Quantitative investigation of geometrical axon guidance via PDMS microstructures for small-scale well-defined neural networks.
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1
Institut für Biomedizinische Technik, ETH Zürich, Switzerland
In the search of unveiling the fundamental mechanisms of brain function and brain computation, we believe that the right scale to look at is the small network scale. Indeed, elementary and identifiable computations are performed by only a handful of neurons, for example time-differentiation of signals to detect moving objects, etc. Furthermore, complex behavior can be built from only 300 neurons as shown by the C.Elegans worm, which has some form of memory for up to 48 hours.
Current microelectrode technologies paired with in-vitro neuroscience offer an appealing solution. Indeed, advances in microelectrode arrays allow to probe neural activity with a temporal resolution of tens of microseconds but also with a spatial resolution of tens of micrometers. In order to disentangle the immense complexity and connectedness of neural structures in-vivo, in-vitro neuroscience provides tools to build neural networks from the bottom up in a controlled fashion. This is of paramount importance to eliminate sample-to-sample variance and thus irreproducibility of the experiments.
Microstructures made of Polydimethyilsiloxane (PDMS) provide considerable advantages as a neural network shaping tool over microelectrode arrays. The physical compartmentalization of cell bodies is solved by making holes in a thin PDMS film. In order to form a network, these holes can be connected by tunnels (microchannels) which are less than 10 microns in height to allow only neurites and axons to grow into them. This type of structure has gained interest because of the ability of the microchannel to favor axon growth in a given direction depending on its geometrical shape. However, there hasn't been a thorough investigation and statistical evaluation of the guiding power of such microchannels.
We have investigated 10 different types of microchannels inspired by various axon guiding principles. Large PDMS structures containing various repetitions of a channel type were placed on Wilco Dishes coated with Poly-D-Lysine. Cells were seeded in compartments connected by one type of channel, and we sequentially delivered red and green fluorescent protein encoding adeno-associated viruses in the sequential compartments. This allowed to distinguish axons growing forward from axons growing backward in the channels. Green-Red pairs of compartments were imaged with a Confocal Laser Scanning Microscope (CLSM). We imaged more than 250 such pairs per channel type for each Day In Vitro (DIV) 6, 12 and 18. The images were segmented by training a Deep Convolutional Neural Network. We present a channel shape which provides over 92% forward guidance even after DIV 18. A small scale circular network was built with 4 nodes and connected in an anti-clockwise direction.
Keywords:
PDMS,
Microstructures,
neural networks,
CLSM.,
axon guidance
Conference:
MEA Meeting 2018 | 11th International Meeting on Substrate Integrated Microelectrode Arrays, Reutlingen, Germany, 4 Jul - 6 Jul, 2018.
Presentation Type:
Poster Presentation
Topic:
Neural Networks
Citation:
Forro
C,
Ihle
S,
Weaver
S,
Thompson-Steckel
G,
Voros
J and
Weydert
S
(2019). Quantitative investigation of geometrical axon guidance via PDMS microstructures for small-scale well-defined neural networks..
Conference Abstract:
MEA Meeting 2018 | 11th International Meeting on Substrate Integrated Microelectrode Arrays.
doi: 10.3389/conf.fncel.2018.38.00076
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Received:
18 Mar 2018;
Published Online:
17 Jan 2019.
*
Correspondence:
Mr. Csaba Forro, Institut für Biomedizinische Technik, ETH Zürich, Gloriastrasse, Switzerland, forro@biomed.ee.ethz.ch