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Tau pathology is a hallmark of several neurodegenerative diseases, including frontotemporal dementia and Alzheimer's disease. However, the sequence of events and the form of tau that confers toxicity are still unclear, due in large part to the lack of physiological models of tauopathy initiation and progression in which to test hypotheses. We have developed a series of targeted mice expressing frontotemporal-dementia-causing mutations in the humanized MAPT gene to investigate the earliest stages of tauopathy. MAPT Int10+3G>A and MAPT S305N;Int10+3G>A lines show abundant hyperphosphorylated tau in the hippocampus and entorhinal cortex, but they do not develop seed-competent fibrillar structures. Accumulation of hyperphosphorylated tau was accompanied by neurite degeneration, loss of viable synapses and indicators of behavioral abnormalities. Our results demonstrate that neuronal toxicity can occur in the absence of fibrillar, higher-order structures and that tau hyperphosphorylation is probably involved in the earliest etiological events in tauopathies showing isoform ratio imbalance., Competing Interests: Competing interests: T.E. serves as a Representative for Phenovance LLC, which provides commercial service using IntelliCage. T.C.S. serves as an Executive Consultant for RIKEN BIO Co. Ltd., which sublicenses App knock-in mice to for-profit organizations. K.E.D. is a board member of Ceracuity LLC. H.Z. has served at scientific advisory boards and/or as a consultant for Abbvie, Acumen, Alector, Alzinova, ALZPath, Annexon, Apellis, Artery Therapeutics, AZTherapies, CogRx, Denali, Eisai, Nervgen, Novo Nordisk, Optoceutics, Passage Bio, Pinteon Therapeutics, Prothena, Red Abbey Labs, reMYND, Roche, Samumed, Siemens Healthineers, Triplet Therapeutics and Wave, has given lectures in symposia sponsored by Cellectricon, Fujirebio, Alzecure, Biogen and Roche, and is a cofounder of Brain Biomarker Solutions in Gothenburg AB (BBS), which is a part of the GU Ventures Incubator Program (outside submitted work). The other authors declare no competing interests., (© 2024. The Author(s).)

Synapses are implicated in many neuropsychiatric illnesses. Here, we provide an overview of in vivo techniques to index synaptic markers in patients. Several positron emission tomography (PET) tracers for synaptic vesicle glycoprotein 2 A (SV2A) show good reliability and selectivity. We review over 50 clinical studies including over 1700 participants, and compare findings in healthy ageing and across disorders, including addiction, schizophrenia, depression, posttraumatic stress disorder, and neurodegenerative disorders, including tauopathies, Huntington's disease and α-synucleinopathies. These show lower SV2A measures in cortical brain regions across most of these disorders relative to healthy volunteers, with the most well-replicated findings in tauopathies, whilst changes in Huntington's chorea, Parkinson's disease, corticobasal degeneration and progressive supranuclear palsy are predominantly subcortical. SV2A PET measures are correlated with functional connectivity across brain networks, and a number of other measures of brain function, including glucose metabolism. However, the majority of studies found no relationship between grey matter volume measured with magnetic resonance imaging and SV2A PET measures. Cognitive dysfunction, in domains including working memory and executive function, show replicated inverse relationships with SV2A measures across diagnoses, and initial findings also suggest transdiagnostic relationships with mood and anxiety symptoms. This suggests that synaptic abnormalities could be a common pathophysiological substrate underlying cognitive and, potentially, affective symptoms. We consider limitations of evidence and future directions; highlighting the need to develop postsynaptic imaging markers and for longitudinal studies to test causal mechanisms., (© 2024. The Author(s).)

The development of novel radiotracers for Positron Emission Tomography (PET) imaging agents targeting the synaptic vesicle glycoprotein 2 A (SV2A), an integral glycoprotein present in the membrane of all synaptic vesicles throughout the central nervous system, provides a method for the in vivo quantification of synaptic density. This is of particular interest in neuropsychiatric disorders given that synaptic alterations appear to underlie disease progression and symptom severity. In this review, we briefly describe the development of these SV2A tracers and the evaluation of quantification methods. Next, we discuss application of SV2A PET imaging to the study of depression, including a review of our findings demonstrating lower SV2A synaptic density in people with significant depressive symptoms and the use of a ketamine drug challenge to examine synaptogenesis in vivo. We then highlight the importance of performing translational PET imaging in animal models in conjunction with clinical imaging. We consider the ongoing challenges, possible solutions, and present preliminary findings from our lab demonstrating the translational benefit and potential of in vivo SV2A imaging in animal models of chronic stress. Finally, we discuss methodological improvements and future directions for SV2A imaging, potentially in conjunction with other neural markers., (© 2024. The Author(s), under exclusive licence to American College of Neuropsychopharmacology.)

Endolymphatic hydrops, increased endolymphatic fluid within the cochlea, is the key pathologic finding in patients with Meniere's disease, a disease of episodic vertigo, fluctuating hearing loss, tinnitus, and aural fullness. Endolymphatic hydrops also can occur after noise trauma and its presence correlates with cochlear synaptopathy, a form of hearing loss caused by reduced numbers of synapses between hair cells and auditory nerve fibers. Here we tested whether there is a mechanistic link between these two phenomena by using multimodal imaging techniques to analyze the cochleae of transgenic mice exposed to blast and osmotic challenge. In vivo cochlear imaging after blast exposure revealed dynamic increases in endolymph that involved hair cell mechanoelectrical transduction channel block but not the synaptic release of glutamate at the hair cell-auditory nerve synapse. In contrast, ex vivo and in vivo auditory nerve imaging revealed that synaptopathy requires glutamate release from hair cells but not endolymphatic hydrops. Thus, although endolymphatic hydrops and cochlear synaptopathy are both observed after noise exposure, one does not cause the other. They are simply co-existent sequelae that derive from the traumatic stimulation of hair cell stereociliary bundles. Importantly, these data argue that Meniere's disease derives from hair cell transduction channel blockade., (© 2024. The Author(s).)

Zika virus (ZIKV) infection was first reported in 2015 in Brazil as causing microcephaly and other developmental abnormalities in newborns, leading to the identification of Congenital Zika Syndrome (CZS). Viral infections have been considered an environmental risk factor for neurodevelopmental disorders outcome, such as Autism Spectrum Disorder (ASD). Moreover, not only the infection per se, but maternal immune system activation during pregnancy, has been linked to fetal neurodevelopmental disorders. To understand the impact of ZIKV vertical infection on brain development, we derived induced pluripotent stem cells (iPSC) from Brazilian children born with CZS, some of the patients also being diagnosed with ASD. Comparing iPSC-derived neurons from CZS with a control group, we found lower levels of pre- and postsynaptic proteins and reduced functional synapses by puncta co-localization. Furthermore, neurons and astrocytes derived from the CZS group showed decreased glutamate levels. Additionally, the CZS group exhibited elevated levels of cytokine production, one of which being IL-6, already associated with the ASD phenotype. These preliminary findings suggest that ZIKV vertical infection may cause long-lasting disruptions in brain development during fetal stages, even in the absence of the virus after birth. These disruptions could contribute to neurodevelopmental disorders manifestations such as ASD. Our study contributes with novel knowledge of the CZS outcomes and paves the way for clinical validation and the development of potential interventions to mitigate the impact of ZIKV vertical infection on neurodevelopment., (© 2024. The Author(s).)

We examined the role of protein tyrosine phosphatase receptor sigma (PTPRS) in the context of Alzheimer's disease and synaptic integrity. Publicly available datasets (BRAINEAC, ROSMAP, ADC1) and a cohort of asymptomatic but "at risk" individuals (PREVENT-AD) were used to explore the relationship between PTPRS and various Alzheimer's disease biomarkers. We identified that PTPRS rs10415488 variant C shows features of neuroprotection against early Tau pathology and synaptic degeneration in Alzheimer's disease. This single nucleotide polymorphism correlated with higher PTPRS transcript abundance and lower p(181)Tau and GAP-43 levels in the CSF. In the brain, PTPRS protein abundance was significantly correlated with the quantity of two markers of synaptic integrity: SNAP25 and SYT-1. We also found the presence of sexual dimorphism for PTPRS, with higher CSF concentrations in males than females. Male carriers for variant C were found to have a 10-month delay in the onset of AD. We thus conclude that PTPRS acts as a neuroprotective receptor in Alzheimer's disease. Its protective effect is most important in males, in whom it postpones the age of onset of the disease., (© 2024. The Author(s).)

Human brains vary across people and over time; such variation is not yet understood in cellular terms. Here we describe a relationship between people's cortical neurons and cortical astrocytes. We used single-nucleus RNA sequencing to analyse the prefrontal cortex of 191 human donors aged 22-97 years, including healthy individuals and people with schizophrenia. Latent-factor analysis of these data revealed that, in people whose cortical neurons more strongly expressed genes encoding synaptic components, cortical astrocytes more strongly expressed distinct genes with synaptic functions and genes for synthesizing cholesterol, an astrocyte-supplied component of synaptic membranes. We call this relationship the synaptic neuron and astrocyte program (SNAP). In schizophrenia and ageing-two conditions that involve declines in cognitive flexibility and plasticity 1,2 -cells divested from SNAP: astrocytes, glutamatergic (excitatory) neurons and GABAergic (inhibitory) neurons all showed reduced SNAP expression to corresponding degrees. The distinct astrocytic and neuronal components of SNAP both involved genes in which genetic risk factors for schizophrenia were strongly concentrated. SNAP, which varies quantitatively even among healthy people of similar age, may underlie many aspects of normal human interindividual differences and may be an important point of convergence for multiple kinds of pathophysiology., (© 2024. The Author(s).)

The ever-growing compendium of genetic variants associated with human pathologies demands new methods to study genotype-phenotype relationships in complex tissues in a high-throughput manner 1,2 . Here we introduce adeno-associated virus (AAV)-mediated direct in vivo single-cell CRISPR screening, termed AAV-Perturb-seq, a tuneable and broadly applicable method for transcriptional linkage analysis as well as high-throughput and high-resolution phenotyping of genetic perturbations in vivo. We applied AAV-Perturb-seq using gene editing and transcriptional inhibition to systematically dissect the phenotypic landscape underlying 22q11.2 deletion syndrome 3,4 genes in the adult mouse brain prefrontal cortex. We identified three 22q11.2-linked genes involved in known and previously undescribed pathways orchestrating neuronal functions in vivo that explain approximately 40% of the transcriptional changes observed in a 22q11.2-deletion mouse model. Our findings suggest that the 22q11.2-deletion syndrome transcriptional phenotype found in mature neurons may in part be due to the broad dysregulation of a class of genes associated with disease susceptibility that are important for dysfunctional RNA processing and synaptic function. Our study establishes a flexible and scalable direct in vivo method to facilitate causal understanding of biological and disease mechanisms with potential applications to identify genetic interventions and therapeutic targets for treating disease., (© 2023. The Author(s).)

Passive immunotherapy is one of the most promising interventions for Alzheimer's disease (AD). However, almost all immune-modulating strategies fail in clinical trials with unclear causes although they attenuate neuropathology and cognitive deficits in AD animal models. Here, we showed that Aβ-targeting antibodies including their lgG1 and lgG4 subtypes induced microglial engulfment of neuronal synapses by activating CR3 or FcγRIIb via the complex of Aβ, antibody, and complement. Notably, anti-Aβ antibodies without Fc fragment, or with blockage of CR3 or FcγRIIb, did not exert these adverse effects. Consistently, Aβ-targeting antibodies, but not their Fab fragments, significantly induced acute microglial synapse removal and rapidly exacerbated cognitive deficits and neuroinflammation in APP/PS1 mice post-treatment, whereas the memory impairments in mice were gradually rescued thereafter. Since the recovery rate of synapses in humans is much lower than that in mice, our findings may clarify the variances in the preclinical and clinical studies assessing AD immunotherapies. Therefore, Aβ-targeting antibodies lack of Fc fragment, or with reduced Fc effector function, may not induce microglial synaptic pruning, providing a safer and more efficient therapeutic alternative for passive immunotherapy for AD., (© 2022. The Author(s).)

Microglia contain multiple mechanisms that shape the synaptic landscape during postnatal development. Whether the synaptic changes mediated by microglia reflect the developmental refinement of neuronal responses in sensory cortices, however, remains poorly understood. In postnatal life, the development of increased orientation and spatial frequency selectivity of neuronal responses in primary visual cortex (V1) supports the emergence of high visual acuity. Here, we used the colony-stimulating factor 1 receptor (CSF1R) inhibitor PLX5622 to rapidly and durably deplete microglia in mice during the juvenile period in which increased orientation and spatial frequency selectivity emerge. Excitatory and inhibitory tuning properties were measured simultaneously using multi-photon calcium imaging in layer II/III of mouse V1. We found that microglia depletion generally increased evoked activity which, in turn, reduced orientation selectivity. Surprisingly, microglia were not required for the emergence of high spatial frequency tuned responses. In addition, microglia depletion did not perturb cortical binocularity, suggesting normal depth processing. Together, our finding that orientation and high spatial frequency selectivity in V1 are differentially supported by microglia reveal that microglia are required normal sensory processing, albeit selectively., (© 2022. The Author(s).)

Accumulation of phosphorylated α-synuclein aggregates has been implicated in several diseases, such as Parkinson's disease (PD) and dementia with Lewy bodies (DLB), and is thought to spread in a prion-like manner. Elucidating the mechanisms of prion-like transmission of α-synuclein is important for the development of therapies for these diseases, but little is known about the details. Here, we injected α-synuclein fibrils into the brains of wild-type mice and examined the early phase of the induction of phosphorylated α-synuclein accumulation. We found that phosphorylated α-synuclein appeared within a few days after the intracerebral injection. It was observed initially in presynaptic regions and subsequently extended its localization to axons and cell bodies.　These results suggest that extracellular α-synuclein fibrils are taken up into the presynaptic region and seed-dependently convert the endogenous normal α-synuclein that is abundant there to an abnormal phosphorylated form, which is then transported through the axon to the cell body., (© 2022. The Author(s).)

The balances between NSCs growth and differentiation, and between glial and neuronal differentiation play a key role in brain regeneration after any pathological conditions. It is well known that the nervous tissue shows a poor recovery after injury due to the factors present in the wounded microenvironment, particularly inflammatory factors, that prevent neuronal differentiation. Thus, it is essential to generate a favourable condition for NSCs and conduct them to differentiate towards functional neurons. Here, we show that neuroinflammation has no effect on NSCs proliferation but induces an aberrant neuronal differentiation that gives rise to dystrophic, non-functional neurons. This is perhaps the initial step of brain failure associated to many neurological disorders. Interestingly, we demonstrate that phosphatidylcholine (PtdCho)-enriched media enhances neuronal differentiation even under inflammatory stress by modifying the commitment of post-mitotic cells. The pro-neurogenic effect of PtdCho increases the population of healthy normal neurons. In addition, we provide evidences that this phospholipid ameliorates the damage of neurons and, in consequence, modulates neuronal plasticity. These results contribute to our understanding of NSCs behaviour under inflammatory conditions, opening up new venues to improve neurogenic capacity in the brain., (© 2021. The Author(s).)

The purpose of this exploratory research is to provide data on synaptopathy in the behavioral variant of frontotemporal dementia (bvFTD). Twelve patients with probable bvFTD were compared to 12 control participants and 12 patients with Alzheimer's disease (AD). Loss of synaptic projections was assessed with [ 18 F]UCBH-PET. Total distribution volume was obtained with Logan method using carotid artery derived input function. Neuroimages were analyzed with SPM12. Verbal fluency, episodic memory and awareness of cognitive impairment were equally impaired in patients groups. Compared to controls, [ 18 F]UCBH uptake tended to decrease in the right anterior parahippocampal gyrus of bvFTD patients. Loss of synaptic projections was observed in the right hippocampus of AD participants, but there was no significant difference in [ 18 F]UCBH brain uptake between patients groups. Anosognosia for clinical disorder was correlated with synaptic density in the caudate nucleus and the anteromedial prefrontal cortex. This study suggests that synaptopathy in bvFTD targets the temporal social brain and self-referential processes., (© 2021. The Author(s).)

The most significant common variant association for schizophrenia (SCZ) reflects increased expression of the complement component 4A (C4A). Yet, it remains unclear how C4A interacts with other SCZ risk genes or whether the complement system more broadly is implicated in SCZ pathogenesis. Here, we integrate several existing, large-scale genetic and transcriptomic datasets to interrogate the functional role of the complement system and C4A in the human brain. Unexpectedly, we find no significant genetic enrichment among known complement system genes for SCZ. Conversely, brain co-expression network analyses using C4A as a seed gene reveal that genes downregulated when C4A expression increases exhibit strong and specific genetic enrichment for SCZ risk. This convergent genomic signal reflects synaptic processes, is sexually dimorphic and most prominent in frontal cortical brain regions, and is accentuated by smoking. Overall, these results indicate that synaptic pathways-rather than the complement system-are the driving force conferring SCZ risk.

Familial encephalopathy with neuroserpin inclusion bodies (FENIB) is a progressive neurodegenerative disease caused by point mutations in the gene for neuroserpin, a serine protease inhibitor of the nervous system. Different mutations are known that are responsible for mutant neuroserpin polymerization and accumulation as inclusion bodies in many cortical and subcortical neurons, thereby leading to cell death, dementia and epilepsy. Many efforts have been undertaken to elucidate the molecular pathways responsible for neuronal death. Most investigations have concentrated on analysis of intracellular mechanisms such as endoplasmic reticulum (ER) stress, ER-associated protein degradation (ERAD) and oxidative stress. We have generated a HEK-293 cell model of FENIB by overexpressing G392E-mutant neuroserpin and in this study we examine trafficking and toxicity of this polymerogenic variant. We observed that a small fraction of mutant neuroserpin is secreted via the ER-to-Golgi pathway, and that this release can be pharmacologically regulated. Overexpression of the mutant form of neuroserpin did not stimulate cell death in the HEK-293 cell model. Finally, when treating primary hippocampal neurons with G392E neuroserpin polymers, we did not detect cytotoxicity or synaptotoxicity. Altogether, we report here that a polymerogenic mutant form of neuroserpin is secreted from cells but is not toxic in the extracellular milieu.

Cerebrovascular lesions seen as white matter hyperintensity in MRI of elderly population caused due to micro-infracts and micro-bleeds contributes to vascular dementia. Such vascular insult caused by impairment in blood flow to specific area in brain involving small vessels can gradually worsen the pathology leading to cognitive deficits. In the present study we developed a transient model of vaso-constriction to study the impact of such pathology by bilateral injection of ET-1 (Endothelin-1; a 21 amino acid vasoconstricting peptide) into lateral ventricles of C57 mice. The impediment in cerebral blood flow decreased CD31 expression in endothelial cells lining the blood vessels around the hippocampal region, leading to memory deficits after 7 days. Activity dependent protein translation, critical for synaptic plasticity was absent in synaptoneurosomes prepared from hippocampal tissue. Further, Akt1- mTOR signaling cascade was downregulated indicating the possible cause for loss of activity dependent protein translation. However, these effects were reversed after 30 days indicating the ephemeral nature of deficits following a single vascular insult. Present study demonstrates that vasoconstriction leading to memory deficit and decline in activity dependent protein translation in hippocampus as a potential molecular mechanism impacting synaptic plasticity.

Cortical pathology contributes to chronic cognitive impairment of patients suffering from the neuroinflammatory disease multiple sclerosis (MS). How such gray matter inflammation affects neuronal structure and function is not well understood. In the present study, we use functional and structural in vivo imaging in a mouse model of cortical MS to demonstrate that bouts of cortical inflammation disrupt cortical circuit activity coincident with a widespread, but transient, loss of dendritic spines. Spines destined for removal show local calcium accumulations and are subsequently removed by invading macrophages or activated microglia. Targeting phagocyte activation with a new antagonist of the colony-stimulating factor 1 receptor prevents cortical synapse loss. Overall, our study identifies synapse loss as a key pathological feature of inflammatory gray matter lesions that is amenable to immunomodulatory therapy.

Auditory neuropathy is caused by the loss of afferent input to the brainstem via the components of the neural pathway comprising inner hair cells and the first order neurons of the spiral ganglion. Recent work has identified the synapse between cochlear primary afferent neurons and sensory hair cells as a particularly vulnerable component of this pathway. Loss of these synapses due to noise exposure or aging results in the pathology identified as hidden hearing loss, an initial stage of cochlear dysfunction that goes undetected in standard hearing tests. We show here that repulsive axonal guidance molecule a (RGMa) acts to prevent regrowth and synaptogenesis of peripheral auditory nerve fibers with inner hair cells. Treatment of noise-exposed animals with an anti-RGMa blocking antibody regenerated inner hair cell synapses and resulted in recovery of wave-I amplitude of the auditory brainstem response, indicating effective reversal of synaptopathy.

The complement component 4 (C4) gene is linked to schizophrenia and synaptic refinement. In humans, greater expression of C4A in the brain is associated with an increased risk of schizophrenia. To investigate this genetic finding and address how C4A shapes brain circuits in vivo, here, we generated a mouse model with primate-lineage-specific isoforms of C4, human C4A and/or C4B. Human C4A bound synapses more efficiently than C4B. C4A (but not C4B) rescued the visual system synaptic refinement deficits of C4 knockout mice. Intriguingly, mice without C4 had normal numbers of cortical synapses, which suggests that complement is not required for normal developmental synaptic pruning. However, overexpressing C4A in mice reduced cortical synapse density, increased microglial engulfment of synapses and altered mouse behavior. These results suggest that increased C4A-mediated synaptic elimination results in abnormal brain circuits and behavior. Understanding pathological overpruning mechanisms has important therapeutic implications in disease conditions such as schizophrenia.

Valproic acid (VPA) is widely prescribed to treat epilepsy. Maternal VPA use is, however, clinically restricted because of the severe risk that VPA may cause neurodevelopmental disorders in offspring, such as autism spectrum disorder. Understanding the negative action of VPA may help to prevent VPA-induced neurodevelopmental disorders. Astrocytes play a vital role in neurodevelopment and synapse function; however, the impact of VPA on astrocyte involvement in neurodevelopment and synapse function has not been examined. In this study, we examined whether exposure of cultured astrocytes to VPA alters neuronal morphology and synapse function of co-cultured neurons. We show that synaptic transmission by inhibitory neurons was small because VPA-exposed astrocytes reduced the number of inhibitory synapses. However, synaptic transmission by excitatory neurons and the number of excitatory synapses were normal with VPA-exposed astrocytes. VPA-exposed astrocytes did not affect the morphology of inhibitory neurons. These data indicate that VPA-exposed astrocytes impair synaptogenesis specifically of inhibitory neurons. Our results indicate that maternal use of VPA would affect not only neurons but also astrocytes and would result in perturbed astrocyte-mediated neurodevelopment.

Climbing fibers from the inferior olive make strong excitatory synapses onto cerebellar Purkinje cell (PC) dendrites and trigger distinctive responses known as complex spikes. We found that, in awake mice, a complex spike in one PC suppressed conventional simple spikes in neighboring PCs for several milliseconds. This involved a new ephaptic coupling, in which an excitatory synapse generated large negative extracellular signals that nonsynaptically inhibited neighboring PCs. The distance dependence of complex spike-simple spike ephaptic signaling, combined with the known CF divergence, allowed a single inferior olive neuron to influence the output of the cerebellum by synchronously suppressing the firing of potentially over 100 PCs. Optogenetic studies in vivo and dynamic clamp studies in slice indicated that such brief PC suppression, as a result of either ephaptic signaling or other mechanisms, could effectively promote firing in neurons in the deep cerebellar nuclei with remarkable speed and precision.

Noise-induced hearing loss (NIHL) is a common health concern with significant social, psychological, and cognitive implications. Moderate levels of acoustic overstimulation associated with tinnitus and impaired speech perception cause cochlear synaptopathy, characterized physiologically by reduction in wave I of the suprathreshold auditory brainstem response (ABR) and reduced number of synapses between sensory hair cells and auditory neurons. The unfolded protein response (UPR), an endoplasmic reticulum stress response pathway, has been implicated in the pathogenesis and treatment of NIHL as well as neurodegeneration and synaptic damage in the brain. In this study, we used the small molecule UPR modulator Integrated Stress Response InhiBitor (ISRIB) to treat noise-induced cochlear synaptopathy in a mouse model. Mice pretreated with ISRIB prior to noise-exposure were protected against noise-induced synapse loss. Male, but not female, mice also exhibited ISRIB-mediated protection against noise-induced suprathreshold ABR wave-I amplitude reduction. Female mice had higher baseline wave-I amplitudes but greater sensitivity to noise-induced wave-I reduction. Our results suggest that the UPR is implicated in noise-induced cochlear synaptopathy, and can be targeted for treatment.

Photoreceptors possess ribbon synapses distinct from the conventional synapses in the brain. Little is known about the function of the BBSome, a complex integral in ciliary and intracellular trafficking, in ribbon synaptic formation. We performed immunohistochemistry using retinas from Bardet-Biedl Syndrome (BBS) mouse models and found that BBS mutant animals have significantly fewer ribbon synapses in the outer plexiform layer and increased ectopic synapses in the outer nuclear layer compared to controls. Many ectopic synapses in BBS mutant retinas are associated with horizontal cell axonal processes that aberrantly intrude into the outer nuclear layer. To determine whether this horizontal cell phenotype is a consequence of retinal degeneration, we examined this phenotype in mice with photoreceptor-specific inactivation of the BBSome induced by Cre recombinase driven by the rhodopsin promoter. At three months of age, despite retinal degeneration, Bbs8 floxed/floxed ; Rho-Cre + mice lack the aberrant intrusion of horizontal cell processes. At 6 months, some horizontal cell processes intrude into the outer nuclear layer in Bbs8 floxed/floxed ; Rho-Cre + mice, but the phenotype does not recapitulate the phenotypic severity observed in young congenital BBS mutant mice. Therefore, the lack of BBSome function negatively impacts retinal synaptogenesis, and causes horizontal cell defects in a potentially cell-autonomous fashion.

Cerebrospinal fluid (CSF) biomarkers based on the core pathological proteins associated with Alzheimer's disease (AD), i.e., amyloid-β (Aβ) and tau protein, are widely regarded as useful diagnostic biomarkers. However, a lack of biomarkers for monitoring the treatment response and indexing clinical severity has proven to be problematic in drug trials targeting Aβ. Therefore, new biomarkers are needed to track non-Aβ and non-tau pathology. Many proteins involved in the pathophysiological progression of AD have shown promise as new biomarkers. Neurodegeneration- and synapse-related biomarkers in CSF (e.g., neurofilament light polypeptide [NFL], neurogranin, and visinin-like protein 1) and blood (e.g., NFL) aid prediction of AD progress, as well as early diagnosis. Neuroinflammation, lipid dysmetabolism, and impaired protein clearance are considered important components of AD pathophysiology. Inflammation-related proteins in the CSF, such as progranulin, intercellular adhesion molecule 1, and chitinase-3-like protein 1 (YKL-40), are useful for the early detection of AD and can represent clinical severity. Several lipid metabolism-associated biomarkers and protein clearance-linked markers have also been suggested as candidate AD biomarkers. Combinations of subsets of new biomarkers enhance their utility in terms of broadly characterizing AD-associated pathological changes, thereby facilitating precise selection of susceptible patients and comprehensive monitoring of the treatment response. This approach could facilitate the development of effective treatments for AD.

The duplication and deletion mutations of the S-SCAM/MAGI-2 gene are associated with schizophrenia and infantile spasms, respectively. S-SCAM is a unique synaptic scaffolding protein that localizes to both excitatory and GABAergic synapses. However, consequences of aberrant S-SCAM expression on GABAergic synapses is little studied. Here we report the effect of S-SCAM knockdown and overexpression on GABAergic synapses. S-SCAM knockdown in cultured hippocampal neurons caused a drastic loss of both pre- and post-synaptic components of GABAergic synapses, indicating its essential role in GABAergic synapse formation and maintenance. Surprisingly, S-SCAM overexpression also attenuated GABAergic synapses, but the effect is mediated by the loss of postsynaptic GABA A receptors, gephyrin, and neuroligin 2 and does not involve presynaptic component vesicular GABA transporters. Overexpression studies using S-SCAM mutants with various domain deletions indicated that GABAergic synapse loss correlates with their ability to increase excitatory synaptic function. Consistently, AMPA receptor antagonist CNQX or calcineurin inhibitor FK506 abolished the S-SCAM overexpression-induced loss of GABA A receptors, supporting that GABAergic synapse loss by S-SCAM overexpression is due to the activity-induced dispersal of synaptic GABA A receptors. These results suggest that abnormal S-SCAM protein levels disrupt excitation/inhibition balance in neurons, which may explain the pathogenic nature of S-SCAM copy number variations.

The transport of N-methyl-d-aspartate receptors (NMDARs) is crucial for neuronal plasticity and synapse formation. Here, we show that KIF3B, a member of the kinesin superfamily proteins (KIFs), supports the transport of vesicles simultaneously containing NMDAR subunit 2A (NR2A) and the adenomatous polyposis coli (APC) complex. Kif3b +/- neurons exhibited a reduction in dendritic levels of both NR2A and NR2B due to the impaired transport of NR2A and increased degradation of NR2B. In Kif3b +/- hippocampal slices, electrophysiological NMDAR response was found decreased and synaptic plasticity was disrupted, which corresponded to a common feature of schizophrenia (SCZ). The histological features of Kif3b +/- mouse brain also mimicked SCZ features, and Kif3b +/- mice exhibited behavioral defects in prepulse inhibition (PPI), social interest, and cognitive flexibility. Indeed, a mutation of KIF3B was specifically identified in human SCZ patients, which was revealed to be functionally defective in a rescue experiment. Therefore, we propose that KIF3B transports NR2A/APC complex and that its dysfunction is responsible for SCZ pathogenesis., (© 2019 The Authors.)

Oligomers of intracellular amyloid β protein (Aβ) are strongly cytotoxic and play crucial roles in synaptic transmission and cognitive function in Alzheimer's disease (AD). However, there is currently no AD model mouse in which to specifically analyze the function of Aβ oligomers only. We have now developed a novel AD model mouse, an Aβ-GFP transgenic mouse (Aβ-GFP Tg), that expresses the GFP-fused human Aβ 1-42 protein, which forms only Aβ oligomers within neurons throughout their life. The fusion proteins are expressed mainly in the hippocampal CA1-CA2 region and cerebral cortex, and are not secreted extracellularly. The Aβ-GFP Tg mice exhibit increased tau phosphorylation, altered spine morphology, decreased expressions of the GluN2B receptor and neuroligin in synaptic regions, attenuated hippocampal long-term potentiation, and impaired object recognition memory compared with non-Tg littermates. Interestingly, these dysfunctions have already appeared in 2-3-months-old animals. The Aβ-GFP fusion protein is bioactive and highly toxic, and induces the similar synaptic dysfunctions as the naturally generated Aβ oligomer derived from postmortem AD patient brains and synthetic Aβ oligomers. Thus, Aβ-GFP Tg mouse is a new tool specialized to analyze the function of Aβ oligomers in vivo and to find subtle changes in synapses in early symptoms of AD.

Noise exposures causing only transient threshold shifts can destroy auditory-nerve synapses without damaging hair cells. Here, we asked whether virally mediated neurotrophin3 (NT3) overexpression can repair this damage. CBA/CaJ mice at 6 wks were injected unilaterally with adeno-associated virus (AAV) containing either NT3 or GFP genes, via the posterior semicircular canal, 3 wks prior to, or 5 hrs after, noise exposure. Controls included exposed animals receiving vehicle only, and unexposed animals receiving virus. Thresholds were measured 2 wks post-exposure, just before cochleas were harvested for histological analysis. In separate virus-injected animals, unexposed cochleas were extracted for qRT-PCR. The GFP reporter showed that inner hair cells (IHCs) were transfected throughout the cochlea, and outer hair cells mainly in the apex. qRT-PCR showed 4- to 10-fold overexpression of NT3 from 1-21 days post-injection, and 1.7-fold overexpression at 40 days. AAV-NT3 delivered prior to noise exposure produced a dose-dependent reduction of synaptopathy, with nearly complete rescue at some cochlear locations. In unexposed ears, NT3 overexpression did not affect thresholds, however GFP overexpression caused IHC loss. In exposed ears, NT3 overexpression increased permanent threshold shifts. Thus, although NT3 overexpression can minimize noise-induced synaptic damage, the forced overexpression may be harmful to hair cells themselves during cochlear overstimulation.

The protein otoferlin plays an essential role at the sensory hair cell synapse. Mutations in otoferlin result in deafness and depending on the species, mild to strong vestibular deficits. While studies in mouse models suggest a role for otoferlin in synaptic vesicle exocytosis and endocytosis, it is unclear whether these functions are conserved across species. To address this question, we characterized the impact of otoferlin depletion in zebrafish larvae and found defects in synaptic vesicle recycling, abnormal synaptic ribbons, and higher resting calcium concentrations in hair cells. We also observed abnormal expression of the calcium binding hair cell genes s100s and parvalbumin, as well as the nogo related proteins rtn4rl2a and rtn4rl2b. Exogenous otoferlin partially restored expression of genes affected by endogenous otoferlin depletion. Our results suggest that in addition to vesicle recycling, depletion of otoferlin disrupts resting calcium levels, alters synaptic ribbon architecture, and perturbs transcription of hair cells specific genes during zebrafish development.

Neuropathic pain can be a debilitating condition with both sensory and affective components, the underlying brain circuitry of which remains poorly understood. In the present study, a basolateral amygdala (BLA)-prefrontal cortex (PFC)-periaqueductal gray (PAG)-spinal cord pathway was identified that is critical for the development of mechanical and thermal hypersensitivity after peripheral nerve injury. It was shown that nerve injury strengthens synaptic input from the BLA onto inhibitory interneurons located in the prelimbic medial PFC, by virtue of reduced endocannabinoid modulation. These augmented synaptic connections mediate a feedforward inhibition of projections from the PFC to the ventrolateral PAG region and its downstream targets. Optogenetic approaches combined with in vivo pharmacology reveal that these BLA-PFC-PAG connections alter pain behaviors by reducing descending noradrenergic and serotoninergic modulation of spinal pain signals. Thus, a long-range brain circuit was identified that is crucial for pain processing and that can potentially be exploited toward targeting neuropathic pain.

Fragile X Syndrome (FXS), a common inheritable form of intellectual disability, is known to alter neocortical circuits. However, its impact on the diverse synapse types comprising these circuits, or on the involvement of astrocytes, is not well known. We used immunofluorescent array tomography to quantify different synaptic populations and their association with astrocytes in layers 1 through 4 of the adult somatosensory cortex of a FXS mouse model, the FMR1 knockout mouse. The collected multi-channel data contained approximately 1.6 million synapses which were analyzed using a probabilistic synapse detector. Our study reveals complex, synapse-type and layer specific changes in the neocortical circuitry of FMR1 knockout mice. We report an increase of small glutamatergic VGluT1 synapses in layer 4 accompanied by a decrease in large VGluT1 synapses in layers 1 and 4. VGluT2 synapses show a rather consistent decrease in density in layers 1 and 2/3. In all layers, we observe the loss of large inhibitory synapses. Lastly, astrocytic association of excitatory synapses decreases. The ability to dissect the circuit deficits by synapse type and astrocytic involvement will be crucial for understanding how these changes affect circuit function, and ultimately defining targets for therapeutic intervention.

A network of communicating tumour cells that is connected by tumour microtubes mediates the progression of incurable gliomas. Moreover, neuronal activity can foster malignant behaviour of glioma cells by non-synaptic paracrine and autocrine mechanisms. Here we report a direct communication channel between neurons and glioma cells in different disease models and human tumours: functional bona fide chemical synapses between presynaptic neurons and postsynaptic glioma cells. These neurogliomal synapses show a typical synaptic ultrastructure, are located on tumour microtubes, and produce postsynaptic currents that are mediated by glutamate receptors of the AMPA subtype. Neuronal activity including epileptic conditions generates synchronised calcium transients in tumour-microtube-connected glioma networks. Glioma-cell-specific genetic perturbation of AMPA receptors reduces calcium-related invasiveness of tumour-microtube-positive tumour cells and glioma growth. Invasion and growth are also reduced by anaesthesia and the AMPA receptor antagonist perampanel, respectively. These findings reveal a biologically relevant direct synaptic communication between neurons and glioma cells with potential clinical implications.

T cells clear virus from the CNS and dynamically regulate brain functions, including spatial learning, through cytokine signaling. Here we determined whether hippocampal T cells that persist after recovery from infection with West Nile virus (WNV) or Zika virus (ZIKV) impact hippocampal-dependent learning and memory. Using newly established models of viral encephalitis recovery in adult animals, we show that in mice that have recovered from WNV or ZIKV infection, T cell-derived interferon-γ (IFN-γ) signaling in microglia underlies spatial-learning defects via virus-target-specific mechanisms. Following recovery from WNV infection, mice showed presynaptic termini elimination with lack of repair, while for ZIKV, mice showed extensive neuronal apoptosis with loss of postsynaptic termini. Accordingly, animals deficient in CD8 + T cells or IFN-γ signaling in microglia demonstrated protection against synapse elimination following WNV infection and decreased neuronal apoptosis with synapse recovery following ZIKV infection. Thus, T cell signaling to microglia drives post-infectious cognitive sequelae that are associated with emerging neurotropic flaviviruses.

Social deficit is a core clinical feature of autism spectrum disorder (ASD) but the underlying neural mechanisms remain largely unclear. We demonstrate that structural and functional impairments occur in glutamatergic synapses in the pyramidal neurons of the anterior cingulate cortex (ACC) in mice with a mutation in Shank3, a high-confidence candidate ASD gene. Conditional knockout of Shank3 in the ACC was sufficient to generate excitatory synaptic dysfunction and social interaction deficits, whereas selective enhancement of ACC activity, restoration of SHANK3 expression in the ACC, or systemic administration of an α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor-positive modulator improved social behavior in Shank3 mutant mice. Our findings provide direct evidence for the notion that the ACC has a role in the regulation of social behavior in mice and indicate that ACC dysfunction may be involved in social impairments in ASD.

Inhibitory extracellular matrices form around mature neurons as perineuronal nets containing chondroitin sulfate proteoglycans that limit axonal sprouting after CNS injury. The enzyme chondroitinase (Chase) degrades inhibitory chondroitin sulfate proteoglycans and improves axonal sprouting and functional recovery after spinal cord injury in rodents. We evaluated the effects of Chase in rhesus monkeys that had undergone C7 spinal cord hemisection. Four weeks after hemisection, we administered multiple intraparenchymal Chase injections below the lesion, targeting spinal cord circuits that control hand function. Hand function improved significantly in Chase-treated monkeys relative to vehicle-injected controls. Moreover, Chase significantly increased corticospinal axon growth and the number of synapses formed by corticospinal terminals in gray matter caudal to the lesion. No detrimental effects were detected. This approach appears to merit clinical translation in spinal cord injury.

Traumatic brain injury (TBI) is a risk factor for Alzheimer's disease (AD), although the mechanisms contributing to this increased risk are unknown. Insulin resistance is an additional risk factor for AD whereby decreased insulin signaling increases synaptic sensitivity to amyloid beta (Aβ) and tau. Considering this, we used rats that underwent a lateral fluid percussion injury at acute and chronic time-points to investigate whether decreased insulin responsiveness in TBI animals is playing a role in synaptic vulnerability to AD pathology. We detected acute and chronic decreases in insulin responsiveness in isolated hippocampal synaptosomes after TBI. In addition to assessing both Aβ and tau binding on synaptosomes, we performed electrophysiology to assess the dysfunctional impact of Aβ and tau oligomers as well as the protective effect of insulin. While we saw no difference in binding or degree of LTP inhibition by either Aβ or tau oligomers between sham and TBI animals, we found that insulin treatment was able to block oligomer-induced LTP inhibition in sham but not in TBI animals. Since insulin treatment has been discussed as a therapy for AD, this gives valuable insight into therapeutic implications of treating AD patients based on one's history of associated risk factors.

Organophosphates account for many of the world's deadliest poisons. They inhibit acetylcholinesterase causing cholinergic crises that lead to seizures and death, while survivors commonly experience long-term neurological problems. Here, we treated brain explants with the organophosphate compound paraoxon and uncovered a unique mechanism of neurotoxicity. Paraoxon-exposed hippocampal slice cultures exhibited progressive declines in synaptophysin, synapsin II, and PSD-95, whereas reduction in GluR1 was slower and NeuN and Nissl staining showed no indications of neuronal damage. The distinctive synaptotoxicity was observed in dendritic zones of CA1 and dentate gyrus. Interestingly, declines in synapsin II dendritic labeling correlated with increased staining for β1 integrin, a component of adhesion receptors that regulate synapse maintenance and plasticity. The paraoxon-induced β1 integrin response was targeted to synapses, and the two-fold increase in β1 integrin was selective as other synaptic adhesion molecules were unchanged. Additionally, β1 integrin-cofilin signaling was triggered by the exposure and correlations were found between the extent of synaptic decline and the level of β1 integrin responses. These findings identified organophosphate-mediated early and lasting synaptotoxicity which can explain delayed neurological dysfunction later in life. They also suggest that the interplay between synaptotoxic events and compensatory adhesion responses influences neuronal fate in exposed individuals.

We present observational evidence from studies on primary cortical cultures from AD transgenic mice, APPSwe/PS1ΔE9 (APP/PS1) mice, for significant decrease in total spine density at DIV-15 and onward. This indicates reduction in potential healthy synapses and strength of connections among neurons. Based on this, a network model of neurons is developed, that explains the consequent loss of coordinated activity and transmission efficiency among neurons that manifests over time. The critical time when structural connectivity in the brain undergoes a phase-transition, from initial robustness to irreparable breakdown, is estimated from this model. We also show how the global efficiency of signal transmission in the network decreases over time. Moreover, the number of multiple paths of high efficiency decreases rapidly as the disease progresses, indicating loss of structural plasticity and inefficiency in choosing alternate paths or desired paths for any pattern of activity. Thus loss of spines caused by β-Amyloid (Aβ) peptide results in disintegration of the neuronal network over time with consequent cognitive dysfunctions in Alzheimer's Disease (AD).

The brains of humans and other mammals are highly vulnerable to interruptions in blood flow and decreases in oxygen levels. Here we describe the restoration and maintenance of microcirculation and molecular and cellular functions of the intact pig brain under ex vivo normothermic conditions up to four hours post-mortem. We have developed an extracorporeal pulsatile-perfusion system and a haemoglobin-based, acellular, non-coagulative, echogenic, and cytoprotective perfusate that promotes recovery from anoxia, reduces reperfusion injury, prevents oedema, and metabolically supports the energy requirements of the brain. With this system, we observed preservation of cytoarchitecture; attenuation of cell death; and restoration of vascular dilatory and glial inflammatory responses, spontaneous synaptic activity, and active cerebral metabolism in the absence of global electrocorticographic activity. These findings demonstrate that under appropriate conditions the isolated, intact large mammalian brain possesses an underappreciated capacity for restoration of microcirculation and molecular and cellular activity after a prolonged post-mortem interval.

The mechanisms of glioma-associated seizures (GAS) have yet to be fully elucidated. Proneural subtype, isocitrate dehydrogenase 1 (IDH1) mutations, and epileptic seizures are closely associated suggesting that aberrant neuronal differentiation contributes to glioma-associated seizures. In a population-based cohort (n = 236), lack of stem cell marker expression (nestin, musashi) was significantly associated with IDH1 mutations and GAS at diagnosis. In vitro data suggested an association of IDH1 mutations and a more differentiated phenotype. Out of eight glioma stem cell (GSC) lines, seven revealed positivity for the synaptic marker protein synaptophysin. Three had synapse-like structures identified by electron microscopy and were either vGlut1 (glutamatergic) or GAD67 (GABAergic) positive. In vivo, >10% synaptophysin-positive tumour cells were present in >90% of all gliomas. Synaptophysin expression was associated with proneural subtype and vGlut1 expression, suggesting that most synapse-like structures in glioma are glutamatergic. However, we found null associations between vGlut1 protein/mRNA expression and survival, GAS at onset, development of GAS after resection, and refractory GAS. Synapse-like structures were neither functional nor activated by spontaneous action potentials or cellular networks. Thus, aberrant neuronal differentiation including glutamatergic synapse-like structures is detectable in glioma but is associated neither with epileptic seizures nor with better survival.

Long-term depression (LTD) of parallel fibre/Purkinje cell synapses has been the favoured explanation for cerebellar motor learning such as classical eyeblink conditioning. Previous evidence against this interpretation has been contested. Here we wanted to test whether a classical conditioning protocol causes LTD. We applied a conditioning protocol, using a train of electrical pulses to the parallel fibres as the conditional stimulus. In order to rule out indirect effects caused by antidromic granule cell activation or output from Purkinje cells that might produce changes in Purkinje cell responsiveness, we focused the analysis on the first pulse in the conditional stimulus, that is, before any indirect effects would have time to occur. Purkinje cells learned to respond with a firing pause to the conditional stimulus. Yet, there was no depression of parallel fibre excitation after training.

Parkinson's disease, the second most common neurodegenerative disorder, affects millions of people globally. There is no cure, and its prevalence will double by 2030. In recent years, numerous causative genes and risk factors for Parkinson's disease have been identified and more than half appear to function at the synapse. Subtle synaptic defects are thought to precede blunt neuronal death, but the mechanisms that are dysfunctional at synapses are only now being unraveled. Here, we review recent work and propose a model where different Parkinson proteins interact in a cell compartment-specific manner at the synapse where these proteins regulate endocytosis and autophagy. While this field is only recently emerging, the work suggests that the loss of synaptic homeostasis may contribute to neurodegeneration and is a key player in Parkinson's disease., (© 2018 The Authors.)

Protein interacting with C kinase (PICK1) is a scaffolding protein that is present in dendritic spines and interacts with a wide array of proteins through its PDZ domain. The best understood function of PICK1 is regulation of trafficking of AMPA receptors at neuronal synapses via its specific interaction with the AMPA GluA2 subunit. Disrupting the PICK1-GluA2 interaction has been shown to alter synaptic plasticity, a molecular mechanism of learning and memory. Lack of potent, selective inhibitors of the PICK1 PDZ domain has hindered efforts at exploring the PICK1-GluA2 interaction as a therapeutic target for neurological diseases. Here, we report the discovery of PICK1 small molecule inhibitors using a structure-based drug design strategy. The inhibitors stabilized surface GluA2, reduced Aβ-induced rise in intracellular calcium concentrations in cultured neurons, and blocked long term depression in brain slices. These findings demonstrate that it is possible to identify potent, selective PICK1-GluA2 inhibitors which may prove useful for treatment of neurodegenerative disorders.

Calpain hyperactivation is implicated in late-stages of neurodegenerative diseases including Alzheimer's disease (AD). However, calpains are also critical for synaptic function and plasticity, and hence memory formation and learning. Since synaptic deficits appear early in AD pathogenesis prior to appearance of overt disease symptoms, we examined if localized dysregulation of calpain-1 and/or 2 contributes to early synaptic dysfunction in AD. Increased activity of synaptosomal calpain-2, but not calpain-1 was observed in presymptomatic 1 month old APP swe /PS1ΔE9 mice (a mouse model of AD) which have no evident pathological or behavioural hallmarks of AD and persisted up to 10 months of age. However, total cellular levels of calpain-2 remained unaffected. Moreover, synaptosomal calpain-2 was hyperactivated in frontal neocortical tissue samples of post-mortem brains of AD-dementia subjects and correlated significantly with decline in tests for cognitive and memory functions, and increase in levels of β-amyloid deposits in brain. We conclude that isoform-specific hyperactivation of calpain-2, but not calpain-1 occurs at the synapse early in the pathogenesis of AD potentially contributing to the deregulation of synaptic signaling in AD. Our findings would be important in paving the way for potential therapeutic strategies for amelioration of cognitive deficits observed in ageing-related dementia disorders like AD.

Increasing evidence suggests that pathological hallmarks of chronic degenerative syndromes progressively spread among interconnected brain areas in a disease-specific stereotyped pattern. Functional brain imaging from patients affected by various neurological syndromes such as traumatic brain injury and stroke indicates that the progression of such diseases follows functional connections, rather than simply spreading to structurally adjacent areas. Indeed, initial damage to a given brain area was shown to disrupt the communication in related brain networks. Using cortico-striatal neuronal networks reconstructed in a microfluidic environment, we investigated the role of glutamate signaling in activity-dependent neuronal survival and trans-synaptic degeneration processes. Using a variety of neuronal insults applied on cortical neurons, we demonstrate that acute injuries such as axonal trauma, focal ischemia, or alteration of neuronal rhythms, lead to glutamate-dependent striatal neuron dysfunction. Interestingly, focal pro-oxidant insults or chronic alteration of spontaneous cortical rhythms provoked dysfunction of distant striatal neurons through abnormal glutamate GluN2B-NMDAR-mediated signaling at cortico-striatal synapses. These results indicate that focal alteration of cortical functions can initiate spreading of dysfunction along neuronal pathways in the brain, reminiscent of diaschisis-like processes.

When exposed to continuous high-level noise, cochlear neurons are more susceptible to damage than hair cells (HCs): exposures causing temporary threshold shifts (TTS) without permanent HC damage can destroy ribbon synapses, permanently silencing the cochlear neurons they formerly activated. While this "hidden hearing loss" has little effect on thresholds in quiet, the neural degeneration degrades hearing in noise and may be an important elicitor of tinnitus. Similar sensory pathologies are seen after blast injury, even if permanent threshold shift (PTS) is minimal. We hypothesized that, as for continuous-noise, blasts causing only TTS can also produce cochlear synaptopathy with minimal HC loss. To test this, we customized a shock tube design to generate explosive-like impulses, exposed anesthetized chinchillas to blasts with peak pressures from 160-175 dB SPL, and examined the resultant cochlear dysfunction and histopathology. We found exposures that cause large >40 dB TTS with minimal PTS or HC loss often cause synapse loss of 20-45%. While synaptopathic continuous-noise exposures can affect large areas of the cochlea, blast-induced synaptopathy was more focal, with localized damage foci in midcochlear and basal regions. These results clarify the pathology underlying blast-induced sensory dysfunction, and suggest possible links between blast injury, hidden hearing loss, and tinnitus.

Despite the many studies focusing on epilepsy, a lot of the basic mechanisms underlying seizure susceptibility are mainly unclear. Here, we studied cellular electrical excitability, as well as excitatory and inhibitory synaptic neurotransmission of CA1 pyramidal neurons from the dorsal hippocampus of a genetic model of epilepsy, the Wistar Audiogenic Rat (WARs) in which limbic seizures appear after repeated audiogenic stimulation. We examined intrinsic properties of neurons, as well as EPSCs evoked by Schaffer-collateral stimulation in slices from WARs and Wistar parental strain. We also analyzed spontaneous IPSCs and quantal miniature inhibitory events. Our data show that even in the absence of previous seizures, GABAergic neurotransmission is reduced in the dorsal hippocampus of WARs. We observed a decrease in the frequency of IPSCs and mIPSCs. Moreover, mIPSCs of WARs had faster rise times, indicating that they probably arise from more proximal synapses. Finally, intrinsic membrane properties, firing and excitatory neurotransmission mediated by both NMDA and non-NMDA receptors are similar to the parental strain. Since GABAergic inhibition towards CA1 pyramidal neurons is reduced in WARs, the inhibitory network could be ineffective to prevent the seizure-dependent spread of hyperexcitation. These functional changes could make these animals more susceptible to the limbic seizures observed during the audiogenic kindling.

Hypoglycosylation of α-dystroglycan (α-DG) resulting from deficiency of protein O-mannosyltransferase 1 (POMT1) may cause severe neuromuscular dystrophies with brain and eye anomalies, named dystroglycanopathies. The retinal involvement of these disorders motivated us to generate a conditional knockout (cKO) mouse experiencing a Pomt1 intragenic deletion (exons 3-4) during the development of photoreceptors, mediated by the Cre recombinase expressed from the cone-rod homeobox (Crx) gene promoter. In this mouse, retinal α-DG was unglycosylated and incapable of binding laminin. Retinal POMT1 deficiency caused significant impairments in both electroretinographic recordings and optokinetic reflex in Pomt1 cKO mice, and immunohistochemical analyses revealed the absence of β-DG and of the α-DG-interacting protein, pikachurin, in the outer plexiform layer (OPL). At the ultrastructural level, noticeable alterations were observed in the ribbon synapses established between photoreceptors and bipolar cells. Therefore, O-mannosylation of α-DG in the retina carried out by POMT1 is crucial for the establishment of proper synapses at the OPL and transmission of visual information from cones and rods to their postsynaptic neurons.

Potentially pathogenic alterations have been identified in individuals with autism spectrum disorders (ASDs) within a variety of key neurodevelopment genes. While this hints at a common ASD molecular etiology, gaps persist in our understanding of the neurodevelopmental mechanisms impacted by genetic variants enriched in ASD patients. Induced pluripotent stem cells (iPSCs) can model neurodevelopment in vitro, permitting the characterization of pathogenic mechanisms that manifest during corticogenesis. Taking this approach, we examined the transcriptional differences between iPSC-derived cortical neurons from patients with idiopathic ASD and unaffected controls over a 135-day course of neuronal differentiation. Our data show ASD-specific misregulation of genes involved in neuronal differentiation, axon guidance, cell migration, DNA and RNA metabolism, and neural region patterning. Furthermore, functional analysis revealed defects in neuronal migration and electrophysiological activity, providing compelling support for the transcriptome analysis data. This study reveals important and functionally validated insights into common processes altered in early neuronal development and corticogenesis and may contribute to ASD pathogenesis.

Glial-neuronal cross-talk has a critical role in the development of neurodegenerative conditions, including Alzheimer's Disease, where it affects neuronal responses to β-amyloid peptide (Aβ)-induced toxicity. We set out to identify factors regulating synaptic responses to Aβ, dissecting the specific role of glial signaling. A low concentration of aggregated Aβ42 induced selective up-regulation of mature brain-derived neurotrophic factor (BDNF) expression and release in rat organotypic hippocampal cultures as well as in cortical pure microglia. Conditioned media from resting (CMC) or Aβ42-treated (CMA) microglia were tested for their effects on synaptophysin expression in SH-SY5Y neuronal-like cells during challenge with Aβ42. Both CMC and CMA prevented Aβ-induced synaptophysin loss. In the presence of Aβ + CMA, synaptophysin was over-expressed, although it appeared partly clumped in cell bodies. Synaptophysin over-expression was not directly dependent on BDNF signaling on neuronal-like cells, but relied on autocrine BDNF action on microglia. FM1-43 labeling experiments revealed compromised synaptic vesicle recycling in Aβ42-treated neuronal-like cells, rescued by microglial conditioned medium. In these conditions, significant and prolonged neuroprotection was observed. Our results point to microglia as a target for early intervention, given its positive role in supporting neuronal compensatory responses to Aβ synaptotoxicity, which potentially lead to their extended survival.