The authors would like to acknowledge the President&#8217;s Research Fund from Saint Louis University awarded to W.S.N.

1. Maintenance of Population Cages
<ol>
	<li>Maintain population cages at 25 &#176;C on a 12 hr light-dark cycle. As long as the control and experimental groups are exposed to the same lighting conditions, then this technique can be performed in a standard laboratory setting.</li>
	<li>Allow females to lay eggs overnight on apple juice-agar plates.</li>
	<li>Collect newly hatched larvae by maintaining plates with newly deposited eggs at 25 &#176;C for 24 hr. Place a small dollop of yeast in the center of the plate to attract hatched larvae.</li>
	<li>Collect 1st instar larvae that have migrated into the yeast paste in the center of the apple juice plate. Use a metal spatula to transfer it to a fresh apple juice plate. Additional yeast paste can be added to ensure there is adequate food until the assays are performed. Grape juice plates can also be used in place of apple juice plates.</li>
	<li>Obtain late 2nd-early 3rd instar larvae by allowing 1st instars to age for 40-48 hr. Within this range the feeding rates are constant13. Age can be confirmed by examination of the mouth hooks as there are distinct changes in this structure with each larval molt.</li>
	<li>Late 2nd-early 3rd instar larvae are collected for behavior assays by gently and extensively washing apple juice plates with water and collecting the larvae on a mesh filter. The larvae are then transferred to an agar plate.</li>
	<li>All analyses are performed in parallel using control and experimental animals.</li>
</ol>
2. Behavioral Paradigm &#8211; Locomotion
<ol>
	<li>Place a single 3rd instar larva on a 2% agar substrate in a 100&#160;mm tissue culture dish and allow the larva to acclimate for 30 sec. Larvae use their cephalopharyngeal sclerites (mouth hooks) to propel their bodies across the surface of the agar substrate. This is done on a separate plate because it is more difficult to visualize the body contractions in the yeast solution as the animal is almost the same color as the yeast.</li>
	<li>Observe and record each posterior to anterior movement over the substrate for a period of 1 min. n = 20 for each genotype. No more than 10 animals should be assayed per plate.</li>
</ol>
3. Behavior Paradigm &#8211; Feeding
<ol>
	<li>Using blunt Inox #5 tweezers, carefully transfer the 3rd instar larva from the locomotor agar plate to the center of an agar-filled plate overlaid with 5&#160;ml of 2% activated baker&#39;s yeast solution. Ensure that the solution is homogenous as the yeast will settle over time. When in the yeast solution, larvae will largely remain in place and feed, facilitating observation of the behavior. The rate of mouth hook contractions directly correlates with the amount of food ingested14.</li>
	<li>Allow larva to acclimate for 30 sec.</li>
	<li>Observe and record the number of mouth hook contractions for a period of 1 min. n = 20 for each genotype.</li>
</ol>
4. Larval Gut Dissections
<ol>
	<li>Make a 4% EM-grade formaldehyde fixation solution in 1x&#160;phosphate-buffered saline (PBS) and place in a 3-well spot glass.</li>
	<li>Carefully dissect out wandering late 3rd instar larval guts in a 3-well glass dish using 1x&#160;PBS solution, making sure each time that the proventriculus is left intact. With one forcep, hold the posterior end, and with the other, hold the mouth hooks. While holding the posterior end immobile, gently pull on the mouth hooks to gain access to the guts. Remove any associated tissues (salivary glands, brain, fat body, etc.), then transfer each gut to the 3-well dish containing the formaldehyde fix. Wandering 3rd instar larva are used because at this stage of development, the larva cease feeding in preparation for pupariation, and the proventriculus is cleared of yeast.</li>
	<li>Incubate guts at 4 &#176;C overnight in an opaque tissue culture box.</li>
	<li>Before removing formaldehyde fixation solution from wells, remove the gastric caeca and clip the midgut ~150 &#181;m2 from the proventriculus so that projections can clearly be viewed without impediment.</li>
	<li>Remove formaldehyde fix from the wells and replace with 1x&#160;PBT (1x&#160;PBS, 0.1% protease-free bovine serum albumin, 0.1% Triton X-100) buffer solution. Thoroughly wash guts 6x for 10 min&#160;in 1x&#160;PBT. Place tissue samples on a mechanical rotator while doing washes.</li>
	<li>Incubate at 4 &#176;C for 1 hr in 10-6 M 5-HT to enhance serotonin signaling. Thoroughly wash guts 6x for 10 min&#160;in 1x&#160;PBT. Previous studies have demonstrated that this concentration of exogenous 5-HT does not affect neuronal architecture or varicosity density in immunohistochemical analyses and simply enhances the signal to noise ratio15-16.</li>
	<li>Incubate at 4 &#176;C overnight in anti-serotonin primary antibody (monoclonal raised in mouse or polyclonal raised in rabbit). Thoroughly wash guts 6x for 10 min&#160;in 1x&#160;PBT. Place tissue samples on a mechanical rotator while doing washes.</li>
	<li>Incubate at 4 &#176;C for 90 min&#160;in secondary antibody (Alexa Fluor 568 goat anti-mouse or anti-rabbit IgG; 1:400 dilution). Thoroughly wash guts 6x for 10 min&#160;in 1x&#160;PBT. Place tissue samples on a mechanical rotator while doing washes.</li>
	<li>Incubate in 4 mM sodium carbonate for 10 min&#160;on a mechanical rotator, then mount in 4% n-propyl gallate/20 mM sodium carbonate, and view under fluorescence. Sodium carbonate is used to convert the samples to the buffer and pH used in the mountant media.</li>
	<li>Capture images of immunostained tissue samples at 400X magnification for analysis.</li>
</ol>
5. Analysis of Neural Circuitry
<ol>
	<li>Neurite fibers were quantified (number and size of varicosities and degree of branching) using Neuroleucida and Neuroexplorer. However, this can also be accomplished manually or using Simple Neurite Tracer (a free application that can be downloaded online).</li>
	<li>Trace the individual fiber projections from the brain to the proventriculus and quantify varicosity number, branches and the number of large varicosities per unit length. The axonal fibers projecting from the brain are bundled into the recurrens nerve and are not accessible for analysis until they reach the proventriculus where they separate and fasciculate.</li>
</ol>

<ol>
	<li>Weiss, E., Maness, P., Lauder, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Why+do+neurotransmitters+act+like+growth+factors?.">Why do neurotransmitters act like growth factors?.</a> Perspect Dev Neurobiol. 5, 323-335 .</li><li>Herlenius, E., Lagercrantz, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neurotransmitters+and+neuromodulators+during+early+human+development.">Neurotransmitters and neuromodulators during early human development.</a> Early Hum. Dev. 65, 21-37 .</li><li>Budnik, V., Wu, C., White, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Altered+branching+of+serotonin-containing+neurons+in+Drosophila+mutants+unable+to+synthesize+serotonin+and+dopamine.">Altered branching of serotonin-containing neurons in Drosophila mutants unable to synthesize serotonin and dopamine.</a> J. Neurosci. 9, 2866-2877 (1989).</li><li>Sodhi, M., Sanders-Bush, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Serotonin+and+brain+development.">Serotonin and brain development.</a> International Review of Neurobiol. 59, 111-174 (2004).</li><li>Goldberg, J., Kater, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Expression+and+function+of+the+neurotransmitter+serotonin+during+development+of+the+Helisoma+nervous+system.">Expression and function of the neurotransmitter serotonin during development of the Helisoma nervous system.</a> Dev. Biol. 131, 483-495 (1989).</li><li>Goldberg, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Serotonin+regulation+of+neurite+outgrowth+in+identified+neurons+from+mature+and+embryonic+Helisoma+triyolvis.">Serotonin regulation of neurite outgrowth in identified neurons from mature and embryonic Helisoma triyolvis.</a> Perspect Dev Neurobiol. 5, 373-387 (1998).</li><li>Haydon, P., McCobb, P., Kater, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Serotonin+selectively+inhibits+growth+cone+motility+and+synaptogenesis+of+specific+identified+neurons.">Serotonin selectively inhibits growth cone motility and synaptogenesis of specific identified neurons.</a> Sci. 226, 561-564 (1984).</li><li>Neckameyer, W. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+trophic+role+for+serotonin+in+the+development+of+a+simple+feeding+circuit.">A trophic role for serotonin in the development of a simple feeding circuit.</a> Dev. Neurosci. 32, 217-237 .</li><li>De Vry, J., Schreiber, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+selected+serotonin+5-HT+1+and+5-HT+2+receptor+agonists+on+feeding+behavior:+possible+mechanisms+of+action.">Effects of selected serotonin 5-HT 1 and 5-HT 2 receptor agonists on feeding behavior: possible mechanisms of action.</a> Neurosci. Biobehav. Rev. 24, 341-353 (2000).</li><li>Schoofs, A., Niederegger, S., van Ooyen, A., Heinzel, H., Spie&#223;, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+brain+can+eat:+Establishing+the+existence+of+a+central+pattern+generator+for+feeding+in+third+instar+larvae+of+Drosophila+virilis+and+Drosophila+melanogaster.">The brain can eat: Establishing the existence of a central pattern generator for feeding in third instar larvae of Drosophila virilis and Drosophila melanogaster.</a> J. Insect Physiol. 56, 695-705 (2010).</li><li>Spie&#223;, R., Schoofs, A., Heinzel, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Anatomy+of+the+stomatogastric+nervous+system+associated+with+the+foregut+in+Drosophila+melanogaster+and+Calliphora+vicin+third+instar+larvae.">Anatomy of the stomatogastric nervous system associated with the foregut in Drosophila melanogaster and Calliphora vicin third instar larvae.</a> J. Morphol. 269, 272-282 (2008).</li><li>Neckameyer, W. S., Bhatt, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neurotrophic+actions+of+dopamine+on+the+development+of+a+serotonergic+feeding+circuit+in+Drosophila+melanogaster.">Neurotrophic actions of dopamine on the development of a serotonergic feeding circuit in Drosophila melanogaster.</a> Biomed Cent NeuroSci. 13, 26 (2012).</li><li>Sewall, D., Burnet, B., Connolly, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Genetic+analysis+of+larval+feeding+behavior+in+Drosophila+melanogaste.">Genetic analysis of larval feeding behavior in Drosophila melanogaste.</a> Genet. Res. 24, 163-173 (1975).</li><li>Joshi, A., Mueller, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evolution+of+higher+feeding+rate+in+Drosophila+due+to+density-dependent+natural+selection.">Evolution of higher feeding rate in Drosophila due to density-dependent natural selection.</a> Evolution. 42, 1090-1093 (1988).</li><li>Budnik, V., Wu, C., White, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Altered+branching+of+serotonin-containing+neurons+in+Drosophila+mutants+unable+to+synthesize+serotonin+and+dopamine.">Altered branching of serotonin-containing neurons in Drosophila mutants unable to synthesize serotonin and dopamine.</a> J. Neurosci. 9, 2866-2877 (1989).</li><li>Sykes, P., Condron, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+and+sensitivity+to+serotonin+of+Drosophila+varicosities+in+the+central+nervous+system.">Development and sensitivity to serotonin of Drosophila varicosities in the central nervous system.</a> Dev. Biol. 286, 207-216 (2005).</li><li>Garrity, P. A., Goodman, M. B., Samuel, A. D., Sengupta, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Running+hot+and+cold:+behavioral+strategies,+neural+circuits,+and+the+molecular+machinery+for+thermotaxis+inC.+elegansand+Drosophila.">Running hot and cold: behavioral strategies, neural circuits, and the molecular machinery for thermotaxis inC. elegansand Drosophila.</a> Genes Dev. 24, 2365-2382 (2010).</li><li>McKemy, D. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Temperature+sensing+across+species.">Temperature sensing across species.</a> Pflugers Archives. 454, 777-791 (2007).</li></ol>

We have nothing to disclose.

Aberrant development of the serotonergic stomatogastric circuit, which occurs during late embryogenesis, will affect its mature function. Changes in the neurite architecture innervating the gut can be correlated with the functional output of the circuit, which is feeding rate (measured by mouth hook contractions in a yeast solution) (Figure 1). The use of the UAS-Gal4 bipartite system in Drosophila makes it possible to specifically target up- or down-regulated expression of a given transcript to...

Drosophila is an extremely powerful model system for studying neural circuit development due to rapid generation time, low experimental cost, and the ability to manipulate and control genetic and environmental factors. Neurogenesis, neuronal path finding and synaptogenesis are conserved between humans and Drosophila; therefore the mechanisms in creating, maintaining and modifying neural circuits are conserved as well.
Classical neurotransmitters, such as serotonin (5-hydroxytryptamine, or 5-HT) can serve as growth factors before adopting their roles as signaling molecules in the mature neural circuit1-3 Previous studies have shown that perturbed levels of 5-HT during embryogenesis alter the connectivity of mature neurons4. Others have shown that ectopic application of 5-HT to cultured Helisoma neurons repress neurite outgrowth as well as synaptogenesis5-7. In Drosophila, developmental 5-HT levels are inversely related to varicosity number and size, as well as the degree of aborization, along the length of neurites projecting to the foregut from the CNS8.
Serotonergic neurotransmission has been shown to modulate feeding behaviors in diverse species, including Drosophila8-9. The feeding circuit in Drosophila is a relatively simple circuit that can be used as a model to correlate the functional output (feeding) with alterations in the development of the axonal projections from the brain to the foregut. Schoofs et al. have shown that Drosophila larval feeding is regulated by central pattern generators that influence the musculature10. While the specific muscular anatomy is not completely understood, it has been shown that the antennal nerve, maxillary nerve, and prothoracic accessory nerve are responsible for the muscular targets involved in the feeding behavior. Most data involving the musculature and nerve anatomy of invertebrate feeding is limited to Calliphora larvae.
The feeding rate of second instar larvae can be assessed by retraction of the cephalopharyngeal sclerites (mouth hooks), and is reproducible and high-throughput. The cephalopharyngeal plates are innervated by fibers from central 5-HT neurons via the frontal nerve. The proventriculus, or foregut, is innervated by serotonergic fibers (recurrens nerve) that fasciculate in the midgut and are responsible for contractions of the foregut (Figure 1)11-12. Changes in axonal branching, and the number and size of varicosities along the neurite length, can be quantitated using immunohistochemical techniques. Manipulating neuronal 5-HT during development, either directly or indirectly, can change the functional output of this feeding circuit, which can be assessed and correlated with changes in the morphology of the neurite architecture.

<table border="0" cellpadding="0" cellspacing="0" width="758">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="40">
			<td height="40" style="height:40px;width:217px;">Eclipse E-800 Microscope</td>
			<td style="width:175px;">Nikon Instruments</td>
			<td style="width:115px;"></td>
			<td style="width:251px;"></td>
		</tr>
		<tr height="60">
			<td height="60" style="height:60px;width:217px;">Neuroleucida</td>
			<td style="width:175px;">MBF Biosciences</td>
			<td style="width:115px;">NL-15</td>
			<td style="width:251px;">Used to analyze gut fiber architecture, not necessary to have</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:217px;">Northern Eclipse</td>
			<td style="width:175px;">Empix Inc</td>
			<td style="width:115px;"></td>
			<td style="width:251px;">Imaging software</td>
		</tr>
		<tr height="60">
			<td height="60" style="height:60px;width:217px;">G-2E/C TRITC EX 528-553</td>
			<td style="width:175px;">Nikon Instruments</td>
			<td style="width:115px;">96312</td>
			<td style="width:251px;">Filter for specific secondary antibody</td>
		</tr>
		<tr height="80">
			<td height="80" style="height:80px;width:217px;">N.A. 0.75; W.D. 0.72 mm; DIC Prism: 40xI, 40x I-C; Spring loaded</td>
			<td style="width:175px;">Nikon Instruments</td>
			<td style="width:115px;">MRH00400</td>
			<td style="width:251px;">Objective used for imaging</td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:217px;">Simple Neurite Tracer</td>
			<td style="width:175px;">NIH Image J</td>
			<td style="width:115px;"></td>
			<td style="width:251px;"><a href="http://fiji.sc/Simple_Neurite_Tracer">http://fiji.sc/Simple_Neurite_Tracer</a></td>
		</tr>
	</tbody>
</table>

functional analysis of the larval feeding circuit in drosophila

The serotonergic feeding circuit in Drosophila melanogaster larvae can be used to investigate neuronal substrates of critical importance during the development of the circuit. Using the functional output of the circuit, feeding, changes in the neuronal architecture of the stomatogastric system can be visualized. Feeding behavior can be recorded by observing the rate of retraction of the mouth hooks, which receive innervation from the brain. Locomotor behavior is used as a physiological control for feeding, since larvae use their mouth hooks to traverse across an agar substrate. Changes in feeding behavior can be correlated with the axonal architecture of the neurites innervating the gut. Using immunohistochemistry it is possible to visualize and quantitate these changes. Improper handling of the larvae during behavior paradigms can alter data as they are very sensitive to manipulations. Proper imaging of the neurite architecture innervating the gut is critical for precise quantitation of number and size of varicosities as well as the extent of branch nodes. Analysis of most circuits allow only for visualization of neurite architecture or behavioral effects; however, this model allows one to correlate the functional output of the circuit with the impairments in neuronal architecture.

The serotonergic feeding circuit in the Drosophila larva can serve as an extremely effective model to observe the influence of particular factors on nervous system development. By quantitating feeding rate, it is possible to link the axonal architecture of the feeding circuit with its functional output (Figure 1). The locomotor assay is used as a physiological control for the retractions of the mouth hooks, since larvae use their mouth hooks to propel themselves across the surface of the agar. T...

Watch this Scientific Journal Video about Functional Analysis of the Larval Feeding Circuit in Drosophila at JoVE.com

Functional Analysis of the Larval Feeding Circuit in Drosophila

The feeding circuit in Drosophila melanogaster larvae serves a simple yet powerful model that allows changes in feeding rate to be correlated with alterations in the stomatogastric neural circuitry. This circuit is composed of central serotonergic neurons that send projections to the mouth hooks as well as the foregut.

Functional Analysis of the Larval Feeding Circuit in Drosophila

The serotonergic  feeding circuit in Drosophila  melanogaster larvae can be used to investigate neuronal substrates of  critical importance during the ...

functional-analysis-of-the-larval-feeding-circuit-in-drosophila

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Neuroscience

10.2K 조회수.  Saint Louis University School of Medicine.  초파리 유충의 먹이 회로는 공급 속도의 변화가 stomatogastric 신경 회로의 변화와 상관 관계가 될 수있는 간단하면서도 강력한 모델을 제공합니다. 이 회로는 입 후크 돌기뿐만 아니라 foregut 보내 중앙 세로토닌 성 신경 세포로 구성된다. 

비디오: Functional Analysis of the Larval Feeding Circuit in Drosophila

Visualization of Larval Segmental Nerves in 3rd Instar Drosophila Larval Preparations

Drosophila melanogaster is emerging as a powerful model system for studying the development and function of the nervous system, particularly because of its convenient genetics and fully sequenced genome. Additionally, the larval nervous system is an ideal model system to study mechanisms of axonal transport as the larval segmental nerves contain bundles of axons with their cell bodies located within the brain and their nerve terminals ending along the length of the body. Here we describe the procedure for visualization of synaptic vesicle proteins within larval segmental nerves. If done correctly, all components of the nervous system, along with associated tissues such as muscles and NMJs, remain intact, undamaged, and ready to be visualized. 3rd instar larvae carrying various mutations are dissected, fixed, incubated with synaptic vesicle antibodies, visualized and compared to wild type larvae. This procedure can be adapted for several different synaptic or neuronal antibodies and changes in the distribution of a variety of proteins can be easily observed within larval segmental nerves.

Visualization of Larval Segmental Nerves in 3rd Instar Drosophila Larval Preparations

Drosophila melanogaster larvae provide an ideal model system to investigate the mechanisms of axonal transport within larval segmental nerves. Using this procedure, 3rd instar larvae carrying various mutations can be compared to wild type larvae.

Drosophila melanogaster is emerging as a powerful model system for studying the development and function of the nervous system, particularly because of ...

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 ...

Morphological Analysis of Drosophila Larval Peripheral Sensory Neuron Dendrites and Axons Using Genetic Mosaics

Nervous system development requires the correct specification of neuron position and identity, followed by accurate neuron class-specific dendritic development and axonal wiring. Recently the dendritic arborization (DA) sensory neurons of the Drosophila larval peripheral nervous system (PNS) have become powerful genetic models in which to elucidate both general and class-specific mechanisms of neuron differentiation.
There are four main DA neuron classes (I-IV)1. They are named in order of increasing dendrite arbor complexity, and have class-specific differences in the genetic control of their differentiation2-10. The DA sensory system is a practical model to investigate the molecular mechanisms behind the control of dendritic morphology11-13 because: 1) it can take advantage of the powerful genetic tools available in the fruit fly, 2) the DA neuron dendrite arbor spreads out in only 2 dimensions beneath an optically clear larval cuticle making it easy to visualize with high resolution in vivo, 3) the class-specific diversity in dendritic morphology facilitates a comparative analysis to find key elements controlling the formation of simple vs. highly branched dendritic trees, and 4) dendritic arbor stereotypical shapes of different DA neurons facilitate morphometric statistical analyses.
DA neuron activity modifies the output of a larval locomotion central pattern generator14-16. The different DA neuron classes have distinct sensory modalities, and their activation elicits different behavioral responses14,16-20. Furthermore different classes send axonal projections stereotypically into the Drosophila larval central nervous system in the ventral nerve cord (VNC)21. These projections terminate with topographic representations of both DA neuron sensory modality and the position in the body wall of the dendritic field7,22,23. Hence examination of DA axonal projections can be used to elucidate mechanisms underlying topographic mapping7,22,23, as well as the wiring of a simple circuit modulating larval locomotion14-17.
We present here a practical guide to generate and analyze genetic mosaics24 marking DA neurons via MARCM (Mosaic Analysis with a Repressible Cell Marker)1,10,25 and Flp-out22,26,27 techniques (summarized in Fig. 1).

Morphological Analysis of Drosophila Larval Peripheral Sensory Neuron Dendrites and Axons Using Genetic Mosaics

The dendritic arborization sensory neurons of the Drosophila larval peripheral nervous system are useful models to elucidate both general and neuron class-specific mechanisms of neuron differentiation. We present a practical guide to generate and analyze dendritic arborization neuron genetic mosaics.

Nervous system development requires the correct specification of neuron position and identity, followed by accurate neuron class-specific dendritic ...

Visualization of Proprioceptors in Drosophila Larvae and Pupae

Proprioception is the ability to sense the motion, or position, of body parts by responding to stimuli arising within the body. In fruitflies and other insects proprioception is provided by specialized sensory organs termed chordotonal organs (ChOs) 2. Like many other organs in Drosophila, ChOs develop twice during the life cycle of the fly. First, the larval ChOs develop during embryogenesis. Then, the adult ChOs start to develop in the larval imaginal discs and continue to differentiate during metamorphosis.
The development of larval ChOs during embryogenesis has been studied extensively 10,11,13,15,16. The centerpiece of each ChO is a sensory unit composed of a neuron and a scolopale cell. The sensory unit is stretched between two types of accessory cells that attach to the cuticle via specialized epidermal attachment cells 1,9,14. When a fly larva moves, the relative displacement of the epidermal attachment cells leads to stretching of the sensory unit and consequent opening of specific transient receptor potential vanilloid (TRPV) channels at the outer segment of the dendrite 8,12. The elicited signal is then transferred to the locomotor central pattern generator circuit in the central nervous system.
Multiple ChOs have been described in the adult fly 7. These are located near the joints of the adult fly appendages (legs, wings and halters) and in the thorax and abdomen. In addition, several hundreds of ChOs collectively form the Johnston's organ in the adult antenna that transduce acoustic to mechanical energy 3,5,17,4.
In contrast to the extensive knowledge about the development of ChOs in embryonic stages, very little is known about the morphology of these organs during larval stages. Moreover, with the exception of femoral ChOs 18 and Johnston's organ, our knowledge about the development and structure of ChOs in the adult fly is very fragmentary.
Here we describe a method for staining and visualizing ChOs in third instar larvae and pupae. This method can be applied together with genetic tools to better characterize the morphology and understand the development of the various ChOs in the fly.

Visualization of Proprioceptors in Drosophila Larvae and Pupae

A method to immunostain and visualize chordotonal organs in larvae and pupae of Drosophila melanogaster is described.

Proprioception is the ability to sense the motion, or position, of body parts by responding to stimuli arising within the body. In fruitflies and other ...

Whole Mount Immunolabeling of Olfactory Receptor Neurons in the Drosophila Antenna

Odorant molecules bind to their target receptors in a precise and coordinated manner. Each receptor recognizes a specific signal and relays this information to the brain. As such, determining how olfactory information is transferred to the brain, modifying both perception and behavior, merits investigation. Interestingly, there is emerging evidence that cellular transduction and transcriptional factors are involved in the diversification of olfactory receptor neuron. Here we provide a robust whole mount immunological labeling method to assay in vivo olfactory receptor neuron organization. Using this method, we identified all olfactory receptor neurons with anti-ELAV antibody, a known pan-neural marker and Or49a-mCD8::GFP, an olfactory receptor neuron specifically expressed in Nba neuron using anti-GFP antibody.

Whole Mount Immunolabeling of Olfactory Receptor Neurons in the Drosophila Antenna

Herein we describe the process of whole mount immunostaining of Drosophila antennae, which enables us to better understand the molecular mechanisms involved in the diversification of olfactory receptor neurons (ORN)s.

Odorant molecules bind to their target receptors in a precise and coordinated manner. Each receptor recognizes a specific signal and relays this ...

Live Imaging of Drosophila Larval Neuroblasts

Stem cells divide asymmetrically to generate two progeny cells with unequal fate potential: a self-renewing stem cell and a differentiating cell. Given their relevance to development and disease, understanding the mechanisms that govern asymmetric stem cell division has been a robust area of study. Because they are genetically tractable and undergo successive rounds of cell division about once every hour, the stem cells of the Drosophila central nervous system, or neuroblasts, are indispensable models for the study of stem cell division. About 100 neural stem cells are located near the surface of each of the two larval brain lobes, making this model system particularly useful for live imaging microscopy studies. In this work, we review several approaches widely used to visualize stem cell divisions, and we address the relative advantages and disadvantages of those techniques that employ dissociated versus intact brain tissues. We also detail our simplified protocol used to explant whole brains from third instar larvae for live cell imaging and fixed analysis applications.

Live Imaging of Drosophila Larval Neuroblasts

This protocol details a streamlined method used to conduct live cell imaging in the context of an intact larval brain. Live cell imaging approaches are invaluable for the study of asymmetric neural stem cell divisions as well as other neurogenic and developmental processes, consistently uncovering mechanisms that were previously overlooked.

Stem cells divide asymmetrically to generate two progeny cells with unequal fate potential: a self-renewing stem cell and a differentiating cell. Given ...

Why Quantification Matters: Characterization of Phenotypes at the Drosophila Larval Neuromuscular Junction

Most studies on morphogenesis rely on qualitative descriptions of how anatomical traits are affected by the disruption of specific genes and genetic pathways. Quantitative descriptions are rarely performed, although genetic manipulations produce a range of phenotypic effects and variations are observed even among individuals within control groups.&#160;Emerging evidence shows that morphology, size and location of organelles play a previously underappreciated, yet fundamental role in cell function and survival. Here we provide step-by-step instructions for performing quantitative analyses of phenotypes at the Drosophila larval neuromuscular junction (NMJ). We use several reliable immuno-histochemical markers combined with bio-imaging techniques and morphometric analyses to examine the effects of genetic mutations on specific cellular processes. In particular, we focus on the quantitative analysis of phenotypes affecting morphology, size and position of nuclei within the striated muscles of Drosophila larvae. The Drosophila larval NMJ is a valuable experimental model to investigate the molecular mechanisms underlying the structure and the function of the neuromuscular system, both in health and disease. However, the methodologies we describe here can be extended to other systems as well.

Why Quantification Matters: Characterization of Phenotypes at the Drosophila Larval Neuromuscular Junction

Morphology, size and location of intracellular organelles are evolutionarily conserved and appear to directly affect their function. Understanding the molecular mechanisms underlying these processes has become an important goal of modern biology. Here we show how these studies can be facilitated by the application of quantitative techniques.

Most studies on morphogenesis rely on qualitative descriptions of how anatomical traits are affected by the disruption of specific genes and genetic ...

Removal of Drosophila Muscle Tissue from Larval Fillets for Immunofluorescence Analysis of Sensory Neurons and Epidermal Cells

Drosophila larval dendritic arborization (da) neurons are a popular model for investigating mechanisms of neuronal morphogenesis. Da neurons develop in communication with the epidermal cells they innervate and thus their analysis benefits from in situ visualization of both neuronally and epidermally expressed proteins by immunofluorescence. Traditional methods of preparing larval fillets for immunofluorescence experiments leave intact the muscle tissue that covers most of the body wall, presenting several challenges to imaging neuronal and epidermal proteins. Here we describe a method for removing muscle tissue from Drosophila larval fillets. This protocol enables imaging of proteins that are otherwise obscured by muscle tissue, improves signal to noise ratio, and facilitates the use of super-resolution microscopy to study da neuron development.

Removal of Drosophila Muscle Tissue from Larval Fillets for Immunofluorescence Analysis of Sensory Neurons and Epidermal Cells

Studies of neuronal morphogenesis using Drosophila larval dendritic arborization (da) neurons benefit from in situ visualization of neuronal and epidermal proteins by immunofluorescence. We describe a procedure that improves immunofluorescence analysis of da neurons and surrounding epidermal cells by removing muscle tissue from the larval body wall.

Drosophila larval dendritic arborization (da) neurons are a popular model for investigating mechanisms of neuronal morphogenesis. Da neurons develop in ...

Using Linear Agarose Channels to Study Drosophila Larval Crawling Behavior

Drosophila larval crawling is emerging as a powerful model to study neural control of sensorimotor behavior. However, larval crawling behavior on flat open surfaces is complex,&#160;including: pausing, turning, and meandering. This complexity in the repertoire of movement hinders detailed analysis of the events occurring during a single crawl stride cycle. To overcome this obstacle, linear agarose channels were made that constrain larval behavior to straight, sustained, rhythmic crawling. In principle, because agarose channels and the Drosophila larval body are both optically clear, the movement of larval structures labeled by genetically-encoded fluorescent probes can be monitored in intact, freely-moving larvae. In the past, larvae were placed in linear channels and crawling at the level of whole organism, segment, and muscle were analyzed1. In the future, larvae crawling in channels can be used for calcium imaging to monitor neuronal activity. Moreover, these methods can be used with larvae of any genotype and with any researcher-designed channel. Thus the protocol presented below is widely applicable for studies using the Drosophila larva as a model to understand motor control.

Using Linear Agarose Channels to Study Drosophila Larval Crawling Behavior

The Drosophila larva is a powerful model system to study neural control of behavior. This publication describes the use of linear agarose channels to elicit sustained bouts of linear crawling and methods to quantify the dynamics of larval structures during repetitive crawling behavior.

Drosophila larval crawling is emerging as a powerful model to study neural control of sensorimotor behavior. However, larval crawling behavior on flat ...

Focal Macropatch Recordings of Synaptic Currents from the Drosophila Larval Neuromuscular Junction

Drosophila neuromuscular junction (NMJ) is an excellent model system to study glutamatergic synaptic transmission. We describe the technique of focal macropatch recordings of synaptic currents from visualized boutons at the Drosophila larval NMJ. This technique requires customized fabrication of recording micropipettes, as well as a compound microscope equipped with a high magnification, long-distance water immersion objective, differential interference contrast (DIC) optics, and a fluorescent attachment. The recording electrode is positioned on the top of a selected synaptic bouton visualized with DIC optics, epi-fluorescence, or both. The advantage of this technique is that it allows monitoring the synaptic activity of a limited number of sites of release. The recording electrode has&#160;a diameter of several microns, and the release sites positioned outside of the electrode rim do&#160;not significantly affect the recorded currents. The recorded synaptic currents have fast kinetics and can be readily resolved. These advantages are especially important for the studies of mutant fly lines with enhanced spontaneous or asynchronous synaptic activity.

Focal Macropatch Recordings of Synaptic Currents from the Drosophila Larval Neuromuscular Junction

Synaptic currents can be recorded focally from visualized synaptic boutons at the Drosophila third instar larvae neuromuscular junction. This technique enables monitoring the activity of a single synaptic bouton.

Drosophila neuromuscular junction (NMJ) is an excellent model system to study glutamatergic synaptic transmission. We describe the technique of focal ...