-
BioRxiv : the Preprint Server For... Mar 2024Axo-axonic cells (AACs), also called chandelier cells (ChCs) in the cerebral cortex, are the most distinctive type of GABAergic interneurons described in the neocortex,...
Axo-axonic cells (AACs), also called chandelier cells (ChCs) in the cerebral cortex, are the most distinctive type of GABAergic interneurons described in the neocortex, hippocampus, and basolateral amygdala (BLA). AACs selectively innervate glutamatergic projection neurons (PNs) at their axon initial segment (AIS), thus may exert decisive control over PN spiking and regulate PN functional ensembles. However, the brain-wide distribution, synaptic connectivity, and circuit function of AACs remains poorly understood, largely due to the lack of specific and reliable experimental tools. Here, we have established an intersectional genetic strategy that achieves specific and comprehensive targeting of AACs throughout the mouse brain based on their lineage () and molecular () markers. We discovered that AACs are deployed across essentially all the pallium-derived brain structures, including not only the dorsal pallium-derived neocortex and medial pallium-derived hippocampal formation, but also the lateral pallium-derived claustrum-insular complex, and the ventral pallium-derived extended amygdaloid complex and olfactory centers. AACs are also abundant in anterior olfactory nucleus, taenia tecta and lateral septum. AACs show characteristic variations in density across neocortical areas and layers and across subregions of the hippocampal formation. Neocortical AACs comprise multiple laminar subtypes with distinct dendritic and axonal arborization patterns. Retrograde monosynaptic tracing from AACs across neocortical, hippocampal and BLA regions reveal shared as well as distinct patterns of synaptic input. Specific and comprehensive targeting of AACs facilitates the study of their developmental genetic program and circuit function across brain structures, providing a ground truth platform for understanding the conservation and variation of a bona fide cell type across brain regions and species.
PubMed: 37986757
DOI: 10.1101/2023.11.07.566059 -
The Journal of Neuroscience : the... Apr 2024Dravet syndrome (DS) is a neurodevelopmental disorder characterized by epilepsy, developmental delay/intellectual disability, and features of autism spectrum disorder,...
Dravet syndrome (DS) is a neurodevelopmental disorder characterized by epilepsy, developmental delay/intellectual disability, and features of autism spectrum disorder, caused by heterozygous loss-of-function variants in encoding the voltage-gated sodium channel α subunit Nav1.1. The dominant model of DS pathogenesis is the "interneuron hypothesis," whereby GABAergic interneurons (INs) express and preferentially rely on Nav1.1-containing sodium channels for action potential (AP) generation. This has been shown for three of the major subclasses of cerebral cortex GABAergic INs: those expressing parvalbumin (PV), somatostatin, and vasoactive intestinal peptide. Here, we define the function of a fourth major subclass of INs expressing neuron-derived neurotrophic factor (Ndnf) in male and female DS (+/-) mice. Patch-clamp electrophysiological recordings of Ndnf-INs in brain slices from +/â mice and WT controls reveal normal intrinsic membrane properties, properties of AP generation and repetitive firing, and synaptic transmission across development. Immunohistochemistry shows that Nav1.1 is strongly expressed at the axon initial segment (AIS) of PV-expressing INs but is absent at the Ndnf-IN AIS. In vivo two-photon calcium imaging demonstrates that Ndnf-INs in +/â mice are recruited similarly to WT controls during arousal. These results suggest that Ndnf-INs are the only major IN subclass that does not prominently rely on Nav1.1 for AP generation and thus retain their excitability in DS. The discovery of a major IN subclass with preserved function in the +/â mouse model adds further complexity to the "interneuron hypothesis" and highlights the importance of considering cell-type heterogeneity when investigating mechanisms underlying neurodevelopmental disorders.
Topics: Animals; Interneurons; Epilepsies, Myoclonic; Mice; NAV1.1 Voltage-Gated Sodium Channel; Female; Male; Disease Models, Animal; Action Potentials; Mice, Inbred C57BL; Mice, Transgenic
PubMed: 38443186
DOI: 10.1523/JNEUROSCI.1977-23.2024 -
Current Research in Neurobiology 2024Parvalbumin-expressing (PV+) inhibitory interneurons drive gamma oscillations (30-80 Hz), which underlie higher cognitive functions. In this review, we discuss two... (Review)
Review
Parvalbumin-expressing (PV+) inhibitory interneurons drive gamma oscillations (30-80 Hz), which underlie higher cognitive functions. In this review, we discuss two groups/aspects of fundamental properties of PV+ interneurons. In the first group (dubbed ), we list properties representing optimal synaptic integration in PV+ interneurons designed to support fast oscillations. For example: [i] Information can neither enter nor leave the neocortex without the engagement of fast PV+ -mediated inhibition; [ii] Voltage responses in PV+ interneuron dendrites integrate linearly to reduce impact of the fluctuations in the afferent drive; and [iii] Reversed somatodendritic Rm gradient accelerates the time courses of synaptic potentials arriving at the soma. In the second group (dubbed ), we list morphological and biophysical properties responsible for (a) short synaptic delays, and (b) efficient postsynaptic outcomes. For example: [i] Fast-spiking ability that allows PV+ interneurons to outpace other cortical neurons (pyramidal neurons). [ii] Myelinated axon (which is only found in the PV+ subclass of interneurons) to secure fast-spiking at the initial axon segment; and [iii] Inhibitory autapses - autoinhibition, which assures brief biphasic voltage transients and supports postinhibitory rebounds. Recent advent of scientific tools, such as viral strategies to target PV cells and the ability to monitor PV cells via in vivo imaging during behavior, will aid in defining the role of PV cells in the CNS. Given the link between PV+ interneurons and cognition, in the future, it would be useful to carry out physiological recordings in the PV+ cell type selectively and characterize if and how psychiatric and neurological diseases affect initiation and propagation of electrical signals in this cortical sub-circuit. Voltage imaging may allow fast recordings of electrical signals from many PV+ interneurons simultaneously.
PubMed: 38616956
DOI: 10.1016/j.crneur.2023.100121 -
Advances in Physiology Education Sep 2023Active learning and practices are strongly encouraged or made mandatory by local, national, and European organizations. Therefore, we set up an interactive practical...
Active learning and practices are strongly encouraged or made mandatory by local, national, and European organizations. Therefore, we set up an interactive practical classroom, engaging all of the attending students of the year ( = 47). Each student was assigned a physiological role (marked on a cardboard sign) in the following events: stimulation on motoneuron dendrites, sodium ions (Na) influx and potassium ions (K) efflux, action potentials onset and saltatory conduction along the axon, acetylcholine (ACh) neurotransmitter exocytosis following Ca influx, ACh binding to postsynaptic membrane receptors, ACh-esterase action, excitatory postsynaptic potential, release of Ca from the sarcoplasmic reticulum, mechanism of muscular contraction and relaxation, and rigor mortis. A sketch was drawn with colored chalks on the ground outside the room: the motoneuron with its dendrites, cell body, initial segment, myelinated axon, and synaptic bouton; the postsynaptic plasma membrane of the muscle fiber; and the sarcoplasmic reticulum. Students each had their own role and were asked to position themselves and move, accordingly. This resulted in a complete, dynamic, and fluid representation being performed. The evaluation of the effectiveness of the students' learning was limited at this pilot stage. However, positive feedback was received in the self-evaluation reports that were written by students on the physiological meaning of their own role, as well as in the satisfaction questionnaires requested by the University. The rate of students who successfully passed the written exam and the rate of correct answers that included the specific topics addressed in this practice were reported. We set up an interactive practical classroom, engaging all the attending students of the year ( = 47). Each student was assigned a physiological role marked on a cardboard sign, starting from motoneuron stimulation up to skeletal muscle contraction and relaxation. Students were asked to actively reproduce physiological events, positioning themselves and moving around and onto drawings on the ground (motoneuron, synapsis, sarcoplasmic reticulum, etc.). Finally, a complete, dynamic, and fluid representation was performed.
Topics: Humans; Motor Neurons; Muscle Contraction; Action Potentials; Synapses; Axons; Muscle, Skeletal
PubMed: 37411014
DOI: 10.1152/advan.00047.2023 -
BioRxiv : the Preprint Server For... Nov 2023Connectomics is a nascent neuroscience field to map and analyze neuronal networks. It provides a new way to investigate abnormalities in brain tissue, including in...
Connectomics is a nascent neuroscience field to map and analyze neuronal networks. It provides a new way to investigate abnormalities in brain tissue, including in models of Alzheimer's disease (AD). This age-related disease is associated with alterations in amyloid-β (Aβ) and phosphorylated tau (pTau). These alterations correlate with AD's clinical manifestations, but causal links remain unclear. Therefore, studying these molecular alterations within the context of the local neuronal and glial milieu may provide insight into disease mechanisms. Volume electron microscopy (vEM) is an ideal tool for performing connectomics studies at the ultrastructural level, but localizing specific biomolecules within large-volume vEM data has been challenging. Here we report a volumetric correlated light and electron microscopy (vCLEM) approach using fluorescent nanobodies as immuno-probes to localize Alzheimer's disease-related molecules in a large vEM volume. Three molecules (pTau, Aβ, and a marker for activated microglia (CD11b)) were labeled without the need for detergents by three nanobody probes in a sample of the hippocampus of the 3xTg Alzheimer's disease model mouse. Confocal microscopy followed by vEM imaging of the same sample allowed for registration of the location of the molecules within the volume. This dataset revealed several ultrastructural abnormalities regarding the localizations of Aβ and pTau in novel locations. For example, two pTau-positive post-synaptic spine-like protrusions innervated by axon terminals were found projecting from the axon initial segment of a pyramidal cell. Three pyramidal neurons with intracellular Aβ or pTau were 3D reconstructed. Automatic synapse detection, which is necessary for connectomics analysis, revealed the changes in density and volume of synapses at different distances from an Aβ plaque. This vCLEM approach is useful to uncover molecular alterations within large-scale volume electron microscopy data, opening a new connectomics pathway to study Alzheimer's disease and other types of dementia.
PubMed: 37961104
DOI: 10.1101/2023.10.24.563674 -
Neuron Apr 2024Dysfunction in sodium channels and their ankyrin scaffolding partners have both been implicated in neurodevelopmental disorders, including autism spectrum disorder...
Dysfunction in sodium channels and their ankyrin scaffolding partners have both been implicated in neurodevelopmental disorders, including autism spectrum disorder (ASD). In particular, the genes SCN2A, which encodes the sodium channel Na1.2, and ANK2, which encodes ankyrin-B, have strong ASD association. Recent studies indicate that ASD-associated haploinsufficiency in Scn2a impairs dendritic excitability and synaptic function in neocortical pyramidal cells, but how Na1.2 is anchored within dendritic regions is unknown. Here, we show that ankyrin-B is essential for scaffolding Na1.2 to the dendritic membrane of mouse neocortical neurons and that haploinsufficiency of Ank2 phenocopies intrinsic dendritic excitability and synaptic deficits observed in Scn2a conditions. These results establish a direct, convergent link between two major ASD risk genes and reinforce an emerging framework suggesting that neocortical pyramidal cell dendritic dysfunction can contribute to neurodevelopmental disorder pathophysiology.
Topics: Animals; Mice; Ankyrins; Autism Spectrum Disorder; Autistic Disorder; Dendrites; NAV1.2 Voltage-Gated Sodium Channel; Neocortex; Pyramidal Cells
PubMed: 38290518
DOI: 10.1016/j.neuron.2024.01.003 -
BioRxiv : the Preprint Server For... May 2024Vertebrate nervous systems use the axon initial segment (AIS) to initiate action potentials and maintain neuronal polarity. The microtubule-associated protein tripartite...
UNLABELLED
Vertebrate nervous systems use the axon initial segment (AIS) to initiate action potentials and maintain neuronal polarity. The microtubule-associated protein tripartite motif containing 46 (TRIM46) was reported to regulate axon specification, AIS assembly, and neuronal polarity through the bundling of microtubules in the proximal axon. However, these claims are based on TRIM46 knockdown in cultured neurons. To investigate TRIM46 function , we examined TRIM46 knockout mice. Contrary to previous reports, we find that TRIM46 is dispensable for AIS formation and maintenance, and axon specification. TRIM46 knockout mice are viable, have normal behavior, and have normal brain structure. Thus, TRIM46 is not required for AIS formation, axon specification, or nervous system function. We also show TRIM46 enrichment in the first ∼100 μm of axon occurs independently of ankyrinG (AnkG), although AnkG is required to restrict TRIM46 only to the AIS. Our results suggest an unidentified protein may compensate for loss of TRIM46 and highlight the need for further investigation of the mechanisms by which the AIS and microtubules interact to shape neuronal structure and function.
SIGNIFICANCE STATEMENT
A healthy nervous system requires the polarization of neurons into structurally and functionally distinct compartments, which depends on both the axon initial segment (AIS) and the microtubule cytoskeleton. In contrast to previous reports, we show that the microtubule-associated protein TRIM46 is not required for axon specification or AIS formation in mice. Our results emphasize the need for further investigation of the mechanisms by which the AIS and microtubules interact to shape neuronal structure and function.
PubMed: 38826451
DOI: 10.1101/2024.05.23.595556 -
The Journal of Physical Chemistry... Jun 2024An artificial tactile receptor is crucial for e-skin in next-generation robots, mimicking the mechanical sensing, signal encoding, and preprocessing functionalities of...
An artificial tactile receptor is crucial for e-skin in next-generation robots, mimicking the mechanical sensing, signal encoding, and preprocessing functionalities of human skin. In the neural network, pressure signals are encoded in spike patterns and efficiently transmitted, exhibiting low power consumption and robust tolerance for bit error rates. Here, we introduce a highly sensitive artificial tactile receptor system integrating a pressure sensor, axon-hillock circuit, and neurotransmitter release device to achieve pressure signal coding with patterned spikes and controlled neurotransmitter release. Owing to the heightened sensitivity of the axon-hillock circuit to pressure-mediated current signals, the artificial tactile receptor achieves a detection limit of 10 Pa that surpasses the human tactile receptors, with a wide response range from 10 to 5 × 10 Pa. Benefiting from the appreciable pressure-responsive performance, the potential application of an artificial tactile receptor in robotic tactile perception has been demonstrated, encompassing tasks such as finger touch and human pulse detection.
Topics: Humans; Pressure; Touch; Robotics; Receptors, Artificial; Neurotransmitter Agents
PubMed: 38804506
DOI: 10.1021/acs.jpclett.4c00869 -
Frontiers in Immunology 2024Subgroups of autoantibodies directed against voltage-gated potassium channel (K) complex components have been associated with immunotherapy-responsive clinical...
INTRODUCTION
Subgroups of autoantibodies directed against voltage-gated potassium channel (K) complex components have been associated with immunotherapy-responsive clinical syndromes. The high prevalence and the role of autoantibodies directly binding K remain, however, controversial. Our objective was to determine K autoantibody binding requirements and to clarify their contribution to the observed immune response.
METHODS
Binding epitopes were studied in sera (n = 36) and cerebrospinal fluid (CSF) (n = 12) from a patient cohort positive for K1.2 but negative for 32 common neurological autoantigens and controls (sera n = 18 and CSF n = 5) by phospho and deep mutational scans. Autoantibody specificity and contribution to the observed immune response were resolved on recombinant cells, cerebellum slices, and nerve fibers.
RESULTS
83% of the patients (30/36) within the studied cohort shared one out of the two major binding epitopes with K1.2-3 reactivity. Eleven percent (4/36) of the serum samples showed no binding. Fingerprinting resolved close to identical sequence requirements for both shared epitopes. K autoantibody response is directed against juxtaparanodal regions in peripheral nerves and the axon initial segment in central nervous system neurons and exclusively mediated by the shared epitopes.
DISCUSSION
Systematic mapping revealed two shared autoimmune responses, with one dominant K1.2-3 autoantibody epitope being unexpectedly prevalent. The conservation of the molecular binding requirements among these patients indicates a uniform autoantibody repertoire with monospecific reactivity. The enhanced sensitivity of the epitope-based (10/12) compared with that of the cell-based detection (7/12) highlights its use for detection. The determined immunodominant epitope is also the primary immune response visible in tissue, suggesting a diagnostic significance and a specific value for routine screening.
Topics: Humans; Autoantibodies; Kv1.2 Potassium Channel; Immunodominant Epitopes; Autoimmunity; Female; Male; Middle Aged; Adult; Autoantigens; Epitope Mapping; Animals
PubMed: 38665908
DOI: 10.3389/fimmu.2024.1329013 -
BioRxiv : the Preprint Server For... Oct 2023Axo-axonic cells (AACs) provide specialized inhibition to the axon initial segment (AIS) of excitatory neurons and can regulate network output and synchrony. Although...
Axo-axonic cells (AACs) provide specialized inhibition to the axon initial segment (AIS) of excitatory neurons and can regulate network output and synchrony. Although hippocampal dentate AACs are structurally altered in epilepsy, physiological analyses of dentate AACs are lacking. We demonstrate that parvalbumin neurons in the dentate molecular layer express PTHLH, an AAC marker, and exhibit morphology characteristic of AACs. Dentate AACs show high-frequency, non-adapting firing but lack persistent firing in the absence of input and have higher rheobase than basket cells suggesting that AACs can respond reliably to network activity. Early after pilocarpine-induced status epilepticus (SE), dentate AACs receive fewer spontaneous excitatory and inhibitory synaptic inputs and have significantly lower maximum firing frequency. Paired recordings and spatially localized optogenetic stimulation revealed that SE reduced the amplitude of unitary synaptic inputs from AACs to granule cells without altering reliability, short-term plasticity, or AIS GABA reversal potential. These changes compromised AAC-dependent shunting of granule cell firing in a multicompartmental model. These early post-SE changes in AAC physiology would limit their ability to receive and respond to input, undermining a critical brake on the dentate throughput during epileptogenesis.
PubMed: 37873292
DOI: 10.1101/2023.10.01.560378