scholarly journals Relative electrical conductivity measurements of the rat frontal cortex and the influence on current source density

2017 ◽  
Author(s):  
Yevgenij Yanovsky ◽  
Jurij Brankačk
Keyword(s):  
Electrical Conductivity ◽  
Current Source ◽  
Pyramidal Cells ◽  
Field Potentials ◽  
Source Density ◽  
Deep Layers ◽  
Layer V ◽  
Relative Electrical Conductivity ◽  
Conductivity Gradient ◽  
Layer Vi

summaryThe relative electrical conductivity gradient with depth was estimated in the frontal cortex of anaesthetized rats. Current source density (CSD) approximations of field potentials evoked by ventromedial thalamic stimulations with an assumed homogeneous electrical conductivity of the neocortical tissue were compared to those with correction for the estimated conductivity gradient. In spite of the cellular heterogeneity the electrical conductivity of the frontal cortical tissue was found to be fairly homogeneous inside the superficial (layers I through IV) or deep layers (V- VI). The relative conductivity increased twofold at the transition between superficial and deep layers. Regardless of this changes CSD analysis of the field potentials evoked by ventromedial thalamic stimulation revealed negligible differences between estimations ignoring the conductivity and those taking the conductivity into account. No sinks or sources appeared or disappeared. Both CSD approximations revealed: 1) a strong sink in layer I representing most likely summed monosynaptic EPSPs of the ventromedial thalamic afferents; 2) a strong sink in layer VI, probably representing summed disynaptic EPSPs on dendrites of layer VI pyramidal cells, generated by axons of upper layer pyramidal cells; and 3) a sink in lower layer V representing probably threesynaptic summed EPSPs on dendrites of layer V pyramidal cells.

Current Source Density Profiles of Stimulus-Specific Adaptation in Rat Auditory Cortex

2009 ◽  
Vol 102 (3) ◽  
pp. 1483-1490 ◽  
Author(s):  
Francois D. Szymanski ◽  
Jose A. Garcia-Lazaro ◽  
Jan W. H. Schnupp
Keyword(s):  
Auditory Cortex ◽  
Current Source ◽  
Primary Auditory Cortex ◽  
Auditory Pathway ◽  
Afferent Input ◽  
Current Source Density ◽  
Specific Adaptation ◽  
Source Density ◽  
Density Analysis ◽  
Layer V

Neurons in primary auditory cortex (A1) are known to exhibit a phenomenon known as stimulus-specific adaptation (SSA), which means that, when tested with pure tones, they will respond more strongly to a particular frequency if it is presented as a rare, unexpected “oddball” stimulus than when the same stimulus forms part of a series of common, “standard” stimuli. Although SSA has occasionally been observed in midbrain neurons that form part of the paraleminscal auditory pathway, it is thought to be weak, rare, or nonexistent among neurons of the leminscal pathway that provide the main afferent input to A1, so that SSA seen in A1 is likely generated within A1 by local mechanisms. To study the contributions that neural processing within the different cytoarchitectonic layers of A1 may make to SSA, we recorded local field potentials in A1 of the rat in response to standard and oddball tones and subjected these to current source density analysis. Although our results show that SSA can be observed throughout all layers of A1, right from the earliest part of the response, there are nevertheless significant differences between layers, with SSA becoming significantly stronger as stimulus-related activity passes from the main thalamorecipient layers III and IV to layer V.

Silent Synapses in the Immature Visual Cortex: Layer-Specific Developmental Regulation

2004 ◽  
Vol 91 (2) ◽  
pp. 1097-1101 ◽  
Author(s):  
Simon Rumpel ◽  
Gunnar Kattenstroth ◽  
Kurt Gottmann
Keyword(s):  
Visual Cortex ◽  
Pyramidal Neurons ◽  
Developmental Regulation ◽  
Pyramidal Cells ◽  
Cortical Plate ◽  
Glutamatergic Synapses ◽  
Silent Synapses ◽  
Deep Layers ◽  
Further Development ◽  
Layer Vi

Central glutamatergic synapses are thought to initially form as immature, so-called silent synapses showing exclusively N-methyl-d-aspartate receptor-mediated synaptic transmission. Postsynaptic insertion of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors during further development leads to a conversion into functional, mature synapses. Here, we tested the hypothesis that, according to the “inside first–outside last” pattern of neocortical layer formation and synaptogenesis, pyramidal cells in the superficial layers might show a higher fraction of silent synapses compared with pyramidal cells in the deep layers. We performed an electrophysiological analysis of glutamatergic synapses in acute rat visual cortex slices during postnatal development. In layer VI pyramidal neurons the incidence of silent synapses was high during the first postnatal week and strongly declined during further development. Surprisingly, in superficial cortical plate pyramidal neurons (immature layers II/III), the fraction of silent synapses was initially very low and increased up to the second postnatal week. Thereafter, a similar decline as found in layer VI pyramidal neurons was observed. Thus the developmental regulation of silent synapses was clearly different in pyramidal neurons from different neocortical layers. The almost complete absence of silent synapses at early stages in layer II/III pyramidal neurons indicates that an initially formed subset of synapses is constitutively functional. This might be important to enable spontaneous activity and latter activity-dependent maturation of synapses.

Entorhinal inputs to hippocampal CA1 and dentate gyrus in the rat: a current-source-density study

1995 ◽  
Vol 73 (6) ◽  
pp. 2392-2403 ◽  
Author(s):  
L. S. Leung ◽  
L. Roth ◽  
K. J. Canning
Keyword(s):  
Dentate Gyrus ◽  
Cell Body ◽  
Granule Cells ◽  
Current Source ◽  
Pyramidal Cells ◽  
Short Latency ◽  
Current Source Density ◽  
Perforant Path ◽  
Stratum Radiatum ◽  
Source Density

1. Laminar profiles of the average evoked potentials and current-source-density analysis were used to study the input provided by the medial perforant path (PP) to the hippocampus in the urethan-anesthetized rat. 2. Stimulation of the PP activated an early latency sink in the middle molecular layer of the dentate gyrus (DG) and in the stratum lacunosum-moleculare in CA1. The DG current sink was generated by excitatory synaptic currents activated by the PP on dentate granule cells. In the normal rat, the peak current sink in the DG was typically five times greater than that of CA1. However, the CA1 sink could be distinguished from the DG sink in several ways: 1) it peaked when the DG sink was subsiding; 2) it showed paired-pulse facilitation, whereas the DG sink did not; and 3) in rats in which the DG was lesioned by local colchicine injection, the DG sink was reduced much more than the CA1 sink. 3. The PP afferents to CA1 required a slightly higher stimulus threshold (> 100 microA) for activation than those projecting to the DG granule cells (< 30 microA). The onset latency of the early CA1 sink (2.5 +/- 0.2 ms, mean +/- SE) was also slightly longer than that of the DG sink (1.7 +/- 0.1 ms), suggesting that the axons of entorhinal layer III cells that project to CA1 have a slightly lower conduction velocity than the axons of the layer II cells that project to the DG. 4. The short-latency current sink activated by the PP in the distal dendritic layers of CA1 was likely provided by excitatory currents at the distal apical dendrites of CA1 pyramidal cells. The accompanying current source was mainly confined to stratum radiatum and appeared not to involve the cell body layer. Thus the electrotonic current spread may not be effective enough to depolarize the cell body or axon hillock. Contribution of interneurons to the above source-sink profile is possible, with the provision that these interneurons must have dendritic processes that span strata radiatum and lacunosum moleculare. 5. Extracellular field recordings provided no evidence that PP evoked a short-latency (< 9 ms) CA1-generated population spike, even with the use of micropipettes filled with mM bicuculline. Similarly, unit recordings in CA1 revealed only long-latency (9-17 ms) unit firing after PP stimulation, corresponding to a late, di/trisynaptic excitation of CA1 via the Schaffer collaterals.(ABSTRACT TRUNCATED AT 400 WORDS)

Dentate EEG spikes and associated interneuronal population bursts in the hippocampal hilar region of the rat

1995 ◽  
Vol 73 (4) ◽  
pp. 1691-1705 ◽  
Author(s):  
A. Bragin ◽  
G. Jando ◽  
Z. Nadasdy ◽  
M. van Landeghem ◽  
G. Buzsaki
Keyword(s):  
Entorhinal Cortex ◽  
Slow Wave Sleep ◽  
Molecular Layer ◽  
Current Source ◽  
Pyramidal Cells ◽  
Suppressive Effect ◽  
Simultaneous Recording ◽  
Field Potentials ◽  
Electrode Arrays ◽  
Hilar Region

1. This paper describes two novel population patterns in the dentate gyrus of the awake rat, termed type 1 and type 2 dentate spikes (DS1, DS2). Their cellular generation and spatial distribution were examined by simultaneous recording of field potentials and unit activity using multiple-site silicon probes and wire electrode arrays. 2. Dentate spikes were large amplitude (2-4 mV), short duration (< 30 ms) field potentials that occurred sparsely during behavioral immobility and slow-wave sleep. Current-source density analysis revealed large sinks in the outer (DS1) and middle (DS2) thirds of the dentate molecular layer, respectively. DS1 and DS2 had similar longitudinal, lateral, and interhemispheric synchrony. 3. Dentate spikes invariably were coupled to synchronous population bursts of putative hilar interneurons. CA3 pyramidal cells, on the other hand were suppressed during dentate spikes. 4. After bilateral removal of the entorhinal cortex, dentate spikes disappeared, whereas sharp wave-associated bursts, reflecting synchronous discharge of the CA3-CA1 network, increased several fold. 5. These physiological characteristics of the dentate spikes suggest that they are triggered by a population burst of layer II stellate cells of the lateral (DS1) and medial (DS2) entorhinal cortex. 6. We suggest that dentate spike-associated synchronized bursts of hilar-region interneurons provide a suppressive effect on the excitability of the CA3-CA1 network in the intact brain.

scholarly journals Non-homogeneous extracellular resistivity affects the current-source density profiles of up–down state oscillations

2011 ◽  
Vol 369 (1952) ◽  
pp. 3802-3819 ◽  
Author(s):  
Maxim Bazhenov ◽  
Peter Lonjers ◽  
Steven Skorheim ◽  
Claude Bedard ◽  
Alain Destexhe
Keyword(s):  
Current Source ◽  
Field Potential ◽  
Current Source Density ◽  
Frequency Filtering ◽  
Extracellular Medium ◽  
Opposite Pattern ◽  
Source Density ◽  
Deep Layers ◽  
Up And Down States ◽  
Inhomogeneous Conductivity

Rhythmic local field potential (LFP) oscillations observed during deep sleep are the result of synchronized electrical activities of large neuronal ensembles, which consist of alternating periods of activity and silence, termed ‘up’ and ‘down’ states, respectively. Current-source density (CSD) analysis indicates that the up states of these slow oscillations are associated with current sources in superficial cortical layers and sinks in deep layers, while the down states display the opposite pattern of source–sink distribution. We show here that a network model of up and down states displays this CSD profile only if a frequency-filtering extracellular medium is assumed. When frequency filtering was modelled as inhomogeneous conductivity, this simple model had considerably more power in slow frequencies, resulting in significant differences in LFP and CSD profiles compared with the constant-resistivity model. These results suggest that the frequency-filtering properties of extracellular media may have important consequences for the interpretation of the results of CSD analysis.

scholarly journals Somadendritic Backpropagation of Action Potentials in Cortical Pyramidal Cells of the Awake Rat

1998 ◽  
Vol 79 (3) ◽  
pp. 1587-1591 ◽  
Author(s):  
György Buzsáki ◽  
Adam Kandel
Keyword(s):  
Action Potentials ◽  
Pyramidal Neurons ◽  
Current Source ◽  
Pyramidal Cells ◽  
Apical Dendrite ◽  
Individual Layer ◽  
Awake Rat ◽  
Density Analysis ◽  
Freely Behaving ◽  
Layer V

Buzsáki, György and Adam Kandel. Somadendritic backpropagation of action potentials in cortical pyramidal cells of the awake rat. J. Neurophysiol. 79: 1587–1591, 1998. The invasion of fast (Na+) spikes from the soma into dendrites was studied in single pyramidal cells of the sensorimotor cortex by simultaneous extracellular recordings of the somatic and dendritic action potentials in freely behaving rats. Field potentials and unit activity were monitored with multiple-site silicon probes along trajectories perpendicular to the cortical layers at spatial intervals of 100 μm. Dendritic action potentials of individual layer V pyramidal neurons could be recorded up to 400 μm from the cell body. Action potentials were initiated at the somatic recording site and traveled back to the apical dendrite at a velocity of 0.67 m/s. Current source density analysis of the action potential revealed time shifted dipoles, supporting the view of active spike propagation in dendrites. The presented method is suitable for exploring the conditions affecting the somadendritic propagation action of potentials in the behaving animal.

Analysis of synaptic events in the opossum piriform cortex with improved current source-density techniques

1989 ◽  
Vol 61 (4) ◽  
pp. 702-718 ◽  
Author(s):  
R. Rodriguez ◽  
L. B. Haberly
Keyword(s):  
Piriform Cortex ◽  
Current Source ◽  
Field Potential ◽  
Pyramidal Cells ◽  
Superficial Layer ◽  
Current Source Density ◽  
Membrane Currents ◽  
Source Density ◽  
Potential Component ◽  
Association Fibers

1. The piriform cortex of the opossum was studied by current source-density (CSD) analysis of field potentials to determine the laminar and temporal distribution of synaptic currents evoked by lateral olfactory tract (LOT) stimulation. 2. Extracellular conductivity was measured as a function of depth at high resolution and incorporated into CSD computations. Inclusion of the conductivity term resulted in relatively subtle changes in the shapes of CSD profiles. Resolution and accuracy of CSD computations was further improved by use of a new smoothing approach and averaging of multiple potential profiles obtained at the same site. 3. The CSD depth profile resulting from LOT stimulation revealed six major synaptic events that were consistently present at anterior, middle, and posterior sites: one during the first (A1) peak of the initial surface negative dichrotic field potential component, three during the second (B1) peak, one during the surface positive field potential component (period 2), and one during the second surface negative component (period 3). In addition, CSD profiles were computed for the population spike generated by synchronous discharge of action potentials. Depths of the net inward and outward membrane currents underlying these events were correlated with the cortical lamination as determined histologically by placement of small dye marks. 4. In agreement with previous reports it is concluded that the large inward membrane current in layer Ia during the A1 wave underlies a monosynaptic EPSP evoked in distal apical dendritic segments of pyramidal cells by afferent fibers. This EPSP displays a marked paired shock facilitation. 5. Based on anatomic and physiological considerations it is concluded that the three spatially and temporally distinct inward membrane currents (sinks) that were observed in layers III, superficial Ib, and mid- to deep-Ib during the B1 wave, underlie disynaptic EPSPs resulting from direct synaptic interactions between pyramidal cells. It is postulated that the layer III sink is generated in basal dendrites largely via local axon collaterals, the superficial layer Ib sink in intermediate apical dendritic segments by association fibers originating in the anterior piriform cortex, and the deep Ib sink in proximal apical segments by association fibers originating largely in the posterior piriform cortex. 6. The latencies of the layer Ia and superficial layer Ib sinks (presumed mono- and large disynaptic EPSPs, respectively) increased from anterior to posterior. Amplitude of the superficial Ib sink relative to the Ia sink increased from anterior to posterior.(ABSTRACT TRUNCATED AT 400 WORDS)

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