Threshold Firing Frequency–Current Relationships of Neurons in Rat Somatosensory Cortex: Type 1 and Type 2 Dynamics

2004 ◽  
Vol 92 (4) ◽  
pp. 2283-2294 ◽  
Author(s):  
T. Tateno ◽  
A. Harsch ◽  
H. P. C. Robinson
Keyword(s):  
Somatosensory Cortex ◽  
Low Frequency ◽  
Firing Frequency ◽  
Spike Generation ◽  
Low Frequencies ◽  
Subthreshold Oscillations ◽  
Wide Range ◽  
Rat Somatosensory Cortex

Neurons and dynamical models of spike generation display two different types of threshold behavior, with steady current stimulation: type 1 [the firing frequency vs. current ( f– I) relationship is continuous at threshold) and type 2 (discontinuous f– I)]. The dynamics at threshold can have profound effects on the encoding of input as spikes, the sensitivity of spike generation to input noise, and the coherence of population firing. We have examined the f– I and frequency–conductance ( f– g) relationships of cells in layer 2/3 of slices of young (15–21 DIV) rat somatosensory cortex, focusing in detail on the nature of the threshold. Using white-noise stimulation, we also measured firing frequency and interspike interval variability as a function of noise amplitude. Regular-spiking (RS) pyramidal neurons show a type 1 threshold, consistent with their well-known ability to fire regularly at very low frequencies. In fast-spiking (FS) inhibitory interneurons, although regular firing is supported over a wide range of frequencies, there is a clear discontinuity in their f– I relationship at threshold (type 2), which has not previously been highlighted. FS neurons are unable to support maintained periodic firing below a critical frequency fc, in the range of 10 to 30 Hz. Very close to threshold, FS cells switch irregularly between bursts of periodic firing and subthreshold oscillations. These characteristics mean that the dynamics of RS neurons are well suited to encoding inputs into low-frequency firing rates, whereas the dynamics of FS neurons are suited to maintaining and quickly synchronizing to gamma and higher-frequency input.

AGN1 vs AGN2 dichotomy as seen from the point of view of ionized outflows

2019 ◽  
Vol 15 (S356) ◽  
pp. 96-96
Author(s):  
Eleonora Sani
Keyword(s):  
Accretion Rate ◽  
Point Of View ◽  
Emission Lines ◽  
Black Hole Mass ◽  
X Ray ◽  
Bolometric Luminosity ◽  
Wide Range ◽  
Strong Contrast

AbstractI present a detailed study of ionized outflows in a large sample of 650 hard X-ray detected AGN. Taking advantage of the legacy value of the BAT AGN Spectroscopic Survey (BASS, DR1), we are able to reveal the faintest wings of the [OIII] emission lines associated with outflows. The sample allows us to derive the incidence of outflows covering a wide range of AGN bolometric luminosity and test how the outflow parameters are related with various AGN power tracers, such as black hole mass, Eddington ratio, luminosity. I’ll show how ionized outflows are more frequently found in type 1.9 and type 1 AGN (50% and 40%) with respect to the low fraction in type 2 AGN (20%). Within such a framework, I’ll demonstrate how type 2 AGN outflows are almost evenly balanced between blue- and red-shifted winds. This, in strong contrast with type 1 and type 1.9 AGN outflows which are almost exclusively blue-shifted. Finally, I’ll prove how the outflow occurrence is driven by the accretion rate, whereas the dependence of outflow properties with respect to the other AGN power tracers happens to be quite mild.

scholarly journals Density of voltage-gated potassium channels is a bifurcation parameter in pyramidal neurons

2015 ◽  
Vol 113 (2) ◽  
pp. 537-549 ◽  
Author(s):  
Hugo Zeberg ◽  
Hugh P. C. Robinson ◽  
Peter Århem
Keyword(s):  
Outward Current ◽  
Pyramidal Cells ◽  
Theoretical Work ◽  
K Channel ◽  
Threshold Dynamics ◽  
Bifurcation Parameter ◽  
Channel Density ◽  
Subthreshold Oscillations

Several types of intrinsic dynamics have been identified in brain neurons. Type 1 excitability is characterized by a continuous frequency-stimulus relationship and, thus, an arbitrarily low frequency at threshold current. Conversely, Type 2 excitability is characterized by a discontinuous frequency-stimulus relationship and a nonzero threshold frequency. In previous theoretical work we showed that the density of Kv channels is a bifurcation parameter, such that increasing the Kv channel density in a neuron model transforms Type 1 excitability into Type 2 excitability. Here we test this finding experimentally, using the dynamic clamp technique on Type 1 pyramidal cells in rat cortex. We found that increasing the density of slow Kv channels leads to a shift from Type 1 to Type 2 threshold dynamics, i.e., a distinct onset frequency, subthreshold oscillations, and reduced latency to first spike. In addition, the action potential was resculptured, with a narrower spike width and more pronounced afterhyperpolarization. All changes could be captured with a two-dimensional model. It may seem paradoxical that an increase in slow K channel density can lead to a higher threshold firing frequency; however, this can be explained in terms of bifurcation theory. In contrast to previous work, we argue that an increased outward current leads to a change in dynamics in these neurons without a rectification of the current-voltage curve. These results demonstrate that the behavior of neurons is determined by the global interactions of their dynamical elements and not necessarily simply by individual types of ion channels.

PIV Analysis of Dynamic Velocity Profiles in Non-Newtonian Drilling Fluids Exposed to Oscillatory Motion

2018 ◽  
Author(s):  
Maduranga Amaratunga ◽  
Roar Nybø ◽  
Rune W. Time
Keyword(s):  
Low Frequency ◽  
Velocity Profiles ◽  
Liquid Column ◽  
Oscillatory Motion ◽  
Velocity Shear ◽  
Drilling Fluids ◽  
Cross Sectional ◽  
Low Frequencies ◽  
Wide Range ◽  
Dynamic Velocity

Drilling fluids experience a wide range of shear rates and oscillatory motion while circulating through the well and also during the operations for solids control. Therefore, it is important to investigate the influence of oscillatory fields on the velocity profiles, shear rate and resulting rheological condition of non-Newtonian polymers, which are additives in drilling fluids. In this paper, we present the dynamic velocity profiles within both Newtonian (deionized water) and non-Newtonian liquids (Polyanionic Cellulose – PAC) exposed to oscillatory motion. A 15 cm × 15 cm square cross-sectional liquid column was oscillated horizontally with very low frequencies (0.75–1.75 Hz) using a laboratory made oscillating table. The dynamic velocity profiles at the bulk of the oscillating liquid column were visualized by the Particle Image Velocimetry (PIV) method, where the motion of fluid is optically visualized using light scattering “seeding” particles. Increased frequency of oscillations lead to different dynamic patterns and ranges of velocity-shear magnitudes. The experiments are part of a comprehensive study aimed at investigating the influence of low frequency oscillations on particle settling in non-Newtonian drilling fluids. It is discussed, how such motion imposed on polymeric liquids influences both flow dynamics as well as local settling velocities of cuttings particles.

Dynamics of Excitatory Synaptic Components in Sustained Firing at Low Rates

2005 ◽  
Vol 93 (6) ◽  
pp. 3370-3380 ◽  
Author(s):  
Claire Wyart ◽  
Simona Cocco ◽  
Laurent Bourdieu ◽  
Jean-Francois Léger ◽  
Catherine Herr ◽  
...  
Keyword(s):  
Metabotropic Glutamate Receptor ◽  
Temporal Dynamics ◽  
Low Frequency ◽  
Firing Frequency ◽  
Excitatory Postsynaptic Potential ◽  
Metabotropic Glutamate ◽  
Wide Range ◽  
Nmdar Activation ◽  
Asynchronous Release ◽  
Low Rate

Sustained firing is necessary for the persistent activity associated with working memory. The relative contributions of the reverberation of excitation and of the temporal dynamics of the excitatory postsynaptic potential (EPSP) to the maintenance of activity are difficult to evaluate in classical preparations. We used simplified models of synchronous excitatory networks, hippocampal autapses and pairs, to study the synaptic mechanisms underlying firing at low rates. Calcium imaging and cell attached recordings showed that these neurons spontaneously fired bursts of action potentials that lasted for seconds over a wide range of frequencies. In 2-wk-old cells, the median firing frequency was low (11 ± 8.8 Hz), whereas in 3- to 4-wk-old cells, it decreased to a very low value (2 ± 1.3 Hz). In both cases, we have shown that the slowest synaptic component supported firing. In 2-wk-old autapses, antagonists of N-methyl-d-aspartate receptors (NMDARs) induced rare isolated spikes showing that the NMDA component of the EPSP was essential for bursts at low frequency. In 3- to 4-wk-old neurons, the very low frequency firing was maintained without the NMDAR activation. However EGTA-AM or α-methyl-4-carboxyphenylglycine (MCPG) removed the very slow depolarizing component of the EPSP and prevented the sustained firing at very low rate. A metabotropic glutamate receptor (mGluR)-activated calcium sensitive conductance is therefore responsible for a very slow synaptic component associated with firing at very low rate. In addition, our observations suggested that the asynchronous release of glutamate might participate also in the recurring bursting.

Somatosensory cortex activity related to position and force

1983 ◽  
Vol 49 (5) ◽  
pp. 1216-1229 ◽  
Author(s):  
V. A. Jennings ◽  
Y. Lamour ◽  
H. Solis ◽  
C. Fromm
Keyword(s):  
Somatosensory Cortex ◽  
Single Neurons ◽  
Limb Position ◽  
Neuronal Populations ◽  
Area 3A ◽  
Position Type ◽  
State Position ◽  
Limb Posture

1. The relation of somatosensory cortex (SI) neuronal activity to actively maintained limb posture was examined by recording from single neurons in the SI of monkeys trained to hold the forearm at different pronation-supination postures and to exert different directions and magnitudes of steady torque. 2. Neurons related to limb position were, in most cases (89%), also related to torque exerted by the limb. Very few neurons related to only position or only torque were found. 3. Two categories of position- and torque-related neurons were found, type 1 and type 2. Type 1 eurneuronal activity resembled the pattern of activity seen in the pronator and supinator muscles; neurons more active with supinating torque also became more active with supinated position, while neurons related to pronating torque were also related to pronated position. Type 2 neurons had a noncongruent relation to position and torque; neurons more active with supinating torque became more active with pronated position, while neurons related to pronating torque were related to supinated position. 4. Position- and torque-related neurons were characterized by having predominantly noncutaneous peripheral inputs and were concentrated in two SI regions identified as area 3a and area 2. 5. It is hypothesized that during actively held limb postures, the activity of the type 1 and type 2 neuronal populations in SI is sufficient to signal uniquely the steady-state position of the limb and the force exerted by the limb.

scholarly journals Rapid Displacement of Cryptosporidium parvum Type 1 by Type 2 in Mixed Infections in Piglets

2003 ◽  
Vol 71 (10) ◽  
pp. 5765-5771 ◽  
Author(s):  
Donna E. Akiyoshi ◽  
Siobhan Mor ◽  
Saul Tzipori
Keyword(s):  
Cryptosporidium Parvum ◽  
Mixed Infection ◽  
Low Frequency ◽  
Time Interval ◽  
Mixed Infections ◽  
Relative Distribution ◽  
Predominant Genotype ◽  
Gnotobiotic Piglets

ABSTRACT Genotypes 1 and 2 of Cryptosporidium parvum are the primary types associated with infections in humans, with type 1 being by far the predominant genotype. The frequency of mixed infection with both genotypes in humans is relatively rare, while type 1, which experimentally infects other mammals, has been found to naturally infect almost exclusively humans. One possible explanation for the absence of type 1 in other mammals and the low frequency of mixed infections in humans is the inability of type 1 to compete with type 2 in nature when both occur simultaneously. To investigate this, we challenged gnotobiotic piglets with equal number of oocysts of type 1 and type 2, given either simultaneously or with type 2 given 24 or 48 h after type 1. The genotype of the oocysts excreted in feces and the relative distribution of each of the genotypes throughout the gut at necropsy were determined. Regardless of the time interval between challenges with the two genotypes, type 2 invariably displaced type 1. The rate of displacement was rapid when both genotypes were given simultaneously, after which no traces of type 1 were detected in the feces or in gut sections by PCR. Infection with type 1 24 or 48 h before challenge with type 2, while permitting type 1 to become established, was still rapidly eliminated within 3 days after challenge with type 2. These observations have major implications regarding the relative perpetuation and survival of these two genotypes in mammals.

scholarly journals Neurofibromatosis: part 2 – clinical management

2015 ◽  
Vol 73 (6) ◽  
pp. 531-543 ◽  
Author(s):  
Pollyanna Barros Batista ◽  
Eny Maria Goloni Bertollo ◽  
Danielle de Souza Costa ◽  
Lucas Eliam ◽  
Karin Soares Gonçalves Cunha ◽  
...  
Keyword(s):  
Clinical Management ◽  
Clinical Manifestations ◽  
Neurofibromatosis Type ◽  
Cutaneous Manifestations ◽  
Wide Range ◽  
Reduced Rate ◽  
Present Text

Part 1 of this guideline addressed the differential diagnosis of the neurofibromatoses (NF): neurofibromatosis type 1 (NF1), neurofibromatosis type 2 (NF2) and schwannomatosis (SCH). NF shares some features such as the genetic origin of the neural tumors and cutaneous manifestations, and affects nearly 80 thousand Brazilians. Increasing scientific knowledge on NF has allowed better clinical management and reduced rate of complications and morbidity, resulting in higher quality of life for NF patients. Most medical doctors are able to perform NF diagnosis, but the wide range of clinical manifestations and the inability to predict the onset or severity of new features, consequences, or complications make NF management a real clinical challenge, requiring the support of different specialists for proper treatment and genetic counseling, especially in NF2 and SCH. The present text suggests guidelines for the clinical management of NF, with emphasis on NF1.

scholarly journals Vitamin D supplementation –Is it the time to stop wasting money on vitamin D?

JMS SKIMS ◽  
2019 ◽  
Vol 22 (1) ◽  
Author(s):  
Shariq R Masoodi
Keyword(s):  
Vitamin D ◽  
Bone Health ◽  
Respiratory Infections ◽  
Vitamin D Supplementation ◽  
Increased Risk ◽  
Wide Range ◽  
Upper Respiratory ◽  
The Relationship

In recent years, vitamin D has received increased attention, as a number of studies have shown its link to the pathogenesis of various diseases. Apart from its benefits on bone health, vitamin D supplementation has been shown beneficial in reducing risk for many chronic diseases including autoimmune diseases, type 2 diabetes, heart disease, many cancers and infectious diseases. Vitamin deficiency has been associated with increased risk of elevated blood pressure, heart attack and stroke in studies. The relationship between vitamin D deficiency and the increased incidence of upper respiratory infections, asthma and eczema, among children, has been observed in several studies. Recent meta-analyzes showed a relationship between vitamin D administration during the early months of life and a lower incidence of type 1 diabetes later in life. Therefore, it is not surprising that Vitamin D supplementation is used to prevent and treat a wide range of diseases, and the use has increased considerably in the last decade.

Sign in / Sign up

Export Citation Format

Share Document