Altered Cortical Ensembles in Mouse Models of Schizophrenia

Neural and neuronal discoordination in schizophrenia: From ensembles through networks to symptoms

Despite the substantial knowledge accumulated by past research, the exact mechanisms of the pathogenesis of schizophrenia and causal treatments still remain unclear. Deficits of cognition and information processing in schizophrenia are today often viewed as the primary and core symptoms of this devastating disorder. These deficits likely result from disruptions in the coordination of neuronal and neural activity. The aim of this review is to bring together convergent evidence of discoordinated brain circuits in schizophrenia at multiple levels of resolution, ranging from principal cells and interneurons, neuronal ensembles and local circuits, to large-scale brain networks. We show how these aberrations could underlie deficits in cognitive control and other higher order cognitive-behavioural functions. Converging evidence from both animal models and patients with schizophrenia is presented in an effort to gain insight into common features of deficits in the brain information processing in this disorder, marked by disruption of several neurotransmitter and signalling systems and severe behavioural outcomes.

GluA4-Targeted AAV Vectors Deliver Genes Selectively to Interneurons while Relying on the AAV Receptor for Entry

Selective gene delivery into subtypes of interneurons remains an important challenge in vector development. Adeno-associated virus (AAV) vector particles are especially promising for intracerebral injections. For cell entry, AAV2 particles are supposed to attach to heparan-sulfate proteoglycans (HSPGs) followed by endocytosis via the AAV receptor (AAVR). Here, we assessed engineered AAV particles deficient in HSPG attachment but competent in recognizing the glutamate receptor 4 (GluA4, also known as GluRD or GRIA4) through a displayed GluA4-specific DARPin (designed ankyrin repeat protein). When injected into the mouse brain, histological evaluation revealed that in various regions, more than 90% of the transduced cells were interneurons, mainly of the parvalbumin-positive subtype. Although part of the selectivity was mediated by the DARPin, the chosen spleen focus-forming virus (SFFV) promoter had contributed as well. Further analysis revealed that the DARPin mediated selective attachment to GluA4-positive cells, whereas gene delivery required expression of AAVR. Our data suggest that cell selectivity of AAV particles can be modified rationally and efficiently through DARPins, but expression of the AAV entry receptor remains essential.

Infraslow State Fluctuations Govern Spontaneous fMRI Network Dynamics

Spontaneous brain activity as assessed with resting-state fMRI exhibits rich spatiotemporal structure. However, the principles by which brain-wide patterns of spontaneous fMRI activity reconfigure and interact with each other remain unclear. We used a framewise clustering approach to map spatiotemporal dynamics of spontaneous fMRI activity with voxel resolution in the resting mouse brain. We show that brain-wide patterns of fMRI co-activation can be reliably mapped at the group and subject level, defining a restricted set of recurring brain states characterized by rich network structure. Importantly, we document that the identified fMRI states exhibit contrasting patterns of functional activity and coupled infraslow network dynamics, with each network state occurring at specific phases of global fMRI signal fluctuations. Finally, we show that autism-associated genetic alterations entail the engagement of atypical functional states and altered infraslow network dynamics. Our results reveal a novel set of fundamental principles guiding the spatiotemporal organization of resting-state fMRI activity and its disruption in brain disorders.

Auditory steady-state EEG response across the schizo-bipolar spectrum

Deviant auditory steady-state responses (aSSRs) in the gamma range (30-90 Hz) may be translational biomarkers for schizophrenia (SZ). This study tests whether aSSR deviations are (i) specific to SZ across the psychosis dimension, (ii) specific to particular frequency bands, and (iii) present in bipolar I disorder without psychosis (BDNP).

METHODS

Beta (20-), low- (40-), and high-gamma (80-Hz) aSSRs were measured with EEG and compared across 113 SZ, 105 schizoaffective disorder (SAD), 99 bipolar disorder with psychosis (BDP), 68 BDNP, and 137 healthy comparison subjects (HC). Standard aSSR measures (single-trial power [STP] and inter-trial phase coherence [ITC]), as well as evoked responses to stimulus onsets/offsets and pre-stimulus power, were quantified. Multivariate canonical discriminant analysis was used to summarize variables that efficiently and maximally differentiated groups.

RESULTS

(i) Psychosis groups showed reduced responses on ITC 20 Hz, STP/ITC 40 Hz, STP/ITC 80 Hz, indicating dimensional reductions in aSSR across the psychosis spectrum not specific to aSSR frequency. For the 40- and 80-Hz ITCs there was greater reduction in SZ compared to SAD, possibly indexing cortical disruptions linked to psychosis without mood symptoms. (ii) All probands had elevated pre-stimulus power, possibly compromising neural entrainment to the steady-state stimuli. (iii) Onset/Offset and 80 Hz ITC responses were most important for group discrimination and showed dimensional reduction across the schizo-bipolar spectrum.

CONCLUSIONS

Deviant aSSRs were found across the schizo-bipolar spectrum at multiple frequencies with psychosis status and severity linked to greatest reductions at low and high gamma.

Developmental dysfunction of prefrontal-hippocampal networks in mouse models of mental illness

Despite inherent difficulties to translate human cognitive phenotype into animals, a large number of animal models for psychiatric disorders, such as schizophrenia, have been developed over the last decades. To which extent they reproduce common patterns of dysfunction related to mental illness and abnormal processes of maturation is still largely unknown. While the devastating symptoms of disease are firstly detectable in adulthood, they are considered to reflect profound miswiring of brain circuitry as result of abnormal development. To reveal whether different disease models share common dysfunction early in life, we investigate the prefrontal-hippocampal communication at neonatal age in (a) mice mimicking the abnormal genetic background (22q11.2 microdeletion, DISC1 knockdown), (b) mice mimicking the challenge by environmental stressors (maternal immune activation during pregnancy), (c) mice mimicking the combination of both aetiologies (dual-hit models) and pharmacological mouse models. Simultaneous extracellular recordings in vivo from all layers of prelimbic subdivision (PL) of prefrontal cortex (PFC) and CA1 area of intermediate/ventral hippocampus (i/vHP) show that network oscillations have a more fragmented structure and decreased power mainly in neonatal mice that mimic both genetic and environmental aetiology of disease. These mice also show layer-specific firing deficits in PL. Similar early network dysfunction was present in mice with 22q11.2 microdeletion. The abnormal activity patterns are accompanied by weaker synchrony and directed interactions within prefrontal-hippocampal networks. Thus, only severe genetic defects or combined genetic environmental stressors are disruptive enough for reproducing the early network miswiring in mental disorders.

In vivo electrophysiological recordings of the effects of antidepressant drugs

Antidepressant drugs are a standard biological treatment for various neuropsychiatric disorders, yet relatively little is known about their electrophysiologic and synaptic effects on mood systems that set moment-to-moment emotional tone. In vivo electrical recording of local field potentials (LFPs) and single neuron spiking has been crucial for elucidating important details of neural processing and control in many other systems, and yet electrical approaches have not been broadly applied to the actions of antidepressants on mood-related circuits. Here we review the literature encompassing electrophysiologic effects of antidepressants in animals, including studies that examine older drugs, and extending to more recently synthesized novel compounds, as well as rapidly acting antidepressants. The existing studies on neuromodulator-based drugs have focused on recording in the brainstem nuclei, with much less known about their effects on prefrontal or sensory cortex. Studies on neuromodulatory drugs have moreover focused on single unit firing patterns with less emphasis on LFPs, whereas the rapidly acting antidepressant literature shows the opposite trend. In a synthesis of this information, we hypothesize that all classes of antidepressants could have common final effects on limbic circuitry. Whereas NMDA receptor blockade may induce a high powered gamma oscillatory state via direct and fast alteration of glutamatergic systems in mood-related circuits, neuromodulatory antidepressants may induce similar effects over slower timescales, corresponding with the timecourse of response in patients, while resetting synaptic excitatory versus inhibitory signaling to a normal level. Thus, gamma signaling may provide a biomarker (or “neural readout”) of the therapeutic effects of all classes of antidepressants.

Sustained rescue of prefrontal circuit dysfunction by antidepressant-induced spine formation

The neurobiological mechanisms underlying the induction and remission of depressive episodes over time are not well understood. Through repeated longitudinal imaging of medial prefrontal microcircuits in the living brain, we found that prefrontal spinogenesis plays a critical role in sustaining specific antidepressant behavioral effects and maintaining long-term behavioral remission. Depression-related behavior was associated with targeted, branch-specific elimination of postsynaptic dendritic spines on prefrontal projection neurons. Antidepressant-dose ketamine reversed these effects by selectively rescuing eliminated spines and restoring coordinated activity in multicellular ensembles that predict motivated escape behavior. Prefrontal spinogenesis was required for the long-term maintenance of antidepressant effects on motivated escape behavior but not for their initial induction.

Neurocognitive and Perceptual Processing in Genetic Mouse Models of Schizophrenia: Emerging Lessons

During the past two decades, the number of animal models of psychiatric disorders has grown exponentially. Of these, genetic animal models that are modeled after rare but highly penetrant mutations hold great promise for deciphering critical molecular, synaptic, and neurocircuitry deficits of major psychiatric disorders, such as schizophrenia. Animal models should aim to focus on core aspects rather than capture the entire human disease. In this context, animal models with strong etiological validity, where behavioral and neurophysiological phenotypes and the features of the disease being modeled are in unambiguous homology, are being used to dissect both elementary and complex cognitive and perceptual processing deficits present in psychiatric disorders at the level of neurocircuitry, shedding new light on critical disease mechanisms. Recent progress in neuroscience along with large-scale initiatives that propose a consistent approach in characterizing these deficits across different laboratories will further enhance the efficacy of these studies that will ultimately lead to identifying new biological targets for drug development.

Group II Metabotropic Glutamate Receptors Mediate Presynaptic Inhibition of Excitatory Transmission in Pyramidal Neurons of the Human Cerebral Cortex

Group II metabotropic glutamate receptor (mGluR) ligands are potential novel drugs for neurological and psychiatric disorders, but little is known about the effects of these compounds at synapses of the human cerebral cortex. Investigating the effects of neuropsychiatric drugs in human brain tissue with preserved synaptic circuits might accelerate the development of more potent and selective pharmacological treatments. We have studied the effects of group II mGluR activation on excitatory synaptic transmission recorded from pyramidal neurons of cortical layers 2-3 in acute slices derived from surgically removed cortical tissue of people with epilepsy or tumors. The application of a selective group II mGluR agonist, LY354740 (0.1-1 μM) inhibited the amplitude and frequency of action potential-dependent spontaneous excitatory postsynaptic currents (sEPSCs). This effect was prevented by the application of a group II/III mGluR antagonist, CPPG (0.1 mM). Furthermore, LY354740 inhibited the frequency, but not the amplitude, of action potential-independent miniature EPSCs (mEPSCs) recorded in pyramidal neurons. Finally, LY354740 did slightly reduce cells' input resistance without altering the holding current of the neurons recorded in voltage clamp at -90 mV. Our results suggest that group II mGluRs are mainly auto-receptors that inhibit the release of glutamate onto pyramidal neurons in layers 2-3 in the human cerebral cortex, thereby regulating network excitability. We have demonstrated the effect of a group II mGluR ligand at human cortical synapses, revealing mechanisms by which these drugs could exert pro-cognitive effects and treat human neuropsychiatric disorders.

Attractor-like Dynamics in Belief Updating in Schizophrenia

Subjects with a diagnosis of schizophrenia (Scz) overweight unexpected evidence in probabilistic inference: such evidence becomes "aberrantly salient." A neurobiological explanation for this effect is that diminished synaptic gain (e.g., hypofunction of cortical NMDARs) in Scz destabilizes quasi-stable neuronal network states (or "attractors"). This attractor instability account predicts that (1) Scz would overweight unexpected evidence but underweight consistent evidence, (2) belief updating would be more vulnerable to stochastic fluctuations in neural activity, and (3) these effects would correlate. Hierarchical Bayesian belief updating models were tested in two independent datasets (n = 80 male and n = 167 female) comprising human subjects with Scz, and both clinical and nonclinical controls (some tested when unwell and on recovery) performing the "probability estimates" version of the beads task (a probabilistic inference task). Models with a standard learning rate, or including a parameter increasing updating to "disconfirmatory evidence," or a parameter encoding belief instability were formally compared. The "belief instability" model (based on the principles of attractor dynamics) had most evidence in all groups in both datasets. Two of four parameters differed between Scz and nonclinical controls in each dataset: belief instability and response stochasticity. These parameters correlated in both datasets. Furthermore, the clinical controls showed similar parameter distributions to Scz when unwell, but were no different from controls once recovered. These findings are consistent with the hypothesis that attractor network instability contributes to belief updating abnormalities in Scz, and suggest that similar changes may exist during acute illness in other psychiatric conditions.SIGNIFICANCE STATEMENT Subjects with a diagnosis of schizophrenia (Scz) make large adjustments to their beliefs following unexpected evidence, but also smaller adjustments than controls following consistent evidence. This has previously been construed as a bias toward "disconfirmatory" information, but a more mechanistic explanation may be that in Scz, neural firing patterns ("attractor states") are less stable and hence easily altered in response to both new evidence and stochastic neural firing. We model belief updating in Scz and controls in two independent datasets using a hierarchical Bayesian model, and show that all subjects are best fit by a model containing a belief instability parameter. Both this and a response stochasticity parameter are consistently altered in Scz, as the unstable attractor hypothesis predicts.

All-optical synaptic electrophysiology probes mechanism of ketamine-induced disinhibition

Optical assays of synaptic strength could facilitate studies of neuronal transmission and its dysregulation in disease. Here we introduce a genetic toolbox for all-optical interrogation of synaptic electrophysiology (synOptopatch) via mutually exclusive expression of a channelrhodopsin actuator and an archaerhodopsin-derived voltage indicator. Optically induced activity in the channelrhodopsin-expressing neurons generated excitatory and inhibitory postsynaptic potentials that we optically resolved in reporter-expressing neurons. We further developed a yellow spine-targeted Ca2+ indicator to localize optogenetically triggered synaptic inputs. We demonstrated synOptopatch recordings in cultured rodent neurons and in acute rodent brain slice. In synOptopatch measurements of primary rodent cultures, acute ketamine administration suppressed disynaptic inhibitory feedbacks, mimicking the effect of this drug on network function in both rodents and humans. We localized this action of ketamine to excitatory synapses onto interneurons. These results establish an in vitro all-optical model of disynaptic disinhibition, a synaptic defect hypothesized in schizophrenia-associated psychosis.

Impaired perceptual learning in a mouse model of Fragile X syndrome is mediated by parvalbumin neuron dysfunction and is reversible

To uncover the circuit-level alterations that underlie atypical sensory processing associated with autism, we adopted a symptom-to-circuit approach in the Fmr1-knockout (Fmr1-/-) mouse model of Fragile X syndrome. Using a go/no-go task and in vivo two-photon calcium imaging, we find that impaired visual discrimination in Fmr1-/- mice correlates with marked deficits in orientation tuning of principal neurons and with a decrease in the activity of parvalbumin interneurons in primary visual cortex. Restoring visually evoked activity in parvalbumin cells in Fmr1-/- mice with a chemogenetic strategy using designer receptors exclusively activated by designer drugs was sufficient to rescue their behavioral performance. Strikingly, human subjects with Fragile X syndrome exhibit impairments in visual discrimination similar to those in Fmr1-/- mice. These results suggest that manipulating inhibition may help sensory processing in Fragile X syndrome.

Distinct and Dynamic ON and OFF Neural Ensembles in the Prefrontal Cortex Code Social Exploration

The medial prefrontal cortex (mPFC) is important for social behavior, but the mechanisms by which mPFC neurons code real-time social exploration remain largely unknown. Here we utilized miniScopes to record calcium activities from hundreds of excitatory neurons in the mPFC while mice freely explored restrained social targets in the absence or presence of the psychedelic drug phencyclidine (PCP). We identified distinct and dynamic ON and OFF neural ensembles that displayed opposing activities to code real-time behavioral information. We further illustrated that ON and OFF ensembles tuned to social exploration carried information of salience and novelty for social targets. Finally, we showed that dysfunctions in these ensembles were associated with abnormal social exploration elicited by PCP. Our findings underscore the importance of mPFC ON and OFF neural ensembles for proper exploratory behavior, including social exploration, and pave the way for future studies elucidating neural circuit dysfunctions in psychiatric disorders.

Restoring wild-type-like CA1 network dynamics and behavior during adulthood in a mouse model of schizophrenia

Schizophrenia is a severely debilitating neurodevelopmental disorder. Establishing a causal link between circuit dysfunction and particular behavioral traits that are relevant to schizophrenia is crucial to shed new light on the mechanisms underlying the pathology. We studied an animal model of the human 22q11 deletion syndrome, the mutation that represents the highest genetic risk of developing schizophrenia. We observed a desynchronization of hippocampal neuronal assemblies that resulted from parvalbumin interneuron hypoexcitability. Rescuing parvalbumin interneuron excitability with pharmacological or chemogenetic approaches was sufficient to restore wild-type-like CA1 network dynamics and hippocampal-dependent behavior during adulthood. In conclusion, our data provide insights into the network dysfunction underlying schizophrenia and highlight the use of reverse engineering to restore physiological and behavioral phenotypes in an animal model of neurodevelopmental disorder.

Altered function and maturation of primary cortical neurons from a 22q11.2 deletion mouse model of schizophrenia

Given its high penetrance, clearly delineated and evolutionary conserved genomic structure, mouse models of the 22q11.2 deletion provide an ideal organism-based and cell-based model of this well-established disease mutation for schizophrenia. In this study we examined the development of changes in intrinsic properties, action potential firing and synaptic transmission using whole-cell patch-clamp recordings of cultured embryonic cortical neurons from Df(16)A ^+/- and WT mice at DIV7 and DIV14, respectively. Compared to neurons from the WT littermates, significantly increased input resistance and decreased rising rate of action potential was observed in Df(16)A ^+/- mice at DIV7 but not at DIV14 indicative of delayed neuronal maturation. Neurons from Df(16)A ^+/- mice also showed significantly higher cellular excitability at both DIV7 and DIV14. Evaluation of Ca²⁺ homeostasis perturbation caused by 22q11.2 deletion using calcium imaging revealed a significantly lower amplitude of calcium elevation and a smaller area under the curve after depolarization in neurons from Df(16)A ^+/- mice at both DIV7 and DIV14. Furthermore, the properties of inhibitory synaptic events were significantly altered in Df(16)A ^+/- mice. We identified changes in mRNA expression profiles, especially in ion channels, receptors, and transporters that may underlie the neurophysiological effects of this mutation. Overall, we show a number of alterations in electrophysiological and calcium homeostatic properties of embryonic cortical neurons from a 22q11.2 deletion mouse model at different culture times and provide valuable insights towards revealing disease mechanisms and discovery of new therapeutic compounds.

The Candidate Schizophrenia Risk Gene DGCR2 Regulates Early Steps of Corticogenesis

BACKGROUND

Alterations in early steps of cortical circuit assembly are thought to play a critical role in vulnerability to schizophrenia (SZ), but the pathogenic impact of SZ-risk mutations on corticogenesis remains to be determined. DiGeorge syndrome critical region 2 (DGCR2) is located in the 22q11.2 locus, whose deletion is a major risk factor for SZ. Moreover, exome sequencing of individuals with idiopathic SZ identified a rare missense mutation in DGCR2, further suggesting that DGCR2 is involved in SZ.

METHODS

Here we investigated the function of Dgcr2 and the pathogenic impact of the SZ-risk DGCR2 mutation in mouse corticogenesis using in utero electroporation targeted to projection neurons.

RESULTS

Dgcr2 knockdown impaired radial locomotion and final translocation of projection neurons, leading to persistent laminar positioning alterations. The DGCR2 missense SZ-risk mutation had a pathogenic impact on projection neuron laminar allocation by reducing protein expression. Mechanistically, we identified Dgcr2 as a novel member of the Reelin complex, regulating the phosphorylation of Reelin-dependent substrates and the expression of Reelin-dependent transcriptional targets.

CONCLUSIONS

Overall, this study provides biological evidence that the SZ-risk gene DGCR2 regulates critical steps of early corticogenesis possibly through a Reelin-dependent mechanism. Additionally, we found that the SZ-risk mutation in DGCR2 has a pathogenic impact on cortical formation by reducing protein expression level, suggesting a functional role for DGCR2 haploinsufficiency in the 22q11.2 deletion syndrome.

Choice for Drug or Natural Reward Engages Largely Overlapping Neuronal Ensembles in the Infralimbic Prefrontal Cortex

Cue-reward associations form distinct memories that can drive appetitive behaviors and are involved in craving for both drugs and natural rewards. Distinct sets of neurons, so-called neuronal ensembles, in the infralimbic area (IL) of the medial prefrontal cortex (mPFC) play a key role in alcohol seeking. Whether this ensemble is specific for alcohol or controls reward seeking in general remains unclear. Here, we compared IL ensembles formed upon recall of drug (alcohol) or natural reward (saccharin) memories in male Wistar rats. Using an experimental framework that allows identification of two distinct reward-associated ensembles within the same animal, we found that cue-induced seeking of either alcohol or saccharin activated ensembles of similar size and organization, whereby these ensembles consist of largely overlapping neuronal populations. Thus, the IL seems to act as a general integration hub for reward seeking behavior, but also contains subsets of neurons that encode for the different rewards.SIGNIFICANCE STATEMENT Cue-reward associations form distinct memories that can act as drivers of appetitive behaviors and are involved in craving for natural rewards as well as for drugs. Distinct sets of neurons, so-called neuronal ensembles, in the infralimbic area of the mPFC play a key role in cue-triggered reward seeking. However, it is unclear whether these ensembles act as broadly tuned controllers of approach behavior or represent the learned associations between specific cues and rewards. Using an experimental framework that allows identification of two distinct reward-associated ensembles within the same animal we find largely overlapping neuronal populations. Repeated activation by two distinct events could reflect the linking of the two memory traces within the same neuron.

Effects of chronic ketamine on hippocampal cross-frequency coupling: implications for schizophrenia pathophysiology

Disrupted neuronal oscillations have been identified as a potentially important biomarker for the perceptual and cognitive symptoms of schizophrenia. Emerging evidences suggest that interactions between different frequency bands, cross-frequency coupling (CFC), serve an important role in integrating sensory and cognitive information and may contribute to disease pathophysiology. In this study, we investigated the effects of 14-day consecutive administration of ketamine (30 mg/kg i.p.) vs. saline on alterations in amplitude and changes in the coupling of low-frequency (0-30 Hz) phase and high-frequency (30-115 Hz) amplitude in the CA1 hippocampus of Long Evans rats. Intracranial electrode recordings were conducted pre- and post-injection while the animals performed a foraging task on a four-arm rectangular maze. Permutation analysis of frequency band-specific change in amplitudes revealed between-group differences in theta (6-12 Hz) and slow gamma (25-50 Hz) but not fast gamma (65-100 Hz) bands at both slow and fast speeds. Chronic ketamine challenge resulted in decreased coupling (pre to post) at slow speeds but increased coupling at faster speeds, compared to either no or modest increased coupling in the saline group. These results demonstrate that chronic ketamine administration alters the interaction of low-frequency phase and high-frequency oscillations chronically and that such coupling varies as a function of locomotive speed. These findings provide evidence for the potential relevance of CFC to the pathophysiology of schizophrenia.

Altered avalanche dynamics in a developmental NMDAR hypofunction model of cognitive impairment

Disturbed activity patterns in cortical networks contribute to the pathophysiology of schizophrenia (SZ). Several lines of evidence implicate NMDA receptor hypofunction in SZ, and blocking NMDA receptor signaling during early neurodevelopment produces cognitive deficits in rodent models that resemble those seen in schizophrenic patients. However, the altered network dynamics underlying these cognitive impairments largely remain to be characterized, especially at the cellular level. Here, we use in vivo two-photon calcium imaging to describe pathological dynamics, occurring in parallel with cognitive dysfunction, in a developmental NMDA receptor hypofunction model. We observed increased synchrony and specific alterations in spatiotemporal activity propagation, which could be causally linked to a previously unidentified persistent bursting phenotype. This phenotype was rescued by acute treatment with the NMDA receptor co-agonist D-serine or the GABA_B receptor agonist baclofen, which similarly rescued working memory performance. It was not reproduced by optogenetic inhibition of fast-spiking interneurons. These results provide novel insight into network-level abnormalities mediating the cognitive impairment induced by NMDA receptor hypofunction.

Neural circuit dysfunction in mouse models of neurodevelopmental disorders

Neuropsychiatric disorders arise from the alteration of normal brain developmental trajectories disrupting the function of specific neuronal circuits. Recent advances in human genetics have greatly accelerated the identification of genes whose variation increases the susceptibility for neurodevelopmental disorders, most notably for autism spectrum disorder (ASD) and schizophrenia. In parallel, experimental studies in animal models-most typically in mice-are beginning to shed light on the role of these genes in the development and function of specific brain circuits. In spite of their limitations, understanding the impact of pathological gene variation in animal models at the level of specific neuronal populations and circuits will likely contribute to orienting human clinical studies in the search for precise disease mechanisms and novel treatments.

Perinatal Hypoxia and Ischemia in Animal Models of Schizophrenia

Intrauterine or perinatal complications constitute a major risk for psychiatric diseases. Infants who suffered from hypoxia-ischemia (HI) are at twofold risk to develop schizophrenia in later life. Several animal models attempt to reproduce these complications to study the yet unknown steps between an insult in early life and outbreak of the disease decades later. However, it is very challenging to find the right type and severity of insult leading to a disease-like phenotype in the animal, but not causing necrosis and focal neurological deficits. By contrast, too mild, repetitive insults may even be protective via conditioning effects. Thus, it is not surprising that animal models of hypoxia lead to mixed results. To achieve clinically translatable findings, better protocols are urgently needed. Therefore, we compare widely used models of hypoxia and HI and propose future directions for the field.

Quantitative assessment of cerebral venous blood T2 in mouse at 11.7T: Implementation, optimization, and age effect

PURPOSE

To develop a non-contrast-agent MRI technique to quantify cerebral venous T₂ in mice.

METHODS

We implemented and optimized a T₂ -relaxation-under-spin-tagging (TRUST) sequence on an 11.7 Tesla animal imaging system. A flow-sensitive-alternating-inversion-recovery (FAIR) module was used to generate control and label images, pair-wise subtraction of which yielded blood signals. Then, a T₂ -preparation module was applied to produce T₂ -weighted images, from which blood T₂ was quantified. We conducted a series of technical studies to optimize the imaging slice position, inversion slab thickness, post-labeling delay (PLD), and repetition time. We also performed three physiological studies to examine the venous T₂ dependence on hyperoxia (N = 4), anesthesia (N = 3), and brain aging (N = 5).

RESULTS

Our technical studies suggested that, for efficient data acquisition with minimal bias in estimated T₂ , a preferred TRUST protocol was to place the imaging slice at the confluence of sagittal sinuses with an inversion-slab thickness of 2.5-mm, a PLD of 1000 ms and a repetition time of 3.5 s. Venous T₂ values under normoxia and hyperoxia (inhaling pure oxygen) were 26.9 ± 1.7 and 32.3 ± 2.2 ms, respectively. Moreover, standard isoflurane anesthesia resulted in a higher venous T₂ compared with dexmedetomidine anesthesia (N = 3; P = 0.01) which is more commonly used in animal functional MRI studies to preserve brain function. Venous T₂ exhibited a decrease with age (N = 5; P < 0.001).

CONCLUSION

We have developed and optimized a noninvasive method to quantify cerebral venous blood T₂ in mouse at 11.7 T. This method may prove useful in studies of brain physiology and pathophysiology in animal models. Magn Reson Med 80:521-528, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

A neurogenetic model for the study of schizophrenia spectrum disorders: the International 22q11.2 Deletion Syndrome Brain Behavior Consortium

Rare copy number variants contribute significantly to the risk for schizophrenia, with the 22q11.2 locus consistently implicated. Individuals with the 22q11.2 deletion syndrome (22q11DS) have an estimated 25-fold increased risk for schizophrenia spectrum disorders, compared to individuals in the general population. The International 22q11DS Brain Behavior Consortium is examining this highly informative neurogenetic syndrome phenotypically and genomically. Here we detail the procedures of the effort to characterize the neuropsychiatric and neurobehavioral phenotypes associated with 22q11DS, focusing on schizophrenia and subthreshold expression of psychosis. The genomic approach includes a combination of whole-genome sequencing and genome-wide microarray technologies, allowing the investigation of all possible DNA variation and gene pathways influencing the schizophrenia-relevant phenotypic expression. A phenotypically rich data set provides a psychiatrically well-characterized sample of unprecedented size (n=1616) that informs the neurobehavioral developmental course of 22q11DS. This combined set of phenotypic and genomic data will enable hypothesis testing to elucidate the mechanisms underlying the pathogenesis of schizophrenia spectrum disorders.

Computational Modeling of Contrast Sensitivity and Orientation Tuning in First-Episode and Chronic Schizophrenia

Computational modeling is a useful method for generating hypotheses about the contributions of impaired neurobiological mechanisms, and their interactions, to psychopathology. Modeling is being increasingly used to further our understanding of schizophrenia, but to date, it has not been applied to questions regarding the common perceptual disturbances in the disorder. In this article, we model aspects of low-level visual processing and demonstrate how this can lead to testable hypotheses about both the nature of visual abnormalities in schizophrenia and the relationships between the mechanisms underlying these disturbances and psychotic symptoms. Using a model that incorporates retinal, lateral geniculate nucleus (LGN), and V1 activity, as well as gain control in the LGN, homeostatic adaptation in V1, lateral excitation and inhibition in V1, and self-organization of synaptic weights based on Hebbian learning and divisive normalization, we show that (a) prior data indicating increased contrast sensitivity for low-spatial-frequency stimuli in first-episode schizophrenia can be successfully modeled as a function of reduced retinal and LGN efferent activity, leading to overamplification at the cortical level, and (b) prior data on reduced contrast sensitivity and broadened orientation tuning in chronic schizophrenia can be successfully modeled by a combination of reduced V1 lateral inhibition and an increase in the Hebbian learning rate at V1 synapses for LGN input. These models are consistent with many current findings, and they predict several relationships that have not yet been demonstrated. They also have implications for understanding changes in brain and visual function from the first psychotic episode to the chronic stage of illness.

Closing gaps in brain disease-from overlapping genetic architecture to common motifs of synapse dysfunction

Recent progress in the synaptic pathophysiology of brain diseases is reviewed. To emphasize the emergence of common motifs in synapse dysfunctions across neurodevelopmental, psychiatric and neurological disorders, conventional clinical boundaries are disregarded and a decidedly trans-diagnostic, potentially unifying view of altered synapse function is promoted. Based on the overlapping genetic architecture of brain disorders, which often converges on genes related to synaptic functions, disease-related changes in basic pre-synaptic and post-synaptic communication, neuromodulation-gated changes in Hebbian plasticity, dynamic interactions between Hebbian and homeostatic plasticity, and changes in synaptic maintenance by autophagy and glial-mediated phagocytosis are highlighted.

Developmental Dysfunction of VIP Interneurons Impairs Cortical Circuits

GABAergic interneurons play important roles in cortical circuit development. However, there are multiple populations of interneurons and their respective developmental contributions remain poorly explored. Neuregulin 1 (NRG1) and its interneuron-specific receptor ERBB4 are critical genes for interneuron maturation. Using a conditional ErbB4 deletion, we tested the role of vasoactive intestinal peptide (VIP)-expressing interneurons in the postnatal maturation of cortical circuits in vivo. ErbB4 removal from VIP interneurons during development leads to changes in their activity, along with severe dysregulation of cortical temporal organization and state dependence. These alterations emerge during adolescence, and mature animals in which VIP interneurons lack ErbB4 exhibit reduced cortical responses to sensory stimuli and impaired sensory learning. Our data support a key role for VIP interneurons in cortical circuit development and suggest a possible contribution to pathophysiology in neurodevelopmental disorders. These findings provide a new perspective on the role of GABAergic interneuron diversity in cortical development. VIDEO ABSTRACT.

Disturbances of novel object exploration and recognition in a chronic ketamine mouse model of schizophrenia

Schizophrenia is a chronic and devastating disease with an overall lifetime risk of 1%. While positive symptoms of schizophrenia such as hallucinations and delusions are reduced by antipsychotic medication based on the inhibition of type 2 dopaminergic receptors (D2R), negative symptoms (e.g. reduced motivation) and cognitive symptoms (e.g. impaired working memory) of schizophrenia are not effectively treated by current medication. This dichotomy might arise in part because of our limited understanding of the pathophysiology of negative and cognitive symptoms in schizophrenia. In addition to genetic approaches, chronic systemic application of NMDA inhibitors such as ketamine have been used to generate rodent models, which displayed several relevant endophenotypes related to negative and cognitive symptoms and might thus facilitate mechanistic studies into the underlying pathophysiology. In this context, previous behavioral testing identified impairments in novel object recognition memory as a key feature in chronic NMDA-inhibitor schizophrenia rodent models. Using a chronic ketamine mouse model, we have however identified are more complex behavioral phenotype including deficits in novel space and novel object exploration in combination deficits in short-term novel object recognition memory. These impairments in novelty discrimination are in line with prefrontal and hippocampal reductions in parvalbumin-expression as well as reduced expression of the early immediate gene c-fos after novel-object exploration in hippocampal areas in our model. Our results indicate that adult C57Bl6N mice chronically treated with ketamine display combined impairments in novelty exploration and recognition, which might represent both motivational (negative) and cognitive symptoms of schizophrenia.