Individual Dendrites Research Articles

Synaptic Integration Gradients in Single Cortical Pyramidal Cell Dendrites

Cortical pyramidal neurons receive thousands of synaptic inputs arriving at different dendritic locations with varying degrees of temporal synchrony. It is not known if different locations along single cortical dendrites integrate excitatory inputs in different ways. Here we have used two-photon glutamate uncaging and compartmental modeling to reveal a gradient of nonlinear synaptic integration in basal and apical oblique dendrites of cortical pyramidal neurons. Excitatory inputs to the proximal dendrite sum linearly and require precise temporal coincidence for effective summation, whereas distal inputs are amplified with high gain and integrated over broader time windows. This allows distal inputs to overcome their electrotonic disadvantage, and become surprisingly more effective than proximal inputs at influencing action potential output. Thus, single dendritic branches can already exhibit nonuniform synaptic integration, with the computational strategy shifting from temporal coding to rate coding along the dendrite.

Morphological Properties in Dopaminergic Neurons of the Rat Midbrain during Early Developmental Stages and One Numerical Approach to Passive-Membrane Modeling

In this study, I aim to understand morphological changes in dopaminergic neurons of the rat midbrain during early developmental stages and their computational properties in the dendrites. To this end, firstly, I measured morphological details of dopaminergic neurons using an immunochemical double-staining technique. In the viewpoint of the Rall's equivalent-cylinder model, secondly, I tested if the data satisfied one of conditions (3/2 power law) of the Rall's model. On the basis of the experimental data, I next investigated if some branches in the individual dendrites had special selectivity in efficient passive propagation of membrane potentials between the branches of individual cells and different cells. The results show that the Rall's 3/2 power law was not satisfied in many branch points and that among branches of each dendrite, specific selectivity in efficient propagation was not found. In addition, I note an implementation method in which the finite element method is applied to one-dimensional cable model of dendrites and give some numerical examples.

Hydrothermal synthesis, characterization and growth mechanism of single crystal lead titanate pyrochlore dendrites

Lead titanate pyrochlore (Pb2Ti2O6) dendrites have been synthesized via hydrothermal treatment of the mixture of lead and titanium hydroxides with the use of ammonia. The products were characterized by XRD, FESEM, TEM, HRTEM, SAED and EDX, respectively. TEM and FESEM show that an individual Pb2Ti2O6 pyrochlore dendrite is composed of a long central trunk and more than three rows of secondary branches. Furthermore, the secondary branches cross the long central trunk exhibiting a cross-like morphology. The SAED patterns reveal the dendrites are single crystalline in nature. And the HRTEM images further demonstrate that both the trunk and the branches all grow along directions. Based on the time-dependent experiments, the analyses of the effects of ammonia and the configuration of cubic pyrochlore structure, the growth mechanism of the single crystal Pb2Ti2O6 pyrochlore dendrites was discussed.

Optimization of homogenizing annealing for Al–Zn5.5–Mg2.5–Cu1.5 alloy

In the course of homogenizing annealing of aluminum alloys prepared by continuous or semi-continuous casting, chemical inhomogeneity is reduced within individual dendrite cells (crystal segregation). This is almost a diffusion process proceeding at a temperature close to the liquid material temperature. In this process there is transfer of soluble intermetallic compounds and eutectics into solid solution, which considerably slows down crystal segregation. The temperature, duration of homogenization, dendrite size, and diffusion time affect homogenization. This article is devoted to optimizing homogenization with respect to its duration and homogenizing annealing temperature, which affect the mechanical properties of the Al–Zn5.5–Mg2.5–Cu1.5 alloy.

Regular mosaic of synaptic contacts among three retinal neurons

Retinal bipolar, amacrine, and ganglion cells contact each other within precisely defined synaptic laminae, but the spatial distribution of contacts between the cells is generally treated as random. Here we show that not to be the case. Excitatory inputs to inner retinal neurons were visualized by introduction of a plasmid coding for the postsynaptic protein PSD95-GFP. Our initial finding was that synapses on the dendrites of retinal ganglion cells are regularly spaced, at 2-3-μm intervals, along the dendrites. Thus, the presence of a PSD95 punctum creates a nearby zone from which other inputs appear to be excluded. Despite their great variation in size and different morphologies, the spacing is similar for the arbors of different retinal ganglion cell types. Regular spacing was also observed for the starburst amacrine cells. This regularity is mirrored in the spacing of axonal varicosities of the stratified bipolar cells, which have a regular, nonrandom interval consistent with that of the PSD95 puncta on ganglion cells. Thus, for each level of the inner plexiform layer all three cell types participate in a single 2D mosaic of synaptic contacts. These findings raise a new set of questions: How does the self-avoidance of synaptic sites along an individual dendrite arise and how is it physically maintained? Why is a regular spacing of inputs important for the computational function of the cells? Finally, which of the three players, if any, is developmentally responsible for the initial establishment of the pattern?

Morphofunctional Changes in Goldfish Mauthner Neurons after Application of β-Amyloid

The effects of applying aggregated beta-amyloid peptide fragment 25-35 on the three-dimensional structure and volume of Mauthner neurons (MN) and on motor asymmetry were assessed in goldfish using reconstructions based on serial histological sections. These experiments showed that the motor asymmetry of the fish was stable in the intact state and in controls and correlated tightly with structural asymmetry of neurons. beta-Amyloid produced large changes or inversion in motor asymmetry, which did not coincide with or even contradicted the structural asymmetry of MN. This occurred as a result of marked dystrophy or, conversely, hypertrophy of individual neurons and their individual dendrites, with changes in their proportions. It is suggested that the harmful action of beta-amyloid on MN structure and the discordant ("incorrect") behavior of the fish may result from mechanical deformation evoked by its tape-like fibrils. Overall, the results lead to the conclusion that MN provide a suitable system for studying the structural aspects of amyloidosis.

Stabilization of Mauthner Neuron Structure on Adaptation of Goldfish to Contralateral Optokinetic Stimulation

We have previously shown that contralateral optokinetic (visual) stimulation (COS) evokes inversion of motor asymmetry in goldfish and three-fold reductions in the volume of the ventral dendrite of the ipsilateral Mauthner neuron (MN). A training regime consisting of repeated daily sessions of COS induced resistance of the motor behavior of the fish to this treatment. We report here our studies of the effects of training sessions of COS on the structure of MN and their components. Daily visual training was found to stabilize the sizes of the dorsal dendrites of MN, significantly increasing their resistance to single prolonged sessions of COS. Thus, repeated stimulation of an individual dendrite induces an adaptive morphological state in the dendrite and in the neuron as a whole. This allows more detailed studies of the role of the individual dendrite in modifying the functional activity of the whole neuron in the mechanisms of adaptation and memory at the cellular level to be performed.

Generation of directional selectivity by individual thin dendrites in neocortical pyramidal neurons

AbstractPatterned 2-photon glutamate uncaging and local GABA iontophoresis were used to test, in brain slices, whether basal and oblique dendrites possess the biophysical machinery to contribute to the directional selectivity exhibited by many sensory neocortical neurons. On average, Distal-to-Proximal (DP) sequences of glutamate stimuli along individual dendrites produced ~1.5-fold larger responses than the same stimuli in reverse order (PD). Proximal inhibition consistent with spatially-offset receptive subfields, preceding PD but following DP sequences, enhanced directionality to ~2.1-fold.

Sparse connectivity in short-term memory networks

Sparse connectivity in short-term memory networks

Optical recording of neuronal activity with a genetically-encoded calcium indicator in anesthetized and freely moving mice

Fluorescent calcium (Ca2+) indicator proteins (FCIPs) are promising tools for functional imaging of cellular activity in living animals. However, they have still not reached their full potential for in vivo imaging of neuronal activity due to limitations in expression levels, dynamic range, and sensitivity for reporting action potentials. Here, we report that viral expression of the ratiometric Ca2+ sensor yellow cameleon 3.60 (YC3.60) in pyramidal neurons of mouse barrel cortex enables in vivo measurement of neuronal activity with high dynamic range and sensitivity across multiple spatial scales. By combining juxtacellular recordings and two-photon imaging in vitro and in vivo, we demonstrate that YC3.60 can resolve single action potential (AP)-evoked Ca2+ transients and reliably reports bursts of APs with negligible saturation. Spontaneous and whisker-evoked Ca2+ transients were detected in individual apical dendrites and somata as well as in local neuronal populations. Moreover, bulk measurements using wide-field imaging or fiber-optics revealed sensory-evoked YC3.60 signals in large areas of the barrel field. Fiber-optic recordings in particular enabled measurements in awake, freely moving mice and revealed complex Ca2+ dynamics, possibly reflecting different behavior-related brain states. Viral expression of YC3.60 – in combination with various optical techniques – thus opens a multitude of opportunities for functional studies of the neural basis of animal behavior, from dendrites to the levels of local and large-scale neuronal populations.

Fractal and shape analyses of manganese dendrites on vein quartz

Manganese dendrites are common along joint planes in a quartz vein in Selayang, northern Kuala Lumpur. Individual dendrites mainly range from about 5 cm to 50 cm in length. They have variable shapes that range from simple shape with few branches to complex intricately branched patterns. Dendrites having different patterns may be found together along the same joint plane and some simple dendrites developed into more intricate forms. Digital photographs of dendrites were taken in the field and then converted to single bit images for fractal analysis. The images were also vectorised to measure the perimeter and area of the dendrites as well as the enclosing convex hull. These basic measurements were used to obtain the fractal dimension, lacunarity, PARIS factor, divergent ratio, fractal divergent ratio and fill factor for nine samples, which cover dendrites of various forms and complexities. The fractal dimension of the dendrites measured using box counting algorithm ranges from 1.57 to 1.88. Generally, dendrites with broad and short branches have larger fractal dimension and those that have thin and long branches have smaller fractal dimension. Lacunarity and fill factor also show the same trend, while PARIS factor, divergent ratio and fractal divergent ratio values are higher in complex and intricately branched dendrites. There are dendrites with similar fractal dimension but have dissimilar patterns. At the same fractal dimension, the lacunarity is smaller for more complex and intricately branched dendrites, while the fractal divergent ratio is larger for dendrites with thinner branches. Although the values of both PARIS factor and divergent ratio increase with the increase in the intensity of branching, these parameters cannot be clearly related to the variation in the pattern of dendrites.

Interferometric method for the analysis of dendrite growth and shape in 3D extended patterns in transparent alloys

In the frame of the DECLIC project of the French Space Agency (CNES), a specific device dedicated to the in situ and real time observation of directional solidification of transparent systems in 3D configuration has been developed. A method based on interferometric analysis is presented to quantitatively characterize the shape and growth of dendrites so that measurements of critical parameters such as tip radius and growth rate of individual dendrites belonging to extended patterns are enabled. First results obtained on a succinonitrile − 0.1 wt% camphor alloy are analysed. The accuracy of measurements and quality of the shape reconstruction are discussed through the comparison of the dendrite contours obtained with different modellings of the dendritic shape (parabolic, parabolic corrected by a 4th order term, power-law).

Regulation of the Proteasome by Neuronal Activity and Calcium/Calmodulin-dependent Protein Kinase II

Protein degradation via the ubiquitin proteasome system has been shown to regulate changes in synaptic strength that underlie multiple forms of synaptic plasticity. It is plausible, therefore, that the ubiquitin proteasome system is itself regulated by synaptic activity. By utilizing live-cell imaging strategies we report the rapid and dynamic regulation of the proteasome in hippocampal neurons by synaptic activity. We find that the blockade of action potentials (APs) with tetrodotoxin inhibited the activity of the proteasome, whereas the up-regulation of APs with bicuculline dramatically increased the activity of the proteasome. In addition, the regulation of the proteasome is dependent upon external calcium entry in part through N-methyl-D-aspartate receptors and L-type voltage-gated calcium channels and requires the activity of calcium/calmodulin-dependent protein kinase II (CaMKII). Using in vitro and in vivo assays we find that CaMKII stimulates proteasome activity and directly phosphorylates Rpt6, a subunit of the 19 S (PA700) subcomplex of the 26 S proteasome. Our data provide a novel mechanism whereby CaMKII may regulate the proteasome in neurons to facilitate remodeling of synaptic connections through protein degradation.

Abstracts from the Thirty-first Annual Meeting of the Association for Chemoreception Sciences

Mice and rats use 1,000 olfactory receptor types to probe chemical space. Each glomerulus in the olfactory bulb receives input from a single receptor type, whose ligand binding properties determine the spectrum of odor responses. In this way, the layout of glomeruli on the bulb forms a two-dimensional map of odors. We recorded the odor responses of dorsal glomeruli in mice expressing synaptopHluorin in sensory nerve terminals. By using a chemically diverse battery of several hundred odors, we could assign unique functional identities to several dozen glomeruli. This allowed us to determine that the position of a given glomerulus varies across individuals by only 1 glomerular spacing, corresponding to a precision of 1 part in 1000. We also asked whether the layout of glomeruli is systematically related to their odor sensitivities. The odor response spectra of two neighboring glomeruli were as dissimilar as those of distant glomeruli. This local diversity of odor responses will have important consequences for how mitral cells sample odor space. We have begun to examine this next stage of processing in the bulb by imaging postsynaptic signals in the dendrites of mitral cells in mice expressing the calcium indicator GCaMP2 and multiphoton microscopy. Initial results indicate that the population responses of AChemS Abstracts A13 mitral cell apical tufts are similar to the presynaptic maps constructed from synaptopHluorin mice. We were also able to record robust odor-evoked responses from a large population of individual lateral dendrites, and are currently analyzing their odor tuning.

Large plasticity and tensile necking of Zr-based bulk-metallic-glass-matrix composites synthesized by the Bridgman solidification

The microstructures of the in situ bulk-metallic-glass-matrix composites are usually controlled by changing the alloy compositions. In this paper, Zr-based bulk-metallic-glass-matrix composites containing dendrites with a fixed composition of Zr37.5Ti32.2Nb7.2Cu6.1Be17.0 are synthesized by the Bridgman solidification. The sizes and volume fractions of dendrites in the composites are controlled by adjusting the withdrawal velocities. A linear relationship between the spanning lengths of individual dendrites and the withdrawal velocities is established. Large plasticity and tensile necking can be obtained by only controlling the cooling condition.

In situ and real-time 3-D microtomography investigation of dendritic solidification in an Al–10 wt.% Cu alloy

The microstructural evolution of an Al–10 wt.% Cu alloy was investigated during solidification at constant cooling rate by in situ synchrotron X-ray microtomography with a resolution of 2.8 μm. Solidification of this alloy leads to a coarse dendritic microstructure which was fully characterized in terms of variation with temperature of the solid fraction, the specific surface area of the solid–liquid interface and the local curvatures of the solid phase. By analysing the evolution with solid fraction of individual dendrites, at least two coarsening mechanisms were clearly identified in addition to solidification growth. The first mechanism involves remelting of small secondary dendrite arms to the benefit of bigger adjacent arms. The second is the coalescence of adjacent secondary arms, with progressive filling of the inter-arm spacing and coalescence at the tips. Although this mechanism preferentially occurs at high solid fractions, these results show that the evolution of the dendritic microstructure during solidification is complex and involves the occurrence of various mechanisms operating concurrently. In situ X-ray tomography thus allows revisiting the various models which have been proposed to account for dendrite coarsening during solidification.

A Centrosomal Cdc20-APC Pathway Controls Dendrite Morphogenesis in Postmitotic Neurons

The ubiquitin ligase anaphase-promoting complex (APC) recruits the coactivator Cdc20 to drive mitosis in cycling cells. However, the nonmitotic functions of Cdc20-APC have remained unexplored. We report that Cdc20-APC plays an essential role in dendrite morphogenesis in postmitotic neurons. Knockdown of Cdc20 in cerebellar slices and in postnatal rats in vivo profoundly impairs the formation of granule neuron dendrite arbors in the cerebellar cortex. Remarkably, Cdc20 is enriched at the centrosome in neurons, and the centrosomal localization is critical for Cdc20-dependent dendrite development. We also find that the centrosome-associated protein histone deacetylase 6 (HDAC6) promotes the polyubiquitination of Cdc20, stimulates the activity of centrosomal Cdc20-APC, and drives the differentiation of dendrites. These findings define a postmitotic function for Cdc20-APC in the morphogenesis of dendrites in the mammalian brain. The identification of a centrosomal Cdc20-APC ubiquitin signaling pathway holds important implications for diverse biological processes, including neuronal connectivity and plasticity.

Single Crystalline FeNi3 Dendrites: Large Scale Synthesis, Formation Mechanism, and Magnetic Properties

Single crystalline FeNi3 dendrites were successfully synthesized in high yield by a simple and facile hydrothermal method without the presence of surfactants and were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), selected area electron diffraction (SAED), energy dispersive X-ray spectroscopy (EDX), and vibrating sample magnetometer (VSM). The individual FeNi3 dendrite consists of a long central trunk with secondary, tertiary, and even quaternary branches. On the dendritic hierarchical structures, several leaves with different lengths of 0.2−2.5 μm and widths of 100 nm to 1 μm are connected to the trunk with a length of 1−5 μm. The reaction parameters such as temperature, the reaction time, the concentration of NaOH, and the initial concentration of Fe3+ ions that affected the FeNi3 morphology were investigated systematically, based on which possible formation mechanism for the dendrites was proposed. Compared with FeNi3 particles, FeNi3 dendritic structures exhibited a decreased saturation magnetization (Ms, 61.6 emu/g) but an enhanced coercivity (Hc, 145.6 Oe) due to their peculiar morphology. To our best knowledge, this is the first report on making crystalline metal alloy dendrites with such a full control.

Mapping single-crystal dendritic microstructure and defects in nickel-base superalloys with synchrotron radiation

Solidification of single-crystal nickel-base superalloys introduces large-scale segregation of constituent elements and defects such as dislocations and mosaicity. By exploiting the energy tunability and interference capabilities of high-brilliance X-ray radiation, key structural features of the dendritic single crystals were mapped over large areas. Interference and diffraction of synchrotron X-rays revealed significant misorientations between individual dendrites in the as-solidified state. For the first time this mosaic structure was quantified for an array of dendrites and correlated with the density of “grown-in” dislocations whose density ranged from 10 7 to 10 8 cm −2. Absorption contrast permitted simultaneous mapping of the distribution of refractory metal additives (e.g. rhenium and tungsten), which segregated preferentially to the dendrite cores with a linear composition gradient toward the interdendritic regions. The results demonstrate that synchrotron X-ray imaging is promising for in situ studies of single-crystal structure and defects in nickel-base superalloys.

A study on particle deposition morphology within a constricted tube in the presence and absence of the detachment mechanism

With/without considering the detachment mechanism, the deposition morphology of Brownian and non-Brownian particles within a constricted tube is investigated by applying the Brownian dynamics simulation method in the present paper. Two different geometric structures, the parabolic constricted tube (PCT) and the sinusoidal constricted tube (SCT), are adopted. The effects of various types of the total interaction energy curves of the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory and increasing flow velocity on the particle deposition morphology are also examined. For PCT without considering the detachment mechanism, under the same interaction energy curve, it is found that the number of non-Brownian particles deposited is higher than that of the Brownian particles. Since the deposition location moves closer to the constriction part of the tube, the number of Brownian and non-Brownian particles increases with a decrease in flow velocity. The SCT behaves differently, it is found that the number of non-Brownian particles deposited is only slightly higher than that of Brownian particles. When the detachment mechanism is considered, same results are obtained for those non-Brownian and Brownian particles within a PCT/SCT with the increase of the flow velocity. When comparing with the deposition morphology between PCT and SCT, it is found that a more uniform dendrite of four or five layers can be formed on the tube walls of PCT than that of SCT. Joining of individual dendrites at the blockage stage is not observed for both PCT and SCT in the present simulation.