Name: tracking drosophila larval behavior in response to optogenetic stimulation of olfactory neurons
Uploaded: 2018-03-21T14:30:00
Description: Watch this Scientific Journal Video about Tracking Drosophila Larval Behavior in Response to Optogenetic Stimulation of Olfactory Neurons at JoVE.com

This work was supported by startup funds from the University of Nevada, Reno and by NIGMS of the National Institute of Health under grant number P20 GM103650.

1. Building a Behavior Arena and Preparing Hardware to Enable Optogenetic Stimulation in the Behavior Arena
<ol>
	<li>To build a light-deprived behavior arena, construct a box with a dimension of 89 x 61 x 66 cm3 (35&#34; L x 24&#34; W x 26&#34; H) made of black colored plexiglass acrylic sheets (3 mm thick) (see Table of Materials). Materials to build such a box should be available at local hardware stores. Place this box on a table-top in the behavior room (Figure 1</s...

<ol>
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Here, we described a method that allows for the measurement of Drosophila larval behavior in response to simultaneous optogenetic activation of olfactory neurons. Previously described larval tracking methods1,8 use different odor delivery technology to activate ORNs. However, these methods cannot control for either the specificity or temporal patterns of ORN activation. Our method overcomes these deficits by using light stimuli instead of odor stimuli fo...

Olfactory information in a Drosophila larva&#39;s environment is sensed by only 21 functionally distinct ORNs, the activities of which ultimately determine larval behavior1,2,3,4. Yet, relatively little is known about the logic by which sensory information is encoded in the activities of these 21 ORNs. There is thus a need to experimentally measure the functional contributions of each larval ORN to behavior.
Although the sensory response profile of the entire repertoire of Drosophila larval ORNs has been studied in detail1,4,5, the contributions of individual ORNs to the olfactory circuit and thereby to navigational behavior remain largely unknown. Difficulties in larval behavior studies, so far, arise due to the inability to spatially and temporally activate single ORNs. A panel of odorants that specifically activate 19 of the 21 Drosophila larval ORNs was recently described1. Each odorant in the panel, at low concentrations, elicits a physiological response only from its cognate ORN. However, at higher concentrations that are normally used for conventional behavior assays, each odorant elicits physiological responses from multiple ORNs1,5,6. Further, odorants in this panel have varied volatilities that complicate interpretation of behavior studies that depend on formation of stable odor gradients7,8. Finally, naturally occurring odor stimuli have a temporal component that is difficult to replicate under laboratory conditions. It is therefore important to develop a method that can measure larval behavior while simultaneously activating individual ORNs in a spatial and temporal manner.
Here, we demonstrate a method that has advantages over previously described larval tracking assays1,8. The tracking assay described in Gershow et al. uses electronically controlled valves to maintain a stable gradient of odor in the behavior arena8. However, due to the level of complex engineering involved to build the odor stimulus setup, this method is difficult to replicate in other laboratories. Further, the issues related to using odorants to specifically activate single ORNs remain unresolved. The tracking assay described in Mathew et al. uses a simpler odor delivery system, but the resulting odor gradient is dependent on the volatility of test odorant and is unstable for long durations of the assay1. Thus, by replacing odor stimuli with light stimuli, our method has the advantages of specificity and precise temporal control of ORN activation and is not dependent on formation of odor gradients of different strengths.
Our method is easy to set up and is appropriate for researchers interested in measuring aspects of Drosophila larval navigation. This technique could be adapted to other model systems provided that the researcher is able to drive the expression of CsChrimson in their favorite system&#39;s neuron(s) of choice. CsChrimson is a red-shifted version of channel rhodopsin. It is activated at wavelengths that are invisible to the larva&#39;s phototaxis system. We are therefore able to manipulate the activity of neurons with specificity, reliability, and reproducibility9. By modifying the custom written software to account for size changes of the subjects, this method could easily be adapted for crawling larvae of other insect species.

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			<td height="40" style="height:40px;width:359px;">Video camera to capture larval movement</td>
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			<td height="33" style="height:33px;">2&#34; Square Threaded Filter Holder for Imaging Lenses&#160;</td>
			<td style="width:296px;">Edmund Optics</td>
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			<td height="33" style="height:33px;">Electronics for optogenetic setup</td>
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			<td height="33" style="height:33px;">Raspberry Pi 2B</td>
			<td>RASPBERRY-PI.org</td>
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			<td height="33" style="height:33px;">3 Channel programmable power supply</td>
			<td>newegg.com</td>
			<td>9SIA3C62037092</td>
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			<td height="33" style="height:33px;">8 Channel optocoupler relay</td>
			<td>amazon.com</td>
			<td>6454319</td>
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			<td height="33" style="height:33px;">630nm Quad-row LED strip lights</td>
			<td>environmentallights.com</td>
			<td>red3528-450-reel</td>
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			<td height="33" style="height:33px;width:359px;">850nm LED strips</td>
			<td>environmentallights.com</td>
			<td>wp-4000K-CC5050-60x2-kit</td>
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			<td height="33" style="height:33px;width:359px;">Software&#160;</td>
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			<td height="33" style="height:33px;width:359px;">Matlab</td>
			<td>Mathworks Inc.</td>
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			<td height="33" style="height:33px;width:359px;">Ubuntu MATE v16.04</td>
			<td>Nubuntu</td>
			<td>https://github.com/yslo/nubuntu</td>
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			<td height="33" style="height:33px;">Other items</td>
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			<td height="33" style="height:33px;">Plexiglass black acrylic</td>
			<td>Home Depot</td>
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			<td height="33" style="height:33px;">Nutrifly fly food</td>
			<td style="width:296px;">Genesee Scientific</td>
			<td>66-112</td>
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			<td height="33" style="height:33px;">Agarose powder</td>
			<td style="width:296px;">Genesee Scientific</td>
			<td>20-102</td>
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			<td height="33" style="height:33px;">22cm X 22cm square petri-dish</td>
			<td style="width:296px;">VWR Inc.</td>
			<td>25382-327</td>
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			<td>Sigma-Aldrich</td>
			<td>D2650</td>
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			<td height="33" style="height:33px;">Sucrose</td>
			<td>Sigma-Aldrich</td>
			<td>84097</td>
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			<td height="33" style="height:33px;">All trans-retinal</td>
			<td>Sigma-Aldrich</td>
			<td>R2500</td>
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			<td height="33" style="height:33px;">Flies</td>
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			<td height="33" style="height:33px;">UAS-IVS-CsChrimson&#160;</td>
			<td>Bloomington Drosophila Stock Center</td>
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			<td height="33" style="height:33px;width:359px;">Orco-Gal4</td>
			<td>Bloomington Drosophila Stock Center</td>
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			<td height="33" style="height:33px;">Or42a-Gal4</td>
			<td>Bloomington Drosophila Stock Center</td>
			<td>9970</td>
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			<td height="33" style="height:33px;">Or7a-Gal4</td>
			<td>Bloomington Drosophila Stock Center</td>
			<td>23907</td>
			<td></td>
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tracking drosophila larval behavior in response to optogenetic stimulation of olfactory neurons

The ability of insects to navigate toward odor sources is based on the activities of their first-order olfactory receptor neurons (ORNs). While a considerable amount of information has been generated regarding ORN responses to odorants, the role of specific ORNs in driving behavioral responses remains poorly understood. Complications in behavior analyses arise due to different volatilities of odorants that activate individual ORNs, multiple ORNs activated by single odorants, and the difficulty in replicating naturally observed temporal variations in olfactory stimuli using conventional odor-delivery methods in the laboratory. Here, we describe a protocol that analyzes Drosophila larval behavior in response to simultaneous optogenetic stimulation of its ORNs. The optogenetic technology used here allows for specificity of ORN activation and precise control of temporal patterns of ORN activation. Corresponding larval movement is tracked, digitally recorded, and analyzed using custom written software. By replacing odor stimuli with light stimuli, this method allows for a more precise control of individual ORN activation in order to study its impact on larval behavior. Our method could be further extended to study the impact of second-order projection neurons (PNs) as well as local neurons (LNs) on larval behavior. This method will thus enable a comprehensive dissection of olfactory circuit function and complement studies on how olfactory neuron activities translate in to behavior responses.

To demonstrate the specificity of ORN activation, our method was successfully applied to determine the impact of two different ORN (ORN::7a &#38; ORN::42a) (ORNs expressing either Or7a or Or42a) activation on larval behavior (Figure 3). Consistent with recent studies that individual larval ORNs are functionally distinct1,10,13, our representative data demonstrates th...

Watch this Scientific Journal Video about Tracking Drosophila Larval Behavior in Response to Optogenetic Stimulation of Olfactory Neurons at JoVE.com

Tracking Drosophila Larval Behavior in Response to Optogenetic Stimulation of Olfactory Neurons

This protocol analyzes navigational behavior of Drosophila larva in response to simultaneous optogenetic stimulation of its olfactory neurons. Light of 630 nm wavelength is used to activate individual olfactory neurons expressing a red-shifted channel rhodopsin. Larval movement is simultaneously tracked, digitally recorded, and analyzed using custom-written software.

Tracking Drosophila Larval Behavior in Response to Optogenetic Stimulation of Olfactory Neurons

The ability of insects to navigate toward odor sources is based on the activities of their first-order olfactory receptor neurons (ORNs). While a ...

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