NMDA receptors, cognition and schizophrenia – Testing the validity of the NMDA receptor hypofunction hypothesis

Temporal imprecision of phase coherence in schizophrenia and psychosis-dynamic mechanisms and diagnostic marker

Schizophrenia (SCZ) is a complex disorder in which various pathophysiological models have been postulated. Brain imaging studies using EEG/MEG and fMRI show altered amplitude and, more recently, decrease in phase coherence in response to external stimuli. What are the dynamic mechanisms of such phase incoherence, and can it serve as a differential-diagnostic marker? Addressing this gap in our knowledge, we uniquely combine a review of previous findings, novel empirical data, and computational-dynamic simulation. The main findings are: (i) the review shows decreased phase coherence in SCZ across a variety of different tasks and frequencies, e.g., task- and frequency-unspecific, which is further supported by our own novel data; (ii) our own data demonstrate diagnostic specificity of decreased phase coherence for SCZ as distinguished from major depressive disorder; (iii) simulation data exhibit increased phase offset in SCZ leading to a precision index, in the millisecond range, of the phase coherence relative to the timing of the external stimulus. Together, we demonstrate the key role of temporal imprecision in phase coherence of SCZ, including its mechanisms (phase offsets, precision index) on the basis of which we propose a phase-based temporal imprecision model of psychosis (PTP). The PTP targets a deeper dynamic layer of a basic disturbance. This converges well with other models of psychosis like the basic self-disturbance and time-space experience changes, as discussed in phenomenological and spatiotemporal psychopathology, as well as with the models of aberrant predictive coding and disconnection as in computational psychiatry. Finally, our results show that temporal imprecision as manifest in decreased phase coherence is a promising candidate biomarker for clinical differential diagnosis of SCZ, and more broadly, psychosis.

Fibroblast growth factor 21 alleviates diabetes-induced cognitive decline

Diabetes mellitus (DM) causes damage to the central nervous system, resulting in cognitive impairment. Fibroblast growth factor 21 (FGF21) exhibits the potential to alleviate neurodegeneration. However, the therapeutic effect of intracerebroventricular (i.c.v) FGF21 infusion on diabetes-induced cognitive decline (DICD) and its potential mechanisms remain unclear. In this study, the impact of FGF21 on DICD was explored, and 1H nuclear magnetic resonance (NMR)-based metabolomics plus 13C NMR spectroscopy in combine with intravenous [1-13C]-glucose infusion were used to investigate the underlying metabolic mechanism. Results revealed that i.c.v FGF21 infusion effectively improved learning and memory performance of DICD mice; neuron loss and apoptosis in hippocampus and cortex were significantly blocked, suggesting a potential neuroprotective role of FGF21 in DICD. Metabolomics results revealed that FGF21 modulated DICD metabolic alterations related to glucose and neurotransmitter metabolism, which are characterized by distinct recovered enrichment of [3-13C]-lactate, [3-13C]-aspartate, [4-13C]-glutamine, [3-13C]-glutamine, [4-13C]-glutamate, and [4-13C]- γ-aminobutyric acid (GABA) from [1-13C]-glucose. Moreover, diabetes-induced neuron injury and metabolic dysfunctions might be mediated by PI3K/AKT/GSK-3β signaling pathway inactivation in the hippocampus and cortex, which were activated by i.c.v injection of FGF21. These findings indicate that i.c.v FGF21 infusion exerts its neuroprotective effect on DICD by remodeling cerebral glucose and neurotransmitter metabolism by activating the PI3K/AKT/GSK-3β signaling pathway.

Regulation of neuronal circHomer1 biogenesis by PKA/CREB/ERK-mediated pathways and effects of glutamate and dopamine receptor blockade

There are currently only very few efficacious drug treatments for SCZ and BD, none of which can significantly ameliorate cognitive symptoms. Thus, further research is needed in elucidating molecular pathways linked to cognitive function and antipsychotic treatment. Circular RNAs (circRNAs) are stable brain-enriched non-coding RNAs, derived from the covalent back-splicing of precursor mRNA molecules. CircHomer1 is a neuronal-enriched, activity-dependent circRNA, derived from the precursor of the long HOMER1B mRNA isoform, which is significantly downregulated in the prefrontal cortex of subjects with psychosis and is able to regulate cognitive function. Even though its relevance to psychiatric disorders and its role in brain function and synaptic plasticity have been well established, little is known about the molecular mechanisms that underlie circHomer1 biogenesis in response to neuronal activity and psychiatric drug treatment. Here we suggest that the RNA-binding protein (RBP) FUS positively regulates neuronal circHomer1 expression. Furthermore, we show that the MEK/ERK and PKA/CREB pathways positively regulate neuronal circHomer1 expression, as well as promote the transcription of Fus and Eif4a3, another RBP previously shown to activate circHomer1 biogenesis. We then demonstrate via both in vitro and in vivo studies that NMDA and mGluR5 receptors are upstream modulators of circHomer1 expression. Lastly, we report that in vivo D2R antagonism increases circHomer1 expression, whereas 5HT2AR blockade reduces circHomer1 levels in multiple brain regions. Taken together, this study allows us to gain novel insights into the molecular circuits that underlie the biogenesis of a psychiatric disease-associated circRNA.

The synergic effects of presynaptic calcium channel antagonists purified from spiders on memory elimination of glutamate-induced excitotoxicity in the rat hippocampus trisynaptic circuit

The hippocampus is a complex area of the mammalian brain and is responsible for learning and memory. The trisynaptic circuit engages with explicit memory. Hippocampal neurons express two types of presynaptic voltage-gated calcium channels (VGCCs) comprising N and P/Q-types. These VGCCs play a vital role in the release of neurotransmitters from presynaptic neurons. The chief excitatory neurotransmitter at these synapses is glutamate. Glutamate has an essential function in learning and memory under normal conditions. The release of neurotransmitters depends on the activity of presynaptic VGCCs. Excessive glutamate activity, due to either excessive release or insufficient uptake from the synapse, leads to a condition called excitotoxicity. This pathological state is common among all neurodegenerative disorders, such as Alzheimer's and Parkinson's diseases. Under these conditions, glutamate adversely affects the trisynaptic circuitry, leading to synaptic destruction and loss of memory and learning performance. This study attempts to clarify the role of presynaptic VGCCs in memory performance and reveals that modulating the activity of presynaptic calcium channels in the trisynaptic pathway can regulate the excitotoxic state and consequently prevent the elimination of neurons and synaptic degradation. All of these can lead to an improvement in learning and memory function. In the current study, two calcium channel blockers-omega-agatoxin-Aa2a and omega-Lsp-IA-were extracted, purified, and identified from spiders (Agelena orientalis and Hogna radiata) and used to modulate N and P/Q VGCCs. The effect of omega-agatoxin-Aa2a and omega-Lsp-IA on glutamate-induced excitotoxicity in rats was evaluated using the Morris water maze task as a behavioral test. The local expression of synaptophysin (SYN) was visualized for synaptic quantification using an immunofluorescence assay. The electrophysiological amplitudes of the field excitatory postsynaptic potentials (fEPSPs) in the input-output and LTP curves of the mossy fiber and Schaffer collateral circuits were recorded. The results of our study demonstrated that N and P/Q VGCC modulation in the hippocampus trisynaptic circuit of rats with glutamate-induced excitotoxicity dysfunction could prevent the destructive consequences of excitotoxicity in synapses and improve memory function and performance.

Transient neonatal hyperglycemia induces metabolic shifts in the rat hippocampus: a 1H NMR-based metabolomics analysis

Diabetes has been reported to induce brain metabolic disturbance, but the effect of transient neonatal hyperglycemia (TNH) on brain metabolism remains unclear. Herein the rats were treated with a single intraperitoneal injection of 100 µg/g body weight of streptozotocin within 12 h after birth and displayed a typical clinical characteristic of TNH. Then we used NMR-based metabolomics to examine the metabolic changes in the hippocampus between TNH and normal control (Ctrl) rats at postnatal 7 days (P7) and 21 days (P21). The results show that TNH rats had significantly increased levels of N-acetyl aspartate, glutamine, aspartate and choline in the hippocampus relative to Ctrl rats at P7. Moreover, we found that the levels of alanine, myo-inositol and choline were significantly lower in TNH rats, although their blood glucose levels have been recovered to the normal level at P21. Therefore, our results suggest that TNH may have a long-term effect on hippocampal metabolic changes mainly involving neurotransmitter metabolism and choline metabolism.

GluN2D Subunit in Parvalbumin Interneurons Regulates Prefrontal Cortex Feedforward Inhibitory Circuit and Molecular Networks Relevant to Schizophrenia

BACKGROUND

Parvalbumin interneuron (PVI) activity synchronizes the medial prefrontal cortex circuit for normal cognitive function, and its impairment may contribute to schizophrenia (SZ). NMDA receptors in PVIs participate in these activities and form the basis for the NMDA receptor hypofunction hypothesis of SZ. However, the role of the GluN2D subunit, which is enriched in PVIs, in regulating molecular networks relevant to SZ is unknown.

METHODS

Using electrophysiology and a mouse model with conditional deletion of GluN2D from PVIs (PV-GluN2D knockout [KO]), we examined the cell excitability and neurotransmission in the medial prefrontal cortex. Histochemical, RNA sequencing analysis and immunoblotting were conducted to understand molecular mechanisms. Behavioral analysis was conducted to test cognitive function.

RESULTS

PVIs in the medial prefrontal cortex were found to express putative GluN1/2B/2D receptors. In a PV-GluN2D KO model, PVIs were hypoexcitable, whereas pyramidal neurons were hyperexcitable. Excitatory neurotransmission was higher in both cell types in PV-GluN2D KO, whereas inhibitory neurotransmission showed contrasting changes, which could be explained by reduced somatostatin interneuron projections and increased PVI projections. Genes associated with GABA (gamma-aminobutyric acid) synthesis, vesicular release, and uptake as well as those involved in formation of inhibitory synapses, specifically GluD1-Cbln4 and Nlgn2, and regulation of dopamine terminals were downregulated in PV-GluN2D KO. SZ susceptibility genes including Disc1, Nrg1, and ErbB4 and their downstream targets were also downregulated. Behaviorally, PV-GluN2D KO mice showed hyperactivity and anxiety behavior and deficits in short-term memory and cognitive flexibility.

CONCLUSIONS

These findings demonstrate that GluN2D in PVIs serves as a point of convergence of pathways involved in the regulation of GABAergic synapses relevant to SZ.

Cognitive Flexibility in Mice: Effects of Puberty and Role of NMDA Receptor Subunits

Cognitive flexibility refers to the ability to adapt flexibly to changing circumstances. In laboratory mice, we investigated whether cognitive flexibility is higher in pubertal mice than in adult mice, and whether this difference is related to the expression of distinct NMDA receptor subunits. Using the attentional set shifting task as a measure of cognitive flexibility, we found that cognitive flexibility was increased during puberty. This difference was more pronounced in female pubertal mice. Further, the GluN2A subunit of the NMDA receptor was more expressed during puberty than after puberty. Pharmacological blockade of GluN2A reduced the cognitive flexibility of pubertal mice to adult levels. In adult mice, the expression of GluN2A, GluN2B, and GluN2C in the orbitofrontal cortex correlated positively with performance in the attentional set shifting task, whereas in pubertal mice this was only the case for GluN2C. In conclusion, the present study confirms the observation in humans that cognitive flexibility is higher during puberty than in adulthood. Future studies should investigate whether NMDA receptor subunit-specific agonists are able to rescue deficient cognitive flexibility, and whether they have the potential to be used in human diseases with deficits in cognitive flexibility.

Developmental Manipulation-Induced Changes in Cognitive Functioning

Schizophrenia is a complex neurodevelopmental disorder with as-yet no identified cause. The use of animals has been critical to teasing apart the potential individual and intersecting roles of genetic and environmental risk factors in the development of schizophrenia. One way to recreate in animals the cognitive impairments seen in people with schizophrenia is to disrupt the prenatal or neonatal environment of laboratory rodent offspring. This approach can result in congruent perturbations in brain physiology, learning, memory, attention, and sensorimotor domains. Experimental designs utilizing such animal models have led to a greatly improved understanding of the biological mechanisms that could underlie the etiology and symptomology of schizophrenia, although there is still more to be discovered. The implementation of the Research and Domain Criterion (RDoC) has been critical in taking a more comprehensive approach to determining neural mechanisms underlying abnormal behavior in people with schizophrenia through its transdiagnostic approach toward targeting mechanisms rather than focusing on symptoms. Here, we describe several neurodevelopmental animal models of schizophrenia using an RDoC perspective approach. The implementation of animal models, combined with an RDoC framework, will bolster schizophrenia research leading to more targeted and likely effective therapeutic interventions resulting in better patient outcomes.

Ameliorative effects of omega-lycotoxin-Gsp2671e purified from the spider venom of Lycosa praegrandis on memory deficits of glutamate-induced excitotoxicity rat model

Memory impairment is one of the main complications of Alzheimer's disease (AD). This condition can be induced by hyper-stimulation of N-Methyl-D-aspartate receptors (NMDARs) of glutamate in the hippocampus, which ends up to pyramidal neurons determination. The release of neurotransmitters relies on voltage-gated calcium channels (VGCCs) such as P/Q-types. Omega-lycotoxin-Gsp2671e (OLG1e) is a P/Q-type VGCC modulator with high affinity and selectivity. This bio-active small protein was purified and identified from the Lycosa praegrandis venom. The effect of this state-dependent low molecular weight P/Q-type calcium modulator on rats was investigated via glutamate-induced excitotoxicity by N-Methyl-D-aspartate. Also, Electrophysiological amplitude of field excitatory postsynaptic potentials (fEPSPs) in the input-output and Long-term potentiation (LTP) curves were recorded in mossy fiber and the amount of synaptophysin (SYN), synaptosomal-associated protein, 25 kDa (SNAP-25), and synaptotagmin 1(SYT1) genes expression were measured using Real-time PCR technique for synaptic quantification. The outcomes of the current study suggest that OLG1e as a P/Q-type VGCC modulator has an ameliorative effect on excitotoxicity-induced memory defects and prevents the impairment of pyramidal neurons in the rat hippocampus.

Functional impairment of cortical AMPA receptors in schizophrenia

Clinical and preclinical studies suggest that some of the behavioral alterations observed in schizophrenia (SZ) may be mechanistically linked to synaptic dysfunction of glutamatergic signaling. Recent genetic and proteomic studies suggest alterations of cortical glutamate receptors of the AMPA-type (AMPARs), which are the predominant ligand-gated ionic channels of fast transmission at excitatory synapses. The impact of gene and protein alterations on the electrophysiological activity of AMPARs is not known in SZ. In this proof of principle work, using human postmortem brain synaptic membranes isolated from the dorsolateral prefrontal cortex (DLPFC), we combined electrophysiological analysis from microtransplanted synaptic membranes (MSM) with transcriptomic (RNA-Seq) and label-free proteomics data in 10 control and 10 subjects diagnosed with SZ. We observed in SZ a reduction in the amplitude of AMPARs currents elicited by kainate, an agonist of AMPARs that blocks the desensitization of the receptor. This reduction was not associated with protein abundance but with a reduction in kainate's potency to activate AMPARs. Electrophysiologically-anchored dataset analysis (EDA) was used to identify synaptosomal proteins that linearly correlate with the amplitude of the AMPARs responses, gene ontology functional annotations were then used to determine protein-protein interactions. Protein modules associated with positive AMPARs current increases were downregulated in SZ, while protein modules that were upregulated in SZ were associated with decreased AMPARs currents. Our results indicate that transcriptomic and proteomic alterations, frequently observed in the DLPFC in SZ, converge at the synaptic level producing a functional electrophysiological impairment of AMPARs.

Pretreatment with Carpolobia lutea ethanol extract prevents schizophrenia-like behavior in mice models of psychosis

ETHNOPHARMACOLOGICAL RELEVANCE

Carpolobia lutea decoction is widely used as a phytotherapeutic against central nervous system-related disorders including insomnia, migraine headache, and mental illness in West and Central Tropical Africa.

AIM

This study was designed to investigate the antipsychotic activity of Carpolobia lutea (EECL) in mice models of psychosis.

METHODS

Male Swiss mice (n = 5/group) were given EECL (100, 200, 400, and 800 mg/kg), haloperidol (1 mg/kg), clozapine (5 mg/kg) and vehicle (10 mL/kg) orally before amphetamine (5 mg/kg)-induced hyperlocomotion and stereotypy, apomorphine (2 mg/kg)-induced stereotypy, or ketamine (10, 30, and 100 mg/kg)-induced hyperlocomotion, enhancement of immobility and cognitive impairment.

RESULTS

EECL (200, 400, and 800 mg/kg) prevented amphetamine- and apomorphine-induced stereotypies, as well as reduced hyperlocomotion induced by amphetamine and ketamine, all of which are predictors of positive symptoms. Regardless of the dose administered, EECL prevented the index of negative symptoms induced by ketamine. Furthermore, higher doses of EECL (400 and 800 mg/kg) also prevented ketamine-induced cognitive impairment, a behavioral phenotype of cognitive symptoms.

CONCLUSION

Pretreatment with EECL demonstrated antipsychotic activity in mice, preventing amphetamine-, apomorphine-, and ketamine-induced schizophrenia-like symptoms, with 800 mg/kg being the most effective dose.

NMDA receptors mediate synaptic plasticity impairment of hippocampal neurons due to arsenic exposure

Endemic arsenism is a worldwide health problem. Chronic arsenic exposure results in cognitive dysfunction due to arsenic and its metabolites accumulating in hippocampus. As the cellular basis of cognition, synaptic plasticity is pivotal in arsenic-induced cognitive dysfunction. N-methyl-D-aspartate receptors (NMDARs) serve physiological functions in synaptic transmission. However, excessive NMDARs activity contributes to exitotoxicity and synaptic plasticity impairment. Here, we provide an overview of the mechanisms that NMDARs and their downstream signaling pathways mediate synaptic plasticity impairment due to arsenic exposure in hippocampal neurons, ways of arsenic exerting on NMDARs, as well as the potential therapeutic targets except for water improvement.

Validation of ketamine as a pharmacological model of thalamic dysconnectivity across the illness course of schizophrenia

N-methyl-D-aspartate receptor (NMDAR) hypofunction is a leading pathophysiological model of schizophrenia. Resting-state functional magnetic resonance imaging (rsfMRI) studies demonstrate a thalamic dysconnectivity pattern in schizophrenia involving excessive connectivity with sensory regions and deficient connectivity with frontal, cerebellar, and thalamic regions. The NMDAR antagonist ketamine, when administered at sub-anesthetic doses to healthy volunteers, induces transient schizophrenia-like symptoms and alters rsfMRI thalamic connectivity. However, the extent to which ketamine-induced thalamic dysconnectivity resembles schizophrenia thalamic dysconnectivity has not been directly tested. The current double-blind, placebo-controlled study derived an NMDAR hypofunction model of thalamic dysconnectivity from healthy volunteers undergoing ketamine infusions during rsfMRI. To assess whether ketamine-induced thalamic dysconnectivity was mediated by excess glutamate release, we tested whether pre-treatment with lamotrigine, a glutamate release inhibitor, attenuated ketamine's effects. Ketamine produced robust thalamo-cortical hyper-connectivity with sensory and motor regions that was not reduced by lamotrigine pre-treatment. To test whether the ketamine thalamic dysconnectivity pattern resembled the schizophrenia pattern, a whole-brain template representing ketamine's thalamic dysconnectivity effect was correlated with individual participant rsfMRI thalamic dysconnectivity maps, generating "ketamine similarity coefficients" for people with chronic (SZ) and early illness (ESZ) schizophrenia, individuals at clinical high-risk for psychosis (CHR-P), and healthy controls (HC). Similarity coefficients were higher in SZ and ESZ than in HC, with CHR-P showing an intermediate trend. Higher ketamine similarity coefficients correlated with greater hallucination severity in SZ. Thus, NMDAR hypofunction, modeled with ketamine, reproduces the thalamic hyper-connectivity observed in schizophrenia across its illness course, including the CHR-P period preceding psychosis onset, and may contribute to hallucination severity.

Schizophrenia

Schizophrenia, characterised by psychotic symptoms and in many cases social and occupational decline, remains an aetiological and therapeutic challenge. Contrary to popular belief, the disorder is modestly more common in men than in women. Nor is the outcome uniformly poor. A division of symptoms into positive, negative, and disorganisation syndromes is supported by factor analysis. Catatonic symptoms are not specific to schizophrenia and so-called first rank symptoms are no longer considered diagnostically important. Cognitive impairment is now recognised as a further clinical feature of the disorder. Lateral ventricular enlargement and brain volume reductions of around 2% are established findings. Brain functional changes occur in different subregions of the frontal cortex and might ultimately be understandable in terms of disturbed interaction among large-scale brain networks. Neurochemical disturbance, involving dopamine function and glutamatergic N-methyl-D-aspartate receptor function, is supported by indirect and direct evidence. The genetic contribution to schizophrenia is now recognised to be largely polygenic. Birth and early life factors also have an important aetiological role. The mainstay of treatment remains dopamine receptor-blocking drugs; a psychological intervention, cognitive behavioural therapy, has relatively small effects on symptoms. The idea that schizophrenia is better regarded as the extreme end of a continuum of psychotic symptoms is currently influential. Other areas of debate include cannabis and childhood adversity as causative factors, whether there is progressive brain change after onset, and the long-term success of early intervention initiatives.

Aberrant maturation and connectivity of prefrontal cortex in schizophrenia-contribution of NMDA receptor development and hypofunction

The neurobiology of schizophrenia involves multiple facets of pathophysiology, ranging from its genetic basis over changes in neurochemistry and neurophysiology, to the systemic level of neural circuits. Although the precise mechanisms associated with the neuropathophysiology remain elusive, one essential aspect is the aberrant maturation and connectivity of the prefrontal cortex that leads to complex symptoms in various stages of the disease. Here, we focus on how early developmental dysfunction, especially N-methyl-D-aspartate receptor (NMDAR) development and hypofunction, may lead to the dysfunction of both local circuitry within the prefrontal cortex and its long-range connectivity. More specifically, we will focus on an "all roads lead to Rome" hypothesis, i.e., how NMDAR hypofunction during development acts as a convergence point and leads to local gamma-aminobutyric acid (GABA) deficits and input-output dysconnectivity in the prefrontal cortex, which eventually induce cognitive and social deficits. Many outstanding questions and hypothetical mechanisms are listed for future investigations of this intriguing hypothesis that may lead to a better understanding of the aberrant maturation and connectivity associated with the prefrontal cortex.

Sex differences between serum total bilirubin levels and cognition in patients with schizophrenia

BACKGROUND

Cognitive deficits are common in patients with schizophrenia (SCZ). Abnormal serum total bilirubin (TBIL) levels have been involved in cognitive deficits associated with neuropsychiatric diseases such as mild cognitive impairment and subcortical ischemic vascular disease. However, this relationship has not yet been fully investigated in patients with SCZ. Therefore, the aim of this study was to investigate the association between the serum TBIL concentration and cognitive deficits in SCZ patients and to determine whether a sex difference exists in the association.

METHODS

A total of 455 participants were eligible and included in this cross-sectional study. Cognition was evaluated using the Montreal Cognitive Assessment. Serum TBIL concentration was measured with an automatic biochemistry analyzer according to the routine protocol in the hospital medical laboratory.

RESULTS

Serum TBIL levels were lower in the cognition impairment group than in the cognition normal group in male patients. In contrast, serum TBIL levels tended to be increased in the cognition impairment group in female patients, although the difference was not significant. Further stepwise multiple regression analysis stratified by sex showed that serum TBIL was independently and positively associated with cognitive function in male patients but not in female patients. Moreover, the association between serum TBIL level and cognitive function was also identified by the propensity score matching (PSM) method in male patients, but not in female patients.

CONCLUSION

These findings suggest that lower serum TBIL levels may be associated with cognitive impairment in male SCZ patients.

Treating cognitive impairment in schizophrenia with GLP-1RAs: an overview of their therapeutic potential

INTRODUCTION

Schizophrenia is a neuropsychiatric disorder that affects approximately 1% of individuals worldwide. There are no available medications to treat cognitive impairment in this patient population currently. Preclinical evidence suggests that glucagon-like peptide-1 receptor agonists (GLP-1 RAs) improve cognitive function. There is a need to evaluate how GLP-1 RAs alter specific domains of cognition and whether they will be of therapeutic benefit in individuals with schizophrenia.

AREAS COVERED

This paper summarizes the effects of GLP-1 RAs on metabolic processes in the brain and how these mechanisms relate to improved cognitive function. We provide an overview of preclinical studies that demonstrate GLP-1 RAs improve cognition and comment on their potential therapeutic benefit in individuals with schizophrenia.

EXPERT OPINION

To understand the benefits of GLP-1 RAs in individuals with schizophrenia, further preclinical research with rodent models relevant to schizophrenia symptomology are needed. Moreover, preclinical studies must focus on using a wider range of behavioral assays to understand whether important aspects of cognition such as executive function, attention, and goal-directed behavior are improved using GLP-1 RAs. Further research into the specific mechanisms of how GLP-1 RAs affect cognitive function and their interactions with antipsychotic medication commonly prescribed is necessary.

Effect of Neonatal Treatment With the NMDA Receptor Antagonist, MK-801, During Different Temporal Windows of Postnatal Period in Adult Prefrontal Cortical and Hippocampal Function

The neonatal MK-801 model of schizophrenia has been developed based on the neurodevelopmental and NMDA receptor hypofunction hypotheses of schizophrenia. This animal model is generated with the use of the NMDA receptor antagonist, MK-801, during different temporal windows of postnatal life of rodents leading to behavioral defects in adulthood. However, no studies have examined the role of specific postnatal time periods in the neonatal MK-801 (nMK-801) rodent model and the resulting behavioral and neurobiological effects. Thus, the goal of this study is to systematically investigate the role of NMDA hypofunction, during specific temporal windows in postnatal life on different cognitive and social behavioral paradigms, as well as various neurobiological effects during adulthood. Both female and male mice were injected intraperitoneally (i.p.) with MK-801 during postnatal days 7-14 (p7-14) or 11-15 (p11-15). Control mice were injected with saline during the respective time period. In adulthood, mice were tested in various cognitive and social behavioral tasks. Mice nMK-801-treated on p7-14 show impaired performance in the novel object, object-to-place, and temporal order object recognition (TOR) tasks, the sociability test, and contextual fear extinction. Mice nMK-801-treated on p11-15 only affects performance in the TOR task, the social memory test, and contextual fear extinction. No differences were identified in the expression of NMDA receptor subunits, the synapsin or PSD-95 proteins, either in the prefrontal cortex (PFC) or the hippocampus (HPC), brain regions significantly affected in schizophrenia. The number of parvalbumin (PV)-expressing cells is significantly reduced in the PFC, but not in the HPC, of nMK-801-treated mice on p7-14 compared to their controls. No differences in PV-expressing cells (PFC or HPC) were identified in nMK-801-treated mice on p11-15. We further examined PFC function by recording spontaneous activity in a solution that allows up state generation. We find that the frequency of up states is significantly reduced in both nMK-801-treated mice on p7-14 and p11-15 compared to saline-treated mice. Furthermore, we find adaptations in the gamma and high gamma activity in nMK-801-treated mice. In conclusion, our results show that MK-801 treatment during specific postnatal temporal windows has differential effects on cognitive and social behaviors, as well as on underlying neurobiological substrates.

Relationships and Interactions between Ionotropic Glutamate Receptors and Nicotinic Receptors in the CNS

Although ionotropic glutamate receptors and nicotinic receptors for acetylcholine (ACh) have usually been studied separately, they are often co-localized and functionally inter-dependent. The objective of this review is to survey the evidence for interactions between the two receptor families and the mechanisms underlying them. These include the mutual regulation of subunit expression, which change the NMDA:AMPA response balance, and the existence of multi-functional receptor complexes which make it difficult to distinguish between individual receptor sites, especially in vivo. This is followed by analysis of the functional relationships between the receptors from work on transmitter release, cellular electrophysiology and aspects of behavior where these can contribute to understanding receptor interactions. It is clear that nicotinic receptors (nAChRs) on axonal terminals directly regulate the release of glutamate and other neurotransmitters, α7-nAChRs generally promoting release. Hence, α7-nAChR responses will be prevented not only by a nicotinic antagonist, but also by compounds blocking the indirectly activated glutamate receptors. This accounts for the apparent anticholinergic activity of some glutamate antagonists, including the endogenous antagonist kynurenic acid. The activation of presynaptic nAChRs is by the ambient levels of ACh released from pre-terminal synapses, varicosities and glial cells, acting as a 'volume neurotransmitter' on synaptic and extrasynaptic sites. In addition, ACh and glutamate are released as CNS co-transmitters, including 'cholinergic' synapses onto spinal Renshaw cells. It is concluded that ACh should be viewed primarily as a modulator of glutamatergic neurotransmission by regulating the release of glutamate presynaptically, and the location, subunit composition, subtype balance and sensitivity of glutamate receptors, and not primarily as a classical fast neurotransmitter. These conclusions and caveats should aid clarification of the sites of action of glutamate and nicotinic receptor ligands in the search for new centrally-acting drugs.

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

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

Quantum energy levels of glutamate modulate neural biophotonic signals

Glutamate is the most abundant excitatory neurotransmitter in the brain, and it plays an essential and important role in neural functions. Current studies have shown that glutamate can induce neural biophotonic activity and transmission, which may involve the mechanism of photon quantum brain; however, it is unclear whether such a mechanism follows the principle of quantum mechanics. Here we show that the action of glutamate on its receptors leads to a decrease in its quantum energy levels, and glutamate then partially or completely loses its function to further induce the biophotonic activity in mouse brain slices. The reduced quantum energy levels of glutamate can be restored by direct-current electrical discharges and the use of energy transfer of chloroplast photosynthesis; hence, the quantum energy recovered glutamate can again induce significant biophotonic activity. Furthermore, the changes in quantum energy levels of glutamate are related to the exchange and transfer of electron energy on its active hydrogen atom. These findings suggest that the glutamate-induced neural biophotonic signals may be involved in the transfer of the quantum energy levels of glutamate, which implies a quantum mechanism of neurotransmitter action.

Efficacy of adjunctive D-Cycloserine for the treatment of schizophrenia: a systematic review and meta-analysis of randomized controlled trials

D-Cycloserine is a partial agonist at the glycine site of the N-methyl-D-aspartate (NMDA) receptor. Results have been inconsistent in trials on the efficacy of D-Cycloserine in patients with schizophrenia. We examined the efficacy of D-Cycloserine against negative and cognitive symptoms (primary and co-primary outcomes). Secondary outcomes were efficacy of D-Cycloserine against positive symptoms and the examination of early treatment outcomes. A systematic literature search was carried out using following selection criteria: Population = Patients with Schizophrenia; Intervention = Trials using D-Cycloserine either as monotherapy or adjuvant therapy; Comparison = Placebo or active comparator; Outcome = Change in negative symptoms, cognitive symptoms and positive symptoms; Study design = Randomized controlled trials with parallel design. We used the Cochrane Collaboration tool for risk of bias for study quality appraisal. Effect sizes for trials were calculated separately for negative, positive and cognitive symptom dimensions using the DerSimonian-Laird random effects model. Seven studies (pooled N = 413) provided data for meta-analysis. The pooled Standardized Mean Difference (SMD) for negative, cognitive, and positive symptom change scores were - 0.32 (95% CI, - 0.75 to 0.11), - 0.05 (95% CI, - 0.91 to 0.81), and - 0.08 (95% CI, - 0.37 to 0.20), respectively. No significant improvement was noted with regard to early outcome. I² values for heterogeneity were 61%, 67%, and 0% for studies assessing negative, cognitive, and positive symptom ratings, respectively. D-Cycloserine did not exhibit significant efficacy in treating negative, cognitive, or positive symptoms of schizophrenia at either study-defined endpoint (4-36 weeks) or at four weeks (early outcome).

Region-specific metabolic characterization of the type 1 diabetic brain in mice with and without cognitive impairment

Type 1 diabetes (T1D) has been reported to cause cognitive decline, but brain metabolic changes during this process are still far from being fully understood. Here, we found that streptozotocin (STZ)-induced T1D mice exhibited impaired learning and memory at 11 weeks after STZ treatment but not at 3 weeks. Therefore, we studied metabolic alterations in six different brain regions of T1D mice with and without cognitive decline, and attempted to identify key metabolic pathways related to diabetic cognitive dysfunction. The results demonstrate that lactate had already increased in all brain regions of T1D mice prior to cognitive decline, but a decreased TCA cycle was only observed in hippocampus, cortex and striatum of T1D mice with cognitive impairment. Reduced N-acetylaspartate and choline were found in all brain regions of T1D mice, irrespective of cognitive decline. In addition, disrupted neurotransmitter metabolism was noted to occur in T1D mice before cognitive deficit. Of note, we found that the level of uridine was significantly reduced in cerebellum, cortex, hypothalamus and midbrain of T1D mice when cognitive decline was presented. Therefore, brain region-specific metabolic alterations may comprise possible biomarkers for the early-diagnosis and monitoring of diabetic cognitive decline. Moreover, down-regulated TCA cycle and pyrimidine metabolism could be closely related to T1D-associated cognitive impairment.

NMR-based metabolomics characterizes metabolic changes in different brain regions of streptozotocin-induced diabetic mice with cognitive decline

Diabetes at advanced age increases rise of cognitive impairment, but its potential mechanisms are still far from being fully understood. In this study, we analyzed the metabolic alterations in six different brain regions between streptozotocin (STZ)-induced diabetic mice with cognitive decline (DM) and age-matched controls (CON) using a ¹H NMR-based metabolomics approach, to explore potential metabolic mechanisms underlying diabetes-induced cognitive decline. The results show that DM mice had a peculiar metabolic phenotype in all brain regions, mainly involving increased lactate level, decreased choline and energy metabolism as well as disrupted astrocyte-neuron metabolism. Furthermore, these metabolic changes exhibited a brain region-specific pattern. Collectively, our results suggest that brain region-specific metabolic disorders may be responsible for diabetes-induced cognitive dysfunction.

Reduced serial dependence suggests deficits in synaptic potentiation in anti-NMDAR encephalitis and schizophrenia

A mechanistic understanding of core cognitive processes, such as working memory, is crucial to addressing psychiatric symptoms in brain disorders. We propose a combined psychophysical and biophysical account of two symptomatologically related diseases, both linked to hypofunctional NMDARs: schizophrenia and autoimmune anti-NMDAR encephalitis. We first quantified shared working memory alterations in a delayed-response task. In both patient groups, we report a markedly reduced influence of previous stimuli on working memory contents, despite preserved memory precision. We then simulated this finding with NMDAR-dependent synaptic alterations in a microcircuit model of prefrontal cortex. Changes in cortical excitation destabilized within-trial memory maintenance and could not account for disrupted serial dependence in working memory. Rather, a quantitative fit between data and simulations supports alterations of an NMDAR-dependent memory mechanism operating on longer timescales, such as short-term potentiation.

Stein, Barbosa et al. show that anti-NMDAR encephalitis and schizophrenia are characterized by reduced serial dependence in spatial working memory. Cortical network simulations show that this can be parsimoniously explained by a reduction in NMDAR-dependent short-term synaptic potentiation in these diseases.

Sex-specific metabolic alterations in the type 1 diabetic brain of mice revealed by an integrated method of metabolomics and mixed-model

Type 1 diabetes (T1D) can cause brain region-specific metabolic disorders, but whether gender influences T1D-related brain metabolic changes is rarely reported. Therefore, here we examined metabolic changes in six different brain regions of male and female mice under normal and T1D conditions using an integrated method of NMR-based metabolomics and linear mixed-model, and aimed to explore sex-specific metabolic changes from normal to T1D. The results demonstrate that metabolic differences occurred in all brain regions between two genders, while the hippocampal metabolism is more likely to be affected by T1D. At the 4th week after streptozotocin treatment, brain metabolic disorders mainly occurred in the cortex and hippocampus in female T1D mice, but the striatum and hippocampus in male T1D mice. In addition, anaerobic glycolysis was significantly altered in male mice, mainly in the striatum, midbrain, hypothalamus and hippocampus, but not in female mice. We also found that female mice exhibited a hypometabolism status relative to male mice from normal to T1D. Collectively, this study suggests that T1D affected brain region-specific metabolic alterations in a sex-specific manner, and may provide a metabolic view on diabetic brain diseases between genders.

Suppression of Parvalbumin Interneuron Activity in the Prefrontal Cortex Recapitulates Features of Impaired Excitatory/Inhibitory Balance and Sensory Processing in Schizophrenia

Accumulating evidence supports parvalbumin expressing inhibitory interneuron (PV IN) dysfunction in the prefrontal cortex as a cause for cognitive impairment associated with schizophrenia (CIAS). PV IN decreased activity is suggested to be the culprit for many of the EEG deficits measured in patients, which correlate with deficits in working memory (WM), cognitive flexibility and attention. In the last few decades, CIAS has been recognized as a heavy burden on the quality of life of patients with schizophrenia, but little progress has been made in finding new treatment options. An important limiting factor in this process is the lack of adequate preclinical models and an incomplete understanding of the circuits engaged in cognition. In this study, we back-translated an auditory stimulation protocol regularly used in human EEG studies into mice and combined it with optogenetics to investigate the role of prefrontal cortex PV INs in excitatory/inhibitory balance and cortical processing. We also assessed spatial WM and reversal learning (RL) during inhibition of prefrontal cortex PV INs. We found significant impairments in trial-to-trial reliability, increased basal network activity and increased oscillation power at 20-60 Hz, and a decreased signal-to-noise ratio, but no significant impairments in behavior. These changes reflect some but not all neurophysiological deficits seen in patients with schizophrenia, suggesting that other neuronal populations and possibly brain regions are involved as well. Our work supports and expands previous findings and highlights the versatility of an approach that combines innovative technologies with back-translated tools used in humans.

Plasma levels of dopamine metabolite correlate with mismatch negativity in patients with schizophrenia

AIM

Mismatch negativity (MMN) deficit is one of the most robust and replicable findings in schizophrenia, and primarily reflects deficient functioning of the N-methyl-D-aspartate (NMDA) receptor system. Although the dopamine receptor is known not to modulate MMN over the short term, it is unclear whether the dopamine system affects MMN in the long term.

METHODS

We explored correlations between MMN and levels of plasma dopamine and serotonin metabolites in 18 patients with schizophrenia psychiatrically evaluated with the Positive and Negative Syndrome Scale (PANSS).

RESULTS

A significant negative correlation exists between MMN amplitude and plasma levels of dopamine metabolites. Plasma serotonin metabolite levels were not correlated with MMN. The PANSS total score and Negative score also showed negative correlations with MMN amplitude.

CONCLUSION

The usual strong therapeutic blockade of dopamine receptors applied in cases of schizophrenia may reduce MMN over the long term.

Pro-cognitive effect of 1MeTIQ on recognition memory in the ketamine model of schizophrenia in rats: the behavioural and neurochemical effects

RATIONALE

Schizophrenia is a mental illness which is characterised by positive and negative symptoms and by cognitive impairments. While the major prevailing hypothesis is that altered dopaminergic and/or glutamatergic transmission contributes to this disease, there is evidence that the noradrenergic system also plays a role in its major symptoms.

OBJECTIVES

In the present paper, we investigated the pro-cognitive effect of 1-methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ) an endogenous neuroprotective compound, on ketamine-modelled schizophrenia in rats.

METHODS

We used an antagonist of NMDA receptors (ketamine) to model memory deficit symptoms in rats. Using the novel object recognition (NOR) test, we investigated the pro-cognitive effect of 1MeTIQ. Additionally, olanzapine, an atypical antipsychotic drug, was used as a standard to compare the pro-cognitive effects of the substances. In vivo microdialysis studies allowed us to verify the changes in the release of monoamines and their metabolites in the rat striatum.

RESULTS

Our study demonstrated that 1MeTIQ, similarly to olanzapine, exhibits a pro-cognitive effect in NOR test and enhances memory disturbed by ketamine treatment. Additionally, in vivo microdialysis studies have shown that ketamine powerfully increased noradrenaline release in the rat striatum, while 1MeTIQ and olanzapine completely antagonised this neurochemical effect.

CONCLUSIONS

1MeTIQ, as a possible pro-cognitive drug, in contrast to olanzapine, expresses beneficial neuroprotective activity in the brain, increasing concentration of the extraneuronal dopamine metabolite, 3-methoxytyramine (3-MT), which plays an important physiological role in the brain as an inhibitory regulator of catecholaminergic activity. Moreover, we first demonstrated the essential role of noradrenaline release in memory disturbances observed in the ketamine-model of schizophrenia, and its possible participation in negative symptoms of the schizophrenia.

Recapitulation of Neuropsychiatric Behavioral Features in Mice Using Acute Low-dose MK-801 Administration

Despite some innate limitations, animal models are a potent investigative tool when used to model specific symptoms of a disorder. For example, MK-801, an N-methyl-D-aspartate receptor antagonist, is used as a pharmacological tool to induce symptoms found in some neuropsychiatric disorders. However, a close examination of literature suggests that the application window of MK-801 doses is relatively narrow between individual behavioral paradigms, necessitating careful characterization of the evoked behavioral aberrations and the doses used to induce them. Moreover, variation in behaviors depending on the animal strain, gender of the subject, and the timing of administration is observed, making it difficult to compare the behavioral characteristics reported in different studies. We aim to characterize the behavioral aberrations induced by different doses of MK-801 in CD-1 mice and create a ready reference for future studies. We used CD-1 mice to recapitulate behavioral impairments resulting from acute administration of MK-801. In 0.1 mg kg⁻¹, we observed diminished spontaneous alteration during the Y-maze test, while 0.12 mg kg⁻¹ resulted in hyperlocomotion and social deficit. Mice treated with 0.2 and 0.3 mg kg⁻¹ of MK-801 demonstrated a decreased self-grooming. Finally, all doses significantly impaired cliff avoidance behaviors suggesting increased impulsivity. These results affirm that MK-801 can effectively model various symptoms of different neuropsychiatric disorders in a dose-dependent manner. The observed sensitivity against spatial-memory impairment and impulsive behaviors at low concentration of MK-801 suggest that MK801 may modulate cognitive function and impulsivity in even lower concentration before it can modulate other behavioral domains.

Evaluation of Clinical Factors Associated with Adverse Drug Events in Patients Receiving Sub-Anesthetic Ketamine Infusions

Introduction

Sub-anesthetic ketamine is frequently used as an analgesic to reduce perioperative opioid consumption and has also been shown to have antidepressant effects. Side effects of ketamine include dizziness, diplopia, nystagmus, and psychomimetic effects. It is unclear what clinical factors may be associated with ketamine-related adverse drug events (ADEs).

Methods

We performed a retrospective review of 95 patients who received sub-anesthetic ketamine infusions at our institution. Data examined associations between ketamine-related ADEs and various clinical characteristics including chronic pain, depression, or psychiatric disorder, patient physical characteristics, chronic opioid use, perioperative opioid use, dose and duration of ketamine infusions, pain scores, and perioperative medications such as serotonergic agents, central nervous system (CNS) depressants, and analgesics.

Results

Overall incidence of ketamine-related ADEs was 29.5% and the incidence of psychomimetic effects was 14.8%. We observed that patients with a history of depression have a lower incidence of ketamine-related ADEs compared to patients without a history of depression (10.3% vs 37.3%; p value = 0.007).

Conclusion

Patients with depression were found to have a statistically significant reduction in the incidence of ketamine-related ADEs. We found no statistically significant positive associations between ketamine-related ADEs and other clinical factors such as a history of chronic pain, psychiatric disease, patient physical characteristics, perioperative opioid use, dose of ketamine infusion, or co-administration of other CNS depressants.

NMDAR PAMs: Multiple Chemotypes for Multiple Binding Sites

The N-methyl-D-aspartate receptor (NMDAR) is a member of the ionotropic glutamate receptor (iGluR) family that plays a crucial role in brain signalling and development. NMDARs are nonselective cation channels that are involved with the propagation of excitatory neurotransmission signals with important effects on synaptic plasticity. NMDARs are functionally and structurally complex receptors, they exist as a family of subtypes each with its own unique pharmacological properties. Their implication in a variety of neurological and psychiatric conditions means they have been a focus of research for many decades. Disruption of NMDAR-related signalling is known to adversely affect higherorder cognitive functions (e.g. learning and memory) and the search for molecules that can recover (or even enhance) receptor output is a current strategy for CNS drug discovery. A number of positive allosteric modulators (PAMs) that specifically attempt to overcome NMDAR hypofunction have been discovered. They include various chemotypes that have been found to bind to several different binding sites within the receptor. The heterogeneity of chemotype, binding site and NMDAR subtype provide a broad landscape of ongoing opportunities to uncover new features of NMDAR pharmacology. Research on NMDARs continues to provide novel mechanistic insights into receptor activation and this review will provide a high-level overview of the research area and discuss the various chemical classes of PAMs discovered so far.

Attenuation Effects of Alpha-Pinene Inhalation on Mice with Dizocilpine-Induced Psychiatric-Like Behaviour

α-Pinene, an organic terpene compound found in coniferous trees, is used as a safe food additive and is contained in many essential oils. Moreover, some studies have shown that α-pinene suppresses neuronal activity. In this study, we investigated whether inhalation of α-pinene suppresses dizocilpine (MK-801-) induced schizophrenia-like behavioural abnormalities in mice. Mice inhaled α-pinene 1 h before the first MK-801 injection. Thirty minutes after MK-801 injection, the open field, spontaneous locomotor activity, elevated plus maze, Y-maze, tail suspension, hot plate, and grip strength tests were conducted as behavioural experiments. Inhalation of α-pinene suppressed the activity of mice in the spontaneous locomotor activity test and although it did not suppress the MK-801-induced increased locomotor activity in the open field test, it remarkably decreased the time that the mice remained in the central area. Inhalation of α-pinene suppressed the MK-801-induced increased total distance travelled in the Y-maze test, whereas it did not alter the MK-801-induced reduced threshold of antinociception in the hot plate test. In the tail suspension and grip strength tests, there was no effect on mouse behaviour by administration of MK-801 and inhalation of α-pinene. These results suggest that α-pinene acts to reduce MK-801-induced behavioural abnormalities resembling those seen in neuropsychiatric disorders. Therefore, both medicinal plants and essential oils containing α-pinene may have potential for therapeutic treatment of schizophrenia.

Neuroprotective effects of Withania somnifera in BPA induced-cognitive dysfunction and oxidative stress in mice

Background

Bisphenol A (BPA), a major endocrine disruptor and a xenobiotic compound is used abundantly in the production of polycarbonate plastics and epoxy resins. Human exposure to this compound is primarily via its leaching from the protective internal epoxy resin coatings of containers into the food and beverages. In addition, the plastics used in dental prostheses and sealants also contain considerable amount of BPA and have a high risk of human exposure. Since it is a well-known endocrine disruptor and closely mimics the molecular structure of human estrogen thereby impairing learning and memory. Withania somnifera (Ws), commonly known as Ashwagandha is known for its varied therapeutic uses in Ayurvedic system of medicine. The present study was undertaken to demonstrate the impairment induced by BPA on the spatial learning, working memory and its alleviation by Ws in Swiss albino mice. The study was conducted on thirty Swiss albino mice, randomly distributed among three groups: control, BPA and BPA + Ws. The behavioral recovery after treatment with Ws was investigated using the Y-maize and Morris water maize test. Whereas, for the estimation of recovery of NMDA receptor which is related to learning and memory in hippocampus region by western blot and immunohistochemistry. Furthermore, the oxidative stress and antioxidant level was assessed by biochemical tests like MDA, SOD and catalase.

Results

The study revealed that administration of Ws alleviated the behavioral deficits induced by BPA. Alongside, Ws treatment reinstated the number of NMDA receptors in hippocampus region and showed anti-oxidative property while ameliorating the endogenous anti-oxidant level in the brain.

Conclusion

These findings suggest that Ws significantly ameliorates the level of BPA intoxicated oxidative stress thereby potentially treating cognitive dysfunction which acts as the primary symptom in a number of neurodegenerative diseases.

Effects of NMDA antagonist dizocilpine (MK-801) are modulated by the number of distractor stimuli in the rodent odor span task of working memory

The rodent odor span task (OST) uses an incrementing non-matching to sample procedure in which a series of odors is presented and selection of the session-novel odor is reinforced. An OST is frequently used to test the effects of neurobiological variables on memory capacity as the number of odors to remember increases during the course of the session. In this regard, one important finding has been that NMDA receptor antagonists selectively impair OST performance at doses that spare accuracy on control tasks. However, in many versions of the odor span task the number of stimuli to remember is confounded with the number of distractor odors presented to the rat on each trial. The present study compared the effects of the NMDA antagonist dizocilpine when the number of choices was held constant at two (one novel odor-S+ and one previously presented distractor odor-S-) and when the number of choice stimuli was permitted to increase up to 10 (one S+ and 9 S-). Dizocilpine impaired OST accuracy at doses that had no effect on a reference memory control task in both 2-choice and 10-choice conditions; however, the dose-response function was shifted to the left in the 10-choice tests. The impairments produced by dizocilpine were exacerbated as the memory load increased in both 2- and 10-choice conditions. These findings support the hypothesis that NMDA antagonism reduces the number of stimuli that rats can remember accurately, but the interaction between the effective DZP dose and the number of distractors shows that drug effects on OST performances may involve attentional factors in addition to memory capacity. The findings also demonstrate that variations in number of OST distractors can be used to alter sensitivity of the task.

Linking phencyclidine intoxication to the tryptophan-kynurenine pathway: Therapeutic implications for schizophrenia

Phencyclidine (PCP) is a dissociative anesthetic that induces psychotic symptoms and neurocognitive deficits in rodents similar to those observed in schizophrenia patients. PCP administration in healthy human subjects induces schizophrenia-like symptoms such as positive and negative symptoms, and a range of cognitive deficits. It has been reported that PCP, ketamine, and related drugs such as N-methyl-D-aspartate-type (NMDA) glutamate receptor antagonists, induce behavioral effects by blocking neurotransmission at NMDA receptors. Further, NMDA receptor antagonists reproduce specific aspects of the symptoms of schizophrenia. Neurochemical models based on the actions of PCP are well established, with increased focus on glutamatergic dysfunction as a basis for both symptoms and cognitive dysfunction in schizophrenia. On the other hand, the endogenous NMDA receptor antagonist, kynurenic acid (KYNA), which is a product of tryptophan-kynurenine pathway (KP) metabolism, is involved in schizophrenia pathogenesis. KYNA concentrations are elevated in the prefrontal cortex and cerebrospinal fluid of patients with schizophrenia. KYNA elevation affects neurotransmitter release in a similar manner to that of psychotomimetic agents such as PCP, underscoring a molecular basis of its involvement in schizophrenia pathophysiology. This review will highlight the relationship between PCP and KP metabolites based on evidence that both exogenous and endogenous NMDA receptor antagonists are involved in the pathogenesis of schizophrenia, and discuss our current understanding of the mechanisms underlying dysfunctional glutamatergic signaling as potential therapeutic targets for schizophrenia.

NMDA receptor-driven calcium influx promotes ischemic human cardiomyocyte apoptosis through a p38 MAPK-mediated mechanism

N-methyl-D-aspartate receptor (NMDAR) activity plays a key role in cerebral ischemia. Although NMDAR is also expressed in cardiomyocytes, little research has been performed on NMDAR activity in myocardial ischemia. Here, using an in vitro oxygen-glucose deprivation (OGD) cardiomyocyte model, we evaluated the effects of NMDAR activity upon calcium influx, viability, apoptosis, and investigated the roles of several key mitogen-activated protein kinases (MAPKs). Primary human neonatal cardiomyocytes were cultured under OGD conditions to mimic in vivo ischemic conditions. Enhancing NMDAR activity via NMDA significantly promoted calcium influx, decreased cell viability, increased apoptosis, and enhanced p38 MAPK phosphorylation in OGD cardiomyocytes (all P < 0.05). These effects were rescued by several calcium-channel blockers (ie, MK-801, La³⁺ , Gap26 peptide, 18β-glycyrrhetinic acid) but most potently rescued via the NMDAR-specific antagonist MK-801 or removal of extracellular free calcium (all P < 0.05). Knocking-down p38 MAPK activity by small-molecule inhibition or genetic methods significantly increased cell viability and reduced apoptosis (all P < 0.05). Enhancing p38 MAPK activity abolished MK-801's apoptosis-reducing effects in a p38 MAPK-dependent manner. In conclusion, NMDAR-driven calcium influx promotes apoptosis in ischemic human cardiomyocytes, an effect which can be attributed to enhanced p38 MAPK activity.

Relationship of Interferon-γ to Cognitive Function in Midlife Women with Schizophrenia

Recent literature suggests that schizophrenia is linked to an abnormal response of the immune system. Interferon-γ is a cytokine that acts as a mediator between immune stimulation and the kynurenine pathway and may be related to cognitive abilities. The objectives of the present study are to determine if serum cytokines are correlated with cognitive function differently in patients with schizophrenia compared to controls. Fourteen midlife (30-70 year-old) females with DSM-IV diagnosis of schizophrenia or schizoaffective disorder and 13 midlife control females were analyzed. Cytokines were collected from serum blood draws and analyzed at the Cytokine Core Lab at the University of Maryland, Baltimore. The RBANS, HVLT-R, and UPSA were performed to measure cognition and social performance. The results demonstrate a non-significant difference between interferon-γ levels in women with schizophrenia compared to controls, but this cytokine appears to correlate to cognitive abilities differently in these groups. There were several significant negative correlations between interferon-γ and cognition in midlife patients with schizophrenia, but only one in the midlife control group. The negative correlations between interferon-γ and cognition in patients with schizophrenia suggest the hypothesis that inflammation and the kynurenine pathway have important roles in this disorder.

Concerns related to ED-mediated effects of Bisphenol A and their regulatory consideration

The extensive database on BPA provides strong evidence of its adverse effects on reproductive, neurobehavioural, metabolic functions and mammary gland. Disruption of estrogenic pathway is central in the mediation of these effects although other modes of action may be involved. BPA has a weak affinity for ERα/β but interaction with extranuclearly located pathways activated by estrogens such as ERRγ and GPER reveals how BPA can act at low doses. The effects are observed later in life after developmental exposure and are associated with pathologies of major societal concern in terms of severity, incidence, impact on quality of life, burden on public health system. The complexity of the dose response raise uncertainties on the possibility to establish safe levels and the scope of ED-mediated effects of BPA may be wider. These concerns fulfill the requirements for ED identification under REACH regulation.

Impairment of learning and memory performances induced by BPA: Evidences from the literature of a MoA mediated through an ED

Many rodent studies and a few non-human primate data report impairments of spatial and non-spatial memory induced by exposure to bisphenol A (BPA), which are associated with neural modifications, particularly in processes involved in synaptic plasticity. BPA-induced alterations involve disruption of the estrogenic pathway as established by reversal of BPA-induced effects with estrogenic receptor antagonist or by interference of BPA with administered estradiol in ovariectomized animals. Sex differences in hormonal impregnation during critical periods of development and their influence on maturation of learning and memory processes may explain the sexual dimorphism observed in BPA-induced effects in some studies. Altogether, these data highly support the plausibility that alteration of learning and memory and synaptic plasticity by BPA is essentially mediated by disturbance of the estrogenic pathways. As memory function in humans involves similar signaling pathways, this mode of action of BPA has the potential to alter human cognitive abilities.

Vaccinia-related kinase 2 modulates role of dysbindin by regulating protein stability

Vaccinia-related kinase 2 (VRK2) is a serine/threonine kinase that belongs to the casein kinase 1 family. VRK2 has long been known for its relationship with neurodegenerative disorders such as schizophrenia. However, the role of VRK2 and the substrates associated with it are unknown. Dysbindin is known as one of the strong risk factors for schizophrenia. The expression of dysbindin is indeed significantly reduced in schizophrenia patients. Moreover, dysbindin is involved in neurite outgrowth and regulation of NMDA receptor signaling. Here, we first identified dysbindin as a novel interacting protein of VRK2 through immunoprecipitation. We hypothesized that dysbindin is phosphorylated by VRK2 and further that this phosphorylation plays an important role in the function of dysbindin. We show that VRK2 phosphorylates Ser 297 and Ser 299 of dysbindin using in vitro kinase assay. In addition, we found that VRK2-mediated phosphorylation of dysbindin enhanced ubiquitination of dysbindin and consequently resulted in the decrease in its protein stability through western blotting. Over-expression of VRK2 in human neuroblastoma (SH-SY5Y) cells reduced neurite outgrowth induced by retinoic acid. Furthermore, a phosphomimetic mutant of dysbindin alleviated neurite outgrowth and affected surface expression of N-methyl-d-aspartate 2A, a subunit of NMDA receptor in mouse hippocampal neurons. Together, our work reveals the regulation of dysbindin by VRK2, providing the association of these two proteins, which are commonly implicated in schizophrenia. OPEN SCIENCE BADGES: This article has received a badge for *Open Materials* because it provided all relevant information to reproduce the study in the manuscript. The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/.

Perinatal administration of phencyclidine alters expression of Lingo-1 signaling pathway proteins in the prefrontal cortex of juvenile and adult rats

Postnatal administration of phencyclidine (PCP) in rodents causes major brain dysfunction leading to severe disturbances in behavior lasting into adulthood. This model is routinely employed to model psychiatric disorders such as schizophrenia, as it reflects schizophrenia-related brain disturbances including increased apoptosis, and disruptions to myelin and plasticity processes. Leucine-rich repeat and Immunoglobin-like domain-containing protein 1 (Lingo-1) is a potent negative regulator of both axonal myelination and neurite extension. The Nogo receptor (NgR)/tumor necrosis factor (TNF) receptor orphan Y (TROY) and/or p75 neurotrophin receptor (p75) complex, with no lysine (K) (WNK1) and myelin transcription factor 1 (Myt1) are co-receptors or cofactors in Lingo-1 signaling pathways in the brain. We have examined the developmental trajectory of these proteins in a neurodevelopmental model of schizophrenia using PCP to determine if Lingo-1 pathways are altered in the prefrontal cortex throughout different stages of life. Sprague-Dawley rats were injected with PCP (10 mg/kg) or saline on postnatal days (PN)7, 9, and 11 and killed at PN12, 5 or 14 weeks for measurement of Lingo-1 signaling proteins in the prefrontal cortex. Myt1 was decreased by PCP at PN12 (P=0.045), and at 14 weeks PCP increased Lingo-1 (P=0.037), TROY (P=0.017), and WNK1 (P=0.003) expression. This is the first study reporting an alteration in Lingo-1 signaling proteins in the rat prefrontal cortex both directly after PCP treatment in early development and in adulthood. We propose that Lingo-1 pathways may be negatively regulating myelination and neurite outgrowth following the administration of PCP, and that this may have implications for the cortical dysfunction observed in schizophrenia.

Autoimmune phenotypes in schizophrenia reveal novel treatment targets

Typical and atypical antipsychotics are the first-line treatments for schizophrenia, but these classes of drugs are not universally effective, and they can have serious side effects that impact compliance. Antipsychotic drugs generally target the dopamine pathways with some variation. As research of schizophrenia pathophysiology has shifted away from a strictly dopamine-centric focus, the development of new pharmacotherapies has waned. A field of inquiry with centuries-old roots is gaining traction in psychiatric research circles and may represent a new frontier for drug discovery in schizophrenia. At the forefront of this investigative effort is the immune system and its many components, pathways and phenotypes, which are now known to actively engage the brain. Studies in schizophrenia reveal an intricate association of environmentally-driven immune activation in concert with a disrupted genetic template. A consistent conduit through this gene-environmental milieu is the gut-brain axis, which when dysregulated can generate pathological autoimmunity. In this review, we present epidemiological and biochemical evidence in support of an autoimmune component in schizophrenia and depict gut processes and a dysbiotic microbiome as a source and perpetuator of autoimmune dysfunction in the brain. Within this framework, we review the role of infectious agents, inflammation, gut dysbioses and autoantibody propagation on CNS pathologies such as neurotransmitter receptor hypofunction and complement pathway-mediated synaptic pruning. We then review the new pharmacotherapeutic horizon and novel agents directed to impact these pathological conditions. At the core of this discourse is the understanding that schizophrenia is etiologically and pathophysiologically heterogeneous and thus its treatment requires individualized attention with disease state variants diagnosed with objective biomarkers.

The location discrimination reversal task in mice is sensitive to deficits in performance caused by aging, pharmacological and other challenges

Deficits in hippocampal-mediated pattern separation are one aspect of cognitive function affected in schizophrenia (SZ) or Alzheimer's disease (AD). To develop novel therapies, it is beneficial to explore this specific aspect of cognition preclinically. The location discrimination reversal (LDR) task is a hippocampal-dependent operant paradigm that evaluates spatial learning and cognitive flexibility using touchscreens. Here we assessed baseline performance as well as multimodal disease-relevant manipulations in mice. Mice were trained to discriminate between the locations of two images where the degree of separation impacted performance. Administration of putative pro-cognitive agents was unable to improve performance at narrow separation. Furthermore, a range of disease-relevant manipulations were characterized to assess whether performance could be impaired and restored. Pertinent to the cholinergic loss in AD, scopolamine (0.1 mg/kg) produced a disruption in LDR, which was attenuated by donepezil (1 mg/kg). Consistent with NMDA hypofunction in cognitive impairment associated with SZ, MK-801 (0.1 mg/kg) also disrupted performance; however, this deficit was not modified by rolipram. Microdeletion of genes associated with SZ (22q11) resulted in impaired performance, which was restored by rolipram (0.032 mg/kg). Since aging and inflammation affect cognition and are risk factors for AD, these aspects were also evaluated. Aged mice were slower to acquire the task than young mice and did not reach the same level of performance. A systemic inflammatory challenge (lipopolysaccharide (LPS), 1 mg/kg) produced prolonged (7 days) deficits in the LDR task. These data suggest that LDR task is a valuable platform for evaluating disease-relevant deficits in pattern separation and offers potential for identifying novel therapies.

Targeting hypothalamic-pituitary-adrenal axis hormones and sex steroids for improving cognition in major mood disorders and schizophrenia: a systematic review and narrative synthesis

Cognitive deficits are a core feature of serious mental illnesses such as schizophrenia, major depressive disorder (MDD) and bipolar disorder (BD) and are a common cause of functional disability. There is limited efficacy of pharmacological interventions for improving the cognitive deficits in these disorders. As pro-cognitive pharmacological treatments are lacking, hormones or drugs that target the endocrine system may become potential candidates for 'repurposing' trials aiming to improve cognition. We aimed to study whether treatment with drugs targeting the hypothalamic-pituitary-adrenal (HPA) axis and sex steroids can improve cognition in patients with schizophrenia, MDD or BD. A systematic search was performed using PubMed (Medline), PsychInfo and clinicaltrials.gov, and a narrative synthesis was included. The systematic review identified 12 studies dealing with HPA-related drugs (mifepristone [n = 3], cortisol synthesis inhibitors [ketoconazole, n = 2], dehydroepiandrosterone [n = 5], fludrocortisone [n = 2]) and 14 studies dealing with sex steroids (oestradiol [n = 2], selective oestrogen receptor modulators [raloxifene, n = 7], pregnenolone [n = 5]). Positive trials were found for BD (mifepristone), MDD (dehydroepiandrosterone and fludrocortisone) and schizophrenia (dehydroepiandrosterone, raloxifene and pregnenolone). A replication of positive findings by at least two clinical trials was found for mifepristone in BD and raloxifene and pregnenolone in schizophrenia. The use of drugs targeting hormones related to the HPA axis and sex steroids is a promising field of research that might help to improve the cognitive outcome of patients with schizophrenia, bipolar disorder and major depressive disorder in the near future.

Neurosteroid pregnenolone sulfate, alone, and as augmentation of lurasidone or tandospirone, rescues phencyclidine-induced deficits in cognitive function and social interaction

BACKGROUND

Pregnenolone sulfate (PregS), an endogenous neurosteroid, which negatively and positively modulates gamma amino butyric acid subunit A (GABA_A) and N-methyl D-aspartate (NMDA) receptors (R) respectively, among other potential neuroplastic changes on synaptic processes, has shown some beneficial effects on treating cognitive impairment associated with schizophrenia (CIAS) and negative symptoms. Lurasidone (Lur), an atypical antipsychotic drug (AAPD), and tandospirone (Tan), a 5-HT_1A R partial agonist, have also been reported to improve cognitive or negative symptoms, or both, in some schizophrenia patients.

METHODS

We tested whether PregS, by itself, and in combination with Lur or Tan could rescue persistent deficits produced by subchronic treatment with the NMDAR antagonist, phencyclidine (PCP)-in episodic memory, executive functioning, and social behavior, using novel object recognition (NOR), operant reversal learning (ORL), and social interaction (SI) tasks, in male C57BL/6 J mice.

RESULTS

PregS (10, but not 3 mg/kg) significantly rescued subchronic PCP-induced NOR and SI deficits. Co-administration of sub-effective doses (SEDs) of PregS (3 mg/kg) + Lur (0.1 mg/kg) or Tan (0.03 mg/kg) rescued scPCP-induced NOR and SI deficits. Further, PregS (30, but not 10 mg/kg) rescued PCP-induced ORL deficit, as did the combination of SED PregS (10 mg/kg) +SED Lur (1 mg/kg) or Tan (1 mg/kg).

CONCLUSION

PregS was effective alone and as adjunctive treatment for treating two types of cognitive impairments and negative symptoms in this schizophrenia model. Further study of the mechanisms by which PregS alone and in combination with AAPDs and 5-HT_1A R partial agonists, rescues the deficits in cognition and SI in this preclinical model is indicated.

Neurotransmitter deficits from frontotemporal lobar degeneration

Frontotemporal lobar degeneration causes a spectrum of complex degenerative disorders including frontotemporal dementia, progressive supranuclear palsy and corticobasal syndrome, each of which is associated with changes in the principal neurotransmitter systems. We review the evidence for these neurochemical changes and propose that they contribute to symptomatology of frontotemporal lobar degeneration, over and above neuronal loss and atrophy. Despite the development of disease-modifying therapies, aiming to slow neuropathological progression, it remains important to advance symptomatic treatments to reduce the disease burden and improve patients' and carers' quality of life. We propose that targeting the selective deficiencies in neurotransmitter systems, including dopamine, noradrenaline, serotonin, acetylcholine, glutamate and gamma-aminobutyric acid is an important strategy towards this goal. We summarize the current evidence-base for pharmacological treatments and suggest strategies to improve the development of new, effective pharmacological treatments.

GLYX-13 Ameliorates Schizophrenia-Like Phenotype Induced by MK-801 in Mice: Role of Hippocampal NR2B and DISC1

Background: Evidence supports that the hypofunction of N-methyl-D-aspartate receptor (NMDAR) and downregulation of disrupted-in-schizophrenia 1 (DISC1) contribute to the pathophysiology of schizophrenia. N-Methyl D-aspartate receptor subtype 2B (NR2B)-containing NMDAR are associated with cognitive dysfunction in schizophrenia. GLYX-13 is an NMDAR glycine-site functional partial agonist and cognitive enhancer that does not induce psychotomimetic side effects. However, it remains unclear whether NR2B plays a critical role in the GLYX-13-induced alleviation of schizophrenia-like behaviors in mice. Methods: The effect of GLYX-13 was tested by observing changes in locomotor activity, novel object recognition ability, and prepulse inhibition (PPI) induced by dizocilpine (known as MK-801) in mice. Lentivirus-mediated NR2B knockdown in the hippocampus was assessed to confirm the role of NR2B in GLYX-13 pathophysiology, using Western blots and immunohistochemistry. Results: The systemic administration of GLYX-13 (0.5 and 1 mg/kg, i.p.) ameliorates MK-801 (0.5 mg/kg, i.p.)-induced hyperlocomotion, deficits in memory, and PPI in mice. Additionally, GLYX-13 normalized the MK-801-induced alterations in signaling molecules, including NR2B and DISC1 in the hippocampus. Furthermore, we found that NR2B knockdown produced memory and PPI deficits without any changes in locomotor activity. Notably, DISC1 levels significantly decreased by NR2B knockdown. However, the effective dose of GLYX-13 did not alleviate the memory and PPI dysfunctions or downregulation of DISC1 induced by NR2B knockdown. Conclusion: Our results suggest GLYX-13 as a candidate for schizophrenia treatment, and NR2B and DISC1 in the hippocampus may account for the molecular mechanisms of GLYX-13.