant of vomiting, they were treated with 10 mg of metoclopramid. Between the five control time points, additional nausea and vomiting was recorded as well, as a secondary objective. The third objective was to measure of the total amount of fentanyl given in the intraoperative period. Results: Patients from the lidocaine group experienced less PONV and they received less fentanyl compared to patients of ketamine and magnesium groups. Patients from the ketamine group had more nausea than other groups. In the magnesium group, the rate of vomiting was higher, and they received higher amounts of fentanyl during surgery. Additional nausea and vomiting occurred in 3 patients in the LG, 2 in the KG, and 3 in the MG between the five control time points. The patients from the magnesium group received the highest dose of fentanyl during surgery (307.50 ± 130.4), followed by the patients from the ketamine group (292.50 ± 60.5), and then patients from the lidocaine group (258.75 ± 60.9). The doses of fentanyl that patients received during surgery in all three groups were not statistically significant. Conclusion: Multimodal anesthesia has been shown to lower PONV 24 hours after laparoscopic cholecystectomy and can lower need for opioids during laparoscopic cholecystectomy.

Dopaminergic dysfunction and excitatory/inhibitory imbalance in treatment-resistant schizophrenia and novel neuromodulatory treatment

Antipsychotic drugs are the mainstay in the treatment of schizophrenia. However, one-third of patients do not show adequate improvement in positive symptoms with non-clozapine antipsychotics. Additionally, approximately half of them show poor response to clozapine, electroconvulsive therapy, or other augmentation strategies. However, the development of novel treatment for these conditions is difficult due to the complex and heterogenous pathophysiology of treatment-resistant schizophrenia (TRS). Therefore, this review provides key findings, potential treatments, and a roadmap for future research in this area. First, we review the neurobiological pathophysiology of TRS, particularly the dopaminergic, glutamatergic, and GABAergic pathways. Next, the limitations of existing and promising treatments are presented. Specifically, this article focuses on the therapeutic potential of neuromodulation, including electroconvulsive therapy, repetitive transcranial magnetic stimulation, transcranial direct current stimulation, and deep brain stimulation. Finally, we propose multivariate analyses that integrate various perspectives of the pathogenesis, such as dopaminergic dysfunction and excitatory/inhibitory imbalance, thereby elucidating the heterogeneity of TRS that could not be obtained by conventional statistics. These analyses can in turn lead to a precision medicine approach with closed-loop neuromodulation targeting the detected pathophysiology of TRS.

Translational control by ketamine and its implications for comorbid cognitive deficits in depressive disorders

Ketamine has shown antidepressant effects in patients with major depressive disorder (MDD) resistant to first-line treatments and approved for use in this patient population. Ketamine induces several forms of synaptic plasticity, which are proposed to underlie its antidepressant effects. However, the molecular mechanism of action directly responsible for ketamine's antidepressant effects remains under active investigation. It was recently demonstrated that the effectors of the mammalian target of rapamycin complex 1 (mTORC1) signalling pathway, namely, eukaryotic initiation factor 4E (eIF4E) binding proteins 1 and 2 (4E-BP1 and 4E-BP2), are central in mediating ketamine-induced synaptic plasticity and behavioural antidepressant-like effect. 4E-BPs are a family of messenger ribonucleic acid (mRNA) translation repressors inactivated by mTORC1. We observed that their expression in inhibitory interneurons mediates ketamine's effects in the forced swim and novelty suppressed feeding tests and the long-lasting inhibition of GABAergic neurotransmission in the hippocampus. In addition, another effector pathway that regulates translation elongation downstream of mTORC1, the eukaryotic elongation factor 2 kinase (eEF2K), has been implicated in ketamine's behavioural effects. We will discuss how ketamine's rapid antidepressant effect depends on the activation of neuronal mRNA translation through 4E-BP1/2 and eEF2K. Furthermore, given that these pathways also regulate cognitive functions, we will discuss the evidence of ketamine's effect on cognitive function in MDD. Overall, the data accrued from pre-clinical research have implicated the mRNA translation pathways in treating mood symptoms of MDD. However, it is yet unclear whether the pro-cognitive potential of subanesthetic ketamine in rodents also engages these pathways and whether such an effect is consistently observed in the treatment-resistant MDD population.

Ketamine use disorder: preclinical, clinical, and neuroimaging evidence to support proposed mechanisms of actions

Ketamine, a noncompetitive NMDA receptor antagonist, has been exclusively used as an anesthetic in medicine and has led to new insights into the pathophysiology of neuropsychiatric disorders. Clinical studies have shown that low subanesthetic doses of ketamine produce antidepressant effects for individuals with depression. However, its use as a treatment for psychiatric disorders has been limited due to its reinforcing effects and high potential for diversion and misuse. Preclinical studies have focused on understanding the molecular mechanisms underlying ketamine's antidepressant effects, but a precise mechanism had yet to be elucidated. Here we review different hypotheses for ketamine's mechanism of action including the direct inhibition and disinhibition of NMDA receptors, AMPAR activation, and heightened activation of monoaminergic systems. The proposed mechanisms are not mutually exclusive, and their combined influence may exert the observed structural and functional neural impairments. Long term use of ketamine induces brain structural, functional impairments, and neurodevelopmental effects in both rodents and humans. Its misuse has increased rapidly in the past 20 years and is one of the most common addictive drugs used in Asia. The proposed mechanisms of action and supporting neuroimaging data allow for the development of tools to identify 'biotypes' of ketamine use disorder (KUD) using machine learning approaches, which could inform intervention and treatment.

Brain Changes Associated With Long-Term Ketamine Abuse, A Systematic Review

Recently, the abuse of ketamine has soared. Therefore, it is of great importance to study its potential risks. The effects of prolonged ketamine on the brain can be observationally studied in chronic recreational users. We performed a systematic review of studies reporting functional and structural brain changes after repeated ketamine abuse. We searched the following electronic databases: Medline, Embase and PsycINFO We screened 11,438 records and 16 met inclusion criteria, totaling 440 chronic recreational ketamine users (2–9.7 years; mean use 2.4 g/day), 259 drug-free controls and 44 poly-drug controls. Long-term recreational ketamine use was associated with lower gray matter volume and less white matter integrity, lower functional thalamocortical and corticocortical connectivity. The observed differences in both structural and functional neuroanatomy between ketamine users and controls may explain some of its long-term cognitive and psychiatric side effects, such as memory impairment and executive functioning. Given the effect that long-term ketamine exposure may yield, an effort should be made to curb its abuse.

Schizophrenia-like endurable behavioral and neuroadaptive changes induced by ketamine administration involve Angiotensin II AT1 receptor

Schizophrenia is a chronic disease affecting 1% worldwide population, of which 30% are refractory to the available treatments: thus, searching for new pharmacological targets is imperative. The acute and repeated ketamine administration are validated preclinical models that recreate the behavioral and neurochemical features of this pathology, including the parvalbumin-expressing interneurons dysfunction. Angiotensin II, through AT₁ receptors (AT₁-R), modulates the dopaminergic and GABAergic neurotransmission. We evaluated the AT₁-R role in the long-term neuronal activation and behavioral alterations induced by repeated ketamine administration. Adult male Wistar rats received AT₁-R antagonist candesartan/vehicle (days 1-10) and ketamine/saline (days 6-10). After 14 days of drug-free, neuronal activation and behavioral analysis were performed. Locomotor activity, social interaction and novel object recognition tests were assessed at basal conditions or after ketamine challenge. Immunostaining for c-Fos, GAD67 and parvalbumin were assessed after ketamine challenge in cingulate, insular, piriform, perirhinal, and entorhinal cortices, striatum, and hippocampus. Additionally, to evaluate the AT₁-R involvement in acute ketamine psychotomimetic effects, the same behavioral tests were performed after 6 days of daily-candesartan and a single-ketamine administration. We found that ketamine-induced long-lasting schizophrenia-like behavioral alterations, and regional-dependent neuronal activation changes, involving the GABAergic neurotransmission system and the parvalbumin-expressing interneurons, were AT₁-R-dependent. The AT₁-R were not involved in the acute ketamine psychotomimetic effects. These results add new evidence to the wide spectrum of action of ketamine and strengthen the AT₁-R involvement in endurable alterations induced by psychostimulants administration, previously proposed by our group, as well as their preponderant role in the development of psychiatric pathologies.

Neurocognitive effects of repeated ketamine infusion treatments in patients with treatment resistant depression: a retrospective chart review

BACKGROUND

Ketamine has emerged as a rapid-acting antidepressant in treatment-resistant depression (TRD) increasingly used in non-research, clinical settings. Few studies, however, have examined neurocognitive effects of repeated racemic ketamine infusion treatments in patients with TRD. In an effort to identify potential effects after serial infusions, we conducted a retrospective chart review to identify statistically significant changes in cognition in patient undergoing serial intravenous infusions; concomitantly, we examined baseline cognition as potential predictor of anti-depressant potential.

METHODS

Twenty-two patients with TRD were examined after they finished the induction phase of 8-10 repeated intravenous ketamine infusions and completed the assessments of their depressive symptoms (measured by the 16-item Quick Inventory of Depressive Symptomatology-Self Report Scale: QIDS-SR16) and cognitive function (measured by the Montreal Cognitive Assessment: MoCA) before the first and the last ketamine treatments.

RESULTS

Repeated ketamine infusions administered through an escalating dose protocol with 8-10 infusion sessions produced a 47.2% reduction response in depression; there was no evidence of impairment as reflected in MoCA testing. There was a moderate association between baseline cognition and antidepressant response with a Pearson correlation of 0.453.

CONCLUSION

In this naturalistic sample of patients with TRD in our clinical service, repeated ketamine infusions significantly decreased depression symptoms without impairing cognitive performance. The baseline cognition may positively predict antidepressant responses of repeated ketamine treatment.

Clinical and behavior characteristics of individuals who used ketamine

This study aims to depict and compare clinical characteristics and risk behavior among groups of individuals using ketamine, polydrugs or smoking cigarette. A total of 185 drug-using participants and 49 smokers participated in this study. A cross-sectional interview was used to collect information on demographics, drug- and sex-related behaviors, HIV serostatus, lower urinary tract symptoms (LUTS), behavioral dispositions. N-back memory test was used to measure short-term memory. Result shows that 10 participants (5.41%) were HIV positive and 14 (7.57%) having LUTS. Individuals with ketamine and polydrugs use have significantly worse drug-related problem than cigarette smokers. Compared to cigarette smokers and ketamine users, individuals with polydrug users scored significantly higher on impulsivity measures. Cigarette smokers performed significantly better than the other two groups on the memory tests. A few patients had been infected with HIV and diagnosed with LUTS. Findings support that memory on short term recalls of patients with ketamine use might be impaired. Study findings warrants the necessarily of further study on influences of using ketamine.

Progress and Pitfalls in Developing Agents to Treat Neurocognitive Deficits Associated with Schizophrenia

Cognitive impairments associated with schizophrenia (CIAS) represent a central element of the symptomatology of this severe mental disorder. CIAS substantially determine the disease prognosis and hardly, if at all, respond to treatment with currently available antipsychotics. Remarkably, all drugs presently approved for the treatment of schizophrenia are, to varying degrees, dopamine D₂/D₃ receptor blockers. In turn, rapidly growing evidence suggests the immense significance of systems other than the dopaminergic system in the genesis of CIAS. Accordingly, current efforts addressing the unmet needs of patients with schizophrenia are primarily based on interventions in other non-dopaminergic systems. In this review article, we provide a brief overview of the available evidence on the importance of specific systems in the development of CIAS. In addition, we describe the promising targets for the development of new drugs that have been used so far. In doing so, we present the most important candidates that have been investigated in the field of the specific systems in recent years and present a summary of the results available at the time of drafting this review (May 2022), as well as the currently ongoing studies.

Neuropsychiatric disorders: An immunological perspective

Neuropsychiatric diseases have traditionally been studied from brain, and mind-centric perspectives. However, mounting epidemiological and clinical evidence shows a strong correlation of neuropsychiatric manifestations with immune system activation, suggesting a likely mechanistic interaction between the immune and nervous systems in mediating neuropsychiatric disease. Indeed, immune mediators such as cytokines, antibodies, and complement proteins have been shown to affect various cellular members of the central nervous system in multitudinous ways, such as by modulating neuronal firing rates, inducing cellular apoptosis, or triggering synaptic pruning. These observations have in turn led to the exciting development of clinical therapies aiming to harness this neuro-immune interaction for the treatment of neuropsychiatric disease and symptoms. Besides the clinic, important theoretical fundamentals can be drawn from the immune system and applied to our understanding of the brain and neuropsychiatric disease. These new frameworks could lead to novel insights in the field and further potentiate the development of future therapies to treat neuropsychiatric disease.

Ketamine for psychotic depression: An overview of the glutamatergic system and ketamine's mechanisms associated with antidepressant and psychotomimetic effects

Approximately 0.35-1% of the general population is afflicted with psychotic depression at some time in their life. Psychotic depression is a subtype of major depressive disorder characterized by mood congruent hallucinations and/or delusions. Patients with psychotic depression often represent the most severe cases, with high relapse and mortality rate. Although treatment guidelines recommend a combination of antidepressants and antipsychotics or electroconvulsive therapy, most patients subsequently relapse due to treatment resistance. Furthermore, with the concern of antipsychotic drug's side effects (e.g., tardive dyskinesia), there is a need for an alternative pharmacotherapy for psychotic depression. Recently, several case studies demonstrated that treatment with ketamine not only ameliorated mood, but also improved psychotic symptoms in patients with treatment-resistant depression and psychotic features. However, the safety of ketamine in these patients is controversial since ketamine is known to induce psychotomimetic and dissociative effects. Additionally, the efficacy and safety of ketamine in patients with psychotic depression has not been established as most clinical trials have excluded these persons due to the theorized risk of aggravating psychotic symptoms. Notwithstanding, it is not established empirically that ketamine treatment in psychotic depression would predictably amplify psychotic symptoms and/or overall illness presentation. Future trials evaluating ketamine in depression should include patients with psychotic features to inform whether ketamine is safe and effective in this subpopulation.

Ketamine as a Treatment for Anorexia Nervosa: A Narrative Review

Anorexia nervosa (AN) is a highly complex disorder to treat, especially in severe and enduring cases. Whilst the precise aetiology of the disorder is uncertain, malnutrition and weight loss can contribute to reductions in grey and white matter of the brain, impairments in neuroplasticity and neurogenesis and difficulties with cognitive flexibility, memory and learning. Depression is highly comorbid in AN and may be a barrier to recovery. However, traditional antidepressants are often ineffective in alleviating depressive symptoms in underweight patients with AN. There is an urgent need for new treatment approaches for AN. This review gives a conceptual overview for the treatment of AN with ketamine. Ketamine has rapid antidepressant effects, which are hypothesised to occur via increases in glutamate, with sequelae including increased neuroplasticity, neurogenesis and synaptogenesis. This article provides an overview of the use of ketamine for common psychiatric comorbidities of AN and discusses particular safety concerns and side effects. Potential avenues for future research and specific methodological considerations are explored. Overall, there appears to be ample theoretical background, via several potential mechanisms, that warrant the exploration of ketamine as a treatment for adults with AN.

(R,S)-ketamine and (2R,6R)-hydroxynorketamine differentially affect memory as a function of dosing frequency

A single subanesthetic infusion of ketamine can rapidly alleviate symptoms of treatment-resistant major depression. Since repeated administration is required to sustain symptom remission, it is important to characterize the potential untoward effects of prolonged ketamine exposure. While studies suggest that ketamine can alter cognitive function, it is unclear to what extent these effects are modulated by the frequency or chronicity of treatment. To test this, male and female adolescent (postnatal day [PD] 35) and adult (PD 60) BALB/c mice were treated for four consecutive weeks, either daily or thrice-weekly, with (R,S)-ketamine (30 mg/kg, intraperitoneal) or its biologically active metabolite, (2R,6R)-hydroxynorketamine (HNK; 30 mg/kg, intraperitoneal). Following drug cessation, memory performance was assessed in three operationally distinct tasks: (1) novel object recognition to assess explicit memory, (2) Y-maze to assess working memory, and (3) passive avoidance to assess implicit memory. While drug exposure did not influence working memory performance, thrice-weekly ketamine and daily (2R,6R)-HNK led to explicit memory impairment in novel object recognition independent of sex or age of exposure. Daily (2R,6R)-HNK impaired implicit memory in the passive-avoidance task whereas thrice-weekly (2R,6R)-HNK tended to improve it. These differential effects on explicit and implicit memory possibly reflect the unique mechanisms by which ketamine and (2R,6R)-HNK alter the functional integrity of neural circuits that subserve these distinct cognitive domains, a topic of clinical and mechanistic relevance to their antidepressant actions. Our findings also provide additional support for the importance of dosing frequency in establishing the cognitive effects of repeated ketamine exposure.

Recreational ketamine-related deaths notified to the National Programme on Substance Abuse Deaths, England, 1997-2019

BACKGROUND

Ketamine is a phencyclidine derivative with dissociative anaesthetic properties. Increasing numbers of individuals in England take ketamine recreationally. Information on deaths arising from such use in England is presented.

METHODS

Cases were extracted on 31 January 2020 from the National Programme on Substance Abuse Deaths database, based on text searches of the cause of death, coroner's verdict and positive toxicology results for the terms 'ketamine' or 'norketamine'.

FINDINGS

During 1997-2005, there were <5 deaths p.a. in which ketamine was implicated. Numbers increased until 2009 (21), plateauing until 2016; thereafter, deaths have risen to about 30 p.a. Decedents' characteristics (N = 283): male 84.1%, mean age 31.2 (SD 10.0) years, employed 56.5%, drug use history 79.6% and living with others 60.3%. Ketamine was detected with other substances in most cases. Main (74.6%) underlying cause of death was accidental poisoning. Ketamine may have impaired judgement in other cases.

CONCLUSIONS

Although controlled, recreational ketamine use and related fatalities continue to increase. Consumers need to be more aware of the potentially fatal risks they face.

An Update to Aircrew Grounding Periods After Ketamine Use

INTRODUCTION: Ketamine is a rapidly acting general anesthetic which is globally used in surgical analgesia, as well as in the management of pain. It is also used as a recreational drug. Because of its widespread use in surgical settings, the use of this drug presents an aeromedical problemin addition, of course, to the underlying condition for which it has been used. The literature around the mechanisms and side effects of ketamine is reasonably mature, and it is possible to make fairly dependable risk management decisions about return to flying based on the information available. Accordingly, following ketamine use it is recommended that aviators be grounded for 48 h following Aviation Medical Examiner review. If review is unavailable, the aviator should be grounded for 1 wk to allow sufficient time to identify the existence of prolonged side effects, such as psychomimetic effects or cognitive changes.Boyd NL, Navathe PD. An update to aircrew grounding periods after ketamine use. Aerosp Med Hum Perform. 2021; 92(8):670-675.

A qualitative and quantitative account of patient's experiences of ketamine and its antidepressant properties

BACKGROUND

Ketamine is central to one of the most rapidly growing areas of neuroscientific research into novel treatments for depression. Limited research has indicated that the psychedelic properties of ketamine may play a role in its antidepressant effects.

AIM

The aim of the current study was to explore the psychedelic experiences and sustained impact of ketamine in major depressive disorder.

METHODS

In the current study, ketamine (0.44 mg/kg) was administered to 32 volunteers with major depressive disorder in a crossover design with the active-placebo remifentanil, in a magnetic resonance imaging (MRI) environment. The 11-dimension altered states of consciousness questionnaire and individual qualitative interviews were used to capture the acute psychedelic experience. The Montgomery-Asberg Depression Rating Scale and further interviewing explored lasting effects. The second qualitative interview took place ⩾3 weeks post-ketamine.

RESULTS

Greater antidepressant response (reduction in Montgomery-Asberg Depression Rating Scale at 24 h) correlated with the 11-dimension altered states of consciousness dimensions: spirituality, experience of unity, and insight. The first qualitative interview revealed that all participants experienced perceptual changes. Additional themes emerged including loss of control and emotional and mood changes. The final interview showed evidence of a psychedelic afterglow, and changes to perspective on life, people, and problems, as well as changes to how participants felt about their depression and treatments.

CONCLUSIONS

The current study provides preliminary evidence for a role of the psychedelic experience and afterglow in ketamine's antidepressant properties. Reflexive thematic analysis provided a wealth of information on participants' experience of the study and demonstrated the psychedelic properties of ketamine are not fully captured by commonly used questionnaires.

First-time offenders for recreational ketamine use under a new penalty system in Taiwan: incidence, recidivism and mortality in national cohorts from 2009 to 2017

BACKGROUND AND AIMS

Ketamine has become a new recreational drug of choice among young people in parts of Asia. Using national databases in Taiwan, this study aimed to (1) examine the yearly trend in the ketamine offence rate over time; (2) estimate the 3-year risk of drug-related re-offence and its correlates among the first-time offenders; and (3) estimate the 3-year standardized mortality ratio (SMR) among the first-time offenders.

DESIGN, SETTING AND PARTICIPANTS

Retrospective cohort studies of offenders for recreational ketamine use in a penalty system initiated in 2009. Offenders for recreational ketamine use were identified from the Administrative Penalty System for Schedule III/IV Substances database from 2009 to 2017, and the re-offence rate and mortality among first-time offenders were assessed via record-linkage within the database as well as with both the criminal drug offence database and the national mortality database. The cohort from 2009 to 2016 (n = 39 178) was used for the recidivism analysis and the cohort from 2009 to 2013 (n = 25 357) was used for the 3-year SMR analysis.

MEASUREMENTS

Recidivism was estimated using survival analysis of the event as re-arrest for using ketamine, more serious illicit drugs (Schedules I/II), or any illicit drugs (ketamine or Schedules I/II). SMRs were estimated for overall and cause-specific death within 3 years after the first offence for ketamine use.

FINDINGS

The age-standardized rates for both prevalent (1.38 per 1000) and first-time offenders (0.65 per 1000) peaked in 2013 and then decreased steadily. The 3-year risk of re-offence was 33.85% [95% confidence interval (CI) = 33.23-34.47%) for ketamine use and 39.52% (95% CI = 39.00-40.04%) for any illicit drug use. These first-time offenders had an SMR of 4.9 (95% CI = 4.3-5.4) for overall mortality, 2.1 (95% CI = 1.6-2.7) for natural deaths and 7.6 (95% CI = 6.7-8.6) for unnatural deaths.

CONCLUSIONS

Recreational ketamine use in Taiwan appears to lead not only to high risk for drug-related re-offence but also to excess mortality.

Methoxphenidine (MXP) induced abnormalities: Addictive and schizophrenia-related behaviours based on an imbalance of neurochemicals in the brain

BACKGROUND AND PURPOSE

Methoxphenidine is a dissociative-based novel psychoactive designer drug. Although fatal accidents from methoxphenidine abuse have been reported, recreational use of the drug continues. We aim to provide scientific supportfor legal regulation of recreational abuse of methoxphenidine by demonstrating its the pharmacological action.

EXPERIMENTAL APPROACH

Addictive potential of methoxphenidine was examined using intravenous self-administration test with rats and conditioned place preference test with mice. Further, a series of behavioural tests (open field test, elevated plus maze test, novel object recognition test, social interaction test and tail suspension test) performed to assess whether methoxphenidine caused schizophrenia-related symptoms in mice. Additionally, neurotransmitter enzyme-linked immunosorbent assay and western blot were used to confirm methoxphenidine-induced neurochemical changes in specific brain regions related to abnormal behaviours.

KEY RESULTS

Methoxphenidine caused addictive behaviours via reinforcing and rewarding effects. Consistently, methoxphenidine induced over-activation of dopamine pathways in the nuclear accumbens, indicating activation of the brain reward circuit. Also, methoxphenidine caused all categories of schizophrenia-related symptoms, including positive symptoms (hyperactivity, impulsivity), negative symptoms (anxiety, social withdrawal, depression) and cognitive impairment. Consistently, methoxphenidine led to the disruption of the hippocampal-prefrontal cortex pathway that is considered to be pathological involved in schizophrenia.

CONCLUSIONS AND IMPLICATIONS

We demonastrate that methoxphenidine causes addictive and schizophrenia-like behaviours and induces neurochemical changes in brain regions associated with these behaviours. We propose that methoxphenidine could be used in developing useful animal disease models and that it also requires legal restrictions on its recreational use.

Intranasal Ketamine for Depression in Adults: A Systematic Review and Meta-Analysis of Randomized, Double-Blind, Placebo-Controlled Trials

Background

There is growing interest in glutamatergic agents as a treatment for depression, especially intranasal ketamine, which has become a hot topic in recent years. We aim to assess the efficacy and safety of intranasal ketamine in the treatment of major depressive disorder (MDD), especially treatment-resistant depression (TRD).

Methods

We searched Medline, EMBASE, and the Cochrane Library until April 1, 2020 to identify double-blind, randomized controlled trials with allocation concealment evaluating intranasal ketamine in major depressive episodes. Clinical remission, response, and depressive symptoms were extracted by two independent raters. The outcome measures were Montgomery–Asberg Depression Rating Scale (MADRS) score improved from baseline, clinical response and remission, dissociative symptoms, and common adverse events. The analyses employed a random-effects model.

Results

Data were synthesized from five randomized controlled trials (RCTs) employing an intranasal esketamine and one RCT employing intranasal ketamine, representing 840 subjects in parallel arms, and 18 subjects in cross-over designs (n = 858 with MDD, n = 792 with TRD). The weighted mean difference of MADRS score was observed to decrease by 6.16 (95% CI 4.44–7.88) in 2–4 h, 9.96 (95% CI 8.97–10.95) in 24 h, and 4.09 (95% CI 2.18–6.00) in 28 day. The pooled relative risk (RR) was 3.55 (95% CI 1.5–8.38, z = 2.89, and p < 0.001) for clinical remission and 3.22 (95% CI 1.85–5.61, z = 4.14, and p < 0.001) for clinical response at 24 h, while the pooled RR was 1.7 (95% CI 1.28–2.24, z = 3.72, and p < 0.001) for clinical remission and 1.48 (95% CI 1.17–1.86, z = 3.28, and p < 0.001) for clinical response at 28 day. Intranasal ketamine was associated with the occurrence of transient dissociative symptoms and common adverse events, but no persistent psychoses or affective switches.

Conclusion

Our meta-analysis suggests that repeated intranasal ketamine conducted a fast-onset antidepression effect in unipolar depression, while the mild and transient adverse effects were acceptable.

Systematic Review Registration

PROSPERO, CRD42020196856.

Neurochemistry of Visual Attention

Visual attention is the cognitive process that mediates the selection of important information from the environment. This selection is usually controlled by bottom-up and top-down attentional biasing. Since for most humans vision is the dominant sense, visual attention is critically important for higher-order cognitive functions and related deficits are a core symptom of many neuropsychiatric and neurological disorders. Here, we summarize the importance and relative contributions of different neuromodulators and neurotransmitters to the neural mechanisms of top-down and bottom-up attentional control. We will not only review the roles of widely accepted neuromodulators, such as acetylcholine, dopamine and noradrenaline, but also the contributions of other modulatory substances. In doing so, we hope to shed some light on the current understanding of the role of neurochemistry in shaping neuron properties contributing to the allocation of attention in the visual field.

Ketamine for depression

Over the last two decades, the dissociative anaesthetic agent ketamine, an uncompetitive N-Methyl-D-Aspartate (NMDA) receptor antagonist, has emerged as a novel therapy for treatment-resistant depression (TRD), demonstrating rapid and robust antidepressant effects within hours of administration. Ketamine is a racemic mixture composed of equal amounts of (S)-ketamine and (R)-ketamine. Although ketamine currently remains an off-label treatment for TRD, an (S)-ketamine nasal spray has been approved for use in TRD (in conjunction with an oral antidepressant) in the United States and Europe. Despite the promise of ketamine, key challenges including how to maintain response, concerns regarding short and long-term side-effects and the potential for abuse remain. This review provides an overview of the history of ketamine, its use in psychiatry and its basic pharmacology. The clinical evidence for the use of ketamine in depression and potential adverse effects associated with treatment are summarized. A synopsis of some of the putative neurobiological mechanisms underlying ketamine's rapid-acting antidepressant effects is provided before finally outlining future research directions, including the need to identify biomarkers for predicting response and treatment targets that may be used in the development of next-generation rapid-acting antidepressants that may lack ketamine's side-effects or abuse potential.

Synthesizing the Evidence for Ketamine and Esketamine in Treatment-Resistant Depression: An International Expert Opinion on the Available Evidence and Implementation

Replicated international studies have underscored the human and societal costs associated with major depressive disorder. Despite the proven efficacy of monoamine-based antidepressants in major depression, the majority of treated individuals fail to achieve full syndromal and functional recovery with the index and subsequent pharmacological treatments. Ketamine and esketamine represent pharmacologically novel treatment avenues for adults with treatment-resistant depression. In addition to providing hope to affected persons, these agents represent the first non-monoaminergic agents with proven rapid-onset efficacy in major depressive disorder. Nevertheless, concerns remain about the safety and tolerability of ketamine and esketamine in mood disorders. Moreover, there is uncertainty about the appropriate position of these agents in treatment algorithms, their comparative effectiveness, and the appropriate setting, infrastructure, and personnel required for their competent and safe implementation. In this article, an international group of mood disorder experts provides a synthesis of the literature with respect to the efficacy, safety, and tolerability of ketamine and esketamine in adults with treatment-resistant depression. The authors also provide guidance for the implementation of these agents in clinical practice, with particular attention to practice parameters at point of care. Areas of consensus and future research vistas are discussed.

Hazy memories in the courtroom: A review of alcohol and other drug effects on false memory and suggestibility

Alcohol and other psychoactive drugs are oftentimes implicated in legal cases. A pertinent question herein is whether such substances might adversely affect testimonies of victims, eyewitnesses, or suspects by propelling the formation of false memory and increasing susceptibility to suggestion. In the current review, we amassed all available evidence on the effects of intoxication on false memory formation and suggestibility, including the substances alcohol, benzodiazepines, cannabis, stimulants, hallucinogens, and antipsychotics. Our review indicated that alcohol and cannabis under certain conditions increased the susceptibility to false memories and/or suggestion with effect sizes ranging from medium to large. When intoxicated during an event, alcohol is most likely to increase this susceptibility at high intoxication levels or after a delay, whereas cannabis exerts detrimental effects during acute intoxication but not necessarily once sober. For other substances, ecologically valid research separating different memory phases is needed. Overall, differences between substances regarding false memory effects exist, suggesting that a nuanced approach is needed when dealing with intoxicated individuals in a legal context.

Contributions of animal models of cognitive disorders to neuropsychopharmacology

Cognitive disorders and symptoms are key features of many mental and neurological diseases, with a large spectrum of impaired domains. Because of their possible evolution and detrimental functioning impact, they are a major pharmacological target for both symptomatic and disease-modifier drugs, while few cognitive enhancers have been marketed with an insufficient efficiency. It explains the need to model these cognitive disorders beyond the modelization of mental or neurological diseases themselves. According to the experimental strategy used to induce cognitive impairment, three categories of models have been identified: neurotransmission-driven models; pathophysiology-driven models; environment-driven models. These three categories of models reflect different levels of integration of endogenous and exogenous mechanisms underlying cognitive disorders in humans. Their comprehensive knowledge and illustration of their pharmacological modulation could help to propose a renewing strategy of drug development in central nervous system (CNS) field at a time when the academic and industrial invest seems to be declining despite the medical and social burden of brain diseases.

Effects of Ketamine on Learning and Memory in the Hippocampus of Rats through ERK, CREB, and Arc

Ketamine has become a popular recreational drug due to its neuronal anesthesia effect and low price. The process of learning and memory is part of the distinctive high-level neural activities in animals. We investigated the effects of subanesthetic and anesthetic doses of ketamine on the learning and memory-related signal transduction mechanisms. We used the Morris water maze test to execute rats' learning and memory ability and detected changes of Arc mRNA and Arc, cAMP-response element-binding protein (CREB), phospho-CREB (p-CREB), extracellular signal-regulated kinase (ERK), and phospho-ERK (p-ERK) protein expression in the hippocampus 10 min and 24 h after administration. Ten min after ketamine injection, the Arc gene and the protein expression levels increased in all groups; p-ERK only increased in the chronic subanesthetic dose group. After 24 h, the Arc gene and the protein expression levels of the subanesthetic dose group increased, but those of the chronic subanesthetic dose group and anesthetic dose group decreased. However, p-ERK increased in all groups. A chronic subanesthetic dose of ketamine could increase learning and memory ability through ERK, CREB, and Arc in a short time, and the high body temperature after the subanesthetic dose of ketamine injection was the main factor leading to changes in Arc. The subanesthetic dose of ketamine regulated learning and memory through ERK, CREB, and ARC 24 h after injection.

Cognitive impairment in chronic ketamine abusers

BACKGROUND

The treatment of ketamine users is substantially challenged by high dropout rates, raising questions regarding contributing factors. A number of studies have highlighted the potential of greater focus on the clinical significance of cognitive impairments in ketamine users. The present study hypothesized that cognitive deficits would play a role in greater risk for treatment dropout in chronic ketamine users.

METHODS

Our study examined cognitive performance in the form of working memory, verbal memory, visual memory and executive function among chronic ketamine users who completed three-month treatment in residential detoxification centres (N = 165), those who dropped out prematurely (N = 121) and drug-free healthy controls (N = 111). The data collection was completed in Hong Kong among the East Asia population.

RESULTS

Compared to healthy controls, cognitive impairments were found in ketamine users, including in verbal/visual memory and executive function. Executive dysfunction was significantly associated with dropout in ketamine users within three months.

CONCLUSION

Our findings suggest that executive dysfunction may have clinical benefits in ketamine users admitted to residential treatment programmes.