We thank Dr. Yuval Gottlieb-Dror for the electroporation illustration. This work was supported by grants to DSD from The National Institute for Psychobiology in Israel and from the Niedersachsen-Israel Research cooperation program and by grants to AK from The Israel Science Foundation, The Israel ministry of health, and The Center of Excellence-Legacy Heritage Biomedical Science partnership.

1. Hindbrain Electroporation
1.1 Egg handling
<ol>
	<li>Place the eggs horizontally in a humidified incubator (37-38.5 &deg;C). Embryos are electroporated after 65-70 hr of incubation, when they reach 16-17 (HH) stage (25-30 somites).</li>
	<li>Remove the eggs from the incubator; they remain in the horizontal position.</li>
</ol>
1.2 Preparations
<ol>
	<li>Pull glass capillaries (0.5 mm diameter).</li>
	<li>Connect bent L-shaped gold Genetrodes electrodes (3 mm diameter) with an adaptor holder to the pulse generator. Electroporation parameters include 25 volts, 5 pulse numbers, 45 msec pulse length, 300 msec pulse intervals.</li>
	<li>Prepare a mouth pipette, 10 ml syringe needle, parafilm strips, a soft brush, sharp dissecting scissors and 25 ml sterile PBS solution. This amount is usually sufficient to handle an egg tray (18 eggs).</li>
	<li>Prepare an adequate mixture of DNA plasmids (5 &mu;g/&mu;l each) and add about 0.025% Fast Green dye to visualize DNA injection. Usually a volume of 4 &mu;l is sufficient for the injection of a tray.</li>
</ol>
1.3 Windowing, Injection and Electroporation
<ol>
	<li>Clean egg shells with 70% ethanol.</li>
	<li>Handle one egg at a time to minimize embryonic exposure time to air.</li>
	<li>Make a hole at the egg pole with the scissors ends and remove 3-4 ml of albumin with the syringe. Do not remove a larger amount of albumin as it reduces viability.</li>
	<li>Open a small oval window (2.5 x 2 cm size) at the upper center of the egg shell using the dissecting scissors.</li>
	<li>Drip few drops of PBS on top of the embryo to prevent dryness during the whole process.</li>
	<li>Load a small amount of the DNA mixture into the glass capillary using a mouth pipette.</li>
	<li>Place the embryo with its posterior end towards you. No ink injection is required at this stage as the embryo is clearly visible. Avoiding ink injection increases embryonic survival. Penetrate the caudal hindbrain by holding the capillary at ~45&deg;. Do not remove any membrane from around the embryo. Inject DNA solution carefully into the hindbrain lumen and exhale without forming air bubbles. DNA solution spreads anteriorly.</li>
	<li>Immediately after DNA injection, place the parallel electrodes at the precise AP and DV hindbrain position you aim to target. Push the electrodes slightly ventrally without touching the heart, as it may reduce viability. Pulse the electroporator. Electrodes should be covered with bubbles to indicate electrical conductivity (Figure 1A).</li>
	<li>Carefully remove the electrodes and drip few drops of PBS to cool the embryo and to remove bubbles. Seal the egg opening properly with a parafilm strip to prevent drying during incubation. Wash electrodes in PBS with the soft brush.</li>
	<li>Place egg in the incubator for the desired length of time. Survival of embryos is approximately 90% 2-3 days after electroporation, and reduces up to 50% 12 days following electroporation.</li>
</ol>
2. Analysis of Embryos
2.1 Flat-mount preparation and immunofluorescence
<ol>
	<li>Flat-mount preparations of the hindbrain can be performed up to E6.5 to easily visualize axons under a microscope or a stereo-microscope.</li>
	<li>Dissect the embryo carefully by separating it from surrounding membranes and blood vessels. Place the embryo in a small silicone-coated Petri dish containing PBS. Attach the embryo to the dish with tungsten pins facing dorsally. Perform a dorsal slit in the hindbrain roof-plate using sharp glass capillaries.</li>
	<li>Using sharp tweezers and micro-scissors hold the upper part of the head and pull the hindbrain tissue very carefully from rostral to caudal. After separation of the hindbrain remove remaining ventral tissues to reach a clean preparation.</li>
	<li>Incubate the hindbrain with 4% paraformaldehyde (PFA) solution for 1-2 hr at room-temperature (RT). Wash the hindbrain with PBT (PBS/0.1% Triton X-100) to remove PFA.</li>
	<li>For Immunofluorescence in flat-mounted hindbrains add 500 &mu;l of blocking solution (5% of goat serum in PBT and incubate for 2 hr at RT Incubate with 1st antibody ON at 4 &deg;C. Wash with PBT (15 min x 3). Incubate with 2nd antibody for 2 hr at RT. Wash with PBT (15 min x 3).</li>
	<li>Place the hindbrain facing dorsally on a glass slide. Add fluorescent mounting media onto the hindbrain. Use glass capillaries or tungsten needles to flatten the hindbrain on the slide.</li>
	<li>Add small amount of grease at each corner to prevent squeezing of the tissue by the cover slip. Carefully place a cover slip on top of the hindbrain and avoid air bubbles. For adherence add nail polish to cover glass edges.</li>
</ol>
2.2 Cryo-sections and Immunofluorescence
<ol>
	<li>Cryo-sections of the brainstem can be performed at any stage to visualize axonal trajectories. Yet, after E6.5 this should be the preferred method due to the difficulty to visualize axons in the flat-mounted embryo, which becomes too thick. Moreover, demonstration of synapses requires sectioning of the tissue and a high-magnification view under a microscope.</li>
	<li>Dissect the embryo and remove all surrounding tissues. Rinse with PBS. Cut the embryo at the caudal part of the medulla using micro-scissors and sharp tweezers. Make a wide incision between the cerebellum and the midbrain and remove the entire brainstem. The tissue should contain the medulla, pons and cerebellum.</li>
	<li>Fix the brainstem in 4% PFA for overnight (ON) at 4 &deg;C, rinse with PBS (10 min x 3), and incubate with 30% sucrose for ON at 4 &deg;C until sinking.</li>
	<li>Embed the hindbrain in a cryo-mold with OCT (Optimal Cutting Temperature) compound, and place it at -20 &deg;C until freezing, as described elsewhere 11.</li>
	<li>Place the OCT block in the cryostat at the desired sectional axis. Section width is 12 &mu;m.</li>
	<li>Dry the slides. Add 100 &mu;l blocking solution on each slide for 2 hr at RT. Add 100 &mu;l of antibodies (diluted in the blocking solution to the desired concentration). Incubation period for 1st and 2nd antibodies is ON at 4 &deg;C or 2 hr at RT, respectively. For each incubation time, gently add parafilm strip on top of the slide to prevent dryness. Wash with PBS (10 min x 3) between antibodies. If required, add 1:1,000 Dapi (4'-6-Diamidino-2-phenylindole), diluted in PBS for 20 min at RT. Rinse with PBS.</li>
	<li>Mount the slide with fluorescent mounting media. Let dry for 1 hr before analysis.</li>
</ol>

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No conflicts of interest declared.

In ovo electroporation is a feasible, reliable, and effective tool to examine cell specification and axonal guidance during chick nervous system development 20. In this protocol we describe a mode of electroporation in the chick hindbrain at E2.75 using enhancer elements which enable the conditional labeling of specific interneurons. This strategy is combined with the PiggyBac-mediated transposition system to insert foreign genes into the chick genome, which enables tracking of axonal routes, projecti...

The hindbrain represents a key relay hub of the nervous system by communicating between the central and peripheral nervous systems via ascending and descending neuronal networks. It regulates basic functions including respiration, consciousness, hearing, and motor coordination 1-3. During early embryonic development, the vertebrate hindbrain is transiently subdivided along its anterior-posterior (AP) axis into repetitive rhombomeres, in which distinct neuronal cell types are formed and generate multiple brainstem nuclei centers 4. The hindbrain is also divided along its dorsal-ventral (DV) axis into a basal and alar plate, at which discrete neuronal progenitors become specified and differentiate in distinct DV locations 3,5,6. How the early AP and DV-specific neuronal patterns are governing the establishment of functional brainstem circuitries is largely unknown.
To gain knowledge on this fundamental question, tools are required in order to label specific subsets of neurons in the early hindbrain and to trace their axonal trajectories and connectivity at more advanced stages. We have previously utilized specific enhancer elements, and a Cre/LoxP-based conditional expression system for tracking axonal trajectory of dorsal spinal interneurons in the early chick embryo 7-9. In the current manuscript we have targeted the hindbrain and upgraded the experimental paradigm for labeling late embryonic hindbrain interneurons, axons and their synaptic targets, using a modified electroporation strategy and the PiggyBac - mediated DNA transposition. Our new strategy allows the tagging of distinct neuronal subtypes in one side of the hindbrain and the tracking of their axonal projections and synaptic sites at various embryonic stages, from 2 up to 12 days following electroporation. Based on this method, we labeled the dorsal-most subgroup of hindbrain interneurons (dA1/Atoh1+ cells) and revealed two contralateral ascending axonal projection patterns, each derives from a different AP location and elongates in a distinct funiculus. dA1 axons were found to project and form synapses in the auditory nuclei, midbrain and in multiple layers of the cerebellum 10.
The combination of chick electroporation, genetic tracing of neurons and analysis of projection sites at much advanced stages of development provides a unique platform to study the formation of neuronal networks in the brain and to elucidate molecular mechanisms that govern circuit formation.

<table border="1">
		<tbody>
		 <tr>
			<td>Name of Reagent/Equipment</td>
			<td>Company</td>
			<td>Catalogue Number</td>
		 </tr>
		 <tr>
			<td>L-shaped gold Genetrodes 3 mm electrodes</td>
			<td>BTX, Harvard Apparatus</td>
			<td>45-0162 </td>
		 </tr>
		 <tr>
			<td>pulse generator, ECM 830</td>
			<td>BTX, Harvard Apparatus</td>
			<td>45-0002</td>
		 </tr>
		 <tr>
			<td>OCT (Optimal Cutting Temperature) Compound</td>
			<td>Tissue-Tek
				Sakura</td>
			<td>4583 O.C.T. Compound </td>
		 </tr>
		 <tr>
			<td>Nail Polish</td>
			<td>From Any Commercial Supplier </td>
			<td></td>
		 </tr>
		</tbody>
 </table>

electroporation of the hindbrain to trace axonal trajectories and synaptic targets in the chick embryo

Electroporation of the chick embryonic neural tube has many advantages such as being quick and efficient for the expression of foreign genes into neuronal cells. In this manuscript we provide a method that demonstrates uniquely how to electroporate DNA into the avian hindbrain at E2.75 in order to specifically label a subset of neuronal progenitors, and how to follow their axonal projections and synaptic targets at much advanced stages of development, up to E14.5. We have utilized novel genetic tools including specific enhancer elements, Cre/Lox - based plasmids and the PiggyBac-mediated DNA transposition system to drive GFP expression in a subtype of hindbrain cells (the dorsal most subgroup of interneurons, dA1). Axonal trajectories and targets of dA1 axons are followed at early and late embryonic stages at various brainstem regions. This strategy contributes advanced techniques for targeting cells of interest in the embryonic hindbrain and for tracing circuit formation at multiple stages of development.

This protocol was recently used to uncover the axonal patterns and projection sites of dA1 subgroup of interneurons in the chick hindbrain 10. To specifically label these axons, an enhancer element (Atoh1), that has previously been characterized as specific for spinal dI1 neurons 8,12,13, was confirmed to be expressed in hindbrain dA1 cells 10. The element was cloned upstream to Cre recombinase and co-electroporated at E2.75 along with a Cre dependent cytoplasmic GFP reporter plasmid (pCA...

Watch this Scientific Journal Video about Electroporation of the Hindbrain to Trace Axonal Trajectories and Synaptic Targets in the Chick Embryo at JoVE.com

Electroporation of the Hindbrain to Trace Axonal Trajectories and Synaptic Targets in the Chick Embryo

How neuronal networks are established in the embryonic brain is a fundamental question in developmental neurobiology. Here we combined an electroporation technique with novel genetic tools, such as Cre/Lox&#x2013;plasmids and PiggyBac-mediated DNA transposition system in the avian hindbrain to label dorsal interneurons and track their axonal projections and synaptic targets at various developmental stages.

Electroporation of  the chick embryonic neural tube has many advantages such as being quick and efficient  for the expression of foreign genes into ...

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Neuroscience

10.8K Views.  The Hebrew University of Jerusalem. Как нейронных сетей устанавливаются в эмбриональном мозге является фундаментальным вопросом в развитии нейробиологии. Здесь мы объединили метод электропорации с новых генетических инструментов, таких как Cre / LOX-плазмиды и PiggyBac ДНК-опосредованного переноса ...

Video: Electroporation of the Hindbrain to Trace Axonal Trajectories and Synaptic Targets in the Chick Embryo

Labeling and Imaging Cells in the Zebrafish Hindbrain

Key to understanding the morphogenetic processes that shape the early vertebrate embryo is the ability to image cells at high resolution. In zebrafish embryos, injection of plasmid DNA results in mosaic expression, allowing for the visualization of single cells or small clusters of cells 1 . We describe how injection of plasmid DNA encoding membrane-targeted Green Fluorescent Protein (mGFP) under the control of a ubiquitous promoter can be used for imaging cells undergoing neurulation. Central to this protocol is the methodology for imaging labeled cells at high resolution in sections and also in real time. This protocol entails the injection of mGFP DNA into young zebrafish embryos. Embryos are then processed for vibratome sectioning, antibody labeling and imaging with a confocal microscope. Alternatively, live embryos expressing mGFP can be imaged using time-lapse confocal microscopy. We have previously used this straightforward approach to analyze the cellular behaviors that drive neural tube formation in the hindbrain region of zebrafish embryos 2. The fixed preparations allowed for unprecedented visualization of cell shapes and organization in the neural tube while live imaging complemented this approach enabling a better understanding of the cellular dynamics that take place during neurulation.

Key to understanding the morphogenetic processes that shape the early embryo is the ability to image cells at high resolution. We describe here a technique for labeling single cells or small clusters of cells in whole zebrafish embryos with membrane-targeted Green Fluorescent Protein.

Key to understanding the morphogenetic processes that shape the early vertebrate embryo is the ability to image cells at high resolution. In zebrafish ...

Production of Chick Embryo Extract for the Cultivation of Murine Neural Crest Stem Cells

The neural crest arises from the neuro-ectoderm during embryogenesis and persists only temporarily. Early experiments already proofed pluripotent progenitor cells to be an integral part of the neural crest1. Phenotypically, neural crest stem cells (NCSC) are defined by simultaneously expressing p75 (low-affine nerve growth factor receptor, LNGFR) and SOX10 during their migration from the neural crest2,3,4,5. These progenitor cells can differentiate into smooth muscle cells, chromaffin cells, neurons and glial cells, as well as melanocytes, cartilage and bone6,7,8,9. To cultivate NCSC in vitro, a special neural crest stem cell medium (NCSCM) is required10. The most complex part of the NCSCM is the preparation of chick embryo extract (CEE) representing an essential source of growth factors for the NCSC as well as for other types of neural explants. Other NCSCM ingredients beside CEE are commercially available. Producing CCE using laboratory standard equipment it is of high importance to know about the challenging details as the isolation, maceration, centrifugation, and filtration processes. In this protocol we describe accurate techniques to produce a maximized amount of pure and high quality CEE.

To cultivate neural crest stem cells (NCSC) in vitro, a special medium (NCSCM) is required. Essential part of NCSCM is chick embryo extract (CEE). We here describe accurate techniques to produce a maximized amount of pure and high quality CEE, including details as the isolation, maceration, centrifugation, and filtration processes.

The neural crest arises from the neuro-ectoderm during embryogenesis and persists only temporarily. Early experiments already proofed pluripotent ...

Fast Micro-iontophoresis of Glutamate and GABA: A Useful Tool to Investigate Synaptic Integration

One of the fundamental interests in neuroscience is to understand the integration of excitatory and inhibitory inputs along the very complex structure of the dendritic tree, which eventually leads to neuronal output of action potentials at the axon. The influence of diverse spatial and temporal parameters of specific synaptic input on neuronal output is currently under investigation, e.g. the distance-dependent attenuation of dendritic inputs, the location-dependent interaction of spatially segregated inputs, the influence of GABAergig inhibition on excitatory integration, linear and non-linear integration modes, and many more.
With fast micro-iontophoresis of glutamate and GABA it is possible to precisely investigate the spatial and temporal integration of glutamatergic excitation and GABAergic inhibition. Critical technical requirements are either a triggered fluorescent lamp, light-emitting diode (LED), or a two-photon scanning microscope to visualize dendritic branches without introducing significant photo-damage of the tissue. Furthermore, it is very important to have a micro-iontophoresis amplifier that allows for fast capacitance compensation of high resistance pipettes. Another crucial point is that no transmitter is involuntarily released by the pipette during the experiment.
Once established, this technique will give reliable and reproducible signals with a high neurotransmitter and location specificity. Compared to glutamate and GABA uncaging, fast iontophoresis allows using both transmitters at the same time but at very distant locations without limitation to the field of view. There are also advantages compared to focal electrical stimulation of axons: with micro-iontophoresis the location of the input site is definitely known and it is sure that only the neurotransmitter of interest is released. However it has to be considered that with micro-iontophoresis only the postsynapse is activated and presynaptic aspects of neurotransmitter release are not resolved. In this article we demonstrate how to set up micro-iontophoresis in brain slice experiments.

In this article we introduce fast micro-iontophoresis of neurotransmitters as a technique to investigate integration of postsynaptic signals with high spatial and temporal precision.

One of the fundamental interests in neuroscience is to understand the integration of excitatory and inhibitory inputs along the very complex structure of ...

Use of pHluorin to Assess the Dynamics of Axon Guidance Receptors in Cell Culture and in the Chick Embryo

During development, axon guidance receptors play a crucial role in regulating axons sensitivity to both attractive and repulsive cues. Indeed, activation of the guidance receptors is the first step of the signaling mechanisms allowing axon tips, the growth cones, to respond to the ligands. As such, the modulation of their availability at the cell surface is one of the mechanisms that participate in setting the growth cone sensitivity. We describe here a method to precisely visualize the spatio-temporal cell surface dynamics of an axon guidance receptor both in vitro and in vivo in the developing chick spinal cord. We took advantage of the pH-dependent fluorescence property of a green fluorescent protein (GFP) variant to specifically detect the fraction of the axon guidance receptor that is addressed to the plasma membrane. We first describe the in vitro validation of such pH-dependent constructs and we further detail their use in vivo, in the chick spinal chord, to assess the spatio-temporal dynamics of the axon guidance receptor of interest.

We describe here the use of a pH-sensitive green fluorescent protein variant, pHluorin, to study the spatio-temporal dynamics of axon guidance receptors trafficking at the cell surface.&#160;The pHluorin-tagged receptor is expressed both in cell culture and in vivo, using electroporation of the chick embryo.

During development, axon guidance receptors play a crucial role in regulating axons sensitivity to both attractive and repulsive cues. Indeed, activation ...

The Olfactory System as a Model to Study Axonal Growth Patterns and Morphology In Vivo

The olfactory system has the unusual capacity to generate new neurons throughout the lifetime of an organism. Olfactory stem cells in the basal portion of the olfactory epithelium continuously give rise to new sensory neurons that extend their axons into the olfactory bulb, where they face the challenge to integrate into existing circuitry. Because of this particular feature, the olfactory system represents a unique opportunity to monitor axonal wiring and guidance, and to investigate synapse formation. Here we describe a procedure for in vivo labeling of sensory neurons and subsequent visualization of axons in the olfactory system of larvae of the amphibian Xenopus laevis. To stain sensory neurons in the olfactory organ we adopt the electroporation technique. In vivo electroporation is an established technique for delivering fluorophore-coupled dextrans or other macromolecules into living cells. Stained sensory neurons and their axonal processes can then be monitored in the living animal either using confocal laser-scanning or multiphoton microscopy. By reducing the number of labeled cells to few or single cells per animal, single axons can be tracked into the olfactory bulb and their morphological changes can be monitored over weeks by conducting series of in vivo time lapse imaging experiments. While the described protocol exemplifies the labeling and monitoring of olfactory sensory neurons, it can also be adopted to other cell types within the olfactory and other systems.

The Olfactory System as a Model to Study Axonal Growth Patterns and Morphology In Vivo

We describe a protocol for in vivo labeling of olfactory sensory neurons by electroporation and subsequent confocal laser-scanning or multiphoton microscopy to visualize neuronal morphology and its development over time.

The olfactory system has the unusual capacity to generate new neurons throughout the lifetime of an organism. Olfactory stem cells in the basal portion of ...

Simultaneous Two-photon In Vivo Imaging of Synaptic Inputs and Postsynaptic Targets in the Mouse Retrosplenial Cortex

This video shows the craniotomy procedure that allows chronic imaging of neurons in the mouse retrosplenial cortex (RSC) using in vivo two-photon microscopy in Thy1-GFP transgenic mouse line. This approach creates a possibility to investigate the correlation of behavioural manipulations with changes in neuronal morphology in vivo.
The cranial window implantation procedure was considered to be limited only to the easily accessible cortex regions such as the barrel field. Our approach allows visualization of neurons in the highly vascularized RSC. RSC is an important element of the brain circuit responsible for spatial memory, previously deemed to be problematic for in vivo two-photon imaging.
The cranial window implantation over the RSC is combined with an injection of mCherry-expressing recombinant adeno-associated virus (rAAVmCherry) into the dorsal hippocampus. The expressed mCherry spreads out to axonal projections from the hippocampus to RSC, enabling the visualization of changes in both presynaptic axonal boutons and postsynaptic dendritic spines in the cortex. 
This technique allows long-term monitoring of experience-dependent structural plasticity in RSC.

Simultaneous Two-photon In Vivo Imaging of Synaptic Inputs and Postsynaptic Targets in the Mouse Retrosplenial Cortex

This video shows the craniotomy procedure that allows chronic imaging of neurons in mouse retrosplenial cortex using in vivo two photon microscopy in Thy1-GFP transgenic line. This approach is combined with injection of mCherry-expressing adeno-associated virus into dorsal hippocampus. These techniques allow long-term monitoring of experience-dependent structural plasticity in RSC.

This video shows the craniotomy procedure that allows chronic imaging of neurons in the mouse retrosplenial cortex (RSC) using in vivo two-photon ...

The Use of Trace Eyeblink Classical Conditioning to Assess Hippocampal Dysfunction in a Rat Model of Fetal Alcohol Spectrum Disorders

Neonatal rats were administered a relatively high concentration of ethyl alcohol (11.9% v/v) during postnatal days 4-9, a time when the fetal brain undergoes rapid organizational change and is similar to accelerated brain changes that occur during the third trimester in humans. This model of fetal alcohol spectrum disorders (FASDs) produces severe brain damage, mimicking the amount and pattern of binge-drinking that occurs in some pregnant alcoholic mothers. We describe the use of trace eyeblink classical conditioning (ECC), a higher-order variant of associative learning, to assess long-term hippocampal dysfunction that is typically seen in alcohol-exposed adult offspring. At 90 days of age, rodents were surgically prepared with recording and stimulating electrodes, which measured electromyographic (EMG) blink activity from the left eyelid muscle and delivered mild shock posterior to the left eye, respectively. After a 5 day recovery period, they underwent 6 sessions of trace ECC to determine associative learning differences between alcohol-exposed and control rats. Trace ECC is one of many possible ECC procedures that can be easily modified using the same equipment and software, so that different neural systems can be assessed. ECC procedures in general, can be used as diagnostic tools for detecting neural pathology in different brain systems and different conditions that insult the brain.

Trace eyeblink classical conditioning (ECC) was used to assess hippocampal-dependent associative learning in adult rats that were administered a high concentration (11.9% v/v) of alcohol during early neonatal brain development. In general, ECC procedures are sound diagnostic tools for detecting brain dysfunction across many psychological and biomedical settings.

Neonatal rats were administered a relatively high concentration of ethyl alcohol (11.9% v/v) during postnatal days 4-9, a time when the fetal brain ...

Recording Synaptic Plasticity in Acute Hippocampal Slices Maintained in a Small-volume Recycling-, Perfusion-, and Submersion-type Chamber System

Even though experiments on brain slices have been in use since 1951, problems remain that reduce the probability of achieving a stable and successful analysis of synaptic transmission modulation when performing field potential or intracellular recordings. This manuscript describes methodological aspects that might be helpful in improving experimental conditions for the maintenance of acute brain slices and for recording field excitatory postsynaptic potentials in a commercially available submersion chamber with an outflow-carbogenation unit. The outflow-carbogenation helps to stabilize the oxygen level in experiments that rely on the recycling of a small buffer reservoir to enhance the cost-efficiency of drug experiments. In addition, the manuscript presents representative experiments that examine the effects of different carbogenation modes and stimulation paradigms on the activity-dependent synaptic plasticity of synaptic transmission.

This protocol describes the stabilization of the oxygen level in a small volume of recycled buffer and methodological aspects of recording activity-dependent synaptic plasticity in submerged acute hippocampal slices.

Even though experiments on brain slices have been in use since 1951, problems remain that reduce the probability of achieving a stable and successful ...

Use of Synaptic Zinc Histochemistry to Reveal Different Regions and Laminae in the Developing and Adult Brain

Characterization of anatomical and functional brain organization and development requires accurate identification of distinct neural circuits and regions in the immature and adult brain. Here we describe a zinc histochemical staining procedure that reveals differences in staining patterns among different layers and brain regions. Others have utilized this procedure not only to reveal the distribution of zinc-containing neurons and circuits in the brain, but also to successfully delineate areal and laminar boundaries in the developing and adult brain in several species. Here we illustrate this staining procedure with images from developing and adult ferret brains. We reveal a zinc-staining pattern that serves as an anatomical marker of areas and layers, and can be reliably used to distinguish visual cortical areas in the developing and adult visual cortex. The main goal of this protocol is to present a histochemical method that allows the accurate identification of layers and regions in the developing and adult brain where other methods fail to do so. Secondarily, in conjunction with densitometric image analysis, this method allows one to assess the distribution of synaptic zinc to reveal potential changes throughout development. This protocol describes in detail the reagents, tools, and steps necessary to successively stain frozen brain sections. Although this protocol is described using ferret brain tissue, it can easily be adapted for use in rodents, cats, or monkeys as well as in other brain regions.

We describe a histochemical procedure that reveals characteristic laminar and areal zinc staining patterns in different brain regions. The zinc-staining pattern may be used in conjunction with other anatomical markers to reliably distinguish layers and regions in the developing and adult brain.

Characterization of anatomical and functional brain organization and development requires accurate identification of distinct neural circuits and regions ...

Combining Optogenetics with Artificial microRNAs to Characterize the Effects of Gene Knockdown on Presynaptic Function within Intact Neuronal Circuits

The purpose of this protocol is to characterize the effect of gene knockdown on presynaptic function within intact neuronal circuits. We describe a workflow on how to combine artificial microRNA (miR)-mediated RNA interference with optogenetics to achieve selective stimulation of manipulated presynaptic boutons in acute brain slices. The experimental approach involves the use of a single viral construct and a single neuron-specific promoter to drive the expression of both an optogenetic probe and artificial miR(s) against presynaptic gene(s). When stereotactically injected in the brain region of interest, the expressed construct makes it possible to stimulate with light exclusively the neurons with reduced expression of the gene(s) under investigation. This strategy does not require the development and maintenance of genetically modified mouse lines and can in principle be applied to other organisms and to any neuronal gene of choice. We have recently applied it to investigate how the knockdown of alternative splice isoforms of presynaptic P/Q-type voltage-gated calcium channels (VGCCs) regulates short-term synaptic plasticity at CA3 to CA1 excitatory synapses in acute hippocampal slices. A similar approach could also be used to manipulate and probe the neuronal circuitry in vivo.

This protocol provides a workflow on how to combine artificial microRNA-mediated RNA interference with optogenetics to stimulate specifically presynaptic boutons with reduced expression of selective gene(s) within intact neuronal circuits.

The purpose of this protocol is to characterize the effect of gene knockdown on presynaptic function within intact neuronal circuits. We describe a ...