| 1. |
- Fransén, Erik, 1962-, et al.
(author)
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Ionic mechanisms in the generation of subthreshold oscillations and action potential clustering in entorhinal layer II stellate neurons
- 2004
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In: Hippocampus. - : Wiley. - 1050-9631 .- 1098-1063. ; 14:3, s. 368-384
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Journal article (peer-reviewed)abstract
- A multi compartmental biophysical model of entorhinal cortex layer II stellate cells was developed to analyze the ionic basis of physiological properties, such as subthreshold membrane potential oscillations, action potential clustering, and the medium afterhyperpolarization. In particular, the simulation illustrates the interaction of the persistent sodium current (I-NaP) and the hyperpolarization activated inward current (I-h) in the generation of subthreshold membrane potential oscillations. The potential role of I-h in contributing to the medium hyperpolarization (mAHP) and rebound spiking was studied. The role of I-h and the slow calcium-activated potassium current I-K(AHP) in action potential clustering was also studied. Representations of I-h and I-NaP were developed with parameters based on voltage-clamp data from whole-cell patch and single channel recordings of stellate cells (Dickson et A, J Neurophysiol 83:2562-2579, 2000; Magistretti and Alonso, J Gen Physiol 114:491-509, 1999; Magistretti et al., J Physiol 521:629-636, 1999a; J Neurosci 19:7334-7341, 1999b). These currents interacted to generate robust subthreshold membrane potentials with amplitude and frequency corresponding to data observed in the whole cell patch recordings. The model was also able to account for effects of pharmacological manipulations, including blockade of I-h with ZD7288, partial blockade with cesium, and the influence of barium on oscillations. In a model with a wider range of currents, the transition from oscillations to single spiking, to spike clustering, and finally tonic firing could be replicated. In agreement with experiment, blockade of calcium channels in the model strongly reduced clustering. In the voltage interval during which no data are available, the model predicts that the slow component of I-h does not follow the fast component down to very short time constants. The model also predicts that the fast component of I-h is responsible for the involvement in the generation of subthreshold oscillations, and the slow component dominates in the generation of spike clusters.
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| 2. |
- Fransén, Erik, 1962-, et al.
(author)
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Role of A-type potassium currents in excitability, network synchronicity, and epilepsy
- 2010
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In: Hippocampus. - : Wiley. - 1050-9631 .- 1098-1063. ; 20:7, s. 877-887
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Journal article (peer-reviewed)abstract
- A range of ionic currents have been suggested to be involved in distinct aspects of epileptogenesis. Based on pharmacological and genetic studies, potassium currents have been implicated, in particular the transient A-type potassium current (K-A). Epileptogenic activity comprises a rich repertoire of characteristics, one of which is synchronized activity of principal cells as revealed by occurrences of for instance fast ripples. Synchronized activity of this kind is particularly efficient in driving target cells into spiking. In the recipient cell, this synchronized input generates large brief compound excitatory postsynaptic potentials (EPSPs). The fast activation and inactivation of K-A lead us to hypothesize a potential role in suppression of such EPSPs. In this work, using computational modeling, we have studied the activation of K-A by synaptic inputs of different levels of synchronicity. We find that K-A participates particularly in suppressing inputs of high synchronicity. We also show that the selective suppression stems from the current's ability to become activated by potentials with high slopes. We further show that K-A suppresses input mimicking the activity of a fast ripple. Finally, we show that the degree of selectivity of K-A can be modified by changes to its kinetic parameters, changes of the type that are produced by the modulatory action of KChIPs and DPPs. We suggest that the wealth of modulators affecting K-A might be explained by a need to control cellular excitability in general and suppression of responses to synchronicity in particular. We also suggest that compounds changing K-A-kinetics may be used to pharmacologically improve epileptic status.
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| 3. |
- Stöber, T M, et al.
(author)
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Selective neuromodulation and mutual inhibition within the CA3–CA2 system can prioritize sequences for replay
- 2020
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In: Hippocampus. - : Wiley. - 1050-9631 .- 1098-1063. ; 30:11, s. 1228-1238
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Journal article (peer-reviewed)abstract
- To make optimal use of previous experiences, important neural activity sequences must be prioritized during hippocampal replay. Integrating insights about the interplay between CA3 and CA2, we propose a conceptual framework that allows the two regions to control which sequences are reactivated. We suggest that neuromodulatory-gated plasticity and mutual inhibition enable discrete assembly sequences in both regions to support each other while suppressing competing sequences. This perspective provides a coherent interpretation for a variety of seemingly disconnected functional properties of CA2 and paves the way for a more general understanding of CA2.
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| 4. |
- Tahvildari, Babak, et al.
(author)
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Switching between on and off states of persistent activity in lateral entorhinal layer III neurons
- 2007
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In: Hippocampus. - : Wiley. - 1050-9631 .- 1098-1063. ; 17:4, s. 257-263
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Journal article (peer-reviewed)abstract
- Persistent neural spiking maintains information during a, working memory task when a stimulus is no longer present. During I retention, this activity needs to be stable to distractors. More importantly, when retention is no longer relevant, cessation of the activity is necessary to enable processing and retention of subsequent information. Here, by means of intracellular recording with sharp microelectrode in in vitro rat brain slices, we demonstrate that single principal layer III neurons of the lateral entorhinal cortex (EC) generate persistent spiking activity with a novel ability to reliably toggle between spiking activity and a silent state. Our data indicates that in the presence of muscarmic receptor activation, persistent activity following an excitatory input may be induced and that a subsequent excitatory input can terminate this activity and cause the neuron to return to a silent state. Moreover, application of inhibitory hyperpolarizing stimuli is neither able to decrease the frequency of the persistent activity nor terminate it. The persistent activity can also be initiated and terminated by synchronized synaptic stimuli of layer II/III of the perirhinal cortex. The neuronal ability to switch On and Off persistent activity may facilitate the concurrent representation of temporally segregated information arriving in the EC and being directed toward the hippocampus.
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| 5. |
- Tigerholm, Jenny, et al.
(author)
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Integration of synchronous synaptic input in CA1 pyramidal neuron depends on spatial and temporal distributions of the input
- 2013
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In: Hippocampus. - : Wiley. - 1050-9631 .- 1098-1063. ; 23:1, s. 87-99
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Journal article (peer-reviewed)abstract
- Highly synchronized neural firing has been discussed in relation to learning and memory, for instance sharp-wave activity in hippocampus. We were interested to study how a postsynaptic CA1 pyramidal neuron would integrate input of different levels of synchronicity. In previous work using computational modeling we studied how the integration depends on dendritic conductances. We found that the transient A-type potassium channel KA was able to selectively suppress input of high synchronicity. In recent years, compartmentalization of dendritic integration has been shown. We were therefore interested to study the influence of localization and pattern of synaptic input over the dendritic tree of the CA1 pyramidal neuron. We find that the selective suppression increases when synaptic inputs are placed on oblique dendrites further out from the soma. The suppression also increases along the radial axis from the apical trunk out to the end of oblique dendrites. We also find that the KA channel suppresses the occurrence of dendritic spikes. Moreover, recent studies have shown interaction between synaptic inputs. We therefore studied the influence of apical tuft input on the integration studied above. We find that excitatory input provides a modulatory influence reducing the capacity of KA to suppress synchronized activity, thus facilitating the excitatory drive of oblique dendritic input. Conversely, inhibitory tuft input increases the suppression by KA providing a larger control of oblique depolarizing factors on the CA1 pyramidal neuron in terms of what constitutes the most effective level of synchronicity. Furthermore, we show that the selective suppression studied above depends on the conductance of the KA channel. KA, as several other potassium channels, is modulated by several neuromodulators, for instance acetylcholine and dopamine, both of which have been discussed in relation to learning and memory. We suggest that dendritic conductances and their modulatory systems may be part of the regulation of processing of information, in particular for how network synchronicity affects learning and memory.
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| 6. |
- von Berlin, Leonie, et al.
(author)
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Early fate bias in neuroepithelial progenitors of hippocampal neurogenesis
- 2023
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In: Hippocampus. - : Wiley. - 1050-9631 .- 1098-1063. ; 33:4, s. 391-401
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Journal article (peer-reviewed)abstract
- Hippocampal adult neural stem cells emerge from progeny of the neuroepithelial lineage during murine brain development. Hippocampus development is increasingly well understood. However, the clonal relationships between early neuroepithelial stem cells and postnatal neurogenic cells remain unclear, especially at the single-cell level. Here we report fate bias and gene expression programs in thousands of clonally related cells in the juvenile hippocampus based on single-cell RNA-seq of barcoded clones. We find evidence for early fate restriction of neuroepithelial stem cells to either neurogenic progenitor cells of the dentate gyrus region or oligodendrogenic, non-neurogenic fate supplying cells for other hippocampal regions including gray matter areas and the Cornu ammonis region 1/3. Our study provides new insights into the phenomenon of early fate restriction guiding the development of postnatal hippocampal neurogenesis.
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| 7. |
- Shin, D. Y., et al.
(author)
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Temperature dependence of magnetic anisotropy in ferromagnetic (Ga,Mn)As films : Investigation by the planar Hall effect
- 2007
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 76:3
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Journal article (peer-reviewed)abstract
- We carried out systematic planar Hall effect (PHE) measurements of GaMnAs ferromagnetic semiconductor film as a function of temperature. The two-step switching of the PHE occurring in the magnetization-reversal process was observed to change significantly as the temperature was increased. To investigate the mechanism responsible for such behavior, the temperature dependence of the PHE was continuously measured (with and without an external magnetic field) after the sample was first magnetized along one of the easy axes to produce an initial single-domain state at 3 K. A detailed temperature dependence of the magnetization direction was then obtained by taking the ratio of the planar Hall resistance measured with and without a magnetic field. As the temperature was increased, the direction of the easy axis of magnetization was observed to change from the [010] crystallographic direction to [110]. This reorientation of the easy axis direction can be understood in terms of the temperature dependence of the relative strengths of the magnetic anisotropy constants (i.e., of the ratio of uniaxial-to-cubic anisotropy) of the GaMnAs film. © 2007 The American Physical Society.
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