Funding provided by the National Science Foundation (IOS-1050701 to B.A.C.), the National Institutes of Health (NS54174 to S.M. and F30DC0111907 to A.M.L-W.), the Uehara Memorial Foundation and the Japan Society for the Promotion of Science (G2205 to T.K.). We thank Julian Meeks for his support and guidance on the topic of extracellular axonal recordings. We thank Carl Hopkins for providing a prototype recording chamber.

<ol>
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No conflicts of interest declared.

Once mastered, this technique will allow one to target identified neurons, including individual axons, for in vivo recordings in many model systems. In addition, this technique allows one to reliably record spike output from neurons with unique anatomical characteristics that make traditional in vivo recording methods challenging. We have utilized this technique to record from ELa "small cells" in mormyrid weakly electric fish. Previous attempts to study the tuning properties of "small cells" were unsuccessful due to challenging recording conditions11, 14. Similar anatomical features create barriers to obtaining single-unit recordings from many different vertebrate auditory and electrosensory neurons8-10. To overcome these challenges in our system, we took advantage of the fact that "small cells" are the only cells in ELa that project to ELp. Thus, retrograde transport of dye placed in ELp limits labeling in ELa to "small cell" somas and axons. Fluorescent labeling of the axons allowed precise electrode placement next to labeled axons, making single-unit recordings from identified cells possible despite inaccessible somas. We attempted somatic recordings, but were unsuccessful, probably due to the surrounding engulfing synapses11,17. However, somatic labeling was clearly visible suggesting that this technique could be used to target somatic recordings in other cell types and other circuits. Fluorescent labeling of neurons through retrograde transport in vivo has been used for guiding targeted recordings in vitro19-21. A similar technique was used for targeted in vivo recordings from motor neurons in zebrafish spinal cord22. Our work represents a novel expansion of this approach, in which both labeling and recording are done in vivo within the brain. Our method demonstrates that in vivo labeling of CNS areas with a retrograde tracer can be expanded to the study of other intact circuits with similarly selective projection neurons. For example, in mammalian auditory processing, the inferior colliculus (IC) serves as an important relay center for inputs from multiple rhombencephalic structures23. Dye injection into the IC would selectively label the projection cells from each of these nuclei. The superior colliculus (SC) serves a similar function for vision24. Spinal cord preparations are particularly well suited for this technique, as the spinal cord is easily accessed, dye injection can occur far from the recording site, and it can be combined with intracellular recording and filling of select neurons to acquire more detailed anatomical information25. Finally, tract-tracing is a well established technique used throughout the central nervous system to map complex circuitry26. Our method can be utilized to add functional information to these studies as has been done with calcium-sensitive indicators in cat visual cortex27.
The surgery, which is well established, reliable, and regularly used for blind in vivo recordings16, must be completed with minimal bleeding and no damage to the surface of the brain to allow the animal and the tissue to survive. With practice, the surgery and dye application can be completed in 30-45 minutes. We successfully labeled "small cell" axons in 67% of the preparations. Most preparations have only 1 or 2 visible labeled axons, but some have as many as 8. Of the 119 labeled units attempted, we obtained single-unit recordings from 26 units distributed over 12 preparations (Table 2). Thus, data were collected from 41% of preparations with labeled axons for an overall success rate of 28%.
The critical aspect of dye application is labeling depth. Shallow insertion of the tungsten wire will result in the dye being washed away. However, if the penetration is too deep, labeled axons will not be visible for targeting. Further, some mechanical damage to the cell must occur for the dye to be adequately taken up25, 28. However, too much damage will kill the cells. We attempted labeling with other dyes and other methods (Table 2), including anterograde labeling through dye injection into ELa paired with recording from labeled axons in ELp (Table 3). We hypothesize that anterograde labeling was not successful because labeling was limited to cells with somatic damage, making them unresponsive. Additionally, pre-synaptic terminals may have been disturbed. By contrast, retrograde labeling minimizes both of these concerns. The amount and location of dye application can be modified according to the particular circuit being studied. Maximal labeling occurs with the greatest dye concentration, which we achieved using coated tungsten wires. However, for labeling axons with deep projections, dye may come off a tungsten needle as it is advanced. In these cases, pressure injection would be more appropriate. Dye uptake and transport are rapid, with labeled axons in our preparation being visible as early as 2 hours post-injection and additional labeled axons appearing as late as 6 hours post-injection. Thus, labeling and recording can be accomplished in a single day, eliminating technical difficulties associated with survival surgery. Timing will vary for each application depending on the distance required for dye transport.
Another critical aspect is electrode placement. It is important to enter the tissue close to the site of the labeled axon to prevent clogging of the tip. For dense tissue such as in ELa, a long, thin shank on the recording electrode minimizes excess movement of surrounding tissue. If a successful recording is not achieved on the first attempt, repeat with fresh electrodes until a recording is obtained or the tissue is disrupted to the point at which the axon is no longer visible. However, it is also important to quickly place the electrode next to the axon to minimize the amount of fluorescent exposure, which can cause phototoxicity, bleaching and may affect physiological properties of the cell29-31.
Once a segment of axon is successfully suctioned into the recording electrode, recordings can be obtained for several hours. If units are consistently lost in less than 1 hour, consider making smaller electrode tips to prevent the axon from slipping out. On the other hand, too small of a tip may result in clogging, low signal-to-noise, or damage to the axon. A steady decrease in spike amplitude and the 'return' of a unit with additional suction is an indication that the tip is too large. Too much suction may cause irreparable damage to the axon. One solution is to allow a small leak in the air line so the pressure slowly returns to zero. Rapidly equalizing the pressure will result in a transient relative-outward 'push' which may expel the axon.
Although this technique represents a major advantage for obtaining targeted recordings from identified projection neurons, it will not be useful for distinguishing local interneurons, as dye would be taken up by all cell types at the injection site. Theoretically, the use of multiple fluorophores with separate injection sites may allow this method to be expanded. For example, comparison of single- versus double-labeling could be used to distinguish interneurons from projection neurons following dual injections at two points in the circuit32. Similarly, retrograde tracers can be combined with other advanced imaging techniques, such as two-photon imaging, as was done recently in zebra finch High Vocal center (HVc)32. Also, recording regions are limited to those near the surface when using epifluorescence microscopes, as we were only able to resolve 1 &mu;m structures within the first 30 &mu;m of tissue. However, this depth could be extended through the use of other microscopy techniques, such as two-photon microscopy33 or objective-coupled planar illumination microscopy34. Overall, this technique represents an important advancement in the study of neural circuits in vivo because it can be used to record from single neurons in many different circuits in a variety of model systems - including those that are relatively inaccessible.

<table border="1" cellspacing="1">
 <tbody>
 <tr>
 <td>Name of the reagent</td>
 <td>Company</td>
 <td>Catalogue number</td>
 <td>Comments</td>
 </tr>
 <tr>
 <td>Tricaine Methanesulfonate</td>
 <td>Sigma-Aldrich</td>
 <td>E10521</td>
 <td>MS-222</td>
 </tr>
 <tr>
 <td>Gallamine Triethiodide </td>
 <td>Sigma-Aldrich</td>
 <td>G8134</td>
 <td>Flaxedil</td>
 </tr>
 <tr>
 <td>Lidocaine Hydrochloride</td>
 <td>Sigma-Aldrich</td>
 <td>L5647</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Hickman's Ringer Solution </td>
 <td>NA</td>
 <td>NA</td>
 <td>NaCl (6.48 g/l), KCl (0.15 g/l), CaCl2&bull;2H20 (0.29 g/l), MgSO4 (0.12 g/l), NaHCO3 (0.084 g/l), NaH2PO4 (0.06 g/l)</td>
 </tr>
 <tr>
 <td>Peristaltic Pump</td>
 <td>Gilson or Rainin</td>
 <td>Minipulse 3 Model 312; RP-1</td>
 <td>10.0 &plusmn; 1.0 rpm, Alternatively, a gravity-fed line with a flow-meter</td>
 </tr>
 <tr>
 <td>Dissection Microscope </td>
 <td>Nikon</td>
 <td>SM2645</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Super Glue</td>
 <td>Super Glue Corporation</td>
 <td>SGH2</td>
 <td>2g tube</td>
 </tr>
 <tr>
 <td>Omni Drill 35</td>
 <td>World Precision Instruments</td>
 <td>503-598</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Ball Mill Carbide Drill Bit #1/4</td>
 <td>World Precision Instruments</td>
 <td>501860</td>
 <td>0.19 DIA (bit diameter = 0.48 mm) </td>
 </tr>
 <tr>
 <td>Low Temp Cautery Kit</td>
 <td>World Precision Instruments</td>
 <td>500391</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Manual Micromanipulator</td>
 <td>World Precision Instruments</td>
 <td>M3301R</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Dextran Conjugated Alexa Fluor 568</td>
 <td>Invitrogen</td>
 <td>D-22912</td>
 <td>2mM concentration; 10,000MW The choice of dye wavelength should be selected to match the microscope filter settings</td>
 </tr>
 <tr>
 <td>Epifluorescent Microscope</td>
 <td>Nikon </td>
 <td>E600 FN</td>
 <td>A remote focus accessory is helpful for fine focus TRITC filter - or appropriate filter to match focal planes for different dye wavelengths</td>
 </tr>
 <tr>
 <td>Low Power Objective</td>
 <td>Nikon</td>
 <td>93182</td>
 <td>CFI Plan Achromat Series, 4X N.A. 0.1, W.D. 30mm</td>
 </tr>
 <tr>
 <td>High Power Objective</td>
 <td>Nikon</td>
 <td>93148</td>
 <td>CFI Fluor Series, 40X WI N.A. 0.8, W.D. 2.0 mm</td>
 </tr>
 <tr>
 <td>White Light Source</td>
 <td>Dolan-Jenner</td>
 <td>Model 190</td>
 <td>Fiber Optic Illuminator</td>
 </tr>
 <tr>
 <td>Fluorescent Light Source </td>
 <td>Lumen Dynamics</td>
 <td>X-Cite 120Q</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Low-light Level Camera</td>
 <td>Photometrics</td>
 <td>CoolSnap ES</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Digital Manometer</td>
 <td>Omega Engineering</td>
 <td>HHP-201</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Motorized Micromanipulator</td>
 <td>Sutter Instruments</td>
 <td>MP-285</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Headstage</td>
 <td>Molecular Devices</td>
 <td>CV-7B</td>
 <td>Axon Instruments</td>
 </tr>
 <tr>
 <td>Amplifier</td>
 <td>Molecular Devices</td>
 <td>MultiClamp 700B</td>
 <td>Axon Instruments</td>
 </tr>
 <tr>
 <td>Data Acquisition System</td>
 <td>Molecular Devices</td>
 <td>Digidata 1322A</td>
 <td>Axon Instruments</td>
 </tr>
 <tr>
 <td>Isolated Pulse Stimulator</td>
 <td>A-M Systems</td>
 <td>2100</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Flaming/Brown Micropipette Puller</td>
 <td>Sutter Instruments</td>
 <td>P-97</td>
 <td>Program settings for our application: Heat: ramp + 1, Pull: '0', Velocity: 60, Time: 90 Box filament</td>
 </tr>
 <tr>
 <td>Pipette Glass</td>
 <td>World Precision Instruments</td>
 <td>1B100F-4</td>
 <td>Borosilicate capillary glass with filament (1 mm OD, 0.58 mm ID) </td>
 </tr>
 </tbody>
</table>

retrograde fluorescent labeling allows for targeted extracellular single-unit recording from identified neurons in vivo

The overall goal of this method is to record single-unit responses from an identified population of neurons. In vivo electrophysiological recordings from individual neurons are critical for understanding how neural circuits function under natural conditions. Traditionally, these recordings have been performed 'blind', meaning the identity of the recorded cell is unknown at the start of the recording. Cellular identity can be subsequently determined via intracellular1, juxtacellular2 or loose-patch3 iontophoresis of dye, but these recordings cannot be pre-targeted to specific neurons in regions with functionally heterogeneous cell types. Fluorescent proteins can be expressed in a cell-type specific manner permitting visually-guided single-cell electrophysiology4-6. However, there are many model systems for which these genetic tools are not available. Even in genetically accessible model systems, the desired promoter may be unknown or genetically homogenous neurons may have varying projection patterns. Similarly, viral vectors have been used to label specific subgroups of projection neurons7, but use of this method is limited by toxicity and lack of trans-synaptic specificity. Thus, additional techniques that offer specific pre-visualization to record from identified single neurons in vivo are needed. Pre-visualization of the target neuron is particularly useful for challenging recording conditions, for which classical single-cell recordings are often prohibitively difficult8-11. The novel technique described in this paper uses retrograde transport of a fluorescent dye applied using tungsten needles to rapidly and selectively label a specific subset of cells within a particular brain region based on their unique axonal projections, thereby providing a visual cue to obtain targeted electrophysiological recordings from identified neurons in an intact circuit within a vertebrate CNS.
The most significant novel advancement of our method is the use of fluorescent labeling to target specific cell types in a non-genetically accessible model system. Weakly electric fish are an excellent model system for studying neural circuits in awake, behaving animals12. We utilized this technique to study sensory processing by "small cells" in the anterior exterolateral nucleus (ELa) of weakly electric mormyrid fish. "Small cells" are hypothesized to be time comparator neurons important for detecting submillisecond differences in the arrival times of presynaptic spikes13. However, anatomical features such as dense myelin, engulfing synapses, and small cell bodies have made it extremely difficult to record from these cells using traditional methods11, 14. Here we demonstrate that our novel method selectively labels these cells in 28% of preparations, allowing for reliable, robust recordings and characterization of responses to electrosensory stimulation.

Watch this Scientific Journal Video about Retrograde Fluorescent Labeling Allows for Targeted Extracellular Single-unit Recording from Identified Neurons In vivo at JoVE.com

Retrograde Fluorescent Labeling Allows for Targeted Extracellular Single-unit Recording from Identified Neurons In vivo

Retrograde transport of fluorescent dye labels a sub-population of neurons based on anatomical projection. Labeled axons can be visually targeted in vivo, permitting extracellular recording from identified axons. This technique facilitates recording when neurons cannot be labeled through genetic manipulation or are difficult to isolate using 'blind' in vivo approaches.

Retrograde Fluorescent Labeling Allows for Targeted Extracellular Single-unit Recording from Identified Neurons In vivo

The overall goal of this method is to record single-unit responses from an identified population of neurons. In vivo electrophysiological recordings from ...

retrograde-fluorescent-labeling-allows-for-targeted-extracellular

Research

JoVE Journal

Neuroscience

19.8K Views.  Washington University in St. Louis. Retrograde transport of fluorescent dye labels a sub-population of neurons based on anatomical projection. Labeled axons can be visually targeted in vivo, permitting extracellular recording from identified axons. This technique facilitates recording when neurons cannot be labeled through genetic manipulation or are difficult to isolate using 'blind' in vivo approaches.

Video: Retrograde Fluorescent Labeling Allows for Targeted Extracellular Single-unit Recording from Identified Neurons In vivo

Dual Somatic Recordings from Gonadotropin-Releasing Hormone (GnRH) Neurons Identified by Green Fluorescent Protein (GFP) in Hypothalamic Slices

Gonadotropin-Releasing Hormone (GnRH) is a small neuropeptide that regulates pituitary release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). These gonadotropins are essential for the regulation of reproductive function. The GnRH-containing neurons are distributed diffusely throughout the hypothalamus and project to the median eminence where they release GnRH from their axon terminals into the hypophysiotropic portal system (1). In the portal capillaries, GnRH travels to the anterior pituitary gland to stimulate release of gonadotropins into systemic circulation. GnRH release is not continuous but rather occurs in episodic pulses. It is well established that the intermittent manner of GnRH release is essential for reproduction (2, 3).
Coordination of activity of multiple GnRH neurons probably underlies GnRH pulses. Total peptide content in GnRH neurons is approximately 1.0 pg/cell (4), of which 30% likely comprises the releasable pool. Levels of GnRH during a pulse (5, 6), suggest multiple GnRH neurons are probably involved in neurosecretion. Likewise, single unit activity extracted from hypothalamic multi-unit recordings during LH release indicates changes in activity of multiple neurons (7). The electrodes with recorded activity during LH pulses are associated with either GnRH somata or fibers (8). Therefore, at least some of this activity arises from GnRH neurons.
The mechanisms that result in synchronized firing in hypothalamic GnRH neurons are unknown. Elucidating the mechanisms that coordinate firing in GnRH neurons is a complex problem. First, the GnRH neurons are relatively few in number. In rodents, there are 800-2500 GnRH neurons. It is not clear that all GnRH neurons are involved in episodic GnRH release. Moreover, GnRH neurons are diffusely distributed (1). This has complicated our understanding of coordination of firing and has made many technical approaches intractable. We have optimized loose cell-attached recordings in current-clamp mode for the direct detection of action potentials and developed a recording approach that allows for simultaneous recordings from pairs of GnRH neurons.

Dual Somatic Recordings from Gonadotropin-Releasing Hormone GnRH Neurons Identified by Green Fluorescent Protein GFP in Hypothalamic Slices

Activity in neuronal systems often requires synchronous action potential discharges from neurons within a specific population. For example, pulses of gonadotropin-releasing hormone (GnRH) likely require coordinated activity between GnRH neurons. We present our methodological approach for reliably obtaining simultaneous electrophysiological recordings from the diffusely distributed GnRH neurons.

Gonadotropin-Releasing Hormone (GnRH) is a small neuropeptide that regulates pituitary release of luteinizing hormone (LH) and follicle-stimulating ...

Single-unit In vivo Recordings from the Optic Chiasm of Rat

Information about the visual world is transmitted to the brain in sequences of action potentials in retinal ganglion cell axons that make up the optic nerve. In vivo recordings of ganglion cell spike trains in several animal models have revealed much of what is known about how the early visual system processes and encodes visual information. However, such recordings have been rare in one of the most common animal models, the rat, possibly owing to difficulty in detecting spikes fired by small diameter axons. The many retinal disease models involving rats motivate a need for characterizing the functional properties of ganglion cells without disturbing the eye, as with intraocular or in vitro recordings. Here, we demonstrate a method for recording ganglion cell spike trains from the optic chiasm of the anesthetized rat. We first show how to fabricate tungsten-in-glass electrodes that can pick up electrical activity from single ganglion cell axons in rat. The electrodes outperform all commercial ones that we have tried. We then illustrate our custom-designed stereotaxic system for in vivo visual neurophysiology experiments and our procedures for animal preparation and reliable and stable electrode placement in the optic chiasm.

Single-unit In vivo Recordings from the Optic Chiasm of Rat

Retinal ganglion cells transmit visual information from the eye to the brain with sequences of action potentials. Here, we demonstrate how to record the action potentials of single ganglion cells in vivo from anesthetized rats.

Information about the visual world is transmitted to the brain in sequences of action potentials in retinal ganglion cell axons that make up the optic ...

Surgical Implantation of Chronic Neural Electrodes for Recording Single Unit Activity and Electrocorticographic Signals

The success of long-term electrophysiological recordings often depends on the quality of the implantation surgery. Here we provide useful information for surgeons who are learning the process of implanting electrode systems. We demonstrate the implantation procedure of both a penetrating and a surface electrode. The surgical process is described from start to finish, including detailed descriptions of each step throughout the procedure. It should also be noted that this video guide is focused towards procedures conducted in rodent models and other small animal models. Modifications of the described procedures are feasible for other animal models.

We provide useful information for surgeons who are learning the process of implanting chronic neural recording electrodes. Techniques for both penetrating and surface electrode systems are described in a rodent animal model.

The success of long-term electrophysiological recordings often depends on the quality of the implantation surgery.  Here we provide useful information for ...

Simultaneous Recording of Calcium Signals from Identified Neurons and Feeding Behavior of Drosophila melanogaster

To study neuronal networks in terms of their function in behavior, we must analyze how neurons operate when each behavioral pattern is generated. Thus, simultaneous recordings of neuronal activity and behavior are essential to correlate brain activity to behavior. For such behavioral analyses, the fruit fly, Drosophila melanogaster, allows us to incorporate genetically encoded calcium indicators such as GCaMP1, to monitor neuronal activity, and to use sophisticated genetic manipulations for optogenetic or thermogenetic techniques to specifically activate identified neurons2-5. Use of a thermogenetic technique has led us to find critical neurons for feeding behavior (Flood et al., under revision). As a main part of feeding behavior, a Drosophila adult extends its proboscis for feeding6 (proboscis extension response; PER), responding to a sweet stimulus from sensory cells on its proboscis or tarsi. Combining the protocol for PER7 with a calcium imaging technique8 using GCaMP3.01, 9, I have established an experimental system, where we can monitor activity of neurons in the feeding center &#x2013; the suboesophageal ganglion (SOG), simultaneously with behavioral observation of the proboscis. I have designed an apparatus ("Fly brain Live Imaging and Electrophysiology Stage": "FLIES") to accommodate a Drosophila adult, allowing its proboscis to freely move while its brain is exposed to the bath for Ca2+ imaging through a water immersion lens. The FLIES is also appropriate for many types of live experiments on fly brains such as electrophysiological recording or time lapse imaging of synaptic morphology. Because the results from live imaging can be directly correlated with the simultaneous PER behavior, this methodology can provide an excellent experimental system to study information processing of neuronal networks, and how this cellular activity is coupled to plastic processes and memory.

Simultaneous Recording of Calcium Signals from Identified Neurons and Feeding Behavior of Drosophila melanogaster

The fruit fly, Drosophila melanogaster, extends its proboscis for feeding, responding to a sugar stimulus from its proboscis or tarsus. I have combined observations of the proboscis extension response (PER) with a calcium imaging technique, allowing us to monitor the activity of neurons in the brain, simultaneously with behavioral observation.

To study neuronal networks in terms of their function in behavior, we must analyze how neurons operate when each behavioral pattern is generated.  Thus, ...

Retrograde Loading of Nerves, Tracts, and Spinal Roots with Fluorescent Dyes

Retrograde labeling of neurons is a standard anatomical method1,2 that has also been used to load calcium and voltage-sensitive dyes into neurons3-6. Generally, the dyes are applied as solid crystals or by local pressure injection using glass pipettes. However, this can result in dilution of the dye and reduced labeling intensity, particularly when several hours are required for dye diffusion. Here we demonstrate a simple and low-cost technique for introducing fluorescent and ion-sensitive dyes into neurons using a polyethylene suction pipette filled with the dye solution. This method offers a reliable way for maintaining a high concentration of the dye in contact with axons throughout the loading procedure.

We describe a simple and low cost technique for introducing high concentration of fluorescent and calcium-sensitive dyes into neurons or any neuronal tract using a polyethylene suction pipette.

Retrograde labeling of neurons is a standard anatomical method1,2 that has also been used to load calcium and voltage-sensitive dyes into neurons3-6. ...

Recording Electrical Activity from Identified Neurons in the Intact Brain of Transgenic Fish

Understanding the cell physiology of neural circuits that regulate complex behaviors is greatly enhanced by using model systems in which this work can be performed in an intact brain preparation where the neural circuitry of the CNS remains intact. We use transgenic fish in which gonadotropin-releasing hormone (GnRH) neurons are genetically tagged with green fluorescent protein for identification in the intact brain. Fish have multiple populations of GnRH neurons, and their functions are dependent on their location in the brain and the GnRH gene that they express1 . We have focused our demonstration on GnRH3 neurons located in the terminal nerves (TN) associated with the olfactory bulbs using the intact brain of transgenic medaka fish (Figure 1B and C). Studies suggest that medaka TN-GnRH3 neurons are neuromodulatory, acting as a transmitter of information from the external environment to the central nervous system; they do not play a direct role in regulating pituitary-gonadal functions, as do the well-known hypothalamic GnRH1 neurons2, 3 .The tonic pattern of spontaneous action potential firing of TN-GnRH3 neurons is an intrinsic property4-6, the frequency of which is modulated by visual cues from conspecifics2 and the neuropeptide kisspeptin 15. In this video, we use a stable line of transgenic medaka in which TN-GnRH3 neurons express a transgene containing the promoter region of Gnrh3 linked to enhanced green fluorescent protein7 to show you how to identify neurons and monitor their electrical activity in the whole brain preparation6.

In this video, we will demonstrate how to record electrical activity from identified single neurons in a whole brain preparation, which preserves complex neural circuits. We use transgenic fish in which gonadotropin-releasing hormone (GnRH) neurons are genetically tagged with a fluorescent protein for identification in the intact brain preparation.

Understanding the cell physiology of neural circuits that regulate complex behaviors is greatly enhanced by using model systems in which this work can be ...

Intracellular Recording, Sensory Field Mapping, and Culturing Identified Neurons in the Leech, Hirudo medicinalis

The freshwater leech, Hirudo medicinalis, is a versatile model organism that has been used to address scientific questions in the fields of neurophysiology, neuroethology, and developmental biology. The goal of this report is to consolidate experimental techniques from the leech system into a single article that will be of use to physiologists with expertise in other nervous system preparations, or to biology students with little or no electrophysiology experience. We demonstrate how to dissect the leech for recording intracellularly from identified neural circuits in the ganglion. Next we show how individual cells of known function can be removed from the ganglion to be cultured in a Petri dish, and how to record from those neurons in culture. Then we demonstrate how to prepare a patch of innervated skin to be used for mapping sensory or motor fields. These leech preparations are still widely used to address basic electrical properties of neural networks, behavior, synaptogenesis, and development. They are also an appropriate training module for neuroscience or physiology teaching laboratories.

Intracellular Recording, Sensory Field Mapping, and Culturing Identified Neurons in the Leech, Hirudo medicinalis

This article describes three nervous system preparations using leeches: intracellular recording from neurons in ventral ganglia, culturing neurons from ventral ganglia, and recording from a patch of innervated skin to map sensory fields.

The freshwater leech, Hirudo medicinalis, is a versatile model organism that has been used to address scientific questions in the fields of ...

Retrograde Labeling of Retinal Ganglion Cells in Adult Zebrafish with Fluorescent Dyes

As retrograde labeling retinal ganglion cells (RGCs) can isolate RGCs somata from dying sites, it has become the gold standard for counting RGCs in RGCs survival and regeneration experiments. Many studies have been performed in mammalian animals to research RGCs survival after optic nerve injury. However, retrograde labeling of RGCs in adult zebrafish has not yet been reported, though some alternative methods can count cell numbers in retinal ganglion cell layers (RGCL). Considering the small size of the adult zebrafish skull and the high risk of death after drilling on the skull, we open the skull with the help of acid-etching and seal the hole with a light curing bond, which could significantly improve the survival rate. After absorbing the dyes for 5 days, almost all the RGCs are labeled. As this method does not need to transect the optic nerve, it is irreplaceable in the research of RGCs survival after optic nerve crush in adult zebrafish. Here, we introduce this method step by step and provide representative results.

We introduce an efficient method to retrograde label retinal ganglion cells (RGCs) in adult zebrafish.

As retrograde labeling retinal ganglion cells (RGCs) can isolate RGCs somata from dying sites, it has become the gold standard for counting RGCs in RGCs ...

A Guide to In vivo Single-unit Recording from Optogenetically Identified Cortical Inhibitory Interneurons

A major challenge in neurophysiology has been to characterize the response properties and function of the numerous inhibitory cell types in the cerebral cortex. We here share our strategy for obtaining stable, well-isolated single-unit recordings from identified inhibitory interneurons in the anesthetized mouse cortex using a method developed by Lima and colleagues1. Recordings are performed in mice expressing Channelrhodopsin-2 (ChR2) in specific neuronal subpopulations. Members of the population are identified by their response to a brief flash of blue light. This technique &#8211; termed &#8220;PINP&#8221;, or Photostimulation-assisted Identification of Neuronal Populations &#8211; can be implemented with standard extracellular recording equipment. It can serve as an inexpensive and accessible alternative to calcium imaging or visually-guided patching, for the purpose of targeting extracellular recordings to genetically-identified cells. Here we provide a set of guidelines for optimizing the method in everyday practice. We refined our strategy specifically for targeting parvalbumin-positive (PV+) cells, but have found that it works for other interneuron types as well, such as somatostatin-expressing (SOM+) and calretinin-expressing (CR+) interneurons.

A Guide to In vivo Single-unit Recording from Optogenetically Identified Cortical Inhibitory Interneurons

Here we describe our strategy for obtaining stable, well-isolated single-unit recordings from identified inhibitory interneurons in the anesthetized mouse cortex. Neurons expressing ChR2 are identified by their response to blue light. The method uses standard extracellular recording equipment, and serves as an inexpensive alternative to calcium imaging or visually-guided patching.

A major challenge in neurophysiology has been to characterize the response properties and function of the numerous inhibitory cell types in the cerebral ...

Perforated Patch-clamp Recording of Mouse Olfactory Sensory Neurons in Intact Neuroepithelium: Functional Analysis of Neurons Expressing an Identified Odorant Receptor

Analyzing the physiological responses of olfactory sensory neurons (OSN) when stimulated with specific ligands is critical to understand the basis of olfactory-driven behaviors and their modulation. These coding properties depend heavily on the initial interaction between odor molecules and the olfactory receptor (OR) expressed in the OSNs. The identity, specificity and ligand spectrum of the expressed OR are critical. The probability to find the ligand of the OR expressed in an OSN chosen randomly within the epithelium is very low. To address this challenge, this protocol uses genetically tagged mice expressing the fluorescent protein GFP under the control of the promoter of defined ORs. OSNs are located in a tight and organized epithelium lining the nasal cavity, with neighboring cells influencing their maturation and function. Here we describe a method to isolate an intact olfactory epithelium and record through patch-clamp recordings the properties of OSNs expressing defined odorant receptors. The protocol allows one to characterize OSN membrane properties while keeping the influence of the neighboring tissue. Analysis of patch-clamp results yields&#160;a precise quantification of ligand/OR interactions, transduction pathways and pharmacology, OSNs&#39; coding properties and their modulation at the membrane level.&#160;

Analyzing the physiological properties of olfactory sensory neurons still faces technical limitations. Here we record them through perforated patch-clamp in an intact preparation of the olfactory epithelium in gene-targeted mice. This technique allows the characterization of membrane properties and responses to specific ligands of neurons expressing defined olfactory receptors.

Analyzing the physiological responses of olfactory sensory neurons (OSN) when stimulated with specific ligands is critical to understand the basis of ...