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Developmental Dynamics : An Official... Jan 2024Tripartite motif (TRIM46) is a relatively novel protein that belongs to tripartite motif family. TRIM46 organizes parallel microtubule arrays on the axons, which are...
BACKGROUND
Tripartite motif (TRIM46) is a relatively novel protein that belongs to tripartite motif family. TRIM46 organizes parallel microtubule arrays on the axons, which are important for neuronal polarity and axonal function. TRIM46 is highly expressed in the brain, but its biological function in adults has not yet been determined.
RESULTS
Trim46 knockout (KO) rat line was established using CRISPR/cas9. Trim46 KO rats had smaller hippocampus sizes, fewer neuronal dendritic arbors and dendritic spines, and shorter and more distant axon initial segment. Furthermore, the protein interaction between endogenous TRIM46 and FK506 binding protein 5 (FKBP5) in brain tissues was determined; Trim46 KO increased hippocampal FKBP5 protein levels and decreased hippocampal protein kinase B (Akt) phosphorylation, gamma-aminobutyric acid type A receptor subunit alpha1 (GABRA1) and glutamate ionotropic receptor NMDA type subunit 1 (NMDAR1) protein levels. Trim46 KO rats exhibited hypoactive behavioral changes such as reduced spontaneous activity, social interaction, sucrose preference, impaired prepulse inhibition (PPI), and short-term reference memory.
CONCLUSIONS
These results demonstrate the significant impact of Trim46 KO on brain structure and behavioral function. This study revealed a novel potential association of TRIM46 with dendritic development and neuropsychiatric behavior, providing new insights into the role of TRIM46 in the brain.
PubMed: 38193537
DOI: 10.1002/dvdy.687 -
ELife Jan 2024Detailed characterization of interneuron types in primary visual cortex (V1) has greatly contributed to understanding visual perception, yet the role of chandelier cells...
Detailed characterization of interneuron types in primary visual cortex (V1) has greatly contributed to understanding visual perception, yet the role of chandelier cells (ChCs) in visual processing remains poorly characterized. Using viral tracing we found that V1 ChCs predominantly receive monosynaptic input from local layer 5 pyramidal cells and higher-order cortical regions. Two-photon calcium imaging and convolutional neural network modeling revealed that ChCs are visually responsive but weakly selective for stimulus content. In mice running in a virtual tunnel, ChCs respond strongly to events known to elicit arousal, including locomotion and visuomotor mismatch. Repeated exposure of the mice to the virtual tunnel was accompanied by reduced visual responses of ChCs and structural plasticity of ChC boutons and axon initial segment length. Finally, ChCs only weakly inhibited pyramidal cells. These findings suggest that ChCs provide an arousal-related signal to layer 2/3 pyramidal cells that may modulate their activity and/or gate plasticity of their axon initial segments during behaviorally relevant events.
Topics: Animals; Mice; Neurons; Pyramidal Cells; Visual Cortex; Interneurons; Arousal
PubMed: 38192196
DOI: 10.7554/eLife.91153 -
Journal of Visualized Experiments : JoVE Dec 2023Bidirectional transport of cargos along the axon is critical for maintaining functional synapses, neural connectivity, and healthy neurons. Axonal transport is disrupted...
Bidirectional transport of cargos along the axon is critical for maintaining functional synapses, neural connectivity, and healthy neurons. Axonal transport is disrupted in multiple neurodegenerative diseases, and projection neurons are particularly vulnerable because of the need to transport cellular materials over long distances and sustain substantial axonal mass. Pathological modifications of several disease-related proteins negatively affect transport, including tau, amyloid-β, α-synuclein, superoxide dismutase, and huntingtin, providing a potential common mechanism by which pathological proteins exert toxicity in disease. Methods to study these toxic mechanisms are necessary to understand neurodegenerative disorders and identify potential therapeutic interventions. Here, cultured primary rodent hippocampal neurons are co-transfected with multiple plasmids to study the effects of pathological proteins on fast axonal transport using live-cell confocal imaging of fluorescently-tagged cargo proteins. We begin with the harvest, dissociation, and culturing of primary hippocampal neurons from rodents. Then, we co-transfect the neurons with plasmid DNA constructs to express fluorescent-tagged cargo protein and wild-type or mutant tau (used as an exemplar of pathological proteins). Axons are identified in live cells using an antibody that binds an extracellular domain of neurofascin, an axon initial segment protein, and an axonal region of interest is imaged to measure fluorescent cargo transport. Using KymoAnalyzer, a freely available ImageJ macro, we extensively characterize the velocity, pause frequency, and directional cargo density of axonal transport, all of which may be affected by the presence of pathological proteins. Through this method, we identify a phenotype of increased cargo pause frequency associated with the expression of pathological tau protein. Additionally, gene-silencing shRNA constructs can be added to the transfection mix to test the role of other proteins in mediating transport disruption. This protocol is easily adaptable for use with other neurodegenerative disease-related proteins and is a reproducible method to study the mechanisms of how those proteins disrupt axonal transport.
Topics: Humans; Axonal Transport; Neurodegenerative Diseases; Neurons; Axons; Interneurons
PubMed: 38189521
DOI: 10.3791/66156 -
Journal of Neurophysiology Feb 2024Microelectrodes serve as a fundamental tool in electrophysiology research throughout the nervous system, providing a means of exploring neural function with a high...
Microelectrodes serve as a fundamental tool in electrophysiology research throughout the nervous system, providing a means of exploring neural function with a high resolution of neural firing information. We constructed a hybrid computational model using the finite element method and multicompartment cable models to explore factors that contribute to extracellular voltage waveforms that are produced by sensory pseudounipolar neurons, specifically smaller A-type neurons, and that are recorded by microelectrodes in dorsal root ganglia. The finite element method model included a dorsal root ganglion, surrounding tissues, and a planar microelectrode array. We built a multicompartment neuron model with multiple trajectories of the glomerular initial segment found in many A-type sensory neurons. Our model replicated both the somatic intracellular voltage profile of Aδ low-threshold mechanoreceptor neurons and the unique extracellular voltage waveform shapes that are observed in experimental settings. Results from this model indicated that tortuous glomerular initial segment geometries can introduce distinct multiphasic properties into a neuron's recorded waveform. Our model also demonstrated how recording location relative to specific microanatomical components of these neurons, and recording distance from these components, can contribute to additional changes in the multiphasic characteristics and peak-to-peak voltage amplitude of the waveform. This knowledge may provide context for research employing microelectrode recordings of pseudounipolar neurons in sensory ganglia, including functional mapping and closed-loop neuromodulation. Furthermore, our simulations gave insight into the neurophysiology of pseudounipolar neurons by demonstrating how the glomerular initial segment aids in increasing the resistance of the stem axon and mitigating rebounding somatic action potentials. We built a computational model of sensory neurons in the dorsal root ganglia to investigate factors that influence the extracellular waveforms recorded by microelectrodes. Our model demonstrates how the unique structure of these neurons can lead to diverse and often multiphasic waveform profiles depending on the location of the recording contact relative to microanatomical neural components. Our model also provides insight into the neurophysiological function of axon glomeruli that are often present in these neurons.
Topics: Ganglia, Spinal; Microelectrodes; Action Potentials; Sensory Receptor Cells; Computer Simulation
PubMed: 38169334
DOI: 10.1152/jn.00385.2023 -
Cell Dec 2023The enhanced cognitive abilities characterizing the human species result from specialized features of neurons and circuits. Here, we report that the hominid-specific...
The enhanced cognitive abilities characterizing the human species result from specialized features of neurons and circuits. Here, we report that the hominid-specific gene LRRC37B encodes a receptor expressed in human cortical pyramidal neurons (CPNs) and selectively localized to the axon initial segment (AIS), the subcellular compartment triggering action potentials. Ectopic expression of LRRC37B in mouse CPNs in vivo leads to reduced intrinsic excitability, a distinctive feature of some classes of human CPNs. Molecularly, LRRC37B binds to the secreted ligand FGF13A and to the voltage-gated sodium channel (Nav) β-subunit SCN1B. LRRC37B concentrates inhibitory effects of FGF13A on Nav channel function, thereby reducing excitability, specifically at the AIS level. Electrophysiological recordings in adult human cortical slices reveal lower neuronal excitability in human CPNs expressing LRRC37B. LRRC37B thus acts as a species-specific modifier of human neuron excitability, linking human genome and cell evolution, with important implications for human brain function and diseases.
Topics: Animals; Humans; Mice; Action Potentials; Axons; Neurons; Pyramidal Cells; Voltage-Gated Sodium Channels
PubMed: 38134874
DOI: 10.1016/j.cell.2023.11.028 -
The Journal of Neuroscience : the... Feb 2024Neurons typically generate action potentials at their axon initial segment based on the integration of synaptic inputs. In many neurons, the axon extends from the soma,...
Neurons typically generate action potentials at their axon initial segment based on the integration of synaptic inputs. In many neurons, the axon extends from the soma, equally weighting dendritic inputs. A notable exception is found in a subset of hippocampal pyramidal cells where the axon emerges from a basal dendrite. This structure allows these axon-carrying dendrites (AcDs) a privileged input route. We found that in male mice, such cells in the CA1 region receive stronger excitatory input from the contralateral CA3, compared with those with somatic axon origins. This is supported by a higher count of putative synapses from contralateral CA3 on the AcD. These findings, combined with prior observations of their distinct role in sharp-wave ripple firing, suggest a key role of this neuron subset in coordinating bi-hemispheric hippocampal activity during memory-centric oscillations.
Topics: Male; Mice; Animals; Pyramidal Cells; Hippocampus; Neurons; Dendrites; Action Potentials; Synapses; CA1 Region, Hippocampal
PubMed: 38123997
DOI: 10.1523/JNEUROSCI.0440-23.2023 -
Annual International Conference of the... Jul 2023The finite element method (FEM) has become an increasingly popular tool for the computational modeling of multiscale biological systems, including the electrode-tissue...
The finite element method (FEM) has become an increasingly popular tool for the computational modeling of multiscale biological systems, including the electrode-tissue interface and the behavior of individual neural cells. However, a significant challenge in these studies is integrating multiple levels of complexity, each with its biophysical properties. This paper presents a single platform solution for modeling these multiscale systems using the finite element method. The proposed method combines different finite element formulations tailored to the specific biophysical properties of each scale into a single unified simulation platform. The results of this method are compared to experimental data to demonstrate the accuracy and efficacy of the proposed approach. With the goal of eliciting the most significant possible response from the retinal ganglion cell's (RGC) multiple components, we devised an electrical stimulation strategy and electrode placement setup that took into account both the RGC's horizontal and vertical location. We found that the activity in a single RGC model could be elicited by a cathodic pulse of amplitude 34 µA. We observed that the optimum electrode placement for a neural response is around the initial axon segment, 30 μm from the soma, and 10 μm above the RGC. Our results show that the proposed method can accurately capture the complex behavior of these multiscale systems and provide a valuable tool for further research in retinal prostheses.Clinical Relevance- To develop efficient electrical stimulation schemes for retinal prosthesis applications, this research can shed light on the behavior of the electrode-tissue interface and individual neural cells. Electrical stimulation of RGCs has shown promise in the application of retinal prostheses. Still, a thorough understanding of the electrode-induced electric field is essential for the design of effective and safe stimulation protocols. Electrical stimulation's side effects may require knowledge of multiple physics disciplines (such as thermal or structural deformation owing to implant placement inside the eye). Finding a solution to diseases that cause vision impairment could be aided by a finite element method (FEM) framework that simulates the neuronal response to extracellular electrical stimulation for realistic 3D cell and electrode geometries.
Topics: Retinal Ganglion Cells; Finite Element Analysis; Computer Simulation; Electrodes; Electric Stimulation
PubMed: 38082879
DOI: 10.1109/EMBC40787.2023.10340593 -
Nature Communications Dec 2023The axon initial segment (AIS) is a specialized neuronal compartment required for action potential generation and neuronal polarity. However, understanding the...
The axon initial segment (AIS) is a specialized neuronal compartment required for action potential generation and neuronal polarity. However, understanding the mechanisms regulating AIS structure and function has been hindered by an incomplete knowledge of its molecular composition. Here, using immuno-proximity biotinylation we further define the AIS proteome and its dynamic changes during neuronal maturation. Among the many AIS proteins identified, we show that SCRIB is highly enriched in the AIS both in vitro and in vivo, and exhibits a periodic architecture like the axonal spectrin-based cytoskeleton. We find that ankyrinG interacts with and recruits SCRIB to the AIS. However, loss of SCRIB has no effect on ankyrinG. This powerful and flexible approach further defines the AIS proteome and provides a rich resource to elucidate the mechanisms regulating AIS structure and function.
Topics: Axon Initial Segment; Proteome; Biotinylation; Axons; Neurons
PubMed: 38081810
DOI: 10.1038/s41467-023-44015-2 -
Frontiers in Cellular Neuroscience 2023Action potentials usually travel orthodromically along a neuron's axon, from the axon initial segment (AIS) toward the presynaptic terminals. Under some circumstances...
INTRODUCTION
Action potentials usually travel orthodromically along a neuron's axon, from the axon initial segment (AIS) toward the presynaptic terminals. Under some circumstances action potentials also travel in the opposite direction, antidromically, after being initiated at a distal location. Given their initiation at an atypical site, we refer to these events as "ectopic action potentials." Ectopic action potentials (EAPs) were initially observed in pathological conditions including seizures and nerve injury. Several studies have described regular-spiking (RS) pyramidal neurons firing EAPs in seizure models. Under nonpathological conditions, EAPs were reported in a few populations of neurons, and our group has found that EAPs can be induced in a large proportion of parvalbumin-expressing interneurons in the neocortex. Nevertheless, to our knowledge there have been no prior reports of ectopic firing in the largest population of neurons in the neocortex, pyramidal neurons, under nonpathological conditions.
METHODS
We performed in vitro recordings utilizing the whole-cell patch clamp technique. To elicit EAPs, we triggered orthodromic action potentialswith either long, progressively increasing current steps, or with trains of brief pulses at 30, 60, or 100 Hz delivered in 3 different ways, varying in stimulus and resting period duration.
RESULTS
We found that a large proportion (72.7%) of neocortical RS cells from mice can fire EAPs after a specific stimulus in vitro, and that most RS cells (56.1%) are capable of firing EAPs across a broad range of stimulus conditions. Of the 37 RS neurons in which we were able to elicit EAPs, it took an average of 863.8 orthodromic action potentials delivered over the course of an average of ~81.4 s before the first EAP was seen. We observed that some cells responded to specific stimulus frequencies while less selective, suggesting frequency tuning in a subset of the cells.
DISCUSSION
Our findings suggest that pyramidal cells can integrate information over long time-scales before briefly entering a mode of self-generated firing that originates in distal axons. The surprising ubiquity of EAP generation in RS cells raises interesting questions about the potential roles of ectopic spiking in information processing, cortical oscillations, and seizure susceptibility.
PubMed: 38034593
DOI: 10.3389/fncel.2023.1267687 -
The Journal of Neuroscience : the... Nov 2023
Topics: Axon Initial Segment; Amyloid beta-Protein Precursor; Neurons; Axons
PubMed: 38030402
DOI: 10.1523/JNEUROSCI.0842-23.2023