Dendritic spines: structure, dynamics and regulation

Glutamatergic synaptic plasticity in medial vestibular nuclei during vestibular compensation

Vestibular compensation, the spontaneous recovery from vestibular dysfunction following unilateral vestibular loss, serves as a valuable model for investigating post-lesion plasticity in the adult central nervous system. Elucidating the mechanisms underlying vestibular compensation also offers promising therapeutic avenues for treating vestibular disorders. While most studies have focused on the dynamics of GABAergic synaptic plasticity and intrinsic cellular adaptations in the ipsilesional medial vestibular nucleus (MVN) after unilateral labyrinthectomy (UL), the role of glutamatergic synaptic plasticity in this process remains largely unexplored. Here, we employed Golgi staining, immunofluorescence, whole-cell patch-clamp recordings, and behavioral assessments to examine the structural and functional dynamics of glutamatergic synapses during vestibular compensation. Our results reveal rapid structural and functional plasticity of glutamatergic transmission in response to UL. Specifically, dendritic spine density and morphology in the ipsilesional MVN recovered to baseline levels within 6 to 24 h post-UL. Furthermore, UL-induced postsynaptic depression of glutamatergic synaptic strength, reflected by a reduced AMPA/NMDA ratio, was reversed within 24 h, likely due to an upregulation of Ca2+-permeable AMPA receptors. In contrast, presynaptic glutamate release probability, as indicated by a reduced frequency of spontaneous excitatory postsynaptic currents, was not fully compensated during this period. These results suggest that while presynaptic properties recover more slowly in ipsilesional MVN neurons following UL, postsynaptic glutamatergic transmission undergoes rapid structural and functional reorganization. The findings highlight glutamatergic synaptic plasticity as a critical driver for vestibular compensation and suggest that pharmacological interventions targeting these mechanisms may accelerate functional recovery, offering potential therapeutic avenues for vestibular disorders.

Elevated NEGR1 in brain induces anxiety or depression-like phenotypes and synaptic dysfunction

Single nucleotide polymorphisms (SNPs) within 1p31.1 region have shown significant associations with depression, and our prior functional genomics pinpointed a regulatory variant rs3101339 among them. However, its precise role in depression pathogenesis remains elusive. In this study, we employed a series of analytical and functional approaches, including regulatory element annotation, brain expression quantitative trait loci (eQTL), reporter gene assay, electrophoretic mobility shift assay (EMSA), and precise genome editing. Our results confirmed that rs3101339 is a causal variant within 1p31.1 with its risk allele C upregulating NEGR1 expression. To further investigate the consequences of NEGR1 upregulation, we overexpressed NEGR1 in specific region of the mouse brain (including medial prefrontal cortex (mPFC) and ventral hippocampus (vHIP)) using stereotaxic injection. Behavioral assessments revealed that elevated NEGR1 levels in the brain, particularly in the vHIP, resulted in working memory impairment as well as anxiety- and depression-like behaviors in mice. Neuronal sparse labeling assay and transmission electron microscopy revealed that NEGR1 overexpressing in the vHIP leads to dendritic spine loss and synaptic ultrastructure abnormality. Immunoprecipitation-mass spectrometry (IP-MS) further identified 67 high-confidence proteins that interacted with NEGR1, many of which are involved in neurotransmitter exocytosis and synaptic vesicle endocytosis. Transcriptomic profiling revealed 94 differentially expressed genes in NEGR1-OE (vHIP) mice compared to control mice (P adj < 0.05), which were enriched in myelination-related signaling pathways (such as myelination, ensheathment of neurons, axon ensheathment in central nervous system, etc.). Together, our findings implicated that the overexpression of the NEGR1 gene in the mouse brain as a potential driver of anxiety- or depression-like phenotypes potentially through impairing synaptic function and myelination.

LUZP1 Regulates Dendritic Spine Maturation and Synaptic Plasticity in the Hippocampal Dentate Gyrus of Mice

Leucine zipper protein 1 (LUZP1) functions in the maintenance and dynamics of the cytoskeleton by interacting with actin and microtubules. Deficiency or mutation of LUZP1 is associated with brain developmental disorders; however, its precise role in brain function remains unclear. We showed that LUZP1 localizes to actin and is highly expressed in CaMKIIα-expressing neurons within the mouse hippocampal dentate gyrus. Depletion of LUZP1 impedes dendritic spine maturation, which is characterized by excess immature filopodia and loss of mature mushroom spines both in vitro and in vivo. LUZP1 knockdown reduces spontaneous electrical activity and synaptic plasticity in hippocampal neurons. Conditional deletion of LUZP1 in CaMKIIα-expressing neurons causes impaired learning and memory behavior in mice of both sexes. Mechanistically, LUZP1 control dendritic maturation by directly interacting with filamin A and modulating the Rac1-PAK1 signaling pathway. These findings shed light on the role of LUZP1 in regulating synaptic plasticity and brain function.

Neuroadaptation in neurodegenerative diseases: compensatory mechanisms and therapeutic approaches

Progressive neuronal loss is a hallmark of neurodegenerative diseases including Alzheimer's, Parkinson's, Huntington's, and Amyotrophic Lateral Sclerosis (ALS), which cause cognitive and motor impairment. Delaying the onset and course of symptoms is largely dependent on neuroadaptation, the brain's ability to restructure in response to damage. The molecular, cellular, and systemic processes that underlie neuroadaptation are examined in this study. These mechanisms include gliosis, neurogenesis, synaptic plasticity, and changes in neurotrophic factors. Axonal sprouting, dendritic remodelling, and compensatory alterations in neurotransmitter systems are important adaptations observed in NDDs; nevertheless, these processes may shift to maladaptive plasticity, which would aid in the advancement of the illness. Amyloid and tau pathology-induced synaptic alterations in Alzheimer's disease emphasize compensatory network reconfiguration. Dopamine depletion causes a major remodelling of the basal ganglia in Parkinson's disease, and non-dopaminergic systems compensate. Both ALS and Huntington's disease rely on motor circuit rearrangement and transcriptional dysregulation to slow down functional deterioration. Neuroadaptation is, however, constrained by oxidative stress, compromised autophagy, and neuroinflammation, particularly in elderly populations. The goal of emerging therapy strategies is to improve neuroadaptation by pharmacologically modifying neurotrophic factors, neuroinflammation, and synaptic plasticity. Neurostimulation, cognitive training, and physical rehabilitation are instances of non-pharmacological therapies that support neuroplasticity. Restoring compensating systems may be possible with the use of stem cell techniques and new gene treatments. The goal of future research is to combine biomarkers and individualized medicines to maximize neuroadaptive responses and decrease the course of illness. In order to reduce neurodegeneration and enhance patient outcomes, this review highlights the dual function of neuroadaptation in NDDs and its potential as a therapeutic target.

SFRP1 upregulation causes hippocampal synaptic dysfunction and memory impairment

Impaired neuronal and synaptic function are hallmarks of early Alzheimer's disease (AD), preceding other neuropathological traits and cognitive decline. We previously showed that SFRP1, a glial-derived protein elevated in AD brains from preclinical stages, contributes to disease progression, implicating glial factors in early pathogenesis. Here, we generate and analyze transgenic mice overexpressing astrocytic SFRP1. SFRP1 accumulation causes early dendritic and synaptic defects in adult mice, followed by impaired synaptic long-term potentiation and cognitive decline, evident only when the animals age, thereby mimicking AD's structural-functional temporal distinction. This phenotype correlates with proteomic changes, including increased structural synaptic proteins like neurexin, which localizes in close proximity with SFRP1 in cultured hippocampal neurons. We conclude that excessive SFRP1 hinders synaptic protein turnover, reducing synaptic plasticity-a mechanism that may underlie the synaptopathy observed in the brains of prodromal AD patients.

D2HGDH Deficiency Regulates Seizures through GSH/Prdx6/ROS-Mediated Excitatory Synaptic Activity

Current antiepileptic drugs are ineffective in one-third of patients with epilepsy; however, identification of genes involved in epilepsy can enable a precision medicine approach. Here, it is demonstrated that downregulating D-2-hydroxyglutarate dehydrogenase (D2HGDH) enhances susceptibility to epilepsy. Furthermore, its potential involvement in the seizure network through synaptic function modulation is investigated. D2HGDH knockdown reduces the glutathione reduced (GSH)/glutathione oxidized (GSSG) ratio and elevates reactive oxygen species (ROS) levels within neurons. Oxidative stress may play a crucial role in the pathogenesis of epilepsy. The specific contribution of each pathway varies among patients, highlighting the complexity of this disease. In this study, downregulation of D2HGDH affects modulation of ROS levels, synaptic transmission, and seizure susceptibility. Furthermore, the acid calcium-independent phospholipase A2 (aiPLA2) inhibitor, MJ33, restores the GSH/GSSG balance and reverses the increase in ROS levels caused by D2HGDH knockdown, resulting in remission of epilepsy-related behaviors. The results demonstrate that downregulation of D2HGDH affects synaptic function by regulating ROS production. These findings support the use of targeted gene therapy as a potential alternative to antioxidant-based treatments for refractory epilepsy.

From Discovery to Innovative Translational Approaches in 80 Years of Fragile X Syndrome Research

Fragile X syndrome (FXS) is the most common inherited cause of intellectual disability and a major genetic contributor to autism spectrum disorder. It is caused by a CGG trinucleotide repeat expansion in the FMR1 gene, resulting in gene silencing and the loss of FMRP, an RNA-binding protein essential for synaptic plasticity. This review covers over 80 years of FXS research, highlighting key milestones, clinical features, genetic and molecular mechanisms, the FXS mouse model, disrupted molecular pathways, and current therapeutic strategies. Additionally, we discuss recent advances including AI-driven combination therapies, CRISPR-based gene editing, and antisense oligonucleotides (ASOs) therapies. Despite these scientific breakthroughs, translating preclinical findings into effective clinical treatments remains challenging. Clinical trials have faced several difficulties, including patient heterogeneity, inconsistent outcome measures, and variable therapeutic responses. Standardized preclinical testing protocols and refined clinical trial designs are required to overcome these challenges. The development of FXS-specific biomarkers could also improve the precision of treatment assessments. Ultimately, future therapies will need to combine pharmacological and behavioral interventions tailored to individual needs. While significant challenges remain, ongoing research continues to offer hope for transformative breakthroughs that could significantly improve the quality of life for individuals with FXS and their families.

Impairment of homeostatic structural plasticity caused by the autism and schizophrenia-associated 16p11.2 duplication

Homeostatic plasticity is essential for information processing and the stability of neuronal circuits, however its relevance to neuropsychiatric disorders remains unclear. The 16p11.2 duplication (BP4-BP5) is a genetic risk factor that strongly predisposes to a range of severe mental illnesses including autism, schizophrenia, intellectual disability, and epilepsy. The duplication consists of a 600 kb region on chromosome 16, including 27 protein-coding genes, with poorly defined effects on neuronal structure and function. Here, we used a mouse model of the 16p11.2 duplication to investigate the impact of this variant on synaptic structure and downstream homeostatic plasticity. We find that 16p11.2 duplication neurons exhibit overly branched dendritic arbors and excessive spine numbers, which host an overabundance of surface AMPA receptor subunit GluA1. Using a homeostatic plasticity paradigm, we show that 16p11.2 duplication neurons fail to undergo synaptic upscaling upon activity deprivation, consistent with disrupted structural plasticity. We also observe that the increased surface abundance of GluA1 occludes further insertion events, a critical mechanism for synaptic plasticity. Finally, we show that genetically correcting the dosage of 16p11.2-encoded Prrt2 to wild-type levels rescues structural spine phenotypes. Our work suggests that aberrant plasticity could contribute to the etiology of neuropsychiatric disorders.

Non-synonymous single nucleotide polymorphisms (nsSNPs) within the extracellular domains of the GPM6A gene impair hippocampal neuron development

Psychiatric disorders are complex pathologies influenced by both environmental and genetic factors, ultimately leading to synaptic plasticity dysfunction. Altered expression levels of neuronal glycoprotein GPM6a or polymorphisms within the GPM6A gene are associated with neuropsychiatric disorders like schizophrenia, depression, and claustrophobia. This protein promotes neurite outgrowth, filopodia formation, dendritic spine, and synapse maintenance in vitro. Although strong evidence suggests that its extracellular domains (ECs) are responsible for its function, the molecular mechanisms linking GPM6a to the onset of such diseases remain unknown. To gain knowledge of these mechanisms, we characterized new non-synonymous polymorphisms (nsSNPs) within the ECs of GPM6a. We identified six nsSNPs (T71P, T76I, M154V, F156Y, R163Q, and T210N) that impair GPM6a-induced plasticity in neuronal cultures without affecting GPM6a expression, folding, and localization to the cell membrane. However, we observed that some of these modified GPM6a's distribution at the cell membrane. Additionally, one of the nsSNPs exhibited alterations in GPM6a oligomerization, highlighting the importance of this amino acid in establishing homophilic cis interactions. Furthermore, we observed that the ability of GPM6a's extracellular domains to interact and induce cell aggregation was significantly decreased in several of the nsSNP variants studied here. Altogether, these results provide new insights into the key residues within GPM6a's extracellular regions that are crucial for its self-association, which is essential for promoting neuronal morphogenesis. Besides, these findings highlight the importance of reverse genetics approaches to gain knowledge on GPM6a's mechanisms of action and the genetic susceptibility of certain GPM6A variants.

The link between impact-induced tensile strain and dendritic spine morphology in porcine brain tissue

Brain tissue as a material presents unique properties with a multitude of cell types and densities, varying degrees of axonal fiber diameters and blood vessels. These neural components are contained within a very viscous environment that upon impact, can result in a variety of tensile, compressive and rotational forces. The depths of the sulcus appear to be particularly vulnerable to biomechanical forces following an impact. The movement and subsequent forces loaded on to the brain have been shown to produce a variety of biomechanical responses that impair neurophysiological functioning at the cellular level. We recently reported a decrease in microtubule associated protein 2 (MAP2) within the depths of the porcine sulcus in an ex vivo model, along with elevated tensile strain in this region within 1 hour after impact. In the current work, using the same impact model, we explored whether changes in spine morphology and density occurred within the same timeframe following impact. The Golgi-Cox method was used to visualize dendritic spine morphology. Cortical pyramidal neurons within the depths and the arms of the sulcus were reconstructed. One hour after impact, there was a change in the distribution of spine type resulting in an increased proportion of mushroom-type spines compared to nonimpacted tissue. The increased proportion of mushroom-type spines was proportional to tensile strain measurements in the apical dendrites. These results demonstrate the sensitivity of dendritic spine morphology to tensile strain within the porcine cortex and suggest a state of hyperexcitability during the hyperacute phase following an impact.

Interferometric Ultra-High Resolution 3D Imaging through Brain Sections

Single-molecule super-resolution microscopy allows pin-pointing individual molecular positions in cells with nanometer precision. However, achieving molecular resolution through tissues is often difficult because of optical scattering and aberrations. We introduced 4Pi single-molecule nanoscopy for brain with in-situ point spread function retrieval through opaque tissue (4Pi-BRAINSPOT), integrating 4Pi single-molecule switching nanoscopy with dynamic in-situ coherent PSF modeling, single-molecule compatible tissue clearing, light-sheet illumination, and a novel quantitative analysis pipeline utilizing the highly accurate 3D molecular coordinates. This approach enables the quantification of protein distribution with sub-15-nm resolution in all three dimensions in complex tissue specimens. We demonstrated 4Pi-BRAINSPOT's capacities in revealing the molecular arrangements in various sub-cellular organelles and resolved the membrane morphology of individual dendritic spines through 50-μm transgenic mouse brain slices. This ultra-high-resolution approach allows us to decipher nanoscale organelle architecture and molecular distribution in both isolated cells and native tissue environments with precision down to a few nanometers.

Brief sleep disruption alters synaptic structures among hippocampal and neocortical somatostatin-expressing interneurons

Study objectives

Brief sleep loss alters cognition and synaptic structures of principal neurons in hippocampus and neocortex. However, while in vivo recording and bioinformatic data suggest that inhibitory interneurons are more strongly affected by sleep loss, it is unclear how sleep and sleep deprivation affect interneurons' synapses. Disruption of the SST+ interneuron population seems to be a critical early sign of neuropathology in Alzheimer's dementia, schizophrenia, and bipolar disorder - and the risk of developing all three is increased by habitual sleep loss. We aimed to test how the synaptic structures of SST+ interneurons in various brain regions are affected by brief sleep disruption.

Methods

We used Brainbow 3.0 to label SST+ interneurons in the dorsal hippocampus, prefrontal cortex, and visual cortex of male SST-CRE transgenic mice, then compared synaptic structures in labeled neurons after a 6-h period of ad lib sleep, or gentle handling sleep deprivation (SD) starting at lights on.

Results

Dendritic spine density among SST+ interneurons in both hippocampus and neocortex was altered in a subregion-specific manner, with increased overall and thin spine density in CA1, dramatic increases in spine volume and surface area in CA3, and small but significant changes (primarily decreases) in spine size in CA1, PFC and V1.

Conclusions

Our suggest that the synaptic connectivity of SST+ interneurons is significantly altered in a brain region-specific manner by a few hours of sleep loss. This suggests a cell type-specific mechanism by which sleep loss disrupts cognition and alters excitatory-inhibitory balance in brain networks.

Dendritic growth and synaptic organization from activity-independent cues and local activity-dependent plasticity

Dendritic branching and synaptic organization shape single-neuron and network computations. How they emerge simultaneously during brain development as neurons become integrated into functional networks is still not mechanistically understood. Here, we propose a mechanistic model in which dendrite growth and the organization of synapses arise from the interaction of activity-independent cues from potential synaptic partners and local activity-dependent synaptic plasticity. Consistent with experiments, three phases of dendritic growth - overshoot, pruning, and stabilization - emerge naturally in the model. The model generates stellate-like dendritic morphologies that capture several morphological features of biological neurons under normal and perturbed learning rules, reflecting biological variability. Model-generated dendrites have approximately optimal wiring length consistent with experimental measurements. In addition to establishing dendritic morphologies, activity-dependent plasticity rules organize synapses into spatial clusters according to the correlated activity they experience. We demonstrate that a trade-off between activity-dependent and -independent factors influences dendritic growth and synaptic location throughout development, suggesting that early developmental variability can affect mature morphology and synaptic function. Therefore, a single mechanistic model can capture dendritic growth and account for the synaptic organization of correlated inputs during development. Our work suggests concrete mechanistic components underlying the emergence of dendritic morphologies and synaptic formation and removal in function and dysfunction, and provides experimentally testable predictions for the role of individual components.

Colistin treatment causes neuronal loss and cognitive impairment via ros accumulation and neuronal plasticity alterations

The rise of antimicrobial resistance has made necessary the increase of the antibacterial arsenal against multidrug-resistant bacteria. In this context, colistin has re-emerged as a first-line antibiotic in critical situations despite its nephro- and neuro- toxicity at peripheral level. However, the mechanism underlying its toxicity remains unknown, particularly in relation to the central nervous system (CNS). Therefore, this study aimed to characterize the molecular mechanisms underlying colistin-induced neurotoxicity in the CNS through a combination of in vitro and in vivo molecular studies along with several in vivo behavioral tests. Following colistin treatment, mice exhibited a significant reduction in body weight together with renal impairment, and locomotor dysfunction. Moreover, our results demonstrated that colistin disrupted the blood-brain barrier, inducing astrogliosis, and triggering apoptosis-related processes probably through the accumulation of reactive oxygen species (ROS) and mitochondrial dysfunction. Further analysis on mice and primary neuronal cultures revealed that colistin administration altered neuronal plasticity by reducing the number of immature neurons in adult neurogenesis and altering the synaptic function through a reduction of the post-synaptic protein PSD95. All these alterations together finally lead to cognitive impairment and depression-like symptoms in mice. These findings provide novel insights into the mechanisms of colistin-induced neurotoxicity in the CNS, highlighting the need for careful monitoring of cognitive function in patients undergoing colistin treatment.

Direct engulfment of synapses by overactivated microglia due to cadmium exposure and the protective role of Nrf2

Cadmium (Cd), a notorious environmental pollutant, has been linked to neurological disorders, but the underlying mechanism remains elusive. We aimed to explore the role of microglia in Cd-induced synaptic damages at environmentally relevant doses and whether microglia directly engulf synaptic structures. Nrf2 is deeply implicated in the status of microglial activation; therefore, we also investigated whether it is involved in the above process. Nrf2 knockout mice and wild-type mice were used to explore prolonged Cd exposure-induced synaptic damages, learning-memory impairments, and microglial activation. We also created Nrf2 knockdown (KD) BV2 microglia to investigate the role of cell-specific Nrf2 in Cd-induced microglial activation. Finally, we developed co-culture systems of either Nrf2-KD or Scramble microglia and primary neurons or HT22 neurons to study the effects of Nrf2-regulated microglial activation on synaptic damages induced by Cd. Moreover, the direct engulfment, a main avenue in microglia that may be responsible for Cd-induced synaptic damages and regulated by Nrf2, was specifically studied in vivo and in vitro, along with underlying specific mechanisms. We found that Cd exposure induced microglial overactivation, and Cd-overactivated microglia impaired synapses through direct engulfment of synaptic structures, which may contribute to learning-memory impairments. Both fractalkine and complement pathways underlay microglial engulfment of synapses due to Cd exposure. Nrf2 was essential in preventing microglial overactivation and subsequent direct engulfment, thus preventing the consequent synaptic damages due to Cd exposure. Overall, the findings suggest that Cd-overactivated microglia damage synapses through direct engulfment, resulting from the activation of fractalkine and complement pathways.

Loss of neuronal βPix isoforms impairs neuronal morphology in the hippocampus and causes behavioral defects

βPix is a guanine nucleotide exchange factor for the Rac1 and Cdc42 small GTPases, which play important roles in dendritic spine morphogenesis by modulating actin cytoskeleton organization. The formation and plasticity of the dendritic spines are essential for normal brain function. Among the alternatively spliced βPix isoforms, βPix-b and βPix-d are expressed specifically in neurons. Our previous studies using cultured hippocampal neurons identified the roles of βPix-b and βPix-d in spine formation and neurite development, respectively. Here, we analyzed the in vivo role of the neuronal βPix isoforms in brain development and function by using βPix neuronal isoform knockout (βPix-NIKO) mice, in which the expression of the βPix-b and βPix-d isoforms is blocked, while the expression of the ubiquitous βPix-a isoform is maintained. Loss of the neuronal βPix isoforms leads to reduced activity of Rac1 and Cdc42, decreased dendritic complexity and spine density, and increased GluN2B and Ca2+/calmodulin-dependent protein kinase IIα expression in the hippocampus. The defects in neurite development, dendritic spine maturation, and synaptic density in cultured βPix-NIKO hippocampal neurons were rescued by the expression of βPix-b or βPix-d. In behavioral studies, βPix-NIKO mice exhibited robust deficits in novel object recognition and decreased anxiety levels. Our findings suggest that neuronal morphogenetic signaling by the neuronal βPix isoforms contributes to normal behaviors.

Reactivation of mTOR signaling slows neurodegeneration in a lysosomal sphingolipid storage disease

Sandhoff disease, a lysosomal storage disorder, is caused by pathogenic variants in the HEXB gene, resulting in the loss of β-hexosaminidase activity and accumulation of sphingolipids including GM2 ganglioside. This accumulation occurs primarily in neurons, and leads to progressive neurodegeneration through a largely unknown process. Lysosomal storage diseases often exhibit dysfunctional mTOR signaling, a pathway crucial for proper neuronal development and function. In this study, Sandhoff disease model mice exhibited reduced mTOR signaling in the brain. To test if restoring mTOR signaling could improve the disease phenotype, we genetically reduced expression of the mTOR inhibitor Tsc2 in these mice. Sandhoff disease mice with reactivated mTOR signaling displayed increased survival rates and motor function, especially in females, increased dendritic-spine density, and reduced neurodegeneration. Tsc2 reduction also partially rescued aberrant synaptic function-related gene expression. These findings imply that enhancing mTOR signaling could be a potential therapeutic strategy for lysosomal-based neurodegenerative diseases.

Super-resolution imaging of fast morphological dynamics of neurons in behaving animals

Neurons are best studied in their native states in which their functional and morphological dynamics support animals' natural behaviors. Super-resolution microscopy can potentially reveal these dynamics in higher details but has been challenging in behaving animals due to severe motion artifacts. Here we report multiplexed, line-scanning, structured illumination microscopy, which can tolerate motion of up to 50 μm s-1 while achieving 150-nm and 100-nm lateral resolutions in its linear and nonlinear forms, respectively. We continuously imaged the dynamics of spinules in dendritic spines and axonal boutons volumetrically over thousands of frames and tens of minutes in head-fixed mouse brains during sleep-wake cycles. Super-resolution imaging of axonal boutons revealed spinule dynamics on a scale of seconds. Simultaneous two-color imaging further enabled analyses of the spatial distributions of diverse PSD-95 clusters and opened up possibilities to study their correlations with the structural dynamics of dendrites in the brains of head-fixed awake mice.

ATAD1 Regulates Neuronal Development and Synapse Formation Through Tuning Mitochondrial Function

Mitochondrial function is essential for synaptic function. ATAD1, an AAA+ protease involved in mitochondrial quality control, governs fission-fusion dynamics within the organelle. However, the distribution and functional role of ATAD1 in neurons remain poorly understood. In this study, we demonstrate that ATAD1 is primarily localized to mitochondria in dendrites and, to a lesser extent, in spines in cultured hippocampal neurons. We found that ATAD1 deficiency disrupts the mitochondrial fission-fusion balance, resulting in mitochondrial fragmentation. This deficiency also impairs dendritic branching, hinders dendritic spine maturation, and reduces glutamatergic synaptic transmission in hippocampal neuron. To further investigate the underlying mechanism, we employed an ATP hydrolysis-deficient mutant of ATAD1 to rescue the neuronal deficits associated with ATAD1 loss. We discovered that the synaptic deficits are independent of the mitochondrial morphology changes but rely on its ATP hydrolysis. Furthermore, we show that ATAD1 loss leads to impaired mitochondrial function, including decreased ATP production, impaired membrane potential, and elevated oxidative stress. In conclusion, our results provide evidence that ATAD1 is crucial for maintaining mitochondrial function and regulating neurodevelopment and synaptic function.

miR-193b-365 microcluster downstream of Fezf2 coordinates neuron-subtype identity and dendritic morphology in cortical projection neurons

Different neuron types develop characteristic axonal and dendritic arborizations that determine their inputs, outputs, and functions. Expression of fate-determinant transcription factors is essential for specification of their distinct identities. However, the mechanisms downstream of fate-determinant factors coordinating different aspects of neuron identity are not understood. Specifically, how distinct projection neurons develop appropriate dendritic arbors that determine their inputs is unknown. Here, we investigate this question in corticospinal and callosal projection neurons. We identified a mechanism linking the corticospinal/corticofugal identity gene Fezf2 with the regulation of dendritic development. We show that miR-193b∼365 microRNA cluster is regulated by Fezf2 and enriched in corticospinal neurons. miR-193b∼365 represses mitogen-activated protein kinase 8 (MAPK8) to regulate corticospinal dendritic development. miR-193b∼365 overexpression in callosal neurons abnormally reduces MAPK8 signal and dendritic complexity. Our findings show that regulation of MAPK8 via miR-193b∼365 cluster regulates dendritic development, providing a mechanism that coordinates projection neuron identity, specified by Fezf2, and neuron-specific dendritic morphology.

Evaluation of dendrite morphology in Wistar and genetic absence epileptic rats

OBJECTIVE

Genetic Absence Epilepsy Rat from Strasbourg (GAERS), a rodent model genetically predisposed to absence epilepsy, serves as an experimental tool to elucidate the neuronal mechanisms underlying human absence epilepsy. This study aimed to investigate the morphological features of dendrites and dendritic spines of pyramidal neurons in somatosensory cortex and hippocampus of Wistar and GAERS rats.

MATERIAL AND METHOD

Adult male GAERS (n = 5) and control Wistar (n = 5) rats were sacrificed by transcardial perfusion and brains were removed. Brain tissues were processed by Golgi impregnation method using FD Rapid GolgiStain Kit. Coronal sections were obtained with a cryostat. Pyramidal neurons in layers V-VI of the somatosensory cortex and the CA1 region of the hippocampus were examined using a light microscope and Neurolucida 360 software. Dendrite nodes, dendrite segments (dendritic branching), dendrite terminations, total dendrite length, dendritic spine density, and dendritic spine types were analyzed.

RESULTS

Compared to Wistar, GAERS exhibited significantly higher numbers of nodes (p = 0.0053, p = 0.0047), segments (p = 0.0036, p = 0.0036), and terminations (p = 0.0033, p = 0.0029) in the dendrites of the somatosensory cortex and the hippocampus, respectively. Furthermore, the total dendrite length (µm) (p = 0.0002, p = 0.0007) and the density of dendritic spines (1/µm) (p = 0.0168, p = 0.0120) were significantly high in GAERS compared to Wistar. When dendritic spine types were evaluated separately, stubby-type dendritic spines in the hippocampus were higher in GAERS compared to Wistar (p = 0.0045).

CONCLUSION

Intense synaptic connections in the somatosensory cortex and the hippocampus of genetic absence epileptic rats led to morphological alterations in the dendrites and the dendritic spines of pyramidal neurons in these regions, potentially contributing to the pathophysiology of absence seizures.

Altered transcriptomes, cell type proportions, and dendritic spine morphology in hippocampus of suicide decedents

BACKGROUND

Suicide is a manner of death resulting from complex environmental and genetic risks that affect millions of people globally. Both structural and functional studies identified the hippocampus as one of the vulnerable brain regions contributing to suicide risk.

METHODS

We have identified the hippocampal tissue transcriptomes, gene ontology, cell type proportions, and dendritic spine morphology in controls (n = 28) and suicide decedents (n = 22). In addition, the transcriptomic signature in iPSC-derived neuronal precursor cells (NPCs) and neurons were also investigated in controls (n = 2) and suicide decedents (n = 2).

RESULTS

The hippocampal tissue transcriptomic data revealed that NPAS4 gene expression was downregulated while ALDH1A2, NAAA, and MLXIPL gene expressions were upregulated in hippocampal tissue of suicide decedents. The gene ontology identified 29 significant pathways including NPAS4-associated gene ontology terms "excitatory post-synaptic potential", "regulation of postsynaptic membrane potential" and "long-term memory" indicating alteration of glutamatergic synapses in the hippocampus of suicide decedents. The cell type deconvolution identified decreased excitatory neuron proportion and an increased inhibitory neuron proportion providing evidence of excitation/inhibition imbalance in the hippocampus of suicide decedents. In addition, suicide decedents had increased dendric spine density in the hippocampus, due to an increase of thin (relatively unstable) dendritic spines, compared to controls. The transcriptomes of iPSC-derived hippocampal-like NPCs and neurons revealed 31 and 33 differentially expressed genes in NPC and neurons, respectively, of suicide decedents.

CONCLUSIONS

Our findings will provide new insights into the hippocampal neuropathology of suicide.

The ventral midline thalamus and long-term memory: What consolidation, what retrieval, what plasticity in rodents?

The ventral midline thalamus, including the reuniens and rhomboid (ReRh) nuclei, connects bidirectionally with the medial prefrontal cortex (mPFC) and hippocampus (Hip), both essential for memory processes. This review compiles and discusses studies on a role for the ReRh nuclei in the system consolidation of memories, also considering their potentially limited participation in memory retrieval or early phases of consolidation. It also examines scientific literature on short- and long-term plasticity in ReRh-mPFC and ReRh-Hip connections, emphasizing plasticity's importance in understanding these nuclei's role in memory. The idea that the two nuclei are at the crossroads of information exchange between the mPFC and the Hip is not new, but the relationship between this status and the plasticity of their connections remains elusive. Since this perspective is relatively recent, our concluding section suggests conceptual and practical avenues for future research, aiming perhaps to bring more order to the apparently multi-functional implication of the ventral midline thalamus in cognition.

Inhibition of IRAP Enhances the Expression of Pro-Cognitive Markers Drebrin and MAP2 in Rat Primary Neuronal Cells

The insulin-regulated aminopeptidase (IRAP; oxytocinase) is part of the M1 aminopeptidase family and is highly expressed in many tissues, including the neocortex and hippocampus of the brain. IRAP is involved in various physiological functions and has been identified as a receptor for the endogenous hexapeptide Angiotensin IV (Ang IV). The binding of Ang IV inhibits the enzymatic activity of IRAP and has been proven to enhance learning and memory in animal models. The macrocyclic compound 9 (C9) is a potent synthetic IRAP inhibitor developed from the previously reported inhibitor HA08. In this study, we have examined compound C9 and its effects on cognitive markers drebrin, microtubule-associated protein 2 (MAP2), and glial fibrillary acidic protein (GFAP) in primary hippocampal and cortical cultures. Cells from Sprague Dawley rats were cultured for 14 days before treatment with C9 for 4 consecutive days. The cells were analysed for protein expression of drebrin, MAP2, GFAP, glucose transporter type 4 (GLUT4), vesicular glutamate transporter 1 (vGluT1), and synapsin I using immunocytochemistry. The gene expression of related proteins was determined using qPCR, and viability assays were performed to evaluate toxicity. The results showed that protein expression of drebrin and MAP2 was increased, and the corresponding mRNA levels were decreased after treatment with C9 in the hippocampal cultures. The ratio of MAP2-positive neurons and GFAP-positive astrocytes was altered and there were no toxic effects observed. In conclusion, the IRAP inhibitor compound C9 enhances the expression of the pro-cognitive markers drebrin and MAP2, which further confirms IRAP as a relevant pharmaceutical target and C9 as a promising candidate for further investigation.

Synaptopodin: a key regulator of Hebbian plasticity

Synaptopodin, an actin-associated protein found in a subset of dendritic spines in telencephalic neurons, has been described to influence both functional and morphological plasticity under various plasticity paradigms. Synaptopodin is necessary and sufficient for the formation of the spine apparatus, stacks of smooth endoplasmic reticulum cisternae. The spine apparatus is a calcium store that locally regulates calcium dynamics in response to different patterns of activity and is also thought to be a site for local protein synthesis. Synaptopodin is present in ~30% of telencephalic large dendritic spines in vivo and in vitro highlighting the heterogeneous microanatomy and molecular architecture of dendritic spines, an important but not well understood aspect of neuroplasticity. In recent years, it has become increasingly clear that synaptopodin is a formidable regulator of multiple mechanisms essential for learning and memory. In fact, synaptopodin appears to be the decisive factor that determines whether plasticity can occur, acting as a key regulator for synaptic changes. In this review, we summarize the current understanding of synaptopodin's role in various forms of Hebbian synaptic plasticity.

Cognitive synaptopathy: synaptic and dendritic spine dysfunction in age-related cognitive disorders

Cognitive impairment is a leading component of several neurodegenerative and neurodevelopmental diseases, profoundly impacting on the individual, the family, and society at large. Cognitive pathologies are driven by a multiplicity of factors, from genetic mutations and genetic risk factors, neurotransmitter-associated dysfunction, abnormal connectomics at the level of local neuronal circuits and broader brain networks, to environmental influences able to modulate some of the endogenous factors. Otherwise healthy older adults can be expected to experience some degree of mild cognitive impairment, some of which fall into the category of subjective cognitive deficits in clinical practice, while many neurodevelopmental and neurodegenerative diseases course with more profound alterations of cognition, particularly within the spectrum of the dementias. Our knowledge of the underlying neuropathological mechanisms at the root of this ample palette of clinical entities is far from complete. This review looks at current knowledge on synaptic modifications in the context of cognitive function along healthy ageing and cognitive dysfunction in disease, providing insight into differential diagnostic elements in the wide range of synapse alterations, from those associated with the mild cognitive changes of physiological senescence to the more profound abnormalities occurring at advanced clinical stages of dementia. I propose the term "cognitive synaptopathy" to encompass the wide spectrum of synaptic pathologies associated with higher brain function disorders.

Pre- and Post-Synaptic protein in the major depressive Disorder: From neurobiology to therapeutic targets

Major depressive disorder (MDD) has demonstrated its negative impact on various aspects of the lives of those affected. Although several therapies have been developed over the years, it remains a challenge for mental health professionals. Thus, understanding the pathophysiology of MDD is necessary to improve existing treatment options or seek new therapeutic alternatives. Clinical and preclinical studies in animal models of depression have shown the involvement of synaptic plasticity in both the development of MDD and the response to available drugs. However, synaptic plasticity involves a cascade of events, including the action of presynaptic proteins such as synaptophysin and synapsins and postsynaptic proteins such as postsynaptic density-95 (PSD-95). Additionally, several factors can negatively impact the process of spinogenesis/neurogenesis, which are related to many outcomes, including MDD. Thus, this narrative review aims to deepen the understanding of the involvement of synaptic formations and their components in the pathophysiology and treatment of MDD.

NMDARs in Alzheimer's Disease: Between Synaptic and Extrasynaptic Membranes

N-methyl-D-aspartate receptors (NMDARs) are glutamate receptors with key roles in synaptic communication and plasticity. The activation of synaptic NMDARs initiates plasticity and stimulates cell survival. In contrast, the activation of extrasynaptic NMDARs can promote cell death underlying a potential mechanism of neurodegeneration occurring in Alzheimer's disease (AD). The distribution of synaptic versus extrasynaptic NMDARs has emerged as an important parameter contributing to neuronal dysfunction in neurodegenerative diseases including AD. Here, we review the concept of extrasynaptic NMDARs, as this population is present in numerous neuronal cell membranes but also in the membranes of various non-neuronal cells. Previous evidence regarding the membranal distribution of synaptic versus extrasynaptic NMDRs in relation to AD mice models and in the brains of AD patients will also be reviewed.

Sex differences in glutamate transmission and plasticity in reward related regions

Disruptions in glutamate homeostasis within the mesolimbic reward circuitry may play a role in the pathophysiology of various reward related disorders such as major depressive disorders, anxiety, and substance use disorders. Clear sex differences have emerged in the rates and symptom severity of these disorders which may result from differing underlying mechanisms of glutamatergic signaling. Indeed, preclinical models have begun to uncover baseline sex differences throughout the brain in glutamate transmission and synaptic plasticity. Glutamatergic synaptic strength can be assessed by looking at morphological features of glutamatergic neurons including spine size, spine density, and dendritic branching. Likewise, electrophysiology studies evaluate properties of glutamatergic neurons to provide information of their functional capacity. In combination with measures of glutamatergic transmission, synaptic plasticity can be evaluated using protocols that induce long-term potentiation or long-term depression. This review will consider preclinical rodent literature directly comparing glutamatergic transmission and plasticity in reward related regions of males and females. Additionally, we will suggest which regions are exhibiting evidence for sexually dimorphic mechanisms, convergent mechanisms, or no sex differences in glutamatergic transmission and plasticity and highlight gaps in the literature for future investigation.

Sex-Specific ADNP/NAP (Davunetide) Regulation of Cocaine-Induced Plasticity

Cocaine use disorder (CUD) is a chronic neuropsychiatric disorder estimated to effect 1-3% of the population. Activity-dependent neuroprotective protein (ADNP) is essential for brain development and functioning, shown to be protective in fetal alcohol syndrome and to regulate alcohol consumption in adult mice. The goal of this study was to characterize the role of ADNP, and its active peptide NAP (NAPVSIPQ), which is also known as davunetide (investigational drug) in mediating cocaine-induced neuroadaptations. Real time PCR was used to test levels of Adnp and Adnp2 in the nucleus accumbens (NAc), ventral tegmental area (VTA), and dorsal hippocampus (DH) of cocaine-treated mice (15 mg/kg). Adnp heterozygous (Adnp +/-)and wild-type (Adnp +/-) mice were further tagged with excitatory neuronal membrane-expressing green fluorescent protein (GFP) that allowed for in vivo synaptic quantification. The mice were treated with cocaine (5 injections; 15 mg/kg once every other day) with or without NAP daily injections (0.4 µg/0.1 ml) and sacrificed following the last treatment. We analyzed hippocampal CA1 pyramidal cells from 3D confocal images using the Imaris x64.8.1.2 (Oxford Instruments) software to measure changes in dendritic spine density and morphology. In silico ADNP/NAP/cocaine structural modeling was performed as before. Cocaine decreased Adnp and Adnp2 expression 2 h after injection in the NAc and VTA of male mice, with mRNA levels returning to baseline levels after 24 h. Cocaine further reduced hippocampal spine density, particularly synaptically weaker immature thin and stubby spines, in male Adnp+/+) mice while increasing synaptically stronger mature (mushroom) spines in Adnp+/-) male mice and thin and stubby spines in females. Lastly, we showed that cocaine interacts with ADNP on a zinc finger domain identical to ketamine and adjacent to a NAP-zinc finger interaction site. Our results implicate ADNP in cocaine abuse, further placing the ADNP gene as a key regulator in neuropsychiatric disorders. Ketamine/cocaine and NAP treatment may be interchangeable to some degree, implicating an interaction with adjacent zinc finger motifs on ADNP and suggestive of a potential sex-dependent, non-addictive NAP treatment for CUD.

A combination of Δ9-tetrahydrocannabinol and cannabidiol modulates glutamate dynamics in the hippocampus of an animal model of Alzheimer's disease

A combination of Δ9-tetrahydrocannabinol (Δ9-THC) and cannabidiol (CBD) at non-psychoactive doses was previously demonstrated to reduce cognitive decline in APP/PS1 mice, an animal model of Alzheimer's disease (AD). However, the neurobiological substrates underlying these therapeutic properties of Δ9-THC and CBD are not fully understood. Considering that dysregulation of glutamatergic activity contributes to cognitive impairment in AD, the present study evaluates the hypothesis that the combination of these two natural cannabinoids might reverse the alterations in glutamate dynamics within the hippocampus of this animal model of AD. Interestingly, our findings reveal that chronic treatment with Δ9-THC and CBD, but not with any of them alone, reduces extracellular glutamate levels and the basal excitability of the hippocampus in APP/PS1 mice. These effects are not related to significant changes in the function and structure of glutamate synapses, as no relevant changes in synaptic plasticity, glutamate signaling or in the levels of key components of these synapses were observed in cannabinoid-treated mice. Our data instead indicate that these cannabinoid effects are associated with the control of glutamate uptake and/or to the regulation of the hippocampal network. Taken together, these results support the potential therapeutic properties of combining these natural cannabinoids against the excitotoxicity that occurs in AD brains.

Development of an in vitro compound screening system that replicate the in vivo spine phenotype of idiopathic ASD model mice

Autism Spectrum Disorder (ASD) is a developmental condition characterized by core symptoms including social difficulties, repetitive behaviors, and sensory abnormalities. Aberrant morphology of dendritic spines within the cortex has been documented in genetic disorders associated with ASD and ASD-like traits. We hypothesized that compounds that ameliorate abnormalities in spine dynamics might have the potential to ameliorate core symptoms of ASD. Because the morphology of the spine is influenced by signal inputs from other neurons and various molecular interactions, conventional single-molecule targeted drug discovery methods may not suffice in identifying compounds capable of ameliorating spine morphology abnormalities. In this study, we focused on spine phenotypes in the cortex using BTBR T + Itpr3 tf /J (BTBR) mice, which have been used as a model for idiopathic ASD in various studies. We established an in vitro compound screening system using primary cultured neurons from BTBR mice to faithfully represent the spine phenotype. The compound library mainly comprised substances with known target molecules and established safety profiles, including those approved or validated through human safety studies. Following screening of this specialized library containing 181 compounds, we identified 15 confirmed hit compounds. The molecular targets of these hit compounds were largely focused on the 5-hydroxytryptamine receptor (5-HTR). Furthermore, both 5-HT1AR agonist and 5-HT3R antagonist were common functional profiles in hit compounds. Vortioxetine, possessing dual attributes as a 5-HT1AR agonist and 5-HT3R antagonist, was administered to BTBR mice once daily for a period of 7 days. This intervention not only ameliorated their spine phenotype but also alleviated their social behavior abnormality. These results of vortioxetine supports the usefulness of a spine phenotype-based assay system as a potent drug discovery platform targeting ASD core symptoms.

Cyclase-associated protein (CAP) inhibits inverted formin 2 (INF2) to induce dendritic spine maturation

The morphology of dendritic spines, the postsynaptic compartment of most excitatory synapses, decisively modulates the function of neuronal circuits as also evident from human brain disorders associated with altered spine density or morphology. Actin filaments (F-actin) form the backbone of spines, and a number of actin-binding proteins (ABP) have been implicated in shaping the cytoskeleton in mature spines. Instead, only little is known about the mechanisms that control the reorganization from unbranched F-actin of immature spines to the complex, highly branched cytoskeleton of mature spines. Here, we demonstrate impaired spine maturation in hippocampal neurons upon genetic inactivation of cyclase-associated protein 1 (CAP1) and CAP2, but not of CAP1 or CAP2 alone. We found a similar spine maturation defect upon overactivation of inverted formin 2 (INF2), a nucleator of unbranched F-actin with hitherto unknown synaptic function. While INF2 overactivation failed in altering spine density or morphology in CAP-deficient neurons, INF2 inactivation largely rescued their spine defects. From our data we conclude that CAPs inhibit INF2 to induce spine maturation. Since we previously showed that CAPs promote cofilin1-mediated cytoskeletal remodeling in mature spines, we identified them as a molecular switch that control transition from filopodia-like to mature spines.

Suppression of eEF2 phosphorylation alleviates synaptic failure and cognitive deficits in mouse models of Down syndrome

INTRODUCTION

Cognitive impairment is a core feature of Down syndrome (DS), and the underlying neurobiological mechanisms remain unclear. Translation dysregulation is linked to multiple neurological disorders characterized by cognitive impairments. Phosphorylation of the translational factor eukaryotic elongation factor 2 (eEF2) by its kinase eEF2K results in inhibition of general protein synthesis.

METHODS

We used genetic and pharmacological methods to suppress eEF2K in two lines of DS mouse models. We further applied multiple approaches to evaluate the effects of eEF2K inhibition on DS pathophysiology.

RESULTS

We found that eEF2K signaling was overactive in the brain of patients with DS and DS mouse models. Inhibition of eEF2 phosphorylation through suppression of eEF2K in DS model mice improved multiple aspects of DS-associated pathophysiology including de novo protein synthesis deficiency, synaptic morphological defects, long-term synaptic plasticity failure, and cognitive impairments.

DISCUSSION

Our data suggested that eEF2K signaling dysregulation mediates DS-associated synaptic and cognitive impairments.

HIGHLIGHTS

Phosphorylation of the translational factor eukaryotic elongation factor 2 (eEF2) is increased in the Down syndrome (DS) brain. Suppression of the eEF2 kinase (eEF2K) alleviates cognitive deficits in DS models. Suppression of eEF2K improves synaptic dysregulation in DS models. Cognitive and synaptic impairments in DS models are rescued by eEF2K inhibitors.

Automatic dendritic spine segmentation in widefield fluorescence images reveal synaptic nanostructures distribution with super-resolution imaging

Dendritic spines are the main sites for synaptic communication in neurons, and alterations in their density, size, and shapes occur in many brain disorders. Current spine segmentation methods perform poorly in conditions with low signal-to-noise and resolution, particularly in the widefield images of thick (10 μm) brain slices. Here, we combined two open-source machine-learning models to achieve automatic 3D spine segmentation in widefield diffraction-limited fluorescence images of neurons in thick brain slices. We validated the performance by comparison with manually segmented super-resolution images of spines reconstructed from direct stochastic optical reconstruction microscopy (dSTORM). Lastly, we show an application of our approach by combining spine segmentation from diffraction-limited images with dSTORM of synaptic protein PSD-95 in the same field-of-view. This allowed us to automatically analyze and quantify the nanoscale distribution of PSD-95 inside the spine. Importantly, we found the numbers, but not the average sizes, of synaptic nanomodules and nanodomains increase with spine size.

The Effects of Sevoflurane and Aβ Interaction on CA1 Dendritic Spine Dynamics and MEGF10-Related Astrocytic Synapse Engulfment

General anesthetics may accelerate the neuropathological changes related to Alzheimer's disease (AD), of which amyloid beta (Aβ)-induced toxicity is one of the main causes. However, the interaction of general anesthetics with different Aβ-isoforms remains unclear. In this study, we investigated the effects of sevoflurane (0.4 and 1.2 maximal alveolar concentration (MAC)) on four Aβ species-induced changes on dendritic spine density (DSD) in hippocampal brain slices of Thy1-eGFP mice and multiple epidermal growth factor-like domains 10 (MEGF10)-related astrocyte-mediated synaptic engulfment in hippocampal brain slices of C57BL/6 mice. We found that both sevoflurane and Aβ downregulated CA1-dendritic spines. Moreover, compared with either sevoflurane or Aβ alone, pre-treatment with Aβ isoforms followed by sevoflurane application in general further enhanced spine loss. This enhancement was related to MEGF10-related astrocyte-dependent synaptic engulfment, only in AβpE3 + 1.2 MAC sevoflurane and 3NTyrAβ + 1.2 MAC sevoflurane condition. In addition, removal of sevoflurane alleviated spine loss in Aβ + sevoflurane. In summary, these results suggest that both synapses and astrocytes are sensitive targets for sevoflurane; in the presence of 3NTyrAβ, 1.2 MAC sevoflurane alleviated astrocyte-mediated synaptic engulfment and exerted a lasting effect on dendritic spine remodeling.

Cognitive integrity in Non-Demented Individuals with Alzheimer's Neuropathology is associated with preservation and remodeling of dendritic spines

INTRODUCTION

Individuals referred to as Non-Demented with Alzheimer's Neuropathology (NDAN) exhibit cognitive resilience despite presenting Alzheimer's disease (AD) histopathological signs. Investigating the mechanisms behind this resilience may unveil crucial insights into AD resistance.

METHODS

DiI labeling technique was used to analyze dendritic spine morphology in control (CTRL), AD, and NDAN post mortem frontal cortex, particularly focusing on spine types near and far from amyloid beta (Aβ) plaques.

RESULTS

NDAN subjects displayed a higher spine density in regions distant from Aβ plaques versus AD patients. In distal areas from the plaques, NDAN individuals exhibited more immature spines, while AD patients had a prevalence of mature spines. Additionally, our examination of levels of Peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (Pin1), a protein associated with synaptic plasticity and AD, showed significantly lower expression in AD versus NDAN and CTRL.

DISCUSSION

These results suggest that NDAN individuals undergo synaptic remodeling, potentially facilitated by Pin1, serving as a compensatory mechanism to preserve cognitive function despite AD pathology.

HIGHLIGHTS

Spine density is reduced near Aβ plaques compared to the distal area in CTRL, AD, and NDAN dendrites. NDAN shows higher spine density than AD in areas far from Aβ plaques. Far from Aβ plaques, NDAN has a higher density of immature spines, AD a higher density of mature spines. AD individuals show significantly lower levels of Pin1 compared to NDAN and CTRL.

Neurogenesis-independent mechanisms of MRI-detectable hippocampal volume increase following electroconvulsive stimulation

Electroconvulsive therapy (ECT) is one of the most effective psychiatric treatments but the underlying mechanisms are still unclear. In vivo human magnetic resonance imaging (MRI) studies have consistently reported ECT-induced transient hippocampal volume increases, and an animal model of ECT (electroconvulsive stimulation: ECS) was shown to increase neurogenesis. However, a causal relationship between neurogenesis and MRI-detectable hippocampal volume increases following ECT has not been verified. In this study, mice were randomly allocated into four groups, each undergoing a different number of ECS sessions (e.g., 0, 3, 6, 9). T2-weighted images were acquired using 11.7-tesla MRI. A whole brain voxel-based morphometry analysis was conducted to identify any ECS-induced brain volume changes. Additionally, a histological examination with super-resolution microscopy was conducted to investigate microstructural changes in the brain regions that showed volume changes following ECS. Furthermore, parallel experiments were performed on X-ray-irradiated mice to investigate the causal relationship between neurogenesis and ECS-related volume changes. As a result, we revealed for the first time that ECS induced MRI-detectable, dose-dependent hippocampal volume increase in mice. Furthermore, increased hippocampal volumes following ECS were seen even in mice lacking neurogenesis, suggesting that neurogenesis is not required for the increase. The comprehensive histological analyses identified an increase in excitatory synaptic density in the ventral CA1 as the major contributor to the observed hippocampal volume increase following ECS. Our findings demonstrate that modification of synaptic structures rather than neurogenesis may be the underlying biological mechanism of ECT/ECS-induced hippocampal volume increase.

Astrocytes in functional recovery following central nervous system injuries

Astrocytes are increasingly recognised as partaking in complex homeostatic mechanisms critical for regulating neuronal plasticity following central nervous system (CNS) insults. Ischaemic stroke and traumatic brain injury are associated with high rates of disability and mortality. Depending on the context and type of injury, reactive astrocytes respond with diverse morphological, proliferative and functional changes collectively known as astrogliosis, which results in both pathogenic and protective effects. There is a large body of research on the negative consequences of astrogliosis following brain injuries. There is also growing interest in how astrogliosis might in some contexts be protective and help to limit the spread of the injury. However, little is known about how astrocytes contribute to the chronic functional recovery phase following traumatic and ischaemic brain insults. In this review, we explore the protective functions of astrocytes in various aspects of secondary brain injury such as oedema, inflammation and blood-brain barrier dysfunction. We also discuss the current knowledge on astrocyte contribution to tissue regeneration, including angiogenesis, neurogenesis, synaptogenesis, dendrogenesis and axogenesis. Finally, we discuss diverse astrocyte-related factors that, if selectively targeted, could form the basis of astrocyte-targeted therapeutic strategies to better address currently untreatable CNS disorders.

The Effects of Appropriate Perioperative Exercise on Perioperative Neurocognitive Disorders: a Narrative Review

Perioperative neurocognitive disorders (PNDs) are now considered the most common neurological complication in older adult patients undergoing surgical procedures. A significant increase exists in the incidence of post-operative disability and mortality in patients with PNDs. However, no specific treatment is still available for PNDs. Recent studies have shown that exercise may improve cognitive dysfunction-related disorders, including PNDs. Neuroinflammation is a key mechanism underlying exercise-induced neuroprotection in PNDs; others include the regulation of gut microbiota and mitochondrial and synaptic function. Maintaining optimal skeletal muscle mass through preoperative exercise is important to prevent the occurrence of PNDs. This review summarizes current clinical and preclinical evidence and proposes potential molecular mechanisms by which perioperative exercise improves PNDs, providing a new direction for exploring exercise-mediated neuroprotective effects on PNDs. In addition, it intends to provide new strategies for the prevention and treatment of PNDs.

Differential behaviors of calcium-induced calcium release in one dimensional dendrite by Nernst-Planck equation, cable model and pure diffusion model

The source and dynamics of calcium is the key factor that regulates dendritic integration. Apart from the voltage-gated and ligand-gated calcium influx, an important source of calcium is from inner store of endoplasmic reticulum with a regenerative process of calcium-induced calcium release (CICR). To trigger this process, inositol 1,4,5-trisphosphate (IP3) and calcium are needed to satisfy certain requirements. The aim of our paper is to investigate how the CICR depends on the dynamics of membrane potential. We utilize one dimensional dendritic model to calculate membrane potential by Nernst-Planck Equation (NPE) and cable model and Pure Diffusion (PD) model, computational simulations are carried out to inject the calcium influx by synaptic stimulation and to predict subsequent CICR and calcium wave propagation. Our results demonstrate that CICR initiation and calcium wave propagation have much difference between electro-diffusion process of NPE and cable model. We find that cable model has lower threshold of IP3 stimulation to trigger CICR but is more difficult for calcium propagation than NPE, PD model requires even higher threshold of IP3 to initiate CICR process and calcium duration is shorter than NPE; the regenerative calcium wave propagates with faster speed in NPE than that in cable model and in PD model. Our work addresses the important role of electro-diffusion dynamics of charged ions in regulating CICR process in dendritic structure; and provides theoretical predictions for neurological process which requires sustaining calcium for downstream signaling processes.

Autism risk gene Cul3 alters neuronal morphology via caspase-3 activity in mouse hippocampal neurons

Autism Spectrum Disorders (ASDs) are neurodevelopmental disorders (NDDs) in which children display differences in social interaction/communication and repetitive stereotyped behaviors along with variable associated features. Cul3, a gene linked to ASD, encodes CUL3 (CULLIN-3), a protein that serves as a key component of a ubiquitin ligase complex with unclear function in neurons. Cul3 homozygous deletion in mice is embryonic lethal; thus, we examine the role of Cul3 deletion in early synapse development and neuronal morphology in hippocampal primary neuronal cultures. Homozygous deletion of Cul3 significantly decreased dendritic complexity and dendritic length, as well as axon formation. Synaptic spine density significantly increased, mainly in thin and stubby spines along with decreased average spine volume in Cul3 knockouts. Both heterozygous and homozygous knockout of Cul3 caused significant reductions in the density and colocalization of gephyrin/vGAT puncta, providing evidence of decreased inhibitory synapse number, while excitatory synaptic puncta vGulT1/PSD95 density remained unchanged. Based on previous studies implicating elevated caspase-3 after Cul3 deletion, we demonstrated increased caspase-3 in our neuronal cultures and decreased neuronal cell viability. We then examined the efficacy of the caspase-3 inhibitor Z-DEVD-FMK to rescue the decrease in neuronal cell viability, demonstrating reversal of the cell viability phenotype with caspase-3 inhibition. Studies have also implicated caspase-3 in neuronal morphological changes. We found that caspase-3 inhibition largely reversed the dendrite, axon, and spine morphological changes along with the inhibitory synaptic puncta changes. Overall, these data provide additional evidence that Cul3 regulates the formation or maintenance of cell morphology, GABAergic synaptic puncta, and neuronal viability in developing hippocampal neurons in culture.

AFM Imaging Reveals MicroRNA-132 to be a Positive Regulator of Synaptic Functions

The modification of synaptic and neural connections in adults, including the formation and removal of synapses, depends on activity-dependent synaptic and structural plasticity. MicroRNAs (miRNAs) play crucial roles in regulating these changes by targeting specific genes and regulating their expression. The fact that somatic and dendritic activity in neurons often occurs asynchronously highlights the need for spatial and dynamic regulation of protein synthesis in specific milieu and cellular loci. MicroRNAs, which can show distinct patterns of enrichment, help to establish the localized distribution of plasticity-related proteins. The recent study using atomic force microscopy (AFM)-based nanoscale imaging reveals that the abundance of miRNA(miR)-134 is inversely correlated with the functional activity of dendritic spine structures. However, the miRNAs that are selectively upregulated in potentiated synapses, and which can thereby support prospective changes in synaptic efficacy, remain largely unknown. Using AFM force imaging, significant increases in miR-132 in the dendritic regions abutting functionally-active spines is discovered. This study provides evidence for miR-132 as a novel positive miRNA regulator residing in dendritic shafts, and also suggests that activity-dependent miRNAs localized in distinct sub-compartments of neurons play bi-directional roles in controlling synaptic transmission and synaptic plasticity.

Neuronal plasticity in hippocampal neurons due to chronic mild stress and after stress removal in postnatal chicks

The avian dorsomedial surface of the cerebral hemisphere is occupied by the hippocampal complex (HCC), which plays an important role in learning, memory, cognitive functions, and regulating instinctive behavior patterns. The objective of the study was to evaluate the effect of chronic mild stress (CMS) in 4, 6, and 8 weeks and after chronic stress removal (CSR) in 6 and 8 weeks, on neuronal plasticity in HCC neurons of chicks through the Golgi-Cox technique. Further, behavioral study and open field test were conducted to test of exploration or of anxiety. The study revealed that the length of CMS and CSR groups shows a similar pattern as in nonstressed (NS) chicks, while weight shows nonsignificant decrease due to CMS as compared to NS and after CSR. The behavioral test depicts that the CMS group took more time to reach the food as compared to the NS and CSR groups. Due to CMS, the dendritic field of multipolar neurons shows significant decrease in 4 weeks, but in 6- and 8-week-old chicks, the multipolar, pyramidal, and stellate neurons depict significant decrease, whereas after CSR all neurons show significant increase in 8-week-old chicks. In 4- and 8-week-old chicks, all neurons depict significant decrease in their spine number, whereas in 6 weeks only multipolar neurons show significant decrease, but after CSR significant increase in 8-week-old chicks was observed. The study revealed that HCC shows continuous neuronal plasticity, which plays a significant role in normalizing and re-establishing the homeostasis in animals to survive.

The role of miRNA134 in pathogenesis and treatment of intractable epilepsy: a review article

MicroRNA-134 (miRNA134) has emerged as a critical regulator in the pathogenesis of epilepsy, particularly in intractable cases resistant to conventional therapies. This review explores the multifaceted roles of miRNA134 in epileptogenesis, focusing on its influence on dendritic spine morphology and synaptic plasticity. Through its interactions with proteins such as LIM kinase 1 (LIMK1), Pumilio 2 (PUM2), and Tubby-like protein 1 (TULP1), miRNA134 modulates various molecular pathways implicated in epilepsy development. Preclinical studies have shown pro-mising results in targeting miRNA134 for mitigating seizure activity, highlighting its potential as a therapeutic target. Furthermore, miRNA134 holds promise as a biomarker for epilepsy diagnosis and prognosis, offering opportunities for personalized treatment approaches. However, further research is warranted to elucidate the precise mechanisms underlying miRNA134's effects and to translate these findings into clinical applications.

Diffusion of brain metabolites highlights altered brain microstructure in type C hepatic encephalopathy: a 9.4 T preliminary study

Introduction

Type C hepatic encephalopathy (HE) is a decompensating event of chronic liver disease leading to severe motor and cognitive impairment. The progression of type C HE is associated with changes in brain metabolite concentrations measured by 1H magnetic resonance spectroscopy (MRS), most noticeably a strong increase in glutamine to detoxify brain ammonia. In addition, alterations of brain cellular architecture have been measured ex vivo by histology in a rat model of type C HE. The aim of this study was to assess the potential of diffusion-weighted MRS (dMRS) for probing these cellular shape alterations in vivo by monitoring the diffusion properties of the major brain metabolites.

Methods

The bile duct-ligated (BDL) rat model of type C HE was used. Five animals were scanned before surgery and 6- to 7-week post-BDL surgery, with each animal being used as its own control. 1H-MRS was performed in the hippocampus (SPECIAL, TE = 2.8 ms) and dMRS in a voxel encompassing the entire brain (DW-STEAM, TE = 15 ms, diffusion time = 120 ms, maximum b-value = 25 ms/μm2) on a 9.4 T scanner. The in vivo MRS acquisitions were further validated with histological measures (immunohistochemistry, Golgi-Cox, electron microscopy).

Results

The characteristic 1H-MRS pattern of type C HE, i.e., a gradual increase of brain glutamine and a decrease of the main organic osmolytes, was observed in the hippocampus of BDL rats. Overall increased metabolite diffusivities (apparent diffusion coefficient and intra-stick diffusivity-Callaghan's model, significant for glutamine, myo-inositol, and taurine) and decreased kurtosis coefficients were observed in BDL rats compared to control, highlighting the presence of osmotic stress and possibly of astrocytic and neuronal alterations. These results were consistent with the microstructure depicted by histology and represented by a decline in dendritic spines density in neurons, a shortening and decreased number of astrocytic processes, and extracellular edema.

Discussion

dMRS enables non-invasive and longitudinal monitoring of the diffusion behavior of brain metabolites, reflecting in the present study the globally altered brain microstructure in BDL rats, as confirmed ex vivo by histology. These findings give new insights into metabolic and microstructural abnormalities associated with high brain glutamine and its consequences in type C HE.

SNX17 Mediates Dendritic Spine Maturation via p140Cap

Sorting nexin17 (SNX17) is a member of the sorting nexin family, which plays a crucial role in endosomal trafficking. Previous research has shown that SNX17 is involved in the recycling or degradation of various proteins associated with neurodevelopmental and neurological diseases in cell models. However, the significance of SNX17 in neurological function in the mouse brain has not been thoroughly investigated. In this study, we generated Snx17 knockout mice and observed that the homozygous deletion of Snx17 (Snx17-/-) resulted in lethality. On the other hand, heterozygous mutant mice (Snx17+/-) exhibited anxiety-like behavior with a reduced preference for social novelty. Furthermore, Snx17 haploinsufficiency led to impaired synaptic transmission and reduced maturation of dendritic spines. Through GST pulldown and interactome analysis, we identified the SRC kinase inhibitor, p140Cap, as a potential downstream target of SNX17. We also demonstrated that the interaction between p140Cap and SNX17 is crucial for dendritic spine maturation. Together, this study provides the first in vivo evidence highlighting the important role of SNX17 in maintaining neuronal function, as well as regulating social novelty and anxiety-like behaviors.

Differential regulations of neural activity and survival in primary cortical neurons by PFOA or PFHpA

Perfluorinated compounds (PFCs), organofluoride compounds comprising carbon-fluorine and carbon-carbon bonds, are used as water and oil repellents in textiles and pharmaceutical tablets; however, they are associated with potential neurotoxic effects. Moreover, the impact of PFCs on neuronal survival, activity, and regulation within the brain remains unclear. Additionally, the mechanisms through which PFCs induce neuronal toxicity are not well-understood because of the paucity of data. This study elucidates that perfluorooctanoic acid (PFOA) and perfluoroheptanoic acid (PFHpA) exert differential effects on the survival and activity of primary cortical neurons. Although PFOA triggers apoptosis in cortical neurons, PFHpA does not exhibit this effect. Instead, PFHpA modifies dendritic spine morphogenesis and synapse formation in primary cortical neuronal cultures, additionally enhancing neural activity and synaptic transmission. This research uncovers a novel mechanism through which PFCs (PFHpA and PFOA) cause distinct alterations in dendritic spine morphogenesis and synaptic activity, shedding light on the molecular basis for the atypical behaviors noted following PFC exposure. Understanding the distinct effects of PFHpA and PFOA could guide regulatory policies on PFC usage and inform clinical approaches to mitigate their neurotoxic effects, especially in vulnerable population.

Egocentric processing of items in spines, dendrites, and somas in the retrosplenial cortex

Egocentric representations of external items are essential for spatial navigation and memory. Here, we explored the neural mechanisms underlying egocentric processing in the retrosplenial cortex (RSC), a pivotal area for memory and navigation. Using one-photon and two-photon calcium imaging, we identified egocentric tuning for environment boundaries in dendrites, spines, and somas of RSC neurons (egocentric boundary cells) in the open-field task. Dendrites with egocentric tuning tended to have similarly tuned spines. We further identified egocentric neurons representing landmarks in a virtual navigation task or remembered cue location in a goal-oriented task, respectively. These neurons formed an independent population with egocentric boundary cells, suggesting that dedicated neurons with microscopic clustering of functional inputs shaped egocentric boundary processing in RSC and that RSC adopted a labeled line code with distinct classes of egocentric neurons responsible for representing different items in specific behavioral contexts, which could lead to efficient and flexible computation.

Between neurons and networks: investigating mesoscale brain connectivity in neurological and psychiatric disorders

The study of brain connectivity has been a cornerstone in understanding the complexities of neurological and psychiatric disorders. It has provided invaluable insights into the functional architecture of the brain and how it is perturbed in disorders. However, a persistent challenge has been achieving the proper spatial resolution, and developing computational algorithms to address biological questions at the multi-cellular level, a scale often referred to as the mesoscale. Historically, neuroimaging studies of brain connectivity have predominantly focused on the macroscale, providing insights into inter-regional brain connections but often falling short of resolving the intricacies of neural circuitry at the cellular or mesoscale level. This limitation has hindered our ability to fully comprehend the underlying mechanisms of neurological and psychiatric disorders and to develop targeted interventions. In light of this issue, our review manuscript seeks to bridge this critical gap by delving into the domain of mesoscale neuroimaging. We aim to provide a comprehensive overview of conditions affected by aberrant neural connections, image acquisition techniques, feature extraction, and data analysis methods that are specifically tailored to the mesoscale. We further delineate the potential of brain connectivity research to elucidate complex biological questions, with a particular focus on schizophrenia and epilepsy. This review encompasses topics such as dendritic spine quantification, single neuron morphology, and brain region connectivity. We aim to showcase the applicability and significance of mesoscale neuroimaging techniques in the field of neuroscience, highlighting their potential for gaining insights into the complexities of neurological and psychiatric disorders.