Coevolution of synchronous activity and connectivity in coupled chaotic oscillators

We investigate the coevolution dynamics of node activities and coupling strengths in coupled chaotic oscillators via a simple threshold adaptive scheme. The coupling strength is synchronous activity regulated, which in turn is able to boost the synchronization remarkably. In the case of weak coupling, the globally coupled oscillators present a highly clustered functional connectivity with a power-law distribution in the tail with γ≃3.1, while for strong coupling, they self-organize into a network with a heterogeneously rich connectivity at the onset of synchronization but exhibit rather sparse structure to maintain the synchronization in noisy environment. The relevance of the results is briefly discussed

Structural determinants underlying the high efficacy of synaptic transmission and plasticity at synaptic boutons in layer 4 of the adult rat 'barrel cortex'

Excitatory layer 4 (L4) neurons in the ‘barrel field’ of the rat somatosensory cortex represent an important component in thalamocortical information processing. However, no detailed information exists concerning the quantitative geometry of synaptic boutons terminating on these neurons. Thus, L4 synaptic boutons were investigated using serial ultrathin sections and subsequent quantitative 3D reconstructions. In particular, parameters representing structural correlates of synaptic transmission and plasticity such as the number, size and distribution of pre- and postsynaptic densities forming the active zone (AZ) and of the three functionally defined pools of synaptic vesicles were analyzed. L4 synaptic boutons varied substantially in shape and size; the majority had a single, but large AZ with opposing pre- and postsynaptic densities that matched perfectly in size and position. More than a third of the examined boutons showed perforations of the postsynaptic density. Synaptic boutons contained on average a total pool of 561 ± 108 vesicles, with ~5 % constituting the putative readily releasable, ~23 % the recycling, and the remainder the reserve pool. These pools are comparably larger than other characterized central synapses. Synaptic complexes were surrounded by a dense network of fine astrocytic processes that reached as far as the synaptic cleft, thus regulating the temporal and spatial glutamate concentration, and thereby shaping the unitary EPSP amplitude. In summary, the geometry and size of AZs, the comparably large readily releasable and recycling pools, together with the tight astrocytic ensheathment, may explain and contribute to the high release probability, efficacy and modulation of synaptic transmission at excitatory L4 synaptic boutons. Moreover, the structural variability as indicated by the geometry of L4 synaptic boutons, the presence of mitochondria and the size and shape of the AZs strongly suggest that synaptic reliability, strength and plasticity is governed and modulated individually at excitatory L4 synaptic boutons

Intra- and interlaminar excitatory synaptic connections of layer 4 spiny neurons and layer 6A pyramidal cells in rat barrel cortex

In the primary somatosensory (barrel) cortex of rodents, layer 4 (L4) and 6A are the main recipient layers of thalamocortical projections. In addition, a subset of L6A pyramidal neurons provide a direct corticothalamic feedback to the thalamus. Thus, neurons in layer 4 and 6A are an integral part of a thalamo-cortical-cortico-thalamic feedback circuit. To better understand the role of the intracortical unit in this circuit, we studied the anatomical and functional properties of excitatory synaptic connections from layer 4 to layer 6A in the rat barrel cortex by making dual whole-cell recordings with dye injection from L4 spiny neurons and L6A pyramidal cells in acute brain slices. Interlaminar monosynaptic L4-to-L6A excitatory connections (n = 17) were relatively rare. They were of low efficacy with an average excitatory postsynaptic potentials (EPSPs) of 0.32 ± 0.19 mV (n = 17) but of moderately high reliability with failure rate of 24.2 ± 17.7% (n = 16) and coefficient of variation (CV) of 0.56 ± 0.16 (n = 16). The EPSP amplitude was either depressing or weakly facilitating with paired-pulse ratio (PPR) of 0.45 - 1.38 (n = 17) at an interstimulus interval of 100 ms. Notably, we found a spatial separation of synaptic inputs on the dendritic domain of the postsynaptic L6A pyramidal cells depending on the presynaptic L4 neuron type: L4 spiny stellate neurons innervated predominantly the distal apical tuft dendrites of L6A pyramidal cells with synapse-to-soma distance of 591 ± 137 μm (n = 6) and elicited slow EPSPs (20-80% rise time = 6.7 ± 2.1 ms and latency = 3.8 ± 1.6 ms, n = 6) in L6A somata, while most of L4 star pyramidal neurons preferentially innervated the proximal basal and apical oblique dendrites with synapse-to-soma distance of 86 ± 54 µm (n = 7) and elicited fast EPSPs (20-80% rise time = 1.5 ± 0.9 ms and latency = 1.7 ± 0.2 ms, n = 7) in L6A somata with some star pyramids also forming synapses on the L6A apical tuft or oblique dendrites (synapse-to-soma distance = 524 ± 167 µm, n = 4) and eliciting relatively slow EPSPs (20-80% rise time = 5.4 ± 1.7 ms and latency = 3.7 ± 0.8 ms, n = 4). Other EPSP characteristics (i.e., amplitude, PPR, failure rate and CV) were not significantly different for the three types of L4-L6A connections. There was a tight correlation between the EPSP rise time, latency, and the synapse-to-soma distance. The synaptic location could not completely predicted solely on the basis of the axo-dendritic overlap suggesting that Peter’s rule of synaptic connectivity was not completely correct here. Using pharmacological treatment and neuronal modeling, we found that the occurrence of ‘slow’ and ‘fast’ EPSPs was not due to different receptor components in the postsynaptic densities but mainly due to the dendritic filtering effect during the EPSP propagation from synaptic location to soma. In addition, the cell-type specific selection of postsynaptic target region was a pre- but not postsynaptic phenomenon. As a comparison, we also performed some paired recordings in layer 4 and 6A and studied the characteristics of excitatory connections in layer 4 and 6A, respectively. For intralaminar monosynaptic L4-L4 and L6A-L6A excitatory connections, we found homogeneous dynamical properties of EPSPs, i.e., fast rise time (20-80% rise time = 1.59 ± 0.49 ms (n = 10) for L4-L4 and 1.39 ± 0.59 ms (n = 5) for L6A-L6A connections) and short latency (latency = 1.17 ± 0.41 ms (n = 10) for L4-L4 and 1.69 ± 0.65 ms (n = 5) for L6A-L6A connections), implying that, for both connections, synaptic inputs to postsynaptic neurons were electrotonically close to somata. The synaptic efficacy of L4-L4 connections were widely distributed from very weak connections (0.30 mV) to very strong ones (4.71 mV) with an average EPSP amplitude of 1.02 ± 1.33 mV (n = 10) compared with L6A-L6A connections that had a substantially lower average EPSP amplitude (0.58 ± 0.50 mV, n = 5), a relatively higher failure rate (17.5 ± 15.0%, n = 5) and a little higher CV (0.53 ± 0.23, n = 5)

Intra- and interlaminar excitatory synaptic connections of layer 4 spiny neurons and layer 6A pyramidal cells in rat barrel cortex

In the primary somatosensory (barrel) cortex of rodents, layer 4 (L4) and 6A are the main recipient layers of thalamocortical projections. In addition, a subset of L6A pyramidal neurons provide a direct corticothalamic feedback to the thalamus. Thus, neurons in layer 4 and 6A are an integral part of a thalamo-cortical-cortico-thalamic feedback circuit. To better understand the role of the intracortical unit in this circuit, we studied the anatomical and functional properties of excitatory synaptic connections from layer 4 to layer 6A in the rat barrel cortex by making dual whole-cell recordings with dye injection from L4 spiny neurons and L6A pyramidal cells in acute brain slices. Interlaminar monosynaptic L4-to-L6A excitatory connections (n = 17) were relatively rare. They were of low efficacy with an average excitatory postsynaptic potentials (EPSPs) of 0.32 ± 0.19 mV (n = 17) but of moderately high reliability with failure rate of 24.2 ± 17.7% (n = 16) and coefficient of variation (CV) of 0.56 ± 0.16 (n = 16). The EPSP amplitude was either depressing or weakly facilitating with paired-pulse ratio (PPR) of 0.45 - 1.38 (n = 17) at an interstimulus interval of 100 ms. Notably, we found a spatial separation of synaptic inputs on the dendritic domain of the postsynaptic L6A pyramidal cells depending on the presynaptic L4 neuron type: L4 spiny stellate neurons innervated predominantly the distal apical tuft dendrites of L6A pyramidal cells with synapse-to-soma distance of 591 ± 137 μm (n = 6) and elicited slow EPSPs (20-80% rise time = 6.7 ± 2.1 ms and latency = 3.8 ± 1.6 ms, n = 6) in L6A somata, while most of L4 star pyramidal neurons preferentially innervated the proximal basal and apical oblique dendrites with synapse-to-soma distance of 86 ± 54 µm (n = 7) and elicited fast EPSPs (20-80% rise time = 1.5 ± 0.9 ms and latency = 1.7 ± 0.2 ms, n = 7) in L6A somata with some star pyramids also forming synapses on the L6A apical tuft or oblique dendrites (synapse-to-soma distance = 524 ± 167 µm, n = 4) and eliciting relatively slow EPSPs (20-80% rise time = 5.4 ± 1.7 ms and latency = 3.7 ± 0.8 ms, n = 4). Other EPSP characteristics (i.e., amplitude, PPR, failure rate and CV) were not significantly different for the three types of L4-L6A connections. There was a tight correlation between the EPSP rise time, latency, and the synapse-to-soma distance. The synaptic location could not completely predicted solely on the basis of the axo-dendritic overlap suggesting that Peter’s rule of synaptic connectivity was not completely correct here. Using pharmacological treatment and neuronal modeling, we found that the occurrence of ‘slow’ and ‘fast’ EPSPs was not due to different receptor components in the postsynaptic densities but mainly due to the dendritic filtering effect during the EPSP propagation from synaptic location to soma. In addition, the cell-type specific selection of postsynaptic target region was a pre- but not postsynaptic phenomenon. As a comparison, we also performed some paired recordings in layer 4 and 6A and studied the characteristics of excitatory connections in layer 4 and 6A, respectively. For intralaminar monosynaptic L4-L4 and L6A-L6A excitatory connections, we found homogeneous dynamical properties of EPSPs, i.e., fast rise time (20-80% rise time = 1.59 ± 0.49 ms (n = 10) for L4-L4 and 1.39 ± 0.59 ms (n = 5) for L6A-L6A connections) and short latency (latency = 1.17 ± 0.41 ms (n = 10) for L4-L4 and 1.69 ± 0.65 ms (n = 5) for L6A-L6A connections), implying that, for both connections, synaptic inputs to postsynaptic neurons were electrotonically close to somata. The synaptic efficacy of L4-L4 connections were widely distributed from very weak connections (0.30 mV) to very strong ones (4.71 mV) with an average EPSP amplitude of 1.02 ± 1.33 mV (n = 10) compared with L6A-L6A connections that had a substantially lower average EPSP amplitude (0.58 ± 0.50 mV, n = 5), a relatively higher failure rate (17.5 ± 15.0%, n = 5) and a little higher CV (0.53 ± 0.23, n = 5)

Cell-Type Specific Neuromodulation of Excitatory and Inhibitory Neurons via Muscarinic Acetylcholine Receptors in Layer 4 of Rat Barrel Cortex

The neuromodulator acetylcholine (ACh) plays an important role in arousal, attention, vigilance, learning and memory. ACh is released during different behavioural states and affects the brain microcircuit by regulating neuronal and synaptic properties. Here, we investigated how a low concentration of ACh (30 μM) affects the intrinsic properties of electrophysiologically and morphologically identified excitatory and inhibitory neurons in layer 4 (L4) of rat barrel cortex. ACh altered the membrane potential of L4 neurons in a heterogeneous manner. Nearly all L4 regular spiking (RS) excitatory neurons responded to bath-application of ACh with a M4 muscarinic ACh receptor-mediated hyperpolarisation. In contrast, in the majority of L4 fast spiking (FS) and non-fast spiking (nFS) interneurons 30 μM ACh induced a depolarisation while the remainder showed a hyperpolarisation or no response. The ACh-induced depolarisation of L4 FS interneurons was much weaker than that in L4 nFS interneurons. There was no clear difference in the response to ACh for three morphological subtypes of L4 FS interneurons. However, in four morpho-electrophysiological subtypes of L4 nFS interneurons, VIP+-like interneurons showed the strongest ACh-induced depolarisation; occasionally, even action potential firing was elicited. The ACh-induced depolarisation in L4 FS interneurons was exclusively mediated by M1 muscarinic ACh receptors; in L4 nFS interneurons it was mainly mediated by M1 and/or M3/5 muscarinic ACh receptors. In a subset of L4 nFS interneurons, a co-operative activation of muscarinic and nicotinic ACh receptors was also observed. The present study demonstrates that low-concentrations of ACh affect different L4 neuron types in a cell-type specific way. These effects result from a specific expression of different muscarinic and/or nicotinic ACh receptors on the somatodendritic compartments of L4 neurons. This suggests that even at low concentrations ACh may tune the excitability of L4 excitatory and inhibitory neurons and their synaptic microcircuits differentially depending on the behavioural state during which ACh is released

Dendritic Target Region-Specific Formation of Synapses Between Excitatory Layer 4 Neurons and Layer 6 Pyramidal Cells

Excitatory connections between neocortical layer 4 (L4) and L6 are part of the corticothalamic feedback microcircuitry. Here we studied the intracortical element of this feedback loop, the L4 spiny neuron-to-L6 pyramidal cell connection. We found that the distribution of synapses onto both putative corticothalamic (CT) and corticocortical (CC) L6 pyramidal cells (PCs) depends on the presynaptic L4 neuron type but is independent of the postsynaptic L6 PC type. L4 spiny stellate cells establish synapses on distal apical tuft dendrites of L6 PCs and elicit slow unitary excitatory postsynaptic potentials (uEPSPs) in L6 somata. In contrast, the majority of L4 star pyramidal neurons target basal and proximal apical oblique dendrites of L6 PCs and show fast uEPSPs. Compartmental modeling suggests that the slow uEPSP time course is primarily the result of dendritic filtering. This suggests that the dendritic target specificity of the 2 L4 spiny neuron types is due to their different axonal projection patterns across cortical layers. The preferential dendritic targeting by different L4 neuron types may facilitate the generation of dendritic Ca2+ or Na+ action potentials in L6 PCs; this could play a role in synaptic gain modulation in the corticothalamic pathway

Density visualization pipeline: a tool for cellular and network density visualization and analysis

Neuron classification is an important component in analyzing network structure and quantifying the effect of neuron topology on signal processing. Current quantification and classification approaches rely on morphology projection onto lower-dimensional spaces. In this paper a 3D visualization and quantification tool is presented. The Density Visualization Pipeline (DVP) computes, visualizes and quantifies the density distribution, i.e., the “mass” of interneurons. We use the DVP to characterize and classify a set of GABAergic interneurons. Classification of GABAergic interneurons is of crucial importance to understand on the one hand their various functions and on the other hand their ubiquitous appearance in the neocortex. 3D density map visualization and projection to the one-dimensional x, y, z subspaces show a clear distinction between the studied cells, based on these metrics. The DVP can be coupled to computational studies of the behavior of neurons and networks, in which network topology information is derived from DVP information. The DVP reads common neuromorphological file formats, e.g., Neurolucida XML files, NeuroMorpho.org SWC files and plain ASCII files. Full 3D visualization and projections of the density to 1D and 2D manifolds are supported by the DVP. All routines are embedded within the visual programming IDE VRL-Studio for Java which allows the definition and rapid modification of analysis workflows

SIZE INSTABILITIES IN THE RING AND LINEAR ARRAYS OF CHAOTIC SYSTEMS

We investigate the dynamical stabilities of ring and linear arrays of chaotic oscillators with asymmetric nearest-neighbor and long-range couplings. It is shown that the instabilities of complete chaotic synchronization occur as the numbers of oscillators are increased beyond critical values which depend on the coupling schemes and coupling parameters of the systems. Based on the master stability function and eigenvalue analysis methods, we give the semi-analytical relations between the critical values and the coupling parameters. Results are demonstrated with numerical simulations in a set of coupled Lorenz oscillators.Dynamical stabilities, master stability function, eigenvalue analysis

Electrophysiological and Morphological Characterization of Neuronal Microcircuits in Acute Brain Slices Using Paired Patch-Clamp Recordings

The combination of patch clamp recordings from two (or more) synaptically coupled neurons (paired recordings) in acute brain slice preparations with simultaneous intracellular biocytin filling allows a correlated analysis of their structural and functional properties. With this method it is possible to identify and characterize both pre- and postsynaptic neurons by their morphology and electrophysiological response pattern. Paired recordings allow studying the connectivity patterns between these neurons as well as the properties of both chemical and electrical synaptic transmission. Here, we give a step-by-step description of the procedures required to obtain reliable paired recordings together with an optimal recovery of the neuron morphology. We will describe how pairs of neurons connected via chemical synapses or gap junctions are identified in brain slice preparations. We will outline how neurons are reconstructed to obtain their 3D morphology of the dendritic and axonal domain and how synaptic contacts are identified and localized. We will also discuss the caveats and limitations of the paired recording technique, in particular those associated with dendritic and axonal truncations during the preparation of brain slices because these strongly affect connectivity estimates. However, because of the versatility of the paired recording approach it will remain a valuable tool in characterizing different aspects of synaptic transmission at identified neuronal microcircuits in the brain