Treating the Synapse in Major Psychiatric Disorders: The Role of Postsynaptic Density Network in Dopamine-Glutamate Interplay and Psychopharmacologic Drugs Molecular Actions

Identification of novel genomic loci for anxiety symptoms and extensive genetic overlap with psychiatric disorders

AIMS

Anxiety disorders are prevalent and anxiety symptoms (ANX) co-occur with many psychiatric disorders. We aimed to identify genomic loci associated with ANX, characterize its genetic architecture, and genetic overlap with psychiatric disorders.

METHODS

We included a genome-wide association study of ANX (meta-analysis of UK Biobank and Million Veterans Program, n = 301,732), schizophrenia (SCZ), bipolar disorder (BIP), major depression (MD), attention-deficit/hyperactivity disorder (ADHD), and autism spectrum disorder (ASD), and validated the findings in the Norwegian Mother, Father, and Child Cohort (n = 95,841). We employed the bivariate causal mixture model and local analysis of covariant association to characterize the genetic architecture including overlap between the phenotypes. Conditional and conjunctional false discovery rate analyses were performed to boost the identification of loci associated with anxiety and shared with psychiatric disorders.

RESULTS

Anxiety was polygenic with 12.9k genetic variants and overlapped extensively with psychiatric disorders (4.1k-11.4k variants) with predominantly positive genetic correlations between anxiety and psychiatric disorders. We identified 119 novel loci for anxiety by conditioning on the psychiatric disorders, and loci shared between anxiety and MDn = 47 $$ \left(n=47\right) $$ , BIPn = 33 $$ \left(n=33\right) $$ , SCZn = 71 $$ \left(n=71\right) $$ , ADHDn = 20 $$ \left(n=20\right) $$ , and ASDn = 5 $$ \left(n=5\right) $$ . Genes annotated to anxiety loci exhibit enrichment for a broader range of biological pathways including cell adhesion and neurofibrillary tangle compared with genes annotated to the shared loci.

CONCLUSIONS

Anxiety is highly polygenic phenotype with extensive genetic overlap with psychiatric disorders, and we identified novel loci for anxiety implicating new molecular pathways. The shared genetic architecture may underlie the extensive cross-disorder comorbidity of anxiety, and the identified molecular underpinnings may lead to potential drug targets.

Neurobiology and medico-legal aspects of suicides among older adults: a narrative review

The task of preventing suicide in older adults is an important social burden as older adults aged above 65 are exposed to singular psychological aspects that increase suicide risks. Moreover, when an older adult corpse is found, the medico-legal inspection represents a fundamental tool to identify the exact cause of death, classifying or excluding it as suicide. In this scenario, this review aims to explore the neurobiological factors that could be related to suicidal behavior in older adults. A further goal of this review is the exploration of the medico-legal aspects surrounding older adult suicides, clarifying the importance of forensic investigation. Particularly, this review examines issues such as neurotransmitter imbalances, cognitive impairment, neuroinflammation, psychosocial factors related to geriatric suicide, and neurodegenerative diseases. Additionally, medico-legal aspects such as policy considerations, legal frameworks, mental health assessments, ethical implications and forensic investigation were explored. Considering the importance of this phenomenon, especially in western countries, a need has emerged for focused screening tools on suicidal behavior among older adults, in order to contain it. Therefore, this review makes an exhaustive appraisal of the literature giving insights into the delicate interplay between neurobiology as well as mental health in relation to older adult suicide within a medico-legal context. The comprehension of different aspects about this complex phenomenon is fundamental to propose new and more effective interventions, supporting tailored initiatives such as family support and improving healthcare, specifically towards vulnerable ageing societies to reduce older adult suicide risks.

Post-Stroke Neuropsychiatric Complications: Types, Pathogenesis, and Therapeutic Intervention

Almost all stroke survivors suffer physical disabilities and neuropsychiatric disturbances, which can be briefly divided into post-stroke neurological diseases and post-stroke psychiatric disorders. The former type mainly includes post-stroke pain, post-stroke epilepsy, and post-stroke dementia while the latter one includes post-stroke depression, post-stroke anxiety, post-stroke apathy and post-stroke fatigue. Multiple risk factors are related to these post-stroke neuropsychiatric complications, such as age, gender, lifestyle, stroke type, medication, lesion location, and comorbidities. Recent studies have revealed several critical mechanisms underlying these complications, namely inflammatory response, dysregulation of the hypothalamic pituitary adrenal axis, cholinergic dysfunction, reduced level of 5-hydroxytryptamine, glutamate-mediated excitotoxicity and mitochondrial dysfunction. Moreover, clinical efforts have successfully given birth to many practical pharmaceutic strategies, such as anti-inflammatory medications, acetylcholinesterase inhibitors, and selective serotonin reuptake inhibitors, as well as diverse rehabilitative modalities to help patients physically and mentally. However, the efficacy of these interventions is still under debate. Further investigations into these post-stroke neuropsychiatric complications, from both basic and clinical perspectives, are urgent for the development of effective treatment strategies.

MDMA-Based Psychotherapy in Treatment-Resistant Post-Traumatic Stress Disorder (PTSD): A Brief Narrative Overview of Current Evidence

Post-traumatic stress disorder (PTSD) is a debilitating mental health disorder that causes significant dysfunction in individuals. Currently, there are many approved pharmacotherapy and psychotherapy treatment options for PTSD, but unfortunately, half of the patients do not respond to traditional therapies. In this article, we review clinical trials and research on 3,4-methylenedioxymethamphetamine (MDMA)-assisted psychotherapy in PTSD patients, its pharmacokinetics, and current treatment guidelines for PTSD. Our findings are based on the results of the efficacy of MDMA-assisted psychotherapy from six phase II randomized controlled trials. MDMA-assisted psychotherapy for PTSD has received the "breakthrough therapy" designation from the FDA. MDMA can reduce PTSD symptoms even in treatment-resistant cases by increasing certain neurohormones, i.e., dopamine, serotonin, norepinephrine, and oxytocin. It also modulates activities in the brain regions involved in fear and anxiety. Future research is needed to show whether the advantages outweigh the disadvantages and whether its use can be integrated into available treatment options for PTSD.

Mechanisms associated with post-stroke depression and pharmacologic therapy

Stroke is one of the most common cerebrovascular diseases, which is the cause of long-term mental illness and physical disability, Post-stroke depression (PSD) is the most common neuropsychiatric complication after stroke, and its mechanisms are characterized by complexity, plurality, and diversity, which seriously affects the quality of survival and prognosis of patients. Studies have focused on and recognized neurotransmitter-based mechanisms and selective serotonin-reuptake inhibitors (SSRIs) can be used to treat PSD. Neuroinflammation, neuroendocrinology, neurotrophic factors, and the site of the stroke lesion may affect neurotransmitters. Thus the mechanisms of PSD have been increasingly studied. Pharmacological treatment mainly includes SSRIs, noradrenergic and specific serotonergic antidepressant (NaSSA), anti-inflammatory drugs, vitamin D, ect, which have been confirmed to have better efficacy by clinical studies. Currently, there is an increasing number of studies related to the mechanisms of PSD. However, the mechanisms and pharmacologic treatment of PSD is still unclear. In the future, in-depth research on the mechanisms and treatment of PSD is needed to provide a reference for the prevention and treatment of clinical PSD.

The Neurobiological Underpinnings of Obsessive-Compulsive Symptoms in Psychosis, Translational Issues for Treatment-Resistant Schizophrenia

Almost 25% of schizophrenia patients suffer from obsessive-compulsive symptoms (OCS) considered a transdiagnostic clinical continuum. The presence of symptoms pertaining to both schizophrenia and obsessive-compulsive disorder (OCD) may complicate pharmacological treatment and could contribute to lack or poor response to the therapy. Despite the clinical relevance, no reviews have been recently published on the possible neurobiological underpinnings of this comorbidity, which is still unclear. An integrative view exploring this topic should take into account the following aspects: (i) the implication for glutamate, dopamine, and serotonin neurotransmission as demonstrated by genetic findings; (ii) the growing neuroimaging evidence of the common brain regions and dysfunctional circuits involved in both diseases; (iii) the pharmacological modulation of dopaminergic, serotoninergic, and glutamatergic systems as current therapeutic strategies in schizophrenia OCS; (iv) the recent discovery of midbrain dopamine neurons and dopamine D1- and D2-like receptors as orchestrating hubs in repetitive and psychotic behaviors; (v) the contribution of N-methyl-D-aspartate receptor subunits to both psychosis and OCD neurobiology. Finally, we discuss the potential role of the postsynaptic density as a structural and functional hub for multiple molecular signaling both in schizophrenia and OCD pathophysiology.

A synaptic molecular dependency network in knockdown of autism- and schizophrenia-associated genes revealed by multiplexed imaging

The complex functions of neuronal synapses depend on their tightly interconnected protein network, and their dysregulation is implicated in the pathogenesis of autism spectrum disorders and schizophrenia. However, it remains unclear how synaptic molecular networks are altered biochemically in these disorders. Here, we apply multiplexed imaging to probe the effects of RNAi knockdown of 16 autism- and schizophrenia-associated genes on the simultaneous joint distribution of 10 synaptic proteins, observing several protein composition phenotypes associated with these risk genes. We apply Bayesian network analysis to infer hierarchical dependencies among eight excitatory synaptic proteins, yielding predictive relationships that can only be accessed with single-synapse, multiprotein measurements performed simultaneously in situ. Finally, we find that central features of the network are affected similarly across several distinct gene knockdowns. These results offer insight into the convergent molecular etiology of these widespread disorders and provide a general framework to probe subcellular molecular networks.

Comparative Study of Time-Dependent Aluminum Exposure and Post-Exposure Recovery Shows Better Improvement in Synaptic Changes and Neuronal Pathology in Rat Brain After Short-Term Exposure

Aluminum is a ubiquitous metal that causes multiple brain pathologies such as, cognitive dysfunction and Alzheimer's disease like symptoms. Exposure to aluminum through drinking water is responsible for hampering learning and memory. This study aimed to compare (1) the time-dependent effect of aluminum exposure (keeping total exposure of 5850 mg/kg same) in two durations, 30 and 45 days, and (2) to compare post-exposure self-recovery effect after 20 days in both (30 and 45 days exposure) groups. Rats were given 130 and 195 mg/kg of AlCl₃·6H₂O for 45 and 30 days respectively, to see the time-dependent exposure effect. At the end of exposure, rats were given distilled water and allowed to self-recover for 20 days to study the recovery. Expression levels of synaptic genes (Syp, SNAP25, Nrxn1/2, PSD95, Shank1/2, Homer1, CamkIV, Nrg1/2 and Kalrn) were measured using qPCR and compared in the exposure and recovery groups. Cellular morphology of the rat brain cortex and hippocampus was also investigated. Damage in lipid and protein profile was measured by employing FTIR. Results showed downregulation of mRNA expression of synaptic genes, plaques deposition, disorganization in lipid and protein profile by increasing membrane fluidity, and disorder and alteration of protein secondary structure after both exposure periods. However, better improvement/recovery in these parameters were observed in recovery group of 30 days aluminum exposure compared to 45 days aluminum exposure group. Taken together, these results suggested that short-term exposure resulted in better restoration of lipid and protein profile after time-dependent exposure of aluminum than prolonged exposure.

Canonical and Non-Canonical Antipsychotics' Dopamine-Related Mechanisms of Present and Next Generation Molecules: A Systematic Review on Translational Highlights for Treatment Response and Treatment-Resistant Schizophrenia

Schizophrenia is a severe psychiatric illness affecting almost 25 million people worldwide and is conceptualized as a disorder of synaptic plasticity and brain connectivity. Antipsychotics are the primary pharmacological treatment after more than sixty years after their introduction in therapy. Two findings hold true for all presently available antipsychotics. First, all antipsychotics occupy the dopamine D2 receptor (D2R) as an antagonist or partial agonist, even if with different affinity; second, D2R occupancy is the necessary and probably the sufficient mechanism for antipsychotic effect despite the complexity of antipsychotics' receptor profile. D2R occupancy is followed by coincident or divergent intracellular mechanisms, implying the contribution of cAMP regulation, β-arrestin recruitment, and phospholipase A activation, to quote some of the mechanisms considered canonical. However, in recent years, novel mechanisms related to dopamine function beyond or together with D2R occupancy have emerged. Among these potentially non-canonical mechanisms, the role of Na²⁺ channels at the dopamine at the presynaptic site, dopamine transporter (DAT) involvement as the main regulator of dopamine concentration at synaptic clefts, and the putative role of antipsychotics as chaperones for intracellular D2R sequestration, should be included. These mechanisms expand the fundamental role of dopamine in schizophrenia therapy and may have relevance to considering putatively new strategies for treatment-resistant schizophrenia (TRS), an extremely severe condition epidemiologically relevant and affecting almost 30% of schizophrenia patients. Here, we performed a critical evaluation of the role of antipsychotics in synaptic plasticity, focusing on their canonical and non-canonical mechanisms of action relevant to the treatment of schizophrenia and their subsequent implication for the pathophysiology and potential therapy of TRS.

Dopamine Dynamics and Neurobiology of Non-Response to Antipsychotics, Relevance for Treatment Resistant Schizophrenia: A Systematic Review and Critical Appraisal

Treatment resistant schizophrenia (TRS) is characterized by a lack of, or suboptimal response to, antipsychotic agents. The biological underpinnings of this clinical condition are still scarcely understood. Since all antipsychotics block dopamine D2 receptors (D2R), dopamine-related mechanisms should be considered the main candidates in the neurobiology of antipsychotic non-response, although other neurotransmitter systems play a role. The aims of this review are: (i) to recapitulate and critically appraise the relevant literature on dopamine-related mechanisms of TRS; (ii) to discuss the methodological limitations of the studies so far conducted and delineate a theoretical framework on dopamine mechanisms of TRS; and (iii) to highlight future perspectives of research and unmet needs. Dopamine-related neurobiological mechanisms of TRS may be multiple and putatively subdivided into three biological points: (1) D2R-related, including increased D2R levels; increased density of D2Rs in the high-affinity state; aberrant D2R dimer or heteromer formation; imbalance between D2R short and long variants; extrastriatal D2Rs; (2) presynaptic dopamine, including low or normal dopamine synthesis and/or release compared to responder patients; and (3) exaggerated postsynaptic D2R-mediated neurotransmission. Future points to be addressed are: (i) a more neurobiologically-oriented phenotypic categorization of TRS; (ii) implementation of neurobiological studies by directly comparing treatment resistant vs. treatment responder patients; (iii) development of a reliable animal model of non-response to antipsychotics.

Transcranial direct current stimulation for bipolar depression: systematic reviews of clinical evidence and biological underpinnings

Despite multiple available treatments for bipolar depression (BD), many patients face sub-optimal responses. Transcranial direct current stimulation (tDCS) has been advocated in the management of different conditions, including BD, especially in treatment-resistant cases. The optimal dose and timing of tDCS, the mutual influence with other concurrently administered interventions, long-term efficacy, overall safety, and biological underpinnings nonetheless deserve additional assessment. The present study appraised the existing clinical evidence about tDCS for bipolar depression, delving into the putative biological underpinnings with a special emphasis on cellular and molecular levels, with the ultimate goal of providing a translational perspective on the matter. Two separate systematic reviews across the PubMed database since inception up to August 8^th 2022 were performed, with fourteen clinical and nineteen neurobiological eligible studies. The included clinical studies encompass 207 bipolar depression patients overall and consistently document the efficacy of tDCS, with a reduction in depression scores after treatment ranging from 18% to 92%. The RCT with the largest sample clearly showed a significant superiority of active stimulation over sham. Mild-to-moderate and transient adverse effects are attributed to tDCS across these studies. The review of neurobiological literature indicates that several molecular mechanisms may account for the antidepressant effect of tDCS in BD patients, including the action on calcium homeostasis in glial cells, the enhancement of LTP, the regulation of neurotrophic factors and inflammatory mediators, and the modulation of the expression of plasticity-related genes. To the best of our knowledge, this is the first study on the matter to concurrently provide a synthesis of the clinical evidence and an in-depth appraisal of the putative biological underpinnings, providing consistent support for the efficacy, safety, and tolerability of tDCS.

Esketamine for treatment‑resistant depression: A review of clinical evidence (Review)

Treatment-resistant depression (TRD) is a challenge for psychiatrists, even after more than seven decades since the first antidepressants were used in clinical practice. Non-monoaminergic-based drugs with antidepressant properties have been developed, but to date, only esketamine and brexanolone have been approved for TRD and postpartum depression, respectively. A narrative review on the efficacy and safety of esketamine in the main categories of depressive disorders has been conducted through four electronic databases (Pubmed, Cochrane, EMBASE and Clarivate/Web of Science) The primary objective of the present review was to find evidence that may support the usefulness of esketamine for patients diagnosed with TRD as well as data about its potential adverse effects in the short and long term. A total of 14 papers were reviewed, and their results support the recommendation of esketamine for treatment of TRD as an add-on to antidepressants, but more data is needed in order to assess its long-term efficacy and safety. It must also be mentioned that there have been a few trials which did not report a significant effect on the severity of depressive symptoms with esketamine in TRD, therefore, caution is indicated for patients initiated on this adjuvant agent. There has been insufficient data to formulate specific guidelines about esketamine administration because evidence about favorable or negative prognostic factors of this treatment has been lacking, and the duration of its administration has not been unanimously accepted. Novel directions for research have been identified, especially in the case of patients with TRD and substance use disorders, geriatric or bipolar depression or in major depression with psychotic features.

SAPAP Scaffold Proteins: From Synaptic Function to Neuropsychiatric Disorders

Excitatory (glutamatergic) synaptic transmission underlies many aspects of brain activity and the genesis of normal human behavior. The postsynaptic scaffolding proteins SAP90/PSD-95-associated proteins (SAPAPs), which are abundant components of the postsynaptic density (PSD) at excitatory synapses, play critical roles in synaptic structure, formation, development, plasticity, and signaling. The convergence of human genetic data with recent in vitro and in vivo animal model data indicates that mutations in the genes encoding SAPAP1-4 are associated with neurological and psychiatric disorders, and that dysfunction of SAPAP scaffolding proteins may contribute to the pathogenesis of various neuropsychiatric disorders, such as schizophrenia, autism spectrum disorders, obsessive compulsive disorders, Alzheimer's disease, and bipolar disorder. Here, we review recent major genetic, epigenetic, molecular, behavioral, electrophysiological, and circuitry studies that have advanced our knowledge by clarifying the roles of SAPAP proteins at the synapses, providing new insights into the mechanistic links to neurodevelopmental and neuropsychiatric disorders.

Physical Activity, Gut Microbiota, and Genetic Background for Children and Adolescents with Autism Spectrum Disorder

It is estimated that one in 100 children worldwide has been diagnosed with autism spectrum disorder (ASD). Children with ASD frequently suffer from gut dysbiosis and gastrointestinal issues, findings which possibly play a role in the pathogenesis and/or severity of their condition. Physical activity may have a positive effect on the composition of the intestinal microbiota of healthy adults. However, the effect of exercise both on the gastrointestinal problems and intestinal microbiota (and thus possibly on ASD) itself in affected children is unknown. In terms of understanding the physiopathology and manifestations of ASD, analysis of the gut-brain axis holds some promise. Here, we discuss the physiopathology of ASD in terms of genetics and microbiota composition, and how physical activity may be a promising non-pharmaceutical approach to improve ASD-related symptoms.

Postsynaptic Proteins at Excitatory Synapses in the Brain—Relationship with Depressive Disorders

Depressive disorders (DDs) are an increasingly common health problem that affects all age groups. DDs pathogenesis is multifactorial. However, it was proven that stress is one of the most important environmental factors contributing to the development of these conditions. In recent years, there has been growing interest in the role of the glutamatergic system in the context of pharmacotherapy of DDs. Thus, it has become increasingly important to explore the functioning of excitatory synapses in pathogenesis and pharmacological treatment of psychiatric disorders (including DDs). This knowledge may lead to the description of new mechanisms of depression and indicate new potential targets for the pharmacotherapy of illness. An excitatory synapse is a highly complex and very dynamic structure, containing a vast number of proteins. This review aimed to discuss in detail the role of the key postsynaptic proteins (e.g., NMDAR, AMPAR, mGluR5, PSD-95, Homer, NOS etc.) in the excitatory synapse and to systematize the knowledge about changes that occur in the clinical course of depression and after antidepressant treatment. In addition, a discussion on the potential use of ligands and/or modulators of postsynaptic proteins at the excitatory synapse has been presented.

p140Cap Regulates the Composition and Localization of the NMDAR Complex in Synaptic Lipid Rafts

The NMDARs are key players in both physiological and pathologic synaptic plasticity because of their involvement in many aspects of neuronal transmission as well as learning and memory. The contribution in these events of different types of GluN2A-interacting proteins is still unclear. The p140Cap scaffold protein acts as a hub for postsynaptic complexes relevant to psychiatric and neurologic disorders and regulates synaptic functions, such as the stabilization of mature dendritic spine, memory consolidation, LTP, and LTD. Here we demonstrate that p140Cap directly binds the GluN2A subunit of NMDAR and modulates GluN2A-associated molecular network. Indeed, in p140Cap KO male mice, GluN2A is less associated with PSD95 both in ex vivo synaptosomes and in cultured hippocampal neurons, and p140Cap expression in KO neurons can rescue GluN2A and PSD95 colocalization. p140Cap is crucial in the recruitment of GluN2A-containing NMDARs and, consequently, in regulating NMDARs' intrinsic properties. p140Cap is associated to synaptic lipid-raft (LR) and to soluble postsynaptic membranes, and GluN2A and PSD95 are less recruited into synaptic LR of p140Cap KO male mice. Gated-stimulated emission depletion microscopy on hippocampal neurons confirmed that p140Cap is required for embedding GluN2A clusters in LR in an activity-dependent fashion. In the synaptic compartment, p140Cap influences the association between GluN2A and PSD95 and modulates GluN2A enrichment into LR. Overall, such increase in these membrane domains rich in signaling molecules results in improved signal transduction efficiency.SIGNIFICANCE STATEMENT Here we originally show that the adaptor protein p140Cap directly binds the GluN2A subunit of NMDAR and modulates the GluN2A-associated molecular network. Moreover, we show, for the first time, that p140Cap also associates to synaptic lipid rafts and controls the selective recruitment of GluN2A and PSD95 to this specific compartment. Finally, gated-stimulated emission depletion microscopy on hippocampal neurons confirmed that p140Cap is required for embedding GluN2A clusters in lipid rafts in an activity-dependent fashion. Overall, our findings provide the molecular and functional dissection of p140Cap as a new active member of a highly dynamic synaptic network involved in memory consolidation, LTP, and LTD, which are known to be altered in neurologic and psychiatric disorders.

Effect of quetiapine on inflammation and immunity: a systematic review

INTRODUCTION

Knowledge about the neurobiology of psychiatric disorders is increasing in the last decades and evidence from literature suggests a central role for immuno-inflammatory mechanisms in these illnesses. The antipsychotic quetiapine acts on dopamine and serotonin signalling and well-established evidence demonstrates that these neurotransmitters can modulate immune functions in healthy and diseased conditions. Starting from this perspective, in the last few decades, a number of studies attempted to identify quetiapine effects on immune functions in order to highlight a possible additional effect of this drug in psychotic diseases, although no conclusive results were obtained.

METHODS

We critically reviewed preclinical and clinical studies evaluating quetiapine effects on immune systems, suggesting strategies for future work in this field.

RESULTS

Computerised search, in PubMed and Embase databases, was performed in March 2020: 120 studies were identified but only 29 relevant papers were selected for detailed review.

CONCLUSION

Despite some interesting preliminary findings about anti-inflammatory effects of quetiapine, mainly supported by preclinical studies, it is possible to conclude further studies are needed to investigate the immunomodulatory effects of this drug and achieve a better understanding of its relevance on clinical outcomes to finally identify new therapeutic approaches in psychiatric treatment.KeypointsMounting evidence points to a role for immuno-inflammatory mechanisms in psychiatric disorders.Quetiapine (QUE) acts on catecholamine (dopamine and norepinephrine) and serotonin signalling.The immunomodulatory effects of catecholamines are well established.Treatment with QUE in psychiatric disorders could leverage immunomodulatory effects.QUE unclear role in immune function modulation suggests future work.

Rational and Translational Implications of D-Amino Acids for Treatment-Resistant Schizophrenia: From Neurobiology to the Clinics

Schizophrenia has been conceptualized as a neurodevelopmental disorder with synaptic alterations and aberrant cortical–subcortical connections. Antipsychotics are the mainstay of schizophrenia treatment and nearly all share the common feature of dopamine D2 receptor occupancy, whereas glutamatergic abnormalities are not targeted by the presently available therapies. D-amino acids, acting as N-methyl-D-aspartate receptor (NMDAR) modulators, have emerged in the last few years as a potential augmentation strategy in those cases of schizophrenia that do not respond well to antipsychotics, a condition defined as treatment-resistant schizophrenia (TRS), affecting almost 30–40% of patients, and characterized by serious cognitive deficits and functional impairment. In the present systematic review, we address with a direct and reverse translational perspective the efficacy of D-amino acids, including D-serine, D-aspartate, and D-alanine, in poor responders. The impact of these molecules on the synaptic architecture is also considered in the light of dendritic spine changes reported in schizophrenia and antipsychotics’ effect on postsynaptic density proteins. Moreover, we describe compounds targeting D-amino acid oxidase and D-aspartate oxidase enzymes. Finally, other drugs acting at NMDAR and proxy of D-amino acids function, such as D-cycloserine, sarcosine, and glycine, are considered in the light of the clinical burden of TRS, together with other emerging molecules.

The Role of Caspase Family in Acute Brain Injury: The Potential Therapeutic Targets in the Future

The caspase family is commonly involved in the pathophysiology of acute brain injury (ABI) through complex apoptotic, pyroptotic, and inflammatory pathways. Current translational strategies for caspase modulation in ABI primarily focus on caspase inhibitors. Because there are no caspase-inhibiting drugs approved for clinical use on the market, the development of caspase inhibitors remains an attractive challenge for researchers and clinicians. Therefore, we conducted the present review with the aim of providing a comprehensive introduction of caspases in ABI. In this review, we summarized the available evidence and potential mechanisms regarding the biological function of caspases. We also reviewed the therapeutic effects of caspase inhibitors on ABI and its subsequent complications. However, various important issues remain unclear, prompting further verification of the efficacy and safety regarding clinical application of caspase inhibitors. We believe that our work will be helpful to further understand the critical role of the caspase family and will provide novel therapeutic potential for ABI treatment.

The Homer1 family of proteins at the crossroad of dopamine-glutamate signaling: An emerging molecular "Lego" in the pathophysiology of psychiatric disorders. A systematic review and translational insight

Once considered only scaffolding proteins at glutamatergic postsynaptic density (PSD), Homer1 proteins are increasingly emerging as multimodal adaptors that integrate different signal transduction pathways within PSD, involved in motor and cognitive functions, with putative implications in psychiatric disorders. Regulation of type I metabotropic glutamate receptor trafficking, modulation of calcium signaling, tuning of long-term potentiation, organization of dendritic spines' growth, as well as meta- and homeostatic plasticity control are only a few of the multiple endocellular and synaptic functions that have been linked to Homer1. Findings from preclinical studies, as well as genetic studies conducted in humans, suggest that both constitutive (Homer1b/c) and inducible (Homer1a) isoforms of Homer1 play a role in the neurobiology of several psychiatric disorders, including psychosis, mood disorders, neurodevelopmental disorders, and addiction. On this background, Homer1 has been proposed as a putative novel target in psychopharmacological treatments. The aim of this review is to summarize and systematize the growing body of evidence on Homer proteins, highlighting the role of Homer1 in the pathophysiology and therapy of mental diseases.

Rapid-acting antidepressants and the circadian clock

A growing number of epidemiological and experimental studies has established that circadian disruption is strongly associated with psychiatric disorders, including major depressive disorder (MDD). This association is becoming increasingly relevant considering that modern lifestyles, social zeitgebers (time cues) and genetic variants contribute to disrupting circadian rhythms that may lead to psychiatric disorders. Circadian abnormalities associated with MDD include dysregulated rhythms of sleep, temperature, hormonal secretions, and mood which are modulated by the molecular clock. Rapid-acting antidepressants such as subanesthetic ketamine and sleep deprivation therapy can improve symptoms within 24 h in a subset of depressed patients, in striking contrast to conventional treatments, which generally require weeks for a full clinical response. Importantly, animal data show that sleep deprivation and ketamine have overlapping effects on clock gene expression. Furthermore, emerging data implicate the circadian system as a critical component involved in rapid antidepressant responses via several intracellular signaling pathways such as GSK3β, mTOR, MAPK, and NOTCH to initiate synaptic plasticity. Future research on the relationship between depression and the circadian clock may contribute to the development of novel therapeutic strategies for depression-like symptoms. In this review we summarize recent evidence describing: (1) how the circadian clock is implicated in depression, (2) how clock genes may contribute to fast-acting antidepressants, and (3) the mechanistic links between the clock genes driving circadian rhythms and neuroplasticity.

Drug Design Targeting the Muscarinic Receptors and the Implications in Central Nervous System Disorders

There is substantial evidence that cholinergic system function impairment plays a significant role in many central nervous system (CNS) disorders. During the past three decades, muscarinic receptors (mAChRs) have been implicated in various pathologies and have been prominent targets of drug-design efforts. However, due to the high sequence homology of the orthosteric binding site, many drug candidates resulted in limited clinical success. Although several advances in treating peripheral pathologies have been achieved, targeting CNS pathologies remains challenging for researchers. Nevertheless, significant progress has been made in recent years to develop functionally selective orthosteric and allosteric ligands targeting the mAChRs with limited side effect profiles. This review highlights past efforts and focuses on recent advances in drug design targeting these receptors for Alzheimer’s disease (AD), schizophrenia (SZ), and depression.

Present and future antipsychotic drugs: a systematic review of the putative mechanisms of action for efficacy and a critical appraisal under a translational perspective

Antipsychotics represent the mainstay of schizophrenia pharmacological therapy, and their role has been expanded in the last years to mood disorders treatment. Although introduced in 1952, many years of research were required before an accurate picture of how antipsychotics work began to emerge. Despite the well-recognized characterization of antipsychotics in typical and atypical based on their liability to induce motor adverse events, their main action at dopamine D2R to elicit the "anti-psychotic" effect, as well as the multimodal action at other classes of receptors, their effects on intracellular mechanisms starting with receptor occupancy is still not completely understood. Significant lines of evidence converge on the impact of these compounds on multiple molecular signaling pathways implicated in the regulation of early genes and growth factors, dendritic spine shape, brain inflammation, and immune response, tuning overall the function and architecture of the synapse. Here we present, based on PRISMA approach, a comprehensive and systematic review of the above mechanisms under a translational perspective to disentangle those intracellular actions and signaling that may underline clinically relevant effects and represent potential targets for further innovative strategies in antipsychotic therapy.

Rare Pathogenic Variants in Genes Implicated in Glutamatergic Neurotransmission Pathway Segregate with Schizophrenia in Pakistani Families

Schizophrenia is a disabling neuropsychiatric disorder of adulthood onset with high heritability. Worldwide collaborations have identified an association of ~270 common loci, with small individual effects and hence weak clinical implications. The recent technological feasibility of exome sequencing enables the identification of rare variants of high penetrance that refine previous findings and improve risk assessment and prognosis. We recruited two multiplex Pakistani families, having 11 patients and 19 unaffected individuals in three generations. We performed genome-wide SNP genotyping, next-generation mate pairing and whole-exome sequencing of selected members to unveil genetic components. Candidate variants were screened in unrelated cohorts of 508 cases, 300 controls and fifteen families (with 51 affected and 47 unaffected individuals) of Pakistani origin. The structural impact of substituted residues was assessed through in silico modeling using iTASSER. In one family, we identified a rare novel microduplication (5q14.1_q14.2) encompassing critical genes involved in glutamate signaling, such as CMYA5, HOMER and RasGRF2. The second family segregates two ultra-rare, predicted pathogenic variants in the GRIN2A (NM_001134407.3: c.3505C>T, (p.R1169W) and in the NRG3 NM_001010848.4: c.1951G>A, (p.E651K). These genes encode for parts of AMPA and NMDA receptors of glutamatergic neurotransmission, respectively, and the variants are predicted to compromise protein function by destabilizing their structures. The variants were absent in the aforementioned cohorts. Our findings suggest that rare, highly penetrant variants of genes involved in glutamatergic neurotransmission are contributing to the etiology of schizophrenia in these families. It also highlights that genetic investigations of multiplex, multigenerational families could be a powerful approach to identify rare genetic variants involved in complex disorders.

Increased use of ketamine for the treatment of depression: Benefits and concerns

Ketamine was initially used as an anesthetic which could induce cognitive impairment and psychomimetic effects. In initial randomized controlled trials (RCTs) that mostly included a small sample size and were investigator-initiated, ketamine reportedly exerted antidepressant effects 1 to 2 h after a single intravenous infusion in patients with major depressive episodes, particularly treatment-resistant depression (TRD). Interest in ketamine was reported in systematic reviews and meta-analyses, however, many were primarily focused on the rapid onset of ketamine effects without equal attention to its safety and tolerability. Furthermore, several meta-analyses were based on many duplicated RCTs. The initial trends emphasized the clinical utility of ketamine as an antidepressant. The development of esketamine nasal spray by a pharmaceutical company led to an RCT with a large sample size and segmented therapeutic strategy, which provided results applicable to patients with TRD in the real-world clinical environment. However, possible effects of ketamine on cognitive function have not yet been investigated in RCTs. In numerous studies, chronic, recreational use of ketamine reportedly substantially impaired cognitive function in most domains. Although results of several human and animal studies indicated the therapeutic use of ketamine for treatment of depression did not induce cognitive impairment, this issue should be further investigated. Based on the current knowledge about ketamine, future antidepressants are expected to be glutamatergic drugs without ketamine-like adverse events (e.g., psychomimetic symptoms and cognitive impairment), but having only ketamine-like therapeutic properties (e.g., rapid antidepressants effects without time lag).

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.

Alpha7 nicotinic-N-methyl-D-aspartate hypothesis in the treatment of schizophrenia and beyond

Development of novel treatments for positive, cognitive, and negative symptoms continue to be a high-priority area of schizophrenia research and a major unmet clinical need. Given that all randomized controlled trials (RCTs) conducted to date failed with one add-on medication/mechanism of action, future RCTs with the same approach are not warranted. Even if the field develops a medication for cognition, others are still needed to treat negative and positive symptoms. Therefore, fixing one domain does not completely solve the problem. Also, targeting the cholinergic system, glutamatergic system, and cholinergic plus alpha7 nicotinic and N-methyl-D-aspartate (NMDA) receptors failed independently. Hence, targeting other less important pathophysiological mechanisms/targets is unlikely to be successful. Meta-analyses of RCTs targeting major pathophysiological mechanisms have found some efficacy signal in schizophrenia; thus, combination treatments with different mechanisms of action may enhance the efficacy signal. The objective of this article is to highlight the importance of conducting RCTs with novel combination treatments in schizophrenia to develop antischizophrenia treatments. Positive RCTs with novel combination treatments that target the alpha7 nicotinic and NMDA receptors simultaneously may lead to a disease-modifying therapeutic armamentarium in schizophrenia. Novel combination treatments that concurrently improve the three domains of psychopathology and several prognostic and theranostic biomarkers may facilitate therapeutic discovery in schizophrenia.

Expression and Regulation of the GABAA Receptor/STEP61 Signaling Pathway in Cerebral Cortical Neurons Treated with Emulsified Isoflurane In Vitro

Emulsified isoflurane (EISO) is an intravenous anesthetic. However, researchers have not clearly determined how emulsified isoflurane affects the central nervous system during the process of anesthesia. The aim of this study was to explore changes in the gamma-aminobutyric acid type A receptor subunit (GABA_A), 61 kD isoform of striatal-enriched protein phosphatase (STEP61) signaling pathway, and epigenetic regulation in cortical neurons after treatment with emulsified isoflurane. After immunological identification, the isolated neurons were randomly divided into three groups: the blank group (Con), intralipid treatment group (FE), and emulsified isoflurane treatment group (EISO). Neuron viability was assayed using cell counting kit-8 (CCK-8). The expression levels of target nucleic acids, proteins, and corresponding ligands were detected. Using real-time polymerase chain reaction (PCR) to assess the promoter methylation of ion channel proteins in the cerebral cortex of rats anesthetized with EISO, we observed changes in promoter methylation of the genes encoding gamma-aminobutyric acid type A receptor α1 subunit (GABA_Aα1), N-methyl-d-aspartate receptor subunit 1 (NMDAR1), and mu opioid receptor 1 (OPRM1), accompanied by changes in the levels of their messenger ribonucleic acids (mRNAs) and proteins. The levels of ligands for these receptors were also altered. EISO altered the methylation rate of the promoter region of channel protein-coding genes involved in the GABA_A/STEP61 signaling pathway in cerebral cortical neurons to regulate gene expression. The ligands for the receptors were also changed.

Antioxidant Properties of Second-Generation Antipsychotics: Focus on Microglia

Recent studies suggest a primary role of oxidative stress in an early phase of the pathogenesis of schizophrenia and a strong neurobiological link has been found between dopaminergic system dysfunction, microglia overactivation, and oxidative stress. Different risk factors for schizophrenia increase oxidative stress phenomena raising the risk of developing psychosis. Oxidative stress induced by first-generation antipsychotics such as haloperidol significantly contributes to the development of extrapyramidal side effects. Haloperidol also exerts neurotoxic effects by decreasing antioxidant enzyme levels then worsening pro-oxidant events. Opposite to haloperidol, second-generation antipsychotics (or atypical antipsychotics) such as risperidone, clozapine, and olanzapine exert a strong antioxidant activity in experimental models of schizophrenia by rescuing the antioxidant system, with an increase in superoxide dismutase and glutathione (GSH) serum levels. Second-generation antipsychotics also improve the antioxidant status and reduce lipid peroxidation in schizophrenic patients. Interestingly, second-generation antipsychotics, such as risperidone, paliperidone, and in particular clozapine, reduce oxidative stress induced by microglia overactivation, decreasing the production of microglia-derived free radicals, finally protecting neurons against microglia-induced oxidative stress. Further, long-term clinical studies are needed to better understand the link between oxidative stress and the clinical response to antipsychotic drugs and the therapeutic potential of antioxidants to increase the response to antipsychotics.

Electroretinographic Abnormalities and Sex Differences Detected with Mesopic Adaptation in a Mouse Model of Schizophrenia: A and B Wave Analysis

Purpose

Mesopic flash electroretinography (fERG) as a tool to identify N-methyl-d-aspartate receptor (NMDAR) hypofunction in subjects with schizophrenia shows great potential. We report the first fERG study in a genetic mouse model of schizophrenia characterized by NMDAR hypofunction from gene silencing of serine racemase (SR) expression (SR-/-), an established risk gene for schizophrenia. We analyzed fERG parameters under various background light adaptations to determine the most significant variables to allow for early identification of people at risk for schizophrenia, prior to onset of psychosis. SR is a risk gene for schizophrenia, and negative and cognitive symptoms antedate the onset of psychosis that is required for diagnosis.

Methods

The scotopic, photopic, and mesopic fERGs were analyzed in male and female mice in both SR-/- and wild-type (WT) mice and also analyzed for sex differences. Amplitude and implicit time of the a- and b-wave components, b-/a-wave ratio, and Fourier transform analysis were analyzed.

Results

Mesopic a- and b-wave implicit times were significantly delayed, and b-wave amplitudes, b/a ratios, and Fourier transform were significantly decreased in the male SR-/- mice compared to WT, but not in female SR-/- mice. No significant differences were observed in photopic or scotopic fERGs between genotype.

Conclusions

The fERG prognostic capability may be improved by examination of background light adaptation, a larger array of light intensities, considering sex as a variable, and performing Fourier transform analyses of all waveforms. This should improve the ability to differentiate between controls and subjects with schizophrenia characterized by NMDAR hypofunction.

MicroRNA-99a is a Potential Target for Regulating Hypothalamic Synaptic Plasticity in the Peri/Postmenopausal Depression Model

Accumulating evidence has demonstrated that there is a growing trend of menopausal women suffering from depression. However, the pathogenesis of menopausal depression still remains unclear. Hence, this paper aims to reveal the pathological mechanisms involved in postmenopausal depression by using a novel peri- to postmenopausal depression model induced by a two-step ovariectomy plus chronic mild stress (CMS). The results of metabolic chambers and serum hormone/cytokine determination revealed that peri/postmenopausal depressive mice exhibited endocrine and metabolic disorders. Electrophysiological recordings indicated that the hippocampal synaptic transmission was compromised. Compared to the sham group, the microRNA-99a (miR-99a) level decreased significantly in the hypothalamus, and its target FK506-binding protein 51 (FKBP51) enormously increased; in contrast, the nuclear translocation of the progesterone receptor (PR) decreased in hypothalamic paraventricular nucleus (PVN) in the peri/postmenopausal depression mouse model. Additionally, synaptic proteins, including postsynaptic density protein 95 (PSD-95) and synaptophysin (SYN), showed a similar decrease in the hypothalamus. Accordingly, the present work suggests that miR-99a may be involved in the regulation of hypothalamic synaptic plasticity and that it might be a potential therapeutic target for peri/postmenopausal depression.

Cellular and Synaptic Dysfunctions in Parkinson's Disease: Stepping out of the Striatum

The basal ganglia (BG) are a collection of interconnected subcortical nuclei that participate in a great variety of functions, ranging from motor programming and execution to procedural learning, cognition, and emotions. This network is also the region primarily affected by the degeneration of midbrain dopaminergic neurons localized in the substantia nigra pars compacta (SNc). This degeneration causes cellular and synaptic dysfunctions in the BG network, which are responsible for the appearance of the motor symptoms of Parkinson’s disease. Dopamine (DA) modulation and the consequences of its loss on the striatal microcircuit have been extensively studied, and because of the discrete nature of DA innervation of other BG nuclei, its action outside the striatum has been considered negligible. However, there is a growing body of evidence supporting functional extrastriatal DA modulation of both cellular excitability and synaptic transmission. In this review, the functional relevance of DA modulation outside the striatum in both normal and pathological conditions will be discussed.

Translating striatal activity from brain slice to whole animal neurophysiology: A guide for neuroscience research integrating diverse levels of analysis

An important goal of this review is highlighting research in neuroscience as examples of multilevel functional and anatomical analyses addressing basic science issues and applying results to the understanding of diverse disorders. The research of Dr. Michael Levine, a leader in neuroscience, exemplifies this approach by uncovering fundamental properties of basal ganglia function and translating these findings to clinical applications. The review focuses on neurophysiological research connecting results from in vitro and in vivo recordings. A second goal is to utilize these research connections to produce novel, accurate descriptions for corticostriatal processing involved in varied, complex functions. Medium spiny neurons in striatum act as integrators combining input with baseline activity creating motivational "events." Basic research on corticostriatal synapses is described and links developed to issues with clinical relevance such as inhibitory gating, self-injurious behavior, and relative reward valuation. Work is highlighted on dopamine-glutamate interactions. Individual medium spiny neurons express both D₁ and D₂ receptors and encode information in a bivalent manner depending upon the mix of receptors involved. Current work on neurophysiology of reward processing has taken advantage of these basic approaches at the cellular and molecular levels. Future directions in studying physiology of reward processing and action sequencing could profit by incorporating the divergent ways dopamine modulates incoming neurochemical signals. Primary investigators leading research teams should mirror Mike Levine's efforts in "climbing the mountain" of scientific inquiry by performing analyses at different levels of inquiry, integrating the findings, and building comprehensive answers to problems unsolvable without this bold approach.

Fluoride Exposure Induces Inhibition of Sodium-and Potassium-Activated Adenosine Triphosphatase (Na+, K+-ATPase) Enzyme Activity: Molecular Mechanisms and Implications for Public Health

In this study, several lines of evidence are provided to show that Na + , K + -ATPase activity exerts vital roles in normal brain development and function and that loss of enzyme activity is implicated in neurodevelopmental, neuropsychiatric and neurodegenerative disorders, as well as increased risk of cancer, metabolic, pulmonary and cardiovascular disease. Evidence is presented to show that fluoride (F) inhibits Na + , K + -ATPase activity by altering biological pathways through modifying the expression of genes and the activity of glycolytic enzymes, metalloenzymes, hormones, proteins, neuropeptides and cytokines, as well as biological interface interactions that rely on the bioavailability of chemical elements magnesium and manganese to modulate ATP and Na + , K + -ATPase enzyme activity. Taken together, the findings of this study provide unprecedented insights into the molecular mechanisms and biological pathways by which F inhibits Na + , K + -ATPase activity and contributes to the etiology and pathophysiology of diseases associated with impairment of this essential enzyme. Moreover, the findings of this study further suggest that there are windows of susceptibility over the life course where chronic F exposure in pregnancy and early infancy may impair Na + , K + -ATPase activity with both short- and long-term implications for disease and inequalities in health. These findings would warrant considerable attention and potential intervention, not to mention additional research on the potential effects of F intake in contributing to chronic disease.

Decoding the Mechanism of Action of Rapid-Acting Antidepressant Treatment Strategies: Does Gender Matter?

Gender differences play a pivotal role in the pathophysiology and treatment of major depressive disorder. This is strongly supported by a mean 2:1 female-male ratio of depression consistently observed throughout studies in developed nations. Considering the urgent need to tailor individualized treatment strategies to fight depression more efficiently, a more precise understanding of gender-specific aspects in the pathophysiology and treatment of depressive disorders is fundamental. However, current treatment guidelines almost entirely neglect gender as a potentially relevant factor. Similarly, the vast majority of animal experiments analysing antidepressant treatment in rodent models exclusively uses male animals and does not consider gender-specific effects. Based on the growing interest in innovative and rapid-acting treatment approaches in depression, such as the administration of ketamine, its metabolites or electroconvulsive therapy, this review article summarizes the evidence supporting the importance of gender in modulating response to rapid acting antidepressant treatment. We provide an overview on the current state of knowledge and propose a framework for rodent experiments to ultimately decode gender-dependent differences in molecular and behavioural mechanisms involved in shaping treatment response.

Altered spinogenesis in iPSC-derived cortical neurons from patients with autism carrying de novo SHANK3 mutations

The synaptic protein SHANK3 encodes a multidomain scaffold protein expressed at the postsynaptic density of neuronal excitatory synapses. We previously identified de novo SHANK3 mutations in patients with autism spectrum disorders (ASD) and showed that SHANK3 represents one of the major genes for ASD. Here, we analyzed the pyramidal cortical neurons derived from induced pluripotent stem cells from four patients with ASD carrying SHANK3 de novo truncating mutations. At 40-45 days after the differentiation of neural stem cells, dendritic spines from pyramidal neurons presented variable morphologies: filopodia, thin, stubby and muschroom, as measured in 3D using GFP labeling and immunofluorescence. As compared to three controls, we observed a significant decrease in SHANK3 mRNA levels (less than 50% of controls) in correlation with a significant reduction in dendritic spine densities and whole spine and spine head volumes. These results, obtained through the analysis of de novo SHANK3 mutations in the patients' genomic background, provide further support for the presence of synaptic abnormalities in a subset of patients with ASD.

Glutamatergic Deficits in Schizophrenia - Biomarkers and Pharmacological Interventions within the Ketamine Model

Background:

The observation that N-methyl-D-aspartate glutamate receptor (NMDAR) antagonists such as ketamine transiently induce schizophrenia-like positive, negative and cognitive symptoms has led to a paradigm shift from dopaminergic to glutamatergic dysfunction in pharmacological models of schizophrenia. NMDAR hypofunction can explain many schizophrenia symptoms directly due to excitatory-to-inhibitory (E/I) imbalance, but also dopaminergic dysfunction itself. However, so far no new drug targeting the NMDAR has been successfully approved. In the search for possible biomarkers it is interesting that ketamine-induced psychopathological changes in healthy participants were accompanied by altered electro-(EEG), magnetoencephalographic (MEG) and functional magnetic resonance imaging (fMRI) signals.

Methods:

We systematically searched PubMed/Medline and Web of Knowledge databases (January 2006 to July 2017) to identify EEG/MEG and fMRI studies of the ketamine model of schizophrenia with human subjects. The search strategy identified 209 citations of which 46 articles met specified eligibility criteria.

Results:

In EEG/MEG studies, ketamine induced changes of event-related potentials, such as the P300 potential and the mismatch negativity, similar to alterations observed in schizophrenia patients. In fMRI studies, alterations of activation were observed in different brain regions, most prominently within the anterior cingulate cortex and limbic structures as well as task-relevant brain regions. These alterations were accompanied by changes in functional connectivity, indicating a balance shift of the underlying brain networks. Pharmacological treatments did alter ketamine-induced changes in EEG/MEG and fMRI studies to different extents.

Conclusion:

This review highlights the potential applicability of the ketamine model for schizophrenia drug development by offering the possibility to assess the effect of pharmacological agents on schizophrenia-like symptoms and to find relevant neurophysiological and neuroimaging biomarkers.

Eradicating Suicide at Its Roots: Preclinical Bases and Clinical Evidence of the Efficacy of Ketamine in the Treatment of Suicidal Behaviors

Despite the continuous advancement in neurosciences as well as in the knowledge of human behaviors pathophysiology, currently suicide represents a puzzling challenge. The World Health Organization (WHO) has established that one million people die by suicide every year, with the impressive daily rate of a suicide every 40 s. The weightiest concern about suicidal behavior is how difficult it is for healthcare professionals to predict. However, recent evidence in genomic studies has pointed out the essential role that genetics could play in influencing person's suicide risk. Combining genomic and clinical risk assessment approaches, some studies have identified a number of biomarkers for suicidal ideation, which are involved in neural connectivity, neural activity, mood, as well as in immune and inflammatory response, such as the mammalian target of rapamycin (mTOR) signaling. This interesting discovery provides the neurobiological bases for the use of drugs that impact these specific signaling pathways in the treatment of suicidality, such as ketamine. Ketamine, an N-methyl-d-aspartate glutamate (NMDA) antagonist agent, has recently hit the headlines because of its rapid antidepressant and concurrent anti-suicidal action. Here we review the preclinical and clinical evidence that lay the foundations of the efficacy of ketamine in the treatment of suicidal ideation in mood disorders, thereby also approaching the essential question of the understanding of neurobiological processes of suicide and the potential therapeutics.

Na⁺, K⁺-ATPase Signaling and Bipolar Disorder

Bipolar disorder (BD) is a severe and common chronic mental illness characterized by recurrent mood swings between depression and mania. The biological basis of the disease is poorly understood and its treatment is unsatisfactory. Although in past decades the "monoamine hypothesis" has dominated our understanding of both the pathophysiology of depressive disorders and the action of pharmacological treatments, recent studies focus on the involvement of additional neurotransmitters/neuromodulators systems and cellular processes in BD. Here, evidence for the participation of Na⁺, K⁺-ATPase and its endogenous regulators, the endogenous cardiac steroids (ECS), in the etiology of BD is reviewed. Proof for the involvement of brain Na⁺, K⁺-ATPase and ECS in behavior is summarized and it is hypothesized that ECS-Na⁺, K⁺-ATPase-induced activation of intracellular signaling participates in the mechanisms underlying BD. We propose that the activation of ERK, AKT, and NFκB, resulting from ECS-Na⁺, K⁺-ATPase interaction, modifies neuronal activity and neurotransmission which, in turn, participate in the regulation of behavior and BD. These observations suggest Na⁺, K⁺-ATPase-mediated signaling is a potential target for drug development for the treatment of BD.

Identification of miR-22-3p, miR-92a-3p, and miR-137 in peripheral blood as biomarker for schizophrenia

MicroRNAs (miRNAs) are a class of endogenous and non-coding single-stranded RNAs with length of about 22 nucleotides, and many are evolutionarily conserved. Although postmortem brain samples provide direct evidence of miRNA dysregulation within the brain, peripheral tissue samples can be obtained from living subjects and have the potential to yield biomarkers that could be used as diagnostic tools. To verify and detect additional miRNAs differentially expressed in peripheral blood and further explore their diagnostic value and function for schizophrenia, we performed a next-generation sequencing approach in combination with a literature search to select appropriate miRNAs. We then used real-time quantitative polymerase chain reaction (RT-qPCR) to identify miRNAs expressed aberrantly in schizophrenia. Binary regression analysis identified miR-22-3p, miR-92a-3p, and miR-137. Analysis of receiver operating characteristics (ROC) indicated that these three miRNAs could be used in combination as a biomarker for schizophrenia. Bioinformatic analyses of these genes and gene ontology (GO) enrichment revealed that the combination of miR-22-3p, miR-92a-3p, and miR-137 was closely associated with synaptic structure and function, which play important roles in the etiology and pathophysiology of schizophrenia.

Big Lessons from Tiny Flies: Drosophila melanogaster as a Model to Explore Dysfunction of Dopaminergic and Serotonergic Neurotransmitter Systems

The brain of Drosophila melanogaster is comprised of some 100,000 neurons, 127 and 80 of which are dopaminergic and serotonergic, respectively. Their activity regulates behavioral functions equivalent to those in mammals, e.g., motor activity, reward and aversion, memory formation, feeding, sexual appetite, etc. Mammalian dopaminergic and serotonergic neurons are known to be heterogeneous. They differ in their projections and in their gene expression profile. A sophisticated genetic tool box is available, which allows for targeting virtually any gene with amazing precision in Drosophila melanogaster. Similarly, Drosophila genes can be replaced by their human orthologs including disease-associated alleles. Finally, genetic manipulation can be restricted to single fly neurons. This has allowed for addressing the role of individual neurons in circuits, which determine attraction and aversion, sleep and arousal, odor preference, etc. Flies harboring mutated human orthologs provide models which can be interrogated to understand the effect of the mutant protein on cell fate and neuronal connectivity. These models are also useful for proof-of-concept studies to examine the corrective action of therapeutic strategies. Finally, experiments in Drosophila can be readily scaled up to an extent, which allows for drug screening with reasonably high throughput.

Scale-Up Synthesis and Identification of GLYX-13, a NMDAR Glycine-Site Partial Agonist for the Treatment of Major Depressive Disorder

GLYX-13, a NMDAR glycine-site partial agonist, was discovered as a promising antidepressant with rapidly acting effects but no ketamine-like side effects. However, the reported synthetic process route had deficiencies of low yield and the use of unfriendly reagents. Here, we report a scaled-up synthesis of GLYX-13 with an overall yield of 30% on the hectogram scale with a column chromatography-free strategy, where the coupling and deprotection reaction conditions were systematically optimized. Meanwhile, the absolute configuration of precursor compound of GLYX-13 was identified by X-ray single crystal diffraction. Finally, the activity of GLYX-13 was verified in the cortical neurons of mice through whole-cell voltage-clamp technique.

Nicotine and caffeine modulate haloperidol-induced changes in postsynaptic density transcripts expression: Translational insights in psychosis therapy and treatment resistance

Caffeine and nicotine are widely used by schizophrenia patients and may worsen psychosis and affect antipsychotic therapies. However, they have also been accounted as augmentation strategies in treatment-resistant schizophrenia. Despite both substances are known to modulate dopamine and glutamate transmission, little is known about the molecular changes induced by these compounds in association to antipsychotics, mostly at the level of the postsynaptic density (PSD), a site of dopamine-glutamate interplay. Here we investigated whether caffeine and nicotine, alone or combined with haloperidol, elicited significant changes in the levels of both transcripts and proteins of the PSD members Homer1 and Arc, which have been implicated in synaptic plasticity, schizophrenia pathophysiology, and antipsychotics molecular action. Homer1a mRNA expression was significantly reduced by caffeine and nicotine, alone or combined with haloperidol, compared to haloperidol. Haloperidol induced significantly higher Arc mRNA levels than both caffeine and caffeine plus haloperidol in the striatum. Arc mRNA expression was significantly higher by nicotine plus haloperidol vs. haloperidol in the cortex, while in striatum gene expression by nicotine was significantly lower than that by both haloperidol and nicotine plus haloperidol. Both Homer1a and Arc protein levels were significantly increased by caffeine, nicotine, and nicotine plus haloperidol. Homer1b mRNA expression was significantly increased by nicotine and nicotine plus haloperidol, while protein levels were unaffected. Locomotor activity was not significantly affected by caffeine, while it was reduced by nicotine. These data indicate that both caffeine and nicotine trigger relevant molecular changes in PSD sites when given in association with haloperidol.

Structure function relations in PDZ-domain-containing proteins: Implications for protein networks in cellular signalling

Protein scaffolds as essential backbones for organization of supramolecular signalling complexes are a recurrent theme in several model systems. Scaffold proteins preferentially employ linear peptide binding motifs for recruiting their interaction partners. PDZ domains are one of the more commonly encountered peptide binding domains in several proteins including those involved in scaffolding functions. This domain is known for its promiscuity both in terms of ligand selection, mode of interaction with its ligands as well as its association with other protein interaction domains. PDZ domains are subject to several means of regulations by virtue of their functional diversity. Additionally, the PDZ domains are refractive to the effect of mutations and maintain their three-dimensional architecture under extreme mutational load. The biochemical and biophysical basis for this selectivity as well as promiscuity has been investigated and reviewed extensively. The present review focuses on the plasticity inherent in PDZ domains and its implications for modular organization as well as evolution of cellular signalling pathways in higher eukaryotes.

Alterations in glutamatergic signaling in the brain of dopamine supersensitivity psychosis and non-supersensitivity psychosis model rats

BACKGROUND

The long-term administration of antipsychotics is known to induce dopamine supersensitivity psychosis (DSP). Although the mechanism of DSP involves mainly a compensatory upregulation of dopamine D2 receptors, the precise mechanisms underlying DSP are unknown. It is known that glutamatergic signaling plays a key role in psychosis. We thus conducted this study to investigate whether glutamatergic signaling plays a role in the development of DSP.

METHODS

Haloperidol (0.75 mg/kg/day for 14 days) or vehicle was administered to rats via osmotic mini-pump. Haloperidol-treated rats were divided into groups of DSP rats and non-DSP rats based on locomotion data. Tissue levels of glutamate, glutamine, glycine, L-serine, D-serine, and GABA and the protein expressions of N-methyl-D-aspartate receptors (NMDAR), glutamic acid decarboxylase (GAD), and serine hydroxymethyltransferase (SHMT) in the rat brain regions were examined.

RESULTS

In the DSP rats, the ratio of GABA to glutamate was significantly increased. In addition, the ratio of L-serine to glycine was increased. The striatal expressions of GAD and SHMT2 in the DSP rats were significantly increased. In contrast, the striatal expression of NMDAR2B in the non-DSP rats was significantly decreased.

CONCLUSIONS

The present study suggests that glutamatergic signaling is relatively decreased to GABA in DSP rats. Our results also showed that excessive doses of haloperidol can induce striatal NMDAR hypofunction in non-DSP rats, which could prevent the formation of tardive dyskinesia but cause treatment resistance. In view of the need for therapeutic strategies for treatment-resistant schizophrenia, further research exploring our present findings is necessary.