Name: using an adapted microfluidic olfactory chip for the imaging of neuronal activity in response to pheromones in male c. elegans head neurons
Uploaded: 2017-09-07T14:00:00
Description: Watch this Scientific Journal Video about Using an Adapted Microfluidic Olfactory Chip for the Imaging of Neuronal Activity in Response to Pheromones in Male C. Elegans Head Neurons at JoVE.com

We would like to thank Manuel Zimmer for providing us with the initial design file that was adapted for use with males; Frank Schroeder for the synthesis and supply of ascr#3; Ross Lagoy for the insight and assistance with imaging and analysis; and Laura Aurilio for the master fabrication and who, alongside Christopher Chute, contributed to the review of this manuscript. Funding for this work was provided under the National Institutes of Health grant 1R01DC016058-01 (J.S.), the National Science Foundation grant CBET 1605679 (D.R.A.), and the Burroughs Wellcome Career Award at the Scientific Interface (D.R.A.).

1. Device Fabrication
NOTE: See reference1.
NOTE: Silicon master molds were fabricated using standard photolithographic techniques for patterning SU-8 photoresist on a silicon master1,7. Photomasks for wafer patterning were printed at 25,000 dpi. The male-adapted device features a Chronis Olfactory Chip design19 with a change in the worm loading port, adapting a ...

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The male-adapted olfactory chip incorporates a turn into a narrower loading port, which allows for more control of the orientation and for the efficient trapping of male C. elegans. This allows for the visualization of both the left and right members of neuronal bilateral pairs, without the need for z-stacking. This curve leads to an orientation away from vertical 100% of the time in worms where only one bilateral pair is targeted with a fluorescent marker, such as ASH (Figure 2D<st...

Microfluidic devices provide increased access to precisely controlled environments, wherein animals, such as the nematode C. elegans, can be experimentally manipulated1. These studies include behavioral assays, calcium imaging studies, or even screenings for specific phenotypes, resulting in more exact measurements of experimental outcomes1,2,3,4,5,6. Microfluidics provide small-scale liquid conditions through which detailed experiments can be run while utilizing minimal amounts of reagents. There is a constant production of new microfluidic device designs, and the use of each varies, from arenas that allow for the natural sinusoidal motion of C. elegans in behavioral assays and neural imaging studies, to trap devices used in neural imaging and olfactory studies, to devices that allow for high-throughput phenotypic analysis in genetic screens4,5,6,7. Following the fabrication of a master mold, microfluidic devices are inexpensive to construct&#8212;given the reusability of the master&#8212;and easy to use, allowing for rapid data generation via high-throughput studies. The fabrication of devices using polymers such as polydimethylsiloxane (PDMS) allows for the creation of new devices within hours.
Calcium imaging studies use genetically encoded calcium indicators (GECIs) expressed in target cells to measure the neural dynamics of those cells in real time8,9,10,11. The transparent nature of C. elegans allows for the recording of the fluorescent levels of these proteins in live animals. Traditionally, GECIs rely on the green fluorescent protein (GFP)-based sensor GFP-Calmodulin-M13 Peptide (GCaMP), although more recent studies have adapted these sensors to allow for better signal-to-noise ratios and red-shifted excitation profiles. Following the development of GCaMP3, proteins with these specifications have varied, including sensors such as GCaMP6s and GCaMP6f (slow and fast fluorescence off-rates, respectively), as well as RFP-Calmodulin-M13 Peptide (RCaMP), which has a red-shifted activation profile. The combination of these GECIs with C. elegans cell-specific gene promoter sequences can target cells of interest, particularly sensory neurons12,13,14,15,16.
While the ease of C. elegans use in microfluidic studies is apparent, almost all studies have focused on hermaphrodites. Despite males only accounting for 0.01-0.02% of the wild type population, invaluable findings can arise from their characterization. While the physical connectome of the hermaphrodite nervous system has been fully mapped for decades17, the male connectome remains incomplete, especially in the head region of the animal18. The use of calcium imaging in males will help to generate an understanding of the male nervous system and the differences that arise between the two sexes. The smaller size of C. elegans adult males prevents effective and reliable trapping in the loading ports of traditional olfactory devices designed for larger hermaphrodites. To address this, a modified version of the Chronis Olfactory Chip19 was developed with a narrower loading port, a lower channel height, and turns in the worm loading port (which rotate the animal), allowing for the visualization of bilateral left/right neuronal pairs. This design permits: (1) the effective trapping of young adult males, (2) a more reliable orientation of the animal for the visualization of both members of bilateral paired neurons, and (3) the precise imaging of neural activity in male neurons.
Increasingly, studies show that C. elegans males respond differently than hermaphrodites to a variety of ascarosides (ascr), or nematode pheromones20,21,22,23,24. Therefore, developing an understanding of the neural dynamics and representations within the male connectome has become even more pertinent. Male C. elegans contain 87 sex-specific neurons not present in the hermaphrodite25,26, altering the connectome in as-yet undetermined ways. Being able to image these unique neural dynamics will allow us to better understand sex-specific responses and neural representations.
This protocol describes the use of a male-adapted olfactory chip for the neural imaging of male C. elegans chemosensation. The nociceptive neuron ASH responds reliably to 1 M glycerol in males, consistent with previous hermaphroditic studies27. Exposure to ascarosides may elicit responses that are variable from animal to animal, requiring a larger number of animals to be tested. The response of the male-specific CEM neurons has previously been shown, through both electrophysiology and calcium imaging studies, to respond variably to ascaroside #323.

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			<td>302832</td>
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			<td style="width:205px;">420250000</td>
			<td>24 cm inner diameter.</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:527px;height:21px;">Weigh Boats</td>
			<td>Cole-Palmer</td>
			<td style="width:205px;">EW-01017-27</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:527px;height:21px;">Classic Plus Balance</td>
			<td>Mettler Toledo</td>
			<td style="width:205px;">PB1501-S/FACT</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:527px;height:21px;">Glass Pasteur Pipettes</td>
			<td>Cole-Palmer</td>
			<td style="width:205px;">EW-25554-06</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:527px;height:21px;">Transfer pipettes</td>
			<td>Genesee Scientific</td>
			<td style="width:205px;">30-202</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:527px;height:21px;">Oven</td>
			<td>Sheldon Manufacturing Inc</td>
			<td style="width:205px;">9120993</td>
			<td>Model Number: 1500E.</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:527px;height:21px;">60 mm, non-vented, sharp edge Petri dishes</td>
			<td>TriTech Research</td>
			<td>T3308</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:527px;height:21px;">Zeiss Axio Observer.A1</td>
			<td>Zeiss</td>
			<td style="width:205px;">-</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:527px;height:21px;">Hammamatsu Orca Flash 4.0 Digital CMOS</td>
			<td>Hammamatsu</td>
			<td style="width:205px;">C11440-22CU</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:527px;height:21px;">Blue Fluorescent Light</td>
			<td>Lumencor</td>
			<td style="width:205px;">SOLA SM6-LCR-SA</td>
			<td>24-30V/7.9A DC.</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:527px;height:21px;">Illumination Adaptor</td>
			<td>Zeiss</td>
			<td style="width:205px;">423302-0000</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:527px;height:21px;">Series 1 and 2 Miniature Inert PTFE Isolation Valve</td>
			<td>Parker</td>
			<td style="width:205px;">001-0017-900</td>
			<td>3-way valve for controlling flow.</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:527px;height:21px;">ValveLink8.2&#174;</td>
			<td>AutoMate Scientific</td>
			<td style="width:205px;">01-18</td>
			<td>Flow Switch Controller</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:527px;height:21px;">Micro Manager</td>
			<td>Micro-Manager</td>
			<td style="width:205px;">-</td>
			<td>Free software, can be downloaded at: https://www.micro-manager.org/wiki/Download_Micro-Manager_Latest_Release</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:527px;height:21px;">ImageJ</td>
			<td>ImageJ</td>
			<td style="width:205px;">-</td>
			<td>Free software, can be downloaded at: https://imagej.nih.gov/ij/download.html</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:527px;height:21px;">Agar, Bacteriological Grade</td>
			<td>Apex</td>
			<td>9012-36-6</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:527px;height:21px;">Peptone</td>
			<td>Apex</td>
			<td>20-260</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="width:527px;height:25px;">CaCl2</td>
			<td>VWR</td>
			<td>BDH0224-1KG</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="width:527px;height:25px;">MgSO4</td>
			<td>Sigma-Aldrich</td>
			<td>230391-1kg</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:527px;height:21px;">Cholesterol</td>
			<td>Alfa Aesar</td>
			<td>A11470</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:527px;height:21px;">Ethanol</td>
			<td>Sigma-Aldrich</td>
			<td>270741-4L</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:527px;height:21px;">Tetramisole</td>
			<td>Sigma-Aldrich</td>
			<td style="width:205px;">L9756-10(G)</td>
			<td>Store at 4 &#176;C.</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:527px;height:21px;">Fluorescein</td>
			<td>Sigma-Aldrich</td>
			<td style="width:205px;">FD2000S-250mg</td>
			<td>Light Sensitive. Store in photoprotective vials.</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:527px;height:21px;">Glycerol</td>
			<td>Sigma-Aldrich</td>
			<td style="width:205px;">G6279-1L</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:527px;height:21px;">Ascaroside #3</td>
			<td>-</td>
			<td style="width:205px;">-</td>
			<td>Synthesized in the Schroeder Lab (Cornell University).</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:527px;height:21px;">NaCl</td>
			<td>Genesee Scientific</td>
			<td style="width:205px;">18-215</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="width:527px;height:25px;">KH2PO4</td>
			<td>BDH</td>
			<td>BDH9268.25</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="width:527px;height:25px;">K2HPO4</td>
			<td>J.T. Baker</td>
			<td>3252-025</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:527px;height:21px;">ASH GCaMP3 line</td>
			<td>-</td>
			<td style="width:205px;">-</td>
			<td>CX10979 (KyEx2865 [psra-6::GCAMP3 @ 100 ng/uL]). Developed in Bargmann lab. Provided from Albrecht Lab library.</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:527px;height:21px;">CEM GCaMP6 line</td>
			<td>-</td>
			<td style="width:205px;">-</td>
			<td>JSR49 (FkEx98[ppkd-2::GCaMP::SL2::dsRED + pBX-1]; pha-1(e2123ts); him-5(e1490); lite-1(ce314)). Developed by Robyn Lints. Provided from Srinivasan Lab library.</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:527px;height:21px;">E. coli (OP50)</td>
			<td>Caenorhabditis Genetics Center</td>
			<td>OP50</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:527px;height:21px;">&#34;Reservoir&#34;</td>
			<td>-</td>
			<td>-</td>
			<td style="width:1260px;">To create a Reservoir: A &#34;30 mL syringe&#34;, is connected to a &#34;Stopcock with Luer connections; 3-way; male lock; 5 flow pattern; non-sterile&#34;, which is connected to a &#34;3 mL syringe&#34; and a &#34;Stainless Steel Blunt Needle 23 Gauge, Polyprolylene Luer&#34;. The &#34;Stainless Steel Blunt Needle 23 Gauge, Polyprolylene Luer&#34; is then inserted into &#34;Soft Tubing&#34; approximately 1/3 of the way down the needle.</td>
		</tr>
	</tbody>
</table>

using an adapted microfluidic olfactory chip for the imaging of neuronal activity in response to pheromones in male c. elegans head neurons

The use of calcium indicators has greatly enhanced our understanding of neural dynamics and regulation. The nematode Caenorhabditis elegans, with its completely mapped nervous system and transparent anatomy, presents an ideal model for understanding real-time neural dynamics using calcium indicators. In combination with microfluidic technologies and experimental designs, calcium-imaging studies using these indicators are performed in both free-moving and trapped animals. However, most previous studies utilizing trapping devices, such as the olfactory chip described in Chronis et al., have devices designed for use in the more common hermaphrodite, as the less common male is both morphologically and structurally dissimilar. An adapted olfactory chip was designed and fabricated for increased efficiency in male neuronal imaging with using young adult animals. A turn was incorporated into the worm loading port to rotate the animals and to allow for the separation of the individual neurons within a bilateral pair in 2D imaging. Worms are exposed to a controlled flow of odorant within the microfluidic device, as described in previous hermaphrodite studies. Calcium transients are then analyzed using the open-source software ImageJ. The procedure described herein should allow for an increased amount of male-based C. elegans calcium imaging studies, deepening our understanding of the mechanisms of sex-specific neuronal signaling.

An example of the overall device setup can be seen in Figure 1A-B. Figure 1A depicts the proper reservoir construction and setup. Figure 1B shows the connections of the reservoirs to the microfluidic device. Figure 1C depicts a microfluidic device with individual ports labeled for clarity.
The ...

Watch this Scientific Journal Video about Using an Adapted Microfluidic Olfactory Chip for the Imaging of Neuronal Activity in Response to Pheromones in Male C. Elegans Head Neurons at JoVE.com

Using an Adapted Microfluidic Olfactory Chip for the Imaging of Neuronal Activity in Response to Pheromones in Male C. Elegans Head Neurons

The use of an adapted &#34;olfactory chip&#34; for the efficient calcium imaging of C. elegans males is described here. Studies of male exposure to glycerol and a pheromone are also shown.

Using an Adapted Microfluidic Olfactory Chip for the Imaging of Neuronal Activity in Response to Pheromones in Male C. Elegans Head Neurons

The use of calcium indicators has greatly enhanced our understanding of neural dynamics and regulation. The nematode Caenorhabditis elegans, with its ...

The overall goal of this procedure is to efficiently trap an image calcium transience in male C.Elegans head neurons upon exposure to pheromones. This method can help answer key questions in the neurobiology field, such as understanding sex specific neural circuit regulation. The main advantage of this technique, is that male C.Elegans can now be imaged efficiently in a micro-fluidic trap device.Generally, individuals new to this method will struggle because loading animals can be difficult at first and biogenic pheromones don't elicit calcium transience in every animal. To begin assembly of the reservoirs, prepare three sets of tubing by inserting a needle into one end and a metal tube into the other. Then, for each reservoir, take a three way luer valve and attach a 30 milliliter syringe with its plunger removed, a three milliliter syringe and the tubing.Fill each reservoir with the appropriate buffer, either stimulus S basal or S basal containing fluorescin. Then, remove any air bubbles from both the reservoir and tubing, by flicking and pumping the syringe. Now, fill a new three milliliter syringe and tubing with S basal and insert into the outlet port of the micro-fluidic device.Gently apply a little pressure to the syringe until the buffer appears at the surface of the inlet holes. Next, connect the flow control, buffer and stimulus reservoir tubes to their appropriate inlet holes, ensuring that liquid drops are present on both the loading port hole and the tubing to be attached. Now, gently apply a little more pressure to the syringe until droplets appear in the worm loading port inlet, then insert a solid blocking pin into that port.Next, remove the syringe from the outlet port and attach an outlet line connected to the house of vacuum. Now, inspect the device for any bubbles in the float channels in the video feed from the microscope. Click on live, to observe the live image and wait for bubbles to naturally dissipate before proceeding.Next, turn on the fluorescent light source and use a GFP filter to confirm proper flow dynamics. Actuate the three wave valve and observe the fluorescent control stream appear in the video feed, when the valve is open. To begin, pick one worm onto an unseeded NGM agar plate and allow the worm to crawl away.Then, float the plate with S basal. Draw up solution containing the worm into the syringe. Now, on the device, turn off the vacuum to stop the flow using the outlet luer valve.Then, remove the solid pin that blocks the worm loading port. Insert the tubing containing worms into the loading port. Open the outlet luer valve and observe the live video feed.Now, apply gentle pressure onto the syringe until the worm appears. Pull the worm back if it enters tail first, it must go in head first to be exposed to the stimulus. The user must pull the worm back before the tail fully enters the channel, otherwise, getting the worm out of the channel is extremely difficult and usually requires flushing the worm completely through the channel and loading a new worm.Now, using pressure from the syringe, advance the worm through the channel and position the worm's head, so it is exposed to the buffer flow but not so far into the channel, that it is free to move about. A small amount of axial or rotational movement is expected in non-paralyzed animals. Although the addition of a paralytic to the buffers nearly eliminates this effect.To decrease the likelihood of movement during trial, use older males which are more efficiently trapped, decrease the width or thickness of the worm loading port or increase the amount of time spent in the paralytic. Use the software to make recordings using blue light excitation. Set the exposure to 100 milliseconds, open the image acquisition window, set the time points to 300 with an interval at zero, then start the image acquisition.After five seconds, apply the stimulus by changing the three way valve controlling the buffers. A 10 second stimulation is a good starting point and the length of stimulus can be adjusted as needed. After the stimulation, switch the flow back by pressing the button again and continue recording until the 30 second video is completed.This allows the g camp fluorescence to return to base line. Now, let the preparation rest for 30 seconds before the next trial. Worms expressing g camp three in the no susceptive neuron, ASH, respond to one molar glycerol with visible changes in fluorescence within the ASH neuron, indicative of neural activity.The neuron should remain in the area of analysis for the entire video, otherwise a movement artifact may occur. If so, move the analysis area for those time points and merge the intensity values to create a single trace. Males who are stimulated with the attractive biogenic pheromone ascaroside three during exposure, calcium transience were measured in the four CEM neurons.From animal to animal and neuron to neuron, the traces varied in shape, sign and magnitude. Thus, it is very important to analyze many animals when studying pheromone responses. After watching this video, you should have a good understanding of how to load a male C elegans into a micro-fluidic device and analyze calcium transience in head neurons.The same process can be used with hermaphrodites, to identify sec specific differences in neural responses. Once mastered, this technique can be done in half an hour for the first animal imaged. After the first recording, a new animal can be loaded in image in about 10 minutes.Following this procedure, other methods like optogenetics can be combined with this protocol in order to further understand how neural circuits are regulated.

Research

JoVE Journal

Neuroscience

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In vivo Laser Axotomy in C. elegans

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A Molecular Readout of Long-term Olfactory Adaptation in C. elegans

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Multi-unit Recording Methods to Characterize Neural Activity in the Locust Schistocerca Americana Olfactory Circuits

Detection and interpretation of olfactory cues are critical for the survival  of many organisms. Remarkably, species across phyla have strikingly similar ...

In vivo Neuronal Calcium Imaging in C. elegans

In vivo Neuronal Calcium Imaging in C. elegans

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Transplantation of Olfactory Ensheathing Cells to Evaluate Functional Recovery after Peripheral Nerve Injury

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Olfactory Neurons Obtained through Nasal Biopsy Combined with Laser-Capture Microdissection: A Potential Approach to Study Treatment Response in Mental Disorders

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Utilizing Combined Methodologies to Define the Role of Plasma Membrane Delivery During Axon Branching and Neuronal Morphogenesis

During neural development, growing axons extend to multiple synaptic partners by elaborating axonal branches. Axon branching is promoted by extracellular ...

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The olfactory system, specialized in the detection, integration and processing of chemical molecules is likely the most thoroughly studied sensory system. ...