scholarly journals Analyzing Branch‐specific Dendritic Spikes Using an Ultrafast Laser Scalpel

2020 ◽  
Vol 8 ◽  
Author(s):  
Michael L. Castañares ◽  
Hans-A. Bachor ◽  
Vincent R. Daria
Keyword(s):  
Cortical Neurons ◽  
Pyramidal Neurons ◽  
Dendritic Tree ◽  
Cortical Layer ◽  
Ultrafast Laser ◽  
Laser Scalpel ◽  
Dendritic Spikes ◽  
Dendritic Spike ◽  
Neuronal Computation

Dendritic spikes facilitate neuronal computation and they have been reported to occur in various regions of the dendritic tree of cortical neurons. Spikes that occur only on a select few branches are particularly difficult to analyze especially in complex and intertwined dendritic arborizations where highly localized application of pharmacological blocking agents is not feasible. Here, we present a technique based on highly targeted dendrotomy to tease out and study dendritic spikes that occur in oblique branches of cortical layer five pyramidal neurons. We first analyze the effect of cutting dendrites in silico and then confirmed in vitro using an ultrafast laser scalpel. A dendritic spike evoked in an oblique branch manifests at the soma as an increase in the afterdepolarization (ADP). The spikes are branch-specific since not all but only a few oblique dendrites are observed to evoke spikes. Both our model and experiments show that cutting certain oblique branches, where dendritic spikes are evoked, curtailed the increase in the ADP. On the other hand, cutting neighboring oblique branches that do not evoke spikes maintained the ADP. Our results show that highly targeted dendrotomy can facilitate causal analysis of how branch-specific dendritic spikes influence neuronal output.

scholarly journals Dendritic spikes in apical oblique dendrites of cortical layer 5 pyramidal neurons

2020 ◽  
Author(s):  
Michael Lawrence G. Castañares ◽  
Greg J. Stuart ◽  
Vincent R. Daria
Keyword(s):  
Sensory Processing ◽  
Pyramidal Neurons ◽  
Low Frequency ◽  
Cortical Layer ◽  
Voltage Gated ◽  
Voltage Gated Calcium Channels ◽  
Basal Dendrites ◽  
Dendritic Spikes ◽  
Specific Computation

AbstractDendritic spikes in layer 5 pyramidal neurons (L5PNs) play a major role in cortical computation. While dendritic spikes have been studied extensively in apical and basal dendrites of L5PNs, whether oblique dendrites, which ramify in the input layers of the cortex, also generate dendritic spikes is unknown. Here we report the existence of dendritic spikes in apical oblique dendrites of L5PNs. In silico investigations indicate that oblique branch spikes are triggered by brief, low-frequency action potential (AP) trains (~40 Hz) and are characterized by a fast sodium spike followed by activation of voltage-gated calcium channels. In vitro experiments confirmed the existence of oblique branch spikes in L5PNs during brief AP trains at frequencies of around 60 Hz. Oblique branch spikes offer new insights into branch-specific computation in L5PNs and may be critical for sensory processing in the input layers of the cortex.

scholarly journals Astrocytic modulation of information processing by layer 5 pyramidal neurons of the mouse visual cortex

2020 ◽  
Author(s):  
Dimitri Ryczko ◽  
Maroua Hanini-Daoud ◽  
Steven Condamine ◽  
Benjamin J. B. Bréant ◽  
Maxime Fougère ◽  
...  
Keyword(s):  
Visual Cortex ◽  
Cortical Neurons ◽  
Calcium Binding ◽  
Pyramidal Neurons ◽  
Binding Protein ◽  
Contextual Information ◽  
Dendritic Tree ◽  
Cortical Layer ◽  
List Type ◽  
Ionic Environment

AbstractThe most complex cerebral functions are performed by the cortex which most important output is carried out by its layer 5 pyramidal neurons. Their firing reflects integration of sensory and contextual information that they receive. There is evidence that astrocytes influence cortical neurons firing through the release of gliotransmitters such as ATP, glutamate or GABA. These effects were described at the network and at the synaptic levels, but it is still unclear how astrocytes influence neurons input-output transfer function at the cellular level. Here, we used optogenetic tools coupled with electrophysiological, imaging and anatomical approaches to test whether and how astrocytic activation affected processing and integration of distal inputs to layer 5 pyramidal neurons (L5PN). We show that optogenetic activation of astrocytes near L5PN cell body prolonged firing induced by distal inputs to L5PN and potentiated their ability to trigger spikes. The observed astrocytic effects on L5PN firing involved glutamatergic transmission to some extent but relied on release of S100β, an astrocytic Ca2+-binding protein that decreases extracellular Ca2+ once released. This astrocyte-evoked decrease of extracellular Ca2+ elicited firing mediated by activation of Nav1.6 channels. Our findings suggest that astrocytes contribute to the cortical fundamental computational operations by controlling the extracellular ionic environment.Key Points SummaryIntegration of inputs along the dendritic tree of layer 5 pyramidal neurons is an essential operation as these cells represent the most important output carrier of the cerebral cortex. However, the contribution of astrocytes, a type of glial cell to these operations is poorly documented.Here we found that optogenetic activation of astrocytes in the vicinity of layer 5 in the mouse primary visual cortex induce spiking in local pyramidal neurons through Nav1.6 ion channels and prolongs the responses elicited in these neurons by stimulation of their distal inputs in cortical layer 1.This effect partially involved glutamatergic signalling but relied mostly on the astrocytic calcium-binding protein S100β, which regulates the concentration of calcium in the extracellular space around neurons.These findings show that astrocytes contribute to the fundamental computational operations of the cortex by acting on the ionic environment of neurons.

scholarly journals Transduction of inflammation from peripheral immune cells to the hippocampus induces neuronal hyperexcitability mediated by Caspase-1 activation

2020 ◽  
Author(s):  
Tarek Shaker ◽  
Bidisha Chattopadhyaya ◽  
Bénédicte Amilhon ◽  
Graziella Di Cristo ◽  
Alexander G. Weil
Keyword(s):  
Pyramidal Neurons ◽  
Mononuclear Cells ◽  
Culture Media ◽  
Cortical Layer ◽  
Peripheral Inflammation ◽  
Potential Contribution ◽  
Peripheral Blood Mononuclear ◽  
Caspase 1 ◽  
Therapeutic Benefits

Abstract 1.1. Background Recent studies report infiltration of peripheral blood mononuclear cells (PBMCs) into the central nervous system (CNS) in epileptic disorders, suggestive of a potential contribution of PBMC extravasation to the generation of seizures. Nevertheless, the underlying mechanisms involved in PBMC infiltrates promoting neuronal predisposition to ictogenesis remain unclear. Therefore, we developed an in vitro model mimicking infiltration of activated PBMCs into the brain in order to investigate potential transduction of inflammatory signals from PBMCs to the CNS.1.2. Methods To establish our model, we first extracted PBMCs from rat spleen, then, immunologically primed PBMCs with lipopolysaccharide (LPS), followed by further activation with nigericin. Thereafter, we co-cultured these activated PBMCs with organotypic cortico-hippocampal brain slice cultures (OCHSCs) derived from the same rat, and compared PBMC-OCHSC co-cultures to OCHSCs exposed to PBMCs in the culture media. We further targeted a potential molecular pathway underlying transduction of peripheral inflammation to OCHSCs by incubating OCHSCs with the Caspase-1 inhibitor VX-765 prior to co-culturing PBMCs with OCHSCs. After 24 hours, we analyzed inflammation markers in the cortex and the hippocampus using semiquantitative immunofluorescence. In addition, we analyzed neuronal activity by whole-cell patch-clamp recordings in cortical layer II/III and hippocampal CA1 pyramidal neurons.1.3. Results In the cortex, co-culturing immunoreactive PBMCs treated with LPS + nigericin on top of OCHSCs upregulated inflammatory markers and enhanced neuronal excitation. In contrast, no excitability changes were detected after adding primed PBMCs (i.e. treated with LPS only), to OCHSCs. Strikingly, in the hippocampus, both immunoreactive and primed PBMCs elicited similar pro-inflammatory and pro-excitatory effects. However, when immunoreactive and primed PBMCs were cultured in the media separately from OCHSCs, only immunoreactive PBMCs gave rise to neuroinflammation and hyperexcitability in the hippocampus, whereas primed PBMCs failed to produce any significant changes. Finally, VX-765 application to OCHSCs, co-cultured with either immunoreactive or primed PBMCs, protected them from neuroinflammation and hippocampal hyperexcitability.1.4. Conclusions Our study shows a higher susceptibility of the hippocampus to peripheral inflammation as compared to the cortex, mediated via Caspase-1-dependent signaling pathways. Thus, our findings suggest that Caspase-1 inhibition may potentially provide therapeutic benefits during hippocampal neuroinflammation and hyperexcitability secondary to peripheral innate immunity.

scholarly journals Active dendrites enable strong but sparse inputs to determine orientation selectivity

2021 ◽  
Vol 118 (30) ◽  
pp. e2017339118
Author(s):  
Lea Goetz ◽  
Arnd Roth ◽  
Michael Häusser
Keyword(s):  
Action Potential ◽  
Pyramidal Neurons ◽  
Potential Output ◽  
Synaptic Inputs ◽  
Active Dendrites ◽  
Strongly Connected ◽  
Dendritic Spikes ◽  
Sensory Responses

The dendrites of neocortical pyramidal neurons are excitable. However, it is unknown how synaptic inputs engage nonlinear dendritic mechanisms during sensory processing in vivo, and how they in turn influence action potential output. Here, we provide a quantitative account of the relationship between synaptic inputs, nonlinear dendritic events, and action potential output. We developed a detailed pyramidal neuron model constrained by in vivo dendritic recordings. We drive this model with realistic input patterns constrained by sensory responses measured in vivo and connectivity measured in vitro. We show mechanistically that under realistic conditions, dendritic Na+ and NMDA spikes are the major determinants of neuronal output in vivo. We demonstrate that these dendritic spikes can be triggered by a surprisingly small number of strong synaptic inputs, in some cases even by single synapses. We predict that dendritic excitability allows the 1% strongest synaptic inputs of a neuron to control the tuning of its output. Active dendrites therefore allow smaller subcircuits consisting of only a few strongly connected neurons to achieve selectivity for specific sensory features.

scholarly journals Unique membrane properties and enhanced signal processing in human neocortical neurons

eLife ◽  
2016 ◽  
Vol 5 ◽  
Author(s):  
Guy Eyal ◽  
Matthijs B Verhoog ◽  
Guilherme Testa-Silva ◽  
Yair Deitcher ◽  
Johannes C Lodder ◽  
...  
Keyword(s):  
Signal Processing ◽  
Cortical Neurons ◽  
Pyramidal Neurons ◽  
Temporal Cortex ◽  
Building Blocks ◽  
Membrane Properties ◽  
Human Neocortex ◽  
Neocortical Neurons ◽  
Fitting In

The advanced cognitive capabilities of the human brain are often attributed to our recently evolved neocortex. However, it is not known whether the basic building blocks of the human neocortex, the pyramidal neurons, possess unique biophysical properties that might impact on cortical computations. Here we show that layer 2/3 pyramidal neurons from human temporal cortex (HL2/3 PCs) have a specific membrane capacitance (Cm) of ~0.5 µF/cm2, half of the commonly accepted 'universal' value (~1 µF/cm2) for biological membranes. This finding was predicted by fitting in vitro voltage transients to theoretical transients then validated by direct measurement of Cm in nucleated patch experiments. Models of 3D reconstructed HL2/3 PCs demonstrated that such low Cm value significantly enhances both synaptic charge-transfer from dendrites to soma and spike propagation along the axon. This is the first demonstration that human cortical neurons have distinctive membrane properties, suggesting important implications for signal processing in human neocortex.

scholarly journals Studying Synaptically Evoked Cortical Responses ex vivo With Combination of a Single Neuron Recording (Whole-Cell) and Population Voltage Imaging (Genetically Encoded Voltage Indicator)

2021 ◽  
Vol 15 ◽  
Author(s):  
Jinyoung Jang ◽  
Mei Hong Zhu ◽  
Aditi H. Jogdand ◽  
Srdjan D. Antic
Keyword(s):  
Pyramidal Neurons ◽  
Ex Vivo ◽  
Brain Slices ◽  
Dendritic Tree ◽  
Response Speed ◽  
Optical Signal ◽  
Cortical Layer ◽  
Cortical Layers ◽  
Whole Cell ◽  
Voltage Imaging

In a typical electrophysiology experiment, synaptic stimulus is delivered in a cortical layer (1–6) and neuronal responses are recorded intracellularly in individual neurons. We recreated this standard electrophysiological paradigm in brain slices of mice expressing genetically encoded voltage indicators (GEVIs). This allowed us to monitor membrane voltages in the target pyramidal neurons (whole-cell), and population voltages in the surrounding neuropil (optical imaging), simultaneously. Pyramidal neurons have complex dendritic trees that span multiple cortical layers. GEVI imaging revealed areas of the brain slice that experienced the strongest depolarization on a specific synaptic stimulus (location and intensity), thus identifying cortical layers that contribute the most afferent activity to the recorded somatic voltage waveform. By combining whole-cell with GEVI imaging, we obtained a crude distribution of activated synaptic afferents in respect to the dendritic tree of a pyramidal cell. Synaptically evoked voltage waves propagating through the cortical neuropil (dendrites and axons) were not static but rather they changed on a millisecond scale. Voltage imaging can identify areas of brain slices in which the neuropil was in a sustained depolarization (plateau), long after the stimulus onset. Upon a barrage of synaptic inputs, a cortical pyramidal neuron experiences: (a) weak temporal summation of evoked voltage transients (EPSPs); and (b) afterhyperpolarization (intracellular recording), which are not represented in the GEVI population imaging signal (optical signal). To explain these findings [(a) and (b)], we used four voltage indicators (ArcLightD, chi-VSFP, Archon1, and di-4-ANEPPS) with different optical sensitivity, optical response speed, labeling strategy, and a target neuron type. All four imaging methods were used in an identical experimental paradigm: layer 1 (L1) synaptic stimulation, to allow direct comparisons. The population voltage signal showed paired-pulse facilitation, caused in part by additional recruitment of new neurons and dendrites. “Synaptic stimulation” delivered in L1 depolarizes almost an entire cortical column to some degree.

scholarly journals Optimizing computer models of corticospinal neurons to replicate in vitro dynamics

2017 ◽  
Vol 117 (1) ◽  
pp. 148-162 ◽  
Author(s):  
Samuel A. Neymotin ◽  
Benjamin A. Suter ◽  
Salvador Dura-Bernal ◽  
Gordon M. G. Shepherd ◽  
Michele Migliore ◽  
...  
Keyword(s):  
Motor Cortex ◽  
Pyramidal Neurons ◽  
Computer Models ◽  
Cortical Layer ◽  
Cortical Layers ◽  
Electrophysiological Properties ◽  
Full Reconstruction ◽  
Resonance Properties ◽  
Oscillation Frequencies

Corticospinal neurons (SPI), thick-tufted pyramidal neurons in motor cortex layer 5B that project caudally via the medullary pyramids, display distinct class-specific electrophysiological properties in vitro: strong sag with hyperpolarization, lack of adaptation, and a nearly linear frequency-current ( F– I) relationship. We used our electrophysiological data to produce a pair of large archives of SPI neuron computer models in two model classes: 1) detailed models with full reconstruction; and 2) simplified models with six compartments. We used a PRAXIS and an evolutionary multiobjective optimization (EMO) in sequence to determine ion channel conductances. EMO selected good models from each of the two model classes to form the two model archives. Archived models showed tradeoffs across fitness functions. For example, parameters that produced excellent F– I fit produced a less-optimal fit for interspike voltage trajectory. Because of these tradeoffs, there was no single best model but rather models that would be best for particular usages for either single neuron or network explorations. Further exploration of exemplar models with strong F– I fit demonstrated that both the detailed and simple models produced excellent matches to the experimental data. Although dendritic ion identities and densities cannot yet be fully determined experimentally, we explored the consequences of a demonstrated proximal to distal density gradient of Ih, demonstrating that this would lead to a gradient of resonance properties with increased resonant frequencies more distally. We suggest that this dynamical feature could serve to make the cell particularly responsive to major frequency bands that differ by cortical layer. NEW & NOTEWORTHY We developed models of motor cortex corticospinal neurons that replicate in vitro dynamics, including hyperpolarization-induced sag and realistic firing patterns. Models demonstrated resonance in response to synaptic stimulation, with resonance frequency increasing in apical dendrites with increasing distance from soma, matching the increasing oscillation frequencies spanning deep to superficial cortical layers. This gradient may enable specific corticospinal neuron dendrites to entrain to relevant oscillations in different cortical layers, contributing to appropriate motor output commands.

scholarly journals Excitatory GABA in Rodent Developing Neocortex In Vitro

2008 ◽  
Vol 100 (2) ◽  
pp. 609-619 ◽  
Author(s):  
Sylvain Rheims ◽  
Marat Minlebaev ◽  
Anton Ivanov ◽  
Alfonso Represa ◽  
Rustem Khazipov ◽  
...  
Keyword(s):  
Cortical Neurons ◽  
Pyramidal Neurons ◽  
Brain Slices ◽  
Reversal Potential ◽  
Pyramidal Cells ◽  
Oscillatory Activity ◽  
Resting Membrane Potential ◽  
Network Oscillations ◽  
Excitatory Gaba

GABA depolarizes immature cortical neurons. However, whether GABA excites immature neocortical neurons and drives network oscillations as in other brain structures remains controversial. Excitatory actions of GABA depend on three fundamental parameters: the resting membrane potential ( Em), reversal potential of GABA ( EGABA), and threshold of action potential generation ( Vthr). We have shown recently that conventional invasive recording techniques provide an erroneous estimation of these parameters in immature neurons. In this study, we used noninvasive single N-methyl-d-aspartate and GABA channel recordings in rodent brain slices to measure both Em and EGABA in the same neuron. We show that GABA strongly depolarizes pyramidal neurons and interneurons in both deep and superficial layers of the immature neocortex (P2–P10). However, GABA generates action potentials in layer 5/6 (L5/6) but not L2/3 pyramidal cells, since L5/6 pyramidal cells have more depolarized resting potentials and more hyperpolarized Vthr. The excitatory GABA transiently drives oscillations generated by L5/6 pyramidal cells and interneurons during development (P5–P12). The NKCC1 co-transporter antagonist bumetanide strongly reduces [Cl−]i, GABA-induced depolarization, and network oscillations, confirming the importance of GABA signaling. Thus a strong GABA excitatory drive coupled with high intrinsic excitability of L5/6 pyramidal neurons and interneurons provide a powerful mechanism of synapse-driven oscillatory activity in the rodent neocortex in vitro. In the companion paper, we show that the excitatory GABA drives layer-specific seizures in the immature neocortex.

Linear to Supralinear Summation of AMPA-Mediated EPSPs in Neocortical Pyramidal Neurons

2000 ◽  
Vol 83 (6) ◽  
pp. 3310-3322 ◽  
Author(s):  
Jilda S. Nettleton ◽  
William J. Spain
Keyword(s):  
Cortical Neurons ◽  
Pyramidal Neurons ◽  
Coincidence Detection ◽  
Layer V ◽  
Layer I ◽  
The Individual ◽  
Dc Current ◽  
Neocortical Pyramidal Neurons

It has been hypothesized that voltage-sensitive conductances present on the dendrites of neurons can influence summation of excitatory postsynaptic potentials (EPSPs) and hence affect how neurons compile information. Greater than linear summation of EPSPs has been postulated to facilitate coincidence detection by cortical neurons. This study examined whether the summation of subthreshold AMPA-mediated EPSPs generated on layer V neocortical pyramidal neurons in vitro was linear and if any nonlinearities could be attributed to dendritic conductances. Evoked EPSPs (1–12 mV) were recorded somatically by means of intracellular sharp electrodes in the presence of 100 μM amino-5-phosphonopentanoic acid (AP-5) and 3 μM bicuculline. Two independent EPSPs were evoked by a stimulating electrode in layer I and another in layers III–V. The areas of stimulation were isolated from each other by a horizontal cut below layer I. By subtracting the algebraic sum of the individual EPSPs from the evoked response when both EPSPs were evoked simultaneously, we determined that they summed linearly to supralinearly. Supralinear summation was more likely when the soma was hyperpolarized by DC current injection. Summation was predominantly linear when postsynaptic conductances (i.e., Na+ and Ca2+) were blocked with intracellular QX-314. The supralinear summation of EPSPs (without QX-314) decreased as the time between inputs was increased from 0 to 30 ms. To determine the role of dendrites in nonlinear summation, we substituted a current pulse (simulated EPSP) delivered at the soma for either or both of the evoked EPSPs. Simulated EPSPs combined with either an evoked EPSP or another simulated EPSP showed significantly less supralinear summation than two evoked EPSPs, indicating that the dendritic conductances were largely responsible for the observed supralinear summation.

scholarly journals α2-Adrenergic Receptors Modify Dendritic Spike Generation Via HCN Channels in the Prefrontal Cortex

2008 ◽  
Vol 99 (1) ◽  
pp. 394-401 ◽  
Author(s):  
Albert M. I. Barth ◽  
E. Sylvester Vizi ◽  
Tibor Zelles ◽  
Balazs Lendvai
Keyword(s):  
Prefrontal Cortex ◽  
Adrenergic Receptors ◽  
Action Potentials ◽  
Pyramidal Neurons ◽  
Apical Dendrite ◽  
Hcn Channels ◽  
Transient Activation ◽  
Dendritic Spikes ◽  
Dendritic Spike ◽  
Frequency Threshold

Although dendritic spikes are generally thought to be restricted to the distal apical dendrite, we know very little about the possible modulatory mechanisms that set the spatial limits of dendritic spikes. Our experiments demonstrated that high-frequency trains of backpropagating action potentials avoided filtering in the apical dendrite and initiated all-or-none dendritic Ca2+ transients associated with dendritic spikes in layer 5 pyramidal neurons of the prefrontal cortex. The block of hyperpolarization-activated currents ( Ih) by ZD7288 could shift the frequency threshold and decreased the number of action potentials required to produce the all-or-none Ca2+ transient. Activation of α2-adrenergic receptors could also shift the frequency domain of spike induction to lower frequencies. Our data suggest that noradrenergic activity in the prefrontal cortex influences dendritic Ih and extends the zone of dendritic spikes in the apical dendrite via α2-adrenergic receptors. This mechanism might be one cellular correlate of the α2-receptor–mediated actions on working memory.

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