Name: levator auris longus preparation for examination of mammalian neuromuscular transmission under voltage clamp conditions
Uploaded: 2018-05-05T14:00:00.000+00:00
Duration: 10 min 45 s
Description: Watch this Scientific Journal Video about Levator Auris Longus Preparation for Examination of Mammalian Neuromuscular Transmission Under Voltage Clamp Conditions at JoVE.com

We thank Dr. Mark M. Rich and Daniel Miranda for editorial comments, Ahmad Khedraki for helping establish this technique, and Wright State University for financial support (startup fund to A.A.V.).

<ol>
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The authors have nothing to disclose.

Described here is the preparation and use of the mouse LAL muscle for the measurement of neuromuscular transmission under current- or voltage-clamp conditions. There are several important points to consider for dissecting out the LAL. Cleaning excess connective tissue from the muscle aids in electrode impalement, as the electrodes can snag the connective tissue when positioning them for impalement. However, only remove connective tissue that can be taken away easily to limit the chances of damaging the muscle. The isolation of the nerve should be performed with care because it is very delicate. To avoid nerve damage, it is helpful to leave some of the surrounding tissue attached to the end of the nerve through which a pin can be placed to secure the nerve to the dish. Also, take care not to crush the nerve when positioning the nerve stimulator. Finally, the order in which the electrodes are impaled into the fiber is important. The blunt electrode is not as easy to impale and should be impaled first. If the sharp electrode were impaled first, the blunt electrode could push the muscle fiber down before it pierces the membrane, possibly causing the sharp electrode to come out of the fiber. This would make it necessary to impale the fiber a second time with the sharp electrode which would cause unnecessary membrane damage. It is also helpful that the amplifier being used can simultaneously measure the current and voltage of the current passing electrode so that a negative deflection in the membrane potential can be observed, indicating that the electrode has been impaled.
One feature of the LAL that can be beneficial is the ability to remove both muscles simultaneously. This can be great for performing electrophysiology and molecular biology experiments in the same animal. This can be accomplished by following essentially the same protocol described here with minor changes. Follow all steps under headings 1-3 doing everything described on the right side as well as the left. At step 4, it is best to begin cutting at the ventrolateral side of the right ear to remove the muscles. As described earlier, always keep the blades pressed against the skull to cut as deep as possible leaving inferior muscles attached to the LAL. Continue to cut towards the right ear past the midline, keeping the blade as deep as possible. At this point, the rest of the procedure is as described in this protocol, only perform the remaining steps on both muscles. Once the muscles have been cleaned, one LAL can be cut away and frozen for later molecular analysis and the other can be used for electrophysiology. It would be difficult to perform electrophysiology studies with both muscles of the same animal. To do so, the midline must be cut to separate the muscles and doing so will likely damage some muscle fibers.
The LAL has long been used to examine neuromuscular transmission because its thin nature allows for the easy identification of motor endplates and excellent ex vivo perfusion1,3,4,5,6,7,8. In addition to the use of 4-di-2-asp, other groups have used rhodamin-conjugated bungarotoxin at low concentrations22. We have used the LAL for electrophysiological examinations, purinergic signaling, and defects in Huntington&#39;s disease16,20. The LAL is also ideal for live-cell imaging studies. For example, several studies have used the LAL to measure synaptic vesicle release and uptake23,24. This can be done using dyes, such as FM 1-43.
Because the endplates can be easily observed with a fluorescent stain, the electrodes can be placed in close proximity to the motor endplate within the length constant of the muscle fiber. Electrode placement at the endplate and the use of a high compliance two-electrode voltage-clamp system enables investigators to fully control the endplate potential with less than 1% error16. This can be important because the commonly used corrections for non-linear summation of synaptic potentials recorded under current-clamp conditions10 do not account for changes in the postsynaptic membrane caused by experimental conditions and/or disease state. For example, reduced resting endplate conductances will amplify postsynaptic potentials19, even those corrected for non-linear summation. In contrast, voltage-clamped postsynaptic currents are not subjected to non-linear summation errors and are independent of the postsynaptic membrane properties. Demonstrating this, we have recently shown contrasting results from endplate potentials compared to currents recorded from hyper-excitable Huntington&#39;s disease skeletal muscle16.
A final key advantage of using the LAL for studying neuromuscular transmission is that recordings are from a single synapse. Neuromuscular transmission recorded from a single, fully voltage-clamped endplate provides some of the most detailed and accurate data on synaptic transmission currently available, which is ideal for modeling and unraveling the complexity of synaptic physiology.

Studying synaptic transmission at the neuromuscular junction provides insights into the dynamic relationship between the nervous and skeletal muscular systems and is an excellent model for examining synaptic physiology. The levator auris longus (LAL) is a thin muscle, allowing for the neuromuscular junctions to be easily visualized. Previous reports have described the convenience of using the LAL to examine synaptic drugs and toxins and have characterized the skeletal muscle fiber type characteristics of the LAL1,2. Numerous studies have used the LAL to examine neuromuscular physiology3,4,5,6,7,8. For electrophysiology, the ability to easily observe LAL neuromuscular junctions allows for the accurate placement of microelectrodes at the motor endplate and greatly reduces space clamp issues in recording synaptic transmission. Current-clamp recordings of the muscle membrane properties, such as the membrane time constant (&#964;m) and input resistance (Rin) are readily obtained. Furthermore, these properties can be measured from the same muscle fibers used to record neuromuscular transmission, allowing for a direct comparison of synaptic function to the muscle membrane properties. Analysis of these data can provide key insights into the physical mechanisms of many neuromuscular diseases and states of altered activity.
A key aspect of the technique described here is the use of voltage-clamp&#160;for synaptic recordings, which are not subject to the non-linearities encountered in current-clamp&#160;and are independent of the muscle membrane properties. Advantages of using voltage-clamp as opposed to current-clamp to examine neuromuscular transmission were established by pioneering efforts in the 1950s9. Under current-clamp, EPPs that exceed 10-15 mV in amplitude are not a linear product of the mEPP amplitude9. For example, if the average mEPP is 1 mV, an EPP of 5 mV can be assumed to be the product of 5 mEPPs (QC of 5); whereas, an EPP of 40 mV will be the product of more than 40 mEPPs. This non-linearity at larger EPPs occurs because the driving force for the EPP, which is the difference between the membrane potential and equilibrium potential for the acetylcholine receptor (~-10 mV), substantially decreases during large EPPs. This issue is avoided in voltage-clamp experiments because the muscle membrane potential does not change during voltage-clamp experiments. A drawback is that voltage-clamp experiments are technically more difficult to complete than current-clamp recording. With this in mind, McLachlan and Martin developed a straightforward mathematical correction that accounts for non-linearities in current-clamp recordings of EPPs10. The corrections work well11,12,13, but importantly, assume that the muscle membrane properties have not been disrupted.
The muscle membrane properties are especially important to consider if studying conditions or disease states that disrupt the muscle. For example, skeletal muscle from the R6/2 transgenic model of Huntington&#39;s disease is hyperexcitable due to a progressive reduction in the resting chloride and potassium currents14,15. As a consequence, mEPPs and EPPs are amplified in the R6/2 skeletal muscle. Certainly, additional factors can alter mEPPs and EPPs. Work with a different model of Huntington&#39;s disease mice (R6/1) found changes in EPPs that seemed to be related to SNARE-proteins8. To assess the mechanisms causing altered neuromuscular transmission, it would be beneficial to eliminate the effects of altered muscle membrane properties by using a voltage-clamp. In a recent study, the R6/2 neuromuscular transmission was studied under both current- and voltage-clamp conditions using the technique described herein. The entirety of the motor endplates were voltage-clamped with less than 1% error by placing two microelectrodes within the length constant of the endplate16. It was shown that voltage-clamp and corrected current-clamp records yielded contrasting measurements of neuromuscular transmission in R6/2 muscle. This highlights that it may be difficult to correct EPPs for non-linearities if the muscle membrane properties have been altered and shows the benefits of obtaining voltage-clamp records that are independent of the muscle membrane properties. The protocol presented herein is ideal for examining conditions or disease states that affect synaptic transmission and the postsynaptic membrane properties.

<table><tbody><tr><td>Olympus Compound Microscope</td><td>Olympus</td><td>BX51WI</td><td></td></tr><tr><td>10x Objective</td><td>Olympus</td><td>UMPLFLN10XW</td><td></td></tr><tr><td>40x Objective</td><td>Olympus</td><td>LUMPLFLN40XW</td><td></td></tr><tr><td>Borosilicate Glass</td><td>Sutter Instruments</td><td>BF150-86-7.5</td><td></td></tr><tr><td>CCD Camera</td><td>Santa Barbara Instruments Group</td><td>ST-7XMEI</td><td></td></tr><tr><td>Mater-9 Pulse Generator</td><td>AMPI</td><td></td><td></td></tr><tr><td>Iso-flex Stimulus Isolator</td><td>AMPI</td><td></td><td></td></tr><tr><td>pCLAMP 10 Data Acquisition and Analysis Software</td><td>Molecular Devices</td><td>1-2500-0180</td><td></td></tr><tr><td>Concentric Bipolar Electrode</td><td>FHC</td><td>CBDSH75</td><td></td></tr><tr><td>Ball-joint Manipulator</td><td>Narishige&amp;nbsp;</td><td></td><td></td></tr><tr><td>Non-metalic Syringes 34 Gauge</td><td>World Precision Instruments</td><td>MF34G-5</td><td></td></tr><tr><td>Nikon Stereomicroscope</td><td>Nikon</td><td>SMZ800N</td><td></td></tr><tr><td>No. 5 Forceps</td><td>Fine Science Tools</td><td></td><td></td></tr><tr><td>Spring Scissors</td><td>Fine Science Tools</td><td>15006-09</td><td></td></tr><tr><td>No. 2 Forceps</td><td>Roboz</td><td>RS-5Q41</td><td></td></tr><tr><td>Microdissecting Scissors</td><td>Roboz</td><td>RS-5912SC</td><td></td></tr><tr><td>Sylgard 184 Silicone Elastomer Kit</td><td>Dow Corning</td><td>2404019862</td><td></td></tr><tr><td>Hair Removal Cream</td><td>Nair</td><td></td><td></td></tr><tr><td>Grass SD9 Stimulator</td><td>Grass Medical</td><td></td><td></td></tr><tr><td>Model P-1000 Micropipette Puller</td><td>Sutter Instruments</td><td>P-1000</td><td></td></tr><tr><td>Axon Digidata 1550 Low-noise Data Acuisition System</td><td>Molecular Devices</td><td></td><td></td></tr><tr><td>Low Pass Bessell Filter</td><td>Warner Instrument Corp.</td><td>LPF-8</td><td></td></tr><tr><td>Left-handed Micromanipulator</td><td>Siskiyou Corp.</td><td>MX1641/45DL</td><td></td></tr><tr><td>Right-handed Micromanipulator</td><td>Siskiyou Corp.</td><td>MX1641/45DR</td><td></td></tr><tr><td>Single Motion Controler</td><td>Siskiyou Corp.</td><td>MC100e</td><td></td></tr><tr><td>Crossed Roller Micromanipulator</td><td>Siskiyou Corp.</td><td>MX1641R</td><td>This was added to the Z-axis of the Left and Right-handed micromanipulators to allow the z axis to be motorized. This custom set-up is cheaper and less bulky than buying a 4-axis motorized micromanipulator. It also allows us to control both micromanipulators with one controller</td></tr><tr><td>All chemicals were orded from Fisher except,</td><td></td><td></td><td></td></tr><tr><td>BTS</td><td>Toronto Research Chemicals</td><td>B315190</td><td></td></tr><tr><td>CTX</td><td>Alomone Labs</td><td>C-270</td><td></td></tr><tr><td>4-Di-2-Asp</td><td>Molecular Probes</td><td></td><td>Molecular probes is no longer a company. Now ordered through Fisher</td></tr></tbody></table>

levator auris longus preparation for examination of mammalian neuromuscular transmission under voltage clamp conditions

This protocol describes a technique to record synaptic transmission from the neuromuscular junction under current-clamp and voltage-clamp conditions. An ex vivo preparation of the levator auris longus (LAL) is used because it is a thin muscle that provides easy visualization of the neuromuscular junction for microelectrode impalement at the motor endplate. This method allows for the recording of spontaneous miniature endplate potentials and currents (mEPPs and mEPCs), nerve-evoked endplate potentials and currents (EPPs and EPCs), as well as the membrane properties of the motor endplate. Results obtained from this method include the quantal content (QC), number of vesicle release sites (n), probability of vesicle release (prel), synaptic facilitation and depression, as well as the muscle membrane time constant (&#964;m) and input resistance. Application of this technique to mouse models of human disease can highlight key pathologies in disease states and help identify novel treatment strategies. By fully voltage-clamping a single synapse, this method provides one of the most detailed analyses of synaptic transmission currently available.

Figure 8 shows an example of the current pulses (Figure 8A) and the voltage responses (Figure 8B) from one LAL fiber under current-clamp from a 12-week-old wild type R6/2 mouse. The presence of mEPPs indicates that these records were taken from the motor endplate. The records were obtained in normal physiological saline solution. These current-clamp records can be analyzed to determine the Rin and &#964;m of that fiber16,19,20.
A representative recording of an EPC and two mEPCs, obtained under voltage-clamp conditions, is shown in Figure 9A. The brief current deflection preceding the EPC is the artifact caused by nerve stimulation. The analysis of mEPCs and EPCs can be made quicker with event detection software. This tool allows the researcher to make a template that can then automatically detect the events within the recording. The events can be superimposed and exported into any data analysis software. Figure 9B shows the superimposed EPCs and mEPCs (inset) from a representative fiber.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/57482/57482fig1.jpg" /> 
Figure 1: General location of the levator auris longus muscle 
The LAL muscle is located on the dorsal surface of the head. The red dotted line highlights the path for cutting the skin for removal on the dorsal (A) and lateral (B) surface. The LAL attaches to the base of the ear, thus approximately 1 mm of skin around the base of the ear should remain intact to avoid cutting the LAL. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57482/57482fig1large.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/57482/57482fig2.jpg" /> 
Figure 2: Exposed levator auris longus muscle 
The LAL (yellow and green) is located just underneath the skin and is the most superficial muscle in the highlighted area. There are two portions of the muscle, the cranial (yellow) and caudal (green) regions. The cranial region emerges from the midline at the first four cervical vertebrae and runs toward the anterior part of the base of the auricle. For reference, the midline is a band of connective tissue that runs from the scapulae (white arrow) toward the nose. The right and left LAL muscle connect at the midline over the cranium. The cranial portion of the LAL is much wider than the caudal portion. The caudal portion attaches near the midline at the fourth and fifth cervical vertebrae and connects to the posterior part of the base of the auricle. During the dissection, keep a couple millimeters of skin around the cartilaginous ear to prevent cutting the LAL, which is marked in the figure by a bracketed dashed line. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57482/57482fig2large.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/57482/57482fig3.jpg" /> 
Figure 3: Crude dissection of the levator auris longus and surrounding muscle 
Once removed from the animal, the tissue is pinned, dorsal side down (LAL on bottom), into a silicone elastomer lined dish using fine pins made as described in section 5.3. Once secured to the bottom of the dish, the overlying muscle layers can be removed. An insect pin through the ear canal is indicated with a white dashed arrow. The yellow arrows show ideal pin placement for removal of unwanted muscles. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57482/57482fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/57482/57482fig4.jpg" /> 
Figure 4: Muscle layer directly inferior to the levator auris longus 
Highlighted in blue is the abductor auris longus (AAL), in red is the auricularis scupularis (AS), and in yellow is the interscutularis (IS). The LAL is the main, underlying muscle in this image. For reference, the ear and surrounding skin is outlined by a solid black line. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57482/57482fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/57482/57482fig5.jpg" /> 
Figure 5: Silicone-elastomer-lined, custom perfusion chamber 
Shown is the custom 35 mm perfusion dish used to secure the LAL for electrophysiological recordings (A). Silicone elastomer has been used to create a surface suitable for pining the tissue. In the center of the chamber is a rounded platform that is helpful when impaling the fibers. The platform supports the muscle fibers from underneath when applying a downward force with electrodes during the impalement process. This platform was shaped by allowing silicone elastomer to form to the curve of a 50 mL conical tube. A slice of this rounded silicone elastomer can then be glued to the bottom of the chamber with more silicone elastomer. An outlined representation of the dish as well as a side-on view are shown in B and C where the perfusion chamber can be seen more clearly. <a href="/files/ftp_upload/57482/57482fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/57482/57482fig6.jpg" /> 
Figure 6: Electrophysiology experiment set-up 
A small bipolar electrode is held in place with a magnetic ball-joint manipulator to stimulate the nerve of the LAL. The microscope stage can be made to easily hold a magnetic platform with the use of an adhesive magnetic material (as can be found at a craft or hardware store for making refrigerator magnets). Also shown are the headstages and electrodes positioned above an LAL sample. An important instrument is the water-immersion, beveled objective with a ceramic dipping cone, as shown. The beveled end allows for easier electrode placement and the ceramic material minimizes electrical noise. <a href="/files/ftp_upload/57482/57482fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" class="xfigimg" src="/files/ftp_upload/57482/57482fig7.jpg" /> 
Figure 7: Neuromuscular junction identification 
All images show the LAL stained with 5 &#181;M 4-Di-2-Asp (Green) to allow for visualization of neuromuscular junctions. (A) A bright band of neuromuscular junctions can be seen (yellow arrows) when viewing the muscle through a 10X objective. Branching axons can also be seen as indicated by the white dashed arrow. (B) Small confocal stacks (5 x 1 &#181;m) of three neuromuscular junctions (yellow arrows). Healthy muscle fibers have clear striations as well as multiple myonuclei that appear as dark spots along the sarcolemma of the fiber (white arrows). Often the axons innervating the neuromuscular junctions can be observed as well. (C) A fiber with a stained neuromuscular junction that is impaled with glass electrodes. The electrodes have been enhanced with a white highlight so that they can be seen more easily. <a href="/files/ftp_upload/57482/57482fig7large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 8" class="xfigimg" src="/files/ftp_upload/57482/57482fig8.jpg" /> 
Figure 8: Current-clamp recording of membrane properties 
Injected current pulses (A) and the resulting membrane potential responses (B) recorded from one fiber of the LAL bathed in physiologic saline solution. <a href="/files/ftp_upload/57482/57482fig8large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 9" class="xfigimg" src="/files/ftp_upload/57482/57482fig9v3.jpg" /> 
Figure 9: Two-electrode voltage-clamp recordings 
A raw trace of an EPC and two mEPCs recorded in two-electrode voltage-clamp (A). Superimposed EPCs and mEPCs (inset) from a single fiber (B). <a href="/files/ftp_upload/57482/57482fig9v3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Levator Auris Longus Preparation for Examination of Mammalian Neuromuscular Transmission Under Voltage Clamp Conditions at JoVE.com

Levator Auris Longus Preparation for Examination of Mammalian Neuromuscular Transmission Under Voltage Clamp Conditions

The protocol described in this paper uses the mouse levator auris longus (LAL) muscle to record spontaneous and nerve-evoked postsynaptic potentials (current-clamp) and currents (voltage-clamp) at the neuromuscular junction. Use of this technique can provide key insights into mechanisms of synaptic transmission under normal and disease conditions.

Levator Auris Longus Preparation for Examination of Mammalian Neuromuscular Transmission Under Voltage Clamp Conditions

This protocol describes a technique to record synaptic transmission from the neuromuscular junction under current-clamp and voltage-clamp conditions. An ...

levator-auris-longus-preparation-for-examination-mammalian

Nanyang Technological University

Research

JoVE Journal

Neuroscience

9.3K Views.  Wright State University. Het protocol beschreven in dit document maakt gebruik van de muis Musculus levator auris longus (LAL) spier graag spontane, zenuw-opgeroepen postsynaptisch potentieel (current-clamp) en stromingen (spanning-klem) op de motorische eindplaat. Gebruik van deze techniek kan belangrijke inzicht verwerven in de mechanismen van synaptische transmissie onder normale en zieke voorwaarden.

Video: Levator Auris Longus Preparation for Examination of Mammalian Neuromuscular Transmission Under Voltage Clamp Conditions

Patch Clamp Recordings on Intact Dorsal Root Ganglia from Adult Rats

Patch clamp studies from dorsal root ganglia (DRGs) neurons have increased our understanding of the peripheral nervous system. Currently, the majority of recordings are conducted on dissociated DRG neurons, which is a standard preparation for most laboratories. Neuronal properties, however, can be altered by axonal injury resulting from enzyme digestion used in acquiring dissociated neurons. Further, dissociated neuron preparations cannot fully represent the microenvironment of the DRG since loss of contact with satellite glial cells that surround the primary sensory neurons is an unavoidable consequence of this method. To overcome the limitations in using conventional dissociated DRG neurons for patch clamp recordings, in this report we describe a method to prepare intact DRGs and conduct patch clamp recordings on individual primary sensory neurons ex vivo. This approach permits the fast and straightforward preparation of intact DRGs, mimicking in vivo conditions by keeping DRG neurons associated with their surrounding satellite glial cells and basement membrane. Furthermore, the method avoids axonal injury from manipulation and enzyme digestion such as when dissociating DRGs. This ex vivo preparation can additionally be used to study the interaction between primary sensory neurons and satellite glial cells.

This manuscript describes how to prepare intact dorsal root ganglia for patch clamp recordings. This preparation maintains the microenvironment for neurons and satellite glial cells, thus avoiding the phenotypic and functional changes seen using dissociated DRG neurons.

Patch clamp studies from dorsal root ganglia (DRGs) neurons have increased our understanding of the peripheral nervous system. Currently, the majority of ...

Biochemistry

Electrophysiological Methods for Recording Synaptic Potentials from the NMJ of Drosophila Larvae

In this video, we describe the electrophysiological methods for recording synaptic transmission at the neuromuscular junction (NMJ) of Drosophila larva. The larval neuromuscular system is a model synapse for the study of synaptic physiology and neurotransmission, and is a valuable research tool that has defined genetics and is accessible to experimental manipulation. Larvae can be dissected to expose the body wall musculature, central nervous system, and peripheral nerves. The muscles of Drosophila and their innervation pattern are well characterized and muscles are easy to access for intracellular recording. Individual muscles can be identified by their location and orientation within the 8 abdominal segments, each with 30 muscles arranged in a pattern that is repeated in segments A2 - A7. Dissected drosophila larvae are thin and individual muscles and bundles of motor neuron axons can be visualized by transillumination1. Transgenic constructs can be used to label target cells for visual identification or for manipulating gene products in specific tissues. In larvae, excitatory junction potentials (EJP&#8217;s) are generated in response to vesicular release of glutamate from the motoneurons at the synapse. In dissected larvae, the EJP can be recorded in the muscle with an intracellular electrode. Action potentials can be artificially evoked in motor neurons that have been cut posterior to the ventral ganglion, drawn into a glass pipette by gentle suction and stimulated with an electrode. These motor neurons have distinct firing thresholds when stimulated, and when they fire simultaneously, they generate a response in the muscle. Signals transmitted across the NMJ synapse can be recorded in the muscles that the motor neurons innervate. The EJP&#8217;s and minature excitatory junction potentials (mEJP&#8217;s) are seen as changes in membrane potential. Electrophysiological responses are recorded at room temperature in modified minimal hemolymph-like solution2 (HL3) that contains 5 mM Mg2+ and 1.5 mM Ca2+. Changes in the amplitude of evoked EJP&#8217;s can indicate differences in synaptic function and structure. Digitized recordings are analyzed for EJP amplitude, mEJP frequency and amplitude, and quantal content.

Here we describe electrophysiological methods for measuring synaptic transmission at the neuromuscular junction of Drosophila larva. Evoked release is initiated artificially by stimulating the motor neuron axons, and transmission through the NMJ can be measured by the postsynaptic response evoked in the muscle.

In this video, we describe the electrophysiological methods for recording synaptic transmission at the neuromuscular junction (NMJ) of Drosophila larva. ...

Biology

Dissecting and Recording from The C. Elegans Neuromuscular Junction

Neurotransmission is the process by which neurons transfer information via chemical signals to their post-synaptic targets, on a rapid time scale. This complex process requires the coordinated activity of many pre- and post-synaptic proteins to ensure appropriate synaptic connectivity, conduction of electrical signals, targeting and priming of secretory vesicles, calcium sensing, vesicle fusion, localization and function of postsynaptic receptors and finally, recycling mechanisms. As neuroscientists it is our goal to elucidate which proteins function in each of these steps and understand their mechanisms of action. Electrophysiological recordings from synapses provide a quantifiable read out of the underlying electrical events that occur during synaptic transmission. By combining this technique with the powerful array of molecular and genetic tools available to manipulate synaptic proteins in C. elegans, we can analyze the resulting functional changes in synaptic transmission. 
The C. elegans NMJs formed between motor neurons and body wall muscles control locomotion, therefore, mutants with uncoordinated locomotory phenotypes (known as unc s) often perturb synaptic transmission at these synapses 1. Since unc mutants are maintained on a rich supply of a bacterial food source, they remain viable as long as they retain some pharyngeal pumping ability to ingest food. This, together with the fact that C. elegans exist as hermaphrodites, allows them to pass on mutant progeny without the need for elaborate mating behaviors. These attributes, coupled with our recent ability to record from the worms NMJs 2,3,7 make this an excellent model organism in which to address precisely how unc mutants impact neurotransmission. 
The dissection method involves immobilizing adult worms using a cyanoacrylic glue in order to make an incision in the worm cuticle exposing the NMJs. Since C. elegans adults are only 1 mm in length the dissection is performed with the use of a dissecting microscope and requires excellent hand-eye coordination. NMJ recordings are made by whole-cell voltage clamping individual body wall muscle cells and neurotransmitter release can be evoked using a variety of stimulation protocols including electrical stimulation, light-activated channel-rhodopsin-mediated depolarization 4 and hyperosmotic saline, all of which will be briefly described.

Application of electrophysiology to accessible synapses provides a quantifiable measure of synaptic activity, useful in analyzing synaptic mutants. This article describes a dissection method used to expose the neuromuscular junctions (NMJ) of Caenorhabditis elegans (C. elegans) and briefly discusses some of the uses to which this preparation can be applied.

Neurotransmission is the process by which neurons transfer information via chemical signals to their post-synaptic targets, on a rapid time scale.   This ...

Electrophysiological Recording in the Drosophila Embryo

Drosophila is a premier genetic model for the study of both embryonic development and functional neuroscience. Traditionally, these fields are quite isolated from each other, with largely independent histories and scientific communities. However, the interface between these usually disparate fields is the developmental programs underlying acquisition of functional electrical signaling properties and differentiation of functional chemical synapses during the final phases of neural circuit formation. This interface is a critically important area for investigation. In Drosophila, these phases of functional development occur during a period of &lt;8 hours (at 25&deg;C) during the last third of embryogenesis. This late developmental period was long considered intractable to investigation owing to the deposition of a tough, impermeable epidermal cuticle. A breakthrough advance was the application of water-polymerizing surgical glue that can be locally applied to the cuticle to enable controlled dissection of late-stage embryos. With a dorsal longitudinal incision, the embryo can be laid flat, exposing the ventral nerve cord and body wall musculature to experimental investigation. Whole-cell patch-clamp techniques can then be employed to record from individually-identifiable neurons and somatic muscles. These recording configurations have been used to track the appearance and maturation of ionic currents and action potential propagation in both neurons and muscles. Genetic mutants affecting these electrical properties have been characterized to reveal the molecular composition of ion channels and associated signaling complexes, and to begin exploration of the molecular mechanisms of functional differentiation. A particular focus has been the assembly of synaptic connections, both in the central nervous system and periphery. The glutamatergic neuromuscular junction (NMJ) is most accessible to a combination of optical imaging and electrophysiological recording. A glass suction electrode is used to stimulate the peripheral nerve, with excitatory junction current (EJC) recordings made in the voltage-clamped muscle. This recording configuration has been used to chart the functional differentiation of the synapse, and track the appearance and maturation of presynaptic glutamate release properties. In addition, postsynaptic properties can be assayed independently via iontophoretic or pressure application of glutamate directly to the muscle surface, to measure the appearance and maturation of the glutamate receptor fields. Thus, both pre- and postsynaptic elements can be monitored separately or in combination during embryonic synaptogenesis. This system has been heavily used to isolate and characterize genetic mutants that impair embryonic synapse formation, and thus reveal the molecular mechanisms governing the specification and differentiation of synapse connections and functional synaptic signaling properties.

Electrophysiological Recording in the Drosophila Embryo

Electrophysiological recordings from Drosophila embryos allow analyses of developing muscle and neuron electrical properties, as well as characterization of functional synaptogenesis at the glutamatergic neuromuscular junction and central cholinergic and GABAergic synapses.

Drosophila is a premier genetic model for the study of both embryonic development and functional neuroscience. Traditionally, these fields are quite ...

Implementing Dynamic Clamp with Synaptic and Artificial Conductances in Mouse Retinal Ganglion Cells

Ganglion cells are the output neurons of the retina and their activity reflects the integration of multiple synaptic inputs arising from specific neural circuits. Patch clamp techniques, in voltage clamp and current clamp configurations, are commonly used to study the physiological properties of neurons and to characterize their synaptic inputs. Although the application of these techniques is highly informative, they pose various limitations. For example, it is difficult to quantify how the precise interactions of excitatory and inhibitory inputs determine response output. To address this issue, we used a modified current clamp technique, dynamic clamp, also called conductance clamp 1, 2, 3 and examined the impact of excitatory and inhibitory synaptic inputs on neuronal excitability. This technique requires the injection of current into the cell and is dependent on the real-time feedback of its membrane potential at that time. The injected current is calculated from predetermined excitatory and inhibitory synaptic conductances, their reversal potentials and the cell's instantaneous membrane potential. Details on the experimental procedures, patch clamping cells to achieve a whole-cell configuration and employment of the dynamic clamp technique are illustrated in this video article. Here, we show the responses of mouse retinal ganglion cells to various conductance waveforms obtained from physiological experiments in control conditions or in the presence of drugs. Furthermore, we show the use of artificial excitatory and inhibitory conductances generated using alpha functions to investigate the responses of the cells.

This video article illustrates the set-up, the procedures to patch cell bodies and how to implement dynamic clamp recordings from ganglion cells in whole-mount mouse retinae. This technique allows the investigation of the precise contribution of excitatory and inhibitory synaptic inputs, and their relative magnitude and timing to neuronal spiking.

Ganglion cells are the output neurons of the  retina and their activity reflects the integration of multiple synaptic inputs  arising from specific neural ...

An In Vitro Adult Mouse Muscle-nerve Preparation for Studying the Firing Properties of Muscle Afferents

Muscle sensory neurons innervating muscle spindles and Golgi tendon organs encode length and force changes essential to proprioception. Additional afferent fibers monitor other characteristics of the muscle environment, including metabolite buildup, temperature, and nociceptive stimuli. Overall, abnormal activation of sensory neurons can lead to movement disorders or chronic pain syndromes. We describe the isolation of the extensor digitorum longus (EDL) muscle and nerve for in vitro study of stretch-evoked afferent responses in the adult mouse. Sensory activity is recorded from the nerve with a suction electrode and individual afferents can be analyzed using spike sorting software. In vitro preparations allow for well controlled studies on sensory afferents without the potential confounds of anesthesia or altered muscle perfusion. Here we describe a protocol to identify and test the response of muscle spindle afferents to stretch. Importantly, this preparation also supports the study of other subtypes of muscle afferents, response properties following drug application and the incorporation of powerful genetic approaches and disease models in mice.

An In Vitro Adult Mouse Muscle-nerve Preparation for Studying the Firing Properties of Muscle Afferents

Muscle sensory neurons are involved in proprioceptor signaling and also report on metabolic state and injury related events. We describe an adult mouse in vitro muscle-nerve preparation for studies on stretch-activated muscle afferents.

Muscle sensory neurons innervating muscle spindles and Golgi tendon organs encode length and force changes essential to proprioception. Additional ...

In Vivo Electrophysiological Measurement of the Rat Ulnar Nerve with Axonal Excitability Testing

Electrophysiology enables the objective assessment of peripheral nerve function in vivo. Traditional nerve conduction measures such as amplitude and latency detect chronic axon loss and demyelination, respectively. Axonal excitability techniques &#34;by threshold tracking&#34; expand upon these measures by providing information regarding the activity of ion channels, pumps and exchangers that relate to acute function and may precede degenerative events. As such, the use of axonal excitability in animal models of neurological disorders may provide a useful in vivo measure to assess novel therapeutic interventions. Here we describe an experimental setup for multiple measures of motor axonal excitability techniques in the rat ulnar nerve.
The animals are anesthetized with isoflurane and carefully monitored to ensure constant and adequate depth of anesthesia. Body temperature, respiration rate, heart rate and saturation of oxygen in the blood are continuously monitored. Axonal excitability studies are performed using percutaneous stimulation of the ulnar nerve and recording from the hypothenar muscles of the forelimb paw. With correct electrode placement, a clear compound muscle action potential that increases in amplitude with increasing stimulus intensity is recorded. An automated program is then utilized to deliver a series of electrical pulses which generate 5 specific excitability measures in the following sequence: stimulus response behavior, strength duration time constant, threshold electrotonus, current-threshold relationship and the recovery cycle.
Data presented here indicate that these measures are repeatable and show similarity between left and right ulnar nerves when assessed on the same day. A limitation of these techniques in this setting is the effect of dose and time under anesthesia. Careful monitoring and recording of these variables should be undertaken for consideration at the time of analysis.

In Vivo Electrophysiological Measurement of the Rat Ulnar Nerve with Axonal Excitability Testing

Axonal excitability techniques provide a powerful tool to examine pathophysiology and biophysical changes that precede irreversible degenerative events. This manuscript demonstrates the use of these techniques on the ulnar nerve of anesthetized rats.

Electrophysiology enables the objective assessment of peripheral nerve function in vivo. Traditional nerve conduction measures such as amplitude and ...

Preparations and Protocols for Whole Cell Patch Clamp Recording of Xenopus laevis Tectal Neurons

The Xenopus tadpole retinotectal circuit, comprised of the retinal ganglion cells (RGCs) in the eye which form synapses directly onto neurons in the optic tectum, is a popular model to study how neural circuits self-assemble. The ability to carry out whole cell patch clamp recordings from tectal neurons and to record RGC-evoked responses, either in vivo or using a whole brain preparation, has generated a large body of high-resolution data about the mechanisms underlying normal, and abnormal, circuit formation and function. Here we describe how to perform the in vivo preparation, the original whole brain preparation, and a more recently developed horizontal brain slice preparation for obtaining whole cell patch clamp recordings from tectal neurons. Each preparation has unique experimental advantages. The in vivo preparation enables the recording of the direct response of tectal neurons to visual stimuli projected onto the eye. The whole brain preparation allows for the RGC axons to be activated in a highly controlled manner, and the horizontal brain slice preparation allows recording from across all layers of the tectum.

Preparations and Protocols for Whole Cell Patch Clamp Recording of Xenopus laevis Tectal Neurons

In this paper, we discuss three brain preparations used for whole cell patch clamp recording to study the retinotectal circuit of Xenopus laevis tadpoles. Each preparation, with its own specific advantages, contributes to the experimental tractability of the Xenopus tadpole as a model to study neural circuit function.

The Xenopus tadpole retinotectal circuit, comprised of the retinal ganglion cells (RGCs) in the eye which form synapses directly onto neurons in the optic ...

Registration of Calcium Transients in Mouse Neuromuscular Junction with High Temporal Resolution using Confocal Microscopy

Estimation of the presynaptic calcium level is a key task in studying synaptic transmission since calcium entry into the presynaptic cell triggers a cascade of events leading to neurotransmitter release. Moreover, changes in presynaptic calcium levels mediate the activity of many intracellular proteins and play an important role in synaptic plasticity. Studying calcium signaling is also important for finding ways to treat neurodegenerative diseases. The neuromuscular junction is a suitable model for studying synaptic plasticity, as it has only one type of neurotransmitter. This article describes the method for loading a calcium-sensitive dye through the cut nerve bundle into the mice's motor nerve endings. This method allows the estimation of all parameters related to intracellular calcium changes, such as basal calcium level and calcium transient. Since the influx of calcium from the cell exterior into the nerve terminals and its binding/unbinding to the calcium-sensitive dye occur within the range of a few milliseconds, a speedy imaging system is required to record these events. Indeed, high-speed cameras are commonly used for the registration of fast calcium changes, but they have low image resolution parameters. The protocol presented here for recording calcium transient allows extremely good spatial-temporal resolution provided by confocal microscopy.

The protocol describes the method of loading a fluorescent calcium dye through the cut nerve into mouse motor nerve terminals. In addition, a unique method for recording fast calcium transients in the peripheral nerve endings using confocal microscopy is presented.

Estimation of the presynaptic calcium level is a key task in studying synaptic transmission since calcium entry into the presynaptic cell triggers a ...

Electroporation and Nerve Injury in Mouse Levator Auris Longus Muscle

Combined In Vivo Electroporation and Short&#45;Term Reinnervation of the Cranial Levator Auris Longus Skeletal Muscle

The neuromuscular junction (NMJ) is the peripheral synapse controlling the contraction of skeletal muscle fibers to allow the coordinated movement of many organisms. At the NMJ, a presynaptic motor axon terminal contacts a muscle postsynaptic domain and is covered by terminal Schwann cells. The integrity and function of the NMJ is compromised under several conditions, including aging, neuromuscular diseases, and traumatic injuries. To analyze the potential contribution of muscle-derived proteins to NMJ maintenance and regeneration, an in vivo gene transfer strategy has been combined with the denervation of the cranial levator auris longus (LAL) muscle after mechanical nerve injury. Previous findings showed that the forced expression of control fluorescent proteins does not alter NMJ organization or neurotransmission. This procedure aims to describe a detailed method of in vivo electroporation of the LAL muscle followed by transection or crushing of the specific branch of the facial nerve innervating cranial muscles, leading to NMJ denervation and reinnervation, respectively. The combination of these experimental strategies in the convenient LAL muscle constitutes an efficient method to study the potential contribution of muscle protein overexpression or silencing in the context of short-term NMJ reinnervation.

Author Spotlight: Regenerative Roles of Muscle Proteins at Neuromuscular Junction Post-Nerve Injury

Here, we present a protocol that combines in vivo electroporation and denervation of the cranial levator auris longus (LAL) muscle. This procedure enables the study of the potential role of muscle-derived proteins in the regeneration of the neuromuscular synapse.

The neuromuscular junction (NMJ) is the peripheral synapse controlling the contraction of skeletal muscle fibers to allow the coordinated movement of many ...

Levator Auris Longus Preparation for Examination of Mammalian Neuromuscular Transmission Under Voltage Clamp Conditions

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