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Transcranial magnetic stimulation (TMS) has quickly progressed from a technical curiosity to a bona-fide tool for neurological research. The impetus has been due to the promising results obtained when using TMS to uncover neural processes in normal human subjects, as well as in the treatment of intractable neurological conditions, such as stroke, chronic depression and epilepsy. The basic principle of TMS is that most neuronal axons that fall within the volume of magnetic stimulation become electrically excited, trigger action potentials and release neurotransmitter into the postsynaptic neurons. What happens afterwards remains elusive, especially in the case of repeated stimulation. Here we discuss the likelihood that certain TMS protocols produce long-term changes in cortical synapses akin to long-term potentiation and long-term depression of synaptic transmission. Beyond the synaptic effects, TMS might have consequences on other neuronal processes, such as genetic and protein regulation, and circuit-level patterns, such as network oscillations. Furthermore, TMS might have non-neuronal effects, such as changes in blood flow, which are still poorly understood. [ABSTRACT FROM AUTHOR]

Subarachnoid hemorrhage (SAH) is a severe form of stroke that can cause unpredictable and diffuse cerebral damage, which is difficult to detect until it becomes irreversible. Therefore, there is a need for a reliable method to identify dysfunctional regions and initiate treatment before permanent damage occurs. Neurobehavioral assessments have been suggested as a possible tool to detect and approximately localize dysfunctional cerebral regions. In this study, we hypothesized that a neurobehavioral assessment battery could be a sensitive and specific method for detecting damage in discrete cerebral regions following SAH. To test this hypothesis, a behavioral battery was employed at multiple time points after SAH induced via an endovascular perforation, and brain damage was confirmed via postmortem histopathological analysis. Our results demonstrate that impairment of sensorimotor function accurately predict damage in the cerebral cortex (AUC 0.905; sensitivity 81.8%; specificity 90.9%) and striatum (AUC 0.913; sensitivity 90.1%; specificity 100%), while impaired novel object recognition is a more accurate indicator of damage to the hippocampus (AUC 0.902; sensitivity 74.1%; specificity 83.3%) than impaired reference memory (AUC 0.746; sensitivity 72.2%; specificity 58.0%). Tests for anxiety-like and depression-like behaviors predict damage to the amygdala (AUC 0.900; sensitivity 77.0%; specificity 81.7%) and thalamus (AUC 0.963; sensitivity 86.3%; specificity 87.8%), respectively. This study suggests that recurring behavioral testing can accurately predict damage in specific brain regions, which could be developed into a clinical battery for early detection of SAH damage in humans, potentially improving early treatment and outcomes., (© 2023. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Rodents establish dominance hierarchy as a social ranking system in which one subject acts as dominant over all the other subordinate individuals. Dominance hierarchy regulates food access and mating opportunities, but little is known about its significance in other social behaviors, for instance during collective navigation for foraging or migration. Here, we implemented a simplified goal-directed spatial task in mice, in which animals navigated individually or collectively with their littermates foraging for food. We compared between conditions and found that the social condition exerts significant influence on individual displacement patterns, even when efficient navigation rules leading to reward had been previously learned. Thus, movement patterns and consequent task performance were strongly dependent on contingent social interactions arising during collective displacement, yet their influence on individual behavior was determined by dominance hierarchy. Dominant animals did not behave as leaders during collective displacement; conversely, they were most sensitive to the social environment adjusting their performance accordingly. Social ranking in turn was associated with specific spontaneous neural activity patterns in the prefrontal cortex and hippocampus, with dominant mice showing higher firing rates, larger ripple oscillations, and stronger neuronal entrainment by ripples than subordinate animals. Moreover, dominant animals selectively increased their cortical spiking activity during collective movement, while subordinate mice did not modify their firing rates, consistent with dominant animals being more sensitive to the social context. These results suggest that dominance hierarchy influences behavioral performance during contingent social interactions, likely supported by the coordinated activity in the hippocampal-prefrontal circuit., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Lara-Vasquez, Espinosa, Morales, Moran, Billeke, Gallagher, Strohl, Huerta and Fuentealba.)

The fetal brain is constantly exposed to maternal IgG before the formation of an effective blood-brain barrier (BBB). Here, we studied the consequences of fetal brain exposure to an antibody to the astrocytic protein aquaporin-4 (AQP4-IgG) in mice. AQP4-IgG was cloned from a patient with neuromyelitis optica spectrum disorder (NMOSD), an autoimmune disease that can affect women of childbearing age. We found that embryonic radial glia cells in neocortex express AQP4. These cells are critical for blood vessel and BBB formation through modulation of the WNT signaling pathway. Male fetuses exposed to AQP4-IgG had abnormal cortical vasculature and lower expression of WNT signaling molecules Wnt 5a and Wnt 7a. Positron emission tomography of adult male mice exposed in utero to AQP4-IgG revealed increased blood flow and BBB leakiness in the entorhinal cortex. Adult male mice exposed in utero to AQP4-IgG had abnormal cortical vessels, fewer dendritic spines in pyramidal and stellate neurons, and more S100β + astrocytes in the entorhinal cortex. Behaviorally, they showed impairments in the object-place memory task. Neural recordings indicated that their grid cell system, within the medial entorhinal cortex, did not map the local environment appropriately. Collectively, these data implicate in utero binding of AQP4-IgG to radial glia cells as a mechanism for alterations of the developing male brain and adds NMOSD to the conditions in which maternal IgG may cause persistent brain dysfunction in offspring.

Background: Extracellular recording represents a crucial electrophysiological technique in neuroscience for studying the activity of single neurons and neuronal populations. The electrodes capture voltage traces that, with the help of analytical tools, reveal action potentials ('spikes') as well as local field potentials. The process of spike sorting is used for the extraction of action potentials generated by individual neurons. Until recently, spike sorting was performed with manual techniques, which are laborious and unreliable due to inherent operator bias. As neuroscientists add multiple electrodes to their probes, the high-density devices can record hundreds to thousands of neurons simultaneously, making the manual spike sorting process increasingly difficult. The advent of automated spike sorting software has offered a compelling solution to this issue and, in this study, we present a simple-to-execute framework for running an automated spike sorter., Methods: Tetrode recordings of freely-moving mice are obtained from the CA1 region of the hippocampus as they navigate a linear track. Tetrode recordings are also acquired from the prelimbic cortex, a region of the medial prefrontal cortex, while the mice are tested in a T maze. All animals are implanted with custom-designed, 3D-printed microdrives that carry 16 electrodes, which are bundled in a 4-tetrode geometry., Results: We provide an overview of a framework for analyzing single-unit data in which we have concatenated the acquisition system (Cheetah, Neuralynx) with analytical software (MATLAB) and an automated spike sorting pipeline (MountainSort). We give precise instructions on how to implement the different steps of the framework, as well as explanations of our design logic. We validate this framework by comparing manually-sorted spikes against automatically-sorted spikes, using neural recordings of the hippocampus and prelimbic cortex in freely-moving mice., Conclusions: We have efficiently integrated the MountainSort spike sorter with Neuralynx-acquired neural recordings. Our framework is easy to implement and provides a high-throughput solution. We predict that within the broad field of bioelectronic medicine, those teams that incorporate high-density neural recording devices to their armamentarium might find our framework quite valuable as they expand their analytical footprint., (© 2021. The Author(s).)

Autism Spectrum Disorder (ASD) is a group of neurodevelopmental conditions that is four times more commonly diagnosed in males than females. While susceptibility genes located in the sex chromosomes have been identified in ASD, it is unclear whether they are sufficient to explain the male bias or whether gonadal hormones also play a key role. We evaluated the sex chromosomal and hormonal influences on the male bias in a murine model of ASD, in which mice are exposed in utero to a maternal antibody reactive to contactin-associated protein-like 2 (Caspr2), which was originally cloned from a mother of a child with ASD (termed C6 mice henceforth). In this model, only male mice are affected. We used the four-core-genotypes (FCG) model in which the Sry gene is deleted from the Y chromosome (Y - ) and inserted into autosome 3 ( TgSry ). Thus, by combining the C6 and FCG models, we were able to differentiate the contributions of sex chromosomes and gonadal hormones to the development of fetal brain and adult behavioral phenotypes. We show that the presence of the Y chromosome, or lack of two X chromosomes, irrespective of gonadal sex, increased the susceptibility to C6-induced phenotypes including the abnormal growth of the developing fetal cerebral cortex, as well as a behavioral pattern of decreased open-field exploration in adult mice. Our results indicate that sex chromosomes are the main determinant of the male bias in the maternal C6-induced model of ASD. The less dominant hormonal effect may be due to modulation by sex chromosome genes of factors involved in gonadal hormone pathways in the brain., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Gata-Garcia, Porat, Brimberg, Volpe, Huerta and Diamond.)

Background: We have found disruption of expression of major transcriptional regulators of circadian rhythm in the kidneys of several mouse models of lupus nephritis. Here we define the consequence of this disturbance with respect to circadian gene expression and renal homeostatic function in a mouse model of lupus nephritis., Methods: Molecular profiling of kidneys from 47 young and 41 nephritic female NZB/W F1 mice was performed at 4 hourly intervals over a 24 h period. Disruption of major circadian transcriptional regulators was confirmed by qPCR. Molecular data was normalized and analyzed for rhythmicity using RAIN analysis. Serum aldosterone and glucose and urine sodium and potassium were measured at 4 hourly intervals in pre-nephritic and nephritic mice and blood pressure was measured every 4 h. Analyses were repeated after induction of complete remission of nephritis using combination cyclophosphamide and costimulatory blockade., Results: We show a profound alteration of renal circadian rhythms in mice with lupus nephritis affecting multiple renal pathways. Using Cosinor analysis we identified consequent alterations of renal homeostasis and metabolism as well as blood pressure dipper status. This circadian dysregulation was partially reversed by remission induction therapy., Conclusions: Our studies indicate the role of inflammation in causing the circadian disruption and suggest that screening for loss of normal blood pressure dipping should be incorporated into LN management. The data also suggest a potential role for circadian agonists in the treatment of lupus nephritis., (© 2021. The Author(s).)

The concept that exposure in utero to maternal anti-brain antibodies contributes to the development of autism spectrum disorders (ASD) has been entertained for over a decade. We determined that antibodies targeting Caspr2 are present at high frequency in mothers with brain-reactive serology and a child with ASD, and further demonstrated that exposure in utero to a monoclonal anti-Caspr2 antibody, derived from a mother of an ASD child, led to an-ASD like phenotype in male offspring. Now we propose a new model to study the effects of in utero exposure to anti-Caspr2 antibody. Dams immunized with the extracellular portion of Caspr2 express anti-Caspr2 antibodies throughout gestation to better mimic the human condition. Male but not female mice born to dams harboring polyclonal anti-Caspr2 antibodies showed abnormal cortical development, decreased dendritic complexity of excitatory neurons and reduced numbers of inhibitory neurons in the hippocampus, as well as repetitive behaviors and impairments in novelty interest in the social preference test as adults. These data supporting the pathogenicity of anti-Caspr2 antibodies are consistent with the concept that anti-brain antibodies present in women during gestation can alter fetal brain development, and confirm that males are peculiarly susceptible.

Background: Macrophage Migration Inhibitory Factor (MIF) is a potent proinflammatory cytokine that promotes the production of other immune mediators. MIF is produced by most cell types in the brain including microglia, astrocytes and neurons. Enhanced expression of MIF might contribute to the persistent activation of glial, chronic neuroinflammation and neurodegeneration. Here, we investigated the effect of MIF on inflammatory markers and spatial learning in a mouse model of sporadic AD and on tau pathology in AD patients., Methods: We examined the effects of MIF deficiency and pharmacological MIF inhibition in vitro and in vivo. In vitro, quantitative PCR and ELISA were used to assess cytokine production of STZ-treated glial cells. In vivo, C57BL/6 mice were subjected to intracerebroventricular streptozotocin injection (3 mg/kg, ICV-STZ). Neuroinflammation and contextual learning performance were assessed using quantitative PCR and fear conditioning, respectively. Pharmacological MIF inhibition was achieved with intraperitoneal injections of ISO-1 (daily, IP, 20 mg/kg in 5% DMSO in 0.9% NaCl) for 4 weeks following ICV-STZ injection. The findings from ISO-1 treated mice were confirmed in MIF knockout C57BL/6. To assess the role of MIF in human AD, cerebrospinal fluid levels of MIF and hyperphosphorylated tau were measured using ELISA., Results: Administration ICV-STZ resulted in hippocampal dependent cognitive impairment. MIF inhibition with ISO-1 significantly improved the STZ-induced impairment in contextual memory performance, indicating MIF-related inflammation as a major contributor to ICV-STZ-induced memory deficits. Furthermore, inhibition of the MIF resulted in reduced cytokine production in vitro and in vivo. In human subjects with AD at early clinical stages, cerebrospinal fluid levels of MIF were increased in comparison with age-matched controls, and correlated with biomarkers of tau hyper-phosphorylation and neuronal injury hinting at MIF levels as a potential biomarker for early-stage AD., Conclusions: The present study indicates the key role of MIF in controlling the chronic cytokine release in neuroinflammation related to tau hyperphosphorylation, neurodegeneration, and clinical manifestations of AD, suggesting the potential of MIF inhibition as therapeutic strategy to slow down neurodegeneration and clinical disease progression.

Patients with Systemic lupus erythematosus (SLE) experience various peripheral and central nervous system manifestations including spatial memory impairment. A subset of autoantibodies (DNRAbs) cross-react with the GluN2A and GluN2B subunits of the NMDA receptor (NMDAR). We find that these DNRAbs act as positive allosteric modulators on NMDARs with GluN2A-containing NMDARs, even those containing a single GluN2A subunit, exhibiting a much greater sensitivity to DNRAbs than those with exclusively GluN2B. Accordingly, GluN2A-specific antagonists provide greater protection from DNRAb-mediated neuronal cell death than GluN2B antagonists. Using transgenic mice to perturb expression of either GluN2A or GluN2B in vivo, we find that DNRAb-mediated disruption of spatial memory characterized by early neuronal cell death and subsequent microglia-dependent pathologies requires GluN2A-containing NMDARs. Our results indicate that GluN2A-specific antagonists or negative allosteric modulators are strong candidates to treat SLE patients with nervous system dysfunction.

Retrotransposons compose a staggering 40% of the mammalian genome. Among them, endogenous retroviruses (ERV) represent sequences that closely resemble the proviruses created from exogenous retroviral infection. ERVs make up 8 to 10% of human and mouse genomes and range from evolutionarily ancient sequences to recent acquisitions. Studies in Drosophila have provided a causal link between genomic retroviral elements and cognitive decline; however, in mammals, the role of ERVs in learning and memory remains unclear. Here we studied 2 independent murine models for ERV activation: muMT strain (lacking B cells and antibody production) and intracerebroventricular injection of streptozotocin (ICVI-STZ). We conducted behavioral assessments (contextual fear memory and spatial learning), as well as gene and protein analysis (RNA sequencing, PCR, immunohistochemistry, and western blot assays). Mice lacking mitochondrial antiviral-signaling protein (MAVS) and mice lacking stimulator of IFN genes protein (STING), 2 downstream sensors of ERV activation, provided confirmation of ERV impact. We found that muMT mice and ICVI-STZ mice induced hippocampal ERV activation, as shown by increased gene and protein expression of the Gag sequence of the transposable element intracisternal A-particle. ERV activation was accompanied by significant hippocampus-related memory impairment in both models. Notably, the deficiency of the MAVS pathway was protective against ICVI-STZ-induced cognitive pathology. Overall, our results demonstrate that ERV activation is associated with cognitive impairment in mice. Moreover, they provide a molecular target for strategies aimed at attenuating retroviral element sensing, via MAVS, to treat dementia and neuropsychiatric disorders., Competing Interests: The authors declare no competing interest., (Copyright © 2019 the Author(s). Published by PNAS.)

Background: Glutamatergic neurons represent the largest neuronal class in the brain and are responsible for the bulk of excitatory synaptic transmission and plasticity. Abnormalities in glutamatergic neurons are linked to several brain disorders and their modulation represents a potential opportunity for emerging bioelectronic medicine (BEM) approaches. Here, we have used a set of electrophysiological assays to identify the effect of the pyrimidine nucleoside uridine on glutamatergic systems in ex vivo brain slices. An improved understanding of glutamatergic synaptic transmission and plasticity, through this type of examination, is critical to the development of potential neuromodulation strategies., Methods: Ex vivo hippocampal slices (400 μm thick) were prepared from mouse brain. We recorded field excitatory postsynaptic potentials (fEPSP) in the CA1's stratum radiatum by stimulation of the CA3 Schaeffer collateral/commissural axons. Uridine was applied at concentrations (3, 30, 300 μM) representing the physiological range present in brain tissue. Synaptic function was studied with input-output (I-O) functions, as well as paired-pulse facilitation (PPF). Synaptic plasticity was studied by applying tetanic stimulation to induce post-tetanic potentiation (PTP), short-term potentiation (STP) and long-term potentiation (LTP). Additionally, we determined whether uridine affected synaptic responses carried solely by n-methyl-d-aspartate receptors (NMDARs), particularly during the oxygen-glucose deprivation (OGD) paradigm., Results: The presence of uridine altered glutamatergic synaptic transmission and plasticity. We found that uridine affected STP and LTP in a concentration-dependent manner. Low-dose uridine (3 μM) had no effect, but higher doses (30 and 300 μM) impaired STP and LTP. Moreover, uridine (300 μM) decreased NMDAR-mediated synaptic responses. Conversely, uridine (at all concentrations tested) had a negligible effect on PPF and basal synaptic transmission, which is mediated primarily by α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs). In addition, uridine (100 μM) exerted a protective effect when the hippocampal slices were challenged with OGD, a widely used model of cerebral ischemia., Conclusions: Using a wide set of electrophysiological assays, we identify that uridine interacts with glutamatergic neurons to alter NMDAR-mediated responses, impair synaptic STP and LTP in a dose-dependent manner, and has a protective effect against OGD insult. This work outlines a strategy to identify deficits in glutamatergic mechanisms for signaling and plasticity that may be critical for targeting these same systems with BEM device-based approaches. To improve the efficacy of potential neuromodulation approaches for treating brain dysfunction, we need to improve our understanding of glutamatergic systems in the brain, including the effects of modulators such as uridine., Competing Interests: Competing interestsThe authors declare that they have no competing interests., (© The Author(s) 2019.)

Rationally designed behavioral tests are important tools to assess the function of specific brain regions. The hippocampus is a crucial neural substrate for spatial cognition, and many studies have linked hippocampal dysfunction with defects on spatial learning and memory in neurological conditions ranging from Alzheimer's disease to autoimmune syndromes, such as neuropsychiatric lupus. While our understanding of hippocampal function, from the molecular to the system levels, has increased dramatically over the last decades, this effort has not yet translated into efficacious therapies for cognitive impairment. We think that the availability of highly validated behavioral paradigms to measure cognition in mouse models is likely to enhance the potential success of preclinical therapeutic modalities. Here, we present an extensive study of the paddling pool task (PPT), first reported by Deacon and Rawlins, in which mice learn to escape from shallow water through a peripheral exit in a circular arena dubbed the clockmaze. We show that the PPT provides highly reliable results when assaying spatial cognition in C57/BL6 mice (120 males, 40 females) and BALB/c mice (40 males, 90 females). Additionally, we develop a robust algorithm for the assessment of escape strategies with clearly quantifiable readouts, enabling fine-granular phenotyping. Notably, the use of spatial strategy increases linearly across trials in the PPT. In a separate cohort of mice, we apply muscimol injections to silence the dorsal CA1 region of the hippocampus and show that the use of the spatial strategy in the PPT relies on the integrity of the dorsal hippocampus. Additionally, we compare directly the PPT and the Morris water maze (MWM) task in C57/BL6 mice (20 males, 20 females) and BALB/c mice (20 males, 20 females) and we find that the PPT induces significantly lower anxiety, exhaustion and hypothermia than the MWM. We conclude that the PPT provides a robust assessment of spatial cognition in mice, which can be applied in conjunction with other tests, to facilitate hypothesis testing and drug development to combat cognitive impairment.

Background: Alcohol abuse affects the brain regions responsible for memory, coordination and emotional processing. Binge alcohol drinking has shown reductions in brain activity, but the molecular targets have not been completely elucidated. We hypothesized that brain cells respond to excessive alcohol by releasing a novel inflammatory mediator, called cold inducible RNA-binding protein (CIRP), which is critical for the decreased brain metabolic activity and impaired cognition., Methods: Male wild type (WT) mice and mice deficient in CIRP (CIRP -/- ) were studied before and after exposure to binge alcohol level by assessment of relative brain glucose metabolism with fluorodeoxyglucose ( 18 FDG) and positron emission tomography (PET). Mice were also examined for object-place memory (OPM) and open field (OF) tasks., Results: Statistical Parametric Analysis (SPM) of 18 FDG-PET uptake revealed marked decreases in relative glucose metabolism in distinct brain regions of WT mice after binge alcohol. Regional analysis (post hoc) revealed that while activity in the temporal (secondary visual) and limbic (entorhinal/perirhinal) cortices was decreased in WT mice, relative glucose metabolic activity was less suppressed in the CIRP -/- mice. Group and condition interaction analysis revealed differing responses in relative glucose metabolism (decrease in WT mice but increase in CIRP -/- mice) after alcohol in brain regions including the hippocampus and the cortical amygdala where the percent changes in metabolic activity correlated with changes in object discrimination performance. Behaviorally, alcohol-treated WT mice were impaired in exploring a repositioned object in the OPM task, and were more anxious in the OF task, whereas CIRP -/- mice were not impaired in these tasks., Conclusion: CIRP released from brain cells could be responsible for regional brain metabolic hypoactivity leading to cognitive impairment under binge alcohol conditions.

Cognitive impairment occurs in 40-90% of patients with systemic lupus erythematosus (SLE), which is characterized by autoantibodies to nuclear antigens, especially DNA. We discovered that a subset of anti-DNA antibodies, termed DNRAbs, cross reacts with the N-methyl-d-aspartate receptor (NMDAR) and enhances NMDAR signaling. In patients, DNRAb presence associates with spatial memory impairment. In a mouse model, DNRAb-mediated brain pathology proceeds through an acute phase of excitotoxic neuron loss, followed by persistent alteration in neuronal integrity and spatial memory impairment. The latter pathology becomes evident only after DNRAbs are no longer detectable in the brain. Here we investigate the mechanism of long-term neuronal dysfunction mediated by transient exposure to antibody. We show that activated microglia and C1q are critical mediators of neuronal damage. We further show that centrally acting inhibitors of angiotensin-converting enzyme (ACE) can prevent microglial activation and preserve neuronal function and cognitive performance. Thus, ACE inhibition represents a strong candidate for clinical trials aimed at mitigating cognitive dysfunction., (© 2018 Nestor et al.)

Background: The vagus nerve plays an important role in the regulation of organ function, including reflex pathways that regulate immunity and inflammation. Recent studies using genetically modified mice have improved our understanding of molecular mechanisms in the neural control of immunity. However, mapping neural signals transmitted in the vagus nerve in mice has been limited by technical challenges. Here, we have standardized an experimental protocol to record compound action potentials transmitted in the vagus nerve., Methods: The vagus nerve was isolated in Balb/c and B6.129S mice, and placed either on a hook or cuff electrode. The electrical signals from the vagus nerve were digitized using either a Neuralynx or Plexon data acquisition system. Changes in the vagus nerve activity in response to anesthesia, feeding and administration of bacterial endotoxin were analyzed., Results: We have developed an electrophysiological recording system to record compound action potentials from the cervical vagus nerve in mice. Cuff electrodes significantly reduce background noise and increase the signal to noise ratio as compared to hook electrodes. Baseline vagus nerve activity varies in response to anesthesia depth and food intake. Analysis of vagus neurograms in different mouse strains (Balb/c and C57BL/6) reveal no significant differences in baseline activity. Importantly, vagus neurogramactivity in wild type and TLR4 receptor knock out mice exhibits receptor dependency of endotoxin mediated signals., Conclusions: These methods for recording vagus neurogram in mice provide a useful tool to further delineate the role of vagus neural pathways in a standardized murine disease model., Competing Interests: Competing interestsDr. Tracey declares that he is the Editor-in Chief of Bioelectronic Medicine. All other authors declare that they have no competing interests as defined by Bioelectronic Medicine, or other interests that might be perceived to influence the results and discussion reported in this paper., (© The Author(s) 2018.)

Long-term sepsis survivors sustain cryptic brain injury that leads to cognitive impairment, emotional imbalance, and increased disability burden. Suitable animal models of sepsis, such as cecal ligation and puncture (CLP), have permitted the analysis of abnormal brain circuits that underlie post-septic behavioral phenotypes. For instance, we have previously shown that CLP-exposed mice exhibit impaired spatial memory together with depleted dendritic arbors and decreased spines in the apical dendrites of pyramidal neurons in the CA1 region of the hippocampus. Here we show that contextual fear conditioning, a form of associative memory for fear, is chronically disrupted in CLP mice when compared to SHAM-operated animals. We also find that the excitatory neurons in the basolateral nucleus of the amygdala (BLA) and the granule cells in the dentate gyrus (DG) display significantly fewer dendritic spines in the CLP group relative to the SHAM mice, although the dendritic arbors and gross morphology of the BLA and DG are comparable between the two groups. Moreover, the basal dendrites of CA1 pyramidal neurons are unaffected in the CLP mice. Taken together, our data indicate that the structural damage in the amygdalar-hippocampal network represents the neural substrate for impaired contextual fear memory in long-term sepsis survivors. Further, our data suggest that the brain injury caused by overwhelming sepsis alters the stability of the synaptic connections involved in associative fear. These results likely have implications for the emotional imbalance observed in human sepsis survivors.

Autism spectrum disorder (ASD) occurs in 1 in 68 births, preferentially affecting males. It encompasses a group of neurodevelopmental abnormalities characterized by impaired social interaction and communication, stereotypic behaviors and motor dysfunction. Although recent advances implicate maternal brain-reactive antibodies in a causative role in ASD, a definitive assessment of their pathogenic potential requires cloning of such antibodies. Here, we describe the isolation and characterization of monoclonal brain-reactive antibodies from blood of women with brain-reactive serology and a child with ASD. We further demonstrate that male but not female mice exposed in utero to the C6 monoclonal antibody, binding to contactin-associated protein-like 2 (Caspr2), display abnormal cortical development, decreased dendritic complexity of excitatory neurons and reduced numbers of inhibitory neurons in the hippocampus, as well as impairments in sociability, flexible learning and repetitive behavior. Anti-Caspr2 antibodies are frequent in women with brain-reactive serology and a child with ASD. Together these studies provide a methodology for obtaining monclonal brain-reactive antibodies from blood B cells, demonstrate that ASD can result from in utero exposure to maternal brain-reactive antibodies of single specificity and point toward the exciting possibility of prognostic and protective strategies.

CALHM1 is a cell surface calcium channel expressed in cerebral neurons. CALHM1 function in the brain remains unknown, but recent results showed that neuronal CALHM1 controls intracellular calcium signaling and cell excitability, two mechanisms required for synaptic function. Here, we describe the generation of Calhm1 knockout (Calhm1(-/-)) mice and investigate CALHM1 role in neuronal and cognitive functions. Structural analysis revealed that Calhm1(-/-) brains had normal regional and cellular architecture, and showed no evidence of neuronal or synaptic loss, indicating that CALHM1 deficiency does not affect brain development or brain integrity in adulthood. However, Calhm1(-/-) mice showed a severe impairment in memory flexibility, assessed in the Morris water maze, and a significant disruption of long-term potentiation without alteration of long-term depression, measured in ex vivo hippocampal slices. Importantly, in primary neurons and hippocampal slices, CALHM1 activation facilitated the phosphorylation of NMDA and AMPA receptors by protein kinase A. Furthermore, neuronal CALHM1 activation potentiated the effect of glutamate on the expression of c-Fos and C/EBPβ, two immediate-early gene markers of neuronal activity. Thus, CALHM1 controls synaptic activity in cerebral neurons and is required for the flexible processing of memory in mice. These results shed light on CALHM1 physiology in the mammalian brain.

The axons of the sensory, or afferent, vagus nerve transmit action potentials to the central nervous system in response to changes in the body's metabolic and physiological status. Recent advances in identifying neural circuits that regulate immune responses to infection, inflammation and injury have revealed that vagus nerve signals regulate the release of cytokines and other factors produced by macrophages. Here we record compound action potentials in the cervical vagus nerve of adult mice and reveal the specific activity that occurs following administration of the proinflammatory cytokines tumor necrosis factor (TNF) and interleukin 1β (IL-1β). Importantly, the afferent vagus neurograms generated by TNF exposure are abolished in double knockout mice lacking TNF receptors 1 and 2 (TNF-R1/2KO), whereas IL-1β-specific neurograms are eliminated in knockout mice lacking IL-1β receptor (IL-1RKO). Conversely, TNF neurograms are preserved in IL-1RKO mice, and IL-1β neurograms are unchanged in TNF-R1/2KO mice. Analysis of the temporal dynamics and power spectral characteristics of afferent vagus neurograms for TNF and IL-1β reveals cytokine-selective signals. The nodose ganglion contains the cell bodies of the sensory neurons whose axons run through the vagus nerve. The nodose neurons express receptors for TNF and IL-1β, and we show that exposing them to TNF and IL-1β significantly stimulates their calcium uptake. Together these results indicate that afferent vagus signals in response to cytokines provide a basic model of nervous system sensing of immune responses., Competing Interests: DISCLOSURE The authors declare that they have no competing interests as defined by Bioelectronic Medicine, or other interests that might be perceived to influence the results and discussion reported in this paper.

We present a succinct review of our approach to study the interactions between the DNA-reactive antibodies that cross-react with the GluN2A and GluN2B subunits of the N-methyl-D-aspartate receptor, denoted DNRABs, and their brain targets in subjects with neuropsychiatric systemic lupus erythematosus (NPSLE). We have analyzed the DNRAB-based brain symptomatology in mouse models of NPSLE by using an integrative neuroscience approach, which includes behavioral assessment coupled with electrophysiological studies of neural networks and synaptic connections in target brain regions, such as the CA1 region of the hippocampus. Our results suggest a framework for understanding the interactions between immune factors and neural networks.

Patients with systemic lupus erythematosus (SLE) experience cognitive abnormalities in multiple domains including processing speed, executive function, and memory. Here we show that SLE patients carrying antibodies that bind DNA and the GluN2A and GluN2B subunits of the N-methyl-d-aspartate receptor (NMDAR), termed DNRAbs, displayed a selective impairment in spatial recall. Neural recordings in a mouse model of SLE, in which circulating DNRAbs penetrate the hippocampus, revealed that CA1 place cells exhibited a significant expansion in place field size. Structural analysis showed that hippocampal pyramidal cells had substantial reductions in their dendritic processes and spines. Strikingly, these abnormalities became evident at a time when DNRAbs were no longer detectable in the hippocampus. These results suggest that antibody-mediated neurocognitive impairments may be highly specific, and that spatial cognition may be particularly vulnerable to DNRAb-mediated structural and functional injury to hippocampal cells that evolves after the triggering insult is no longer present.

Extracellular superoxide dismutase (EC-SOD) is an isoform of SOD normally found both intra- and extra-cellularly and accounting for most SOD activity in blood vessels. Here we explored the role of EC-SOD in protecting against brain damage induced by chronic hypoxia. EC-SOD Transgenic mice, were exposed to hypoxia (FiO2.1%) for 10 days (H-KI) and compared to transgenic animals housed in room air (RA-KI), wild type animals exposed to hypoxia (H-WT or wild type mice housed in room air (RA-WT). Overall brain metabolism evaluated by positron emission tomography (PET) showed that H-WT mice had significantly higher uptake of 18FDG in the brain particularly the hippocampus, hypothalamus, and cerebellum. H-KI mice had comparable uptake to the RA-KI and RA-WT groups. To investigate the functional state of the hippocampus, electrophysiological techniques in ex vivo hippocampal slices were performed and showed that H-KI had normal synaptic plasticity, whereas H-WT were severely affected. Markers of oxidative stress, GFAP, IBA1, MIF, and pAMPK showed similar values in the H-KI and RA-WT groups, but were significantly increased in the H-WT group. Caspase-3 assay and histopathological studies showed significant apoptosis/cell damage in the H-WT group, but no significant difference in the H-KI group compared to the RA groups. The data suggest that EC-SOD has potential prophylactic and therapeutic roles in diseases with compromised brain oxygenation.

Systemic lupus erythematosus (SLE) is characterized by multiorgan inflammation, neuropsychiatric disorders (NPSLE), and anti-nuclear antibodies. We previously identified a subset of anti-DNA antibodies (DNRAb) cross-reactive with the N-methyl-D-aspartate receptor, present in 30% to 40% of patients, able to enhance excitatory post-synaptic potentials and trigger neuronal apoptosis. DNRAb+ mice exhibit memory impairment or altered fear response, depending on whether the antibody penetrates the hippocampus or amygdala. Here, we used 18F-fluorodeoxyglucose (FDG) microPET to plot changes in brain metabolism after regional blood-brain barrier (BBB) breach. In DNRAb+ mice, metabolism declined at the site of BBB breach in the first 2 weeks and increased over the next 2 weeks. In contrast, DNRAb- mice exhibited metabolic increases in these regions over the 4 weeks after the insult. Memory impairment was present in DNRAb+ animals with hippocampal BBB breach and altered fear conditioning in DNRAb+ mice with amygdala BBB breach. In DNRAb+ mice, we observed an inverse relationship between neuron number and regional metabolism, while a positive correlation was observed in DNRAb- mice. These findings suggest that local metabolic alterations in this model take place through different mechanisms with distinct time courses, with important implications for the interpretation of imaging data in SLE subjects.

N-methyl-D-aspartate receptors (NMDAR) in the hippocampus participate in encoding and recalling the location of objects in the environment, but the ensemble mechanisms by which NMDARs mediate these processes have not been completely elucidated. To address this issue, we examined the firing patterns of place cells in the dorsal CA1 area of the hippocampus of mice (n = 7) that performed an object place memory (OPM) task, consisting of familiarization (T1), sample (T2), and choice (T3) trials, after systemic injection of 3-[(±)2-carboxypiperazin-4yl]propyl-1-phosphate (CPP), a specific NMDAR antagonist. Place cell properties under CPP (CPP-PCs) were compared to those after control saline injection (SAL-PCs) in the same mice. We analyzed place cells across the OPM task to determine whether they signaled the introduction or movement of objects by NMDAR-mediated changes of their spatial coding. On T2, when two objects were first introduced to a familiar chamber, CPP-PCs and SAL-PCs showed stable, vanishing or moving place fields in addition to changes in spatial information (SI). These metrics were comparable between groups. Remarkably, previously inactive CPP-PCs (with place fields emerging de novo on T2) had significantly weaker SI increases than SAL-PCs. On T3, when one object was moved, CPP-PCs showed reduced center-of-mass (COM) shift of their place fields. Indeed, a subset of SAL-PCs with large COM shifts (>7 cm) was largely absent in the CPP condition. Notably, for SAL-PCs that exhibited COM shifts, those initially close to the moving object followed the trajectory of the object, whereas those far from the object did the opposite. Our results strongly suggest that the SI changes and COM shifts of place fields that occur during the OPM task reflect key dynamic properties that are mediated by NMDARs and might be responsible for binding object identity with location.

State-of-the-art electrophysiological recordings from the brains of freely behaving animals allow researchers to simultaneously examine local field potentials (LFPs) from populations of neurons and action potentials from individual cells, as the animal engages in experimentally relevant tasks. Chronically implanted microdrives allow for brain recordings to last over periods of several weeks. Miniaturized drives and lightweight components allow for these long-term recordings to occur in small mammals, such as mice. By using tetrodes, which consist of tightly braided bundles of four electrodes in which each wire has a diameter of 12.5 μm, it is possible to isolate physiologically active neurons in superficial brain regions such as the cerebral cortex, dorsal hippocampus, and subiculum, as well as deeper regions such as the striatum and the amygdala. Moreover, this technique insures stable, high-fidelity neural recordings as the animal is challenged with a variety of behavioral tasks. This manuscript describes several techniques that have been optimized to record from the mouse brain. First, we show how to fabricate tetrodes, load them into driveable tubes, and gold-plate their tips in order to reduce their impedance from MΩ to KΩ range. Second, we show how to construct a custom microdrive assembly for carrying and moving the tetrodes vertically, with the use of inexpensive materials. Third, we show the steps for assembling a commercially available microdrive (Neuralynx VersaDrive) that is designed to carry independently movable tetrodes. Finally, we present representative results of local field potentials and single-unit signals obtained in the dorsal subiculum of mice. These techniques can be easily modified to accommodate different types of electrode arrays and recording schemes in the mouse brain.

Severe sepsis, a syndrome that complicates infection and injury, affects 750,000 annually in the United States. The acute mortality rate is approximately 30%, but, strikingly, sepsis survivors have a significant disability burden: up to 25% of survivors are cognitively and physically impaired. To investigate the mechanisms underlying persistent cognitive impairment in sepsis survivors, here we developed a murine model of severe sepsis survivors following cecal ligation and puncture (CLP) to study cognitive impairments. We observed that serum levels of high mobility group box 1 (HMGB1), a critical mediator of acute sepsis pathophysiology, are increased in sepsis survivors. Significantly, these levels remain elevated for at least 4 wks after CLP. Sepsis survivors develop significant, persistent impairments in learning and memory, and anatomic changes in the hippocampus associated with a loss of synaptic plasticity. Administration of neutralizing anti-HMGB1 antibody to survivors, beginning 1 wk after onset of peritonitis, significantly improved memory impairments and brain pathology. Administration of recombinant HMGB1 to naïve mice recapitulated the memory impairments. Together, these findings indicate that elevated HMGB1 levels mediate cognitive decline in sepsis survivors, and suggest that it may be possible to prevent or reverse cognitive impairments in sepsis survivors by administration of anti-HMGB1 antibodies.

The medial temporal lobe (MTL) encompasses a network of interconnected cortical areas that is considered the neural substrate for some types of memory, such as spatial, episodic, recognition, and associative memory. Within the MTL, the subiculum has been well characterized in terms of its connectivity and structure, but its functional role remains elusive. A long-held view is that the subiculum is mainly involved in spatial encoding because it exhibits spatially selective firing and receives prominent projections from the CA1 field, which is an essential substrate for spatial memory. However, the dorsal subiculum (DS) is also reciprocally connected to the perirhinal and postrhinal cortices, which are critically involved in recognition memory. This connectivity pattern suggests that DS might encode not only spatial signals but also recognition signals. Here, we examined this hypothesis by recording with multi-electrodes in DS and CA1 of freely behaving mice, as they performed the novel object recognition (NOR) task. Analysis of network oscillations revealed that theta power was significantly higher in DS when mice explored novel objects as compared to familiar objects and that this theta modulation was absent in CA1. We also found significant differences in coherence between DS and CA1, in the theta and gamma bands, depending on whether mice examined objects or engaged in spatial exploration. Furthermore, single-unit recordings revealed that DS cells did not exhibit phase-locked firing to theta and differed from CA1 place cells in that they had multiple peaks of spatially selective firing. We also detected DS units that were responsive specifically to novel object exploration, indicating that a subset of DS neurons were tuned to novelty during the NOR task. We have thus identified clear neurophysiological correlates for recognition within the DS, at the network and single-unit levels, strongly suggesting that it participates in encoding recognition-related signals.

Systemic lupus erythematosus (SLE), a disease of women during childbearing years, is characterized by the production of double-stranded DNA antibodies. A subset of these antibodies, present in 40% of patients, cross-reacts with the NR2A and NR2B subunits of the N-methyl-d-aspartate receptor (NMDAR). In this study, we show that, in mouse models, these antibodies cause a loss of female fetus viability by inducing apoptosis of NR2A-expressing neurons within the brainstem late in fetal development; gender specificity derives from a time-dependent increased expression of NR2A in female brainstem or increased vulnerability of female fetal neurons to signaling through NR2A-containing NMDARs. This paradigm is consistent with available data on the sex ratio of live births of women with SLE. It represents a novel mechanism by which maternal autoantibodies can severely affect fetal health in a gender-specific fashion and raises the question of how many maternal antibodies affect brain development or exhibit gender-specific fetal effects.

A new study entitled "Normal gut microbiota modulates brain development and behavior", published in the Proceedings of the National Academy of Sciences, requires that we reconsider the notion that the brain is an immune-privileged site. The authors demonstrate that intestinal microbiota must be present within a set time-frame for normal synaptogenesis to occur in the brain. In the absence of intestinal microbiota, histopathological and behavioral abnormalities arise. These observations necessitate a new look at the many interconnections of the immune system and the brain, suggesting new frontiers for research and new therapeutic strategies for neurodevelopmental diseases., (Copyright © 2011 WILEY Periodicals, Inc.)

The mediators of tissue damage in systemic lupus erythematosus (SLE) such as antibodies, cytokines and activated immune cells have direct access to most organs in the body but must penetrate the blood-brain barrier (BBB) to gain access to brain tissue. We hypothesized that compromise of the BBB occurs episodically such that the brain will acquire tissue damage slowly and not at the same rate as other organs. On the basis of these assumptions, we wished to determine if duration of disease correlated with brain injury, as measured with functional magnetic resonance imaging (fMRI), and if this was independent of degree of tissue damage in other organs. We investigated differences in brain activation patterns using fMRI in 13 SLE patients stratified by disease duration of ≤2 years (short-term [ST]) or ≥10 years (long-term [LT]). Two fMRI paradigms were selected to measure working memory and emotional response (fearful faces task). Performance in the working memory task was significantly better in the ST group for one and two shape recall; however, both groups did poorly with three shape recall. Imaging studies demonstrated significantly increased cortical activation in the ST group in regions associated with cognition during the two shape retention phase of the working memory task (P < 0.001) and increased amygdala (P < 0.05) and superior parietal (P < 0.01) activation in response to the fearful faces paradigm. In conclusion, analysis of activation patterns stratified by performance accuracy, differences in co-morbid disease, corticosteroid doses or disease activity suggests that these observed differences are attributable to SLE effects on the central nervous system exclusive of vascular disease or other confounding influences. Our hypothesis is further supported by the lack of correlation between regional brain abnormalities on fMRI and the Systemic Lupus International Collaborating Clinics (SLICC) damage index.

Systemic lupus erythematosus (SLE) is characterized by the presence of autoantibodies that can mediate tissue damage in multiple organs. The underlying aetiology of SLE autoantibodies remains unknown, and treatments aimed at eliminating B cells, or limiting their function, have demonstrated limited therapeutic benefit. Thus, the current therapies for SLE are based on the concept of nonspecific immunosuppression and consist of nonsteroidal anti-inflammatory drugs (NSAIDS), corticosteroids, anti-malarials and cytotoxic drugs, all of which have serious adverse side effects including organ damage. The major auto-specificity in SLE is double-stranded (ds) DNA. Many anti-dsDNA antibodies cross-react with non-DNA antigens that may be the direct targets for their pathogenic activity. Studying anti-dsDNA antibodies present in SLE patients and in animal models of lupus, we have identified a subset of anti-dsDNA antibodies which is pathogenic in the brain as well as in the kidney. We have recently demonstrated that specific peptides, or small molecules, can protect target organs from antibody-mediated damage. Thus, it might be possible to treat the aspects of autoimmune disease without inducing major immunosuppression and ensuing infectious complications., (© 2010 The Association for the Publication of the Journal of Internal Medicine.)

Damaging interactions between antibodies and brain antigenic targets may be responsible for an expanding range of neurological disorders. In the case of systemic lupus erythematosus (SLE), patients generate autoantibodies (AAbs) that frequently bind dsDNA. Although some symptoms of SLE may arise from direct reactivity to dsDNA, much of the AAb-mediated damage originates from cross-reactivity with other antigens. We have studied lupus AAbs that bind dsDNA and cross-react with the NR2A and NR2B subunits of the NMDA receptor (NMDAR). In adult mouse models, when the blood-brain barrier is compromised, these NMDAR-reactive AAbs access the brain and elicit neuronal death with ensuing cognitive dysfunction and emotional disturbance. The cellular mechanisms that underlie these deleterious effects remain incompletely understood. Here, we show that, at low concentration, the NMDAR-reactive AAbs are positive modulators of receptor function that increase the size of NMDAR-mediated excitatory postsynaptic potentials, whereas at high concentration, the AAbs promote excitotoxicity through enhanced mitochondrial permeability transition. Other synaptic receptors are completely unaffected by the AAbs. NMDAR activation is required for producing both the synaptic and the mitochondrial effects. Our study thus reveals the mechanisms by which NMDAR-reactive AAbs trigger graded cellular alterations, which are likely to be responsible for the transient and permanent neuropsychiatric symptoms observed in patients with SLE. Our study also provides a model in which local AAb concentration determines the exact nature of the cellular response.

The understanding that recovery of brain function after stroke is imperfect has prompted decades of effort to engender speedier and better recovery through environmental manipulation. Clinical evidence has shown that the performance plateau exhibited by patients with chronic stroke, usually signaling an end of standard rehabilitation, might represent a period of consolidation rather than a performance optimum. These results highlight the difficulty of translating pertinent neurological data into pragmatic changes in clinical programs. This opinion piece focuses on upper limb impairment reduction after robotic training. We propose that robotic devices be considered as novel tools that might be used alone or in combination with novel pharmacology and other bioengineered devices. Additionally, robotic devices can measure motor performance objectively and will contribute to a detailed phenotype of stroke recovery.

gamma-Aminobutyric acid (GABA) regulates the proliferation and migration of olfactory bulb (OB) interneuron progenitors derived from the subventricular zone (SVZ), but the role of GABA in the differentiation of these progenitors has been largely unexplored. This study examines the role of GABA in the differentiation of OB dopaminergic interneurons using neonatal forebrain organotypic slice cultures prepared from transgenic mice expressing green fluorescent protein (GFP) under the control of the tyrosine hydroxylase (Th) gene promoter (ThGFP). KCl-mediated depolarization of the slices induced ThGFP expression. The addition of GABA to the depolarized slices further increased GFP fluorescence by inducing ThGFP expression in an additional set of periglomerular cells. These findings show that GABA promoted differentiation of SVZ-derived OB dopaminergic interneurons and suggest that GABA indirectly regulated Th expression and OB dopaminergic neuron differentiation through an acceleration of the maturation rate for the dopaminergic progenitors. Additional studies revealed that the effect of GABA on ThGFP expression required activation of L- and P/Q-type Ca2+ channels as well as GABA(A) and GABA(B) receptors. These voltage-gated Ca2+ channels and GABA receptors have previously been shown to be required for the coexpressed GABAergic phenotype in the OB interneurons. Together, these findings suggest that Th expression and the differentiation of OB dopaminergic interneurons are coupled to the coexpressed GABAergic phenotype and demonstrate a novel role for GABA in neurogenesis., (Copyright 2009 Wiley-Liss, Inc.)

Dysregulated cholesterol metabolism is a major risk factor for atherosclerosis and other late-onset disorders, such as Alzheimer's disease. The scavenger receptor, class B, type I (SR-BI) is critical in maintaining the homeostasis of cholesterol and alpha-tocopherol. SR-BI binds high-density lipoproteins (HDL) and mediates the selective transfer of cholesteryl esters and alpha-tocopherol from circulating HDL to cells. SR-BI is also involved in reverse cholesterol transport from peripheral tissues into the liver. Previous studies using SR-BI genetic knockout mice indicated that the deletion of SR-BI resulted in an accelerated onset of atherosclerosis. We hypothesized that SR-BI-dependent lipid dysregulation might disrupt brain function leading to cognitive impairment. Here, we report that very old SR-BI knockout mice show deficient synaptic plasticity (long-term potentiation) in the CA1 region of the hippocampus. Very old SR-BI KO mice also display selective impairments in recognition memory and spatial memory. Thus, SR-BI influences neural and cognitive processes, a finding that highlights the contribution of cholesterol and alpha-tocopherol homeostasis in proper cognitive function.

Systemic lupus erythematosus (SLE) is an autoimmune disease mediated by autoantibodies and preferentially affecting women of childbearing age. Because the offspring of mothers with SLE show a high frequency of learning disorders, we hypothesized that maternally transferred autoantibodies that bind DNA and the N-methyl-D-aspartate receptor (NMDAR) could have a pathogenic role during fetal brain development. Here we describe a maternal SLE mouse model wherein pregnant dams harbored DNA-specific, NMDAR-specific autoantibodies throughout gestation. High titers of these autoantibodies in maternal circulation led to histological abnormalities in fetal brain and subsequent cognitive impairments in adult offspring. These data support a paradigm in which in utero exposure to neurotoxic autoantibodies causes abnormal brain development with long-term consequences. This paradigm may apply to multiple congenital neuropsychiatric disorders.

The brain demands oxygen and glucose to fulfill its roles as the master regulator of body functions as diverse as bladder control and creative thinking. Chemical and electrical transmission in the nervous system is rapidly disrupted in stroke as a result of hypoxia and hypoglycemia. Despite being highly evolved in its architecture, the human brain appears to utilize phylogenetically conserved homeostatic strategies to combat hypoxia and ischemia. Specifically, several converging lines of inquiry have demonstrated that the transcription factor hypoxia-inducible factor-1 (HIF1-1) mediates the activation of a large cassette of genes involved in adaptation to hypoxia in surviving neurons after stroke. Accordingly, pharmacological or molecular approaches that engage hypoxic adaptation at the point of one of its sensors (e.g., inhibition of HIF prolyl 4 hydroxylases) leads to profound sparing of brain tissue and enhanced recovery of function. In this review, we discuss the potential mechanisms that could subserve protective and restorative effects of augmenting hypoxic adaptation in the brain. The strategy appears to involve HIF-dependent and HIF-independent pathways and more than 70 genes and proteins activated transcriptionally and post-transcriptionally that can act at cellular, local, and system levels to compensate for oxygen insufficiency. The breadth and depth of this homeostatic program offers a hopeful alternative to the current pessimism towards stroke therapeutics.

Neuropsychiatric systemic lupus erythematosus, which often entails cognitive disturbances and memory loss, has become a major complication for lupus patients. Previously, we developed a murine model of neuropsychiatric lupus based on Abs that cross-react with dsDNA and the NMDA receptor (NMDAR). We showed that these murine Abs impair cognition when they access the CNS through a breach in the blood-brain barrier (BBB) triggered by lipopolysaccharide. Because studies show that lupus patients possess anti-NMDAR Abs in their serum and cerebrospinal fluid, we decided to investigate whether these human Abs contribute to cognitive dysfunction. Here, we show that serum with reactivity to DNA and NMDAR extracted from lupus patients elicited cognitive impairment in mice receiving the serum intravenously and given lipopolysaccharide to compromise the BBB integrity. Brain histopathology showed hippocampal neuron damage, and behavioral testing revealed hippocampus-dependent memory impairment. To determine whether anti-NMDAR Abs exist in the brains of systemic lupus erythematosus patients, we eluted IgG from a patient's brain. The IgG bound DNA and NMDAR and caused neuronal apoptosis when injected into mouse brains. We examined four more brains of patients with neuropsychiatric lupus and found that they displayed endogenous IgG colocalizing with anti-NMDAR Abs. Our results indicate that lupus patients have circulating anti-NMDAR Abs capable of causing neuronal damage and memory deficit, if they breach the BBB, and that the Abs exist within patients' brains. Which aspects of neuropsychiatric lupus may be mediated by anti-NMDAR Abs, how often, and in which patients are now important clinical questions.

It is widely thought that Alzheimer's disease (AD) begins as a malfunction of synapses, eventually leading to cognitive impairment and dementia. Homeostatic synaptic scaling is a mechanism that could be crucial at the onset of AD but has not been examined experimentally. In this process, the synaptic strength of a neuron is modified so that the overall excitability of the cell is maintained. Here, we investigate whether synaptic scaling mediated by l-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) contributes to pathology in double knockin (2 x KI) mice carrying human mutations in the genes for amyloid precursor protein and presenilin-1. By using whole-cell recordings, we show that 2 x KI mice exhibit age-related downscaling of AMPAR-mediated evoked currents and spontaneous, miniature currents. Electron microscopic analysis further corroborates the synaptic AMPAR decrease. Additionally, 2 x KI mice show age-related deficits in bidirectional plasticity (long-term potentiation and long-term depression) and memory flexibility. These results suggest that AMPARs are important synaptic targets for AD and provide evidence that cognitive impairment may involve downscaling of postsynaptic AMPAR function.

Systemic lupus erythematosus is an autoimmune disease in which most patients express Abs that bind double-stranded DNA. Recent work has shown that a subset of lupus Abs can crossreact with the NR2A and NR2B subunits of the NMDA receptor. This receptor is expressed in neurons throughout the brain but is at highest density within cells of the hippocampus, amygdala, and hypothalamus. The neurons in the CNS are normally protected from brain-reactive Abs by the blood-brain barrier (BBB); however, a breach in the barrier's integrity exposes neurons to potentially pathogenic Abs. Previously, we have shown that mice that are immunized with a peptide mimetope of DNA produce lupus-like Abs that crossreact with DNA and the NMDA receptor. Moreover, after abrogation of the BBB by treatment with lipopolysaccharide, the immunized mice display hippocampal neuron damage with ensuing memory impairment. Given that rises in epinephrine can increase cerebral blood flow and can cause leaks in the BBB, we decided to investigate whether epinephrine could act as a permissive agent for Ab-mediated neurotoxicity. Here, we show that peptide-immunized mice, given epinephrine to open the BBB, lose neurons in the lateral amygdala and develop a behavioral disorder characterized by a deficient response to fear-conditioning paradigms. Thus, the agent used to open the BBB determines which brain region is made vulnerable to neurotoxic Abs, and Abs that penetrate brain tissue can cause changes not only in cognitive competence, but also in emotional behavior.

Classic immunologic teaching describes the brain as an immunologically privileged site. Studies of neuroimmunology have focused for many years almost exclusively on multiple sclerosis, a disease in which inflammatory cells actually infiltrate brain tissue, and the rodent model of this disease, experimental allergic encephalitis. Over the past decade, however, increasingly, brain-reactive antibodies have been demonstrated in the serum of patients with numerous neurological diseases. The contribution these antibodies make to neuronal dysfunction has, in general, not been determined. Here, we describe recent studies showing that serum antibodies to the N-methyl-D-aspartate receptor occur frequently in patients with systemic lupus erythematosus and can cause alterations in cognition and behavior following a breach in the blood-brain barrier.

Post-mortem cortices from patients diagnosed with Alzheimer's disease (AD) exhibit reduced levels of drebrin, an F-actin binding protein of dendritic spines and shafts. We used a mouse model of familial AD (FAD) to determine whether the density of cortical spines engaged in asymmetric (presumably excitatory) synapses and containing drebrin A is reduced and if so, whether this occurs prior to the emergence of beta amyloid deposits, when only soluble beta amyloid (Abeta) is present. Quantitative electron microscopic immunocytochemistry revealed that by 6 months, the proportion of postsynaptic spines with drebrin A within somatosensory cortex layer I was smaller for the FAD model mice, when compared to the corresponding region of WT mice (P < 0.0005). However, the areal density of postsynaptic spines containing drebrin A was relatively constant from 3 to 18 months and beyond for both genotypes, suggesting that drebrin A confers stability to postsynaptic spines. Further measurements confirmed that the reduced proportion of drebrin A-containing spines in brains of FAD mice at 6 months is due to the greater size and areal density of spine profiles lacking drebrin A. Thus, soluble Abeta could affect spines lacking drebrin A more strongly than spines containing drebrin A. At 6 months and older, a larger fraction of spinous drebrin A in 2xKI mice was located near the synaptic membrane, as compared to those of WT mice. This pattern may reflect an altered trafficking of synaptic molecules within spines, a factor adding to the decline of synaptic function and plasticity.

Patients with lupus (SLE) experience progressive cognitive loss without evidence of CNS vascular disease or inflammation. SLE patients produce anti-DNA antibodies that crossreact with NMDA receptors and are capable of mediating excitotoxic death. We now show that mice induced by antigen to express these antibodies have no neuronal damage until breakdown of the blood-brain barrier occurs. Following administration of lipopolysaccharide (LPS) to immunized mice, antibodies gain access to the brain. They bind preferentially to hippocampal neurons and cause neuronal death with resulting cognitive dysfunction and altered hippocampal metabolism on magnetic resonance spectroscopy. Memantine, an NMDA receptor antagonist, given prior to LPS administration, prevents neuronal damage. Thus, systemic immune responses can cause cognitive impairment in the absence of an inflammatory cascade, implicating the immune system in yet another arena of human pathobiology. Furthermore, NMDA receptor antagonists prevent antibody-mediated damage and may constitute a new approach to therapy in SLE.

In humans the hippocampus is required for episodic memory, which extends into the spatial and temporal domains. Work on the rodent hippocampus has shown that NMDA receptor (NMDAR) -mediated plasticity is essential for spatial memory. Here, we have examined whether hippocampal NMDARs are also needed for temporal memory. We applied trace fear conditioning to knockout mice lacking NMDARs only in hippocampal CA1 pyramidal cells. This paradigm requires temporal processing because the conditional and unconditional stimuli are separated by 30 s (trace). We found that knockout mice failed to memorize this association but were indistinguishable from normal animals when the trace was removed. Thus, NMDARs in CA1 are crucial for the formation of memories that associate events across time.

We have examined the role of NMDA receptor-mediated neural activity in the formation of periphery-related somatosensory patterns, using genetically engineered mice. We demonstrate that ectopic expression of a transgene of an NMDAR1 splice variant rescues neonatally fatal NMDAR1 knockout (KO) mice, although the average life span varies depending on the level of the transgene expression. In NMDAR1 KO mice with "high" levels of the transgene expression, sensory periphery-related patterns were normal along both the trigeminal and dorsal column pathways. In the KO mice with "low" levels of the transgene expression, the patterns were absent in the trigeminal pathway. Our results indicate that NMDA receptor-mediated neural activity plays a critical role in pattern formation along the ascending somatosensory pathways.

We have produced a mouse strain in which the deletion of the NMDAR1 gene is restricted to the CA1 pyramidal cells of the hippocampus by using a new and general method that allows CA1-restricted gene knockout. The mutant mice grow into adulthood without obvious abnormalities. Adult mice lack NMDA receptor-mediated synaptic currents and long-term potentiation in the CA1 synapses and exhibit impaired spatial memory but unimpaired nonspatial learning. Our results strongly suggest that activity-dependent modifications of CA1 synapses, mediated by NMDA receptors, play an essential role in the acquisition of spatial memories.