Synaptic basis of social dysfunction: a focus on postsynaptic proteins linking group-I mGluRs with AMPARs and NMDARs

Histone variant H2BE enhances chromatin accessibility in neurons to promote synaptic gene expression and long-term memory

Histone proteins affect gene expression through multiple mechanisms, including through exchange with histone variants. Recent findings link histone variants to neurological disorders, yet few are well studied in the brain. Most notably, widely expressed variants of H2B remain elusive. We applied recently developed antibodies, biochemical assays, and sequencing approaches to reveal broad expression of the H2B variant H2BE and defined its role in regulating chromatin structure, neuronal transcription, and mouse behavior. We find that H2BE is enriched at promoters, and a single unique amino acid allows it to dramatically enhance chromatin accessibility. Further, we show that H2BE is critical for synaptic gene expression and long-term memory. Together, these data reveal a mechanism linking histone variants to chromatin accessibility, transcriptional regulation, neuronal function, and memory. This work further identifies a widely expressed H2B variant and uncovers a single histone amino acid with profound effects on genomic structure.

Histone variant H2BE enhances chromatin accessibility in neurons to promote synaptic gene expression and long-term memory

Regulation of histone proteins affects gene expression through multiple mechanisms including exchange with histone variants. However, widely expressed variants of H2B remain elusive. Recent findings link histone variants to neurological disorders, yet few are well studied in the brain. We applied new tools including novel antibodies, biochemical assays, and sequencing approaches to reveal broad expression of the H2B variant H2BE, and defined its role in regulating chromatin structure, neuronal transcription, and mouse behavior. We find that H2BE is enriched at promoters and a single unique amino acid allows it to dramatically enhance chromatin accessibility. Lastly, we show that H2BE is critical for synaptic gene expression and long-term memory. Together, these data reveal a novel mechanism linking histone variants to chromatin regulation, neuronal function, and memory. This work further identifies the first widely expressed H2B variant and uncovers a single histone amino acid with profound effects on genomic structure.

The Shank3Venus/Venus knock in mouse enables isoform-specific functional studies of Shank3a

Background

Shank3 is a scaffolding protein essential for the organization and function of the glutamatergic postsynapse. Monogenic mutations in SHANK3 gene are among the leading genetic causes of Autism Spectrum Disorders (ASD). The multiplicity of Shank3 isoforms seems to generate as much functional diversity and yet, there are no tools to study endogenous Shank3 proteins in an isoform-specific manner.

Methods

In this study, we created a novel transgenic mouse line, the Shank3^Venus/Venus knock in mouse, which allows to monitor the endogenous expression of the major Shank3 isoform in the brain, the full-length Shank3a isoform.

Results

We show that the endogenous Venus-Shank3a protein is localized in spines and is mainly expressed in the striatum, hippocampus and cortex of the developing and adult brain. We show that Shank3^Venus/+ and Shank3^Venus/Venus mice have no behavioral deficiency. We further crossed Shank3^Venus/Venus mice with Shank3^ΔC/ΔC mice, a model of ASD, to track the Venus-tagged wild-type copy of Shank3a in physiological (Shank3^Venus/+) and pathological (Shank3^Venus/ΔC) conditions. We report a developmental delay in brain expression of the Venus-Shank3a isoform in Shank3^Venus/ΔC mice, compared to Shank3^Venus/+ control mice.

Conclusion

Altogether, our results show that the Shank3^Venus/Venus mouse line is a powerful tool to study endogenous Shank3a expression, in physiological conditions and in ASD.

CRISPR-mediated activation of autism gene Itgb3 restores cortical network excitability via mGluR5 signaling

Many mutations in autism spectrum disorder (ASD) affect a single allele, indicating a key role for gene dosage in ASD susceptibility. Recently, haplo-insufficiency of ITGB3, the gene encoding the extracellular matrix receptor β3 integrin, was associated with ASD. Accordingly, Itgb3 knockout (KO) mice exhibit autism-like phenotypes. The pathophysiological mechanisms of Itgb3 remain, however, unknown, and the potential of targeting this gene for developing ASD therapies uninvestigated. By combining molecular, biochemical, imaging, and pharmacological analyses, we establish that Itgb3 haplo-insufficiency impairs cortical network excitability by promoting extra-synaptic over synaptic signaling of the metabotropic glutamate receptor mGluR5, which is similarly dysregulated in fragile X syndrome, the most frequent monogenic form of ASD. To assess the therapeutic potential of regulating Itgb3 gene dosage, we implemented CRISPR activation and compared its efficacy with that of a pharmacological rescue strategy for fragile X syndrome. Correction of neuronal Itgb3 haplo-insufficiency by CRISPR activation rebalanced network excitability as effectively as blockade of mGluR5 with the selective antagonist MPEP. Our findings reveal an unexpected functional interaction between two ASD genes, thereby validating the pathogenicity of ITGB3 haplo-insufficiency. Further, they pave the way for exploiting CRISPR activation as gene therapy for normalizing gene dosage and network excitability in ASD.

Quantification of Metabotropic Glutamate Receptor 5 Availability With Both [11C]ABP688 and [18F]FPEB Positron Emission Tomography in the Sapap3 Knockout Mouse Model for Obsessive-Compulsive-like Behavior

BACKGROUND

This study provides a first direct comparison between positron emission tomography radioligands targeting the allosteric site of the metabotropic glutamate receptor 5 (mGluR5): [¹¹C]ABP688 and [¹⁸F]FPEB. A blocking paradigm was set up to substantiate the common binding site of both radioligands. Second, both radioligands were applied in Sapap3 knockout (KO) mice showing compulsive-like behavior characterized by a lower in vivo mGluR5 availability.

METHODS

First, wild-type mice (n = 7) received four position emission tomography/computed tomography scans: a [¹¹C]ABP688 scan, a [¹⁸F]FPEB scan, and two blocking scans using cold FPEB and cold ABP688, respectively. A second experiment compared both radioligands in wild-type (n = 7) and KO (n = 10) mice. The simplified reference tissue model was used to calculate the nondisplaceable binding potential representing the in vivo availability of mGluR5 in the brain.

RESULTS

Using cold FPEB as a blocking compound for [¹¹C]ABP688 micro-positron emission tomography and vice versa, we observed averaged global reductions in mGluR5 availability of circa 98% for [¹¹C]ABP688 and 82%-96% for [¹⁸F]FPEB. For KOs, the [¹¹C]ABP688 nondisplaceable binding potential was on average 25% lower compared with wild-type control mice (p < .0001-.001), while this was about 17% for [¹⁸F]FPEB (p < .05).

CONCLUSIONS

The current findings substantiate a common binding site and suggest a strong relationship between mGluR5 availability levels measured with both radioligands. In Sapap3 KO mice, a reduced mGluR5 availability could therefore be demonstrated with both radioligands. With [¹¹C]ABP688, higher significance levels were achieved in more brain regions. These findings suggest [¹¹C]ABP688 as a preferable radiotracer to quantify mGluR5 availability, as exemplified here in a model for compulsive-like behavior.

Neuroligins in neurodevelopmental conditions: how mouse models of de novo mutations can help us link synaptic function to social behavior

Neurodevelopmental conditions (or neurodevelopmental disorders, NDDs) are highly heterogeneous with overlapping characteristics and shared genetic etiology. The large symptom variability and etiological heterogeneity have made it challenging to understand the biological mechanisms underpinning NDDs. To accommodate this individual variability, one approach is to move away from diagnostic criteria and focus on distinct dimensions with relevance to multiple NDDs. This domain approach is well suited to preclinical research, where genetically modified animal models can be used to link genetic variability to neurobiological mechanisms and behavioral traits. Genetic factors associated with NDDs can be grouped functionally into common biological pathways, with one prominent functional group being genes associated with the synapse. These include the neuroligins (Nlgns), a family of postsynaptic transmembrane proteins that are key modulators of synaptic function. Here, we review how research using Nlgn mouse models has provided insight into how synaptic proteins contribute to behavioral traits associated with NDDs. We focus on how mutations in different Nlgns affect social behaviors, as differences in social interaction and communication are a common feature of most NDDs. Importantly, mice carrying distinct mutations in Nlgns share some neurobiological and behavioral phenotypes with other synaptic gene mutations. Comparing the functional implications of mutations in multiple synaptic proteins is a first step towards identifying convergent neurobiological pathways in multiple brain regions and circuits.

From Physiology to Pathology of Cortico-Thalamo-Cortical Oscillations: Astroglia as a Target for Further Research

The electrographic hallmark of childhood absence epilepsy (CAE) and other idiopathic forms of epilepsy are 2.5-4 Hz spike and wave discharges (SWDs) originating from abnormal electrical oscillations of the cortico-thalamo-cortical network. SWDs are generally associated with sudden and brief non-convulsive epileptic events mostly generating impairment of consciousness and correlating with attention and learning as well as cognitive deficits. To date, SWDs are known to arise from locally restricted imbalances of excitation and inhibition in the deep layers of the primary somatosensory cortex. SWDs propagate to the mostly GABAergic nucleus reticularis thalami (NRT) and the somatosensory thalamic nuclei that project back to the cortex, leading to the typical generalized spike and wave oscillations. Given their shared anatomical basis, SWDs have been originally considered the pathological transition of 11-16 Hz bursts of neural oscillatory activity (the so-called sleep spindles) occurring during Non-Rapid Eye Movement (NREM) sleep, but more recent research revealed fundamental functional differences between sleep spindles and SWDs, suggesting the latter could be more closely related to the slow (<1 Hz) oscillations alternating active (Up) and silent (Down) cortical activity and concomitantly occurring during NREM. Indeed, several lines of evidence support the fact that SWDs impair sleep architecture as well as sleep/wake cycles and sleep pressure, which, in turn, affect seizure circadian frequency and distribution. Given the accumulating evidence on the role of astroglia in the field of epilepsy in the modulation of excitation and inhibition in the brain as well as on the development of aberrant synchronous network activity, we aim at pointing at putative contributions of astrocytes to the physiology of slow-wave sleep and to the pathology of SWDs. Particularly, we will address the astroglial functions known to be involved in the control of network excitability and synchronicity and so far mainly addressed in the context of convulsive seizures, namely (i) interstitial fluid homeostasis, (ii) K⁺ clearance and neurotransmitter uptake from the extracellular space and the synaptic cleft, (iii) gap junction mechanical and functional coupling as well as hemichannel function, (iv) gliotransmission, (v) astroglial Ca²⁺ signaling and downstream effectors, (vi) reactive astrogliosis and cytokine release.

HIF-1 α may play a role in late pregnancy hypoxia-induced autism-like behaviors in offspring rats

Autism spectrum disorder (ASD) is a neurodevelopmental disorder that can be caused by various factors. The present study aimed to determine whether prenatal hypoxia can lead to ASD and the role of hypoxia-inducible factor-1α (HIF-1α) in this process. We constructed a prenatal hypoxia model of pregnant rats by piping nitrogen and oxygen mixed gas, with an oxygen concentration of 10 ± 0.5 %, into the self-made hypoxia chamber. Rats were subjected to different extents of hypoxia treatments at different points during pregnancy. The results showed that hypoxia for 6 h on the 17th gestation day is most likely to lead to autistic behavior in offspring rats, including social deficits, repetitive behaviors, and impaired learning and memory. The mRNA expression level of TNF-α also increased in hypoxia-induced autism group and valproic acid (VPA) group. Western blotting analysis showed increased levels of hypoxia inducible factor 1 alpha (HIF-1α) and decreased levels of phosphatase and tensin homolog (PTEN) in the hypoxic-induced autism group. Meanwhile, N-methyl d-aspartate receptor subtype 2 (NR2A) and glutamate ionotropic receptor AMPA type subunit 2 (GluR2) were upregulated in the hypoxic-induced autism group. HIF-1α might play a role in hypoxia-caused autism-like behavior and its regulatory effect is likely to be achieved by regulating synaptic plasticity.

Temporal Quantitative Proteomics of mGluR-induced Protein Translation and Phosphorylation in Neurons

At neuronal synapses, activation of group I metabotropic glutamate receptors (mGluR1/5) triggers a form of long-term depression (mGluR-LTD) that relies on new protein synthesis and the internalization of AMPA-type glutamate receptors. Dysregulation of these processes has been implicated in the development of mental disorders such as autism spectrum disorders and therefore merit a better understanding on a molecular level. Here, to study mGluR-induced signaling pathways, we integrated quantitative phosphoproteomics with the analyses of newly synthesized proteins via bio-orthogonal amino acids (azidohomoalanine) in a pulsed labeling strategy in cultured hippocampal neurons stimulated with DHPG, a specific agonist for group I mGluRs. We identified several kinases with important roles in DHPG-induced mGluR activation, which we confirmed using small molecule kinase inhibitors. Furthermore, changes in the AMPA receptor endocytosis pathway in both protein synthesis and protein phosphorylation were identified, whereby Intersectin-1 was validated as a novel player in this pathway. This study revealed several new insights into the molecular pathways downstream of group I mGluR activation in hippocampal neurons, and provides a rich resource for further analyses.

The Transcriptomic Analysis of NSC-34 Motor Neuron-Like Cells Reveals That Cannabigerol Influences Synaptic Pathways: A Comparative Study with Cannabidiol

More than 120 cannabinoids were isolated from Cannabis sativa. In particular, Cannabidiol (CBD) and Cannabigerol (CBG) represent the two most studied non-psychoactive cannabinoids. However, CBG is less studied and less data are available on its biological properties and influence on synaptic transmission. On the contrary, CBD is already known to modulate brain excitatory glutamate, inhibitory γ-aminobutyric acid (GABA) and dopamine neurotransmission. In this study, using Next-Generation Sequencing (NGS) technology, we evaluated how CBG (1 or 5 µM) and CBD (1 or 5 µM) influence the transcriptome of the main neurotransmission pathways in NSC-34 motor neuron-like cells. At first, we evaluated that CBG and CBD were not cytotoxic and decreased the expression of pro-apoptotic genes. CBG and CBD are able to influence the expression of the genes involved in glutamate, GABA and dopamine signaling. Interestingly, the transcriptional changes induced by CBG were similar compared to CBD.

Progression of obsessive compulsive disorder-like grooming in Sapap3 knockout mice: A longitudinal [11C]ABP688 PET study

We aimed to evaluate [3-(6-methyl-pyridin-2-ylethynyl)-cyclohex-2-enone-0-¹¹C-methyloxime] ([¹¹C]ABP688) small animal positron emission tomography (μPET) as a biomarker to visualize possible longitudinal changes in metabotropic glutamate receptor 5 (mGluR5) availability in the brain of SAP90/PSD-95 associated protein 3 (Sapap3) knockout (ko) mice, showing obsessive compulsive disorder (OCD)-like behavior.

METHODS

Alongside the assessment of grooming, we performed [¹¹C]ABP688 μPET/CT imaging in wildtype (wt; n=10) and ko (n=11) mice both at 3 and 9 months. Using the simplified reference tissue method (SRTM), the nondisplaceable binding potential (BP_ND) was calculated representing the in vivo availability of the metabotropic glutamate receptor 5 (mGluR5) in the brain with the cerebellum as a reference region. Longitudinal voxel-based statistical parametric mapping (SPM) was performed on BP_ND images. Results were verified using [¹¹C]ABP688 ex vivo autoradiography, [³H]ABP688 in vitro autoradiography, and mGluR5 immunohistochemistry.

RESULTS

Cross-sectional comparisons revealed significantly increased grooming parameters in ko animals, at both time points. A significant longitudinal increase in % grooming duration (+268.25%; p<0.05) reflected aggravation of this behavior in ko mice. [¹¹C]ABP688 μPET revealed significantly lower mGluR5 availability in the cortex, striatum, hippocampus, and amygdala of ko mice at both ages. A significant longitudinal BP_ND decline was present for ko mice (p<0.01: cortex -17.14%, striatum -19.82%, amygdala -23.57%; p<0.05: hippocampus -15.53%), which was confirmed by SPM (p<0.01).

CONCLUSION

Sapap3 ko mice show a decline in mGluR5 availability in OCD relevant brain regions parallel to the worsening of OCD-like behavior. This demonstrates a potential role for [¹¹C]ABP688 PET as a biomarker to monitor disease progression in vivo.

Intra- and Extracellular Pillars of a Unifying Framework for Homeostatic Plasticity: A Crosstalk Between Metabotropic Receptors and Extracellular Matrix

In the face of chronic changes in incoming sensory inputs, neuronal networks are capable of maintaining stable conditions of electrical activity over prolonged periods of time by adjusting synaptic strength, to amplify or dampen incoming inputs [homeostatic synaptic plasticity (HSP)], or by altering the intrinsic excitability of individual neurons [homeostatic intrinsic plasticity (HIP)]. Emerging evidence suggests a synergistic interplay between extracellular matrix (ECM) and metabotropic receptors in both forms of homeostatic plasticity. Activation of dopaminergic, serotonergic, or glutamate metabotropic receptors stimulates intracellular signaling through calmodulin-dependent protein kinase II, protein kinase A, protein kinase C, and inositol trisphosphate receptors, and induces changes in expression of ECM molecules and proteolysis of both ECM molecules (lecticans) and ECM receptors (NPR, CD44). The resulting remodeling of perisynaptic and synaptic ECM provides permissive conditions for HSP and plays an instructive role by recruiting additional signaling cascades, such as those through metabotropic glutamate receptors and integrins. The superimposition of all these signaling events determines intracellular and diffusional trafficking of ionotropic glutamate receptors, resulting in HSP and modulation of conditions for inducing Hebbian synaptic plasticity (i.e., metaplasticity). It also controls cell-surface delivery and activity of voltage- and Ca2+-gated ion channels, resulting in HIP. These mechanisms may modify epileptogenesis and become a target for therapeutic interventions.

Evidence for a Contribution of the Nlgn3/Cyfip1/Fmr1 Pathway in the Pathophysiology of Autism Spectrum Disorders

Autism Spectrum Disorders (ASD) are characterized by heterogeneity both in their presentation and their genetic aetiology. In order to discover points of convergence common to different cases of ASD, attempts were made to identify the biological pathways genes associated with ASD contribute to. Many of these genes were found to play a role in neuronal and synaptic development and function. Among these genes are FMR1, CYFIP1 and NLGN3, all present at the synapse and reliably linked to ASD. In this review, we evaluate the evidence for the contribution of these genes to the same biological pathway responsible for the regulation of structural and physiological plasticity. Alterations in dendritic spine density and turnover, as well as long-term depression (LTD), were found in mouse models of mutations of all three genes. This overlap in the phenotypes associated with these mouse models likely arises from the molecular interaction between the protein products of FMR1, CYFIP1, and NLG3. A number of other proteins linked to ASD are also likely to participate in these pathways, resulting in further downstream effects. Overall, a synaptic pathway centered around FMR1, CYFIP1, and NLG3 is likely to contribute to the phenotypes associated with structural and physiological plasticity characteristic of ASD.

Abnormal mGluR-mediated synaptic plasticity and autism-like behaviours in Gprasp2 mutant mice

Autism spectrum disorder (ASD) is characterized by dysfunction in social interactions, stereotypical behaviours and high co-morbidity with intellectual disability. A variety of syndromic and non-syndromic neurodevelopmental disorders have been connected to alterations in metabotropic glutamate receptor (mGluR) signalling. These receptors contribute to synaptic plasticity, spine maturation and circuit development. Here, we investigate the physiological role of Gprasp2, a gene linked to neurodevelopmental disabilities and involved in the postendocytic sorting of G-protein-coupled receptors. We show that Gprasp2 deletion leads to ASD-like behaviour in mice and alterations in synaptic communication. Manipulating the levels of Gprasp2 bidirectionally modulates the surface availability of mGluR₅ and produces alterations in dendritic complexity, spine density and synaptic maturation. Loss of Gprasp2 leads to enhanced hippocampal long-term depression, consistent with facilitated mGluR-dependent activation. These findings demonstrate a role for Gprasp2 in glutamatergic synapses and suggest a possible mechanism by which this gene is linked to neurodevelopmental diseases.

A competitive model for striatal action selection

The direct and indirect pathway striatal medium spiny neurons (dMSNs and iMSNs) have long been linked to action selection, but the precise roles of these neurons in this process remain unclear. Here, we review different models of striatal pathway function, focusing on the classic "go/no-go" model which posits that dMSNs facilitate movement while iMSNs inhibit movement, and the "complementary" model, which argues that dMSNs facilitate the selection of specific actions while iMSNs inhibit potentially conflicting actions. We discuss the merits and shortcomings of these models and propose a "competitive" model to explain the contribution of these two pathways to behavior. The "competitive" model argues that rather than inhibiting conflicting actions, iMSNs are tuned to the same actions that dMSNs facilitate, and the two populations "compete" to determine the animal's behavioral response. This model provides a theoretical explanation for how these pathways work together to select actions. In addition, it provides a link between action selection and behavioral reinforcement, via modulating synaptic strength at inputs onto dMSNs and iMSNs. Finally, this model makes predictions about how imbalances in the activity of these pathways may underlie behavioral traits associated with psychiatric disorders. Understanding the roles of these striatal pathways in action selection may help to clarify the neuronal mechanisms of decision-making under normal and pathological conditions.

HIF-1<alpha> Repression of PTEN Transcription Mediates Protective Effects of BMSCs on Neurons During Hypoxia

Neonatal hypoxic-ischemic brain damage (HIBD) is a cerebral hypoxic-ischemic disease caused by a variety of insults during the perinatal period, leading to varying degrees of cognitive dysfunction. Mesenchymal stem cells play an important role in functional recovery, but the mechanism is not yet clear. It has been reported that HIF-1<alpha> and PTEN are involved in the process of hypoxia-ischemia, but the specific roles that these proteins play remains to be understood. In this study, we performed oxygen glucose deprivation (OGD) or CoCl₂ preconditioning on hippocampal neurons to simulate a hypoxic environment in vitro, and then co-cultured them with BMSCs, to observe the effect of BMSCs and the role of HIF-1<alpha>. In addition, bpV, an inhibitor of PTEN was added to OGD neurons to determine the role of PTEN during hypoxia. We found that the levels of cell damage and apoptosis in OGD neurons decreased significantly after co-culture with BMSCs. Apoptosis was increased when HIF-1<alpha> was inhibited, but neurons remained protected when PTEN was suppressed. We further established that HIF-1<alpha> was enriched at the PTEN promoter both in BMSCs and hippocampal neurons, with increased enrichment under hypoxic conditions, leading to reduced transcription of PTEN. Our findings support the conclusion that CoCl₂ preconditioning of BMSCs can simulate hypoxic conditions and can protect OGD neurons, an effect that is mediated through activation of the HIF-1<alpha> system and repression of PTEN transcription.

Role of VTA dopamine neurons and neuroligin 3 in sociability traits related to nonfamiliar conspecific interaction

Atypical habituation and aberrant exploration of novel stimuli have been related to the severity of autism spectrum disorders (ASDs), but the underlying neuronal circuits are unknown. Here we show that chemogenetic inhibition of dopamine (DA) neurons of the ventral tegmental area (VTA) attenuates exploration toward nonfamiliar conspecifics and interferes with the reinforcing properties of nonfamiliar conspecific interaction in mice. Exploration of nonfamiliar stimuli is associated with the insertion of GluA2-lacking AMPA receptors at excitatory synapses on VTA DA neurons. These synaptic adaptations persist upon repeated exposure to social stimuli and sustain conspecific interaction. Global or VTA DA neuron-specific loss of the ASD-associated synaptic adhesion molecule neuroligin 3 alters the behavioral response toward nonfamiliar conspecifics and the reinforcing properties of conspecific interaction. These behavioral deficits are accompanied by an aberrant expression of AMPA receptors and an occlusion of synaptic plasticity. Altogether, these findings link impaired exploration of nonfamiliar conspecifics to VTA DA neuron dysfunction in mice.

Individuals with autism spectrum disorder have alteration in social and novelty behaviors. Here, Bellone and colleagues show that chemogenetic inhibition of mouse dopamine neurons in the ventral tegmental area can blunt exploration towards unfamiliar conspecifics, and that these behavioral deficits are recapitulated in mice lacking neuroligin3 gene product.

Circadian rhythm and sleep-wake systems share the dynamic extracellular synaptic milieu

The mammalian circadian and sleep-wake systems are closely aligned through their coordinated regulation of daily activity patterns. Although they differ in their anatomical organization and physiological processes, they utilize overlapping regulatory mechanisms that include an assortment of proteins and molecules interacting within the extracellular space. These extracellular factors include proteases that interact with soluble proteins, membrane-attached receptors and the extracellular matrix; and cell adhesion molecules that can form complex scaffolds connecting adjacent neurons, astrocytes and their respective intracellular cytoskeletal elements. Astrocytes also participate in the dynamic regulation of both systems through modulating neuronal appositions, the extracellular space and/or through release of gliotransmitters that can further contribute to the extracellular signaling processes. Together, these extracellular elements create a system that integrates rapid neurotransmitter signaling across longer time scales and thereby adjust neuronal signaling to reflect the daily fluctuations fundamental to both systems. Here we review what is known about these extracellular processes, focusing specifically on areas of overlap between the two systems. We also highlight questions that still need to be addressed. Although we know many of the extracellular players, far more research is needed to understand the mechanisms through which they modulate the circadian and sleep-wake systems.

Gene expression changes in the ventral hippocampus and medial prefrontal cortex of adolescent alcohol-preferring (P) rats following binge-like alcohol drinking

Binge drinking of alcohol during adolescence is a serious public health concern with long-term consequences, including decreased hippocampal and prefrontal cortex volume and deficits in memory. We used RNA sequencing to assess the effects of adolescent binge drinking on gene expression in these regions. Male adolescent alcohol-preferring (P) rats were exposed to repeated binge drinking (three 1-h sessions/day during the dark/cycle, 5 days/week for 3 weeks starting at 28 days of age; ethanol intakes of 2.5-3 g/kg/session). Ethanol significantly altered the expression of 416 of 11,727 genes expressed in the ventral hippocampus. Genes and pathways involved in neurogenesis, long-term potentiation, and axonal guidance were decreased, which could relate to the impaired memory function found in subjects with adolescent alcohol binge-like exposure. The decreased expression of myelin and cholesterol genes and apparent decrease in oligodendrocytes in P rats could result in decreased myelination. In the medial prefrontal cortex, 638 of 11,579 genes were altered; genes in cellular stress and inflammatory pathways were increased, as were genes involved in oxidative phosphorylation. Overall, the results of this study suggest that adolescent binge-like alcohol drinking may alter the development of the ventral hippocampus and medial prefrontal cortex and produce long-term consequences on learning and memory, and on control of impulsive behaviors.

Dlgap1 knockout mice exhibit alterations of the postsynaptic density and selective reductions in sociability

The scaffold protein DLGAP1 is localized at the post-synaptic density (PSD) of glutamatergic neurons and is a component of supramolecular protein complexes organized by PSD95. Gain-of-function variants of DLGAP1 have been associated with obsessive-compulsive disorder (OCD), while haploinsufficient variants have been linked to autism spectrum disorder (ASD) and schizophrenia in human genetic studies. We tested male and female Dlgap1 wild type (WT), heterozygous (HT), and knockout (KO) mice in a battery of behavioral tests: open field, dig, splash, prepulse inhibition, forced swim, nest building, social approach, and sucrose preference. We also used biochemical approaches to examine the role of DLGAP1 in the organization of PSD protein complexes. Dlgap1 KO mice were most notable for disruption of protein interactions in the PSD, and deficits in sociability. Other behavioral measures were largely unaffected. Our data suggest that Dlgap1 knockout leads to PSD disruption and reduced sociability, consistent with reports of DLGAP1 haploinsufficient variants in schizophrenia and ASD.

The DLGAP family: neuronal expression, function and role in brain disorders

The neurotransmitter glutamate facilitates neuronal signalling at excitatory synapses. Glutamate is released from the presynaptic membrane into the synaptic cleft. Across the synaptic cleft glutamate binds to both ion channels and metabotropic glutamate receptors at the postsynapse, which expedite downstream signalling in the neuron. The postsynaptic density, a highly specialized matrix, which is attached to the postsynaptic membrane, controls this downstream signalling. The postsynaptic density also resets the synapse after each synaptic firing. It is composed of numerous proteins including a family of Discs large associated protein 1, 2, 3 and 4 (DLGAP1-4) that act as scaffold proteins in the postsynaptic density. They link the glutamate receptors in the postsynaptic membrane to other glutamate receptors, to signalling proteins and to components of the cytoskeleton. With the central localisation in the postsynapse, the DLGAP family seems to play a vital role in synaptic scaling by regulating the turnover of both ionotropic and metabotropic glutamate receptors in response to synaptic activity. DLGAP family has been directly linked to a variety of psychological and neurological disorders. In this review we focus on the direct and indirect role of DLGAP family on schizophrenia as well as other brain diseases.

The expression of plasticity-related genes in an acute model of stress is modulated by chronic desipramine in a time-dependent manner within medial prefrontal cortex

It is well established that stress plays a major role in the pathogenesis of neuropsychiatric diseases. Stress-induced alteration of synaptic plasticity has been hypothesized to underlie the morphological changes observed by neuroimaging in psychiatric patients in key regions such as hippocampus and prefrontal cortex (PFC). We have recently shown that a single acute stress exposure produces significant short-term alterations of structural plasticity within medial PFC. These alterations were partially prevented by previous treatment with chronic desipramine (DMI). In the present study we evaluated the effects of acute Foot-shock (FS)-stress and pre-treatment with the traditional antidepressant DMI on the gene expression of key regulators of synaptic plasticity and structure. Expression of Homer, Shank, Spinophilin, Densin-180, and the small RhoGTPase related gene Rac1 and downstream target genes, Limk1, Cofilin1 and Rock1 were investigated 1 day (1d), 7 d and 14d after FS-stress exposure. We found that DMI specifically increases the short-term expression of Spinophilin, as well as Homer and Shank family genes, and that both acute stress and DMI exert significant long-term effects on mRNA levels of genes involved in spine plasticity. These findings support the knowledge that acute FS stress and antidepressant treatment induce both rapid and sustained time-dependent alterations in structural components of synaptic plasticity in rodent medial PFC.

Novel Shank3 mutant exhibits behaviors with face validity for autism and altered striatal and hippocampal function

Mutations/deletions in the SHANK3 gene are associated with autism spectrum disorders and intellectual disability. Here, we present electrophysiological and behavioral consequences in novel heterozygous and homozygous mice with a transcriptional stop cassette inserted upstream of the PDZ domain-coding exons in Shank3 (Shank3^E13 ). Insertion of a transcriptional stop cassette prior to exon 13 leads to loss of the two higher molecular weight isoforms of Shank3. Behaviorally, both Shank3^E13 heterozygous (HET) and homozygous knockout (KO) mice display increased repetitive grooming, deficits in social interaction tasks, and decreased rearing. Shank3^E13 KO mice also display deficits in spatial memory in the Morris water maze task. Baseline hippocampal synaptic transmission and short-term plasticity are preserved in Shank3^E13 HET and KO mice, while both HET and KO mice exhibit impaired hippocampal long-term plasticity. Additionally, Shank3^E13 HET and KO mice display impaired striatal glutamatergic synaptic transmission. These results demonstrate for the first time in this novel Shank3 mutant that both homozygous and heterozygous mutation of Shank3 lead to behavioral abnormalities with face validity for autism along with widespread synaptic dysfunction. Autism Res 2017, 10: 42-65. © 2016 International Society for Autism Research, Wiley Periodicals, Inc.

SHANK3 controls maturation of social reward circuits in the VTA

Haploinsufficiency of SHANK3, encoding the synapse scaffolding protein SHANK3, leads to a highly penetrant form of Autism Spectrum Disorder (ASD). How SHANK3 insufficiency affects specific neural circuits and this is related to specific ASD symptoms remains elusive. Here we used shRNA to model Shank3 insufficiency in the Ventral Tegmental Area (VTA) of mice. We identified dopamine (DA) and GABA cell-type specific changes in excitatory synapse transmission that converge to reduce DA neuron activity and generate behavioral deficits, including impaired social preference. Administration of a positive allosteric modulator of the type 1 metabotropic glutamate receptors (mGluR1) during the first postnatal week restored DA neuron excitatory synapse transmission and rescued the social preference defects, while optogenetic DA neuron stimulation was sufficient to enhance social preference. Collectively, these data reveal the contribution of impaired VTA function to social behaviors and identify mGluR1 modulation during postnatal development as a potential treatment strategy.

Comprehensive behavioral analysis of RNG105 (Caprin1) heterozygous mice: Reduced social interaction and attenuated response to novelty

RNG105 (also known as Caprin1) is a major RNA-binding protein in neuronal RNA granules, and is responsible for mRNA transport to dendrites and neuronal network formation. A recent study reported that a heterozygous mutation in the Rng105 gene was found in an autism spectrum disorder (ASD) patient, but it remains unclear whether there is a causal relation between RNG105 deficiency and ASD. Here, we subjected Rng105(+/-) mice to a comprehensive behavioral test battery, and revealed the influence of RNG105 deficiency on mouse behavior. Rng105(+/-) mice exhibited a reduced sociality in a home cage and a weak preference for social novelty. Consistently, the Rng105(+/-) mice also showed a weak preference for novel objects and novel place patterns. Furthermore, although the Rng105(+/-) mice exhibited normal memory acquisition, they tended to have relative difficulty in reversal learning in the spatial reference tasks. These findings suggest that the RNG105 heterozygous knockout leads to a reduction in sociality, response to novelty and flexibility in learning, which are implicated in ASD-like behavior.

Ethanol-Associated Changes in Glutamate Reward Neurocircuitry: A Minireview of Clinical and Preclinical Genetic Findings

Herein, we have reviewed the role of glutamate, the major excitatory neurotransmitter in the brain, in a number of neurochemical, -physiological, and -behavioral processes mediating the development of alcohol dependence. The findings discussed include results from both preclinical as well as neuroimaging and postmortem clinical studies. Expression levels for a number of glutamate-associated genes and/or proteins are modulated by alcohol abuse and dependence. These changes in expression include metabotropic receptors and ionotropic receptor subunits as well as different glutamate transporters. Moreover, these changes in gene expression parallel the pharmacologic manipulation of these same receptors and transporters. Some of these gene expression changes may have predated alcohol abuse and dependence because a number of glutamate-associated polymorphisms are related to a genetic predisposition to develop alcohol dependence. Other glutamate-associated polymorphisms are linked to age at the onset of alcohol-dependence and initial level of response/sensitivity to alcohol. Finally, findings of innate and/or ethanol-induced glutamate-associated gene expression differences/changes observed in a genetic animal model of alcoholism, the P rat, are summarized. Overall, the existing literature indicates that changes in glutamate receptors, transporters, enzymes, and scaffolding proteins are crucial for the development of alcohol dependence and there is a substantial genetic component to these effects. This indicates that continued research into the genetic underpinnings of these glutamate-associated effects will provide important novel molecular targets for treating alcohol abuse and dependence.

Synapsin IIb as a functional marker of submissive behavior

Dominance and submissiveness are important functional elements of the social hierarchy. By employing selective breeding based on a social interaction test, we developed mice with strong and stable, inheritable features of dominance and submissiveness. In order to identify candidate genes responsible for dominant and submissive behavior, we applied transcriptomic and proteomic studies supported by molecular, behavioral and pharmacological approaches. We clearly show here that the expression of Synapsin II isoform b (Syn IIb) is constitutively upregulated in the hippocampus and striatum of submissive mice in comparison to their dominant and wild type counterparts. Moreover, the reduction of submissive behavior achieved after mating and delivery was accompanied by a marked reduction of Syn IIb expression. Since submissiveness has been shown to be associated with depressive-like behavior, we applied acute SSRI (Paroxetine) treatment to reduce submissiveness in studied mice. We found that reduction of submissive behavior evoked by Paroxetine was paired with significantly decreased Syn IIb expression. In conclusion, our findings indicate that submissiveness, known to be an important element of depressive-like behavioral abnormalities, is strongly linked with changes in Syn IIb expression.

T-Brain-1--A Potential Master Regulator in Autism Spectrum Disorders

T-Brain-1 (TBR1), a causative gene in autism spectrum disorders (ASDs), encodes a brain-specific T-box transcription factor. It is therefore possible that TBR1 controls the expression of other autism risk factors. The downstream genes of TBR1 have been identified using microarray and promoter analyses. In this study, we annotated individual genes downstream of TBR1 and investigated any associations with ASDs through extensive literature searches. Of 124 TBR1 target genes, 23 were reported to be associated with ASDs. In addition, one gene, Kiaa0319, is a known causative gene for dyslexia, a disorder frequently associated with autism. A change in expression level in 10 of these 24 genes has been previously confirmed. We further validated the alteration of RNA expression levels of Kiaa0319, Baiap2, and Gad1 in Tbr1 deficient mice. Among these 24 genes, four transcription factors Auts2, Nfia, Nr4a2, and Sox5 were found, suggesting that TBR1 controls a transcriptional cascade relevant to autism pathogenesis. A further five of the 24 genes (Cd44, Cdh8, Cntn6, Gpc6, and Ntng1) encode membrane proteins that regulate cell adhesion and axonal outgrowth. These genes likely contribute to the role of TBR1 in regulation of neuronal migration and axonal extension. Besides, decreases in Grin2b expression and increases in Gad1 expression imply that neuronal activity may be aberrant in Tbr1 deficient mice. These analyses provide direction for future experiments to reveal the pathogenic mechanism of autism.

Neural targets in the study and treatment of social cognition in autism spectrum disorder

The purpose of this chapter is to present results from recent research on social cognition in autism spectrum disorder (ASD). The clinical phenomenology and neuroanatomical circuitry of ASD are first briefly described. The neuropharmacology of social cognition in animal models of ASD and humans is then addressed. Next, preclinical and clinical research on the neurohormone oxytocin is reviewed. This is followed by a presentation of results from preclinical and clinical studies on the excitatory amino acid glutamate. Finally, the role of neuroinflammation in ASD is addressed from the perspectives of preclinical neuroscience and research involving humans with ASD.