Ketamine and phencyclidine: the good, the bad and the unexpected

KETAMINE: Neural- and network-level changes

Ketamine is a widely used clinical drug that has several functional and clinical applications, including its use as an anaesthetic, analgesic, anti-depressive, anti-suicidal agent, among others. Among its diverse behavioral effects, it influences short-term memory and induces psychedelic effects. At the neural level across different brain areas, it modulates neural firing rates, neural tuning, brain oscillations, and modularity, while promoting hypersynchrony and random connectivity between neurons. In our recent studies we demonstrated that topical application of ketamine on the visual cortex alters neural tuning and promotes vigorous connectivity between neurons by decreasing their firing variability. Here, we begin with a brief review of the literature, followed by results from our lab, where we synthesize a dendritic model of neural tuning and network changes following ketamine application. This model has potential implications for focused modulation of cortical networks in clinical settings. Finally, we identify current gaps in research and suggest directions for future studies, particularly emphasizing the need for more animal experiments to establish a platform for effective translation and synergistic therapies combining ketamine with other protocols such as training and adaptation. In summary, investigating ketamine's broader systemic effects, not only provides deeper insight into cognitive functions and consciousness but also paves the way to advance therapies for neuropsychiatric disorders.

A Behavioral and Electroencephalographic Study of Anesthetic State Induced by MK-801 Combined with Haloperidol, Ketamine and Riluzole in Mice

BACKGROUND

Ketamine is an intravenous anesthetic that acts as a channel blocker on the N-methyl- d -aspartate (NMDA) receptor, a glutamate receptor subtype. MK-801 is the most potent compound among noncompetitive NMDA receptor antagonists. Ketamine induces loss of the righting reflex (LORR) in rodents, which is one of the indicators of unconsciousness, whereas high doses of MK-801 produce ataxia, but not LORR. In contrast, we previously reported that MK-801 combined with a low dose of the dopamine receptor antagonist haloperidol-induced LORR in mice. To assess a neurophysiologically distinct brain state and demonstrate unconsciousness, electroencephalograms (EEG) need to be examined together with LORR. Therefore, we herein investigated EEG changes after the systemic administration of MK-801 alone or in combination with haloperidol, and compared them with those induced by ketamine, the glutamate release inhibitor riluzole, and the γ-aminobutyric acid type A receptor agonist propofol.

METHODS

All drugs were intraperitoneally administered to adult male ddY mice (n = 168). General anesthesia was evaluated based on the righting reflex test. Animals who exhibited no righting for more than 30 seconds were considered to have LORR. In a separate group of mice, EEG of the primary visual cortex was recorded before and after the administration of MK-801 (3.0 mg/kg) alone or in combination with haloperidol (0.2 mg/kg), ketamine (150 mg/kg), riluzole (30 mg/kg), or propofol (240 mg/kg). The waveforms recorded were analyzed using EEG power spectra and spectrograms.

RESULTS

The high dose of MK-801 alone did not induce LORR, whereas MK-801 combined with haloperidol produced LORR in a dose-dependent manner. Ketamine, riluzole, and propofol also dose-dependently induced LORR. In the EEG study, MK-801 alone induced a significant increase in δ power, while MK-801 plus haloperidol exerted similar effects on not only δ, but also θ and α power during LORR, suggesting that increases in δ, θ, and α power were necessary for LORR. The results obtained on MK-801 plus haloperidol were similar to those on ketamine in the behavioral and EEG studies, except for an increase in γ power by ketamine during LORR. Propofol significantly increased δ, θ, α, and β power during LORR. However, the EEG results obtained using riluzole, which produced a unique pattern of lower amplitude activity spanning most frequencies, markedly differed from those with the other drugs.

CONCLUSIONS

This study revealed differences in EEG changes induced by various sedatives. The results obtained on MK-801 alone and MK-801 plus haloperidol suggest the importance of dopamine transmission in maintaining the righting reflex.

[Psychedelic and dissociative agents in psychiatry: challenges in the treatment]

With the discovery of the antidepressive effects of ketamine and the increasing withdrawal of the pharmaceutical industry from the development of new psychotropic drugs, the psychiatric research into the clinical application of hallucinogens in psychiatry has literally blossomed in the last two decades. Promising results for various treatment approaches with psychedelic agents, such lysergic acid diethylamide (LSD) and psilocybin, and dissociative agents, such as ketamine and esketamine, have raised great hopes among researchers, clinicians and patients in recent years, so that there was already talk of a new era in psychiatry. As one of the first of these substances, in December 2019 intranasal esketamine was approved in the USA and the EU for the treatment of treatment-resistant depression and Switzerland followed in 2020. Recently, psilocybin was approved in Australia, Canada and Switzerland for compassionate use in exceptional cases for the treatment of depression, while large approval studies with various psychedelic agents are currently ongoing worldwide. The medical application of psychedelic agents and ketamine/esketamine is considered to be safe; however, as with all new forms of treatment it is of crucial importance that, in addition to the hopes, the specific challenges of these new treatment approaches must also be carefully considered and assessed. Excessive expectations and an insufficient risk-benefit estimation are detrimental to the patients and the reputation of the treating physician. Although a possible paradigm shift in the care of mental health is already being discussed, this review article consciously concentrates on the possible risks of treatment and the methodological weaknesses of the studies carried out so far.

Psychotropic Drugs Reemerging as Headache Medicines

Scientific and public attention on the therapeutic effects of psychedelics and other psychoactive compounds in headache disorders has recently grown. The use and reported therapeutic effects of such treatments have long been reported, though formal clinical trials are only recently taking place. When considering how these substances might be further studied and eventually applied, it is important to consider the specific headache disorder, the particular drug, and the mode of use. No singular protocol will be applicable across all headache disorders and drugs. In this leading article, the nuance required to consider the value of classic psychedelics, ketamine, and cannabinoids as headache medicines is presented.

Effects of association between resveratrol and ketamine on behavioral and biochemical analysis in mice

Resveratrol (3,5,4'-trihydroxy-trans-stilbene), a phenol commonly found in grapes and wine, has been associated as protective in experimental models involving alterations in different neurotransmitter systems. However, studies are reporting that resveratrol could have adverse effects. This study evaluated if the association of a low dose of ketamine and resveratrol could induce behavioral manifestations associated with biochemical alterations. Moreover, the effects of treatment with resveratrol and/or ketamine on monoamine oxidase (MAO) activity, oxidative stress markers, and IL-6 levels in the brain were also investigated. Male Swiss mice received a low dose of ketamine (20 mg/kg) for 14 consecutive days, and resveratrol (10, 30, or 100 mg/kg) from day 8 up to day 14 of the experimental period, intraperitoneally. Locomotor, stereotyped behavior, Y-maze, novel recognition object test (NORT), and social interaction were quantified as well as ex vivo analysis of MAO activity, IL-6 levels, and oxidative stress markers (TBARS and total thiol levels) in brain tissues. Ketamine per se reduced the number of bouts of stereotyped behavior on day 8 of the experimental period. Resveratrol per se reduced the locomotor and exploratory activity in the open field, the time of exploration of new objects in the NORT, MAO-A activity in the striatum and increased the IL-6 levels in the cortex. These effects were attenuated when the mice were co-treated with ketamine and resveratrol. There was a decrease in MAO-A activity in the cortex of mice treated with ketamine + resveratrol 100 mg/kg. No significant alterations were found in oxidative stress markers. Resveratrol does not appear to cause summative effects with ketamine on behavioral alterations. However, the effect of resveratrol per se, mainly on locomotor and exploratory activity, should be better investigated.

Esketamine: Less Drowsiness, More Analgesia

Racemic ketamine is a 1:1 mixture of 2 enantiomers that turn light in opposite direction: Dextrorotatory esketamine is approximately 4 times more affine for the N-methyl-D-aspartate (NMDA) receptor than levorotatory arketamine, which may explain why esketamine is about twice as potent as an analgesic and anesthetic as the racemate. Esketamine has attracted renewed interest in view of the opioid crisis, racemic ketamine's abuse, and esketamine's approval for expanded use. We evaluated the anesthesia literature concerning mental, cardiovascular, cerebral, and antinociceptive effects of esketamine published in English between 1980 and 2022. The review shows that esketamine and racemic ketamine are not "the same" at clinically equivalent analgesic and anesthetic dose: Psychomimetic effects seem to be essentially related to NMDA receptor blockade and esketamine is not devoid of unwanted mental impact. However, it probably involves less cholinergic inhibition. Cognitive disturbances during arousal, awakening, and recovery from the drug are less, and less pronounced with esketamine. The drug allows for an approximately 50% dose reduction in anesthesia and analgesia which goes along with a higher clearance and shorter recovery time as compared to racemic ketamine. In comparison of esketamine with placebo, esketamine shows cardiocirculatory stabilizing and neuroprotective effects which can be seen in anesthesia induction, cardiac surgery, and analgesia and sedation in brain injury. Evidence of esketamine's antinociceptive efficacy is inconsistent, although a recent meta-analysis reports improved pain relief after surgery in a study with short observation time. To better define esketamine's place, direct head-to-head comparison with the racemate at equi-analgesic/anesthetic dose is warranted.

A combined toxicokinetic and metabolic approach to investigate deschloro-N-ethylketamine exposure in a multidrug user

The use of new psychoactive substances derived from ketamine is rarely reported in France. A chronic GHB, 3-MMC, and methoxetamine consumer presented a loss of consciousness in a chemsex context and was referred to the intensive care unit with a rapid and favorable outcome. To investigate the chemicals responsible for the intoxication, a comprehensive analysis was conducted on the ten plasma samples collected over a 29.5-hour period, urine obtained upon admission, a 2-cm hair strand sample, and a seized crystal. These analyses were performed using liquid chromatography hyphenated to high resolution tandem mass spectrometry operating in targeted and untargeted modes. Additionally, analyses using gas chromatography coupled to mass spectrometry and nuclear magnetic resonance were conducted to probe the composition of the seized crystal. The molecular network-based approach was employed for data processing in non-targeted analyses. It allowed to confirm a multidrug exposure encompassing GHB, methyl-(aminopropyl)benzofuran (MAPB), (aminopropyl)benzofuran (APB), methylmethcathinone, chloromethcathinone, and a new psychoactive substance belonging to the arylcyclohexylamine family namely deschloro-N-ethyl-ketamine (O-PCE). Molecular network analysis facilitated the annotation of 27 O-PCE metabolites, including phase II compounds not previously reported. Plasma kinetics of O-PCE allowed the estimation of the elimination half-life of ∼5 hours. Kinetics of O-PCE metabolites was additionally characterized, possibly useful as surrogate biomarkers of consumption. We also observed marked alterations in lipid metabolism related to poly consumption of drugs. In conclusion, this case report provides a comprehensive analysis of exposure to O-PCE in a multidrug user including kinetic and metabolism data in human.

Synthesis and Structure-Activity Relationships for Glutamate Transporter Allosteric Modulators

Excitatory amino acid transporters (EAATs) are essential CNS proteins that regulate glutamate levels. Excess glutamate release and alteration in EAAT expression are associated with several CNS disorders. Previously, we identified positive allosteric modulators (PAM) of EAAT2, the main CNS transporter, and have demonstrated their neuroprotective properties in vitro. Herein, we report on the structure-activity relationships (SAR) for the analogs identified from virtual screening and from our medicinal chemistry campaign. This work identified several selective EAAT2 positive allosteric modulators (PAMs) such as compounds 4 (DA-023) and 40 (NA-014) from a library of analogs inspired by GT949, an early generation compound. This series also provides nonselective EAAT PAMs, EAAT inhibitors, and inactive compounds that may be useful for elucidating the mechanism of EAAT allosteric modulation.

Features of biliary tract diseases in ketamine abusers: a systematic review of case reports

BACKGROUND AND AIMS

Anesthesiologists prefer ketamine for certain surgeries due to its effectiveness as a non-competitive inhibitor of the N-methyl-D-aspartate receptor in the brain. Recently, this agent has also shown promise as an antidepressant. However, ketamine can cause hallucinogenic effects and is sometimes abused as an illicit drug. Ketamine abuse has been associated with liver and bile duct complications. This systematic study aims to better understand cholangiopathy in ketamine abusers by reviewing case reports.

METHODS AND MATERIAL

In this systematic review, a comprehensive literature search was conducted with the terms "biliary tract diseases" and "ketamine". Case reports and case series of adult patients with documented ketamine abuse and reported cholangiopathy or biliary tract disease were included. We extracted the data of relevant information and the results were reported through narrative synthesis and descriptive statistics.

RESULTS

A total of 48 studies were initially identified, and 11 studies were finally included in the review. The mean age of the patients was 25.88 years. Of the 17 patients, 64.7% were men. Symptoms often included abdominal pain, nausea, and vomiting. Most patients were discharged with improved symptoms and liver function. Common bile duct dilation and other findings were observed in imaging results and other diagnostic studies.

CONCLUSION

This review highlights the diverse presentations and diagnostic modalities used in ketamine-induced cholangiography. These patients tend to be young men with deranged liver function tests and abdominal pain, which should be taken into consideration. These patients often require a multidisciplinary approach in their management.

Exploring Novel Antidepressants Targeting G Protein-Coupled Receptors and Key Membrane Receptors Based on Molecular Structures

Major Depressive Disorder (MDD) is a complex mental disorder that involves alterations in signal transmission across multiple scales and structural abnormalities. The development of effective antidepressants (ADs) has been hindered by the dominance of monoamine hypothesis, resulting in slow progress. Traditional ADs have undesirable traits like delayed onset of action, limited efficacy, and severe side effects. Recently, two categories of fast-acting antidepressant compounds have surfaced, dissociative anesthetics S-ketamine and its metabolites, as well as psychedelics such as lysergic acid diethylamide (LSD). This has led to structural research and drug development of the receptors that they target. This review provides breakthroughs and achievements in the structure of depression-related receptors and novel ADs based on these. Cryo-electron microscopy (cryo-EM) has enabled researchers to identify the structures of membrane receptors, including the N-methyl-D-aspartate receptor (NMDAR) and the 5-hydroxytryptamine 2A (5-HT2A) receptor. These high-resolution structures can be used for the development of novel ADs using virtual drug screening (VDS). Moreover, the unique antidepressant effects of 5-HT1A receptors in various brain regions, and the pivotal roles of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) and tyrosine kinase receptor 2 (TrkB) in regulating synaptic plasticity, emphasize their potential as therapeutic targets. Using structural information, a series of highly selective ADs were designed based on the different role of receptors in MDD. These molecules have the favorable characteristics of rapid onset and low adverse drug reactions. This review offers researchers guidance and a methodological framework for the structure-based design of ADs.

Differential Effects of Aripiprazole on Electroencephalography-Recorded Gamma-Band Auditory Steady-State Response, Spontaneous Gamma Oscillations and Behavior in a Schizophrenia Rat Model

The available antipsychotics for schizophrenia (SZ) only reduce positive symptoms and do not significantly modify SZ neurobiology. This has raised the question of the robustness and translational value of methods employed during drug development. Electroencephalography (EEG)-based measures like evoked and spontaneous gamma oscillations are considered robust translational biomarkers as they can be recorded in both patients and animal models to probe a key mechanism underlying all SZ symptoms: the excitation/inhibition imbalance mediated by N-methyl-D-aspartate receptor (NMDAr) hypofunction. Understanding the effects of commercialized atypical antipsychotics on such measures could therefore contribute to developing better therapies for SZ. Yet, the effects of such drugs on these EEG readouts are unknown. Here, we studied the effect of the atypical antipsychotic aripiprazole on the gamma-band auditory steady-state response (ASSR), spontaneous gamma oscillations and behavioral features in a SZ rat model induced by the NMDAr antagonist MK-801. Interestingly, we found that aripiprazole could not normalize MK-801-induced abnormalities in ASSR, spontaneous gamma oscillations or social interaction while it still improved MK-801-induced hyperactivity. Suggesting that aripiprazole is unable to normalize electrophysiological features underlying SZ symptoms, our results might explain aripiprazole's inefficacy towards the social interaction deficit in our model but also its limited efficacy against social symptoms in patients.

In vitro and in vivo metabolism of 3-Methoxyeticyclidine in human liver microsomes, a zebrafish model, and two human urine samples based on liquid chromatography-high-resolution mass spectrometry

3-Methoxyeticyclidine (3-MeO-PCE), a phencyclidine-type substance, has a higher N-methyl-D-aspartate receptor binding affinity than phencyclidine and an involvement in fatal intoxication cases. The aim of this study was to identify new biomarkers and biotransformation pathways for 3-MeO-PCE. In vitro models were established using zebrafish and human liver microsomes for analysis of the phases I and II metabolites of 3-MeO-PCE by liquid chromatography-high-resolution mass spectrometry. Urine samples of known 3-MeO-PCE consumers in forensic cases were then subjected to analysis. Overall, 14 metabolites were identified in zebrafish and human liver microsomes, allowing postulation of the following metabolic pathways: hydroxylation, O-demethylation, N-dealkylation, dehydrogenation, combination, and glucuronidation or sulfation. 3-MeO-PCE and three metabolites (M2, M3, and M6) were detected in urine. We recommended M2 (the hydroxylation product) as a potential biomarker for documenting 3-MeO-PCE intake in clinical and forensic cases.

Influence of the dose of ketamine used on schizophrenia-like symptoms in mice: A correlation study with TH, GAD67, and PPAR-γ

Schizophrenia is a chronic, debilitating mental illness that has not yet been completely understood. In this study, we aimed to investigate the effects of different doses of ketamine, a non-competitive NMDA receptor antagonist, on the positive- and negative-like symptoms of schizophrenia. We also explored whether these effects are related to changes in the immunoreactivity of GAD67, TH, and PPAR-γ in brain structures. To conduct the study, male mice received ketamine (20-40 mg/kg) or its vehicle (0.9 % NaCl) intraperitoneally for 14 consecutive days. We quantified stereotyped behavior, the time of immobility in the forced swimming test (FST), and locomotor activity after 7 or 14 days. In addition, we performed ex vivo analysis of the immunoreactivity of GAD, TH, and PPAR-γ, in brain tissues after 14 days. The results showed that ketamine administration for 14 days increased the grooming time in the nose region at all tested doses. It also increased immobility in the FST at 30 mg/kg doses and decreased the number of rearing cycles during stereotyped behavior at 40 mg/kg. These behavioral effects were not associated with changes in locomotor activity. We did not observe any significant alterations regarding the immunoreactivity of brain proteins. However, we found that GAD and TH were positively correlated with the number of rearing during the stereotyped behavior at doses of 20 and 30 mg/kg ketamine, respectively. GAD was positively correlated with the number of rearing in the open field test at a dose of 20 mg/kg. TH was inversely correlated with immobility time in the FST at a dose of 30 mg/kg. PPAR-γ was inversely correlated with the number of bouts of stereotyped behavior at a dose of 40 mg/kg of ketamine. In conclusion, the behavioral alterations induced by ketamine in positive-like symptoms were reproduced with all doses tested and appear to depend on the modulatory effects of TH, GAD, and PPAR-γ. Conversely, negative-like symptoms were associated with a specific dose of ketamine.

MK-801 and cognitive functions: Investigating the behavioral effects of a non-competitive NMDA receptor antagonist

RATIONALE

MK-801 (dizocilpine) is a non-competitive NMDA receptor antagonist originally explored for anticonvulsant potential. Despite its original purpose, its amnestic properties led to the development of pivotal models of various cognitive impairments widely employed in research and greatly impacting scientific progress. MK-801 offers several advantages; however, it also presents drawbacks, including inducing dose-dependent hyperlocomotion or ambiguous effects on anxiety, which can impact the interpretation of behavioral research results.

OBJECTIVES

The present review attempts to summarize and discuss the effects of MK-801 on different types of memory and cognitive functions in animal studies.

RESULTS

A plethora of behavioral research suggests that MK-801 can detrimentally impact cognitive functions. The specific effect of this compound is influenced by variables including developmental stage, gender, species, strain, and, crucially, the administered dose. Notably, when considering the undesirable effects of MK-801, doses up to 0.1 mg/kg were found not to induce stereotypy or hyperlocomotion.

CONCLUSION

Dizocilpine continues to be of significant importance in preclinical research, facilitating the exploration of various procognitive therapeutic agents. However, given its potential undesirable effects, it is imperative to meticulously determine the appropriate dosages and conduct supplementary evaluations for any undesirable outcomes, which could complicate the interpretation of the findings.

Nicotine Exposure in a Phencyclidine-Induced Mice Model of Schizophrenia: Sex-Selective Medial Prefrontal Cortex Protein Markers of the Combined Insults in Adolescent Mice

Tobacco misuse as a comorbidity of schizophrenia is frequently established during adolescence. However, comorbidity markers are still missing. Here, the method of label-free proteomics was used to identify deregulated proteins in the medial prefrontal cortex (prelimbic and infralimbic) of male and female mice modelled to schizophrenia with a history of nicotine exposure during adolescence. Phencyclidine (PCP), used to model schizophrenia (SCHZ), was combined with an established model of nicotine minipump infusions (NIC). The combined insults led to worse outcomes than each insult separately when considering the absolute number of deregulated proteins and that of exclusively deregulated ones. Partially shared Reactome pathways between sexes and between PCP, NIC and PCPNIC groups indicate functional overlaps. Distinctively, proteins differentially expressed exclusively in PCPNIC mice reveal unique effects associated with the comorbidity model. Interactome maps of these proteins identified sex-selective subnetworks, within which some proteins stood out: for females, peptidyl-prolyl cis-trans isomerase (Fkbp1a) and heat shock 70 kDa protein 1B (Hspa1b), both components of the oxidative stress subnetwork, and gamma-enolase (Eno2), a component of the energy metabolism subnetwork; and for males, amphiphysin (Amph), a component of the synaptic transmission subnetwork. These are proposed to be further investigated and validated as markers of the combined insult during adolescence.

Structural insights into NMDA receptor pharmacology

N-methyl-d-aspartate receptors (NMDARs) comprise a subfamily of ionotropic glutamate receptors that form heterotetrameric ligand-gated ion channels and play fundamental roles in neuronal processes such as synaptic signaling and plasticity. Given their critical roles in brain function and their therapeutic importance, enormous research efforts have been devoted to elucidating the structure and function of these receptors and developing novel therapeutics. Recent studies have resolved the structures of NMDARs in multiple functional states, and have revealed the detailed gating mechanism, which was found to be distinct from that of other ionotropic glutamate receptors. This review provides a brief overview of the recent progress in understanding the structures of NMDARs and the mechanisms underlying their function, focusing on subtype-specific, ligand-induced conformational dynamics.

N-methyl-D-aspartate receptor hypofunction as a potential contributor to the progression and manifestation of many neurological disorders

N-methyl-D-aspartate receptors (NMDA) are glutamate-gated ion channels critical for synaptic transmission and plasticity. A slight variation of NMDAR expression and function can result in devastating consequences, and both hyperactivation and hypoactivation of NMDARs are detrimental to neural function. Compared to NMDAR hyperfunction, NMDAR hypofunction is widely implicated in many neurological disorders, such as intellectual disability, autism, schizophrenia, and age-related cognitive decline. Additionally, NMDAR hypofunction is associated with the progression and manifestation of these diseases. Here, we review the underlying mechanisms of NMDAR hypofunction in the progression of these neurological disorders and highlight that targeting NMDAR hypofunction is a promising therapeutic intervention in some neurological disorders.

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".

Maturation of GABAergic Synaptic Transmission From Neocortical Parvalbumin Interneurons Involves N-methyl-D-aspartate Receptor Recruitment of Cav2.1 Channels

N-methyl-D-aspartate receptor (NMDAR) hypofunction during brain development is likely to contribute to the manifestation of schizophrenia (SCZ) in young adulthood. The cellular targets of NMDAR hypofunction appear to be at least in part corticolimbic fast-spiking (FS) interneurons. However, functional alterations in parvalbumin (PV)-positive FS interneurons following NMDAR hypofunction are poorly understood. Paired patch-clamp recordings from murine cortical PV interneurons and pyramidal neurons revealed that genetic deletion of NMDAR subunit Grin1 in prospective PV interneurons before the second postnatal week impaired evoked- and synchronized-GABA release. Whereas intrinsic excitability and spiking characteristics were also disturbed by Grin1 deletion, neither restoring their excitability by K⁺ channel blockade nor increasing extracellular Ca²⁺ rescued the GABA release. GABA release was also insensitive to the Cav2.1 channel antagonist ω-agatoxin IVA. Heterozygous deletion of Cacna1a gene (encoding Cav2.1) in PV interneurons produced a similar GABA release phenotype as the Grin1 mutants. Treatment with the Cav2.1/2.2 channel agonist GV-58 augmented somatic Ca²⁺ currents and GABA release in Cacna1a-haploinsufficient PV interneurons, but failed to enhance GABA release in the Grin1-deleted PV interneurons. Taken together, our results suggest that Grin1 deletion in prospective PV interneurons impairs proper maturation of membrane excitability and Cav2.1-recruited evoked GABA release. This may increase synaptic excitatory/inhibitory ratio in principal neurons, contributing to the emergence of SCZ-like phenotypes.

The Roles of Glutamate Receptors and Their Antagonists in Status Epilepticus, Refractory Status Epilepticus, and Super-Refractory Status Epilepticus

Status epilepticus (SE) is a neurological emergency with a high mortality rate. When compared to chronic epilepsy, it is distinguished by the durability of seizures and frequent resistance to benzodiazepine (BZD). The Receptor Trafficking Hypothesis, which suggests that the downregulation of γ-Aminobutyric acid type A (GABAA) receptors, and upregulation of N-methyl-D-aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors play major roles in the establishment of SE is the most widely accepted hypothesis underlying BZD resistance. NMDA and AMPA are ionotropic glutamate receptor families that have important excitatory roles in the central nervous system (CNS). They are both essential in maintaining the normal function of the brain and are involved in a variety of neuropsychiatric diseases, including epilepsy. Based on animal and human studies, antagonists of NMDA and AMPA receptors have a significant impact in ending SE; albeit most of them are not yet approved to be in clinically therapeutic guidelines, due to their psychomimetic adverse effects. Although there is still a dearth of randomized, prospective research, NMDA antagonists such as ketamine, magnesium sulfate, and the AMPA antagonist, perampanel, are regarded to be reasonable optional adjuvant therapies in controlling SE, refractory SE (RSE) or super-refractory SE (SRSE), though there are still a lack of randomized, prospective studies. This review seeks to summarize and update knowledge on the SE development hypothesis, as well as clinical trials using NMDA and AMPA antagonists in animal and human studies of SE investigations.

The effect of lansoprazole on MK-801-induced schizophrenia-like behaviors in mice

As a heterogeneous disorder, schizophrenia is known to be associated with neuroinflammation. A recent study showed that several cytokines are higher in the plasma and cerebrospinal fluid of schizophrenia patients. Lansoprazole, a proton pump inhibitor used for treating erosive esophagitis, has been reported to reduce INF-γ-induced neurotoxicity and decrease inflammatory cytokines including IL-1β, IL-6, and TNF-α. These findings persuaded us to examine whether lansoprazole ameliorates schizophrenia-like symptoms. The schizophrenia mouse model was induced by the acute administration of MK-801, an NMDA receptor antagonist. Sensorimotor gating, Barnes maze, and social novelty preference tests were conducted to evaluate schizophrenia-like behaviors. We found that lansoprazole (0.3, 1, or 3 mg/kg) ameliorated sensorimotor gating deficits, spatial learning, and social deficits caused by MK-801 treatment (0.2 mg/kg). The catalepsy test, balance beam test, and rotarod test were performed to reveal the adverse effects of lansoprazole on motor coordination. The behavioral results indicated that lansoprazole did not result in any motor function deficits. Moreover, lansoprazole decreased inflammatory cytokines including IL-6 and TNF-α only in the cortex, but not in the hippocampus. Collectively, these results suggest that lansoprazole could be a potential candidate for treating schizophrenia patients who suffer from sensorimotor gating deficits or social disability without any motor-related adverse effects.

Esketamine and Psilocybin—The Comparison of Two Mind-Altering Agents in Depression Treatment: Systematic Review

This publication discusses two compounds belonging to the psychoactive substances group which are studied in the context of depression treatment—psilocybin and esketamine. The former is a naturally occurring psychedelic. The latter was invented in the laboratory exactly 60 years ago. Although the substances were controversial in the past, recent studies indicate the potential of those substances as novel antidepressant agents. The PubMed/MEDLINE database was used to identify articles for systematic review, using the following search terms: (depression) AND (psilocybin) OR (ketamine). From 617 items, only 12 articles were obtained in the final analyses. Three articles were devoted to psilocybin in depression treatment and nine to esketamine. In most studies, esketamine showed a significant reduction in both depressive symptoms and suicidal ideation shortly after intake and after a month of treatment compared to baseline and to standard-of-care antidepressant agents. Psilocybin’s antidepressive effects occurred one day after intake and after 6–7 weeks of treatment and were maintained for up to 6 or 8 months of follow-up. One study indicated that psilocybin’s effects are comparable with and may be superior to escitalopram treatment. Both esketamine and psilocybin demonstrated rapid and long-term effects in reducing depression symptoms and, after overcoming some limitations, may be considered as novel antidepressant agents in future.

Inhibition of NMDA receptors through a membrane-to-channel path

N-methyl-d-aspartate receptors (NMDARs) are transmembrane proteins that are activated by the neurotransmitter glutamate and are found at most excitatory vertebrate synapses. NMDAR channel blockers, an antagonist class of broad pharmacological and clinical significance, inhibit by occluding the NMDAR ion channel. A vast literature demonstrates that NMDAR channel blockers, including MK-801, phencyclidine, ketamine, and the Alzheimer’s disease drug memantine, can bind and unbind only when the NMDAR channel is open. Here we use electrophysiological recordings from transfected tsA201 cells and cultured neurons, NMDAR structural modeling, and custom-synthesized compounds to show that NMDAR channel blockers can enter the channel through two routes: the well-known hydrophilic path from extracellular solution to channel through the open channel gate, and also a hydrophobic path from plasma membrane to channel through a gated fenestration (“membrane-to-channel inhibition” (MCI)). Our demonstration that ligand-gated channels are subject to MCI, as are voltage-gated channels, highlights the broad expression of this inhibitory mechanism.

Wilcox et al. (2022) show that NMDA receptor channel blockers, some of which are clinically important drugs, can access their binding site via 2 routes: a well-known path from the extracellular solution, and another path through the plasma membrane.

THE effect of general anesthetics on genetic absence epilepsy in WAG/Rij rats

AIM

To establish safe and straightforward anesthesia used in experiments, we examined the effect of ketamine, ketamine/xylazine, urethane, chloral hydrate, pentobarbital, isoflurane, dexmedetomidine, and dexmedetomidine/ketamine on epileptiform activity in genetic absence epilepsy (WAG\Rij) rats.

MATERIALS AND METHOD

Sixty-three male WAG/Rij rats weighing (170-190 g) were used. Tripolar electrodes were inserted into the skull. After ECoG activities were recorded for each animal for 2 hours as controls, , the anesthetic substances were administered and the recording continued for another 2 hours. All the anesthetic substances were administered intraperitoneally except isoflurane, which was administered by inhalation.The PowerLab system was used for electrophysiological activity recording and analysis.

RESULTS

The administration of ketamine (90 mg/kg), ketamine/xylazine (90/10 mg/kg), urethane (1.25 g/kg), chloral hydrate (175 mg/kg), pentobarbital (50-90 mg/kg), isoflurane (induction 5%, maintaining 3-4%), dexmedetomidine (0.5-1 mg/kg), and dexmedetomidine/ketamine (50/90 mg/kg), significantly decreased the total number of SWD, the total number of spikes, and the SWD duration (p < 0,05). The mean duration of SWD was not affected in pentobarbital (50-90 mg/kg), isoflurane (induction 5%, maintaining 3-4%), dexmedetomidine (0.5-1 mg/kg), and Dexmedetomidine/ketamine (50/90 mg/kg) groups (p > 0.05). Time scale showed a significant decrease in the total number of SWD in the first 20 minutes (P < 0.001) for all groups except dexmedetomidine (0.5-1 mg/kg), and dexmedetomidine/ketamine (50/90 mg/kg) groups (p > 0.05).

CONCLUSION

The anesthetics we used significantly reduced the epileptiform activity immediately after the administration, except dexmedetomidine and dexmedetomidine/ketamine groups, so we recommend using dexmedetomidine and Dexmedetomidine/ketamine in electrophysiological studies accompanied by anesthetics.

The abuse liability of ketamine: A scoping review of preclinical and clinical studies

While ketamine has been used clinically over the past decades, it has only been recently shown to be a promising therapy for treatment-resistant depression (TRD). However, ketamine and related dissociative agents may also be misused recreationally, creating significant concerns for abuse liability when prescribed for depression. Although the abuse potential of ketamine is widely recognized, there is limited evidence on the differential abuse liability of ketamine enantiomers, (S)-ketamine and (R)-ketamine. The current scoping review aims to summarize the extant literature on the abuse liability of (R,S)-ketamine and the enantiomers. A systematic search was conducted on the Embase, Medline, and APA PsycInfo databases from 1947 to July 29, 2021. Clinical and preclinical studies that assessed the abuse potential of (R,S)-ketamine, (S)-ketamine, and (R)-ketamine were screened and assessed for eligibility by two independent reviewers. A total of 65 eligible studies were identified; 55 were preclinical studies and 10 were clinical studies. Only 4 preclinical studies evaluated the abuse liability of ketamine enantiomers. Available preclinical evidence suggests that (R,S)-ketamine and (S)-ketamine have greater risk for abuse compared to (R)-ketamine. (R)-ketamine, at the antidepressant-relevant doses in rodents, appears to be safe with minimal liability for abuse. Although the abuse potential of (R,S)-ketamine is well-established in animals, limited clinical studies indicate that single or repeated ketamine administrations in professionally controlled settings did not result in misuse, dependence, diversion and/or gateway activity in patients with TRD. However, most clinical studies were retrospective and did not systematically evaluate the abuse liability of ketamine via validated psychological scales/questionnaires. Future randomized controlled trials are warranted to ascertain the abuse liability of racemic, (S)- and (R)-ketamine in TRD population, especially among patients with comorbid substance use disorders.

Safety and effectiveness of NMDA receptor antagonists for depression: A multidisciplinary review

Ketamine, an anesthetic available since 1970, and esketamine, its newer S-enantiomer, provide a novel approach for the treatment of depression and other psychiatric disorders. At subanesthetic doses, the two drugs, along with their older congener, phencyclidine (PCP), induce a transient, altered mental state by blocking the N-methyl-D-aspartate (NMDA) receptor for glutamate, the primary excitatory neurotransmitter in the mammalian central nervous system. This multidisciplinary review examines the pharmacology/direct effects on consciousness, effectiveness in depression and acute suicidality, and safety of these fast-acting NMDA antagonists. To capture the essence of 60 years of peer-reviewed literature, we used a semi-structured approach to the subtopics, each of which required a different search strategy. We review the evidence for the three primary reported benefits of the two clinical drugs when used for depression: success in difficult-to-treat patients, rapid onset of action within a day, and immediate effects on suicidality. Key safety issues include the evidence-and lack thereof-for the effects of repeatedly inducing this altered mental state, and whether an adequate safety margin exists to rule out the neurotoxic effects seen in animal studies. This review includes evidence from multiple sources that raise substantial questions about both safety and effectiveness of ketamine and esketamine for psychiatric disorders.

GluN3A excitatory glycine receptors control adult cortical and amygdalar circuits

GluN3A is an atypical glycine-binding subunit of NMDA receptors (NMDARs) whose actions in the brain are mostly unknown. Here, we show that the expression of GluN3A subunits controls the excitability of mouse adult cortical and amygdalar circuits via an unusual signaling mechanism involving the formation of excitatory glycine GluN1/GluN3A receptors (eGlyRs) and their tonic activation by extracellular glycine. eGlyRs are mostly extrasynaptic and reside in specific neuronal populations, including the principal cells of the basolateral amygdala (BLA) and SST-positive interneurons (SST-INs) of the neocortex. In the BLA, tonic eGlyR currents are sensitive to fear-conditioning protocols, are subject to neuromodulation by the dopaminergic system, and control the stability of fear memories. In the neocortex, eGlyRs control the in vivo spiking of SST-INs and the behavior-dependent modulation of cortical activity. GluN3A-containing eGlyRs thus represent a novel and widespread signaling modality in the adult brain, with attributes that strikingly depart from those of conventional NMDARs.

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In mice, GluN3A is expressed by SST-INs in the cortex and pyramidal neurons in the BLA

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GluN3A assembles as excitatory glycine GluN1/GluN3A receptors (eGlyRs)

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eGlyRs detect extracellular glycine levels and generate tonic excitatory currents

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eGlyRs tune the function of SST-INs in cortex and alter the formation of fear memories in BLA

Structural insights into binding of therapeutic channel blockers in NMDA receptors

Excitatory signaling mediated by N-methyl-D-aspartate receptor (NMDAR) is critical for brain development and function, as well as for neurological diseases and disorders. Channel blockers of NMDARs are of medical interest owing to their potential for treating depression, Alzheimer's disease, and epilepsy. However, precise mechanisms underlying binding and channel blockade have remained limited owing to challenges in obtaining high-resolution structures at the binding site within the transmembrane domains. Here, we monitor the binding of three clinically important channel blockers: phencyclidine, ketamine, and memantine in GluN1-2B NMDARs at local resolutions of 2.5-3.5 Å around the binding site using single-particle electron cryo-microscopy, molecular dynamics simulations, and electrophysiology. The channel blockers form different extents of interactions with the pore-lining residues, which control mostly off-speeds but not on-speeds. Our comparative analyses of the three unique NMDAR channel blockers provide a blueprint for developing therapeutic compounds with minimal side effects.

Modified climbing fiber/Purkinje cell synaptic connectivity in the cerebellum of the neonatal phencyclidine model of schizophrenia

Synaptogenesis and neural network remodeling are at their maximum during the perinatal period of human brain development. Perturbations of this highly sensitive stage might underlie the etiology of neurodevelopmental disorders. Subchronic neonatal administration of phencyclidine, a drug of abuse, has been used to model schizophrenia in rodents. In this model, we found specific long-term synaptic changes in Purkinje cells and transient gene expression changes in the cerebellum. While transient increased neuronal activity in the cerebellum, induced using chemogenetics, reproduces some phencyclidine-induced molecular changes, it is insufficient to reproduce the long-term synaptic effects. Our results show the complex mechanism of action of phencyclidine on the development of neuronal connectivity and further highlight the potential contribution of cerebellar defects in psychiatric diseases.

Environmental perturbations during the first years of life are a major factor in psychiatric diseases. Phencyclidine (PCP), a drug of abuse, has psychomimetic effects, and neonatal subchronic administration of PCP in rodents leads to long-term behavioral changes relevant for schizophrenia. The cerebellum is increasingly recognized for its role in diverse cognitive functions. However, little is known about potential cerebellar changes in models of schizophrenia. Here, we analyzed the characteristics of the cerebellum in the neonatal subchronic PCP model. We found that, while the global cerebellar cytoarchitecture and Purkinje cell spontaneous spiking properties are unchanged, climbing fiber/Purkinje cell synaptic connectivity is increased in juvenile mice. Neonatal subchronic administration of PCP is accompanied by increased cFos expression, a marker of neuronal activity, and transient modification of the neuronal surfaceome in the cerebellum. The largest change observed is the overexpression of Ctgf, a gene previously suggested as a biomarker for schizophrenia. This neonatal increase in Ctgf can be reproduced by increasing neuronal activity in the cerebellum during the second postnatal week using chemogenetics. However, it does not lead to increased climbing fiber/Purkinje cell connectivity in juvenile mice, showing the complexity of PCP action. Overall, our study shows that administration of the drug of abuse PCP during the developmental period of intense cerebellar synaptogenesis and circuit remodeling has long-term and specific effects on Purkinje cell connectivity and warrants the search for this type of synaptic changes in psychiatric diseases.

Ketamine as a therapeutic agent for depression and pain: mechanisms and evidence

Ketamine is an anesthetic drug which is now used to treat chronic pain conditions and psychiatric disorders, especially depression. It is an N-methyl-D-aspartate (NMDA) receptor antagonist with additional effects on α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, opioid receptors, and monoaminergic receptors. This article focuses on ketamine's role in treating depression and pain, two commonly comorbid challenging conditions with potentially shared neurobiologic circuitry. Many clinical trials have utilized intravenous or intranasal ketamine for treating depression and pain. Intravenous ketamine is more bioavailable than intranasal ketamine and both are effective for acute depressive episodes. Intravenous ketamine is advantageous for post-operative analgesia and is associated with a reduction in total opioid requirements. Few studies have treated chronic pain or concurrent depression and pain with ketamine. Larger, randomized control trials are needed to examine the safety and efficacy of intravenous vs. intranasal ketamine, ideal target populations, and optimal dosing to treat both depression and pain.

Hallucinogenic drugs and their potential for treating fear-related disorders: Through the lens of fear extinction

Fear-related disorders, mainly phobias and post-traumatic stress disorder, are highly prevalent, debilitating disorders that pose a significant public health problem. They are characterized by aberrant processing of aversive experiences and dysregulated fear extinction, leading to excessive expression of fear and diminished quality of life. The gold standard for treating fear-related disorders is extinction-based exposure therapy (ET), shown to be ineffective for up to 35% of subjects. Moreover, ET combined with traditional pharmacological treatments for fear-related disorders, such as selective serotonin reuptake inhibitors, offers no further advantage to patients. This prompted the search for ways to improve ET outcomes, with current research focused on pharmacological agents that can augment ET by strengthening fear extinction learning. Hallucinogenic drugs promote reprocessing of fear-imbued memories and induce positive mood and openness, relieving anxiety and enabling the necessary emotional engagement during psychotherapeutic interventions. Mechanistically, hallucinogens induce dynamic structural and functional neuroplastic changes across the fear extinction circuitry and temper amygdala's hyperreactivity to threat-related stimuli, effectively mitigating one of the hallmarks of fear-related disorders. This paper provides the first comprehensive review of hallucinogens' potential to alleviate symptoms of fear-related disorders by focusing on their effects on fear extinction and the underlying molecular mechanisms. We overview both preclinical and clinical studies and emphasize the advantages of hallucinogenic drugs over current first-line treatments. We highlight 3,4-methylenedioxymethamphetamine and ketamine as the most effective therapeutics for fear-related disorders and discuss the potential molecular mechanisms responsible for their potency with implications for improving hallucinogen-assisted psychotherapy.

The role of ketamine-induced beta activity in the treatment of refractory status epilepticus. Is the EEG useful to determine responder's rate? A retrospective study

INTRODUCTION

Multiple investigations have been done to evaluate the possible effect of ketamine in the treatment of status epilepticus (SE).

OBJECTIVES

To evaluate the electrographic effect of ketamine on EEG, and its clinical utility following-up refractory and super refractory status epilepticus (SRSE).

METHODS

Retrospective review of 24 patients with SE. Clinical record and Video-electroencephalogram (video-EEG) of all included patients were reviewed. The patients' EEGs were then monitored for any immediate changes after administration of the first dose of ketamine as well as at the time patients would be predicted to have peak serum concentration of ketamine. Patients with cessation of electrographic seizures and no SE recurrence within the same admissions were categorized as "Responders". Statistical differences between qualitative variables were analyzed using chi square test. Differences between median were analyzed by Mann-Whitney U test. Difference between groups were considered significant when p < 0.05.

RESULTS

We identified 24 patients with SE. Twelve out of 24 (50%) had SRSE and 12 out of 24 (50%) had refractory status epilepticus (RSE). The appearance of superimposed beta activity after ketamine was initiated was associated with a higher responder rate (100% versus 33.3% in the responder group versus the non-responder group respectively). Notably, the presence of a burst suppression pattern had no significant association with one group compared to the other (41.6% versus 33.3%, in the responder group vs the non-responder group respectively).

CONCLUSIONS

Background superimposed beta activity induced by ketamine is an early and reliable EEG finding associated with status epilepticus termination.

Ketamine: A Potential Adjunct for Severe Benzodiazepine Withdrawal

Following the abrupt cessation of benzodiazepine therapy, patients can present with acute life-threatening withdrawal. Medical management of benzodiazepine withdrawal is typically undertaken with benzodiazepines either through loading dose with gradual taper or symptom triggered treatment, though adjuvant anxiolytics and anticonvulsants are often used. Ketamine, increasingly utilized as an adjunct in the treatment of alcohol withdrawal, may represent an effective medication in the treatment of benzodiazepine withdrawal. In this case report, a 27-year-old male with a history of benzodiazepine and opioid abuse presented to our emergency department with a chief complaint of drug withdrawal. Despite standard treatment with large amounts of benzodiazepine, barbiturate, opioid, and adjunctive medications, the patient remained with severe withdrawal syndrome until an infusion of ketamine (0.5mg/kg in 30 minutes) was administered resulting in significant improvement of the patient symptoms. This case demonstrates the potential role of ketamine as an adjunct medication in the treatment of benzodiazepine withdrawal.

Hallucinogen Use and Misuse in Older Adults

Hallucinogens, or psychedelics, are substances/drugs that have been used for over a millennium. The most well known are LSD, psilocybin, mescaline, and PCP. These substances may induce hallucinations as well as cause somatic and psychological symptoms. Because of the Controlled Substances Act of 1970, there has been very little research done to determine the long-term consequences or perhaps potential benefit of misuse and abuse of hallucinogens. Typically, these drugs are not abused but more often misused. Recently, there has been a renewed interest in these compounds, which may lead to possible therapeutic options.

Pairing of neonatal phencyclidine exposure and acute adolescent stress in male rats as a novel developmental model of schizophrenia

Improved understanding of the neurophysiological and neurochemical mechanisms underlying schizophrenia is essential for the identification of biological markers and developing new therapeutic targets. The development of behaviorally faithful, predictive animal models is crucial to this endeavor. We have developed a novel two-hit paradigm designed to recapitulate in rodents the developmental process leading to appearance of human schizophrenia symptomatology. The model pairs neonatal administration of the NMDA receptor (NMDAR) open-channel blocker phencyclidine (PCP 10 mg/kg) to male rats at 7, 9 and 11 days of age, with later adolescent exposure (34 days of age) to a single prolonged stress paradigm consisting of 2 h restraint, followed by 20 min of forced swimming. Four experimental groups were examined: vehicle and no stress (VEH-NS), vehicle plus stress (VEH-S), PCP and no stress (PCP-NS), and PCP plus stress (PCP-S). Only pairing of neonatal PCP with single prolonged adolescent stress caused deficits in novel object recognition memory and increased anxiety-like behavior in the elevated plus maze task, without altering locomotor activity. In a separate cohort of animals, the PCP-S group showed significant reduction in magnitude of hippocampal long-term potentiation (LTP) at Schaffer collateral-CA1 synapses following a single pair of theta-burst stimuli (TBS), while LTP was diminished in both PCP treated groups when elicited by a second pair of TBS. These results suggest that the combination of neonatal PCP and acute adolescent stress are necessary for lasting cognitive impairment and anxiety-like phenotype, and that these behavioral impairments may be due to deficits in LTP in hippocampus, and perhaps elsewhere in the brain.

Low Doses of Psilocybin and Ketamine Enhance Motivation and Attention in Poor Performing Rats: Evidence for an Antidepressant Property

Long term benefits following short-term administration of high psychedelic doses of serotonergic and dissociative hallucinogens, typified by psilocybin and ketamine respectively, support their potential as treatments for psychiatric conditions such as major depressive disorder. The high psychedelic doses induce perceptual experiences which are associated with therapeutic benefit. There have also been anecdotal reports of these drugs being used at what are colloquially referred to as "micro" doses to improve mood and cognitive function, although currently there are recognized limitations to their clinical and preclinical investigation. In the present studies we have defined a low dose and plasma exposure range in rats for both ketamine (0.3-3 mg/kg [10-73 ng/ml]) and psilocybin/psilocin (0.05-0.1 mg/kg [7-12 ng/ml]), based on studies which identified these as sub-threshold for the induction of behavioral stereotypies. Tests of efficacy were focused on depression-related endophenotypes of anhedonia, amotivation and cognitive dysfunction using low performing male Long Evans rats trained in two food motivated tasks: a progressive ratio (PR) and serial 5-choice (5-CSRT) task. Both acute doses of ketamine (1-3 mg/kg IP) and psilocybin (0.05-0.1 mg/kg SC) pretreatment increased break point for food (PR task), and improved attentional accuracy and a measure of impulsive action (5-CSRT task). In each case, effect size was modest and largely restricted to test subjects characterized as "low performing". Furthermore, both drugs showed a similar pattern of effect across both tests. The present studies provide a framework for the future study of ketamine and psilocybin at low doses and plasma exposures, and help to establish the use of these lower concentrations of serotonergic and dissociative hallucinogens both as a valid scientific construct, and as having a therapeutic utility.

Application and assessment of deep learning for the generation of potential NMDA receptor antagonists

Uncompetitive antagonists of the N-methyl d-aspartate receptor (NMDAR) have demonstrated therapeutic benefit in the treatment of neurological diseases such as Parkinson's and Alzheimer's, but some also cause dissociative effects that have led to the synthesis of illicit drugs. The ability to generate NMDAR antagonists in silico is therefore desirable for both new medication development and preempting and identifying new designer drugs. Recently, generative deep learning models have been applied to de novo drug design as a means to expand the amount of chemical space that can be explored for potential drug-like compounds. In this study, we assess the application of a generative model to the NMDAR to achieve two primary objectives: (i) the creation and release of a comprehensive library of experimentally validated NMDAR phencyclidine (PCP) site antagonists to assist the drug discovery community and (ii) an analysis of both the advantages conferred by applying such generative artificial intelligence models to drug design and the current limitations of the approach. We apply, and provide source code for, a variety of ligand- and structure-based assessment techniques used in standard drug discovery analyses to the deep learning-generated compounds. We present twelve candidate antagonists that are not available in existing chemical databases to provide an example of what this type of workflow can achieve, though synthesis and experimental validation of these compounds are still required.

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.

Overview of schizophrenia research and treatment in Pakistan

Mental health is the most neglected health sector in Pakistan, and the majority of citizens have limited or no access to primary and secondary psychiatric services. The incidence of schizophrenia (SCZ) has increased at an alarming rate in Pakistan, relative to that of other psychiatric disorders. While numerous studies have investigated SCZ, few have addressed the issue about the Pakistani population. In the present review, the researchers discuss current data integral to the prevalence, pathophysiology, and molecular genetics of SCZ; treatment approaches to the disease; and patient responses to drugs prescribed for SCZ in Pakistan. Most Pakistani patients exhibit poor responses to antipsychotic drugs. Based on our review, the researchers hypothesize that genetic dissimilarities between Pakistani and Western populations contribute to such poor responses. Consequently, an understanding of such genetic differences and the provision of personalized treatment may simultaneously aid in improving SCZ treatment in Pakistan.

Repurposing of Drugs-The Ketamine Story

An intranasal formulation of esketamine, the S enantiomer of ketamine, in conjunction with an oral antidepressant, has been approved by the FDA for treating treatment-resistant major depressive disorder (TRD) in 2019, almost 50 years after it was approved as an intravenous anesthetic. In contrast to traditional antidepressants, ketamine shows a rapid (within 2 h) and sustained (∼7 days) antidepressant effect and has significant positive effects on antisuicidal ideation. Ketamine's antidepressant mechanism is predominantly mediated by the N-methyl-d-aspartate receptor (NMDA) receptor, although NMDA-independent mechanisms are not ruled out. At the neurocircuitry level, ketamine affects the brain's reward and mood circuitry located in the corticomesolimbic structures involving the hippocampus, nucleus accumbens, and prefrontal cortex. Repurposing of ketamine for treating TRD provided a new understanding of the pathophysiology of depression, a paradigm shift from monoamine to glutamatergic neurotransmission, thus making it a unique tool to investigate the brain and its complex neurocircuitries.

Hydroxynorketamine Blocks N-Methyl-d-Aspartate Receptor Currents by Binding to Closed Receptors

Ketamine, a dissociative anesthetic, is experiencing a clinical resurgence as a fast-acting antidepressant. In the central nervous system, ketamine acts primarily by blocking NMDA receptor currents. Although it is generally safe in a clinical setting, it can be addictive, and several of its derivatives are being investigated as preferable alternatives. 2R,6R-Hydroxynorketamine (HNK), a ketamine metabolite, reproduces some of the therapeutic effects of ketamine and appears to lack abuse liability. Here, we report a systematic investigation of the effects of HNK on macroscopic responses elicited from recombinant NMDA receptors expressed in human embryonic kidney 293 cells. We found that, like ketamine, HNK reduced NMDA receptor currents in a dose-, pH-, and voltage-dependent manner. Relative to ketamine, it had 100-fold-lower potency (46 µM at pH 7.2), 10-fold-slower inhibition onset, slower apparent dissociation rate, weaker voltage dependence, and complete competition by magnesium. Notably, HNK inhibition was fully effective when applied to resting receptors. These results revealed unexpected properties of hydroxynorketamine that warrant its further investigation as a possible therapeutic in pathologies associated with NMDA receptor dysfunction. SIGNIFICANCE STATEMENT: NMDA receptors are excitatory ion channels with fundamental roles in synaptic transmission and plasticity, and their dysfunction associates with severe neuropsychiatric disorders. 2R,6R-Hydroxynorketamine, a metabolite of ketamine, mimics some of the neuroactive properties of ketamine and may lack its abuse liability. Results show that 2R,6R-hydroxynorketamine blocks NMDA receptor currents with low affinity and weak voltage dependence and is effective when applied to resting receptors. These properties highlight its effectiveness to a subset of NMDA receptor responses and recommend it for further investigation.

Glutamate in schizophrenia: Neurodevelopmental perspectives and drug development

Research into the neurobiological processes that may lead to the onset of schizophrenia places growing emphasis on the glutamatergic system and brain development. Preclinical studies have shown that neurodevelopmental, genetic, and environmental factors contribute to glutamatergic dysfunction and schizophrenia-related phenotypes. Clinical research has suggested that altered brain glutamate levels may be present before the onset of psychosis and relate to outcome in those at clinical high risk. After psychosis onset, glutamate dysfunction may also relate to the degree of antipsychotic response and clinical outcome. These findings support ongoing efforts to develop pharmacological interventions that target the glutamate system and could suggest that glutamatergic compounds may be more effective in specific patient subgroups or illness stages. In this review, we consider the updated glutamate hypothesis of schizophrenia, from a neurodevelopmental perspective, by reviewing recent preclinical and clinical evidence, and discuss the potential implications for novel therapeutics.

Neuroimmunological antibody-mediated encephalitis and implications for diagnosis and therapy in neuropsychiatry

The past decade has seen a surge of reports and investigations into cases of autoimmune-mediated encephalitis. The increasing recognition of these disorders is especially of relevance to the fields of neurology and psychiatry. Autoimmune encephalitis involves antibodies against synaptic receptors, neuronal cell surface proteins and intracellular targets. These disorders feature prominent symptoms of cognitive impairment and behavioural changes, often associated with the presence of seizures. Early in the clinical course, autoimmune encephalitis may manifest as psychiatric symptoms of psychosis and involve psychiatry as an initial point of contact. Although commonly associated with malignancy, these disorders can present in the absence of an inciting neoplasm. The identification of autoimmune encephalitis is of clinical importance as a large proportion of individuals experience a response to immunotherapy. This review focuses on the current state of knowledge on n-methyl-d-aspartate (NMDA) receptor-associated encephalitis and limbic encephalitis, the latter predominantly involving antibodies against the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor, the γ-aminobutyric acid (GABA)B receptor and leucine-rich glioma-inactivated 1 (LGI1) protein. In addition, we briefly describe anti-dopamine D2 receptor encephalitis. A summary of the literature will focus on common clinical presentations and course, diagnostic approaches and response to treatment. Since a substantial proportion of patients with autoimmune encephalitis exhibit symptoms of psychosis, the relevance of this disorder to theories of psychosis and schizophrenia will also be discussed.

The Abuse Potential of Novel Synthetic Phencyclidine Derivative 1-(1-(4-Fluorophenyl)Cyclohexyl)Piperidine (4'-F-PCP) in Rodents

The dissociative anesthetic phencyclidine (PCP) and PCP derivatives, including 4′-F-PCP, are illegally sold and abused worldwide for recreational and non-medical uses. The psychopharmacological properties and abuse potential of 4′-F-PCP have not been fully characterized. In this study, we evaluated the psychomotor, rewarding, and reinforcing properties of 4′-F-PCP using the open-field test, conditioned place preference (CPP), and self-administration paradigms in rodents. Using Western immunoblotting, we also investigated the expression of dopamine (DA)-related proteins and DA-receptor-mediated downstream signaling cascades in the nucleus accumbens (NAc) of 4′-F-PCP-self-administering rats. Intraperitoneal administration of 10 mg/kg 4′-F-PCP significantly increased locomotor and rearing activities and increased CPP in mice. Intravenous administration of 1.0 mg/kg/infusion of 4′-F-PCP significantly enhanced self-administration during a 2 h session under fixed ratio schedules, showed a higher breakpoint during a 6 h session under progressive ratio schedules of reinforcement, and significantly altered the expression of DA transporter and DA D1 receptor in the NAc of rats self-administering 1.0 mg/kg 4′-F-PCP. Additionally, the expression of phosphorylated (p) ERK, pCREB, c-Fos, and FosB/ΔFosB in the NAc was significantly enhanced by 1.0 mg/kg 4′-F-PCP self-administration. Taken together, these findings suggest that 4′-F-PCP has a high potential for abuse, given its robust psychomotor, rewarding, and reinforcing properties via activation of DAergic neurotransmission and the downstream signaling pathways in the NAc.

Antidepressant Effects of (S)-Ketamine through a Reduction of Hyperpolarization-Activated Current Ih

Compelling evidence suggests that a single sub-anesthetic dose of (R,S)-ketamine exerts rapid and robust antidepressant effects. However, the cellular mechanisms underlying the antidepressant effects of (R,S)-ketamine remain unclear. Here, we show that (S)-ketamine reduced dendritic but not somatic hyperpolarization-activated current I_h of dorsal CA1 neurons in unstressed rats, whereas (S)-ketamine decreased both somatic and dendritic I_h in chronic unpredictable stress (CUS) rats. The reduction of I_h by (S)-ketamine was independent of NMDA receptors, barium-sensitive conductances, and cAMP-dependent signaling pathways in both unstressed and CUS groups. (S)-ketamine pretreatment before the onset of depression prevented CUS-induced behavioral phenotypes and neuropathological changes of dorsal CA1 neurons. Finally, in vivo infusion of thapsigargin-induced anxiogenic- and anhedonic-like behaviors and upregulation of functional I_h, but these were reversed by (S)-ketamine. Our results suggest that (S)-ketamine reduces or prevents I_h from being increased following CUS, which contributes to the rapid antidepressant effects and resiliency to CUS.

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(S)-ketamine reduced the CUS-induced upregulation of somatic I_h

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This was independent of NMDAR, Ba²⁺-sensitive conductances, and cAMP signaling

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(S)-ketamine pretreatment before the onset of depression provided resiliency to CUS

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In vivo thapsigargin-induced changes in behaviors were reversed by (S)-ketamine