Name: in vivo optical calcium imaging of learning-induced synaptic plasticity in drosophila melanogaster
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Description: Watch this Scientific Journal Video about In Vivo Optical Calcium Imaging of Learning-Induced Synaptic Plasticity in Drosophila melanogaster at JoVE.com

This work was supported by the German Research Council through the Collaborative Research Center SFB 889 &#34;Mechanisms of Sensory Processing&#34; and the Research Unit FOR 2705 &#34;Dissection of a Brain Circuit: Structure, Plasticity and Behavioral Function of the Drosophila Mushroom Body&#34;.

1. Transgenic fruit flies, Drosophila melanogaster
<ol>
	<li>Cross female virgin and male flies (raised at 25 &#176;C in 60% relative humidity on a 12 h light/dark cycle) carrying the desired Gal4 and UAS constructs25, respectively, to produce flies in which specific neurons of interest express a genetically encoded calcium indicator.</li>
	<li>Age the female progeny of the above cross until they are in the range of 3-6 days post-eclosion. Female flies are preferable because of their slightly larger size.</li>
</ol>
2. Preparation of the fruit fly for in vivo calcium imaging
<ol>
	<li>Select a single female fly and anesthetize on ice for no longer than 5 min.</li>
	<li>Using fine forceps, place the fly in the imaging chamber (demonstrated in Figure 1c). Ensure the thorax and legs are in contact with the electrical wires in the bottom of the chamber and that the head lays flat. Fix the position of the fly using clear adhesive tape. 
	NOTE: This protocol requires a custom-built chamber in which the flies are fixed, with the head capsule accessible for opening, and the flies able to receive both odor stimulations to the antennae and electric shocks to the thorax and legs (Figure 1).</li>
	<li>Using a surgical scalpel blade fixed to the scalpel handle (see Table of Materials), cut a window in the tape around the head of the fly, leaving the antennae covered and only the anterior-most portion of the thorax exposed.</li>
	<li>Surround the sides and back of the head with blue-light curing glue, carefully manipulated using an insect pin held by concave-convex jaws. Set the glue using a blue light-emitting LED lamp.</li>
	<li>Check that the glue is completely set and clear any residual unhardened glue from the dorsal surface of the fly head.</li>
	<li>Apply a drop of Ringer&#39;s solution24 (see Table of Materials) to cover the exposed cuticle of the head.</li>
	<li>Using a very fine-bladed stab knife, cut through the cuticle. For the most efficient removal of the cuticle, first cut across the posterior of the head using the ocelli as a starting point. Then, cut up each side, medial to the eyes, to form a flap of the cuticle that can be easily torn off using forceps.</li>
	<li>Remove any excess cuticle that may block the brain region of interest.</li>
	<li>Carefully clear the dorsal surface of any trachea using fine forceps, avoiding disruption of the brain tissue itself. Remove and refresh Ringer&#39;s solution24 (see Table of Materials) as required to clear the area of tissue debris.</li>
	<li>Place the hypodermic odor delivery needle in position, approximately 1 cm from the head of the fly. Ensure there is nothing that could obstruct odor delivery to the antennae.</li>
	<li>At the microscope, connect the imaging chamber to the odor-delivery system via the hypodermic odor delivery needle.</li>
	<li>To allow the fly to fully to recover from anesthesia and surgery, and to adapt to the air flow, implement a 10 min resting period at this stage.</li>
</ol>
3. In vivo calcium imaging
<ol>
	<li>Use a multiphoton microscope equipped with an infrared laser and a water immersion objective (see Table of Materials), installed on a vibration-isolated table. For the visualization of GFP-based calcium indicators, tune the laser to an excitation wavelength of 920 nm and install a GFP band-pass filter.</li>
	<li>Using the coarse Z adjustment knob, scan through the Z axis of the brain and locate the brain region of interest. Use the crop function to focus scanning on only this area to minimize scan time, and to rotate the scan view such that the anterior of the head is facing downwards.</li>
	<li>Adjust the frame size to 512 x 512 px, scan speed to &#62; 4 Hz, and scan region (in the Y dimension) so that the neurons of interest are covered.</li>
</ol>
4. Visualization of odor-evoked calcium transients through olfactory conditioning
<ol>
	<li>Use an odor delivery system19,26 that can deliver several odor stimuli in a temporally precise manner.
	<ol>
		<li>Use an additional computer to control the device, and to communicate with the imaging microscope software to coordinate odor stimulations with image capture during experiments.</li>
		<li>Initiate a pre-programmed macro package capable of linking the image acquisition software and odor delivery program (e.g., a VBA macro package installed in the microscope control software, see Table of Materials) that is responsive to an external input trigger provided by the initiation of an odor delivery protocol in a separate program).</li>
	</ol>
	</li>
	<li>Start the measurement by monitoring &#34;pre-training&#34;/na&#239;ve odor-evoked calcium transients at a resolution of 512 x 512 px and a frame rate of 4 Hz. Deliver a 2.5 s odor stimulus flanked by additional image acquisition for 6.25 s preceding odor onset (to establish an F0 baseline value) and 12.5 s after odor offset. Repeat this with a second odorant and then with a third odorant.</li>
	<li>Continue 3 min after this measurement with classical conditioning (&#34;training&#34;) the fly.
	<ol>
		<li>Select one of the odors presented in the &#34;pre-training&#34; phase to become the CS+ odor and another to become the CS- odor. Present the CS+ odor using the computer-controlled odor-deliver system for 60 s alongside twelve 90 V electric shocks.</li>
		<li>After a 60 s break, present the CS- odor alone for 60 s. Use as odorants 4-methylcyclohexanol and 3-octanol. Do not present the third odorant (e.g., 1-octen-3-ol) during this training as it is used as control only before (step 4.2.) and after (step 4.4) the training phase.</li>
	</ol>
	</li>
	<li>Measure the &#34;post-training&#34; odor-evoked calcium transients again by repeating the &#34;pre-training&#34; odor stimulation protocol (step 4.2.) 3 min after finishing the training phase (step 4.3). 
	NOTE: The timing of this step should reflect the time of interest after memory formation (e.g., carry out this step 3-4 min after the conditioning step to investigate short-term memory). Typically, flies can survive for several hours in this preparation.</li>
	<li>Save imaging files in an appropriate format (e.g., Tiff) for later image analysis.</li>
</ol>
5. Image analysis
<ol>
	<li>To analyze images, open Tiff (or similar) files in the image analysis software such as Fiji27.</li>
	<li>Align the stacks using a movement correction algorithm to ensure minimal movement in the X and Y directions. Discard any recordings that show strong movement in the Z axis.</li>
	<li>Select the tool of the software used to mark a region of interest (ROI) around the area that is to be examined. This should be as precise as possible to limit the influence of background fluorescence.</li>
	<li>Use the respective tool of the software to extract temporal fluorescence intensity data as data files from the selected ROI, such that a value is generated for each frame of the recording.</li>
	<li>Open the data using a data analysis program to calculate the &#916;F/F0 values for each odor trace. F0 = average fluorescence in the 2 s before odor onset. &#916;F = the difference between the raw fluorescence in a given frame and F0. From these values, calculate a &#916;F/F0 value for each frame which can be plotted against time to reflect relative fluorescence throughout the odor stimulus period.</li>
</ol>

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The authors have nothing to disclose.

The dissection of the neural circuitry underlying learning and memory is a prominent goal in the field of neuroscience. The genetic accessibility of Drosophila and the breadth and ease of behavioral testing makes this an ideal tool to investigate such phenomena. Here, a method is presented with which it is possible to visualize, within individual flies, the modulation that occurs at a subcellular level as a result of olfactory conditioning. By carrying out both pre-training and post-training visualization of odor-evoked calcium dynamics, first established by our group17, it is possible to draw a direct, within-animal comparison between na&#239;ve and learned odor responses and, therefore, examine the plasticity of neurons of interest. This confers an advantage to this protocol over en masse assessments (used in classical olfactory conditioning) because pre- and post-training states can be quantitatively assessed for individuals, which allows one to determine inter-individual variability. Moreover, the training procedure performed directly under the microscope is largely equivalent to the classical olfactory conditioning paradigm typically used in behavioral experiments and does not involve artificial optogenetic stimulation of neurons. Of course, handling the small flies and carefully opening the head capsule without damaging the brain tissue while keeping the sensory organs intact requires a level of expertise that can be gained by meticulous and repeated training, not unlike the extent seen in physiological assessments such as electrophysiology.
Additionally, the potential to use localized calcium indicators to examine plasticity at the single neuron level is demonstrated - adding greater precision to the neuronal circuit dissection. This is exemplified by showing a learning-induced depression of a postsynaptic response in a well-investigated MB output neuron28,29. Drosophila strains expressing a variety of synaptically localized fluorescence sensors under UAS control are available, e.g., expressing the presynaptically localized sensor Synaptophysin-GCaMP3 or the red fluorescent sensor of synaptic transmission Synaptophysin-pHTomato20. Of course, the variety of fluorescence sensor proteins can be implemented using the protocol described above.
Optical imaging techniques are in general limited by the temporal and spatial resolution of the microscopic image acquisition system (e.g., a two-photon microscope) and the temporal resolution of the sensor itself (e.g., the kinetics of the calcium sensor). Electrophysiological recordings, e.g., using patch clamp electrophysiology from somata of neurons in the Drosophila brain, still offer an unmatched temporal resolution, but without providing any spatial precision. Due to the specificity of the gene expression in neurons of interest combined with the subcellular localization of the sensor, optical imaging techniques can potentially complement electrophysiological techniques to uncover neuronal plasticity underlying learning and memory formation. The continuous progress in the development of fluorescence sensors will perhaps provide the possibility to fuse sensor proteins with faster kinetics or higher signal-to-noise ratios (e.g., GCaMP6 variants23) with synaptically localized proteins like dHomer. Also, recent advances in establishing microscopic techniques with faster acquisition rates or higher spatial resolution will prove invaluable in further fine-tuning of our approach.

Deciphering where and how the information is acquired in the brain through learning and subsequently stored as memory constitutes one of the most challenging tasks in neuroscience1. Neuroscientific research has led to the concept of a change in synaptic transmission as the neuronal substrate that underlies learning and memory formation2,3. It is hypothesized that, during learning, synaptic connections between neuronal ensembles that are active during the perception of a stimulus become modified such that their combined activity pattern can be retrieved during memory recall, thereby instructing future behavioral action4. These &#34;engram cells&#34; and their synapses are often distributed across brain regions and levels of processing, which makes it difficult to assign observed changes in synaptic transmission to the learning of a task or a stimulus. To localize and visualize those synaptic changes that are causally linked to a specific learning task one needs an appropriate model system that allows for precisely confining those synapses.
For such an endeavor, Drosophila melanogaster is particularly suitable because it combines relative brain simplicity, behavioral richness, and experimental accessibility. Among the well-established model organisms, Drosophila is situated between the nematode C. elegans and genetically tractable mammals like mice in terms of neuronal complexity. The stereotypic number of neurons (~300) and limited behavioral repertoire is observed in C. elegans. Mammals, on the other hand, have millions of neurons and staggering behavioral complexity. The brain of the fruit fly is, with its ~100,000, neurons significantly smaller than the brains of most vertebrates, and many of the neurons are individually identifiable5. Yet, Drosophila demonstrate a broad spectrum of complex behaviors, including an ability to exhibit robust associative olfactory learning and memory formation, first described over 40 years ago6. In the course of this classical conditioning procedure, groups of flies are subjected to an odor as the conditioned stimulus (CS+) while they receive a punishing electric shock as the unconditioned stimulus (US). A second odor (CS-) is then presented without any punishment. Thereby, the animals learn to avoid the odor associated with the punishment, which can be tested in a subsequent choice situation between the two odors, CS+ and CS-. Work on dissecting the neuronal substrate underlying this behavior in Drosophila has identified the mushroom bodies (MB) as the primary site of the &#34;engram&#34;7,8,9,10 and, therefore, the circuitry of this brain region was and is the subject of intense research in order to uncover the logic by which a memory engram is acquired and stored (recently reviewed in11,12).
The Drosophila MB consists of ~2,000 intrinsic neurons (Kenyon cells) per hemisphere, organized in parallel axonal projections13. Axons of olfactory projection neurons are extended to the lateral protocerebra and to the MB calyces, the main dendritic input site of the MB and receive olfactory input from antennal lobes. The long, parallel axons bundle of Kenyon cells constitute the peduncle and the lobes. Most Kenyon cells bifurcate forming horizontal &#946;/&#946;&#39;-lobes by extending one collateral towards the midline of the brain, and the vertical &#945;/&#945;&#39;-lobes by extending second collateral projecting in the dorsal-anterior direction. The other group of Kenyon cells forms the horizontal &#947;-lobes13 of the MB where the learning process and subsequent short-term memory formation could be localized10. The MB lobes receive afferent input and provide efferent output, both of which are typically restricted to distinct compartmental sub-regions along the Kenyon cell axons14,15,16. In particular, afferent dopaminergic MB input neurons have been shown to mediate value-based, e.g., punitive, reinforcing effects in associative olfactory learning15,17. Stereotypic and individually identifiable efferent MB output neurons from the mushroom body lobes integrate information across large numbers of Kenyon cells, target diverse brain areas and bear behavior-instructive appetitive or aversive information15. This neuronal architecture has led to a concept of the organization of the associative engram. Odors are relatively precisely encoded by sparsely activated ensembles of Kenyon cells. The coincident activity of these Kenyon cell ensembles and release of dopamine - evoked by punishing stimuli - modulates transmission from Kenyon cell presynapses onto MB output neurons such that the animals will subsequently avoid this particular smell10,12. We use this rather precisely defined and localized engram as a paradigmatic case to illustrate how these learning-dependent changes in synaptic activity can be determined and monitored.
The value of Drosophila as a model system relies strongly on the unmatched genetic toolbox that allows one to express transgenes for identifying, monitoring, and controlling single neurons within complex circuits18. The advent of techniques for neuronal activity monitoring - such as calcium imaging, discussed here - have allowed for the determination of neuronal activity patterns in response to a specific stimulus. By combining specific Gal4-driven expression of genetically encoded calcium indicators (GECIs) with olfactory stimulation, one can visualize the odor-evoked calcium dynamics of neurons of interest19. In this protocol, it is shown that by further coupling this technique with a classical conditioning paradigm, it is possible to examine these olfactory responses in the context of learning. Learning-induced plasticity can be further dissected using GECIs that are not only localized to a single specific neuron, but also to specific subcompartments of a neuron. Pech et al.20 established a selection of tools that allow exactly this. By targeting GCaMP321 to either the pre- or postsynapse - via linkage to the vertebrate Synaptophysin or dHomer, respectively20- the differential modulation of these sites can be distinguished. This localization confers, in this context, an advantage over most GECIs that are ubiquitously present throughout the cytosol - e.g., GCaMP22, GCaMP321, or GCaMP623 - because it means that pre- and postsynaptic transients can be distinguished from the overall integrated calcium influx that occurs as a result of neuron activation. This can provide clues about the location and types of plasticity that occur as a result of or that cause learning and memory formation. As an example, the protocol provided here shows the value of this tool in deciphering the modulation of MB output neurons during olfactory associative learning by targeting the expression of the calcium sensor to only the postsynapse. By monitoring, within an individual fly, odor-evoked activity before and after olfactory conditioning a direct comparison can be drawn between a na&#239;ve odor response and a learned odor response. Whilst fixed in the same imaging chamber, flies are exposed to a selection of odors. Then, they receive an aversive associative conditioning protocol in which one of these odors is paired with electric shock (becoming the CS+) and another odor is presented without reinforcement (becoming the CS-). Finally, the flies are again exposed to the same odors as in the first step. Calcium dynamics are observed using two-photon microscopy.

<table><tbody><tr><td>1-Octen-3-ol</td><td>Sigma-Aldrich, St. Louis, MO, USA</td><td>O5284</td><td>Chemical used as odorant</td></tr><tr><td>3-Octanol</td><td>Sigma-Aldrich, St. Louis, MO, USA</td><td>218405</td><td>Chemical used as odorant</td></tr><tr><td>4-Methylcyclohexanol</td><td>Sigma-Aldrich, St. Louis, MO, USA</td><td>153095</td><td>Chemical used as odorant</td></tr><tr><td>Bandpass filter for EGFP (525/50 nm)</td><td>Carl Zeiss Microscopy GmbH, Jena, Germany</td><td></td><td></td></tr><tr><td>Clear adhesive tape</td><td>Tesa SE, Norderstedt, Germany</td><td></td><td>Standard claer adhesive tape</td></tr><tr><td>Concave-convex jaws</td><td>Fine Science Tools, North Vancouver, Canada</td><td>10053-09</td><td>Blade Holders with concave-convex jaws</td></tr><tr><td>Fine forceps</td><td>Fine Science Tools, North Vancouver, Canada</td><td>11412-11</td><td>Forceps with tip 0.1 x 0.06mm</td></tr><tr><td>Hypodermic needle</td><td>Sterican - B. Braun, Melsungenk, Germany</td><td>4665120</td><td>1.20x40mm</td></tr><tr><td>Insect Minutien pins</td><td>Fine Science Tools, North Vancouver, Canada</td><td>26002-10</td><td>Diameter 0.1mm, tip 0.0125mm</td></tr><tr><td>Kentoflow</td><td>Kent Express Dental Supplies, Gillingham, UK</td><td>953683</td><td>Blue light-curing glue</td></tr><tr><td>Microscope slide</td><td>Carl Roth GmbH &amp;amp; Co. KG, Karlsruhe, Germany</td><td>0656.1</td><td>Standard objective slide 76 x 26 mm</td></tr><tr><td>Mineral oil</td><td>Sigma-Aldrich, St. Louis, MO, USA</td><td>M8410</td><td>Used as diluent for odorants</td></tr><tr><td>Mode-locked Ti-Sapphire laser Chameleon Vision 2</td><td>Coherent Inc., Santa Clara, CA, USA</td><td></td><td>Tunable infrared femtosecond laser</td></tr><tr><td>Multiphoton Microscope LSM 7MP equipped with BiG detectors</td><td>Carl Zeiss Microscopy GmbH, Jena, Germany</td><td></td><td>Multiphoton microscope, multiple companies provide similar devices.</td></tr><tr><td>Plan-Apochromat 20x (NA = 1.0) water immersion objective</td><td>Carl Zeiss Microscopy GmbH, Jena, Germany</td><td>421452-9900-000</td><td>Objective W &quot;Plan-Apochromat&quot; 20x/1.0 DIC M27 70mm</td></tr><tr><td>Ringer&#039;s solution</td><td>n.a.</td><td>n.a.</td><td>5mM KCl, 130mM NaCl, 2mM MgCl&lt;sub&gt;2&lt;/sub&gt;, 2mM CaCl&lt;sub&gt;2&lt;/sub&gt;, 5mM Hepes-NaOH, 36mM sucrose, pH = 7.4</td></tr><tr><td>Stab knife</td><td>Sharpoint, Surgical Specialties Corporation, Reading, PA, USA</td><td>72-1551</td><td>5.0mm Straight restricted blade depth</td></tr><tr><td>Surgical scalpel blade</td><td>Swann-Morton, Sheffield, UK</td><td>0303</td><td>Product No. 11</td></tr><tr><td>Surgical scalpel handle</td><td>Swann-Morton, Sheffield, UK</td><td>0907</td><td>Product No. 7S/S</td></tr><tr><td>Visual Basics of Applicatons (VBA) software to receive a trigger&lt;br/&gt; from the odor-delivery device and the electric shock&lt;br/&gt; application device (power supply) to interact with the&lt;br/&gt; ZEN software from Zeiss that controls the microscope.</td><td>Custom-written and available upon request</td><td>n.a.</td><td>n.a.</td></tr></tbody></table>

in vivo optical calcium imaging of learning-induced synaptic plasticity in drosophila melanogaster

Decades of research in many model organisms have led to the current concept of synaptic plasticity underlying learning and memory formation. Learning-induced changes in synaptic transmission are often distributed across many neurons and levels of processing in the brain. Therefore, methods to visualize learning-dependent synaptic plasticity across neurons are needed. The fruit fly Drosophila melanogaster represents a particularly favorable model organism to study neuronal circuits underlying learning. The protocol presented here demonstrates a way in which the processes underlying the formation of associative olfactory memories, i.e., synaptic activity and their changes, can be monitored in vivo. Using the broad array of genetic tools available in Drosophila, it is possible to specifically express genetically encoded calcium indicators in determined cell populations and even single cells. By fixing a fly in place, and opening the head capsule, it is possible to visualize calcium dynamics in these cells whilst delivering olfactory stimuli. Additionally, we demonstrate a set-up in which the fly can be subjected, simultaneously, to electric shocks to the body. This provides a system in which flies can undergo classical olfactory conditioning - whereby a previously na&#239;ve odor is learned to be associated with electric shock punishment - at the same time as the representation of this odor (and other untrained odors) is observed in the brain via two-photon microscopy. Our lab has previously reported the generation of synaptically localized calcium sensors, which enables one to confine the fluorescent calcium signals to pre- or postsynaptic compartments. Two-photon microscopy provides a way to spatially resolve fine structures. We exemplify this by focusing on neurons integrating information from the mushroom body, a higher-order center of the insect brain. Overall, this protocol provides a method to examine the synaptic connections between neurons whose activity is modulated as a result of olfactory learning.

An example of images acquired with the above protocol can be seen in Figure 2. dHomer-GCaMP3 is expressed in an MB output neuron whose dendrites innervate the compartment 1 of the MB &#947;-lobe (the neuron is termed MVP228,29) and is genetically targeted using the split-Gal4 line MB112C16. Also, demonstrated is the difference in the subcellular localization of a cytosolic and the post-synaptically localized calcium indicator. When comparing Figures 2a and Figure 2f, one can clearly observe the specific, compartmentalized expression of the dHomer-GCaMP3 sensor14 - with no expression in the axonal compartments of the neuron, and a punctuated signal visible in the dendritic compartment. Clear - though the lower amplitude - odor responses can be seen in flies expressing dHomer-GCaMP3 (Figure 2, lower panels), compared to flies expressing cytosolic GCaMP6f23 (Figure 2, upper panels). This demonstrates that the tool is effective for the visualization of olfactory responses at the level of the postsynapse, and, therefore, provides an additional specificity to the examination of the neural circuits underlying, in this case, odor encoding and olfactory learning.
An example of the latter can be seen in Figure 3. In this experiment, dHomer-GCaMP3 is expressed as in Figure 2 - in the mushroom body output neuron MVP2. This is a neuron known to be modulated through olfactory learning such that presynaptic depression as a result of aversive olfactory conditioning is reflected in a deceased postsynaptic response to the trained odor28,29 and here a confirmation of this result is shown using this in vivo calcium imaging protocol. The calcium traces shown in Figure 3 represent exemplary data from one individual fly. Note that the noise level and amplitude can vary between individual preparations (e.g., compare Figure 2e and Figure 3c-e). Therefore, a within-animal comparison of pre- vs. post-training provides a way to account for inter-individual variability. Of course, the protocol is suitable to be transferred to imaging of other neurons of interest.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/60288/60288fig1.jpg" /> 
Figure 1: Construction of a mounting chamber and preparation of a fly for imaging. (a) Steps for the construction of the fly mounting chamber. The base is formed of a standard microscope slide (1) covered with a fine plastic mesh (2). Two electrical wires carrying opposing charges (3) are glued to the slide on either side. The wires are stripped and bent to cross the slide (4) running parallel with one another but not in contact. Layers of clear adhesive tape (5) are added until reaching the height of a fly (approximately 1 mm). A channel is cut through the tape vertically (6), approximately 1 mm wide to fit the width of a fly. An elevated platform made of clear adhesive tape (7) is built just above the electrical wires to form a pillow for the fly&#39;s head whilst the thorax is on top of the wires. (b) Schematic illustration of the fly positioned under the two-photon microscope. The odor stimulation is achieved through a hypodermic needle positioned in front of the fly&#39;s head (inserted through the channel in the tape (6) and on top of the platform (7) to direct the odors to the antennae). (c)-(h) Fixing and opening of the fly head. (c) A fly fixed inside the imaging chamber, inside the channel (Scale bar = 1 mm) and held in place by a fresh piece of clear adhesive tape over the whole fly. (d) Magnified view of the fly in position. Scale bar = 0.1 mm. (e) A window is cut into the tape around the head of the fly. (f) The head is further fixed with blue light-curing glue. (g) The head capsule is covered with Ringer&#39;s solution and opened. (h) Completed preparation of the brain with excess tissue and trachea (white tissue visible in (g) removed). <a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/60288/60288fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/60288/60288fig2.jpg" /> 
Figure 2: Postsynaptically-localized calcium visualized using dHomer-GCaMP3. (a) Confocal microscopy images showing the expression of cytosolically localized GCaMP6f (i) and postsynaptically localized dHomer-GCaMP3 (ii) in the MB output neuron MVP2. Green arrow indicates the &#947;1 subregion of the MB &#947;-lobe. Scale bars = 15 &#181;m. (b)-(d) Images captured using two-photon excitation microscopy of the genotypes above, showing the in vivo fluorescence of the respective calcium sensors. (b) F0 (baseline fluorescence) images, demonstrated as an average intensity projection of the 2 s before odor onset. Scale bars = 10 &#181;m. (c) Fodor images (fluorescence during odor stimulation), demonstrated as an average intensity projection over the odor response period (2.5 s). (d) &#916;F images generated by subtracting F0 image from Fodor image, to show actual odor response signal. (e) &#916;F/F0 traces from the above flies of the respective genotypes through an odor stimulation (grey bar). <a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/60288/60288fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/60288/60288fig3.jpg" /> 
Figure 3: Learning-induced postsynaptic plasticity visualized via dHomer-GCaMP3. (a) Schematic of conditioning protocols used in these experiments. Na&#239;ve odor responses, before conditioning (&#34;pre&#34;) are measured first. Then each fly experiences one of three possible conditioning protocols: &#34;Paired&#34;, where one odor (CS+) is paired with electric shocks (US) and another (CS-) is not reinforced; &#34;Odors only&#34;, where only the odors are presented, both without reinforcement, to control for odor exposure effects; and &#34;Shocks only&#34;, where only electric shocks are presented without any odor stimuli, to control for shock exposure effects. After this conditioning phase, flies are then exposed to the &#34;Pre&#34; odors again to test for altered odor-evoked activity (&#34;Post&#34;). (b) An example of odor response modulation as a result of the paired odor/shock presentation. Strong suppression of the response to the CS+ odor can be seen in the &#947;1 subregion (dotted line). (c)-(e) Odor response traces from the same fly as in (b), showing that this suppression effect is only observed in the case of the trained odor. <a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/60288/60288fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about In Vivo Optical Calcium Imaging of Learning-Induced Synaptic Plasticity in Drosophila melanogaster at JoVE.com

In Vivo Optical Calcium Imaging of Learning-Induced Synaptic Plasticity in Drosophila melanogaster

Here we present a protocol with which pre- and/or postsynaptic calcium can be visualized in the context of Drosophila learning and memory. In vivo calcium imaging using synaptically localized calcium sensors is combined with a classical olfactory conditioning paradigm such that the synaptic plasticity underlying this type of associative learning may be determined.

In Vivo Optical Calcium Imaging of Learning-Induced Synaptic Plasticity in Drosophila melanogaster

Decades of research in many model organisms have led to the current concept of synaptic plasticity underlying learning and memory formation. ...

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Neuroscience

8.9K Views.  University of Göttingen. Here we present a protocol with which pre- and/or postsynaptic calcium can be visualized in the context of Drosophila learning and memory. In vivo calcium imaging using synaptically localized calcium sensors is combined with a classical olfactory conditioning paradigm such that the synaptic plasticity underlying this type of associative learning may be determined.

Video: In Vivo Optical Calcium Imaging of Learning-Induced Synaptic Plasticity in Drosophila melanogaster

In vivo Visualization of Synaptic Vesicles Within Drosophila Larval Segmental Axons

Elucidating the mechanisms of axonal transport has shown to be very important in determining how defects in long distance transport affect different neurological diseases. Defects in this essential process can have detrimental effects on neuronal functioning and development. We have developed a dissection protocol that is designed to expose the Drosophila larval segmental nerves to view axonal transport in real time. We have adapted this protocol for live imaging from the one published by Hurd and Saxton (1996) used for immunolocalizatin of larval segmental nerves. Careful dissection and proper buffer conditions are critical for maximizing the lifespan of the dissected larvae. When properly done, dissected larvae have shown robust vesicle transport for 2-3 hours under physiological conditions. We use the UAS-GAL4 method 1 to express GFP-tagged APP or synaptotagmin vesicles within a single axon or many axons in larval segmental nerves by using different neuronal GAL4 drivers. Other fluorescently tagged markers, for example mitochrondria (MitoTracker) or lysosomes (LysoTracker), can be also applied to the larvae before viewing. GFP-vesicle movement and particle movement can be viewed simultaneously using separate wavelengths.

In vivo Visualization of Synaptic Vesicles Within Drosophila Larval Segmental Axons

This protocol discusses the live dissection of Drosophila larvae for the purpose of imaging the movement of GFP tagged axonal vesicles on microtubule tracks.

Elucidating the mechanisms of axonal transport has shown to be very important in determining how defects in long distance transport affect different ...

Imaging Calcium in Drosophila at Egg Activation

Egg activation is a universal process that includes a series of events to allow the fertilized egg to complete meiosis and initiate embryonic development. One aspect of egg activation, conserved across all organisms examined, is a change in the intracellular concentration of calcium (Ca2+) often termed a 'Ca2+ wave'. While the speed and number of oscillations of the Ca2+ wave varies between species, the change in intracellular Ca2+ is key in bringing about essential events for embryonic development. These changes include resumption of the cell cycle, mRNA regulation, cortical granule exocytosis, and rearrangement of the cytoskeleton.
In the mature Drosophila egg, activation occurs in the female oviduct prior to fertilization, initiating a series of Ca2+-dependent events. Here we present a protocol for imaging the Ca2+ wave in Drosophila. This approach provides a manipulable model system to interrogate the mechanism of the Ca2+ wave and the downstream changes associated with it.

Imaging Calcium in Drosophila at Egg Activation

This article describes an adaptable ex vivo protocol for visualizing Ca2+ during egg activation in Drosophila.

Egg activation is a universal process that includes a series of events to allow the fertilized egg to complete meiosis and initiate embryonic development. ...

Developmental Biology

Calcium Imaging of Odor-evoked Responses in the Drosophila Antennal Lobe

The antennal lobe is the primary olfactory center in the insect brain and represents the anatomical and functional equivalent of the vertebrate olfactory bulb1-5. Olfactory information in the external world is transmitted to the antennal lobe by olfactory sensory neurons (OSNs), which segregate to distinct regions of neuropil called glomeruli according to the specific olfactory receptor they express. Here, OSN axons synapse with both local interneurons (LNs), whose processes can innervate many different glomeruli, and projection neurons (PNs), which convey olfactory information to higher olfactory brain regions.
Optical imaging of the activity of OSNs, LNs and PNs in the antennal lobe - traditionally using synthetic calcium indicators (e.g. calcium green, FURA-2) or voltage-sensitive dyes (e.g. RH414) - has long been an important technique to understand how olfactory stimuli are represented as spatial and temporal patterns of glomerular activity in many species of insects6-10. Development of genetically-encoded neural activity reporters, such as the fluorescent calcium indicators G-CaMP11,12 and Cameleon13, the bioluminescent calcium indicator GFP-aequorin14,15, or a reporter of synaptic transmission, synapto-pHluorin16 has made the olfactory system of the fruitfly, Drosophila melanogaster, particularly accessible to neurophysiological imaging, complementing its comprehensively-described molecular, electrophysiological and neuroanatomical properties2,4,17. These reporters can be selectively expressed via binary transcriptional control systems (e.g. GAL4/UAS18, LexA/LexAop19,20, Q system21) in defined populations of neurons within the olfactory circuitry to dissect with high spatial and temporal resolution how odor-evoked neural activity is represented, modulated and transformed22-24.
Here we describe the preparation and analysis methods to measure odor-evoked responses in the Drosophila antennal lobe using G-CaMP25-27. The animal preparation is minimally invasive and can be adapted to imaging using wide-field fluorescence, confocal and two-photon microscopes.

Calcium Imaging of Odor-evoked Responses in the Drosophila Antennal Lobe

We describe an established technique to measure and analyze odor-evoked calcium responses in the antennal lobe of living Drosophila melanogaster.

The antennal lobe is the primary olfactory center in the insect brain and represents the anatomical and functional equivalent of the vertebrate olfactory ...

In vivo Imaging of Intact Drosophila Larvae at Sub-cellular Resolution

Recent improvements in optical imaging, genetically encoded fluorophores and genetic tools allowing efficient establishment of desired transgenic animal lines have enabled biological processes to be studied in the context of a living, and in some instances even behaving, organism. In this protocol we will describe how to anesthetize intact Drosophila larvae, using the volatile anesthetic desflurane, to follow the development and plasticity of synaptic populations at sub-cellular resolution1-3. While other useful methods to anesthetize Drosophila melanogaster larvae have been previously described4,5,6,7,8, the protocol presented herein demonstrates significant improvements due to the following combined key features: (1) A very high degree of anesthetization; even the heart beat is arrested allowing for lateral resolution of up to 150 nm1, (2) a high survival rate of &gt; 90% per anesthetization cycle, permitting the recording of more than five time-points over a period of hours to days2 and (3) a high sensitivity enabling us in 2 instances to study the dynamics of proteins expressed at physiological levels. In detail, we were able to visualize the postsynaptic glutamate receptor subunit GluR-IIA expressed via the endogenous promoter1 in stable transgenic lines and the exon trap line FasII-GFP1. (4) In contrast to other methods4,7 the larvae can be imaged not only alive, but also intact (i.e. non-dissected) allowing observation to occur over a number of days1. The accompanying video details the function of individual parts of the in vivo imaging chamber2,3, the correct mounting of the larvae, the anesthetization procedure, how to re-identify specific positions within a larva and the safe removal of the larvae from the imaging chamber.

In vivo Imaging of Intact Drosophila Larvae at Sub-cellular Resolution

This protocol describes a reliable method for anesthetization and imaging of intact Drosophila melanogaster larvae. We have utilized the volatile anesthetic desflurane to allow for repetitive imaging at sub-cellular resolution and re-identification of structures for up to a few days1.

Recent improvements in optical imaging, genetically encoded fluorophores and genetic tools allowing efficient establishment of desired transgenic animal ...

Biology

In Vivo Single-Molecule Tracking at the Drosophila Presynaptic Motor Nerve Terminal

An increasing number of super-resolution microscopy techniques are helping to uncover the mechanisms that govern the nanoscale cellular world. Single-molecule imaging is gaining momentum as it provides exceptional access to the visualization of individual molecules in living cells. Here, we describe a technique that we developed to perform single-particle tracking photo-activated localization microscopy (sptPALM) in Drosophila larvae. Synaptic communication relies on key presynaptic proteins that act by docking, priming, and promoting the fusion of neurotransmitter-containing vesicles with the plasma membrane. A range of protein-protein and protein-lipid interactions tightly regulates these processes and the presynaptic proteins therefore exhibit changes in mobility associated with each of these key events. Investigating how mobility of these proteins correlates with their physiological function in an intact live animal is essential to understanding their precise mechanism of action. Extracting protein mobility with high resolution in vivo requires overcoming limitations such as optical transparency, accessibility, and penetration depth. We describe how photoconvertible fluorescent proteins tagged to the presynaptic protein Syntaxin-1A can be visualized via slight oblique illumination and tracked at the motor nerve terminal or along the motor neuron axon of the third instar Drosophila larva.

In Vivo Single-Molecule Tracking at the Drosophila Presynaptic Motor Nerve Terminal

Here we illustrate how single molecule photo-activated localization microscopy can be carried out on the motor nerve terminal of a live Drosophila melanogaster third instar larva.

An increasing number of super-resolution microscopy techniques are helping to uncover the mechanisms that govern the nanoscale cellular world. ...

Monitoring Epileptiform Events in Drosophila via Calcium Imaging

Ex Vivo Calcium Imaging for Drosophila Model of Epilepsy

Epilepsy is a neurological disorder characterized by recurrent seizures, partially correlated with genetic origin, affecting over 70 million individuals worldwide. Despite the clinical importance of epilepsy, the functional analysis of neural activity in the central nervous system is still to be developed. Recent advancements in imaging technology, in combination with stable expression of genetically encoded calcium indicators, such as GCaMP6, have revolutionized the study of epilepsy at both brain-wide and single-cell resolution levels. Drosophila melanogaster has emerged as a tool for investigating the molecular and cellular mechanisms underlying epilepsy due to its sophisticated molecular genetics and behavioral assays. In this study, we present a novel and efficient protocol for ex vivo calcium imaging in GCaMP6-expressing adult Drosophila to monitor epileptiform activities. The whole brain is prepared from cac, a well-known epilepsy gene, knockdown flies for calcium imaging with a confocal microscope to identify the neural activity as a follow-up to the bang-sensitive seizure-like behavior assay. The cac knockdown flies showed a higher rate of seizure-like behavior and abnormal calcium activities, including more large spikes and fewer small spikes than wild-type flies. The calcium activities were correlated to seizure-like behavior. This methodology serves as an efficient methodology in screening the pathogenic genes for epilepsy and exploring the potential mechanism of epilepsy at the cellular level.

Author Spotlight: Insights into the Techniques and Findings of Recent Advancements in Epilepsy Research 

Here, we present a protocol for ex vivo calcium imaging in GCaMP6-expressing adult Drosophila to monitor epileptiform activities. The protocol provides a valuable tool for investigating ictal events in adult Drosophila through ex vivo calcium imaging, allowing for exploration of the potential mechanisms of epilepsy at the cellular levels.

Epilepsy is a neurological disorder characterized by recurrent seizures, partially correlated with genetic origin, affecting over 70 million individuals ...

In Vivo Calcium Imaging of Taste-Induced Neural Responses in Adult Drosophila

For nearly two decades, in vivo calcium imaging has been an effective method for measuring cellular responses to taste stimuli in the fruit fly model organism, Drosophila melanogaster. A key strength of this methodology is its ability to record taste-induced neural responses in awake animals without the need for anesthesia. This approach employs binary expression systems (e.g., Gal4-UAS) to express the calcium indicator GCaMP in specific neurons of interest. This protocol describes a procedure in which flies expressing GCaMP are mounted with the labellum securely positioned, enabling fluorescence in the brain to be recorded at millisecond resolution under a confocal microscope while a solution is applied to the labellum, stimulating all labellar taste sensilla. The examples provided focus on calcium responses in primary gustatory receptor neurons of D. melanogaster. However, this approach can be adapted to record from other neurons of interest within the brain of Drosophilids or other insect species. This imaging method enables researchers to simultaneously record collective calcium responses from groups of gustatory neurons across the labellum, complementing electrophysiological tip recordings that quantify action potentials from individual neurons. The in vivo calcium imaging technique outlined here has been instrumental in uncovering molecular and cellular mechanisms of chemosensation, identifying unique temporal response patterns in primary taste neurons, investigating mechanisms of gustatory modulation, and exploring taste processing in downstream circuits.

A calcium imaging approach enables the recording of taste-induced responses in the brains of awake flies while a solution is applied to the labellum. Primary gustatory responses in Drosophila melanogaster are used as an example, but this protocol can be adapted to study downstream neurons or other species.

For nearly two decades, in vivo calcium imaging has been an effective method for measuring cellular responses to taste stimuli in the fruit fly model ...

Drosophila In Vivo Calcium Imaging: A Method for Functional Imaging of Neuronal Activity

Source: Hancock, C. E., et al. <a href="https://www-jove-com.bdigitaluss.remotexs.co/video/60288/" target="_blank">In Vivo Optical Calcium Imaging of Learning-Induced Synaptic Plasticity in Drosophila melanogaster</a>. J. Vis. Exp. (2019).
This video describes in vivo calcium imaging in Drosophila neurons using GCaMP. The featured protocol clip shows how to record changes in GCaMP fluorescence from mushroom body neurons during an olfactory conditioning experiment.

Source: Hancock, C. E., et al. In Vivo Optical Calcium Imaging of Learning-Induced Synaptic Plasticity in Drosophila melanogaster. J. Vis. Exp. (2019).
...

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Drosophila melanogaster (fruit fly)

Adult

In Vivo Calcium Imaging Using Synaptically Localized Calcium Sensors in Drosophila melanogaster

Source: Hancock, C. E. et al., <a href="https://app-jove-com.bdigitaluss.remotexs.co/v/60288">In Vivo Optical Calcium Imaging of Learning-Induced Synaptic Plasticity in Drosophila melanogaster.</a>&#160;J. Vis. Exp. (2019).
This video demonstrates a method for in vivo calcium imaging using synaptically localized calcium sensors in flies. It outlines the steps for preparing the flies for microscopy, conducting olfactory conditioning, and visualizing odor-induced calcium influx.

1. Transgenic fruit flies,&#160;Drosophila melanogaster

	Cross female virgin and male flies (raised at 25 &#176;C in 60% relative humidity on a 12 h ...

In Vivo Optical Calcium Imaging of Learning-Induced Synaptic Plasticity in Drosophila melanogaster

Summary

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Chapters in this video

In vivo Visualization of Synaptic Vesicles Within Drosophila Larval Segmental Axons

Imaging Calcium in Drosophila at Egg Activation

Calcium Imaging of Odor-evoked Responses in the Drosophila Antennal Lobe

In vivo Imaging of Intact Drosophila Larvae at Sub-cellular Resolution

In Vivo Single-Molecule Tracking at the Drosophila Presynaptic Motor Nerve Terminal

Ex Vivo Calcium Imaging for Drosophila Model of Epilepsy

In Vivo Calcium Imaging of Taste-Induced Neural Responses in Adult Drosophila

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