Axons emanating from dendrites: phylogenetic repercussions with Cajalian hues

Triarhou, Lazaros C.

doi:10.3389/fnana.2014.00133

Cited by 18 publications

(25 citation statements)

References 27 publications

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“…[23,24] As an “axon hillock” is not obvious for such cells, we define the “neck” as the distance from the proximal end of the AIS to the soma. The neck length was 31 ± 24 μm (mean ± s.d., N = 26) for AISs of dendritic origin and 7 ± 7 μm ( N = 23) for AISs of somatic origin.…”

Section: Resultsmentioning

confidence: 99%

The Axon Initial Segment is the Dominant Contributor to the Neuron's Extracellular Electrical Potential Landscape

et al. 2018

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Extracellular voltage fields, produced by a neuron’s action potentials, provide a widely used means for studying neuronal and neuronal-network function. The neuron’s soma and dendrites are thought to drive the extracellular action potential (EAP) landscape, while the axon’s contribution is usually considered less important. However, by recording voltages of single neurons in dissociated rat cortical cultures and Purkinje cells in acute mouse cerebellar slices through hundreds of densely packed electrodes, it is found, instead, that the axon initial segment dominates the measured EAP landscape, and, surprisingly, the soma only contributes to a minor extent. As expected, the recorded dominant signal has negative polarity (charge entering the cell) and initiates at the distal end. Interestingly, signals with positive polarity (charge exiting the cell) occur near some but not all dendritic branches and occur after a delay. Such basic knowledge about which neuronal compartments contribute to the extracellular voltage landscape is important for interpreting results from all electrical readout schemes. Finally, initiation of the electrical activity at the distal end of the axon initial segment (AIS) and subsequent spreading into the axon proper and backward through the proximal AIS toward the soma are confirmed. The corresponding extracellular waveforms across different neuronal compartments could be tracked.

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Section: Resultsmentioning

confidence: 99%

The Axon Initial Segment is the Dominant Contributor to the Neuron's Extracellular Electrical Potential Landscape

et al. 2018

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“…The SCNs in the TeO of the avian midbrain were already identified more than a century ago by Ramón y Cajal (). The characteristic morphology led him to assume that the soma was not involved in the propagation of dendritic input to the axon, which points to an alternative signal flow of nerve impulses (Triarhou, ). Knowing the input and output regions and the unique morphology of SCNs, we were interested in a more detailed view of the morphology, in particular of the soma and the action potential generation site to better understand the integration of dendritic input in SCNs.…”

Section: Discussionmentioning

confidence: 99%

“…Regarding the morphology and the location of the AIS in SCNs, incoming visual information could directly jump onto the axon without passing the soma as proposed in the concept of axopetal information flow by Ramón y Cajal (; see also: Häusser et al, ; Thome et al, ; Triarhou, ). This may lead to a faster processing of the visual information receiving from the retinorecipient layers.…”

Section: Discussionmentioning

confidence: 99%

Expression patterns of ion channels and structural proteins in a multimodal cell type of the avian optic tectum

Lischka

Ladel

Luksch

et al. 2017

J of Comparative Neurology

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The midbrain is an important subcortical area involved in distinct functions such as multimodal integration, movement initiation, bottom-up, and top-down attention. Our group is particularly interested in cellular computation of multisensory integration. We focus on the visual part of the avian midbrain, the optic tectum (TeO, counterpart to mammalian superior colliculus). This area has a layered structure with the great advantage of distinct input and output regions. In chicken, the TeO is organized in 15 layers where visual input targets the superficial layers while auditory input terminates in deeper layers. One specific cell type, the Shepherd's crook neuron (SCN), extends dendrites in both input regions. The characteristic feature of these neurons is the axon origin at the apical dendrite. The molecular identity of this characteristic region and thus, the site of action potential generation are of particular importance to understand signal flow and cellular computation in this neuron. We present immunohistochemical data of structural proteins (NF200, Ankyrin G, and Myelin) and ion channels (Pan-Na , Na 1.6, and K 3.1b). NF200 is strongly expressed in the axon. Ankyrin G is mainly expressed at the axon initial segment (AIS). Myelination starts after the AIS as well as the distribution of Na channels on the axon. The subtype Na 1.6 has a high density in this region. K 3.1b is restricted to the soma, the primary neurite and the axon branch. The distribution of functional molecules in SCNs provides insight into the information flow and the integration of sensory modalities in the TeO of the avian midbrain.

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“…An AIS was considered to have a dendritic origin if it began at a neurite branch point, whose other branch expresses microtubule-associated protein 2 (MAP2; a molecular marker of somatodendritic regions) and not AnkG. Out of the 49 neurons from 12 cultures (neurons that may have had overlapping voltage signals were excluded), 26 had an AIS with a dendritic origin, which is a common phenomenon observed in a variety of preparations (Triarhou, 2014). As an ‘axon hillock’ is not obvious for such cells, we define the ‘neck’ as the distance from the proximal end of the AIS to the soma.…”

Section: Resultsmentioning

confidence: 99%

The axon initial segment drives the neuron’s extracellular action potential

Bakkum

Radivojević

Obien

et al. 2018

Preprint

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Extracellular voltage fields produced by a neuron’s action potentials provide a primary means for studying neuron function, yet their biophysical sources remain ambiguous. The neuron’s soma and dendrites are thought to drive the extracellular action potential (EAP), while the axon is usually ignored. However, by recording voltages of single neurons in dissociated rat cortical cultures and Purkinje cells in acute mouse cerebellar slices at hundreds of sites, we find instead that the axon initial segment dominates the EAP, and, surprisingly, the soma shows little or no influence. As expected, this signal has negative polarity (charge entering the cell) and initiates at the distal end. Interestingly, signals with positive polarity (charge exiting the cell) occur near some but not all dendritic branches and occur after a delay. Such basic knowledge about which neuronal compartments contribute to the extracellular voltage field is important for interpreting results from all electrical readout schemes. Moreover, this finding shows that changes in the AIS position and function can be observed in high spatiotemporal detail by means of high-density extracellular electrophysiology.Key points summaryThe neuron’s soma and dendrites are thought to give rise to its extracellular voltage signal, while signals from the axon are usually considered negligible.Instead, we found that the largest amplitude of the extracellular signal originates from the axon initial segment, not from the soma.This finding shows that changes in the AIS position and function can be observed in high spatiotemporal detail by means of high-density extracellular electrophysiology.AbbreviationsACSFartificial cerebrospinal fluidAISaxon initial segmentAnkGankyrin-GCMOScomplementary-metal-oxide-semiconductorDMEMDulbecco’s modified eagle mediumEAPextracellular action potentialGAD67-GFPglutamic acid decarboxylase 67-green fluorescent proteinMAP2microtubule-associated protein 2.

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Axons emanating from dendrites: phylogenetic repercussions with Cajalian hues

Cited by 18 publications

References 27 publications

The Axon Initial Segment is the Dominant Contributor to the Neuron's Extracellular Electrical Potential Landscape

The Axon Initial Segment is the Dominant Contributor to the Neuron's Extracellular Electrical Potential Landscape

Expression patterns of ion channels and structural proteins in a multimodal cell type of the avian optic tectum

The axon initial segment drives the neuron’s extracellular action potential

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