Neuregulin 1 transgenic mice display reduced mismatch negativity, contextual fear conditioning and social interactions

Early life social instability stress causes lasting cognitive decrement and elevated hippocampal stress-related gene expression

BACKGROUND

Early life stress may have profound effects on brain health, yielding both short- and long-term cognitive or psychiatric impairment. Early life Social Instability Stress (SIS) in rodents has been used to model the effects of early chronic human stress. While many studies have assessed acute and short-term responses to this stressor, less attention has been paid to the lasting effects of early life stress in rodents.

METHODS

The current study utilized SIS in young mice to assess the impact of early life adversity over the lifespan. Mice were assessed in adulthood between the ages of 18 to 66 weeks for changes in behaviors associated with anxiety, affect, sociability, aggression, motivation, and recognition memory. Additionally, mice were assessed for changes in glucocorticoid level and hippocampal mRNA expression in a subset of genes that display alterations in humans following exposure to stress (CRHR1, CRHR2, FKBP5, SLC6A4).

RESULTS

Mice exposed to early SIS showed disrupted memory and increased hippocampal expression of FKBP5, CRHR2 and SLC6A4 mRNA compared to non-stressed mice. Importantly, there was a significant association between increased FKBP5 and CRHR2 with reduced recognition memory. Additionally, mice exposed to SIS showed increased responding on a progressive ratio schedule of reinforcement, indicating that reduction in memory performance was not mediated by decreased effort.

CONCLUSIONS

Ecologically-relevant social stress in mice causes long-term decrements in recognition memory, possibly mediated by persistent changes in moderators of the stress cascade. Additionally, animals exposed to early life stress showed increased motivation for reward, which may contribute to a host of hedonic seeking behaviors throughout life. These data suggest that SIS can be used to evaluate therapeutic interventions to attenuate or reverse lasting effects of early life adversity.

Non-invasive electroencephalographical (EEG) recording system in awake monkeys

Background

Human clinical studies reported that several electroencephalographical (EEG) parameters can be used as biomarkers of psychiatric disorders. EEGs recorded from non-human primates (monkeys) is useful for understanding of human pathologies of psychiatric disorders and development of new therapeutic agents.

New methods

In this study, we expand a previous non-invasive head holding system with face masks for awake monkeys to be applied to scalp EEG recording. The new design of a head holding system allows to attach scalp EEG electrodes on the positions comparable to human electrode placement and to present auditory stimuli.

Results

With this system, we could record auditory evoked potentials (AEPs) in auditory sensory gating and oddball paradigms, which are often used as biomarkers of psychiatric disorders in animal models and human patients. The recorded AEPs were comparable to previous human clinical data.

Comparison with existing methods

Compared with previous non-invasive head holding systems, top, side (cheek and ears), and rear of the head can be open for attachment of EEG electrodes and auditory stimulation in the present system.

Conclusions

The results suggest that the present system is useful in EEG recording from awake monkeys. Furthermore, this system can be applied to eye-tracking and chronic intra-cerebral recording experiments.

Beneficial Effects of Fingolimod on Social Interaction, CNS and Peripheral Immune Response in the BTBR Mouse Model of Autism

Autism Spectrum Disorders (ASD) are neurodevelopmental disorders characterized by social communication deficits and repetitive/stereotyped behaviours. We evaluated the effects of a chronic treatment with the immunomodulator drug Fingolimod (FTY720 - a non-selective Sphingosine 1-Phosphate Receptor ligand) in an ASD model, the BTBR T⁺tf/J (BTBR) mouse strain. In adult BTBR males, chronic FTY720 treatment (4 weeks) increased social and vocal response during a male-female interaction and hippocampal expression of BDNF and Neuregulin 1, two trophic factors reduced in BTBR when compared to control C57 mice. FTY720 also re-established the expression of IL-1β and MnSOD in the hippocampus, whereas it did not modify IL-6 mRNA content. In addition to its central effect, FTY720 modulated the activation state of peripheral macrophages in the BTBR model, both in basal conditions and after stimulation with an immune challenge. Furthermore, IL-6 mRNA colonic content of BTBR mice, reduced when compared with C57 mice, was normalized by chronic treatment with FTY720. Our study, while indicating FTY720 as a tool to attenuate relevant alterations of the BTBR neurobehavioural phenotype, emphasizes the importance of gut mucosal immune evaluation as an additional target that deserve to be investigated in preclinical studies of anti-inflammatory therapeutic approaches in ASD.

Destruction of ERP responses to deviance in an auditory oddball paradigm in amyloid infusion mice with memory deficits

The amyloid-β (Aβ) oligomer is considered one of the major pathogens responsible for neuronal and synaptic loss in Alzheimer’s disease (AD) brains. Although the neurotoxic mechanisms of Aβ have been widely investigated, experimental evidence for the direct linkage between neural signaling and cognitive impairments in association with peptide oligomers is lacking. Here, we conducted an auditory oddball paradigm utilizing an Aβ-infused Alzheimer’s disease mouse model and interpreted the results based on Y-maze behavioral tests. We acutely injected Aβ oligomers into the intracerebroventricular brain region of normal mice to induce Aβ-associated cognitive impairments. During the auditory oddball paradigm, electroencephalograms (EEG) were recorded from frontal and parietal cortex of Aβ-infused and control mice. The event-related potentials (ERPs) elicited by auditory stimuli showed no significant difference in Aβ-infused mice compared to control mice. On the other hand, the differential ERP signature elicited by oddball sound stimuli was destructed in the Aβ-infused mice group. We noticed that ERP traces to standard and deviant tones were not significantly different in the Aβ group, while the control group showed differences in the amplitude of ERP components. In particular, the difference in the first negative component (N1) between standard and deviant tone, which indexes the sensory memory system, was significantly reduced in the parietal cortex of Aβ-infused mice. These findings demonstrate the direct influence of Aβ oligomers on the functional integrity of cortical areas in vivo. Furthermore, the N1 amplitude difference may provide a potential marker of sensory memory deficits in a mouse model of AD and yield additional targets for drug assessment in AD.

Src deficient mice demonstrate behavioral and electrophysiological alterations relevant to psychiatric and developmental disease

Much evidence suggests that hypofunction of the N-methyl-d-aspartate glutamate receptor (NMDAR) may contribute broadly towards a subset of molecular, cognitive and behavioral abnormalities common among psychiatric and developmental diseases. However, little is known about the specific molecular changes that lead to NMDAR dysfunction. As such, personalized approaches to remediating NMDAR dysfunction based on a specific etiology remains a challenge. Sarcoma tyrosine kinase (Src) serves as a hub for multiple signaling mechanisms affecting GluN2 phosphorylation and can be disrupted by convergent alterations of various signaling pathways. We recently showed reduced Src signaling in post mortem tissue from schizophrenia patients, despite increased MK-801 binding and NMDA receptor complex expression in the postsynaptic density (PSD). These data suggest that Src dysregulation may be an important underlying mechanism responsible for reduced glutamate signaling. Despite this evidence for a central role of Src in NMDAR signaling, little is known about how reductions in Src activity might regulate phenotypic changes in cognition and behavior. As such, the current study sought to characterize behavioral and electrophysiological phenotypes in mice heterozygous for the Src Acl gene (Src+/- mice). Src+/- mice demonstrated decreased sociability and working memory relative to Src+/+ (WT) mice while no significant differences were seen on locomotive activity and anxiety-related behavior. In relation to WT mice, Src+/- mice showed decreased mid-latency P20 auditory event related potential (aERP) amplitudes, decreased mismatch negativity (MMN) and decreased evoked gamma power, which was only present in males. These data indicate that Src+/- mice are a promising new model to help understand the pathophysiology of these electrophysiological, behavioral and cognitive changes. As such, we propose that Src+/- mice can be used in the future to evaluate potential therapeutic approaches by targeting increased Src activity as a common final pathway for multiple etiologies of SCZ and other diseases characterized by reduced glutamate function.

Effect of age onset on schizophrenia-like phenotypes and underlying mechanisms in model mice

In humans, schizophrenia with onset in adolescence or adult has distinct features. To understand whether schizophrenia with either adolescence- or adult-onset have distinct phenotypes and cellular mechanisms in schizophrenia model mice, we altered Nrg1 signaling during either adolescence or adult mice via injection of anti-Nrg1 antibodies. We found that in either early-onset schizophrenia (EOS)- or late-onset schizophrenia (LOS)-like mice, certain behavior phenotypes are shared including hyperlocomotion, impaired working memory and impaired fear conditioning. Anxiety appears to be largely unaffected. In vitro electrophysiology in brain slices showed altered excitation/inhibition balance in EOS-like mice towards enhanced synaptic excitation, but intrinsic excitability of the fast-spiking GABAergic neurons was elevated in the LOS-like mice. Thus, although schizophrenia-like main phenotypes appear to be preserved in both age onset model mice, there are distinct differences in cellular mechanisms between them. We suggest that these differences are important for more precise diagnosis and more effective treatment of schizophrenia.

Nrg1 deficiency modulates the behavioural effects of prenatal stress in mice

Little is known about the exact genes that confer vulnerability or resilience to environmental stressors during early neurodevelopment. Partial genetic deletion of neuregulin 1 (Nrg1) moderates the neurobehavioural effects of stressors applied in adolescence and adulthood, however, no study has yet examined its impact on prenatal stress. Here we examined whether Nrg1 deficiency in mice modulated the impact of prenatal stress on various behaviours in adulthood. Male heterozygous Nrg1 mice were mated with wild-type female mice who then underwent daily restraint stress from days 13 to 19 of gestation. Surprisingly, prenatal stress had overall beneficial effects by facilitating sensorimotor gating, increasing sociability, decreasing depressive-like behaviour, and improving spatial memory in adulthood. Such benefits were not due to any increase in maternal care, as prenatal stress decreased nurturing of the offspring. Nrg1 deficiency negated the beneficial behavioural effects of prenatal stress on all measures except sociability. However, Nrg1 deficiency interacted with prenatal stress to trigger locomotor hyperactivity. Nrg1 deficiency, prenatal stress or their combination failed to alter acute stress-induced plasma corticosterone concentrations. Collectively these results demonstrate that Nrg1 deficiency moderates the effects of prenatal stress on adult behaviour, but it does so in a complex, domain-specific fashion.

Abnormal auditory mismatch fields in adults with autism spectrum disorder

The auditory mismatch field (MMF) is a pre-attentive processing component, reflecting neural discrimination and inhibitory processing. Abnormal MMFs have been reported in children with autism spectrum disorder (ASD) along with an association with abnormal language comprehension; however, relatively little is known about MMF abnormalities to contrasting vowel stimuli in adults with ASD. To better understand the neurophysiological mechanisms underlying auditory language discrimination of vowel stimuli in individuals with ASD, magnetoencephalography was used to measure MMFs during an auditory oddball paradigm with vowel stimuli (/a/ and /u/) in adults with ASD. MMFs arising from left and right superior temporal gyrus are reported from nine high-functioning right handed males with ASD (22.22 ± 5.74yrs) and sixteen typically developing (TD) right handed males (27.25 ± 6.63yrs). The MMF was delayed in adults with ASD (188.90 ± 5.8 ms) as compared to the TD participants (173.08 ± 4.31 ms, p < 0.05). Replicating previous findings in children, the earlier M100 component to single stimulus tokens was also delayed in adults with ASD (108.59 ± 4.1 ms) compared to the TD participants (94.60 ± 3.0 ms, p < 0.05). However, there was no correlation between delayed M100 latency and MMF latency. Furthermore, whereas TD participants showed a leftward lateralization of MMF amplitude, participants with ASD showed an opposite (rightward) lateralization. Findings suggest that adults with ASD have hemispherically- and temporally- abnormal auditory discrimination processing in addition to and distinct from abnormal neurophysiological mechanisms in earlier cortical responses.

Toward the Language Oscillogenome

Language has been argued to arise, both ontogenetically and phylogenetically, from specific patterns of brain wiring. We argue that it can further be shown that core features of language processing emerge from particular phasal and cross-frequency coupling properties of neural oscillations; what has been referred to as the language ‘oscillome.’ It is expected that basic aspects of the language oscillome result from genetic guidance, what we will here call the language ‘oscillogenome,’ for which we will put forward a list of candidate genes. We have considered genes for altered brain rhythmicity in conditions involving language deficits: autism spectrum disorders, schizophrenia, specific language impairment and dyslexia. These selected genes map on to aspects of brain function, particularly on to neurotransmitter function. We stress that caution should be adopted in the construction of any oscillogenome, given the range of potential roles particular localized frequency bands have in cognition. Our aim is to propose a set of genome-to-language linking hypotheses that, given testing, would grant explanatory power to brain rhythms with respect to language processing and evolution.

Altered hippocampal gene expression and structure in transgenic mice overexpressing neuregulin 1 (Nrg1) type I

Transgenic mice overexpressing the type I isoform of neuregulin 1 (Nrg1; NRG1) have alterations in hippocampal gamma oscillations and an age-emergent deficit in hippocampus-dependent spatial working memory. Here, we examined the molecular and morphological correlates of these findings. Microarrays showed over 100 hippocampal transcripts differentially expressed in Nrg1^{tg-type I} mice, with enrichment of genes related to neuromodulation and, in older mice, of genes involved in inflammation and immunity. Nrg1^{tg-type I} mice had an enlarged hippocampus with a widened dentate gyrus. The results show that Nrg1 type I impacts on hippocampal gene expression and structure in a multifaceted and partly age-related way, complementing the evidence implicating Nrg1 signaling in aspects of hippocampal function. The findings are also relevant to the possible role of NRG1 signaling in the pathophysiology of schizophrenia or other disorders affecting this brain region.

Overexpression of Neuregulin 1 Type III Confers Hippocampal mRNA Alterations and Schizophrenia-Like Behaviors in Mice

Neuregulin 1 (NRG1) is a schizophrenia candidate gene whose protein product is involved in neuronal migration, survival, and synaptic plasticity via production of specific isoforms. Importantly, NRG1 type III (NRG1 III) mRNA is increased in humans inheriting a schizophrenia risk haplotype for the NRG1 gene (HapICE), and NRG1 protein levels can be elevated in schizophrenia. The nature by which NRG1 type III overexpression results in schizophrenia-like behavior and brain pathology remains unclear, therefore we constructed a transgenic mouse with Nrg1 III overexpression in forebrain neurons (CamKII kinase+). Here, we demonstrate construct validity for this mouse model, as juvenile and adult Nrg1 III transgenic mice exhibit an overexpression of Nrg1 III mRNA and Nrg1 protein in multiple brain regions. Furthermore, Nrg1 III transgenic mice have face validity as they exhibit schizophrenia-relevant behavioral phenotypes including deficits in social preference, impaired fear-associated memory, and reduced prepulse inhibition. Additionally, microarray assay of hippocampal mRNA uncovered transcriptional alterations downstream of Nrg1 III overexpression, including changes in serotonin receptor 2C and angiotensin-converting enzyme. Transgenic mice did not exhibit other schizophrenia-relevant behaviors including hyperactivity, social withdrawal, or an increased vulnerability to the effects of MK-801 malate. Our results indicate that this novel Nrg1 III mouse is valid for modeling potential pathological mechanisms of some schizophrenia-like behaviors, for determining what other neurobiological changes may be downstream of elevated NRG1 III levels and for preclinically testing therapeutic strategies that may be specifically efficacious in patients with the NRG1 (HapICE) risk genotype.

Mismatch negativity in preclinical models of schizophrenia

Schizophrenia is a mental disorder associated with profoundly disruptive positive and negative symptomology that result in difficulties building close relationships with others, performing daily tasks and sustaining independent living, resulting in poor social, vocational and occupational attainment (functional outcome). Mismatch Negativity (MMN) is a change in the sensory event-related potential that occurs in response to deviation from an established pattern of stimulation. Patients with schizophrenia show a reduction in MMN that is positively associated with impaired cognition and poor functional outcome. This has led to interest in MMN as a potential clinical and pre-clinical biomarker of fundamental neural processes responsible for reduced functional outcome. To date, relatively few studies have sought to assess MMN in non-human primates or rodents. The validity of these studies will be reviewed using criteria used to identify true deviance detection based MMN responses in human subjects. Although MMN has been difficult to establish in pre-clinical models the weight of evidence suggests that non-human animals show true deviance based MMN.

Delayed Mismatch Field Latencies in Autism Spectrum Disorder with Abnormal Auditory Sensitivity: A Magnetoencephalographic Study

Although abnormal auditory sensitivity is the most common sensory impairment associated with autism spectrum disorder (ASD), the neurophysiological mechanisms remain unknown. In previous studies, we reported that this abnormal sensitivity in patients with ASD is associated with delayed and prolonged responses in the auditory cortex. In the present study, we investigated alterations in residual M100 and MMFs in children with ASD who experience abnormal auditory sensitivity. We used magnetoencephalography (MEG) to measure MMF elicited by an auditory oddball paradigm (standard tones: 300 Hz, deviant tones: 700 Hz) in 20 boys with ASD (11 with abnormal auditory sensitivity: mean age, 9.62 ± 1.82 years, 9 without: mean age, 9.07 ± 1.31 years) and 13 typically developing boys (mean age, 9.45 ± 1.51 years). We found that temporal and frontal residual M100/MMF latencies were significantly longer only in children with ASD who have abnormal auditory sensitivity. In addition, prolonged residual M100/MMF latencies were correlated with the severity of abnormal auditory sensitivity in temporal and frontal areas of both hemispheres. Therefore, our findings suggest that children with ASD and abnormal auditory sensitivity may have atypical neural networks in the primary auditory area, as well as in brain areas associated with attention switching and inhibitory control processing. This is the first report of an MEG study demonstrating altered MMFs to an auditory oddball paradigm in patients with ASD and abnormal auditory sensitivity. These findings contribute to knowledge of the mechanisms for abnormal auditory sensitivity in ASD, and may therefore facilitate development of novel clinical interventions.

Behavioral abnormalities with disruption of brain structure in mice overexpressing VGF

VGF nerve growth factor inducible (VGF) is a neuropeptide induced by nerve growth factor and brain-derived neurotrophic factor. This peptide is involved in synaptic plasticity, neurogenesis, and neurite growth in the brain. Patients with depression and bipolar disorder have lower-than-normal levels of VGF, whereas patients with schizophrenia and other cohorts of patients with depression have higher-than-normal levels. VGF knockout mice display behavioral abnormalities such as higher depressive behavior and memory dysfunction. However, it is unclear whether upregulation of VGF affects brain function. In the present study, we generated mice that overexpress VGF and investigated several behavioral phenotypes and the brain structure. These adult VGF-overexpressing mice showed (a) hyperactivity, working memory impairment, a higher depressive state, and lower sociality compared with wild-type mice; (b) lower brain weight without a change in body weight; (c) increased lateral ventricle volume compared with wild-type mice; and (d) striatal morphological defects. These results suggest that VGF may modulate a variety of behaviors and brain development. This transgenic mouse line may provide a useful model for research on mental illnesses.

ErbB4 signaling in the prelimbic cortex regulates fear expression

Many psychiatric diseases such as post-traumatic stress disorder (PTSD) are characterized by abnormal processing of emotional stimuli particularly fear. The medial prefrontal cortex (mPFC) is critically involved in fear expression. However, the molecular mechanisms underlying this process are largely unknown. Neuregulin-1 (NRG1) reportedly regulates pyramidal neuronal activity via ErbB4 receptors, which are abundant in parvalbumin (PV)-expressing interneurons in the PFC. In this study, we aimed to determine how NRG1/ErbB4 signaling in the mPFC modulates fear expression and found that tone-cued fear conditioning increased NRG1 expression in the mPFC. Tone-cued fear conditioning was inhibited following neutralization of endogenous NRG1 and specific inhibition or genetic ablation of ErbB4 in the prelimbic (PL) cortex but not in the infralimbic cortex. Furthermore, ErbB4 deletion specifically in PV neurons impaired tone-cued fear conditioning. Notably, overexpression of ErbB4 in the PL cortex is sufficient to reverse impaired fear conditioning in PV-Cre;ErbB4^-/- mice. Together, these findings identify a previously unknown signaling pathway in the PL cortex that regulates fear expression. As both NRG1 and ErbB4 are risk genes for schizophrenia, our study may shed new light on the pathophysiology of this disorder and help to improve treatments for psychiatric disorders such as PTSD.

Ablation of neuropsin-neuregulin 1 signaling imbalances ErbB4 inhibitory networks and disrupts hippocampal gamma oscillation

Parvalbumin-expressing interneurons are pivotal for the processing of information in healthy brain, whereas the coordination of these functions is seriously disrupted in diseased brain. How these interneurons in the hippocampus participate in pathological functions remains unclear. We previously reported that neuregulin 1 (NRG1)-ErbB4 signaling, which is actuated by neuropsin, is important for coordinating brain plasticity. Neuropsin cleaves mature NRG1 (bound to extracellular glycosaminoglycans) in response to long-term potentiation or depression, liberating a soluble ligand that activates its receptor, ErbB4. Here, we show in mice that kainate-induced status epilepticus transiently elevates the proteolytic activity of neuropsin and stimulates cFos expression with a time course suggesting that activation of ErbB4- and parvalbumin-expressing interneurons follows the excitation and subsequent silencing of pyramidal neurons. In neuropsin-deficient mice, kainate administration impaired signaling and disrupted the neuronal excitation-inhibition balance (E/I balance) in hippocampal networks, by decreasing the activity of parvalbumin-positive interneurons while increasing that of pyramidal neurons, resulting in the progression of status epilepticus. Slow, but not fast, gamma oscillations in neuropsin-deficient mice showed reduced power. Intracerebroventricular infusion of the soluble NRG1 ligand moiety restored the E/I balance, status epilepticus and gamma oscillations to normal levels. These results suggest that the neuropsin-NRG1 signaling system has a role in pathological processes underlying temporal lobe epilepsy by regulating the activity of parvalbumin-expressing interneurons, and that neuropsin regulates E/I balance and gamma oscillations through NRG1-ErbB4 signaling toward parvalbumin-expressing interneurons. This neuronal system may be a useful target of pharmacological therapies against cognitive disorders.

Sociability Deficits and Altered Amygdala Circuits in Mice Lacking Pcdh10, an Autism Associated Gene

BACKGROUND

Behavioral symptoms in individuals with autism spectrum disorder (ASD) have been attributed to abnormal neuronal connectivity, but the molecular bases of these behavioral and brain phenotypes are largely unknown. Human genetic studies have implicated PCDH10, a member of the δ2 subfamily of nonclustered protocadherin genes, in ASD. PCDH10 expression is enriched in the basolateral amygdala, a brain region implicated in the social deficits of ASD. Previous reports indicate that Pcdh10 plays a role in axon outgrowth and glutamatergic synapse elimination, but its roles in social behaviors and amygdala neuronal connectivity are unknown. We hypothesized that haploinsufficiency of Pcdh10 would reduce social approach behavior and alter the structure and function of amygdala circuits.

METHODS

Mice lacking one copy of Pcdh10 (Pcdh10^+/-) and wild-type littermates were assessed for social approach and other behaviors. The lateral/basolateral amygdala was assessed for dendritic spine number and morphology, and amygdala circuit function was studied using voltage-sensitive dye imaging. Expression of Pcdh10 and N-methyl-D-aspartate receptor (NMDAR) subunits was assessed in postsynaptic density fractions of the amygdala.

RESULTS

Male Pcdh10^+/- mice have reduced social approach behavior, as well as impaired gamma synchronization, abnormal spine morphology, and reduced levels of NMDAR subunits in the amygdala. Social approach deficits in Pcdh10^+/- male mice were rescued with acute treatment with the NMDAR partial agonist d-cycloserine.

CONCLUSIONS

Our studies reveal that male Pcdh10^+/- mice have synaptic and behavioral deficits, and establish Pcdh10^+/- mice as a novel genetic model for investigating neural circuitry and behavioral changes relevant to ASD.

Neuregulin-1 mutant mice indicate motor and sensory deficits, indeed few references for schizophrenia endophenotype model

Neuregulins (Nrg) are a gene family that binds to tyrosine kinase receptors of the ErbB family. The protein of Nrg1 is to be involved in heart formation, migration of neurons, axonal pathfinding and synaptic function. A relation between Nrg1 and schizophrenia is assumed. Chronic impairment in schizophrenia is characterized by different positive and negative symptoms. Detectable markers of this disease in human and in animal models are activity, social behavior and sensory processing. In this study we compared heterozygous Nrg1 mutant mice in behavior and quantification of dopaminergic and serotoninergic neurons with wild type-like littermates. In the Nrg1 mutant mice the epidermal growth factor-like domain is replaced by the neomycin resistance gene. We found significant differences in locomotor and pain perception behavior. No differences were found in specific schizophrenia social interaction and prepulse inhibition behavior. The number of dopaminergic and serotoninergic neurons did not differ in the investigated regions ventral tegmental area, substantia nigra, periaqueductal grey and raphe nuclei. In conclusion, this analyzed Nrg1 mutant mice model did not serve as a complete schizophrenia model. Particular aspects of schizophrenia disease in locomotor and sensory behavior deficits could represent in this Nrg1 mutant mice. Beside several different models could Nrg1 deficiency represent an endophenotype of schizophrenia disease.

GABA-B Agonist Baclofen Normalizes Auditory-Evoked Neural Oscillations and Behavioral Deficits in the Fmr1 Knockout Mouse Model of Fragile X Syndrome

Fragile X syndrome is a genetic condition resulting from FMR1 gene mutation that leads to intellectual disability, autism-like symptoms, and sensory hypersensitivity. Arbaclofen, a GABA-B agonist, has shown efficacy in some individuals with FXS but has become unavailable after unsuccessful clinical trials, prompting interest in publicly available, racemic baclofen. The present study investigated whether racemic baclofen can remediate abnormalities of neural circuit function, sensory processing, and behavior in Fmr1 knockout mice, a rodent model of fragile X syndrome. Fmr1 knockout mice showed increased baseline and auditory-evoked high-frequency gamma (30-80 Hz) power relative to C57BL/6 controls, as measured by electroencephalography. These deficits were accompanied by decreased T maze spontaneous alternation, decreased social interactions, and increased open field center time, suggestive of diminished working memory, sociability, and anxiety-like behavior, respectively. Abnormal auditory-evoked gamma oscillations, working memory, and anxiety-related behavior were normalized by treatment with baclofen, but impaired sociability was not. Improvements in working memory were evident predominantly in mice whose auditory-evoked gamma oscillations were dampened by baclofen. These findings suggest that racemic baclofen may be useful for targeting sensory and cognitive disturbances in fragile X syndrome.

The dysconnection hypothesis (2016)

Twenty years have passed since the dysconnection hypothesis was first proposed (Friston and Frith, 1995; Weinberger, 1993). In that time, neuroscience has witnessed tremendous advances: we now live in a world of non-invasive neuroanatomy, computational neuroimaging and the Bayesian brain. The genomics era has come and gone. Connectomics and large-scale neuroinformatics initiatives are emerging everywhere. So where is the dysconnection hypothesis now? This article considers how the notion of schizophrenia as a dysconnection syndrome has developed - and how it has been enriched by recent advances in clinical neuroscience. In particular, we examine the dysconnection hypothesis in the context of (i) theoretical neurobiology and computational psychiatry; (ii) the empirical insights afforded by neuroimaging and associated connectomics - and (iii) how bottom-up (molecular biology and genetics) and top-down (systems biology) perspectives are converging on the mechanisms and nature of dysconnections in schizophrenia.

Neuregulin 3 Knockout Mice Exhibit Behaviors Consistent with Psychotic Disorders

Neuregulin 3 (NRG3) is a paralog of NRG1. Genetic studies in schizophrenia demonstrate that risk variants in NRG3 are associated with cognitive and psychotic symptom severity, and several intronic single nucleotide polymorphisms in NRG3 are associated with delusions in patients with schizophrenia. In order to gain insights into the biological function of the gene, we generated a novel Nrg3 knockout (KO) mouse model and tested for neurobehavioral phenotypes relevant to psychotic disorders. KO mice displayed novelty-induced hyperactivity, impaired prepulse inhibition of the acoustic startle response, and deficient fear conditioning. No gross cytoarchitectonic or layer abnormalities were noted in the brain of KO mice. Our findings suggest that deletion of the Nrg3 gene leads to alterations consistent with aspects of schizophrenia. We propose that KO mice will provide a valuable animal model to determine the role of the NRG3 in the molecular pathogenesis of schizophrenia and other psychotic disorders.

Molecular genetic models related to schizophrenia and psychotic illness: heuristics and challenges

Schizophrenia is a heritable disorder that may involve several common genes of small effect and/or rare copy number variation, with phenotypic heterogeneity across patients. Furthermore, any boundaries vis-à-vis other psychotic disorders are far from clear. Consequently, identification of informative animal models for this disorder, which typically relate to pharmacological and putative pathophysiological processes of uncertain validity, faces considerable challenges. In juxtaposition, the majority of mutant models for schizophrenia relate to the functional roles of a diverse set of genes associated with risk for the disorder or with such putative pathophysiological processes. This chapter seeks to outline the evidence from phenotypic studies in mutant models related to schizophrenia. These have commonly assessed the degree to which mutation of a schizophrenia-related gene is associated with the expression of several aspects of the schizophrenia phenotype or more circumscribed, schizophrenia-related endophenotypes; typically, they place specific emphasis on positive and negative symptoms and cognitive deficits, and extend to structural and other pathological features. We first consider the primary technological approaches to the generation of such mutants, to include their relative merits and demerits, and then highlight the diverse phenotypic approaches that have been developed for their assessment. The chapter then considers the application of mutant phenotypes to study pathobiological and pharmacological mechanisms thought to be relevant for schizophrenia, particularly in terms of dopaminergic and glutamatergic dysfunction, and to an increasing range of candidate susceptibility genes and copy number variants. Finally, we discuss several pertinent issues and challenges within the field which relate to both phenotypic evaluation and a growing appreciation of the functional genomics of schizophrenia and the involvement of gene × environment interactions.

Oxytocin reduces amygdala activity, increases social interactions, and reduces anxiety-like behavior irrespective of NMDAR antagonism

Standard dopamine therapies for schizophrenia are not efficacious for negative symptoms of the disease, including asociality. This reduced social behavior may be due to glutamatergic dysfunction within the amygdala, leading to increased fear and social anxiety. Several studies have demonstrated the prosocial effects of oxytocin in schizophrenia patients. Therefore, this study evaluates the effect of subchronic oxytocin on EEG activity in amygdala of mice during performance of the three-chamber social choice and open field tests following acute ketamine as a model of glutamatergic dysfunction. Oxytocin did not restore social deficits introduced by ketamine but did significantly increase sociality in comparison to the control group. Ketamine had no effect on time spent in the center during the open field trials, whereas oxytocin increased overall center time across all groups, suggesting a reduction in anxiety. Amygdala activity was consistent across all drug groups during social and nonsocial behavioral trials. However, oxytocin reduced overall amygdala EEG power during the two behavioral tasks. Alternatively, ketamine did not significantly affect EEG power throughout the tasks. Decreased EEG power in the amygdala, as caused by oxytocin, may be related to both reduced anxiety and increased social behaviors. Data suggest that separate prosocial and social anxiety pathways may mediate social preference.

Electrophysiological Endophenotypes for Schizophrenia

Endophenotypes are quantitative, heritable traits that may help to elucidate the pathophysiologic mechanisms underlying complex disease syndromes, such as schizophrenia. They can be assessed at numerous levels of analysis; here, we review electrophysiological endophenotypes that have shown promise in helping us understand schizophrenia from a more mechanistic point of view. For each endophenotype, we describe typical experimental procedures, reliability, heritability, and reported gene and neurobiological associations. We discuss recent findings regarding the genetic architecture of specific electrophysiological endophenotypes, as well as converging evidence from EEG studies implicating disrupted balance of glutamatergic signaling and GABAergic inhibition in the pathophysiology of schizophrenia. We conclude that refining the measurement of electrophysiological endophenotypes, expanding genetic association studies, and integrating data sets are important next steps for understanding the mechanisms that connect identified genetic risk loci for schizophrenia to the disease phenotype.

Altered resonance properties of somatosensory responses in mice deficient for the schizophrenia risk gene Neuregulin 1

To reveal the neuronal underpinnings of sensory processing deficits in patients with schizophrenia, previous studies have investigated brain activity in response to sustained sensory stimulation at various frequencies. This paradigm evoked neural activity at the stimulation frequency and harmonics thereof. During visual and auditory stimulation that elicited enhanced or 'resonant' responses in healthy controls, patients with schizophrenia displayed reduced activity. The present study sought to elucidate the cellular basis of disease-related deficits in sensory resonance properties using mice heterozygous for the schizophrenia susceptibility gene Neuregulin 1 (NRG1). We applied repetitive whisker stimulation at 1-15 Hz, a range relevant to whisking behavior in mice, and measured cellular activity in the primary somatosensory cortex. At frequencies where control mice displayed enhancements in measures of response magnitude and precision, NRG1 (+/-) mutants showed reductions. Our results demonstrate for the first time a link between a mutation of a schizophrenia risk gene and altered neuronal resonance properties in sensory cortex.

Neuronal migration abnormalities and its possible implications for schizophrenia

Schizophrenia is a complex mental disorder that displays behavioral deficits such as decreased sensory gating, reduced social interaction and working memory deficits. The neurodevelopmental model is one of the widely accepted hypotheses of the etiology of schizophrenia. Subtle developmental abnormalities of the brain which stated long before the onset of clinical symptoms are thought to lead to the emergence of illness. Schizophrenia has strong genetic components but its underlying molecular pathogenesis is still poorly understood. Genetic linkage and association studies have identified several genes involved in neuronal migrations as candidate susceptibility genes for schizophrenia, although their effect size is small. Recent progress in copy number variation studies also has identified much higher risk loci such as 22q11. Based on these genetic findings, we are now able to utilize genetically-defined animal models. Here we summarize the results of neurodevelopmental and behavioral analysis of genetically-defined animal models. Furthermore, animal model experiments have demonstrated that embryonic and perinatal neurodevelopmental insults in neurogenesis and neuronal migrations cause neuronal functional and behavioral deficits in affected adult animals, which are similar to those of schizophrenic patients. However, these findings do not establish causative relationship. Genetically-defined animal models are a critical approach to explore the relationship between neuronal migration abnormalities and behavioral abnormalities relevant to schizophrenia.

Reverse translation of clinical electrophysiological biomarkers in behaving rodents under acute and chronic NMDA receptor antagonism

Electroencephalogram (EEG) stands out as a highly translational tool for psychiatric research, yet rodent and human EEG are not typically obtained in the same way. In this study we developed a tool to record skull EEG in awake-behaving rats in a similar manner to how human EEG are obtained and then used this technique to test whether acute NMDA receptor antagonism alters rodent EEG signals in a similar manner as in humans. Acute MK-801 treatment elevated gamma power and reduced beta band power, which closely mirrored EEG data from healthy volunteers receiving acute ketamine. To explore the mechanisms behind these oscillatory changes, we examined the effects of GABA-A receptor blockade, finding that picrotoxin (PTX) recapitulated the decrease in sound-evoked beta oscillations observed with acute MK-801, but did not produce changes in gamma band power. Chronic treatment with either PTX or MK-801 did not affect frequency-specific oscillatory activity when tested 24 h after the last drug injection, but decreased total broadband oscillatory power. Overall, this study validated a novel platform for recording rodent EEG and demonstrated similar oscillatory changes after acute NMDA receptor antagonism in both humans and rodents, suggesting that skull EEG may be a powerful tool for further translational studies.

Mismatch negativity (MMN) deficiency: a break-through biomarker in predicting psychosis onset

Currently, the mismatch negativity (MMN) deficit is one of the most robust and replicable findings in schizophrenia, reflecting cognitive and functional decline, psychosocial and socio-occupational impairment, and executive dysfunction in these patients. An important break-through has very recently taken place here in the prediction of conversion to psychosis when the MMN in particular to change in tone duration was recorded in clinically at risk-mental state (ARMS) individuals. Attenuations in the MMN in these patients may be very useful in helping clinicians determine who are most likely to develop a psychotic disorder, as we will review in the present article.

Perinatal asphyxia alters neuregulin-1 and COMT gene expression in the medial prefrontal cortex in rats

Epidemiological studies suggest that perinatal complications, particularly hypoxia-related ones, increase the risk of schizophrenia. Recent genetic studies of the disorder have identified several putative susceptibility genes, some of which are known to be regulated by hypoxia. It can be postulated therefore that birth complications that cause hypoxia in the fetal brain may be associated with a dysregulation in the expression of some of the schizophrenia candidate genes. To test this, we used an animal model of perinatal asphyxia, in which rat pups were exposed to 15 min of intrauterine anoxia during Caesarean section birth, and examined the expression of mRNA of five of the putative susceptibility genes (NRG1, ErbB4, AKT1, COMT and BDNF) by real-time quantitative PCR in the medial prefrontal cortex (mPFC) and the hippocampus at 6 and 12 weeks after birth. The expression of NRG1 mRNA was significantly decreased in the mPFC, but not in the hippocampus, at 6 and 12 weeks after birth. In addition, a significant increase in COMT mRNA expression was observed in the mPFC at 12 weeks. The alteration in mRNA levels of NRG1 and COMT was not associated with a change in their protein levels. These results suggest that perinatal asphyxia may lead to disturbances in the PFC, which in turn may exert a long-lasting influence on the expression of specific genes, such as NRG1 and COMT. Our results also suggest that translational interruption may occur in this model of perinatal asphyxia.

Schizophrenia and Depression Co-Morbidity: What We have Learned from Animal Models

Patients with schizophrenia are at an increased risk for the development of depression. Overlap in the symptoms and genetic risk factors between the two disorders suggests a common etiological mechanism may underlie the presentation of comorbid depression in schizophrenia. Understanding these shared mechanisms will be important in informing the development of new treatments. Rodent models are powerful tools for understanding gene function as it relates to behavior. Examining rodent models relevant to both schizophrenia and depression reveals a number of common mechanisms. Current models which demonstrate endophenotypes of both schizophrenia and depression are reviewed here, including models of CUB and SUSHI multiple domains 1, PDZ and LIM domain 5, glutamate Delta 1 receptor, diabetic db/db mice, neuropeptide Y, disrupted in schizophrenia 1, and its interacting partners, reelin, maternal immune activation, and social isolation. Neurotransmission, brain connectivity, the immune system, the environment, and metabolism emerge as potential common mechanisms linking these models and potentially explaining comorbid depression in schizophrenia.

Sleep and circadian rhythm disruption and recognition memory in schizophrenia

Schizophrenia patients often show irregularities in sleep and circadian rhythms and deficits in recognition memory. Similar phenotypes are seen in schizophrenia-relevant genetic mouse models, such as synaptosomal associated protein of 25 kDa (Snap-25) point mutant mice, vasoactive intestinal peptide receptor 2 (Vipr2) knockout mice, and neuregulin 1 (Nrg1)-deficient mice. Sleep and circadian abnormalities and impaired recognition memory may be causally related in both schizophrenia patients and schizophrenia-relevant mouse models, since sleep deprivation, abnormal photic input, and the manipulation of core clock genes (cryptochrome 1/2) can all disrupt object recognition memory in rodent models. The recognition deficits observed in patients and mouse models (both schizophrenia-related and -unrelated) are discussed here in terms of the dual-process theory of recognition, which postulates that there are two recognition mechanisms-recollection versus familiarity-that can be selectively impaired by brain lesions, neuropsychiatric conditions, and putatively, sleep and circadian rhythm disruption. However, based on this view, the findings from patient studies and studies using genetic mouse models (Nrg1 deficiency) seem to be inconsistent with each other. Schizophrenia patients are impaired at recollection (and to a lesser extent, familiarity judgments), but Nrg1-deficient mice are impaired at familiarity-based object recognition, raising concerns regarding the validity of using these genetically modified mice to model recognition phenotypes observed in patients. This issue can be resolved in future animal studies by examining performance in different variants of the spontaneous recognition task-the standard, perirhinal cortex-dependent, object recognition task versus the hippocampus-dependent object-place recognition task-in order to see which of the two recognition mechanisms is more disrupted.

Sensory encoding in Neuregulin 1 mutants

Schizophrenic patients show altered sensory perception as well as changes in electrical and magnetic brain responses to sustained, frequency-modulated sensory stimulation. Both the amplitude and temporal precision of the neural responses differ in patients as compared to control subjects, and these changes are most pronounced for stimulation at gamma frequencies (20-40 Hz). In addition, patients display enhanced spontaneous gamma oscillations, which has been interpreted as 'neural noise' that may interfere with normal stimulus processing. To investigate electrophysiological markers of aberrant sensory processing in a model of schizophrenia, we recorded neuronal activity in primary somatosensory cortex of mice heterozygous for the schizophrenia susceptibility gene Neuregulin 1. Sensory responses to sustained 20-70 Hz whisker stimulation were analyzed with respect to firing rates, spike precision (phase locking) and gamma oscillations, and compared to baseline conditions. The mutants displayed elevated spontaneous firing rates, a reduced gain in sensory-evoked spiking and gamma activity, and reduced spike precision of 20-40 Hz responses. These findings present the first in vivo evidence of the linkage between a genetic marker and altered stimulus encoding, thus suggesting a novel electrophysiological endophenotype of schizophrenia.

Synaptic plasticity, neural circuits, and the emerging role of altered short-term information processing in schizophrenia

Synaptic plasticity alters the strength of information flow between presynaptic and postsynaptic neurons and thus modifies the likelihood that action potentials in a presynaptic neuron will lead to an action potential in a postsynaptic neuron. As such, synaptic plasticity and pathological changes in synaptic plasticity impact the synaptic computation which controls the information flow through the neural microcircuits responsible for the complex information processing necessary to drive adaptive behaviors. As current theories of neuropsychiatric disease suggest that distinct dysfunctions in neural circuit performance may critically underlie the unique symptoms of these diseases, pathological alterations in synaptic plasticity mechanisms may be fundamental to the disease process. Here we consider mechanisms of both short-term and long-term plasticity of synaptic transmission and their possible roles in information processing by neural microcircuits in both health and disease. As paradigms of neuropsychiatric diseases with strongly implicated risk genes, we discuss the findings in schizophrenia and autism and consider the alterations in synaptic plasticity and network function observed in both human studies and genetic mouse models of these diseases. Together these studies have begun to point toward a likely dominant role of short-term synaptic plasticity alterations in schizophrenia while dysfunction in autism spectrum disorders (ASDs) may be due to a combination of both short-term and long-term synaptic plasticity alterations.

Neuregulin-ERBB signaling in the nervous system and neuropsychiatric diseases

Neuregulins (NRGs) comprise a large family of growth factors that stimulate ERBB receptor tyrosine kinases. NRGs and their receptors, ERBBs, have been identified as susceptibility genes for diseases such as schizophrenia (SZ) and bipolar disorder. Recent studies have revealed complex Nrg/Erbb signaling networks that regulate the assembly of neural circuitry, myelination, neurotransmission, and synaptic plasticity. Evidence indicates there is an optimal level of NRG/ERBB signaling in the brain and deviation from it impairs brain functions. NRGs/ERBBs and downstream signaling pathways may provide therapeutic targets for specific neuropsychiatric symptoms.

Genetically modified mice related to schizophrenia and other psychoses: seeking phenotypic insights into the pathobiology and treatment of negative symptoms

Modelling negative symptoms in any animal model, particularly in mice mutant for genes related to schizophrenia, is complicated by the absence of the following key elements that might assist in developing validation criteria: clinical clarity surrounding this symptom constellation; any clear association between negative symptoms and pathological signature(s) in the brain; and therapeutic strategies with material clinical efficacy against these symptoms. In this review, the application of mutant mouse models to the study of negative symptoms is subjected to critical evaluation, focussing on the following challenges: (a) conceptual issues relating to negative symptoms and their evaluation in mutant models; (b) measurement of negative symptoms in mice, in terms of social behaviour, motivational deficits/avolition and anhedonia; (c) studies in mutants with disruption of genes either regulating aspects of neurotransmission implicated in schizophrenia or associated with risk for psychotic illness; (d) the disaggregation of behavioural phenotypes into underlying pathobiological processes, as a key to the development of new therapeutic strategies for negative symptoms. Advances in genetic and molecular technologies are facilitating these processes, such that more accurate models of putative schizophrenia-linked genetic abnormalities are becoming feasible. This progress in terms of mimicking the genetic contribution to distinct domains of psychopathology associated with psychotic illness must be matched by advances in conceptual/clinical relevance and sensitivity/specificity of phenotypic assessments at the level of behaviour.

Distinct phenotypes of new transmembrane-domain neuregulin 1 mutant mice and the rescue effects of valproate on the observed schizophrenia-related cognitive deficits

Accumulating evidence suggests that neuregulin 1 (NRG1) might be involved in the neurodevelopment, neural plasticity, GABAergic neurotransmission, and pathogenesis of schizophrenia. NRG1 is abundantly expressed in the hippocampus, and emerging studies have begun to reveal the link between NRG1 signaling and cognitive deficits in schizophrenic patients. Because the transmembrane domain of NRG1 is vital for both forward and reverse signaling cascades, new Nrg1-deficient mice that carry a truncation of the transmembrane domain of the Nrg1 gene were characterized and used in this study to test a NRG1 loss-of-function hypothesis for schizophrenia. Both male and female Nrg1 heterozygous mutant mice and their wild-type littermates were used in a series of 4 experiments to characterize the impact of Nrg1 on behavioral phenotypes and to determine the importance of Nrg1 in the regulation of hippocampal neuromorphology and local GABAergic interneurons. First, a comprehensive battery of behavioral tasks indicated that male Nrg1-deficient mice exhibited significant impairments in cognitive functions. Second, pharmacological challenges were conducted and revealed that Nrg1 haploinsufficiency altered GABAergic activity in males. Third, although no genotype-specific neuromorphological alterations were found in the hippocampal CA1 pyramidal neurons, significant reductions in the hippocampal expressions of GAD67 and parvalbumin were revealed in the Nrg1-deficient males. Fourth, chronic treatment with valproate rescued the observed behavioral deficits and hippocampal GAD67 reduction in Nrg1-deficient males. Collectively, these results indicate the potential therapeutic effect of valproate and the importance of Nrg1 in the regulation of cognitive functions and hippocampal GABAergic interneurons, especially in males.

Animal Models of Psychosis: Current State and Future Directions

Psychosis is an abnormal mental state characterized by disorganization, delusions and hallucinations. Animal models have become an increasingly important research tool in the effort to understand both the underlying pathophysiology and treatment of psychosis. There are multiple animal models for psychosis, with each formed by the coupling of a manipulation and a measurement. In this manuscript we do not address the diseases of which psychosis is a prominent comorbidity. Instead, we summarize the current state of affairs and future directions for animal models of psychosis. To accomplish this, our manuscript will first discuss relevant behavioral and electrophysiological measurements. We then provide an overview of the different manipulations that are combined with these measurements to produce animal models. The strengths and limitations of each model will be addressed in order to evaluate its cross-species comparability.

Mismatch negativity: translating the potential

The mismatch negativity (MMN) component of the auditory event-related potential has become a valuable tool in cognitive neuroscience. Its reduced size in persons with schizophrenia is of unknown origin but theories proposed include links to problems in experience-dependent plasticity reliant on N-methyl-d-aspartate glutamate receptors. In this review we address the utility of this tool in revealing the nature and time course of problems in perceptual inference in this illness together with its potential for use in translational research testing animal models of schizophrenia-related phenotypes. Specifically, we review the reasons for interest in MMN in schizophrenia, issues pertaining to the measurement of MMN, its use as a vulnerability index for the development of schizophrenia, the pharmacological sensitivity of MMN and the progress in developing animal models of MMN. Within this process we highlight the challenges posed by knowledge gaps pertaining to the tool and the pharmacology of the underlying system.