NMDA receptor antagonists ketamine and PCP have direct effects on the dopamine D(2) and serotonin 5-HT(2)receptors-implications for models of schizophrenia

The N-methyl-d-aspartate receptor hypothesis of ketamine's antidepressant action: evidence and controversies

Substantial clinical evidence has unravelled the superior antidepressant efficacy of ketamine: in comparison to traditional antidepressants targeting the monoamine systems, ketamine, as an N-methyl-d-aspartate receptor (NMDAR) antagonist, acts much faster and more potently. Surrounding the antidepressant mechanisms of ketamine, there is ample evidence supporting an NMDAR-antagonism-based hypothesis. However, alternative arguments also exist, mostly derived from the controversial clinical results of other NMDAR inhibitors. In this article, we first summarize the historical development of the NMDAR-centred hypothesis of rapid antidepressants. We then classify different NMDAR inhibitors based on their mechanisms of inhibition and evaluate preclinical as well as clinical evidence of their antidepressant effects. Finally, we critically analyse controversies and arguments surrounding ketamine's NMDAR-dependent and NMDAR-independent antidepressant action. A better understanding of ketamine's molecular targets and antidepressant mechanisms should shed light on the future development of better treatment for depression. This article is part of a discussion meeting issue 'Long-term potentiation: 50 years on'.

Effects of ketamine and esketamine on preventing postpartum depression after cesarean delivery: A meta-analysis

BACKGROUND

Ketamine and esketamine has been suggested to have potential efficacy in preventing postpartum depression (PPD) recent years. The aim of this meta-analysis was to evaluate the effectiveness of ketamine and esketamine on PPD after cesarean delivery.

METHODS

We systematically searched PubMed, Embase, and the Cochrane Library for studies investigating the efficacy of ketamine and esketamine in preventing PPD. The primary outcomes of this study were risk ratios (RRs) and EPDS scores (Edinburgh Postnatal Depression Scale) in relation to PPD after ketamine and esketamine. The second outcomes were the postoperative adverse events.

RESULTS

Thirteen randomized controlled trials (RCTs) and one retrospective study including 2916 patients were analyzed, including six on the use of ketamine and eight on the use of esketamine. The risk ratios and EPDS scores of PPD were significantly decreased in the ketamine/esketamine group compared to those in the control group in one week and four weeks postoperative periods. Subgroup analyses showed that high dosage, administrated in patient controlled intravenous analgesia (PCIA) method and only esketamine exhibited a significant reduction in the incidence and EPDS scores of PPD in one week and four week postoperative. However, the incidences of postoperative adverse events, such as dizziness, diplopia, hallucination, and headache were significantly higher in the ketamine/esketamine group than that in the control group.

CONCLUSION

Ketamine and esketamine appear to be effective in preventing PPD in the one week and four week postoperative periods after cesarean delivery with moderate certainty of evidence. But they can also lead to some short-term complications too. Future high-quality studies are needed to confirm the efficacy of ketamine and esketamine in different countries.

The Stable Gastric Pentadecapeptide BPC 157 Pleiotropic Beneficial Activity and Its Possible Relations with Neurotransmitter Activity

We highlight the particular aspects of the stable gastric pentadecapeptide BPC 157 pleiotropic beneficial activity (not destroyed in human gastric juice, native and stable in human gastric juice, as a cytoprotection mediator holds a response specifically related to preventing or recovering damage as such) and its possible relations with neurotransmitter activity. We attempt to resolve the shortage of the pleiotropic beneficial effects of BPC 157, given the general standard neurotransmitter criteria, in classic terms. We substitute the lack of direct conclusive evidence (i.e., production within the neuron or present in it as a precursor molecule, released eliciting a response on the receptor on the target cells on neurons and being removed from the site of action once its signaling role is complete). This can be a network of interconnected evidence, previously envisaged in the implementation of the cytoprotection effects, consistent beneficial particular evidence that BPC 157 therapy counteracts dopamine, serotonin, glutamate, GABA, adrenalin/noradrenalin, acetylcholine, and NO-system disturbances. This specifically includes counteraction of those disturbances related to their receptors, both blockade and over-activity, destruction, depletion, tolerance, sensitization, and channel disturbances counteraction. Likewise, BPC 157 activates particular receptors (i.e., VGEF and growth hormone). Furthermore, close BPC 157/NO-system relations with the gasotransmitters crossing the cell membrane and acting directly on molecules inside the cell may envisage particular interactions with receptors on the plasma membrane of their target cells. Finally, there is nerve-muscle relation in various muscle disturbance counteractions, and nerve-nerve relation in various encephalopathies counteraction, which is also exemplified specifically by the BPC 157 therapy application.

NMDA glutamate receptor antagonist MK-801 induces proteome changes in adult human brain slices which are partially counteracted by haloperidol and clozapine

Deciphering the molecular pathways associated with N-methyl-D-aspartate receptor (NMDAr) hypofunction and its interaction with antipsychotics is necessary to advance our understanding of the basis of schizophrenia, as well as our capacity to treat this disease. In this regard, the development of human brain-derived models that are amenable to studying the neurobiology of schizophrenia may contribute to filling the gaps left by the widely employed animal models. Here, we assessed the proteomic changes induced by the NMDA glutamate receptor antagonist MK-801 on human brain slice cultures obtained from adult donors submitted to respective neurosurgery. Initially, we demonstrated that MK-801 diminishes NMDA glutamate receptor signaling in human brain slices in culture. Next, using mass-spectrometry-based proteomics and systems biology in silico analyses, we found that MK-801 led to alterations in proteins related to several pathways previously associated with schizophrenia pathophysiology, including ephrin, opioid, melatonin, sirtuin signaling, interleukin 8, endocannabinoid, and synaptic vesicle cycle. We also evaluated the impact of both typical and atypical antipsychotics on MK-801-induced proteome changes. Interestingly, the atypical antipsychotic clozapine showed a more significant capacity to counteract the protein alterations induced by NMDAr hypofunction than haloperidol. Finally, using our dataset, we identified potential modulators of the MK-801-induced proteome changes, which may be considered promising targets to treat NMDAr hypofunction in schizophrenia. This dataset is publicly available and may be helpful in further studies aimed at evaluating the effects of MK-801 and antipsychotics in the human brain.

The impact of early life stress and schizophrenia on motor and cognitive functioning: an experimental study

Background

Early life stress (ELS) and parental psychopathology, such as schizophrenia (SZ), have been associated with altered neurobiological and behavioral outcomes later in life. Previous studies have investigated the effects of ELS and parental SZ on various aspects of behavior, however, we have studied the combined effects of these stressors and how they interact, as individuals in real-life situations may experience multiple stressors simultaneously.

Objective

The aim of this study was to investigate the impact of ELS and schizophrenia on locomotor activity, anxiety-like behavior, exploratory tendencies, and spatial memory in Sprague Dawley (SD) rats.

Methods

Male and female SD pups were randomly assigned to eight groups: control, ELS, schizophrenia, and ELS + schizophrenia. ELS was induced by prenatal stress (maternal stress) and maternal separation (MS) during the first 2 weeks of life, while SZ was induced by subcutaneous administration of ketamine. Behavioral tests included an open field test (OFT) for motor abilities and a Morris water maze (MWM) for cognitive abilities. ANOVA and post hoc Tukey tests were utilized to analyze the data.

Results

Our results show that ELS and parental psychopathology had enduring effects on SZ symptoms, particularly psychomotor retardation (p < 0.05). The OFT revealed increased anxiety-like behavior in the ELS group (p = 0.023) and the parental psychopathology group (p = 0.017) compared to controls. The combined ELS and parental psychopathology group exhibited the highest anxiety-like behavior (p = 0.006). The MWM analysis indicated impaired spatial memory in the ELS group (p = 0.012) and the combined ELS and parental psychopathology group (p = 0.003) compared to controls. Significantly, the exposure to ELS resulted in a decrease in the population of glial fibrillary acidic protein-positive (GFAP+) astrocytes. However, this effect was reversed by positive parental mental health.

Conclusion

Our findings highlight the interactive effects of ELS and parental psychopathology on anxiety-like behavior and spatial memory in rats. ELS was linked to increased anxiety-like behavior, while SZ was associated with anhedonia-like behavior. Positive parenting augments neuroplasticity, synaptic function, and overall cognitive capacities.

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.

Exploring the Potential Utility of Psychedelic Therapy for Patients With Amyotrophic Lateral Sclerosis

Background: Amyotrophic lateral sclerosis (ALS) is an aggressive, terminal neurodegenerative disease that causes death of motor neurons and has an average survival time of 3-4 years. ALS is the most common motor neuron degenerative disease and is increasing in prevalence. There is a pressing need for more effective ALS treatments as available pharmacotherapies do not reverse disease progression or provide substantial clinical benefit. Furthermore, despite psychological distress being highly prevalent in ALS patients, psychological treatments remain understudied. Psychedelics (i.e., serotonergic psychedelics and related compounds like ketamine) have seen a resurgence of research into therapeutic applications for treating a multitude of neuropsychiatric conditions, including psychiatric and existential distress in life-threatening illnesses. Methods: We conducted a narrative review to examine the potential of psychedelic assisted-psychotherapy (PAP) to alleviate psychiatric and psychospiritual distress in ALS. We also discussed the safety of using psychedelics in this population and proposed putative neurobiological mechanisms that may therapeutically intervene on ALS neuropathology. Results: PAP has the potential to treat psychological dimensions and may also intervene on neuropathological dimensions of ALS. Robust improvements in psychiatric and psychospiritual distress from PAP in other populations provide a strong rationale for utilizing this therapy to treat ALS-related psychiatric and existential distress. Furthermore, relevant neuroprotective properties of psychedelics warrant future preclinical trials to investigate this area in ALS models. Conclusion: PAP has the potential to serve as an effective treatment in ALS. Given the lack of effective treatment options, researchers should rigorously explore this therapy for ALS in future trials.

Exploring the Role of Drug Repurposing in Bridging the Hypoxia-Depression Connection

High levels of oxidative stress are implicated in hypoxia, a physiological response to low levels of oxygen. Evidence supports a connection between this response and depression. Previous studies indicate that tryptophan hydroxylase can be negatively affected in hypoxia, impairing serotonin synthesis and downstream pathways. Some studies also hypothesize that increasing hypoxia-inducible factor-1 (HIF-1) levels may be a new therapeutic modality for depression. Hence, this study delved into the influence of hypoxia on the cellular response to drugs designed to act in depression. By the induction of hypoxia in SH-SY5Y cells through a hypoxia incubator chamber or Cobalt Chloride treatment, the effect of Mirtazapine, an antidepressant, and other drugs that interact with serotonin receptors (TCB-2, Dextromethorphan, Ketamine, Quetiapine, Scopolamine, Celecoxib, and Lamotrigine) on SH-SY5Y cellular viability and morphology was explored. The selection of drugs was initially conducted by literature search, focusing on compounds with established potential for employment in depression therapy. Subsequently, we employed in silico approaches to forecast their ability to traverse the blood-brain barrier (BBB). This step was particularly pertinent as we aimed to assess their viability for inducing potential antidepressant effects. The effect of these drugs in hypoxia under the inhibition of HIF-1 by Echinomycin was also tested. Our results revealed that all the potential repurposed drugs promoted cell viability, especially when hypoxia was chemically induced. When combined with Echinomycin, all drugs decreased cellular viability, possibly by the inability to interact with HIF-1.

L-Carnitine Prevents Behavioural Alterations in Ketamine-Induced Schizophrenia in Mice: Possible Involvement of Oxidative Stress and Inflammation Pathways

Schizophrenia is a chronic mental complaint known as cognitive impairment. There has been evidence that inflammation and oxidative stress play a main role in schizophrenia pathophysiology. This study aimed to investigate the effects of l-carnitine, as a potent antioxidant, on the treatment of behavioural and biochemical disturbances in mice with ketamine-induced schizophrenia. In this study, schizophrenia was induced in mice by ketamine (25 mg/kg/day, i.p). Before induction of schizophrenia, mice were treated with l-carnitine (100, 200, and 400 mg/kg/day, i.p). Then, behavioural impairments were evaluated by open field (OF) assessment and social interaction test (SIT). After brain tissue isolation, reactive oxygen species (ROS), glutathione concentration (GSH), lipid peroxidation (LPO), protein carbonyl oxidation, superoxide dismutase activity (SOD), and glutathione peroxidase activity (GPx) were assessed as oxidative stress markers. Furthermore, inflammatory biomarkers such as tumour necrosis factor alpha (TNF-α) and nitric oxide (NO) were evaluated in brain tissue. Our results showed ketamine increased inflammation and oxidative damage in brain tissue that was similar to behaviour disorders in mice. Interestingly, l-carnitine significantly decreased oxidative stress and inflammatory markers compared with ketamine-treated mice. In addition, l-carnitine prevented and reversed ketamine-induced alterations in the activities of SOD and GPx enzymes in mice's brains. Also, improved performance in OFT (locomotor activity test) and SIT was observed in l-carnitine-treated mice. These data provided evidence that, due to the antioxidant and anti-inflammatory effects of l-carnitine, it has a neuroprotective effect on mice model of schizophrenia.

Narrative Review: Low-Dose Ketamine for Pain Management

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

Tritium NMR: A compilation of data and a practical guide

The present review is focused on experimental methods and structural applications of tritium NMR. It consists of five parts covering accordingly, introduction, brief overview, early (based on the papers appearing before 2000), more recent (based on the papers appeared in the interim of 2000 to 2015), and recent (based on the papers that appeared after 2015) reports. A special interest in this review is focused on practical aspects of tritium NMR spectroscopy, which is thoroughly illustrated by its numerous applications in chemistry and biochemistry.

Role of the mesolimbic dopamine pathway in the antidepressant effects of ketamine

Depression is a complex and highly heterogeneous disorder which diagnosis is based on an exceedingly variable set of clinical symptoms. Current treatments focus almost exclusively on the manipulation of monoamine neurotransmitter systems, but despite considerable efforts, these remain inadequate for a significant proportion of those afflicted by the disorder. The emergence of racemic (R, S)-ketamine as a fast-acting antidepressant has provided an exciting new path for the study of major depressive disorder (MDD) and the search for better therapeutics for its treatment. Previous work suggested that ketamine's mechanism of action is primarily mediated via blockaded of N-methyl-d-aspartate (NMDA) receptors, however, this is an area of active research and clinical and preclinical evidence now indicate that ketamine acts on multiple systems. The last couple of decades have cemented the mesolimbic dopamine reward pathway's involvement in the pathogenesis of MDD and related mood disorders. Exposure to negative stress dysregulates dopamine neuronal activity disrupting reward and motivational processes resulting in anhedonia (lack of pleasure), a hallmark symptom of depression. Although the mechanism(s) underlying ketamine's antidepressant activity continue to be elucidated, current evidence indicate that its therapeutic effects are mediated, at least in part, via long-lasting synaptic changes and subsequent molecular adaptations in brain regions within the mesolimbic dopamine system. Notwithstanding, ketamine is a drug of abuse, and this liability may pose limitations for long term use as an antidepressant. This review outlines the current knowledge of ketamine's actions within the mesolimbic dopamine system and its abuse potential. This article is part of the Special Issue on 'Ketamine and its Metabolites'.

The psychotomimetic ketamine disrupts the transfer of late sensory information in the corticothalamic network

In prodromal and early schizophrenia, disorders of attention and perception are associated with structural and chemical brain abnormalities and with dysfunctional corticothalamic networks exhibiting disturbed brain rhythms. The underlying mechanisms are elusive. The non-competitive NMDA receptor antagonist ketamine simulates the symptoms of prodromal and early schizophrenia, including disturbances in ongoing and task & sensory-related broadband beta-/gamma-frequency (17-29 Hz/30-80 Hz) oscillations in corticothalamic networks. In normal healthy subjects and rodents, complex integration processes, like sensory perception, induce transient, large-scale synchronised beta/gamma oscillations in a time window of a few hundred ms (200-700 ms) after the presentation of the object of attention (e.g., sensory stimulation). Our goal was to use an electrophysiological multisite network approach to investigate, in lightly anesthetised rats, the effects of a single psychotomimetic dose (2.5 mg/kg, subcutaneous) of ketamine on sensory stimulus-induced oscillations. Ketamine transiently increased the power of baseline beta/gamma oscillations and decreased sensory-induced beta/gamma oscillations. In addition, it disrupted information transferability in both the somatosensory thalamus and the related cortex and decreased the sensory-induced thalamocortical connectivity in the broadband gamma range. The present findings support the hypothesis that NMDA receptor antagonism disrupts the transfer of perceptual information in the somatosensory cortico-thalamo-cortical system.

Roles of the monoaminergic system in the antidepressant effects of ketamine and its metabolites

While the molecular target of (R,S)-ketamine (ketamine) is thought to be the NMDA receptor, subanesthetic doses of ketamine have been known to modulate monoaminergic neurotransmission in the central nervous system. Although the involvement of the serotonergic system in the antidepressant effects of ketamine has been reported in most studies of this topic, some recent studies have reported that the dopaminergic system plays a key role in the effects of ketamine. Additionally, several lines of evidence suggest that the antidepressant-like effects of (R)-ketamine might be independent of the monoaminergic system. Ketamine metabolites also differ considerably in their ability to regulate monoamine neurotransmitters relative to (S)-ketamine and (R)-ketamine, while (2R,6R)-hydroxynorketamine might share common serotonergic signaling mechanisms with ketamine. In the current review, we summarize the effects of ketamine and its metabolites on monoamine neurotransmission in the brain and discuss the potential roles of the monoaminergic system in the mechanism of action of ketamine.

Endogenous Modulators of NMDA Receptor Control Dendritic Field Expansion of Cortical Neurons

Impairments of N-methyl-D-aspartate receptor (NMDAR) activity have been implicated in several neuropsychiatric disorders, with pharmacological inhibition of NMDAR-mediated currents and associated neurobehavioral changes considered as a model of schizophrenia. We analyzed the effects of brief and long-term exposure of rat cortical cultures to the most prevalent endogenous modulators of NMDAR (kynurenic acid, pregnenolone sulfate, spermidine, and zinc) on neuronal viability, stimulation-induced release of glutamate, and dendritic morphology with synaptic density. Both, glutamate release and neuronal viability studies revealed no difference between the test and control groups. No differences were also observed in the number of dendritic branching and length, or density of synaptic connections and neuronal soma size. Comparison of the extent of dendritic projections and branching patterns, however, revealed enhanced distal arborization with the expansion of the dendritic area under prolonged treatment of cultures with physiological concentrations of NMDAR modulators, with differences reaching significance in spermidine and pregnenolone sulfate tests. Measurements of the density of glutamatergic synapses showed consistency across all neuronal groups, except those treated with pregnenolone sulfate, which showed a reduction of PSD-95-positive elements. Overall, our data suggest that constitutive glutamatergic activity mediated by NMDAR controls the dendritic field expansion and can influence the integrative properties of cortical neurons.

Experimental Medicine Approaches in Early-Phase CNS Drug Development

Traditionally, Phase 1 clinical trials were largely conducted in healthy normal volunteers and focused on collection of safety, tolerability, and pharmacokinetic data. However, in the CNS therapeutic area, with more drugs failing in later phase development, Phase 1 trials have undergone an evolution that includes incorporation of novel approaches involving novel study designs, inclusion of biomarkers, and early inclusion of patients to improve the pharmacologic understanding of novel CNS-active compounds early in clinical development with the hope of improving success in later phase pivotal trials. In this chapter, the authors will discuss the changing landscape of Phase 1 clinical trials in CNS, including novel trial methodology, inclusion of pharmacodynamic biomarkers, and experimental medicine approaches to inform early decision-making in clinical development.

Ketamine and its metabolites: Potential as novel treatments for depression

Depression is a well-known serious mental illness, and the onset of treatment using traditional antidepressants is frequently delayed by several weeks. Moreover, numerous patients with depression fail to respond to therapy. One major breakthrough in antidepressant therapy is that subanesthetic ketamine doses can rapidly alleviate depressive symptoms within hours of administering a single dose, even in treatment-resistant patients. However, specific mechanisms through which ketamine exerts its antidepressant effects remain elusive, leading to concerns regarding its rapid and long-lasting antidepressant effects. N-methyl-d-aspartate receptor (NMDAR) antagonists like ketamine are reportedly associated with serious side effects, such as dissociative symptoms, cognitive impairment, and abuse potential, limiting the large-scale clinical use of ketamine as an antidepressant. Herein, we reviewed the pharmacological properties of ketamine and the mechanisms of action underlying the rapid antidepressant efficacy, including the disinhibition hypothesis and synaptogenesis, along with common downstream effector pathways such as enhanced brain-derived neurotrophic factor and tropomyosin-related kinase B signaling, activation of the mechanistic target of rapamycin complex 1 and transforming growth factor β1. We focused on evidence supporting the relevance of these potential mechanisms of ketamine and its metabolites in mediating the clinical efficacy of the drug. Given its reported antidepressant efficacy in preclinical studies and limited undesirable adverse effects, (R)-ketamine may be a safer, more controllable, rapid antidepressant. Overall, understanding the potential mechanisms of action of ketamine and its metabolites in combination with pharmacology may help develop a new generation of rapid antidepressants that maximize antidepressant effects while avoiding unfavorable adverse effects. This article is part of the Special Issue on 'Ketamine and its Metabolites'.

Effects of Taurine in Mice and Zebrafish Behavioral Assays With Translational Relevance to Schizophrenia

BACKGROUND

Altered redox state and developmental abnormalities in glutamatergic and GABAergic transmission during development are linked to the behavioral changes associated with schizophrenia. As an amino acid that exerts antioxidant and inhibitory actions in the brain, taurine is a potential candidate to modulate biological targets relevant to this disorder. Here, we investigated in mice and zebrafish assays whether taurine prevents the behavioral changes induced by acute administration of MK-801 (dizocilpine), a glutamate N-methyl-D-aspartate (NMDA) receptor antagonist.

METHODS

C57BL/6 mice were i.p. administered with saline or taurine (50, 100, and 200 mg/kg) followed by MK-801 (0.15 mg/kg). Locomotor activity, social interaction, and prepulse inhibition of the acoustic startle reflex were then assessed in different sets of animals. Zebrafish were exposed to tank water or taurine (42, 150, and 400 mg/L) followed by MK-801 (5 µM); social preference and locomotor activity were evaluated in the same test.

RESULTS

MK-801 induced hyperlocomotion and disrupted sensorimotor gating in mice; in zebrafish, it reduced sociability and increased locomotion. Taurine was mostly devoid of effects and did not counteract NMDA antagonism in mice or zebrafish.

DISCUSSION

Contradicting previous clinical and preclinical data, taurine did not show antipsychotic-like effects in the present study. However, it still warrants consideration as a preventive intervention in animal models relevant to the prodromal phase of schizophrenia; further studies are thus necessary to evaluate whether and how taurine might benefit patients.

Use of plant-based hallucinogens and dissociative agents: U.S. Time Trends, 2002-2019

Aims

Information on time trends in use of different plant-based hallucinogens is lacking. The current study used nationally representative U.S. data to assess overall and age-specific time trends in the prevalence of lifetime and 12-month use of plant-based hallucinogens and dissociative agents.

Methods

Participants were respondents aged ≥ 12 years (N = 1,006,051) from the National Survey on Drug Use and Health, 2002-2019. Predictors were continuous years. Outcomes included illicit use of peyote, mescaline, psilocybin, ketamine, salvia, and tryptamine. Sociodemographic variables (gender; age; race/ethnicity; educational level; family income) were modeled as covariates. Trends were estimated overall and by age (12-17, 18-25, 26+). Prevalence differences [PDs] were obtained for each category, along with 95 % confidence intervals [CI].

Results

Increases in lifetime use were observed for psilocybin (2002-2019 PD=+1.61), tryptamine (2006-2014 PD=+0.55; 2015-2019 PD=+0.44), and ketamine (2006-2014 PD=+0.27; 2015-2019 PD=+0.21). Mescaline use decreased (PD = -0.89). While overall lifetime salvia use increased between 2006 and 2014 (PD=+1.81), prevalence did not change between 2015 and 2019. Twelve-month use of tryptamine and ketamine increased between 2006 and 2014 (PD=+0.14; +0.03, respectively). Twelve-month ketamine use also increased from 2015 to 2019 (PD=+0.03). By age, participants aged 12-17 and 18-25 showed decreases in use of most types of hallucinogens, but those age 26+ generally showed increases.

Conclusions

While use of plant-based hallucinogens and dissociative agents remains rare, lifetime use of ketamine, tryptamine, and psilocybin is increasing in adults. Considering these increases alongside concerns about unsupervised use of illicit products whose dose and composition is uncertain, clinicians and policymakers should remain mindful of the rising rates of illicit use in the general population.

Dual action of ketamine confines addiction liability

Ketamine is used clinically as an anaesthetic and a fast-acting antidepressant, and recreationally for its dissociative properties, raising concerns of addiction as a possible side effect. Addictive drugs such as cocaine increase the levels of dopamine in the nucleus accumbens. This facilitates synaptic plasticity in the mesolimbic system, which causes behavioural adaptations and eventually drives the transition to compulsion^1-4. The addiction liability of ketamine is a matter of much debate, in part because of its complex pharmacology that among several targets includes N-methyl-D-aspartic acid (NMDA) receptor (NMDAR) antagonism^5,6. Here we show that ketamine does not induce the synaptic plasticity that is typically observed with addictive drugs in mice, despite eliciting robust dopamine transients in the nucleus accumbens. Ketamine nevertheless supported reinforcement through the disinhibition of dopamine neurons in the ventral tegmental area (VTA). This effect was mediated by NMDAR antagonism in GABA (γ-aminobutyric acid) neurons of the VTA, but was quickly terminated by type-2 dopamine receptors on dopamine neurons. The rapid off-kinetics of the dopamine transients along with the NMDAR antagonism precluded the induction of synaptic plasticity in the VTA and the nucleus accumbens, and did not elicit locomotor sensitization or uncontrolled self-administration. In summary, the dual action of ketamine leads to a unique constellation of dopamine-driven positive reinforcement, but low addiction liability.

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.

The chemical induction of synaesthesia

OBJECTIVE

Preliminary research suggests that experiences resembling synaesthesia are frequently reported under the influence of a diverse range of chemical substances although the incidence, chemical specificity, and characteristics of these effects are poorly understood.

METHODS

Here we surveyed recreational drug users and self-reported developmental synaesthetes regarding their use of 28 psychoactive drugs from 12 different drug classes and whether they had experienced synaesthesia under the influence of these substances.

RESULTS

The drug class of tryptamines exhibited the highest incidence rates of drug-induced synaesthesia in controls and induction rates of novel forms of synaesthesia in developmental synaesthetes. Induction incidence rates in controls were strongly correlated with the corresponding induction and enhancement rates in developmental synaesthetes. In addition, the use of lysergic acid diethylamide (LSD) was the strongest predictor of drug-induced synaesthesia in both controls and developmental synaesthetes. Clear evidence was observed for a clustering of synaesthesia-induction rates as a function of drug class in both groups, denoting non-random incidence rates within drug classes. Sound-colour synaesthesia was the most commonly observed type of induced synaesthesia. Further analyses suggest the presence of synaesthesia-prone individuals, who were more likely to experience drug-induced synaesthesia with multiple drugs.

CONCLUSIONS

These data corroborate the hypothesized link between drug-induced synaesthesia and serotoninergic activity, but also suggest the possibility of alternative neurochemical pathways involved in the induction of synaesthesia. They further imply that the induction and modulation of synaesthesia in controls and developmental synaesthetes share overlapping mechanisms and that certain individuals may be more susceptible to experiencing induced synaesthesia with different drugs.

Targeting Affective Mood Disorders With Ketamine to Prevent Chronic Postsurgical Pain

The phencyclidine-derivative ketamine [2-(2-chlorophenyl)-2-(methylamino)cyclohexan-1-one] was added to the World Health Organization's Model List of Essential Medicines in 1985 and is also on the Model List of Essential Medicines for Children due to its efficacy and safety as an intravenous anesthetic. In sub-anesthetic doses, ketamine is an effective analgesic for the treatment of acute pain (such as may occur in the perioperative setting). Additionally, ketamine may have efficacy in relieving some forms of chronic pain. In 2019, Janssen Pharmaceuticals received regulatory-approval in both the United States and Europe for use of the S-enantiomer of ketamine in adults living with treatment-resistant major depressive disorder. Pre-existing anxiety/depression and the severity of postoperative pain are risk factors for development of chronic postsurgical pain. An important question is whether short-term administration of ketamine can prevent the conversion of acute postsurgical pain to chronic postsurgical pain. Here, we have reviewed ketamine's effects on the biopsychological processes underlying pain perception and affective mood disorders, focusing on non-NMDA receptor-mediated effects, with an emphasis on results from human trials where available.

Dysfunctional Heteroreceptor Complexes as Novel Targets for the Treatment of Major Depressive and Anxiety Disorders

Among mental diseases, major depressive disorder (MDD) and anxiety deserve a special place due to their high prevalence and their negative impact both on society and patients suffering from these disorders. Consequently, the development of novel strategies designed to treat them quickly and efficiently, without or at least having limited side effects, is considered a highly important goal. Growing evidence indicates that emerging properties are developed on recognition, trafficking, and signaling of G-protein coupled receptors (GPCRs) upon their heteromerization with other types of GPCRs, receptor tyrosine kinases, and ionotropic receptors such as N-methyl-D-aspartate (NMDA) receptors. Therefore, to develop new treatments for MDD and anxiety, it will be important to identify the most vulnerable heteroreceptor complexes involved in MDD and anxiety. This review focuses on how GPCRs, especially serotonin, dopamine, galanin, and opioid heteroreceptor complexes, modulate synaptic and volume transmission in the limbic networks of the brain. We attempt to provide information showing how these emerging concepts can contribute to finding new ways to treat both MDD and anxiety disorders.

Management of Postoperative Pain in Patients Following Spine Surgery: A Narrative Review

Perioperative pain management is a unique challenge in patients undergoing spine surgery due to the increased incidence of both pre-existing chronic pain conditions and chronic postsurgical pain. Peri-operative planning and counseling in spine surgery should involve an interdisciplinary approach that includes consideration of patient-level risk factors, as well as pharmacologic and non-pharmacologic pain management techniques. Consideration of psychological factors and patient focused education as an adjunct to these measures is paramount in developing a personalized perioperative pain management plan. Understanding the currently available body of knowledge surrounding perioperative opioid management, management of opioid use disorder, regional/neuraxial anesthetic techniques, ketamine/lidocaine infusions, non-opioid oral analgesics, and behavioral interventions can be useful in developing a comprehensive, multi-modal treatment plan among patients undergoing spine surgery. Although many of these techniques have proved efficacious in the immediate postoperative period, long-term follow-up is needed to define the impact of such approaches on persistent pain and opioid use. Future techniques involving the use of precision medicine may help identify phenotypic and physiologic characteristics that can identify patients that are most at risk of developing persistent postoperative pain after spine surgery.

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.

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.

Mechanisms of ketamine and its metabolites as antidepressants

Treating major depression is a medical need that remains unmet by monoaminergic therapeutic strategies that commonly fail to achieve symptom remission. A breakthrough in the treatment of depression was the discovery that the anesthetic (R,S)-ketamine (ketamine), when administered at sub-anesthetic doses, elicits rapid (sometimes within hours) antidepressant effects in humans that are otherwise resistant to monoaminergic-acting therapies. While this finding was revolutionary and led to the FDA approval of (S)-ketamine (esketamine) for use in adults with treatment-resistant depression and suicidal ideation, the mechanisms underlying how ketamine or esketamine elicit their effects are still under active investigation. An emerging view is that metabolism of ketamine may be a crucial step in its mechanism of action, as several metabolites of ketamine have neuroactive effects of their own and may be leveraged as therapeutics. For example, (2R,6R)-hydroxynorketamine (HNK), is readily observed in humans following ketamine treatment and has shown therapeutic potential in preclinical tests of antidepressant efficacy and synaptic potentiation while being devoid of the negative adverse effects of ketamine, including its dissociative properties and abuse potential. We discuss preclinical and clinical studies pertaining to how ketamine and its metabolites produce antidepressant effects. Specifically, we explore effects on glutamate neurotransmission through N-methyl D-aspartate receptors (NMDARs) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs), synaptic structural changes via brain derived neurotrophic factor (BDNF) signaling, interactions with opioid receptors, and the enhancement of serotonin, norepinephrine, and dopamine signaling. Strategic targeting of these mechanisms may result in novel rapid-acting antidepressants with fewer undesirable side effects compared to ketamine.

Distribution of Aquaporin-4 channels in hippocampus and prefrontal cortex in mk-801-treated balb/c mice

Functional disorders of the glymphatic system and Aquaporin-4 (AQP-4) channels take part in the pathophysiology of neurodegenerative disease. The aim of this study was to describe the distribution of AQP-4 channels in the prefrontal cortex and hippocampus in a mouse model of NMDA receptor blocking agent-induced schizophrenia-like behavior model. NMDA receptor antagonist MK-801 was used to produce the experimental schizophrenia model. MK-801 injections were administered for eleven days to Balb/c mice intraperitoneally. Beginning from the sixth day of injection, the spatial learning and memory of the mice were tested by the Morris water maze (MWM) task. A group of mice was injected with MK-801 for ten days without the MWM task. Hippocampus and prefrontal specimens were collected from this group. Tissue samples were stained immunohistochemically and AQP-4 channels were examined by electron microscope. Time to find the platform was significantly longer at MK-801 injected group than the control group at the MWM task. Also, time spent at the target quadrant by the MK-801 group was shorter compared to the control group. AQP-4 expression increased significantly at MK-801 group glial cells, neuronal perikaryon, perineuronal and pericapillary spaces. In the MK-801 group, there was remarkable damage in neurons and glial cells. Increased AQP-4 channel expression and neurodegeneration at the MK-801 group induced with schizophrenia-like behavior model. MK-801 induced NMDA receptor blockade causes a decline in cognitive and memory functions. Increased AQP-4 expression at the prefrontal cortex and hippocampus to elicit and transport products of synaptic neurotransmitters and end metabolites is suggested.

Novel Insights Into the Neurobiology of the Antidepressant Response From Ketamine Research: A Mini Review

The serendipitous discovery of ketamine’s antidepressant effects represents one of the major landmarks in neuropsychopharmacological research of the last 50 years. Ketamine provides an exciting challenge to traditional concepts of antidepressant drug therapy, producing rapid antidepressant effects seemingly without targeting monoaminergic pathways in the conventional way. In consequence, the advent of ketamine has spawned a plethora of neurobiological research into its putative mechanisms. Here, we provide a brief overview of current theories of antidepressant drug action including monoaminergic signaling, disinhibition of glutamatergic neurotransmission, neurotrophic and neuroplastic effects, and how these might relate to ketamine. Given that research into ketamine has not yet yielded new therapies beyond ketamine itself, current knowledge gaps and limitations of available studies are also discussed.

On no man's land: Subjective experiences during unresponsive and responsive sedative states induced by four different anesthetic agents

To understand how anesthetics with different molecular mechanisms affect consciousness, we explored subjective experiences recalled after responsive and unresponsive sedation induced with equisedative doses of dexmedetomidine, propofol, sevoflurane, and S-ketamine in healthy male participants (N = 140). The anesthetics were administered in experimental setting using target-controlled infusion or vapouriser for one hour. Interviews conducted after anesthetic administration revealed that 46.9% (n = 46) of arousable participants (n = 98) reported experiences, most frequently dreaming or memory incorporation of the setting. Participants receiving dexmedetomidine reported experiences most often while S-ketamine induced the most multimodal experiences. Responsiveness at the end of anesthetic administration did not affect the prevalence or content of reported experiences. These results demonstrate that subjective experiences during responsive and unresponsive sedation are common and anesthetic agents with different molecular mechanisms of action may have different effects on the prevalence and complexity of the experiences, albeit in the present sample the differences between drugs were minute.

Identification of Molecular Markers of Clozapine Action in Ketamine-Induced Cognitive Impairment: A GPCR Signaling PathwayFinder Study

Background: Cognitive disorders associated with schizophrenia are closely linked to prefrontal cortex (PFC) dysfunction. Administration of the non-competitive NMDA receptor antagonist ketamine (KET) induces cognitive impairment in animals, producing effects similar to those observed in schizophrenic patients. In a previous study, we showed that KET (20 mg/kg) induces cognitive deficits in mice and that administration of clozapine (CLZ) reverses this effect. To identify biochemical mechanisms related to CLZ actions in the context of KET-induced impairment, we performed a biochemical analysis using the same experimental paradigm—acute and sub-chronic administration of these drugs (0.3 and 1 mg/kg). Methods: Since the effect of CLZ mainly depends on G-protein-related receptors, we used the Signaling PathwayFinder Kit to identify 84 genes involved in GPCR-related signal transduction and then verified the genes that were statistically significantly different on a larger group of mice using RT-PCR and Western blot analyses after the administration of acute and sub-chronic drugs. Results: Of the 84 genes involved in GPCR-related signal transduction, the expression of six, βarrestin1, βarrestin2, galanin receptor 2 (GalR2), dopamine receptor 2 (DRD2), metabotropic glutamate receptor 1 (mGluR1), and metabotropic glutamate receptor 5 (mGluR5), was significantly altered. Since these genes affect the levels of other signaling proteins, e.g., extracellular signal-regulated kinase 1/2 (ERK1/2), G protein-coupled receptor kinase 2 (Grk2), and G protein-gated inwardly rectifying potassium 3 (Girk3), we determined their levels in PFC using Western blot. Most of the observed changes occurred after acute treatment with 0.3 mg/kg CLZ. We showed that acute treatment with CLZ at a lower dose significantly increased βarrestin1 and ERK1/2. KET treatment induced the upregulation of βarrestin1. Joint administration of these drugs had no effect on the βarrestin1 level. Conclusion: The screening kit we used to study the expression of GPCR-related signal transduction allowed us to select several important genes affected by CLZ. However, the obtained data do not explain the mechanism of action of CLZ that is responsible for reversing KET-induced cognitive impairment.

Prevention and reversal of ketamine-induced experimental psychosis in mice by the neuroactive flavonoid, hesperidin: The role of oxidative and cholinergic mechanisms

Currently, prevailing evidence have identified cholinergic and oxidative pathways as important therapeutic targets for abating ketamine-induced schizophrenia-like behavior. Thus, this study evaluated the ability of hesperidin, a naturally occurring antioxidant and neuroprotective flavonoid, to prevent and reverse ketamine-induced schizophrenia-like behaviors and changes in cholinergic, oxidative and nitrergic status in mice. Forty-eight male Swiss mice were allotted into the preventive and reversal studies with 4 groups (n = 6) each. In the preventive study, groups 1 and 2 received vehicle (10 mL/kg/p.o./day), while groups 3 and 4 had hesperidin (100 mg/kg/p.o./day) for 14 days, but ketamine (20 mg/kg/i.p./day) was concurrently given to groups 2 and 4 from days 8-14. In the reversal study, groups 1 and 3 received vehicle, groups 2 and 4 were pretreated with ketamine for 14 days. Nevertheless, groups 3 and 4 additionally received hesperidin from days 8-14. Thereafter, schizophrenia-like behavior from exploratory activity, open-field (positive symptoms), Y-maze (cognitive symptoms) and social interaction (negative symptoms) tests were evaluated. Brain levels of oxidative/nitrergic (glutathione, superoxide-dismutase, malondialdehyde and nitrite levels) and cholinergic (acetylcholinesterase activity) markers were measured in the prefrontal-cortex, striatum and hippocampus. Hesperidin prevents and reverses ketamine-induced hyperactivities, social withdrawal and cognitive impairment. Also, hesperidin prevented and reversed ketamine-induced decrease in glutathione and superoxide-dismutase levels in the prefrontal-cortical, striatal and hippocampal brain regions in mice. Consequently, hesperidin attenuated ketamine-induced increase in malondialdehyde, nitrite levels and acetylcholinesterase activities in the prefrontal-cortex, striatum and hippocampus, respectively. The study showed that hesperidin prevents and reverses ketamine-induced schizophrenia-like behavior through inhibition of oxidative/nitrergic stress and acetylcholinesterase activity in mice brains. Therefore, these findings suggest that hesperidin dietary supplementation could provide natural nutritional intervention to protect against epigenetic-induced mental ill-health like schizophrenia, and thus serve as an important agent for nutritional psychiatry.

Assessment of antidepressant-like effects of dextromethorphan on differential reinforcement of low-rate 72-s performance in rats

The effectiveness of ketamine for treatment-resistant depression along with several other clinical advantages, such as rapid onset and reduced adverse effects associated with serotonin transporter inhibition, has garnered interest in other similar acting psychedelics as novel antidepressant drugs. The antitussive dextromethorphan exhibits glutamate N-methyl-d-aspartate receptor antagonism, sigma-1 receptor agonism, and serotonin reuptake inhibition, which has exhibited antidepressant effects in limited human studies and animal models. The present study sought to further examine dextromethorphan using a differential reinforcement of low-rate 72-s schedule, which can be used to screen antidepressant drugs, in male and female rats. The tricyclic antidepressant drug imipramine and the psychostimulant d-amphetamine also were examined. Sex differences were not shown for baseline performance or for the drugs tested. Further, performance did not differ between the estrus and diestrus stages. Dextromethorphan alone and with quinidine produced an antidepressant-like effect by reducing the number of responses emitted, increasing the number of reinforcers earned, and shifting inter-response times to the right, although significant response suppression occurred at these doses. An antidepressant-like effect was shown with imipramine, but d-amphetamine increased the number of responses emitted and did not affect the number of reinforcers earned. The present findings provide additional support for antidepressant effects produced by dextromethorphan.

Pharmaco-Magnetic Resonance as a Tool for Monitoring the Medication-Related Effects in the Brain May Provide Potential Biomarkers for Psychotic Disorders

The neurodegenerative and neurodevelopmental hypotheses represent the basic etiological framework for the origin of schizophrenia. Additionally, the dopamine hypothesis, adopted more than two decades ago, has repeatedly asserted the position of dopamine as a pathobiochemical substrate through the action of psychostimulants and neuroleptics on the mesolimbic and mesocortical systems, giving insight into the origin of positive and negative schizophrenic symptoms. Meanwhile, cognitive impairments in schizophrenia remain incompletely understood but are thought to be present during all stages of the disease, as well as in the prodromal, interictal and residual phases. On the other hand, observations on the effects of NMDA antagonists, such as ketamine and phencyclidine, reveal that hypoglutamatergic neurotransmission causes not only positive and negative but also cognitive schizophrenic symptoms. This review aims to summarize the different hypotheses about the origin of psychoses and to identify the optimal neuroimaging method that can serve to unite them in an integral etiological framework. We systematically searched Google scholar (with no concern to the date published) to identify studies investigating the etiology of schizophrenia, with a focus on impaired central neurotransmission. The complex interaction between the dopamine and glutamate neurotransmitter systems provides the long-needed etiological concept, which combines the neurodegenerative hypothesis with the hypothesis of impaired neurodevelopment in schizophrenia. Pharmaco-magnetic resonance imaging is a neuroimaging method that can provide a translation of scientific knowledge about the neural networks and the disruptions in and between different brain regions, into clinically applicable and effective therapeutic results in the management of severe psychotic disorders.

The dopamine D2 agonist quinpirole impairs frontal mismatch responses to sound frequency deviations in freely moving rats

Aim

A reduced mismatch negativity (MMN) response is a promising electrophysiological endophenotype of schizophrenia that reflects neurocognitive impairment. Dopamine dysfunction is associated with symptoms of schizophrenia. However, whether the dopamine system is involved in MMN impairment remains controversial. In this study, we investigated the effects of the dopamine D2‐like receptor agonist quinpirole on mismatch responses to sound frequency changes in an animal model.

Methods

Event‐related potentials were recorded from electrocorticogram electrodes placed on the auditory and frontal cortices of freely moving rats using a frequency oddball paradigm consisting of ascending and equiprobable (ie, many standards) control sequences before and after the subcutaneous administration of quinpirole. To detect mismatch responses, difference waveforms were obtained by subtracting nondeviant control waveforms from deviant waveforms.

Results

Here, we show the significant effects of quinpirole on frontal mismatch responses to sound frequency deviations in rats. Quinpirole delayed the frontal N18 and P30 mismatch responses and reduced the frontal N55 MMN‐like response, which resulted from the reduction in the N55 amplitude to deviant stimuli. Importantly, the magnitude of the N55 amplitude was negatively correlated with the time of the P30 latency in the difference waveforms. In contrast, quinpirole administration did not clearly affect the temporal mismatch responses recorded from the auditory cortex.

Conclusion

These results suggest that the disruption of dopamine D2‐like receptor signaling by quinpirole reduces frontal MMN to sound frequency deviations and that delays in early mismatch responses are involved in this MMN impairment.

The subcutaneous administration of quinpirole delayed early mismatch response latencies and reduced a late MMN‐like response amplitude recorded from the frontal cortex but had no effect on those recorded from the auditory cortex. These observations suggest that increased dopamine D2‐like receptor signaling impairs MMN generation to sound frequency changes in the frontal cortex and that the neurochemical mechanisms of MMN vary according to the cortical area. As MMN is associated with cognitive function, these new findings may help develop treatment modalities for cognitive dysfunctions in schizophrenia.

Sustained NMDA receptor hypofunction impairs brain-derived neurotropic factor signalling in the PFC, but not in the hippocampus, and disturbs PFC-dependent cognition in mice

BACKGROUND

Cognitive deficits profoundly impact on the quality of life of patients with schizophrenia. Alterations in brain derived neurotrophic factor (BDNF) signalling, which regulates synaptic function through the activation of full-length tropomyosin-related kinase B receptors (TrkB-FL), are implicated in the aetiology of schizophrenia, as is N-methyl-D-aspartate receptor (NMDA-R) hypofunction. However, whether NMDA-R hypofunction contributes to the disrupted BDNF signalling seen in patients remains unknown.

AIMS

The purpose of this study was to characterise BDNF signalling and function in a preclinical rodent model relevant to schizophrenia induced by prolonged NMDA-R hypofunction.

METHODS

Using the subchronic phencyclidine (PCP) model, we performed electrophysiology approaches, molecular characterisation and behavioural analysis.

RESULTS

The data showed that prolonged NMDA-R antagonism, induced by subchronic PCP treatment, impairs long-term potentiation (LTP) and the facilitatory effect of BDNF upon LTP in the medial prefrontal cortex (PFC) of adult mice. Additionally, TrkB-FL receptor expression is decreased in the PFC of these animals. By contrast, these changes were not present in the hippocampus of PCP-treated mice. Moreover, BDNF levels were not altered in the hippocampus or PFC of PCP-treated mice. Interestingly, these observations are paralleled by impaired performance in PFC-dependent cognitive tests in mice treated with PCP.

CONCLUSIONS

Overall, these data suggest that NMDA-R hypofunction induces dysfunctional BDNF signalling in the PFC, but not in the hippocampus, which may contribute to the PFC-dependent cognitive deficits seen in the subchronic PCP model. Additionally, these data suggest that targeting BDNF signalling may be a mechanism to improve PFC-dependent cognitive dysfunction in schizophrenia.

The Perception of the Müller-Lyer Visual Illusion in Schizophrenics and Non-human Primates: A Translational Approach

The Müller-Lyer Illusion (MLI) has been suggested as a potential marker for the perceptual impairments observed in schizophrenia patients. Along with some positive symptoms, these deficits are not easily modeled in rodent experiments, and novel animal models are warranted. Previously, MK-801 was shown to reduce susceptibility to MLI in monkeys, raising the prospects of an effective perception-based model. Here, we evaluate the translational feasibility of the MLI task under NMDA receptor blockage as a primate model for schizophrenia. In Experiment 1, eight capuchin monkeys (Sapajus spp.) were trained on a touchscreen MLI task. Upon reaching the learning criteria, the monkeys were given ketamine (0.3 mg/kg; i.m.) or saline on four consecutive days and then retested on the MLI task. In Experiment 2, eight chronic schizophrenia patients (and eight matching controls) were tested on the Brentano version of the MLI. Under saline treatment, monkeys were susceptible to MLI, similarly to healthy human participants. Repeated ketamine administrations, however, failed to improve their performance as previous results with MK-801 had shown. Schizophrenic patients, on the other hand, showed a higher susceptibility to MLI when compared to healthy controls. In light of the present and previous studies, the MLI task shows consistent results across monkeys and humans. In spite of potentially being an interesting translational model of schizophrenia, the MLI task warrants further refinement in non-human primates and a broader sample of schizophrenia subtypes.

Ketamine's schizophrenia-like effects are prevented by targeting PTP1B

Subanesthetic doses of ketamine induce schizophrenia-like behaviors in mice including hyperlocomotion and deficits in working memory and sensorimotor gating. Here, we examined the effect of in vivo ketamine administration on neuronal properties and endocannabinoid (eCB)-dependent modulation of synaptic transmission onto layer 2/3 pyramidal neurons in brain slices of the prefrontal cortex, a region tied to the schizophrenia-like behavioral phenotypes of ketamine. Since deficits in working memory and sensorimotor gating are tied to activation of the tyrosine phosphatase PTP1B in glutamatergic neurons, we asked whether PTP1B contributes to these effects of ketamine. Ketamine increased membrane resistance and excitability of pyramidal neurons. Systemic pharmacological inhibition of PTP1B by Trodusquemine restored these neuronal properties and prevented each of the three main ketamine-induced behavior deficits. Ketamine also reduced mobilization of eCB by pyramidal neurons, while unexpectedly reducing their inhibitory inputs, and these effects of ketamine were blocked or occluded by PTP1B ablation in glutamatergic neurons. While ablation of PTP1B in glutamatergic neurons prevented ketamine-induced deficits in memory and sensorimotor gating, it failed to prevent hyperlocomotion (a psychosis-like phenotype). Taken together, these results suggest that PTP1B in glutamatergic neurons mediates ketamine-induced deficits in eCB mobilization, memory and sensorimotor gating whereas PTP1B in other cell types contributes to hyperlocomotion. Our study suggests that the PTP1B inhibitor Trodusquemine may represent a new class of fast-acting antipsychotic drugs to treat schizophrenia-like symptoms.

The Role of G Protein-Coupled Receptors (GPCRs) and Calcium Signaling in Schizophrenia. Focus on GPCRs Activated by Neurotransmitters and Chemokines

Schizophrenia is a common debilitating disease characterized by continuous or relapsing episodes of psychosis. Although the molecular mechanisms underlying this psychiatric illness remain incompletely understood, a growing body of clinical, pharmacological, and genetic evidence suggests that G protein-coupled receptors (GPCRs) play a critical role in disease development, progression, and treatment. This pivotal role is further highlighted by the fact that GPCRs are the most common targets for antipsychotic drugs. The GPCRs activation evokes slow synaptic transmission through several downstream pathways, many of them engaging intracellular Ca²⁺ mobilization. Dysfunctions of the neurotransmitter systems involving the action of GPCRs in the frontal and limbic-related regions are likely to underly the complex picture that includes the whole spectrum of positive and negative schizophrenia symptoms. Therefore, the progress in our understanding of GPCRs function in the control of brain cognitive functions is expected to open new avenues for selective drug development. In this paper, we review and synthesize the recent data regarding the contribution of neurotransmitter-GPCRs signaling to schizophrenia symptomology.

The multiple faces of ketamine in anaesthesia and analgesia

Objective

Ketamine is an anaesthetic agent with a unique dissociative profile and pharmacological effects ranging from the induction and maintenance of anaesthesia to analgesia and sedation, depending on the dose. This article provides information for the clinical use of ketamine in anaesthesia, in both conventional and special circumstances.

Methods

This is a non-systematic review of the literature, through a PubMed search up to February 2021.

Results

With a favourable pharmacokinetic profile, ketamine is used in hospital and prehospital settings for emergency situations. It is suitable for patients with many heart conditions and, unlike other anaesthetics, its potential for cardiorespiratory depression is low. Furthermore, it may be used when venous access is difficult as it may be administered through various routes. Ketamine is the anaesthetic of choice for patients with bronchospasm thanks to its bronchodilatory and anti-inflammatory properties.

Conclusion

With a favourable pharmacokinetic profile, ketamine is used in hospital and prehospital settings for emergency situations and is suitable for patients with many cardiac and respiratory conditions.

New insights on nitric oxide: Focus on animal models of schizophrenia

Schizophrenia is a devastating complex disorder characterised by a constellation of behavioral deficits with the underlying mechanisms not fully known. Nitric oxide (NO) has emerged as a key signaling molecule implicated in schizophrenia. Three nitric oxide sinthases (NOS), endothelial, neuronal, and inducible, release NO within the cell. Animal models of schizophrenia are grouped in four groups, neurovedelopmental, glutamatergic, dopaminergic and genetic. In this review, we aim to evaluate changes in NO levels in animal models of schizophrenia and the resulting long-lasting behavioral and neural consequences. In particular, NO levels are substantially modified, region-specific, in various neurodevelopmental models, e.g. bilateral excitotoxic lesion of the ventral hippocampus (nVHL), maternal immune activation and direct NO manipulations early in development, among others. In regards to glutamatergic models of schizophrenia, phencyclidine (PCP) administration increases NO levels in the prefrontal cortex (PFC) and ventral hippocampus. As far as genetic models are concerned, neuronal NOS knock-out mice display schizophrenia-related behaviors. Administration of NO donors can reverse schizophrenia-related behavioral deficits. While most modifications in NO are derived from neuronal NOS, recent evidence indicates that PCP treatment increases NO from the inducible NOS isoform. From a pharmacological perspective, treatment with various antipsychotics including clozapine, haloperidol and risperidone normalize NO levels in the PFC as well as improve behavioral deficits in nVHL rats. NO induced from the neuronal and inducible NOS is relevant to schizophrenia and warrants further research.

Consciousness among delta waves: a paradox?

A common observation in EEG research is that consciousness vanishes with the appearance of delta (1 - 4 Hz) waves, particularly when those waves are high amplitude. High amplitude delta oscillations are very frequently observed in states of diminished consciousness, including slow wave sleep, anaesthesia, generalised epileptic seizures, and disorders of consciousness such as coma and vegetative state. This strong correlation between loss of consciousness and high amplitude delta oscillations is thought to stem from the widespread cortical deactivation that occurs during the "down states" or troughs of these slow oscillations. Recently, however, many studies have reported the presence of prominent delta activity during conscious states, which casts doubt on the hypothesis that high amplitude delta oscillations are an indicator of unconsciousness. These studies include work in Angelman syndrome, epilepsy, behavioural responsiveness during propofol anaesthesia, postoperative delirium, and states of dissociation from the environment such as dreaming and powerful psychedelic states. The foregoing studies complement an older, yet largely unacknowledged, body of literature that has documented awake, conscious patients with high amplitude delta oscillations in clinical reports from Rett syndrome, Lennox-Gastaut syndrome, schizophrenia, mitochondrial diseases, hepatic encephalopathy, and nonconvulsive status epilepticus. At the same time, a largely parallel body of recent work has reported convincing evidence that the complexity or entropy of EEG and magnetoencephalogram or MEG signals strongly relates to an individual's level of consciousness. Having reviewed this literature, we discuss plausible mechanisms that would resolve the seeming contradiction between high amplitude delta oscillations and consciousness. We also consider implications concerning theories of consciousness, such as integrated information theory and the entropic brain hypothesis. Finally, we conclude that false inferences of unconscious states can be best avoided by examining measures of electrophysiological complexity in addition to spectral power.

Ketamine Use for Cancer and Chronic Pain Management

Ketamine, an N-methyl-D-aspartate receptor antagonist, is widely known as a dissociative anesthetic and phencyclidine derivative. Due to an undesirable adverse event profile when used as an anesthetic it had widely fallen out of human use in favor of more modern agents. However, it has recently been explored for several other indications such as treatment resistant depression and chronic pain. Several recent studies and case reports compiled here show that ketamine is an effective analgesic in chronic pain conditions including cancer-related neuropathic pain. Of special interest is ketamine’s opioid sparing ability by counteracting the central nervous system sensitization seen in opioid induced hyperalgesia. Furthermore, at the sub-anesthetic concentrations used for analgesia ketamine’s safety and adverse event profiles are much improved. In this article, we review both the basic science and clinical evidence regarding ketamine’s utility in chronic pain conditions as well as potential adverse events.

Ketamine reduces temporal expectation in the rhesus monkey

RATIONALE

Ketamine, a well-known general dissociative anesthetic agent that is a non-competitive antagonist of the N-methyl-D-aspartate receptor, perturbs the perception of elapsed time and the expectation of upcoming events.

OBJECTIVE

The objective of this study was to determine the influence of ketamine on temporal expectation in the rhesus monkey.

METHODS

Two rhesus monkeys were trained to make a saccade between a central warning stimulus and an eccentric visual target that served as imperative stimulus. The delay between the warning and the imperative stimulus could take one of four different values randomly with the same probability (variable foreperiod paradigm). During experimental sessions, a subanesthetic low dose of ketamine (0.25-0.35 mg/kg) was injected i.m. and the influence of the drug on movement latency was measured.

RESULTS

We found that in the control conditions, saccadic latencies strongly decreased with elapsed time before the appearance of the visual target showing that temporal expectation built up during the delay period between the warning and the imperative stimulus. However, after ketamine injection, temporal expectation was significantly reduced in both subjects. In addition, ketamine also increased average movement latency but this effect could be dissociated from the reduction of temporal expectation.

CONCLUSION

In conclusion, a subanesthetic dose of ketamine could have two independent effects: increasing reaction time and decreasing temporal expectation. This alteration of temporal expectation could explain cognitive deficits observed during ketamine use.

1-Phenylcyclohexan-1-amine hydrochloride (PCA HCl) alters mesolimbic dopamine system accompanied by neuroplastic changes: A neuropsychopharmacological evaluation in rodents

The recreational use of N-methyl-D-aspartate (NMDA) antagonist phencyclidine (PCP) and ketamine have grown rapidly due to their psychotomimetic properties. These compounds induce both non-fatal and fatal adverse effects and despite the enhanced regulation, they are continuously synthesized and are being sold in the illegal drug market, including 1-phenylcyclohexan-1-amine hydrochloride (PCA). Therefore, we evaluated its abuse potential through the conditioned-place preference (CPP), self-administration, and locomotor sensitization paradigms. Pretreatment with SCH 2 3390 and haloperidol was also performed during a CPP test. We used ELISA to measure dopamine (DA) levels and western blotting to determine effects on the DA-related proteins as well as on phosphorylated CREB, deltaFosB, and brain-derived neurotrophic factor (BDNF) in the ventral tegmental area (VTA) and nucleus accumbens (NAc). Finally, we examined the effects on brain wave activity using electroencephalography (EEG). PCA induced CPP in mice and was self-administered by rats, suggesting that PCA has rewarding and reinforcing properties. PCA increased locomotor of mice on the first treatment and challenge days. SCH 23390 and haloperidol blocked the CPP. PCA altered the DA, tyrosine hydroxylase, dopamine D1 and D2 receptors as well as p-CREB and deltaFosB. Also, PCA altered the delta and gamma waves in the brain, which were then normalized by SCH 2 3390 and haloperidol. The present findings indicate that PCA may induce abuse potential through the dopaminergic system and probably accompanied with alterations in brain wave activity which is similar to that of other psychotomimetic NMDA antagonists. We advocate thorough monitoring of PCP analogs as they pose potential harm to public health.

An Update on Glutamatergic System in Suicidal Depression and on the Role of Esketamine

BACKGROUND

A research on mood disorder pathophysiology has hypothesized abnormalities in glutamatergic neurotransmission, by suggesting further investigation on glutamatergic N-methyl-Daspartate (NMDA) receptor modulators in treating Major Depressive Disorder (MDD). Esketamine (ESK), an NMDA receptor antagonist able to modulate glutamatergic neurotransmission has been recently developed as an intranasal formulation for treatment-resistant depression (TRD) and for rapid reduction of depressive symptomatology, including suicidal ideation in MDD patients at imminent risk for suicide.

OBJECTIVE

The present study aims at investigating recent clinical findings on research on the role of the glutamatergic system and ESK in treating suicidal depression in MDD and TRD.

METHODS

A systematic review was here carried out on PubMed/Medline, Scopus and the database on U.S. N.I.H. Clinical Trials (https://clinicaltrials.gov) and the European Medical Agency (EMA) (https://clinicaltrialsregister.eu) from inception until October 2019.

RESULTS

Intravenous infusion of ESK is reported to elicit rapid-acting and sustained antidepressant activity in refractory patients with MDD and TRD. In phase II studies, intranasal ESK demonstrated a rapid onset and a persistent efficacy in patients with TRD as well as in MDD patients at imminent risk for suicide. However, some data discrepancies have emerged in phase III studies.

CONCLUSION

The U.S. Food and Drug Administration (FDA) granted fast track and Breakthrough Therapy Designation to Janssen Pharmaceuticals®, Inc. for intranasal ESK in 2013 for treatment-resistant depression (TRD) and in 2016 for the treatment of MDD with an imminent risk of suicide. However, further studies should be implemented to investigate the long-term efficacy and safety of intranasal ESK.

Differential effects of glutamate N-methyl-D-aspartate receptor antagonists on risky choice as assessed in the risky decision task

RATIONALE

Risky choice can be measured using the risky decision task (RDT). In the RDT, animals choose between a large, risky option that is paired with probabilistic foot shock and a small, safe option that is never paired with shock. To date, studies examining the neurochemical basis of decision-making in the RDT have focused primarily on the dopaminergic system but have not focused on the glutamatergic system, which has been implicated in risky decision-making.

OBJECTIVES

Because glutamate is known to play a critical role in decision-making, we wanted to determine the contribution of the glutamatergic system to performance in the RDT.

METHODS

In the experiment, 32 rats (16 male; 16 female) were tested in the RDT. The probability of receiving a foot shock increased across the session (ascending schedule) for half of the rats but decreased across the session (descending schedule) for half of the rats. Following training, rats received injections of the N-methyl-D-aspartate (NMDA) receptor competitive antagonist CGS 19755 (0, 1.0, 2.5, 5.0 mg/kg; s.c.) and the GluN2B-selective antagonist Ro 63-1908 (0, 0.1, 0.3, 1.0 mg/kg; s.c.).

RESULTS

CGS 19755 (2.5 and 5.0 mg/kg) increased risky choice in males and females trained on the ascending schedule. Ro 63-1908 (1.0 mg/kg) decreased risky choice, but only in male rats trained on the ascending schedule.

CONCLUSIONS

Although NMDA receptor antagonists differentially alter risky choice in the RDT, the current results show that NMDA receptors are an important mediator of decision-making involving probabilistic delivery of positive punishment.