We would like to thank Yoichi Miyahara for many helpful discussions and insights. MA and PG acknowledge funding from NSERC.

All procedures detailed below were approved by McGill University&#39;s Animal Care Committee and conformed to the guidelines of the Canadian Council of Animal Care.
1. Standardization of Neuronal Cultures Using Microfluidic Devices: Device Assembly
<ol>
	<li>Select a suitable microfluidic device for the desired experiment. To connect neurons within the same population, use the Neuro Devices (Figure 1) and to connect neurons in different populations use the Co-Cu...

<ol>
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The author Margaret H Magdesian is the CEO of Ananda Devices that produces instruments used in this Article.

Using standard micromanipulation and innovative microfluidic devices, a new technique was developed to rapidly initiate, elongate and precisely connect new functional neuronal circuits over large distances. Pipette micromanipulation is a common tool in most neuroscience labs4,13. The real challenge to achieving reproducible and reliable results was standardization of healthy, precisely positioned neuronal cultures for the duration of the experiment (which can be ...

Injuries to the adult central nervous system (CNS) may lead to permanent disability due to multiple mechanisms that limit axonal regrowth1. Following injury, many CNS axons do not form a new growth cone and fail to mount an effective regenerative response2. Furthermore, damage and scar tissue surrounding CNS lesions significantly inhibit axonal growth1,2,3. Current therapies to promote CNS regeneration after injury have focused on enhancing the intrinsic growth potential of the injured neuron and on masking the inhibitors of axonal extension associated with myelin debris and the glial scar1,3. Despite this, the capacity to regenerate long axons to distant targets and to form appropriate functional synapses remains severely limited4,5,6,7.
In the present work, microbeads, pipette micromanipulation, and microfluidic devices are used to rapidly initiate, elongate, and precisely connect new functional neuronal circuits over long distances. Previous work has shown that poly-D-lysine-coated beads (PDL-beads) induce membrane adhesion followed by the clustering of synaptic vesicle complexes and the formation of functional presynaptic boutons8. It was also shown that when the PDL-bead is mechanically pulled away after presynaptic differentiation, the synaptic protein cluster follows the bead, initiating a new neurite9. The following procedure exploits this fact along with the ability to culture embryonic hippocampal neurons of rats into organized regions on a coverslip using polydimethylsiloxane (PDMS) microfluidic devices to precisely rewire a neuronal circuit.
These PDMS microfluidic devices are non-toxic, optically transparent and consist of two chambers connected by a system of microchannels. Once assembled on a coverslip, each device serves as a mold to guide neuronal growth and maintain healthy neuronal cultures on precise patterns for longer than 4 weeks in vitro.
Here, a framework is presented in which to investigate the limits of extension and functionality of the new neurite. New, functional neurites are created and positioned to controllably (re)wire neuronal networks. The extension rates achieved are faster than 20 &#181;m/min over millimeter-scale distances and functional connections are established. These results show, unexpectedly, that the intrinsic capacity of these neurites for elongation is much faster than previously thought. This proposed mechanical approach bypasses slow chemical strategies and enables controlled connection to a specific target. This technique opens new avenues for the in vitro study of novel therapies to restore neuronal connectivity after injury. It also enables the manipulation and rewiring of neuronal networks to investigate fundamental aspects of neuronal signal processing and neuronal function in vitro.

<table border="0" cellpadding="0" cellspacing="0" width="836">
	<tbody>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">Co-culture devices</td>
			<td style="width:104px;">Ananda Devices</td>
			<td style="width:119px;"></td>
			<td style="width:397px;">Commercially available at http://www.anandadevices.com</td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">Neuro devices</td>
			<td style="width:104px;">Ananda Devices</td>
			<td style="width:119px;"></td>
			<td>Commercially available at http://www.anandadevices.com</td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">No. 1 Glass Coverslip 25 mm Round</td>
			<td style="width:104px;">Warner Instruments</td>
			<td style="width:119px;">64-0705</td>
			<td></td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">35mm Glass Bottom Dishes #0, Uncoated, Gamma-Irradiated</td>
			<td style="width:104px;">MatTex Incorporation</td>
			<td style="width:119px;">P35G-0-20-C</td>
			<td></td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">35mm cell culture dish, Non-Pyrogenic, Sterile</td>
			<td style="width:104px;">Corning Inc</td>
			<td style="width:119px;">430165</td>
			<td></td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">95mmx15mm Petri Dish, Slippable Lid, Sterile Polystyrene</td>
			<td style="width:104px;">Fisherbrand</td>
			<td>FB0875714G</td>
			<td></td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">50mL Centrifuge tubes with printed graduations and flat caps</td>
			<td style="width:104px;">VWR</td>
			<td style="width:119px;">89039-656</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">15mL Polypropylene Conical Tube, 17x120mm style, Non Pyrogenic, Sterile</td>
			<td>Falcon</td>
			<td>352097</td>
			<td></td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">Neurobasal Medium</td>
			<td style="width:104px;">Life Technologies</td>
			<td style="width:119px;">21103-049</td>
			<td>Extracellular solution</td>
		</tr>
		<tr height="81">
			<td height="81" style="height:81px;width:216px;">B-27 Supplement (50X), serum free</td>
			<td style="width:104px;">B-27 Supplement (50X), serum free</td>
			<td style="width:119px;">17504044</td>
			<td>Extracellular solution</td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">Pennicilin, Streptomyocin, Glutamine</td>
			<td style="width:104px;">Thermo Fisher Scientific&#160;</td>
			<td>11995-065</td>
			<td>Extracellular solution</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">200uL Pipettors</td>
			<td style="width:104px;">VWR</td>
			<td>89079-458</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:216px;">2-20uL Pipettors</td>
			<td style="width:104px;">Aerosol Resistant Tips</td>
			<td style="width:119px;">2149P</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">BD Falcon 3mL Transfer Pipettes [Non-sterile]</td>
			<td>BD Falcon</td>
			<td>357524</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Glucose</td>
			<td style="width:104px;">Gibco</td>
			<td style="width:119px;">15023-021</td>
			<td>Extracellular solution</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">HEPES</td>
			<td style="width:104px;">Sigma</td>
			<td style="width:119px;">7365-45-9</td>
			<td>Extracellular solution/Beads</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">NaCl</td>
			<td style="width:104px;">Sigma-Aldrich</td>
			<td style="width:119px;">7647-14-5</td>
			<td>Extracellular solution</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">KCl</td>
			<td style="width:104px;">Sigma-Aldrich</td>
			<td style="width:119px;">7447-40-7</td>
			<td>Extracellular solution</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">CaCl2</td>
			<td style="width:104px;">Sigma-Aldrich</td>
			<td style="width:119px;">10043-52-4</td>
			<td>Extracellular solution</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">MgCl2</td>
			<td style="width:104px;">Sigma-Aldrich</td>
			<td style="width:119px;">7786-30-3</td>
			<td>Extracellular solution</td>
		</tr>
		<tr height="61">
			<td height="61" style="height:61px;width:216px;">#5 Dumont Dumostar Tweezers 11cm</td>
			<td style="width:104px;">World Precision Instruments</td>
			<td>500233</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Dissection tools</td>
			<td>Braun, Aesculap</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Poly-D-lysine Hydrobromide</td>
			<td>Sigma-Aldrich</td>
			<td>P6407</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:216px;">Micro particles based on polystyrene, 10 um</td>
			<td style="width:104px;">Sigma-Aldrich</td>
			<td style="width:119px;">72986</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:216px;">Borosilicate tubes</td>
			<td style="width:104px;">King Precision Glass, Inc.</td>
			<td style="width:119px;">14696-2</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:216px;">Horizontal Pipette Puller</td>
			<td style="width:104px;">Sutter Instruments</td>
			<td style="width:119px;">Brown-Flaming P-97</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:216px;">Micromanipulators, PCS-5000 Series</td>
			<td style="width:104px;">SD Instruments</td>
			<td style="width:119px;">MC7600R</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">1 ml Syringe</td>
			<td style="width:104px;">BD Luer-Lok</td>
			<td>309628</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Inverted Microscope</td>
			<td style="width:104px;">Olympus&#160;</td>
			<td style="width:119px;">IX71</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:216px;">Objective</td>
			<td style="width:104px;">Olympus</td>
			<td style="width:119px;">UIS2, LUCPLFLN 40X</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">CCD Camera</td>
			<td style="width:104px;">Photometrics</td>
			<td style="width:119px;">Cascade II: 512</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Leibovitz&#39;s (1x) L-15 Medium</td>
			<td>Life Technologies</td>
			<td>11415-064</td>
			<td>Rat Dissection</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Typsin-EDTA (0.05%), Phenol red</td>
			<td>Life Technologies</td>
			<td>25300054</td>
			<td>Rat Dissection</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">DMEM (1x) Dulbecco&#39;s Modified Eagle Medium [+4.5 g/L D-Glucose, + L-Glutamine, + 110 mg/L Sodium Pyruvate]</td>
			<td>Life Technologies</td>
			<td>11995-065</td>
			<td>Rat Dissection</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">HBSS (1x) Hank&#39;s Balanced Salt Solution [- Calcium Chloride, - Magnesium Chloride, - Magnesium Sulfate]</td>
			<td>Life Technologies</td>
			<td>14170-112</td>
			<td>Rat Dissection</td>
		</tr>
	</tbody>
</table>

rewiring neuronal circuits: a new method for fast neurite extension and functional neuronal connection

Brain and spinal cord injury may lead to permanent disability and death because it is still not possible to regenerate neurons over long distances and accurately reconnect them with an appropriate target. Here a procedure is described to rapidly initiate, elongate, and precisely connect new functional neuronal circuits over long distances. The extension rates achieved reach over 1.2 mm/h, 30-60 times faster than the in vivo rates of the fastest growing axons from the peripheral nervous system (0.02 to 0.04 mm/h)28 and 10 times faster than previously reported for the same neuronal type at an earlier stage of development4. First, isolated populations of rat hippocampal neurons are grown for 2-3 weeks in microfluidic devices to precisely position the cells, enabling easy micromanipulation and experimental reproducibility. Next, beads coated with poly-D-lysine (PDL) are placed on neurites to form adhesive contacts and pipette micromanipulation is used to move the resulting bead-neurite complex. As the bead is moved, it pulls out a new neurite that can be extended over hundreds of micrometers and functionally connected to a target cell in less than 1 h. This process enables experimental reproducibility and ease of manipulation while bypassing slower chemical strategies to induce neurite growth. Preliminary measurements presented here demonstrate a neuronal growth rate far exceeding physiological ones. Combining these innovations allows for the precise establishment of neuronal networks in culture with an unprecedented degree of control. It is a novel method that opens the door to a plethora of information and insights into signal transmission and communication within the neuronal network as well as being a playground in which to explore the limits of neuronal growth. The potential applications and experiments are widespread with direct implications for therapies that aim to reconnect neuronal circuits after trauma or in neurodegenerative diseases.

Embryonic rat hippocampal neurons are cultured in microfluidic devices to enable precise positioning of cells, PDL-beads and micromanipulators. The first step is to properly assemble the microfluidic device on a glass coverslip or dish. It is essential that the microfluidic device be well attached to the substrate to avoid cells exiting the chambers and moving under the parts of the device that should be sealed (Figure 1a). To maintain healthy cultures for se...

Watch this Scientific Journal Video about Rewiring Neuronal Circuits: A New Method for Fast Neurite Extension and Functional Neuronal Connection at JoVE.com

Rewiring Neuronal Circuits: A New Method for Fast Neurite Extension and Functional Neuronal Connection

This procedure describes how to rapidly initiate, extend and connect neurites organized in microfluidic chambers using poly-D-lysine-coated beads fixed to micropipettes that guide neurite elongation.

Brain and spinal cord injury may lead to permanent disability and death because it is still not possible to regenerate neurons over long distances and ...

The overall goal of this procedure is to initiate new neurites, rapidly extend them, and precisely connect them to target cells. This procedure is only possible by using cells grown in a controlled and reproducible environment. This method allows us to answer key questions in neuroscience.What limits the growth rate of neurons? How fast can they grow? Do mechanical clues play a role?We can also study how synapses are formed, how do neurons find a target cell? How do synapses age, mature? And thirdly, we can start building systematically neural networks, study how neurons compute.The main advantages of this technique are that it enables easy manipulation, experimental reproducibility, and ultimately a high degree of control at the single-cell level. To begin this procedure, clean and prepare the desired number of sterile cover slips. Next, coat each cover slip with 0.5 to 1 milliliters of 100 microgram per milliliter PDL for at least two hours at room temperature.After that, wash the cover slips twice with water and remove all the liquid. Let them dry in a sterile environment for 5 to 10 minutes or until the surface is completely dry. Then, place the microfluidic devices with the patterns facing up under the UV light in a biosafety cabinet for 10 minutes.After 10 minutes, place a microfluidic device with the pattern facing down in contact with the clean cover slip. Use the tweezers to softly press the device so it adheres to the glass. To fill the single population device with medium, add 50 microliters of complete cell medium to the right upper well.And then add another 50 microliters of complete cell medium to the well diagonal to it. To fill the multiple populations device with medium, add 30 microliters of complete NBM to one row of wells. Make sure the medium flows between the wells.Then, add 50 microliters of medium to each of the remaining wells. Place the devices in a bigger plate with an open dish of autoclaved water, and place the dish in the incubator for one to two hours while preparing the cell culture. Now, remove the medium from the upper wells of the microfluidic devices without emptying the wells.Then, add 20 microliters of the concentrated cell solution into the top right well of the microfluidic device, and check in the microscope how cells flow inside the single population microfluidic device. To plate cells in the multiple populations device, add 20 microliters of the concentrated cell solution into each of the top wells. Under the microscope, check if the cells are inside the chambers.Afterwards, place the devices in the incubator for 15 to 30 minutes to promote cell attachment to the substrate. After the cells attach to the substrate, add 40 microliters of NBM to the two top wells of the single population device. This will help remove the air bubbles from the micro channels.Add 20 microliters of MBM to the top wells of the multiple populations device, the same wells where the cells were injected. The media should protrude slightly to form a positive meniscus, and give the wells a muffin top aspect. One to two days before the microfluidic device's removal, add two milliliters of pre-warmed NBM to each sample dish and flood the chambers.Then, keep the devices in the incubator. Subsequently, use sterile tweezers and a pipette tip to remove the microfluidic devices from the cover slips leaving a patterned configuration of neurons. In this procedure, and 40 to 60 microliters of the prepared PDL coated beads to the cell culture.Then, return the sample to the incubator for one hour to promote the formation of synaptic contacts. Subsequently, install the sample in an experimental setup such that the cells can be assessed from above by two micropipettes, and also be accessed optically. In this configuration, a CCD camera is located on the side port of the microscope for image capture.Connect each pipette filled with saline to a one milliliter syringe, then perfuse the sample with physiological saline solution. Next, under the microscope, check the gap between the two isolated neuronal populations to insure that the two populations are not naturally connected. Select a PDL bead that is not attached to the neuron in the field of view.Align the bead with a micropipette tip by focusing on the bead and then on the micropipette. Subsequently, bring the tip as close as possible to the bead by monitoring it through the microscope. Then, apply negative pressure to the pipette to pick up the bead, and maintain the negative pressure throughout the experiment.Now, select a PDL bead attached to a neuron in the field of view, and attach it to the second micropipette using suction. Pull the PDL bead neuron complex by slowly moving either the micromanipulator or the sample stage at 0.5 micrometers per minute for 1 micrometer, and pause for five minutes to allow neurite initiation. Pull the PDL bead neuron complex by slowly moving it laterally at 0.5 micrometers per minute over two micrometers, then pause for five minutes to allow neurite elongation.After successful initiation and neurite extension for the first five micrometers, continuously pull the neurite at 20 micrometers per minute. To connect the neurons, select a region rich in neurites. Use other beads to gauge the pipette tip height above the cover slip, and lower the PDL bead neurite complex so that it physically contacts the neurites.Leave the PDL bead neurite complex in contact with the target neurite while manipulating the second micropipette. Then, lower the second pipette with the second PDL bead on top of the newly formed neurite about 20 micrometers from the first bead, and use the second PDL bead to push the new neurite filament towards the target cell. Next, hold both beads in place for at least one hour.Verify the absence of focal swelling, a thickening of the neurites contacting the bead, with the microscope. During this time, slowly change the medium of the sample from physiological saline to pre-warmed carbon dioxide equilibrated NBM. Release the bead from the second pipette by releasing the suction.If the new neurite remains attached, release the first bead as well. Afterward, carefully place the sample back in the incubator to strengthen the neuronal connection for future experiments. You can use whole cell patch clamp recordings to investigate the electrical functionality of the micromanipulated connection.Shown here are the isolated neuronal populations separated by a 100 micrometer gap in PDMS microdevices. Pair to patch clamp recordings were performed in whole-cell configuration, and the mechanically induced connections were analyzed, and compared with those in naturally connected neuronal populations, and non-connected populations. The electrical responses after pre-synaptic action potential recorded from the neurons connected naturally and by micromanipulation are significantly higher and temporarily correlate with the pre-synaptic activity.Once mastered, this technique can be performed in eight hours if done properly, and while attempting this procedure, it is important to remember to have healthy and well-patterned long term cell cultures to guarantee fast and reproducible results. Following this procedure different methods can be used to verify the electrical functionality of the micromanipulated connection. After watching this video, you should have a good understanding of how to grow cell populations in microfluidic chambers, and use pipette manipulations to initiate, extend, and connect neurites.

rewiring-neuronal-circuits-new-method-for-fast-neurite-extension

Research

JoVE Journal

Neuroscience

8.7K Views.  McGill University. The overall goal of this procedure is to initiate new neurites, rapidly extend them, and precisely connect them to target cells. This procedure is only possible by using cells grown in a controlled and reproducible environment. This method allows us to answer key questions in neuroscience.What limits the growth rate of neurons? How fast can they grow? Do mechanical clues play a role?We can also study how synapses are formed, how do neurons find a target cell? How do synapses age...