[Show abstract][Hide abstract] ABSTRACT: Neuronal differentiation is under the tight control of both biochemical and physical information arising from neighboring cells and micro-environment. Here we wished to assay how external geometrical constraints applied to the cell body and/or the neurites of hippocampal neurons may modulate axonal polarization in vitro. Through the use of a panel of non-specific poly-L-lysine micropatterns, we manipulated the neuronal shape. By applying geometrical constraints on the cell body we provided evidence that centrosome location was not predictive of axonal polarization but rather follows axonal fate. When the geometrical constraints were applied to the neurites trajectories we demonstrated that axonal specification was inhibited by curved lines. Altogether these results indicated that intrinsic mechanical tensions occur during neuritic growth and that maximal tension was developed by the axon and expressed on straight trajectories. The strong inhibitory effect of curved lines on axon specification was further demonstrated by their ability to prevent formation of multiple axons normally induced by cytochalasin or taxol treatments. Finally we provided evidence that microtubules were involved in the tension-mediated axonal polarization, acting as curvature sensors during neuronal differentiation. Thus, biomechanics coupled to physical constraints might be the first level of regulation during neuronal development, primary to biochemical and guidance regulations.
PLoS ONE 03/2012; 7(3):e33623. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An approach is developped to gain control over the polarity of neuronal networks at the cellular level by physically constraining cell development by the use of micropatterns. It is demonstrated that the position and path of individual axons, the cell extension that propagates the neuron output signal, can be chosen with a success rate higher than 85%. This allows the design of small living computational blocks above silicon nanowires.
[Show abstract][Hide abstract] ABSTRACT: Our project is based on the elaboration of in vitro neuron networks as simplified models to explore the relation between neuronal architecture and biological function. Beyond a control of soma and neurite position, our first goal was to achieve in-vitro axonal differentiation of embryonic E18 hippocampal mice neurons by the mean of geometrical growth constraints, i.e. by the use of adhesive micro-patterns on silanized glass substrates. Such a process thus excludes chemical guidance or specific adhesion mechanisms. This study explores two different types of geometrical constraints. The first one, based on the centrosome role and localization, is applied to the soma, and force a choosen neurite to differentiate into an axon with 39% of efficacy (N= 160 cells, 3 different cultures). The second one derives from the suggested relationship between neurite mechanical tension and axonal differentiation, and is based on the design of wavy neurite's shape. Its efficacy reach 0.51% (N= 300 cells, 3 different cultures). The combinaison of these two constraints into a final pattern yields an efficacy of 82% (N= 83 cells, 2 different cultures). These results not only provide an important tool for creating neural model networks but also point out an important role of intrinsic neurite tension during axon differentiation.
[Show abstract][Hide abstract] ABSTRACT: Neural circuit architecture is a fundamental characteristic of the brain, and how architecture is bound to biological functions is still an open question. Some neuronal geometries seen in the retina or the cochlea are intriguing: information is processed in parallel by several entities like in "pooling" networks which have recently drawn the attention of signal processing scientists. These systems indeed exhibit the noise-enhanced processing effect, which is also actively discussed in the neuroscience community at the neuron scale. The aim of our project is to use in-vitro ordered neuron networks as living paradigms to test ideas coming from the computational science. The different technological bolts that have to be solved are enumerated and the first results are presented. A neuron is a polarised cell, with an excitatory axon and a receiving dendritic tree. We present how soma confinement and axon differentiation can be induced by surface functionalization techniques. The recording of large neuron networks, ordered or not, is also detailed and biological signals shown. The main difficulty to access neural noise in the case of weakly connected networks grown on micro electrode arrays is explained. This open the door to a new detection technology suitable for sub-cellular analysis and stimulation, whose development will constitute the next step of this project.
[Show abstract][Hide abstract] ABSTRACT: In this study we compare the neural activity of a population of neurons recorded with a MEA to simulations of equivalent networks obtained on a computer when bicuculline, an antagonist of inhibitory connections, is introduced into the nutritive solution. The aim of this study is to obtain a model producing extra-cellular data that match the synchronicity of two different real networks: a cell culture and an oraganotypic hippocampus slice. A one compartment model of neuron and a neuron-electrode model are used to simulate experiments. Parameters of the models are fitted to match in vivo data. It is shown that the variation of the noise level at the synaptic level induces a variation in the period of the bursting effect of bicuculline and produces variation in amplitude of the recorded signal.
[Show abstract][Hide abstract] ABSTRACT: Neuronal differentiation is under the tight control of biochemical and physical information arising from micro-environment. Here, through a panel of poly-L-lysine micropatterns, we wished to assay how external geometrical constraints of neurons may modulate axonal polarization. Constraints applied to either the cell body or to the neurite directions revealed the existence of a differential mechanical tension between the nascent axon and other neurites. Also, we show that centrosome location is not predictive of axonal polarization but responds to the force exerted by the nascent axon. Using curved trajectories for neurite growth inhibited axonal differentiation and prevented formation of multiple axons normally induced by cytochalasin or taxol treatments. Finally we provide evidence that microtubules act as curvature sensors during neuronal differentiation. Thus, biomechanics coupled to physical constraints might be the first level of regulation during neuronal development, primary to biochemical and guidance regulations.
[Show abstract][Hide abstract] ABSTRACT: When bicuculline an antagonist of inhibitory connections is introduced in the nutritive solution of an in vivo preparation containing neural networks, a synchronous activity of the neural network is observed. Observation of this activity with micro electrodes arrays presents signals containing periodic bursts of activity. The aim of this study is to obtain the same behavior with simulations. Models of excitatory neural networks coupled to models of measures with micro electrode are tested and the parameters are adjusted. It is shown that the level of noise on synaptic transmission triggers a periodic bursting activity of the neural network like the one observed in experimental conditions. Introduction of delays and durations for the synaptic transmission, and adjustments of the parameters enable to obtain different patterns of bursting.