NMDA receptor regulation of memory and behavior in humans

Efficacy and Safety of Intravenous Magnesium Sulfate in Spinal Surgery: A Systematic Review and Meta-Analysis

Optimizing pain management in spinal surgery is crucial for preventing adverse events due to delayed mobilization. Magnesium sulfate has potential benefits in spinal surgery because of its analgesic properties and modulation of neurotransmitters and autonomic nervous system. Existing evidence regarding the use of magnesium sulfate is partial and controversial, necessitating a comprehensive meta-analysis to evaluate its efficacy and safety. The aim of this study was to conduct a comprehensive meta-analysis to evaluate the efficacy and safety of magnesium sulfate in spinal surgery compared to other available options. This meta-analysis adhered to the PRISMA guidelines. Patients undergoing spinal surgery were included, with the intervention group receiving intravenous magnesium sulfate (MS) at various doses or combinations, whereas the comparison group received other alternatives or a placebo. The efficacy and safety outcomes were assessed. Data were collected from multiple databases and analyzed using Review Manager version 5.4. Heterogeneity was assessed and fixed- or random-effects models were applied. The meta-analysis included eight studies (n = 541). Magnesium sulfate demonstrated significant reductions in pain at 24 h (MD -0.20, 95% CI: -0.39 to -0.02) and opioid consumption (SMD -0.66, 95% CI: -0.95 to -0.38) compared to placebo. Additionally, a decrease in the use of muscle relaxants (SMD -0.91, 95% CI: -1.65 to -0.17) and remifentanil (SMD -1.52, 95% CI: -1.98 to -1.05) was observed. In contrast, an increase in extubation time (MD 2.42, 95% CI: 1.14 to 3.71) and verbal response (MD 1.85, 95% CI: 1.13 to 2.58) was observed compared to dexmedetomidine. In conclusion, magnesium sulfate administration in spinal surgery reduced pain and opioid consumption, and prolonged orientation and verbal response. No significant differences in blood pressure or heart rate were observed between the groups.

Perinatal exposure to atazanavir-based antiretroviral regimens in a mouse model leads to differential long-term motor and cognitive deficits dependent on the NRTI backbone

Background

Combination antiretroviral therapy (ART) use in pregnancy has been pivotal in improving maternal health and reducing perinatal HIV transmission. However, children born HIV-exposed uninfected fall behind their unexposed peers in several areas including neurodevelopment. The contribution of in utero ART exposure to these deficits is not clear. Here we present our findings of neurocognitive outcomes in adult mice exposed in utero to ART.

Methods

Dams were treated with a combination of ritonavir-boosted atazanavir with either abacavir plus lamivudine (ABC/3TC + ATV/r) or tenofovir disoproxil fumarate plus emtricitabine (TDF/FTC + ATV/r), or water as a control, administered daily from day of plug detection to birth. Offspring underwent a battery of behavioral tests that investigated motor performance and cognition starting at 6-weeks of age and ending at 8 months. Changes in brain structure were assessed using magnetic resonance imaging and immunohistochemistry. Expression of genes involved in neural circuitry and synaptic transmission were assessed in the hippocampus, a region strongly associated with memory formation, using qPCR.

Findings

Pups exposed to TDF/FTC + ATV/r showed increased motor activity and exploratory drive, and deficits in hippocampal-dependent working memory and social interaction, while pups exposed to ABC/3TC + ATV/r showed increased grooming, and deficits in working memory and social interaction. Significant volumetric reductions in the brain were seen only in the ABC/3TC + ATV/r group and were associated with reduced neuronal counts in the hippocampus. Altered neurotransmitter receptor mRNA expression as well as changes in expression of the neurotrophic factor BDNF and its receptors were observed in both ART-exposed groups in a sex-dependent manner.

Interpretation

In our model, in utero ART exposure had long-term effects on brain development and cognitive and motor outcomes in adulthood. Our data show that neurological outcomes can be influenced by the type of nucleoside reverse transcriptase inhibitor backbone of the regimen and not just the base drug, and display sex differences.

Behavioral Disorders of Spatial Cognition in Patients with Mild Cognitive Impairment due to Alzheimer's Disease: Preliminary Findings from the BDSC-MCI Project

(1) Background: Spatial cognition (SC) is one of the earliest cognitive domains to be impaired in the course of Alzheimer's disease (AD), resulting in spatial disorientation and becoming lost even in familiar surroundings as later dementia symptoms. To date, few studies have identified initial alterations of spatial navigation (SN) in the premorbid AD phase by real-world paradigms, and none have adopted an innovative technological apparatus to better detect gait alterations as well as physiological aspects correlated to spatial disorientation (SD). The present study aimed at exploring initial SN defects in patients with prodromal AD via a naturalistic task by using a sensory garment. (2) Methods: 20 community-dwelling patients with Mild Cognitive Impairment (MCI) due to AD and 20 age/education controls were assessed on their sequential egocentric and allocentric navigation abilities by using a modified version of the Detour Navigation Test (DNT-mv). (3) Results: When compared to controls, patients with MCI due to AD exhibited higher wrong turns (WT) and moments of hesitation (MsH) in the DNT-mv, reflecting difficulties both in sequential egocentric and allocentric navigation, depending on hippocampal deterioration. Moreover, they reported more complaints about their SN competencies and lower long-term visuospatial memory abilities than controls. Remarkably, WTs and MsH manifested in the allocentric naturalistic task of the DNT-mv were associated with autonomic nervous system alteration pertaining to cardiac functioning in the whole sample. (4) Conclusions: Naturalistic navigation tests of hippocampal function using a continuous non-invasive monitoring device can provide early markers of spatial disorientation in patients with MCI due to AD. Future studies should develop cognitive remediation techniques able to enhance SC residual abilities in patients at high risk of conversion into dementia and ecological paradigms to be replicated on a large scale.

Myelinating Co-Culture as a Model to Study Anti-NMDAR Neurotoxicity

Anti-NMDA receptor (NMDAR) encephalitis is frequently associated with demyelinating disorders (e.g., multiple sclerosis (MS), neuromyelitis optica spectrum disorder (NMOSD), myelin oligodendrocyte glycoprotein-associated disease (MOGAD)) with regard to clinical presentation, neuropathological and cerebrospinal fluid findings. Indeed, autoantibodies (AABs) against the GluN1 (NR1) subunit of the NMDAR diminish glutamatergic transmission in both neurons and oligodendrocytes, leading to a state of NMDAR hypofunction. Considering the vital role of oligodendroglial NMDAR signaling in neuron-glia communication and, in particular, in tightly regulated trophic support to neurons, the influence of GluN1 targeting on the physiology of myelinated axon may be of importance. We applied a myelinating spinal cord cell culture model that contains all major CNS cell types, to evaluate the effects of a patient-derived GluN1-specific monoclonal antibody (SSM5) on neuronal and myelin integrity. A non-brain reactive (12D7) antibody was used as the corresponding isotype control. We show that in cultures at the late stage of myelination, prolonged treatment with SSM5, but not 12D7, leads to neuronal damage. This is characterized by neurite blebbing and fragmentation, and a reduction in the number of myelinated axons. However, this significant toxic effect of SSM5 was not observed in earlier cultures at the beginning of myelination. Anti-GluN1 AABs induce neurodegenerative changes and associated myelin loss in myelinated spinal cord cultures. These findings may point to the higher vulnerability of myelinated neurons towards interference in glutamatergic communication, and may refer to the disturbance of the NMDAR-mediated oligodendrocyte metabolic supply. Our work contributes to the understanding of the emerging association of NMDAR encephalitis with demyelinating disorders.

A systematic review and quantitative synthesis of the long-term psychiatric sequelae of pediatric autoimmune encephalitis

BACKGROUND

Long-term neuropsychiatric sequelae of autoimmune encephalitis (AE) remain understudied, particularly in pediatric-onset AE. We aimed to synthesize the published data on ongoing psychiatric symptoms in pediatric-onset AE.

METHODS

The Pubmed, PyscINFO, Web of Science databases were searched from their inception years to August 23, 2021, and 29 studies were identified and analyzed. We also performed a quantitative synthesis of available patient data from the 29 studies combined with a cohort of anti-NMDA receptor (NMDAR) AE from our institution to examine the associations between acute treatment course and long-term psychiatric outcome.

RESULTS

At long-term follow up, 52.4% of the cases with pediatric-onset AE had any persistent symptom and 36.0% had at least one psychiatric symptom. Pooled data found that 36.3% of pediatric-onset anti-NMDAR AE had ongoing psychiatric symptoms. Using a univariate logistic regression analysis, we found that abnormal initial EEG, use of certain immunotherapies, and persistent cognitive impairments were associated with ongoing psychiatric symptoms.

LIMITATIONS

Limitations of the existing literature included a significant paucity of outcomes measured using consistent, objective methods. Limitations of the systematic review included the wide variability among the studies reviewed, which rendered a meta-analysis impossible and beyond the scope of the paper.

CONCLUSION

Chronic psychiatric and behavioral problems remain present in one-third of children months to years after onset of AE. Larger scaled prospective observational studies with a consistent standardized battery of testing are needed to examine impact of specific clinical features and immunotherapies on long-term mental health outcomes.

Chronic developmental exposure to low-dose ([C8mim][PF6]) induces neurotoxicity and behavioural abnormalities in rats

Ionic liquids (ILs) are widely used for their physical and chemical properties. Toxicological assessments of ILs could help to avoid their threat to human health, but these are rarely reported, and no assessments of IL neurotoxicity in mammals have been performed. Here, we aimed to evaluate the neurotoxicity of chronic 1-octyl-3-methylimidazolium hexafluorophosphate ([C8mim][PF6]) (0, 1 mg/kg) exposure during development on rats. Our results indicated that chronic exposure to low-dose ([C8mim][PF6]) induces behavioural abnormalities, including cognitive deficits, social communication disorders, and sensory gating function impairment. Moreover, rats subjected to chronic ([C8mim][PF6]) exposure showed hypofunction of glutamatergic excitatory synapses, including increased expression of NMDA receptor subunits, increased density and immaturity of dendritic spines, and increased expression of PSD95. Additionally, ([C8mim][PF6]) exposure resulted in hippocampal-specific inflammatory activation, indicated by increased levels of proinflammatory factors, elevated nuclear localisation of NF-κB, and activation of microglia and astrocytes. In conclusion, chronic exposure to low-dose ([C8mim][PF6]) induced neurotoxicity, including damage to glutamatergic excitatory synapses and inflammatory activation, which may illuminate the associated behavioural abnormalities. The results presented here may be helpful for the safe use of ILs in the future.

[18F]ALX5406: A Brain-Penetrating Prodrug for GlyT1-Specific PET Imaging

Selective inhibition of glycine transporter 1 (GlyT1) has emerged as a potential approach to alleviate N-methyl-d-aspartate receptor (NMDAR) hypofunction in patients with schizophrenia and cognitive decline. ALX5407 is a potent and selective inhibitor of GlyT1 derived from the metabolic intermediate sarcosine (N-methylglycine) that showed antipsychotic potential in a number of animal models. Whereas clinical application of ALX5407 is limited by adverse effects on motor performance and respiratory function, a suitably radiolabeled drug could represent a promising PET tracer for the visualization of GlyT1 in the brain. Herein, [¹⁸F]ALX5407 and the corresponding methyl ester, [¹⁸F]ALX5406, were prepared by alcohol-enhanced copper mediated radiofluorination and studied in vitro in rat brain slices and in vivo in normal rats. [¹⁸F]ALX5407 demonstrated accumulation consistent with the distribution of GlyT1 in in vitro autoradiographic studies but no brain uptake in μPET experiments in naı̈ve rats. In contrast, the methyl ester [¹⁸F]ALX5406 rapidly entered the brain and was enzymatically transformed into [¹⁸F]ALX5407, resulting in a regional accumulation pattern consistent with GlyT1 specific binding. We conclude that [¹⁸F]ALX5406 is a promising and easily accessible PET probe for preclinical in vivo imaging of GlyT1 in the brain.

Postconditioning with Sevoflurane or Propofol Alleviates Lipopolysaccharide-Induced Neuroinflammation but Exerts Dissimilar Effects on the NR2B Subunit and Cognition

Neuroinflammation can cause cognitive deficits, and preexisting neuroinflammation is observed frequently in the clinic after trauma, surgery, and infection. Patients with preexisting neuroinflammation often need further medical treatment under general anesthesia. However, the effects of postconditioning with general anesthetics on preexisting neuroinflammation have not been determined. In this study, adult rats were posttreated with sevoflurane or propofol after intracerebroventricular administration of lipopolysaccharide. The effects of sevoflurane or propofol postconditioning on neuroinflammation-induced recognition memory deficits were detected. Our results found that postconditioning with sevoflurane but not propofol reversed the selective spatial recognition memory impairment induced by neuroinflammation, and these differential effects did not appear to be associated with the similar anti-neuroinflammatory responses of general anesthetics. However, postconditioning with propofol induced a selective long-lasting upregulation of extrasynaptic NR2B-containing N-methyl-D-aspartate receptors in the dorsal hippocampus, which downregulated the cAMP response element-binding signaling pathway and impaired spatial recognition memory. Additionally, the NR2B antagonists memantine and Ro25-6981 reversed this neurotoxicity induced by propofol postconditioning. Taken together, these results indicate that under preexisting neuroinflammation, postconditioning with sevoflurane can provide reliable neuroprotection by attenuating lipopolysaccharide-induced neuroinflammation, apoptosis, and neuronal loss and eventually improving spatial recognition deficits. However, although posttreatment with propofol also has the same anti-neuroinflammatory effects, the neurotoxicity caused by propofol postconditioning following neuroinflammation warrants further consideration.

Repeated Restraint Stress Led to Cognitive Dysfunction by NMDA Receptor-Mediated Hippocampal CA3 Dendritic Spine Impairments in Juvenile Sprague-Dawley Rats

Although numerous studies have indicated that chronic stress causes cognitive dysfunction with the impairment of synaptic structures and functions, the relationship between cognitive deficits induced by repeated restraint stress and the level of NMDA receptors in the subregion of the hippocampus has been relatively unknown until now. In this study, 3-week-old male Sprague-Dawley rats were exposed to repeated restraint stress for seven consecutive days, their cognitive functions were evaluated through behavioral tests, and then they were sacrificed for electrophysiological, morphological, and biochemical assays. Chronic repeated restraint stress led to cognitive and electrophysiological impairments, with a reduced density of dendritic spines. We also found that the protein level of NMDA receptors only increased in the hippocampal CA3 region. Nevertheless, repeated restraint stress-induced cognitive and synaptic dysfunction were effectively reversed by Ro25-6981, an inhibitor of the GluN2B receptor. These findings suggest that repeated restraint stress-induced synaptic and cognitive deficits are probably mediated through NMDA receptors.

Prenatal THC exposure raises kynurenic acid levels in the prefrontal cortex of adult rats

Cannabis remains one of the most widely used illicit drugs during pregnancy. The main psychoactive component of marijuana (Δ⁹-tetrahydrocannabinol, THC) is correlated with untoward physiological effects in the offspring. Neurobehavioral and cognitive impairments have been reported in longitudinal studies on children and adolescents prenatally exposed to marijuana, and a link to psychiatric disorders has been proposed. Interestingly, the deleterious effects of prenatal cannabis use are similar to those observed in adult rats prenatally exposed to (L)-kynurenine, the direct bioprecursor of the neuroactive metabolite kynurenic acid (KYNA). We therefore investigated whether alterations in KYNA levels in the rat brain might play a role in the long-term consequences of prenatal cannabinoid exposure. Pregnant Wistar rats were treated daily with THC [5 mg/kg, p.o.] from gestational day (GD)5 through GD20. Using in vivo microdialysis in the medial prefrontal cortex, adult animals were then used to determine the extracellular levels of KYNA and glutamate. Compared to controls, extracellular basal KYNA levels were higher, and basal glutamate levels were lower, in prenatally THC-exposed rats. These rats also showed abnormal short-term memory. Following an additional acute challenge with a low dose of kynurenine (5 mg/kg i.p.) in adulthood, the increase in extracellular KYNA levels in the mPFC was more pronounced in in prenatally THC-exposed rats. These effects could be causally related to the cognitive dysfunction seen in prenatally THC-exposed rats. In the translational realm, these experiments raise the prospect of prevention of KYNA neosynthesis as a promising novel approach to combat some of the detrimental long-term effects of prenatal cannabis use.

A detailed mechanism of the oxidative half-reaction of d-amino acid oxidase: another route for flavin oxidation

d-Amino acid oxidase (DAAO) is a flavoenzyme whose inhibition is expected to have therapeutic potential in schizophrenia. DAAO catalyses hydride transfer from the substrate to the flavin in the reductive half-reaction, and the flavin is reoxidized by O2 in the oxidative half-reaction. Quantum mechanical/molecular mechanical calculations were performed and their results together with available experimental information were used to elucidate the detailed mechanism of the oxidative half-reaction. The reaction starts with a single electron transfer from FAD to O2, followed by triplet-singlet transition. FAD oxidation is completed by a proton coupled electron transfer to the oxygen species and the reaction terminates with H2O2 formation by proton transfer from the oxidized substrate to the oxygen species via a chain of water molecules. The substrate plays a double role by facilitating the first electron transfer and by providing a proton in the last step. The mechanism differs from the oxidative half-reaction of other oxidases.

Exercise Intensity Influences Prefrontal Cortex Oxygenation during Cognitive Testing

Activation changes in the prefrontal cortex (PFC) regions have been linked to acute exercise-induced improvements in cognitive performance. The type of exercise performed may influence PFC activation, and further impact cognitive function. The present study aimed to compare PFC activation during cognitive testing after moderate-intensity, high intensity, and yoga exercises, and to determine if PFC activation is linked to cognitive performance. Eight subjects (four male and four female), aged 35 ± 5 completed a control, high intensity, moderate intensity, and yoga exercises followed by administration of a cognitive task (NIH Toolbox Fluid Cognition). Left and right PFC activation (LPFC and RPFC, respectively) were evaluated by measuring hemoglobin difference (Hbdiff) changes during post-exercise cognitive assessment using functional near infrared spectroscopy (fNIRS). Activation during the cognitive test was higher in the LPFC after moderate intensity exercise compared to control, high intensity, and yoga (5.30 ± 6.65 vs. 2.26 ± 2.40, 2.50 ± 1.48, 2.41 ± 2.36 μM, p < 0.05, respectively). A negative relationship was detected between LPFC and processing speed after exercise. PFC activation did not align with cognitive performance. However, acute exercise, regardless of type, appeared to alter neural processing. Specifically, less PFC activation was required for a given neural output after exercise.

How could N-Methyl-D-Aspartate Receptor Antagonists Lead to Excitation Instead of Inhibition?

N-methyl-D-aspartate receptors (NMDARs) are a family of ionotropic glutamate receptors mainly known to mediate excitatory synaptic transmission and plasticity. Interestingly, low-dose NMDAR antagonists lead to increased, instead of decreased, functional connectivity; and they could cause schizophrenia- and/or antidepressant-like behavior in both humans and rodents. In addition, human genetic evidences indicate that NMDAR loss of function mutations underlie certain forms of epilepsy, a disease featured with abnormal brain hyperactivity. Together, they all suggest that under certain conditions, NMDAR activation actually lead to inhibition, but not excitation, of the global neuronal network. Apparently, these phenomena are rather counterintuitive to the receptor's basic role in mediating excitatory synaptic transmission. How could it happen? Recently, this has become a crucial question in order to fully understand the complexity of NMDAR function, particularly in disease. Over the past decades, different theories have been proposed to address this question. These include theories of “NMDARs on inhibitory neurons are more sensitive to antagonism”, or “basal NMDAR activity actually inhibits excitatory synapse”, etc. Our review summarizes these efforts, and also provides an introduction of NMDARs, inhibitory neurons, and their relationships with the related diseases. Advances in the development of novel NMDAR pharmacological tools, particularly positive allosteric modulators, are also included to provide insights into potential intervention strategies.

T-lymphocytes response persists following Plasmodium berghei strain Anka infection resolution and may contribute to later experimental cerebral malaria outcomes

Several studies have proposed cerebral malaria (CM) as a CD4+ and CD8+ T lymphocyte-mediated disease. However, there are no data regarding the recruitment and/or persistence of these cells in the CNS following the phase of infection resolution. Glutamate-mediate excitotoxicity has also been implicated in CM. Blockade of glutamate NMDA receptors by its noncompetitive antagonist MK801 modulates cytokine and neurotrophic factors expression preventing cognitive and depressive-like behavior in experimental CM. Herein, we aim to investigate the role of T lymphocytes in later outcomes in CM, and whether the protective role of MK801 is associated with T lymphocytes response.

Autoantibodies and Psychosis

Research into antibody-mediated disease, in response to immune dysfunction or to tumour development, has rapidly expanded in recent years. Antibodies binding to neuroreceptors can cause psychiatric features, including psychosis, in a minority of patients as well as neurological features. The responsiveness of some of these cases to immunotherapy supports the hypothesis that antibody-associated mechanisms play a role in the pathogenesis of psychotic diseases. The purpose of this chapter is to review autoantibodies that are most likely to be relevant for patients with psychotic symptoms. Herein, we describe receptor structure and mechanism of action, clinical and psychiatric features for the growing number of neuronal surface antibodies, including those to the N-methyl-D-aspartate (NMDA) receptor. The identification of a subgroup of patients with psychiatric features having antibody-mediated disease highlights the importance of considering the diagnosis, particularly in those patients presenting with a first episode of psychosis.

Other drug use does not impact cognitive impairments in chronic ketamine users

BACKGROUND

Ketamine abuse causes cognitive impairments, which negatively impact on users' abstinence, prognosis, and quality of life.

RESULTS

of cognitive impairments in chronic ketamine users have been inconsistent across studies, possibly due to the small sample sizes and the confounding effects of concomitant use of other illicit drugs. This study investigated the cognitive impairment and its related factors in chronic ketamine users with a large sample size and explored the impact of another drug use on cognitive functions.

METHODS

Cognitive functions, including working, verbal and visual memory and executive functions were assessed in ketamine users: 286 non-heavy other drug users and 279 heavy other drug users, and 261 healthy controls. Correlations between cognitive impairment and patterns of ketamine use were analysed.

RESULTS

Verbal and visual memory were impaired, but working memory and executive functions were intact for all ketamine users. No significant cognitive differences were found between the two ketamine groups. Greater number of days of ketamine use in the past month was associated with worse visual memory performance in non-heavy other drug users. Higher dose of ketamine use was associated with worse short-term verbal memory in heavy other drug users.

CONCLUSION

Verbal and visual memory are impaired in chronic ketamine users. Other drug use appears to have no impact on ketamine users' cognitive performance.

Hippocampal protein kinase D1 is necessary for DHPG-induced learning and memory impairments in rats

Background

Understanding molecular mechanisms underlying the induction of learning and memory impairments remains a challenge. Recent investigations have shown that the activation of group I mGluRs (mGluR1 and mGluR5) in cultured hippocampal neurons by application of (S)-3,5-Dihydroxyphenylglycine (DHPG) causes the regulated internalization of N-methyl-D-aspartate receptors (NMDARs), which subsequently activates protein kinase D1 (PKD1). Through phosphorylating the C-terminals of the NMDAR GluN2 subunits, PKD1 down-regulates the activity of remaining (non-internalized) surface NMDARs. The knockdown of PKD1 does not affect the DHPG-induced inhibition of AMPA receptor-mediated miniature excitatory post-synaptic currents (mEPSCs) but prevents the DHPG-induced inhibition of NMDAR-mediated mEPSCs in vitro. Thus, we investigated the in vivo effects of bilateral infusions of DHPG into the hippocampal CA1 area of rats in the Morris water maze (MWM) and the novel object discrimination (NOD) tests.

Methods

A total of 300 adult male Sprague Dawley rats (250–280 g) were used for behavioral tests. One hundred ninety four were used in MWM test and the other 106 rats in the NOD test. Following one week of habituation to the vivarium, rats were bilaterally implanted under deep anesthesia with cannulas aimed at the CA1 area of the hippocampus (CA1 coordinates in mm from Bregma: AP -3.14; lateral +/-2; DV -3.0). Through implanted cannulas artificial cerebrospinal fluid (ACSF), the group1 mGluR antagonist 6-Methyl-2-(phenylethynyl)pyridine (MPEP), the dynamin-dependent internalization inhibitor Dynasore, or the PKD1 inhibitor CID755673 were infused into the bilateral hippocampal CA1 areas (2 μL per side, over 5 min). The effects of these infusions and the effects of PKD1 knockdown were examined in MWM or NOD test.

Results

DHPG infusion increased the latency to reach the platform in the MWM test and reduced the preference for the novel object in the NOD task. We found that the DHPG effects were dose-dependent and could be maintained for up to 2 days. Notably, these effects could be prevented by pre-infusion of the group1 mGluR antagonist MPEP, the dynamin-dependent internalization inhibitor Dynasore, the PKD1 inhibitor CID755673, or by PKD1 knockdown in the hippocampal CA1 area.

Conclusion

Altogether, these findings provide direct evidence that PKD1-mediated signaling may play a critical role in the induction of learning and memory impairments by DHPG infusion into the hippocampal CA1 area.

Impaired social behaviors and minimized oxytocin signaling of the adult mice deficient in the N-methyl-d-aspartate receptor GluN3A subunit

The N-methyl-d-aspartate receptor (NMDAR) has been implicated in the pathophysiology of neurological diseases, such as schizophrenia, autism spectrum disorders (ASD), and Alzheimer's disease (AD), whose unique clinical hallmark is a constellation of impaired social and/or cognitive behaviors. GluN3A (NR3A) is a unique inhibitory subunit in the NMDAR complex. The role of GluN3A in social behavioral activities is obscure. In this study, we sought to evaluate altered social activities in adult GluN3A knockout (KO) mice. GluN3A KO mice spent less time in reciprocal social interaction in the social interaction test compared to wild-type (WT) mice. A social approach test using a three-chamber system confirmed that mice lacking GluN3A had lower sociability and did not exhibit a preference for social novelty. GluN3A KO mice displayed abnormal food preference in the social transmission of food preference task and low social interaction activity in the five-trial social memory test, but without social memory deficits. Using a home cage monitoring system, we observed reduced social grooming behavior in GluN3A KO mice. Signaling genes that might mediate the altered social behaviors were examined in the prefrontal cortex, hippocampus, and thalamus. Among nine genes examined, the expression of the oxytocin receptor was significantly lower in the prefrontal cortex of GluN3A KO mice than that in WT mice. Oxytocin treatment rescued social activity deficits in GluN3A KO mice. These findings support a novel idea that a chronic state of moderate increases in NMDAR activities may lead to downregulation of the oxytocin signaling and impaired behavioral activities that are seen in psychiatric/neurodegenerative disorders.

Role of α7nAChR-NMDAR in sevoflurane-induced memory deficits in the developing rat hippocampus

Detrimental effects of volatile anaesthetics, including sevoflurane, on the structure and function of the developing brain have been reported. The internalization of N-methyl-D-aspartate receptors (NMDARs) contributes to anaesthetic neurotoxicity. Both nicotinic acetylcholine receptors (nAChRs) and NMDAR play a critical role in the development of the nervous system. Moreover, nAChR can interact with NMDAR, and previous studies have demonstrated modulation of NMDAR by nAChR. In our study, we used an α7 nicotinic acetylcholine receptor (α7nAChR) agonist and α7nAChR antagonist to explore the role of α7nAChR and NMDAR in sevoflurane-induced long-term effects on memory and dendritic spine both in vivo and in vitro. The results revealed that the activation of α7nAChR attenuated the development of sevoflurane-induced memory deficit and dendritic spine changes, which might be by regulating NR2B-containing NMDAR trafficking from the intracellular pool to the cell surface pool in the hippocampus. Moreover, we demonstrated that α7nAChR could regulate NR2B-containing NMDAR via Src-family tyrosine kinase (SFK). Thus, our current study indicates that the trafficking of NR2B-containing NMDAR is regulated by α7nAChR via SFK in neonatal rat hippocampus, which may be secondary to sevoflurane-induced cognitive deficits in the developing hippocampus.

Interactions between the Kynurenine and the Endocannabinoid System with Special Emphasis on Migraine

Both the kynurenine and the endocannabinoid systems are involved in several neurological disorders, such as migraine and there are increasing number of reports demonstrating that there are interactions of two systems. Although their cooperation has not yet been implicated in migraine, there are reports suggesting this possibility. Additionally, the individual role of the endocannabinoid and kynurenine system in migraine is reviewed here first, focusing on endocannabinoids, kynurenine metabolites, in particular kynurenic acid. Finally, the function of NMDA and cannabinoid receptors in the trigeminal system-which has a crucial role in the pathomechanisms of migraine-will also be discussed. The interaction of the endocannabinoid and kynurenine system has been demonstrated to be therapeutically relevant in a number of pathological conditions, such as cannabis addiction, psychosis, schizophrenia and epilepsy. Accordingly, the cross-talk of these two systems may imply potential mechanisms related to migraine, and may offer new approaches to manage the treatment of this neurological disorder.

Enhancing Effects of NMDA-Receptor Blockade on Extinction Learning and Related Brain Activation Are Modulated by BMI

A distributed network including prefrontal and hippocampal regions is involved in context-related extinction learning as well as in renewal. Renewal describes the recovery of an extinguished response if the context of extinction differs from the context of recall. Animal studies have demonstrated that prefrontal, but not hippocampal N-methyl-D-aspartate receptor (NMDAR) antagonism disrupted extinction learning and processing of task context. However, human studies of NMDAR in extinction learning are lacking, while NMDAR antagonism yielded contradictory results in other learning tasks. This fMRI study investigated the role of NMDAR for human behavioral and brain activation correlates of extinction and renewal. Healthy volunteers received a single dose of the NMDAR antagonist memantine prior to extinction of previously acquired stimulus-outcome associations presented in either identical or novel contexts. We observed better, and partly faster, extinction learning in participants receiving the NMDAR antagonist compared to placebo. However, memantine did not affect renewal. In both extinction and recall, the memantine group showed a deactivation in extinction-related brain regions, particularly in the prefrontal cortex, while hippocampal activity was increased. This higher hippocampal activation was in turn associated with the participants' body mass index (BMI) and extinction errors. Our results demonstrate potentially dose-related enhancing effects of memantine and highlight involvement of hippocampal NMDAR in context-related extinction learning.

Changes in hippocampal AMPA receptors and cognitive impairments in chronic ketamine addiction models: another understanding of ketamine CNS toxicity

Ketamine has been reported to impair human cognitive function as a recreational drug of abuse. However, chronic effects of ketamine on central nervous system need to be further explored. We set out to establish chronic ketamine addiction models by giving mice a three or six month course of daily intraperitoneal injections of ketamine, then examined whether long-term ketamine administration induced cognition deficits and changed hippocampal post-synaptic protein expression in adult mice. Behavior tests results showed that mice exhibited dose- and time-dependent learning and memory deficits after long-term ketamine administration. Western blot results showed levels of GluA1, p-S845 and p-S831 proteins demonstrated significant decline with ketamine 60 mg/kg until six months administration paradigm. But levels of p-S845 and p-S831 proteins exhibited obvious increase with ketamine 60 mg/kg three months administration paradigm. NR1 protein levels significantly decrease with ketamine 60 mg/kg three and six months administration paradigm. Our results indicate that reduced expression levels and decreased phosphorylation levels of hippocampal post-synaptic membrane GluA1- containing AMPA receptors maybe involved in cognition impairment after long-term ketamine administration. These findings provide further evidence for the cognitive damage of chronic ketamine addiction as a recreational drug.

Glutamatergic stimulation induces GluN2B translation by the nitric oxide-Heme-Regulated eIF2α kinase in cortical neurons

The activation of N-Methyl D-Aspartate Receptor (NMDAR) by glutamate is crucial in the nervous system function, particularly in memory and learning. NMDAR is composed by two GluN1 and two GluN2 subunits. GluN2B has been reported to participate in the prevalent NMDAR subtype at synapses, the GluN1/2A/2B. Here we studied the regulation of GluN2B expression in cortical neurons finding that glutamate up-regulates GluN2B translation through the action of nitric oxide (NO), which induces the phosphorylation of the eukaryotic translation initiation factor 2 α (eIF2α). It is a process mediated by the NO-heme-regulated eIF2α kinase (HRI), as the effect was avoided when a specific HRI inhibitor or a HRI small interfering RNA (siHRI) were used. We found that the expressed GluN2B co-localizes with PSD-95 at the postsynaptic ending, which strengthen the physiological relevance of the proposed mechanism. Moreover the receptors bearing GluN2B subunits upon NO stimulation are functional as high Ca2+ entry was measured and increases the co-localization between GluN2B and GluN1 subunits. In addition, the injection of the specific HRI inhibitor in mice produces a decrease in memory retrieval as tested by the Novel Object Recognition performance. Summarizing our data suggests that glutamatergic stimulation induces HRI activation by NO to trigger GluN2B expression and this process would be relevant to maintain postsynaptic activity in cortical neurons.

Mutation screening of GRIN2B in schizophrenia and autism spectrum disorder in a Japanese population

N-methyl-d-aspartate receptors (NMDARs) play a critical role in excitatory synaptic transmission and plasticity in the central nervous systems. Recent genetics studies in schizophrenia (SCZ) show that SCZ is susceptible to NMDARs and the NMDAR signaling complex. In autism spectrum disorder (ASD), several studies report dysregulation of NMDARs as a risk factor for ASD. To further examine the association between NMDARs and SCZ/ASD development, we conducted a mutation screening study of GRIN2B which encodes NR2B subunit of NMDARs, to identify rare mutations that potentially cause diseases, in SCZ and ASD patients (n = 574 and 152, respectively). This was followed by an association study in a large sample set of SCZ, ASD, and normal healthy controls (n = 4145, 381, and 4432, respectively). We identified five rare missense mutations through the mutation screening of GRIN2B. Although no statistically significant association between any single mutation and SCZ or ASD was found, one of its variant, K1292R, is found only in the patient group. To further examine the association between mutations in GRIN2B and SCZ/ASD development, a larger sample size and functional experiments are needed.

Withanone, an Active Constituent from Withania somnifera, Affords Protection Against NMDA-Induced Excitotoxicity in Neuron-Like Cells

Withania somnifera has immense pharmacologic and clinical uses. Owing to its similar pharmacologic activity as that of Korean Ginseng tea, it is popularly called as Indian ginseng. In most cases, extracts of this plant have been evaluated against various diseases or models of disease. However, little efforts have been made to evaluate individual constituents of this plant for neurodegenerative disorders. Present study was carried out to evaluate Withanone, one of the active constituents of Withania somnifera against NMDA-induced excitotoxicity in retinoic acid, differentiated Neuro2a cells. Cells were pre-treated with 5, 10 and 20 μM doses of Withanone and then exposed to 3-mM NMDA for 1 h. MK801, a specific NMDA receptor antagonist, was used as positive control. The results indicated that NMDA induces significant death of cells by accumulation of intracellular Ca²⁺, generation of reactive oxygen species (ROS), loss of mitochondrial membrane potential, crashing of Bax/Bcl-2 ratio, release of cytochrome c, increased caspase expression, induction of lipid peroxidation as measured by malondialdehyde levels and cleavage of poly(ADP-ribose) polymerase-1 (Parp-1), which is indicative of DNA damage. All these parameters were attenuated with various doses of Withanone pre-treatment. These results suggest that Withanone may serve as potential neuroprotective agent.

Perinatal sulfamonomethoxine exposure influences physiological and behavioral responses and the brain mTOR pathway in mouse offspring

Sulfamonomethoxine (SMM) is widely used in the veterinary field in China. Although some clinical surveys have revealed that sulfonamide antibiotics cause adverse nervous system symptoms, the related mechanisms of maternal SMM exposure on the neurobehavioral development of offspring remain unclear. Here, we investigated the effects of perinatal SMM exposure on the physiological and behavioral responses of pubertal offspring mice and the underlying mechanisms. We randomly allocated pregnant mice into the groups treated with SMM at different doses and the saline-treated groups. Maternal mice were orally administered SMM daily from gestational day 1 to postpartum day 21. On postnatal day (PND) 22, the parameters of growth, endocrine hormones, and brain amino acid composition were assessed, as well as the brain transcript levels of key genes involved in the mammalian target of rapamycin (mTOR) signaling pathway. From PND 50 to 55, a battery of behavioral tests relevant to anxiety and memory were then administered. Analysis of the results indicated that the pups, particularly the pubertal female offspring, showed anxiety-like behavior. Moreover, the pubertal offspring showed cognitive impairments and fat accumulation. Furthermore, the relative mRNA expression of genes involved in the mTOR signaling pathway in females on PND 22 was elevated, whereas the expression of N-methyl-d-aspartate receptor 2B (NR2B) was reduced. Together, the results showed that perinatal SMM exposure perturbs neuroendocrine functions, and further alters gene expression in the mTOR pathway and NR2B gene expression early in life, which may contribute to brain dysfunction in pubertal life.

Preferential Inhibition of Tonically over Phasically Activated NMDA Receptors by Pregnane Derivatives

Postsynaptic N-methyl-d-aspartate receptors (NMDARs) phasically activated by presynaptically released glutamate are critical for synaptic transmission and plasticity. However, under pathological conditions, excessive activation of NMDARs by tonically increased ambient glutamate contributes to excitotoxicity associated with various acute and chronic neurological disorders. Here, using heterologously expressed GluN1/GluN2A and GluN1/GluN2B receptors and rat autaptic hippocampal microisland cultures, we show that pregnanolone sulfate inhibits NMDAR currents induced by a prolonged glutamate application with a higher potency than the NMDAR component of EPSCs. For synthetic pregnanolone derivatives substituted with a carboxylic acid moiety at the end of an aliphatic chain of varying length and attached to the steroid skeleton at C3, the difference in potency between tonic and phasic inhibition increased with the length of the residue. The steroid with the longest substituent, pregnanolone hemipimelate, had no effect on phasically activated receptors while inhibiting tonically activated receptors. In behavioral tests, pregnanolone hemipimelate showed neuroprotective activity without psychomimetic symptoms. These results provide insight into the influence of steroids on neuronal function and stress their potential use in the development of novel therapeutics with neuroprotective action.

SIGNIFICANCE STATEMENT

Synaptic activation of N-methyl-d-aspartate receptors (NMDARs) plays a key role in synaptic plasticity, but excessive tonic NMDAR activation mediates excitotoxicity associated with many neurological disorders. Therefore, there is much interest in pharmacological agents capable of selectively blocking tonically activated NMDARs while leaving synaptically activated NMDARs intact. Here, we show that an endogenous neurosteroid pregnanolone sulfate is more potent at inhibiting tonically than synaptically activated NMDARs. Further, we report that a novel synthetic analog of pregnanolone sulfate, pregnanolone hemipimelate, inhibits tonic NMDAR currents without inhibiting the NMDAR component of the EPSC and shows neuroprotective activity in vivo without inducing psychomimetic side effects. These results suggest steroids may have a clinical advantage over other known classes of NMDAR inhibitors.

D-Serine in neurobiology: CNS neurotransmission and neuromodulation

Homochirality is fundamental for life. L-Amino acids are exclusively used as substrates for the polymerization and formation of peptides and proteins in living systems. However, D- amino acids were recently detected in various living organisms, including mammals. Of these D-amino acids, D-serine has been most extensively studied. D-Serine was found to play an important role as a neurotransmitter in the human central nervous system (CNS) by binding to the N-methyl- D-aspartate receptor (NMDAr). D-Serine binds with high affinity to a co-agonist site at the NMDAr and, along with glutamate, mediates several vital physiological and pathological processes, including NMDAr transmission, synaptic plasticity and neurotoxicity. Therefore, a key role for D-serine as a determinant of NMDAr mediated neurotransmission in mammalian CNS has been suggested. In this context, we review the known functions of D-serine in human physiology, such as CNS development, and pathology, such as neuro-psychiatric and neurodegenerative diseases related to NMDAr dysfunction.

Major dorsoventral differences in the modulation of the local CA1 hippocampal network by NMDA, mGlu5, adenosine A2A and cannabinoid CB1 receptors

Recent research points to diversification in the local neuronal circuitry between dorsal (DH) and ventral (VH) hippocampus that may be involved in the large-scale functional segregation along the long axis of the hippocampus. Here, using CA1 field recordings from rat hippocampal slices, we show that activation of N-methyl-d-aspartate receptors (NMDARs) reduced excitatory transmission more in VH than in DH, with an adenosine A1 receptor-independent mechanism, and reduced inhibition and enhanced postsynaptic excitability only in DH. Strikingly, co-activation of metabotropic glutamate receptor-5 (mGluR5) with NMDAR, by CHPG and NMDA respectively, strongly potentiated the effects of NMDAR in DH but had not any potentiating effect in VH. Furthermore, the synergistic actions in DH were occluded by blockade of adenosine A2A receptors (A2ARs) by their antagonist ZM 241385 demonstrating a tonic action of these receptors in DH. Exogenous activation of A2ARs by 4-[2-[[6-amino-9-(N-ethyl-β-D-ribofuranuronamidosyl)-9H-purin-2-yl]amino]ethyl]benzenepropanoic acid hydrochloride (CGS 21680) did not change the effects of mGluR5-NMDAR co-activation in either hippocampal pole. Importantly, blockade of cannabinoid CB1 receptors (CB1Rs) by their antagonist 1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-4-morpholinyl-1H-pyrazole-3-carboxamide (AM 281) restricted the synergistic actions of mGluR5-NMDARs on excitatory synaptic transmission and postsynaptic excitability and abolished their effect on inhibition. Furthermore, AM 281 increased the excitatory transmission only in DH indicating that CB1Rs were tonically active in DH but not VH. Removing the magnesium ions from the perfusion medium neither stimulated the interaction between mGluR5 and NMDAR in VH nor augmented the synergy of the two receptors in DH. These findings show that the NMDAR-dependent modulation of fundamental parameters of the local neuronal network, by mGluR5, A2AR and CB1R, markedly differs between DH and VH. We propose that the higher modulatory role of A2AR and mGluR5, in combination with the role of CB1Rs, provide DH with higher functional flexibility of its NMDARs, compared with VH.

Negative Allosteric Modulators Selective for The NR2B Subtype of The NMDA Receptor Impair Cognition in Multiple Domains

Antidepressant activity of N-methyl-D-aspartate (NMDA) receptor antagonists and negative allosteric modulators (NAMs) has led to increased investigation of their behavioral pharmacology. NMDA antagonists, such as ketamine, impair cognition in multiple species and in multiple cognitive domains. However, studies with NR2B subtype-selective NAMs have reported mixed results in rodents including increased impulsivity, no effect on cognition, impairment or even improvement of some cognitive tasks. To date, the effects of NR2B-selective NAMs on cognitive tests have not been reported in nonhuman primates. The current study evaluated two selective NR2B NAMs, CP101,606 and BMT-108908, along with the nonselective NMDA antagonists, ketamine and AZD6765, in the nonhuman primate Cambridge Neuropsychological Test Automated Battery (CANTAB) list-based delayed match to sample (list-DMS) task. Ketamine and the two NMDA NR2B NAMs produced selective impairments in memory in the list-DMS task. AZD6765 impaired performance in a non-specific manner. In a separate cohort, CP101,606 impaired performance of the nonhuman primate CANTAB visuo-spatial Paired Associates Learning (vsPAL) task with a selective impairment at more difficult conditions. The results of these studies clearly show that systemic administration of a selective NR2B NAM can cause transient cognitive impairment in multiple cognitive domains.

GLYX-13 (rapastinel) ameliorates subchronic phencyclidine- and ketamine-induced declarative memory deficits in mice

GLYX-13 (rapastinel), a tetrapeptide (Thr-Pro-Pro-Thr-amide), has been reported to have fast acting antidepressant properties in man based upon its N-methyl-D-aspartate receptor (NMDAR) glycine site functional partial agonism. Ketamine, a non-competitive NMDAR antagonist, also reported to have fast acting antidepressant properties, produces cognitive impairment in rodents and man, whereas rapastinel has been reported to have cognitive enhancing properties in rodents, without impairing cognition in man, albeit clinical testing has been limited. The goal of this study was to compare the cognitive impairing effects of rapastinel and ketamine in novel object recognition (NOR), a measure of declarative memory, in male C57BL/6J mice treated with phencyclidine (PCP), another NMDAR noncompetitive antagonist known to severely impair cognition, in both rodents and man. C57BL/6J mice given a single dose or subchronic ketamine (30 mg/kg.i.p.) showed acute or persistent deficits in NOR, respectively. Acute i.v. rapastinel (1.0 mg/kg), did not induce NOR deficit. Pre-treatment with rapastinel significantly prevented acute ketamine-induced NOR deficit. Rapastinel (1.0 mg/kg, but not 0.3 mg/kg, iv) significantly reversed both subchronic ketamine- and subchronic PCP-induced NOR deficits. Rapastinel also potentiated the atypical antipsychotic drug with antidepressant properties, lurasidone, to restore NOR in subchronic ketamine-treated mice. These findings indicate that rapastinel, unlike ketamine, does not induce a declarative memory deficit in mice, and can prevent or reverse the ketamine-induced NOR deficit. Further study is required to determine if these differences translate during clinical use of ketamine and rapastinel as fast acting antidepressant drugs and if rapastinel could have non-ionotropic effects as an add-on therapy with antipsychotic/antidepressant medications.

Regulated internalization of NMDA receptors drives PKD1-mediated suppression of the activity of residual cell-surface NMDA receptors

Background

Constitutive and regulated internalization of cell surface proteins has been extensively investigated. The regulated internalization has been characterized as a principal mechanism for removing cell-surface receptors from the plasma membrane, and signaling to downstream targets of receptors. However, so far it is still not known whether the functional properties of remaining (non-internalized) receptor/channels may be regulated by internalization of the same class of receptor/channels. The N-methyl-D-aspartate receptor (NMDAR) is a principal subtype of glutamate-gated ion channel and plays key roles in neuronal plasticity and memory functions. NMDARs are well-known to undergo two types of regulated internalization – homologous and heterologous, which can be induced by high NMDA/glycine and DHPG, respectively. In the present work, we investigated effects of regulated NMDAR internalization on the activity of residual cell-surface NMDARs and neuronal functions.

Results

In electrophysiological experiments we discovered that the regulated internalization of NMDARs not only reduced the number of cell surface NMDARs but also caused an inhibition of the activity of remaining (non-internalized) surface NMDARs. In biochemical experiments we identified that this functional inhibition of remaining surface NMDARs was mediated by increased serine phosphorylation of surface NMDARs, resulting from the activation of protein kinase D1 (PKD1). Knockdown of PKD1 did not affect NMDAR internalization but prevented the phosphorylation and inhibition of remaining surface NMDARs and NMDAR-mediated synaptic functions.

Conclusion

These data demonstrate a novel concept that regulated internalization of cell surface NMDARs not only reduces the number of NMDARs on the cell surface but also causes an inhibition of the activity of remaining surface NMDARs through intracellular signaling pathway(s). Furthermore, modulating the activity of remaining surface receptors may be an effective approach for treating receptor internalization-induced changes in neuronal functions of the CNS.

Electronic supplementary material

The online version of this article (doi:10.1186/s13041-015-0167-1) contains supplementary material, which is available to authorized users.

Age-related deficits in synaptic plasticity rescued by activating PKA or PKC in sensory neurons of Aplysia californica

Brain aging is associated with declines in synaptic function that contribute to memory loss, including reduced postsynaptic response to neurotransmitters and decreased neuronal excitability. To understand how aging affects memory in a simple neural circuit, we studied neuronal proxies of memory for sensitization in mature vs. advanced age Aplysia californica (Aplysia). L-Glutamate- (L-Glu-) evoked excitatory currents were facilitated by the neuromodulator serotonin (5-HT) in sensory neurons (SN) isolated from mature but not aged animals. Activation of protein kinase A (PKA) and protein kinase C (PKC) signaling rescued facilitation of L-Glu currents in aged SN. Similarly, PKA and PKC activators restored increased excitability in aged tail SN. These results suggest that altered synaptic plasticity during aging involves defects in second messenger systems.

Aging in Sensory and Motor Neurons Results in Learning Failure in Aplysia californica

The physiological and molecular mechanisms of age-related memory loss are complicated by the complexity of vertebrate nervous systems. This study takes advantage of a simple neural model to investigate nervous system aging, focusing on changes in learning and memory in the form of behavioral sensitization in vivo and synaptic facilitation in vitro. The effect of aging on the tail withdrawal reflex (TWR) was studied in Aplysia californica at maturity and late in the annual lifecycle. We found that short-term sensitization in TWR was absent in aged Aplysia. This implied that the neuronal machinery governing nonassociative learning was compromised during aging. Synaptic plasticity in the form of short-term facilitation between tail sensory and motor neurons decreased during aging whether the sensitizing stimulus was tail shock or the heterosynaptic modulator serotonin (5-HT). Together, these results suggest that the cellular mechanisms governing behavioral sensitization are compromised during aging, thereby nearly eliminating sensitization in aged Aplysia.

In vivo evidence for neuroplasticity in older adults

Neuroplasticity can be conceptualized as an intrinsic property of the brain that enables modification of function and structure in response to environmental demands. Neuroplastic strengthening of synapses is believed to serve as a critical mechanism underlying learning, memory, and other cognitive functions. Ex vivo work investigating neuroplasticity has been done on hippocampal slices using high frequency stimulation. However, in vivo neuroplasticity in humans has been difficult to demonstrate. Recently, a long-term potentiation-like phenomenon, a form of neuroplastic change, was identified in young adults by differences in visual evoked potentials (VEPs) that were measured before and after tetanic visual stimulation (TVS). The current study investigated whether neuroplastic changes in the visual pathway can persist in older adults. Seventeen healthy subjects, 65 years and older, were recruited from the community. Subjects had a mean age of 77.4 years, mean education of 17 years, mean MMSE of 29.1, and demonstrated normal performance on neuropsychological tests. 1Hz checkerboard stimulation, presented randomly to the right or left visual hemi-field, was followed by 2min of 9Hz stimulation (TVS) to one hemi-field. After 2min of rest, 1Hz stimulation was repeated. Temporospatial principal component analysis was used to identify the N1b component of the VEPs, at lateral occipital locations, in response to 1Hz stimulation pre- and post-TVS. Results showed that the amplitude of factors representing the early and late N1b component was substantially larger after tetanic stimulation. These findings indicate that high frequency visual stimulation can enhance the N1b in cognitively high functioning old adults, suggesting that neuroplastic changes in visual pathways can continue into late life. Future studies are needed to determine the extent to which this marker of neuroplasticity is sustained over a longer period of time, and is influenced by age, cognitive status, and neurodegenerative disease.

Chronic administration of ketamine mimics the perturbed sense of body ownership associated with schizophrenia

RATIONALE

Subanaesthetic ketamine infusion in healthy volunteers induces experiences redolent of early psychosis, including changes in the experience of one's own body. It is not clear, however, whether repeated self-administration of ketamine has a sustained effect on body representation that is comparable to that found during acute administration.

OBJECTIVES

We sought to establish whether chronic ketamine use resulted in disturbances to sense of body ownership.

METHODS

Following on from our work on the effects of acute ketamine infusion, we used the rubber hand illusion (RHI) to experimentally manipulate the sense of body ownership in chronic ketamine users, compared to healthy controls.

RESULTS

Chronic ketamine users experienced the RHI more strongly and reported more body-image aberrations, even though they had not recently taken the drug.

CONCLUSIONS

These findings suggest that the chronic ketamine model for psychosis models more long-lasting changes in sense of ownership, perhaps more akin to schizophrenia.

Identification and characterization of the NMDA receptor and its role in regulating reproduction in the cockroach Diploptera punctata

The NMDA receptor (NMDAR) plays important roles in excitatory neurotransmission and in the regulation of reproduction in mammals. NMDAR in insects comprises two subunits, NR1 and NR2. In this study, we identified two NR1 paralogs and eleven NR2 alternatively spliced variants in the cockroach Diploptera punctata. This is the first report of NR1 paralogs in insects. The tissue distributions and expression profiles of DpNR1A, DpNR1B and DpNR2 in different tissues were also investigated. Previous studies have demonstrated NMDA-stimulated biosynthesis of juvenile hormone (JH) in the corpora allata through the influx of extracellular Ca2+ in Diploptera punctata. However, our data show that the transcript levels of DpNR1A, DpNR1B and DpNR2 were low in the corpora allata. MK-801, a high-affinity antagonist of NMDAR, did not show any effect on JH biosynthesis in vitro. In addition, neither partial knockdown of DpNR2 nor in vivo treatment with a physiologically relevant dose of MK-801 resulted in any significant change in JH biosynthesis or basal oocyte growth. Injection of animals with a high dose of MK-801 (30 µg per animal per injection), which paralyzed the animals for 4–5 h, resulted in a significant decrease in JH biosynthesis on days 4 and 5. However, the reproductive events during the first gonadotrophic cycle in female D. punctata were unaffected. Thus, NMDAR does not appear to play important roles in the regulation of JH biosynthesis or mediate reproduction of female D. punctata.

NMDA Receptor Antagonist Ketamine Distorts Object Recognition by Reducing Feedback to Early Visual Cortex

It is a well-established fact that top-down processes influence neural representations in lower-level visual areas. Electrophysiological recordings in monkeys as well as theoretical models suggest that these top-down processes depend on NMDA receptor functioning. However, this underlying neural mechanism has not been tested in humans. We used fMRI multivoxel pattern analysis to compare the neural representations of ambiguous Mooney images before and after they were recognized with their unambiguous grayscale version. Additionally, we administered ketamine, an NMDA receptor antagonist, to interfere with this process. Our results demonstrate that after recognition, the pattern of brain activation elicited by a Mooney image is more similar to that of its easily recognizable grayscale version than to the pattern evoked by the identical Mooney image before recognition. Moreover, recognition of Mooney images decreased mean response; however, neural representations of separate images became more dissimilar. So from the neural perspective, unrecognizable Mooney images all "look the same", whereas recognized Mooneys look different. We observed these effects in posterior fusiform part of lateral occipital cortex and in early visual cortex. Ketamine distorted these effects of recognition, but in early visual cortex only. This suggests that top-down processes from higher- to lower-level visual areas might operate via an NMDA pathway.

Spermine reverses lipopolysaccharide-induced memory deficit in mice

Background

Lipopolysaccharide (LPS) induces neuroinflammation and memory deficit. Since polyamines improve memory in various cognitive tasks, we hypothesized that spermine administration reverses LPS-induced memory deficits in an object recognition task in mice. The involvement of the polyamine binding site at the N-methyl-D-aspartate (NMDA) receptor and cytokine production in the promnesic effect of spermine were investigated.

Methods

Adult male mice were injected with LPS (250 μg/kg, intraperitoneally) and spermine (0.3 to 1 mg/kg, intraperitoneally) or ifenprodil (0.3 to 10 mg/kg, intraperitoneally), or both, and their memory function was evaluated using a novel object recognition task. In addition, cortical and hippocampal cytokines levels were measured by ELISA four hours after LPS injection.

Results

Spermine increased but ifenprodil decreased the recognition index in the novel object recognition task. Spermine, at doses that did not alter memory (0.3 mg/kg, intraperitoneally), reversed the cognitive impairment induced by LPS. Ifenprodil (0.3 mg/kg, intraperitoneally) reversed the protective effect of spermine against LPS-induced memory deficits. However, spermine failed to reverse the LPS-induced increase of cortical and hippocampal cytokine levels.

Conclusions

Spermine protects against LPS-induced memory deficits in mice by a mechanism that involves GluN2B receptors.

Influence of kynurenine 3-monooxygenase (KMO) gene polymorphism on cognitive function in schizophrenia

BACKGROUND

Cognitive deficits compromise quality of life and productivity for individuals with schizophrenia and have no effective treatments. Preclinical data point to the kynurenine pathway of tryptophan metabolism as a potential target for pro-cognitive drug development. We have previously demonstrated association of a kynurenine 3-monooxygenase (KMO) gene variant with reduced KMO gene expression in postmortem schizophrenia cortex, and neurocognitive endophenotypic deficits in a clinical sample. KMO encodes kynurenine 3-monooxygenase (KMO), the rate-limiting microglial enzyme of cortical kynurenine metabolism. Aberration of the KMO gene might be the proximal cause of impaired cortical kynurenine metabolism observed in schizophrenia. However, the relationship between KMO variation and cognitive function in schizophrenia is unknown. This study examined the effects of the KMO rs2275163C>T C (risk) allele on cognitive function in schizophrenia.

METHODS

We examined the association of KMO polymorphisms with general neuropsychological performance and P50 gating in a sample of 150 schizophrenia and 95 healthy controls.

RESULTS

Consistent with our original report, the KMO rs2275163C>T C (risk) allele was associated with deficits in general neuropsychological performance, and this effect was more marked in schizophrenia compared with controls. Additionally, the C (Arg452) allele of the missense rs1053230C>T variant (KMO Arg452Cys) showed a trend effect on cognitive function. Neither variant affected P50 gating.

CONCLUSIONS

These data suggest that KMO variation influences a range of cognitive domains known to predict functional outcome. Extensive molecular characterization of this gene would elucidate its role in cognitive function with implications for vertical integration with basic discovery.

Impaired pre-attentive auditory processing in fibromyalgia: A mismatch negativity (MMN) study

OBJECTIVE

Fibromyalgia (FM) patients often show deficits in cognitive functions such as attention and working memory. We assumed that pre-attentive information processing, a crucial element in human perception and cognition, would be altered in FM patients. Thus, the objective of this study was to determine whether FM patients exhibit alterations in pre-attentive processing as assessed by auditory mismatch negativity (MMN).

METHODS

Auditory evoked magnetic fields were recorded in FM patients (n=18) and healthy control subjects (n=21) during a duration-deviant auditory oddball paradigm. The magnetic mismatch negativity (MMNm) was obtained by subtracting responses to standard tones from responses to deviant tones. Pressure pain thresholds over the thenar and trapezius muscles were determined using an algometer.

RESULTS

MMNm peak amplitudes in right hemispheres were attenuated, and the directional asymmetry coefficient of the MMNm amplitude was lower in FM patients, indicating a more leftward asymmetry than in healthy control subjects. Smaller right MMNm amplitude was associated with lower pressure pain thresholds of thenar muscles in FM patients.

CONCLUSIONS

Our results suggested that pre-attentive processing of auditory information is impaired in FM patients.

SIGNIFICANCE

This study provided neurophysiological evidence of impaired pre-attentive sensory change detection in FM.

The kynurenine pathway as a therapeutic target in cognitive and neurodegenerative disorders

Understanding the neurochemical basis for cognitive function is one of the major goals of neuroscience, with a potential impact on the diagnosis, prevention and treatment of a range of psychiatric and neurological disorders. In this review, the focus will be on a biochemical pathway that remains under-recognized in its implications for brain function, even though it can be responsible for moderating the activity of two neurotransmitters fundamentally involved in cognition - glutamate and acetylcholine. Since this pathway - the kynurenine pathway of tryptophan metabolism - is induced by immunological activation and stress, it also stands in a unique position to mediate the effects of environmental factors on cognition and behaviour. Targeting the pathway for new drug development could, therefore, be of value not only for the treatment of existing psychiatric conditions, but also for preventing the development of cognitive disorders in response to environmental pressures.