bioRxiv Subject Collection: Neuroscience's Journal
[Most Recent Entries]
[Calendar View]
Monday, February 3rd, 2025
| Time |
Event |
| 4:43a |
Dose Escalation in Pentylenetetrazol Kindling Detects Differences in Chronic Seizure Susceptibility
Objective: Pentylenetetrazol (PTZ) kindling is a widely used model for inducing epileptogenesis and evaluating long-term seizure susceptibility differences among animals. This model is typically performed by chronic, repetitive exposures to a constant subconvulsive PTZ dose. However, the effectiveness of the commonly used subconvulsive dose (35mg/kg) varies among different animal groups and experimental conditions due to factors such as species, age, sex, and genetic background. The objective of this study was to characterize a novel model of kindling, the PTZ Dose Escalation (PTZ-DE) model, which assesses chronic seizure threshold with enhanced sensitivity by empirically determining the minimally effective dose to induce PTZ kindling for specific experimental conditions. Methods: This study investigated the efficacy and validity of the PTZ-DE model by comparing its performance to the standard PTZ kindling approach across a series of conditions. First, the ability of the PTZ-DE model to produce the gradual increase in chronic seizure severity response characteristic of PTZ kindling was compared to the standard model across multiple animal background characteristics (strain, sex). Next, the validity of this model was investigated by determining whether the PTZ-DE model could replicate similar changes in chronic seizure susceptibility previously published using the standard approach after traumatic brain injury (TBI). Lastly, the PTZ-DE model efficacy to detect seizure differences was measured in a condition (glyburide treatment) in which alterations to chronic seizure susceptibility were not detected with standard kindling. Results: This study found that the PTZ-DE model corrects for background differences in PTZ susceptibility, replicates known differences in chronic seizure thresholds after TBI, and identifies new alterations in seizure threshold not detected with traditional kindling methods. Significance: The PTZ-DE model may prove to be a superior tool to standard PTZ kindling for discovering new pathological mechanisms of epileptogenesis and for developing targeted therapies for chronic seizure management, as evidenced by its ability to detect subtle differences in seizure susceptibility across various experimental conditions. | | 6:06a |
Neuronal endolysosomal acidification relies on interactions between transmembrane protein 184B (TMEM184B) and the vesicular proton pump
Disruption of endolysosomal acidification is a hallmark of several neurodevelopmental and neurodegenerative disorders. Impaired acidification causes accumulation of toxic protein aggregates and disrupts neuronal homeostasis, yet the molecular mechanisms regulating endolysosomal pH in neurons remain poorly understood. A critical regulator of lumenal acidification is the vacuolar ATPase (V-ATPase), a proton pump whose activity depends on dynamic assembly of its V0 and V1 subdomains. In this study, we identify transmembrane protein 184B (TMEM184B) as a novel regulator of endolysosomal acidification in neurons. TMEM184B is an evolutionarily conserved 7-pass transmembrane protein required for synaptic structure and function, and sequence variation in TMEM184B causes neurodevelopmental disorders, but the mechanism for this effect is unknown. We performed proteomic analysis of TMEM184B-interacting proteins and identified enrichment of components involved in endosomal trafficking and function, including the V-ATPase. TMEM184B localizes to early and late endosomes, further supporting a role in the endosomal system. Loss of TMEM184B results in significant reductions in endolysosomal acidification within cultured mouse cortical neurons. This alteration in pH is associated with impaired assembly of the V-ATPase V0 and V1 subcomplexes in the TMEM184B mutant mouse brain, suggesting a mechanism by which TMEM184B promotes flux through the endosomal pathway. Overall, these findings identify a new contributor in maintaining endosomal function and provide a mechanistic basis for disrupted neuronal function in human TMEM184B-associated nervous system disorders.
Significance StatementEndolysosomal acidification is essential for neuronal protein homeostasis, yet its regulation in neurons remains poorly understood. Here, we identify TMEM184B as a key regulator of this process, establishing its first known cellular role. We show that TMEM184B interacts with vacuolar ATPase (V-ATPase) components and promotes the assembly of its V0 and V1 subdomains, facilitating lumenal acidification. Loss of TMEM184B disrupts endolysosomal pH in neurons, potentially impairing proteostasis. These findings reveal a critical function for TMEM184B in neuronal maintenance and provide mechanistic insight into its link to neurological disorders. This work advances our understanding of endolysosomal regulation and suggests TMEM184B regulation could improve outcomes in diseases involving lysosomal dysfunction. | | 6:06a |
A Sensitive Soma-localized Red Fluorescent Calcium Indicator for Multi-Modality Imaging of Neuronal Populations In Vivo
Recent advancements in genetically encoded calcium indicators, particularly those based on green fluorescent proteins, have optimized their performance for monitoring neuronal activities in a variety of model organisms. However, progress in developing red-shifted GECIs, despite their advantages over green indicators, has been slower, resulting in fewer options for end-users. In this study, we explored topological inversion and soma-targeting strategies, which are complementary to conventional mutagenesis, to re-engineer a red genetically encoded calcium indicator, FRCaMP, for enhanced in vivo performance. The resulting sensors, FRCaMPi and soma-targeted FRCaMPi (SomaFRCaMPi), exhibit up to 2-fold higher dynamic range and peak {Delta}F/F0 per single AP compared to widely used jRGECO1a in neurons in culture and in vivo. Compared to jRGECO1a and FRCaMPi, SomaFRCaMPi reduces erroneous correlation of neuronal activity in the brains of mice and zebrafish by two- to four-fold due to diminished neuropil contamination without compromising the signal-to-noise ratio. Under wide-field imaging in primary somatosensory and visual cortex in mice with high labeling density (80-90%), SomaFRCaMPi exhibits up to 40% higher SNR and decreased artifactual correlation across neurons. Altogether, SomaFRCaMPi improves the accuracy and scale of neuronal activity imaging at single-neuron resolution in densely labeled brain tissues due to a 2-3-fold enhanced automated neuronal segmentation, 50% higher fraction of responsive cells, up to 2-fold higher SNR compared to jRGECO1a. Our findings highlight the potential of SomaFRCaMPi, comparable to the most sensitive soma-targeted GCaMP, for precise spatial recording of neuronal populations using popular imaging modalities in model organisms such as zebrafish and mice. | | 9:31a |
Prenatal adversity configures a subpopulation of ventral dentate granule cells for recruitment to drive innate anxiety
Adverse prenatal environment is a risk factor for the development of psychiatric disorders. Although studies have implicated epigenetic mechanisms, little is known about how epigenomic changes come about and lead to abnormal behaviors in affected individuals. We sought to identify epigenomic and transcriptomic signatures induced by a proinflammatory gestational environment in the ventral dentate gyrus (vDG), a hippocampal region linked to avoidance of threatening contexts, that persist and promote anxiety-like behavior in mice. Here we show that adversity shifted the methylation of enhancers and promoters with intermediate methylation and altered synapse-related gene expression, resulting in epigenetic and transcriptional heterogeneity in the vDG. Exposure to an anxiogenic environment recruited vDG neurons with the most transcriptional alterations. Differentially expressed synapse-relevant genes in ensemble neurons tended to be differentially methylated. Finally, this ensemble exhibited higher activity in threatening than safe environment suggesting a prenatal adversity-induced epigenetic and neurobiological sequence that leads to anxiety. | | 3:21p |
Association of human gut microbiota with Alzheimers disease pathogenesis: An exploratory clinical study
The relationship between Alzheimer's disease (AD) onset and the brain-gut axis has garnered increasing attention. This study aimed to investigate the potential role of the brain-gut axis in AD pathogenesis, with a specific focus on microbiota composition. This exploratory study enrolled 10 patients with AD and 13 healthy adults, grouped by age ([≤]30 years, 31-40 years, and [≥]41 years). Fecal samples were collected, and 16S rRNA gene sequencing was employed to analyze differences in fecal microbiota composition at the bacterial species level. Certain bacterial species appeared more abundant in the AD group (e.g., Ruminococcus inulinivorans and Ruminococcus torques), while others were relatively more abundant in healthy adults (e.g., Prevotella vulgatus 1, Bacteroides wexlerae, Clostridium butyricum, and Alistipes rectalis). However, these differences were not statistically significant, likely because of the limited sample size. These findings suggest that fecal microbiota composition may differ between patients with AD and healthy individuals, with a potential intermediate group at risk of AD development. Larger-scale clinical studies are necessary to further elucidate the bacterial species associated with AD pathogenesis, potentially enabling the use of microbiota composition as a screening tool to distinguish between healthy individuals, patients with AD, and those with preclinical AD. | | 3:21p |
On CA1 ripple oscillations: reevaluating asynchronicity evidence
Sharp-wave ripples (SWRs) are hippocampal network oscillations associated with memory consolidation. They are characterized by the co-occurrence of fast and slow field potentials across CA1 layers: the fast-frequency oscillations, known as ripples, are prominent in the pyramidal cell layer, where they coincide with increased neuronal spiking, while slower negative transients, referred to as sharp waves, occur simultaneously in the stratum radiatum. SWRs have traditionally been considered globally synchronous across the hippocampus; however, recent evidence suggests that ripples may be less synchronous than previously thought, particularly between the two hemispheres (Villalobos et al., 2017). In this study, we revisited this question using a unique dataset from probes spanning the septo-temporal axis of CA1. Our results demonstrate that ripples are phase-locked within but not between hemispheres, although their occurrence remains time-locked across both the septo-temporal axis and hemispheres. We also observed similar synchronicity pattern for spiking activity: neurons are locally phase-coupled and globally time-coupled to ripple events. Interneurons exhibit a much stronger phase coupling to both ipsilateral and contralateral ripples than pyramidal neurons. These findings suggest that ripples are locally phase-coupled through pyramidal-interneuron interactions, with global time-locking likely driven by a common bilateral CA3 input and potentially modulated by interneuron circuits. | | 4:30p |
Regulation of hippocampal excitatory synapse development by the adhesion G-protein coupled receptor Brain-specific angiogenesis inhibitor 2 (BAI2/ADGRB2)
Glutamatergic synapses and their associated dendritic spines are critical information processing sites within the brain. Proper development of these specialized cellular junctions is important for normal brain functionality. Synaptic adhesion G protein-coupled receptors (aGPCRs) have been identified as regulators of synapse development and function. While two members of the Brain-specific angiogenesis inhibitor (BAI/ADGRB) subfamily of synaptic aGPCRs, BAI1/ADGRB1 and BAI3/ADGRB3, have been found to mediate synapse and spine formation, BAI2/ADGRB2 function remains uncharacterized at the synapse. Here, we show that endogenous BAI2 is expressed throughout the nervous system with prominent expression in synapse dense regions of the hippocampus. In dissociated hippocampal cultures, BAI2 is highly enriched at large postsynaptic sites, defined by the size of the postsynaptic scaffold PSD95. Loss of BAI2 negatively impacts glutamatergic synapses across development in dissociated hippocampal cultures. In contrast, GABAergic synapse density is unchanged. Furthermore, BAI2 deficient neurons have significant alterations in spine morphology with decreased density of mature PSD95-containing mushroom-shaped spines compared with wild-type neurons. Interestingly, no major alterations in dendritic complexity were observed in BAI2 deficient neurons, in contrast to previous results for the other BAIs. The reduction in mature mushroom-shaped spine is commensurate with a reduction in spine volume and head diameter. Altogether, these results demonstrate that the aGPCR BAI2 is an important regulator of glutamatergic synapse and PSD95-associated spine development in cultured hippocampal neurons. These results expand the knowledge of the BAI subfamily of aGPCRs in mediating excitatory synapse and spine development and highlight differences unique to BAI2. | | 4:30p |
Shared Alteration of Whole-Brain Connectivity and Olfactory Deficits in Multiple Autism Mouse Models
Autism spectrum disorder (ASD) is a disconnection condition influenced by both heterogeneous genetic and environmental factors, yet it remains unclear whether common connectivity deficits exist. Here, we demonstrate that different ASD-linked mutations lead to distinct circuit abnormalities but share deficits in the piriform cortex and olfactory discrimination. Using advanced artificial intelligence, we developed a whole-brain mapping platform to analyze the distribution of the Thy1-YFP projection neurons in three ASD mouse models (Tbr1+/-, Nf1+/-, Vcp+/R95G). Our analysis revealed changes in axonal patterns and neuronal distribution, indicating deficits in projection neuron differentiation and maintenance. Notably, the piriform cortex consistently exhibited reduced YFP+ cells and signals and impaired functionality across all models. Visual and somatosensory cortices were also affected, but the patterns varied. These findings highlight that the sensory regions, especially the piriform cortex, are susceptible to ASD-related mutations, strengthening the notion that different sensory experiences are common in ASD. | | 4:30p |
The NeflE397K mouse model demonstrates muscle pathology and motor function deficits consistent with CMT2E
Charcot-Marie-Tooth (CMT) disease affects approximately 1 in 2,500 people and represents a heterogeneous group of inherited peripheral neuropathies characterized by progressive motor and sensory dysfunction. CMT type 2E is a result of mutations in the neurofilament light (NEFL) gene with predominantly autosomal dominant inheritance, often presenting with a progressive neuropathy with distal muscle weakness, sensory loss, gait disturbances, foot deformities, reduced nerve conduction velocity (NCV) without demyelination and typically reduced compound muscle action potential (CMAP) amplitude values. Several Nefl mouse models exist that either alter the mouse Nefl gene or overexpress a mutated human NEFL transgene, each recapitulating various aspects of CMT2E disease. We generated the orthologous NEFLE396K mutation in the mouse C57BL/6 background, NeflE397K. In a separate report, we extensively characterized the electrophysiology deficits and axon pathology in NeflE397K mice. In this manuscript, we report our characterization of NeflE397K motor function deficits, muscle pathology and changes in breathing Nefl+/E397K and NeflE397K/E397K mice demonstrated progressive motor coordination deficits and muscle weakness through the twelve months of age analyzed, consistent with our electrophysiology findings. Additionally, Nefl+/E397K and NeflE397K/E397K mice showed alterations in muscle fiber area, diameter and composition as disease developed. Lastly, Nefl mutant mice showed increased number of apneas under normoxia conditions and increased erratic breathing as well as tidal volume under respiratory challenge conditions. NeflE397K/E397K mice phenotypes and pathology were consistently more severe than Nefl+/E397K mice. Collectively, these novel CMT2E models present with a clinically relevant phenotype and make it an ideal model for the evaluation of therapeutics. | | 4:30p |
Protein-Like Polymer for Inhibition of Tau Fibril Propagation in Human-Derived Models of Neurodegeneration
The misfolding, aggregation, and spread of tau protein fibrils underlie tauopathies, a diverse class of neurodegenerative diseases for which effective treatments remain elusive. Among these are corticobasal dementia (CBD) and progressive supranuclear palsy (PSP), canonical examples of 4-repeat (4R) tauopathies characterized by tau isoforms exclusively with four microtubule-binding repeat domains. We target this 4R tau isoform-specific mechanism by focusing on misfolded tau's distinctive stem-loop-stem structural motif formed by the junction of the 4R-defining alternatively spliced exon and the adjacent constitutive exon. A synthetic peptide based on this stem-loop-stem sequence can induce aggregation and spread in an isoform-specific manner. Here, we develop a protein-like polymer (PLP) in which multiple copies of this synthetic peptide form a brush-like structure capable of preventing tau aggregation by binding and capping fibril ends in vitro, in human brain organoids, and in cellular models with an EC50 of 105 +/- 14 nM. PLPs demonstrate robust activity against fibrils derived from CBD and PSP patient brains and a PS19 mouse tauopathy model. Previous tau-targeted treatments have primarily focused on broad tau clearance, aggregation inhibition, or microtubule stabilization, often lacking isoform specificity and precision. In contrast, this approach targets the 4R tau isoform's unique structural motif, offering a tailored therapeutic intervention for diseases like CBD and PSP. Supported by prior studies showing blood-brain barrier penetrance and safety profiles, this tau-binding PLP offers a promising translational path toward clinical applications in tauopathy treatment. | | 4:30p |
Post-Ictal Gamma Oscillations Predict Hippocampal Structural Integrity in Mesial Temporal Lobe Epilepsy
The underlying histopathology and epileptic network of patients with mesial temporal lobe epilepsy (mTLE) are difficult to ascertain. Here, we report a novel electrical activity following seizure termination, termed post-ictal gamma oscillations (PIGOs), recorded in mice with intrahippocampal kainic acid injection and a patient with mTLE. PIGOs are characterized by a spectral shift of increased power in gamma frequencies relative to decreased power in other frequencies, generating a gamma peak. PIGOs are accompanied by increased intracellular calcium levels among parvalbumin-positive interneurons and a direct current shift. Only a subgroup of animals in the study had PIGOs. These animals had less pronounced hippocampal sclerosis (HS) than those without PIGOs. To illustrate the translational potential of these findings, we analyzed data from two patients with unilateral mTLE, one with PIGOs and the other without. The patient with PIGOs had symmetrical hippocampi on neuroimaging, whereas the other exhibited overly decreased interictal glucose uptake in left hippocampus, suggesting left-sided HS. After receiving laser ablation of mesial temporal regions, the patient with PIGOs became seizure-free, whereas the other did not. Our results suggest that PIGOs may serve as a biomarker for a milder form of HS in patients with mTLE and for predicting treatment outcomes. | | 4:30p |
Fmr1 KO causes delayed rebound spike timing in mediodorsal thalamocortical neurons through regulation of HCN channel activity
Background: The neurodevelopmental disorder Fragile X syndrome (FXS) results from hypermethylation of the FMR1 gene which prevents FMRP production. FMRP modulates the expression and function of a wide variety of proteins, including voltage-gated ion channels such as Hyperpolarization-Activated Cyclic Nucleotide gated (HCN) channels, which are integral to rhythmic activity in thalamic structures. Thalamocortical pathology, particularly involving the mediodorsal thalamus (MD), has been implicated in neurodevelopmental disorders. MD connectivity with mPFC is integral to executive functions like working memory and social behaviors that are disrupted in FXS. Methods: We used a combination of retrograde labeling and ex vivo brain slice whole cell electrophysiology in 40 wild type and 42 Fmr1 KO male mice to investigate how a lack of Fmr1 affects intrinsic cellular properties in lateral (MD-L) and medial (MD-M) MD neurons that project to the medial prefrontal cortex (MD[->]mPFC neurons). Results: In MD-L neurons, Fmr1 knockout caused a decrease in HCN-mediated membrane properties such as voltage sag and membrane afterhyperpolarization. These changes in subthreshold properties were accompanied by changes in suprathreshold neuron properties such as the variability of action potential burst timing. Conclusions: In Fmr1 knockout mice, reduced HCN channel activity in MD[->]mPFC neurons impairs both the timing and magnitude of HCN-mediated membrane potential regulation. Changes in response timing may adversely affect rhythm propagation in Fmr1 KO thalamocortical circuitry. MD thalamic neurons are critical for maintaining rhythmic activity involved in cognitive and affective functions. Understanding specific mechanisms of thalamocortical circuit activity may lead to therapeutic interventions for individuals with FXS. | | 4:30p |
Multi-output computation by single neuron biophysics in a visual system
As long anticipated (Sandberg and Bostrom 2008; Seung 2012; Szigeti et al. 2014), connectomics is providing a new foundation for brain simulation by replacing theoretical assumptions about network connectivity with solid empirical facts. Connectomics also yields detailed information about neuronal morphology, which is useful for simulating the biophysics of single neurons (Yang et al. 2016; Meier and Borst 2019; T. X. Liu et al. 2022). Here I introduce a formalism for simulating a brain as a network of synapses interacting via an effective resistance matrix. By computing this matrix for fly visual interneurons, I find evidence that some neurons may be true multi-output devices, neither well approximated as "point neurons" (Lappalainen et al. 2024; Shiu et al. 2024), nor as collections of functionally independent compartments (Meier and Borst 2019). Within a linear approximation, such a neuron is instead equivalent to a hierarchy of virtual neurons that spatially pool over multiple length scales. The computational powers of multi-output neurons may support highly sophisticated normalizations in the fly visual system (Seung 2024a). |
|