Name: examining monosynaptic connections in drosophila using tetrodotoxin resistant sodium channels
Uploaded: 2018-02-14T14:00:00
Description: Watch this Scientific Journal Video about Examining Monosynaptic Connections in Drosophila Using Tetrodotoxin Resistant Sodium Channels at JoVE.com

We would like to thank Joshua Singer, Jonathan Schenk, as well as thoughtful reviewers for comments on the manuscript. We would also like to thank Ben White and Harold Zakon for discussions on the technique. Jonathan Schenk provided the data for Figure 3A. This work was supported by a Whitehall Foundation Grant and an NIH R21 to QG.

1. Prepare Flies and Identify GAL4 promoter Lines
<ol>
	<li>Select a GAL4 promoter line and cross it with flies carrying both the UAS-NaChBac transgene and an optogenetic transgene for activation. 
	NOTE: UAS-CsChrimson11 is selected due to its high conductance and the ease with which it activates NaChBac-mediated action potentials. Both UAS-NaChBac and UAS-CsChrimson are available from the Bloomington Stocks Repository.</li>
	<li>Prepare all-trans retinal as a stock solution in ethanol (35...

<ol>
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TERPS analysis compliments current techniques used for circuit cracking by enabling the detection of synapses between identified neurons. Specifically, the approach reveals monosynaptic connections by broadly silencing action potentials with TTX while restoring excitability in a select population of neurons with the TTX-insensitive sodium channel NaChBac. Synaptic release is elicited by optogenetic stimulation while postsynaptic events are monitored with whole-cell recordings. TERPS distinguishes itself from other approa...

A major goal of neuroscience is to map the connections between neurons to understand how information flows through circuits. Numerous approaches and resources have become available to test for functional connectivity between neurons in a range of model systems1,2. To generate the most accurate wiring diagrams using electrophysiology, it is important to resolve whether observed connections between two cells are direct and monosynaptic versus indirect and polysynaptic. A gold standard for making this distinction in mammalian neurons is to measure the latency between single action potentials in the presynaptic cells and the onset of excitatory postsynaptic currents (EPSCs) in the second neuron. Monosynaptic connections should have short latencies of a few milliseconds and low variability3. This approach can be complicated in invertebrate neurons because synapses may occur in their dendrites far from the somatic recording site, causing delays in detection due to long electrotonic distances between postsynaptic conductances and the recording electrode. Such delays can introduce ambiguity regarding poly- versus monosynaptic contributions. Additionally, small synaptic events may decay before reaching the somatic recordings site, and driving stronger presynaptic activity, is likely to recruit polysynaptic events.
Various techniques have been developed to test for monosynaptic connections in invertebrates. One approach uses high divalent cation solutions (Hi-Di) containing excess Mg++ and Ca++. This solution blocks polysynaptic connections by reducing release probability and increasing action potential threshold to favor detection of monosynaptic input4,5. Determining the precise ratio of Mg++ to Ca++ required, however, is not trivial and polysynaptic contributions may persist for even modest stimulation6. An alternative approach called GFP Reconstitution Across Synaptic Partners (GRASP) takes advantage of the proximity between pre- and postsynaptic membranes found at synapses to infer a monosynaptic connection 7. Here, a component of green fluorescent protein (GFP) is expressed in one neuron, and the complementary fragment of the molecule is expressed in a putative postsynaptic partner. The presence of fluorescence indicates that the two neurons are in close enough proximity to permit reconstitution of the GFP molecule and implies the existence of a synapse. GRASP can report synapses falsely, though, if two cells have closely apposed membranes, as in a nerve or fascicle. Variants of GRASP eliminate such false positives by tethering the presynaptic fragment of GFP directly to synaptobrevin, thus allowing reconstitution only at active synapses8. While GRASP and its variants have been instrumental in determining functional connectivity in the Drosophila CNS, some connections may not be made visible by GRASP if the distances between pre- and postsynaptic partners is relatively large. This is particularly pertinent in the assessment of volume transmission associated with neuromodulation9 or GABAergic inhibition10.
Here, a complementary and novel technique is demonstrated for testing direct monosynaptic connections in the Drosophila CNS. This method, called Tetrodotoxin Engineered Resistance for Probing Synapses (TERPS), works by co-expression of the tetrodotoxin (TTX)-resistant sodium channel, NaChBac, and an optogenetic activator in a presynaptic cell while recording from putative postsynaptic partners9. In the presence of TTX, all action potential-mediated activity is suppressed in cells other than those expressing NaChBac. The NaChBac channel selectively restores excitability in the targeted presynaptic cell(s), permitting light-evoked synaptic transmission. This method permits strong activation of the presynaptic neurons, such that connections can be resolved postsynaptically by somatic recording while reducing the probability of recruiting polysynaptic circuits. Importantly, this technique permits the study of volume transmission and reveals the spread of transmitter released from a single neuron throughout a circuit. In addition, TERPS can reveal the chemical nature of the connection through conventional pharmacology. TERPS is suitable for use in any model system that allows the transgenic expression of TTX-insensitive sodium channels.

<table border="0" cellpadding="0" cellspacing="0" width="946">
	<tbody>
		<tr height="40">
			<td height="40" style="height:40px;width:216px;">UAS-csChrimson</td>
			<td style="width:219px;">Bloomington Drosophila Stock Center</td>
			<td style="width:344px;">55135</td>
			<td style="width:167px;">Used as a neural activator</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">UAS-NaChBac</td>
			<td>Bloomington Drosophila Stock Center</td>
			<td>9466</td>
			<td style="width:167px;">Resotores excitibility in cells in TTX</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Tetrodotoxin</td>
			<td>Tochris</td>
			<td>1078</td>
			<td style="width:167px;">Special permission may be needed to purchase TTX as it is a controlled substance</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">all trans-Retinal</td>
			<td>Sigma-Aldrichall trans-Retinal</td>
			<td>R2500</td>
			<td style="width:167px;">Require co-factor for channelrhodopsin</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:216px;">Weldable 321 Stainless Steel&#160;Sheet,&#160;0.002&#34;&#160;Thick,&#160;10&#34;&#160;Wide</td>
			<td>McMaster Carr</td>
			<td>3254K7</td>
			<td style="width:167px;">Used to make custom fly holder. Custom foil can be laser cut at pololu.com from the provided PDF file</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Dissection Microscope</td>
			<td>Zeiss</td>
			<td>Stemi 2000-C</td>
			<td style="width:167px;">Used for dissection of preparation</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Waxer</td>
			<td>Almore</td>
			<td>Eectra Waxer 66000</td>
			<td style="width:167px;">Used during dissection to secure fly in foil</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Paraffin Wax</td>
			<td>Joann</td>
			<td>4917217</td>
			<td style="width:167px;">Used with waxer</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Number 5 forceps</td>
			<td>Fine Science Tools</td>
			<td>#5CO</td>
			<td style="width:167px;">Used for dissection and desheathing</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Dissection Scissors</td>
			<td>Fine Science Tools</td>
			<td>15001-08</td>
			<td style="width:167px;">Used to remove parts of the cuticle during dissection</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Tungsten wire</td>
			<td>A-M Systems</td>
			<td>797500</td>
			<td style="width:167px;">Use with electrolysis to make sharpened needles for dissection</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Reciculating Peristaltic Pump</td>
			<td>Simply Pumps (Amazon)</td>
			<td>PM200S</td>
			<td style="width:167px;">for recirculating TTX</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Speed Controller for peristaltic pump</td>
			<td>Zitrades (Amazon)</td>
			<td style="width:344px;">N/A</td>
			<td style="width:167px;">PWM Dimming Controller For LED Lights or Ribbon, 12 Volt 8 Amp,Adjustable Brightness Light Switch Dimmer Controller DC12V 8A 96W for Led Strip Light B</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Versa-Mount&#160;Precision Compressed Air Regulator</td>
			<td>McMaster Carr</td>
			<td style="width:344px;">1804T1</td>
			<td style="width:167px;">For applying positive pressure during patching</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Glass capilaries</td>
			<td>World Precision Instruments</td>
			<td style="width:344px;">TW150F-3</td>
			<td style="width:167px;">For patch pipettes</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Multipurpose Gauge</td>
			<td>McMaster Carr</td>
			<td>3846K431</td>
			<td style="width:167px;">Gauge for pressure regulator</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Electrophysiology Camera</td>
			<td>Dage MTI&#160;</td>
			<td>IR-1000</td>
			<td style="width:167px;">Any camera that works in the IR range (850 nm) will work. You do not want to use red illumination as this can activate csChrimson</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">IR LED</td>
			<td>Thorlabs&#160;</td>
			<td>M850F2</td>
			<td style="width:167px;">For oblique illumination</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">fiber optic for IR LED</td>
			<td>Thorlabs</td>
			<td>M89L01</td>
			<td style="width:167px;">Couples to IR LED</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Objective lens&#160;</td>
			<td>Olympus 40X</td>
			<td>LUMPlanFLN</td>
			<td style="width:167px;">This can be used on most microscipes and works well for visualizing fly neurons.</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Amber LED</td>
			<td>Thorlabs</td>
			<td>M590L3d</td>
			<td style="width:167px;">For visualizing RFP and mCherry</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Blue LED</td>
			<td>Thorlabs</td>
			<td>M470L3d</td>
			<td style="width:167px;">For visualizing GFP</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">GFP filter set</td>
			<td>Chroma</td>
			<td>49011</td>
			<td style="width:167px;">For visualizing GFP or stimulating channel2rhodopsin</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Custom mCherry Filter Set</td>
			<td>Chroma</td>
			<td style="width:344px;">&#160;et580/25x and t600lpxr (from the 49306 set) but with an et610lp barrier/emission optic</td>
			<td style="width:167px;">Use only if you wish to patch identified neurons with channel2rhodopsin</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Dichroic to combine Amber and blue LED</td>
			<td>Thorlabs</td>
			<td style="width:344px;">DMLP550R</td>
			<td style="width:167px;">Use only patch under mCherry and excite channel2rhodopsin with blue light.</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Red LED</td>
			<td>LEDSupply</td>
			<td>Cree XPE 620 - 630 nm</td>
			<td style="width:167px;">Used to drive csChrimson</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">LED Driver</td>
			<td>LEDSupply</td>
			<td>3021-D-E-1000</td>
			<td style="width:167px;">Used to drive LEDs for optogenetic stimulation</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Manipulator</td>
			<td>Sutter Instruments</td>
			<td>MP-225</td>
			<td style="width:167px;">Used to position pipette during recordings</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Patchclamp Amplifier</td>
			<td>A-M Systems</td>
			<td>Model 2400</td>
			<td style="width:167px;">An equivalent amplifier is suitable</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Bessel Filter</td>
			<td>Warner Instruments&#160;</td>
			<td>LPF 202A</td>
			<td style="width:167px;">Auxillary filter used to filter current trace to oscilloscope during patching.</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Data Acquisition System&#160;</td>
			<td>National Instruments</td>
			<td>NI PCIe-6321&#160;&#160;&#160;&#160;&#160;&#160; 781044-01</td>
			<td style="width:167px;">Used to record data from amplifier to computer</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Connector Block - BNC Terminal BNC-2090A</td>
			<td>National Instruments</td>
			<td>779556-01</td>
			<td style="width:167px;">Used to connect amplifier to DAQ card.</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Steel Foil&#160;</td>
			<td>McMaster Carr</td>
			<td>3254K7</td>
			<td style="width:167px;">Steel foil for custom recording chamber</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Magnets</td>
			<td>K&#38;J Magnetics</td>
			<td>D42</td>
			<td style="width:167px;">To secure recording chamber to ring stand</td>
		</tr>
		<tr height="100">
			<td height="100" style="height:100px;">1/16&#34; Cell Cast Acrylic Clear</td>
			<td>Pololu</td>
			<td></td>
			<td style="width:167px;">Used to make custom recording chamber. Acrylic can be laser cut at pololu.com from the provided PDF file</td>
		</tr>
	</tbody>
</table>

examining monosynaptic connections in drosophila using tetrodotoxin resistant sodium channels

Here, a new technique termed Tetrotoxin (TTX) Engineered Resistance for Probing Synapses (TERPS) is applied to test for monosynaptic connections between target neurons. The method relies on co-expression of a transgenic activator with the tetrodotoxin-resistant sodium channel, NaChBac, in a specific presynaptic neuron. Connections with putative post-synaptic partners are determined by whole-cell recordings in the presence of TTX, which blocks electrical activity in neurons that do not express NaChBac. This approach can be modified to work with any activator or calcium imaging as a reporter of connections. TERPS adds to the growing set of tools available for determining connectivity within networks. However, TERPS is unique in that it also reliably reports bulk or volume transmission and spillover transmission.

TERPS is used to distinguish between mono- and polysynaptic contributions in synaptic connections between neurons. While weak stimulation of a cell may be used to test direct connections, driving greater presynaptic activity often recruits polysynaptic connections (Figure 1A). TERPS works by co-expressing the TTX-insensitive sodium channel NaChBac and an optogenetic activator, and testing connections in the presence of TTX to eliminate polysynaptic connection...

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Examining Monosynaptic Connections in Drosophila Using Tetrodotoxin Resistant Sodium Channels

This article features a method to test the monosynaptic connections between neurons by employing tetrodotoxin and the tetrodotoxin-resistant sodium channel, NaChBac.

Examining Monosynaptic Connections in Drosophila Using Tetrodotoxin Resistant Sodium Channels

Here, a new technique termed Tetrotoxin (TTX) Engineered Resistance for Probing Synapses (TERPS) is applied to test for monosynaptic connections between ...

The overall goal of this technique is to identify monosynaptic connections electrophysiologically in drosophila using tetrodotoxin resistant sodium channels. The main advantages of this technique is that it is straightforward and can reveal the chemical nature of synapses. It is also suitable for the study of volume or bulk transmission.Generally, in videos new to this method, we struggle because of the difficulty of the dissection. By simply understanding the method, however, the logic is easily transferable to other model systems such as mice. For the recordings, have patch pipettes for the resistance near seven megaohms.Also, have external recording saline with a pH of 7.3 or less aerated continuously with carbogen containing 95%oxygen and 5%carbon dioxide. For the subjects, have a fly stock expressing csChrimson, propagating on food containing 0.2 millimolar of all trans-Retinal. For the recordings, select one to three-day-old adults.Load them into a glass scintillation vial and immobilize it using one minute exposure to ice-cold conditions. Then, lower the light level on the dissecting scope and coarse forceps to load an anesthetized fly into the custom-made recording chamber. Secure the fly to the chamber by surrounding with wax or UV curable epoxy.Position it dorsal side up with the foil roughly halfway up the thorax. The key to obtaining a great preparation is having the hole cut in the foil to be just the right size, so the fly is not squeezed nor able to fall through. Illuminate the preparation with optical fiber lights from either side and keep them as dim as possible.Next, cover the preparation with four to six drops of recording saline. Next, sharpen the tungsten wire or filament for the dissection. Apply about 20 volts of AC current to a potassium nitrate-saturated solution and repeatedly dip the tip of the wire very quickly into the solution.After 20 dips, the tip will be sharp. Now, adjust the lights to provide just enough visibility to use the sharpened wire to expose the brain by removing the cuticle, followed by the trachea and fat bodies. To access the antennal lobes, use a bent tungsten wire to gently tuck the antenna under the foil shield.Then use sharp forceps to gently tear away the glial sheathing covering the area of interest. Now transfer the preparation to the electrophysiology rig to make recordings. At the rig, immediately start perfusing the preparation with recording saline, bubbled with carbogen.Use a gravity-fed saline solution reservoir placed above the microscope stage. To collect the waste saline, use a vacuum line and a 2 liter flask. Next, load the patch pipette with 4 microliters of internal recording solution and attach the pipette to a micromanipulator.Then, zero the amplifier's offset and set the amplifier to deliver test pulses. Then, adjust IR oblique illumination in order to obtain a clear view of the brain. Now, while applying positive pressure to the pipette, approach the cell with the pipette.When contact with the cell is made, release the positive pressure to seal the pipette to the membrane. Then, set the holding potential of the membrane to minus 60 millivolts. And the pipette should form a gigaohm seal with the cell membrane.The holding current should drop to as low sub-picoamp level. To obtain constant gigaohm seals, make sure to keep your pipette clean by keeping positive pressure and avoid hitting tissue or approaching your cells. To proceed, set the amplifier to deliver test pulses from minus 50 to minus 60 millivolts.The test pulses will reveal a large capacitative transient representing the current necessary to charge the patch pipette. To remove capacitative transience, adjust the capacity compensation knobs on the amplifier. Now, apply brief pulses of negative pressure to rupture the cell membrane and obtain the whole cell configuration.A large increase in the capacitative transience indicates success. A small increase in the holding current should also be observed. Then, set the amplifier to current clamp mode.And adjust the cell's potential to between minus 50 and minus 60 millivolts. In preparation, configure the data acquisition system as indicated in the tech's protocol. The system requires a high-powered red LED positioned beneath the preparation, positioned to illuminate the fly at 0.238 milliwatts per square millimeter.Now, activate the presynaptic neurons optogenetically, using pulsed red light in csChrimson expression. Other methods can also be used. Before applying tetrodotoxin, a synaptic connection should be visible in response to a 40 millisecond light pulse.No response means a connection is unlikely. The holding potential may be adjusted to emphasize the excitatory or inhibitory connections, accordingly. Once a connection is verified, set up the saline profusion for recirculation at the saline.Set the pump so the saline level in the bath stays stable. Then, add enough tetrodotoxin to the system for a final concentration of one micromolar. This should stop the spiking activity of the patched neuron.If not, add more tetrodotoxin to the system. Now, apply brief pulses of red light to activate what is likely to be a monosynaptic connection. Then, proceed with adding pharmacological antagonists to the recirculating saline to test the chemical nature of the synaptic connections.Transgenic expression of the tetrodotoxin in sensitive sodium channel notchback rescues excitability in neurons and results in a large plateau potential. Interneurons in the antennal lobe respond to odors. However, excitatory post-synaptic currents are not easily resolved at the soma.So, do the responses arise directly from olfactory receptor neuron input? Using tERPs reveals that the olfactory receptor neurons make direct connections with the local interneurons. Stimulation of the serotonergic neurons in the antennal lobe results in a mixture of excitation and inhibition in local interneurons.Application of methysergide, a broad 5HT-receptor antagonist, blocked a slow hyperpolarization, but had no effect on the depolarization, while mecamylamine blocks the fast depolarization. This suggests that the stimulation is cholinergic. tERPs was used to resolve extrasynaptic volume transmission that occurs with either GABA or neuromodulators.In one example, application of tetrodotoxin did not suppress an inhibitory signal in the local interneuron. This inhibition was blocked using the serotonin antagonist, methysergide, suggesting a direct signal from a specific serotonergic neuron. After watching this video, you should have a good understanding of how to obtain whole cell recordings from drosophila neurons and assess their conductivity using tERPs.While attempting this procedure, it's important to remember to be patient and practice the difficult dissection repeatedly. Once mastered, this technique can be done in about an hour if it is performed properly. Following this procedure, other methods like pharmacology can be performed in order to answer additional questions like the nature of the chemical synapse.Don't forget that working with tetrodotoxin can be extremely hazardous and precautions, such as wearing gloves and working with small volumes, should always be taken while performing these procedures.

examining-monosynaptic-connections-drosophila-using-tetrodotoxin

Research

JoVE Journal

Neuroscience

Examining Local Network Processing using Multi-contact Laminar Electrode Recording

Cortical layers are ubiquitous structures throughout neocortex1-4 that consist of highly recurrent local networks. In recent years, significant progress has been made in our understanding of differences in response properties of neurons in different cortical layers5-8, yet there is still a great deal left to learn about whether and how neuronal populations encode information in a laminar-specific manner.
Existing multi-electrode array techniques, although informative for measuring responses across many millimeters of cortical space along the cortical surface, are unsuitable to approach the issue of laminar cortical circuits. Here, we present our method for setting up and recording individual neurons and local field potentials (LFPs) across cortical layers of primary visual cortex (V1) utilizing multi-contact laminar electrodes (Figure 1; Plextrode U-Probe, Plexon Inc).
The methods included are recording device construction, identification of cortical layers, and identification of receptive fields of individual neurons. To identify cortical layers, we measure the evoked response potentials (ERPs) of the LFP time-series using full-field flashed stimuli. We then perform current-source density (CSD) analysis to identify the polarity inversion accompanied by the sink-source configuration at the base of layer 4 (the sink is inside layer 4, subsequently referred to as granular layer9-12). Current-source density is useful because it provides an index of the location, direction, and density of transmembrane current flow, allowing us to accurately position electrodes to record from all layers in a single penetration6, 11, 12.

A fundamental issue in our understanding of cortical circuitry is how networks in different cortical layers encode sensory information. Here we describe electrophysiological techniques utilizing multi-contact laminar electrodes to record single-units and local field potentials and present analyses to identify cortical layers.

Cortical layers are ubiquitous structures throughout neocortex1-4 that consist of highly recurrent local networks. In recent years, significant progress ...

Correlating Behavioral Responses to fMRI Signals from Human Prefrontal Cortex: Examining Cognitive Processes Using Task Analysis

The aim of this methods paper is to describe how to implement a neuroimaging technique to examine complementary brain processes engaged by two similar tasks. Participants' behavior during task performance in an fMRI scanner can then be correlated to the brain activity using the blood-oxygen-level-dependent signal. We measure behavior to be able to sort correct trials, where the subject performed the task correctly and then be able to examine the brain signals related to correct performance. Conversely, if subjects do not perform the task correctly, and these trials are included in the same analysis with the correct trials we would introduce trials that were not only for correct performance. Thus, in many cases these errors can be used themselves to then correlate brain activity to them. We describe two complementary tasks that are used in our lab to examine the brain during suppression of an automatic responses: the stroop1 and anti-saccade tasks. The emotional stroop paradigm instructs participants to either report the superimposed emotional 'word' across the affective faces or the facial 'expressions' of the face stimuli1,2. When the word and the facial expression refer to different emotions, a conflict between what must be said and what is automatically read occurs. The participant has to resolve the conflict between two simultaneously competing processes of word reading and facial expression. Our urge to read out a word leads to strong 'stimulus-response (SR)' associations; hence inhibiting these strong SR's is difficult and participants are prone to making errors. Overcoming this conflict and directing attention away from the face or the word requires the subject to inhibit bottom up processes which typically directs attention to the more salient stimulus. Similarly, in the anti-saccade task3,4,5,6, where an instruction cue is used to direct only attention to a peripheral stimulus location but then the eye movement is made to the mirror opposite position. Yet again we measure behavior by recording the eye movements of participants which allows for the sorting of the behavioral responses into correct and error trials7 which then can be correlated to brain activity. Neuroimaging now allows researchers to measure different behaviors of correct and error trials that are indicative of different cognitive processes and pinpoint the different neural networks involved.

The goal of our research is to correlate behavior to brain activity. Accurate behavioral measures and imaging techniques allow us to elucidate brain-behavior relationships.

The aim of this methods paper is to describe how to implement a neuroimaging technique to examine complementary brain processes engaged by two similar ...

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 ...

Multi-photon Intracellular Sodium Imaging Combined with UV-mediated Focal Uncaging of Glutamate in CA1 Pyramidal Neurons

Multi-photon fluorescence microscopy has enabled the analysis of morphological and physiological parameters of brain cells in the intact tissue with high spatial and temporal resolution. Combined with electrophysiology, it is widely used to study activity-related calcium signals in small subcellular compartments such as dendrites and dendritic spines. In addition to calcium transients, synaptic activity also induces postsynaptic sodium signals, the properties of which are only marginally understood. Here, we describe a method for combined whole-cell patch-clamp and multi-photon sodium imaging in cellular micro domains of central neurons. Furthermore, we introduce a modified procedure for ultra-violet (UV)-light-induced uncaging of glutamate, which allows reliable and focal activation of glutamate receptors in the tissue. To this end, whole-cell recordings were performed on Cornu Ammonis subdivision 1 (CA1) pyramidal neurons in acute tissue slices of the mouse hippocampus. Neurons were filled with the sodium-sensitive fluorescent dye SBFI through the patch-pipette, and multi-photon excitation of SBFI enabled the visualization of dendrites and adjacent spines. To establish UV-induced focal uncaging, several parameters including light intensity, volume affected by the UV uncaging beam, positioning of the beam as well as concentration of the caged compound were tested and optimized. Our results show that local perfusion with caged glutamate (MNI-Glutamate) and its focal UV-uncaging result in inward currents and sodium transients in dendrites and spines. Time course and amplitude of both inward currents and sodium signals correlate with the duration of the uncaging pulse. Furthermore, our results show that intracellular sodium signals are blocked in the presence of blockers for ionotropic glutamate receptors, demonstrating that they are mediated by sodium influx though this pathway. In summary, our method provides a reliable tool for the investigation of intracellular sodium signals induced by focal receptor activation in intact brain tissue.

We describe the combination of focal UV-induced photo-activation of neuro-active compounds with whole-cell patch-clamp and multi-photon imaging of intracellular sodium transients in dendrites and spines of hippocampal neurons in acute tissue slices of the mouse brain.

Multi-photon fluorescence microscopy has enabled the analysis of morphological and physiological parameters of brain cells in the intact tissue with high ...

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 ...

A Simple Way to Measure Alterations in Reward-seeking Behavior Using Drosophila melanogaster

We describe a protocol for measuring ethanol self-administration in fruit flies (Drosophila melanogaster) as a proxy for changes in reward states. We demonstrate a simple way to tap into the fly reward system, modify experiences related to natural reward, and use voluntary ethanol consumption as a measure for changes in reward states. The approach serves as a relevant tool to study the neurons and genes that play a role in experience-mediated changes of internal state. The protocol is composed of two discrete parts: exposing the flies to rewarding and nonrewarding experiences, and assaying voluntary ethanol consumption as a measure of the motivation to obtain a drug reward. The two parts can be used independently to induce the modulation of experience as an initial step for further downstream assays or as an independent two-choice feeding assay, respectively. The protocol does not require a complicated setup and can therefore be applied in any laboratory with basic fly culture tools.

A Simple Way to Measure Alterations in Reward-seeking Behavior Using Drosophila melanogaster

We describe a protocol for inducing rewarding and nonrewarding experiences in fruit flies (Drosophila melanogaster) using voluntary ethanol consumption as a measure for changes in reward states.

We describe a protocol for measuring ethanol self-administration in fruit flies (Drosophila melanogaster) as a proxy for changes in reward states. We ...

Quantitative Cell Biology of Neurodegeneration in Drosophila Through Unbiased Analysis of Fluorescently Tagged Proteins Using ImageJ

With the rising prevalence of neurodegenerative diseases, it is increasingly important to understand the underlying pathophysiology that leads to neuronal dysfunction and loss. Fluorescence-based imaging tools and technologies enable unprecedented analysis of subcellular neurobiological processes, yet there is still a need for unbiased, reproducible, and accessible approaches for extracting quantifiable data from imaging studies. We have developed a simple and adaptable workflow to extract quantitative data from fluorescence-based imaging studies using Drosophila models of neurodegeneration. Specifically, we describe an easy-to-follow, semi-automated approach using Fiji/ImageJ to analyze two cellular processes: first, we quantify protein aggregate content and profile in the Drosophila optic lobe using fluorescent-tagged mutant huntingtin proteins; and second, we assess autophagy-lysosome flux in the Drosophila visual system with ratiometric-based quantification of a tandem fluorescent reporter of autophagy. Importantly, the protocol outlined here includes a semi-automated segmentation step to ensure all fluorescent structures are analyzed to minimize selection bias and to increase resolution of subtle comparisons. This approach can be extended for the analysis of other cell biological structures and processes implicated in neurodegeneration, such as proteinaceous puncta (stress granules and synaptic complexes), as well as membrane-bound compartments (mitochondria and membrane trafficking vesicles). This method provides a standardized, yet adaptable reference point for image analysis and quantification, and could facilitate reliability and reproducibility across the field, and ultimately enhance mechanistic understanding of neurodegeneration.

Quantitative Cell Biology of Neurodegeneration in Drosophila Through Unbiased Analysis of Fluorescently Tagged Proteins Using ImageJ

We have developed a simple and adaptable workflow to extract quantitative data from fluorescence-imaging-based cell biological studies of protein aggregation and autophagic flux in the central nervous system of Drosophila models of neurodegeneration.

With the rising prevalence of neurodegenerative diseases, it is increasingly important to understand the underlying pathophysiology that leads to neuronal ...

Quantification of Macronutrients Intake in a Thermogenetic Neuronal Screen using Drosophila Larvae

Foraging and feeding behaviors allow animals to access sources of energy and nutrients essential for their development, health, and fitness. Investigating the neuronal regulation of these behaviors is essential for the understanding of the physiological and molecular mechanisms underlying nutritional homeostasis. The use of genetically tractable animal models such as worms, flies, and fish greatly facilitates these types of studies. In the last decade, the fruit fly Drosophila melanogaster has been used as a powerful animal model by neurobiologists investigating the neuronal control of feeding and foraging behaviors. While undoubtedly valuable, most studies examine adult flies. Here, we describe a protocol that takes advantage of the simpler larval nervous system to investigate neuronal substrates controlling feeding behaviors when larvae are exposed to diets differing in their protein and carbohydrates content. Our methods are based on a quantitative colorimetric no-choice feeding assay, performed in the context of a neuronal thermogenetic-activation screen. As a read-out, the amount of food eaten by larvae over a 1 h interval was used when exposed to one of the three dye-labeled diets that differ in their protein to carbohydrates (P:C) ratios. The efficacy of this protocol is demonstrated in the context of a neurogenetic screen in larval Drosophila, by identifying candidate neuronal populations regulating the amount of food eaten in diets of different macronutrient quality. We were also able to classify and group the genotypes tested into phenotypic classes. Besides a brief review of the currently available methods in the literature, the advantages and limitations of these methods are discussed and, also, some suggestions are provided about how this protocol might be adapted to other specific experiments.

Quantification of Macronutrients Intake in a Thermogenetic Neuronal Screen using Drosophila Larvae

Described here is a protocol that enables the colorimetric quantification of the amount of food eaten within a defined interval of time by Drosophila melanogaster larvae exposed to diets of different macronutrient quality. These assays are conducted in the context of a neuronal thermogenetic screen.

Foraging and feeding behaviors allow animals to access sources of energy and nutrients essential for their development, health, and fitness. Investigating ...

Unraveling the Role of Discrete Areas of the Rat Brain in the Regulation of Ovulation through Reversible Inactivation by Tetrodotoxin Microinjections

Many experimental approaches have been used for studying the role of the brain in the regulation of ovulation. Examples include the lesion and deafferentation of neuronal groups, which are both invasive methods that permanently impair the integrity of the target area. These methods are accompanied by collateral effects that can affect the analysis of acute and temporal regulatory mechanisms. The stereotaxic implantation of guide cannulas aimed at specific brain regions, followed by a recovery period, allows researchers to microinject different drugs after the disappearance of the undesired effects of the surgery. Tetrodotoxin has been used to determine the roles of several brain areas in diverse physiological processes because it transiently inhibits the sodium-dependent action potentials, thus blocking all neural activity in the target region. This protocol combines this method with strategies for the assessment of the estrous cycle and ovulation to reveal the role of discrete brain regions in the regulation of ovulation at particular times of any given stage of the estrous cycle. Awake and unrestrained rats (Rattus norvegicus) were used to avoid the blocking effects that anesthetics and stress hormones exert on ovulation. This protocol can be easily adapted to other species, brain targets and pharmacological agents to study different physiological processes. Future improvements to this method include the design of a microinjection system using glass capillaries of small diameter instead of guide cannulas. This will reduce the amount of tissue damaged during the implantation and decrease the spread of the infused drugs outside the target area.

This protocol describes the construction of a low-cost microinjection system, its stereotaxic implantation into deep-brain structures and the procedure for timed microinjections of tetrodotoxin in awake and unrestrained rats. The goal is to reveal the participation of hypothalamic structures in the regulation of ovulation by inhibiting their neural activity.

Many experimental approaches have been used for studying the role of the brain in the regulation of ovulation. Examples include the lesion and ...

A Standardized Pipeline for Examining Human Cerebellar Grey Matter Morphometry using Structural Magnetic Resonance Imaging

Multiple lines of research provide compelling evidence for a role of the cerebellum in a wide array of cognitive and affective functions, going far beyond its historical association with motor control. Structural and functional neuroimaging studies have further refined understanding of the functional neuroanatomy of the cerebellum beyond its anatomical divisions, highlighting the need for the examination of individual cerebellar subunits in healthy variability and neurological diseases. This paper presents a standardized pipeline for examining cerebellum grey matter morphometry that combines high-resolution, state-of-the-art approaches for optimized and automated cerebellum parcellation (Automatic Cerebellum Anatomical Parcellation using U-Net Locally Constrained Optimization; ACAPULCO) and voxel-based registration of the cerebellum (Spatially Unbiased Infra-tentorial Template; SUIT) for volumetric quantification. 
The pipeline has broad applicability to a range of neurological diseases and is fully automated, with manual intervention only required for quality control of the outputs. The pipeline is freely available, with substantial accompanying documentation, and can be run on Mac, Windows, and Linux operating systems. The pipeline is applied in a cohort of individuals with Friedreich ataxia (FRDA), and representative results, as well as recommendations on group-level inferential statistical analyses, are provided. This pipeline could facilitate reliability and reproducibility across the field, ultimately providing a powerful methodological approach for characterizing and tracking cerebellar structural changes in neurological diseases.

A standardized pipeline is presented for examining cerebellum grey matter morphometry. The pipeline combines high-resolution, state-of-the-art approaches for optimized and automated cerebellum parcellation and voxel-based registration of the cerebellum for volumetric quantification.

Multiple lines of research provide compelling evidence for a role of the cerebellum in a wide array of cognitive and affective functions, going far beyond ...