The authors would like to acknowledge support from the Samuel Oschin Comprehensive Cancer Institute Cancer Research Forum Award as well as funds from the Regenerative Medicine Institute of Cedars-Sinai, and the Guerin Family. The project described was supported in the form of a CTSI Core Voucher funded by the National Center for Research Resources, Grant UL1RR033176, and is now at the National Center for Advancing Translational Sciences, Grant UL1TR000124. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.

This procedure is in accordance with Cedars-Sinai IACUC requirements. Investigators should ensure institutional IACUC compliance prior to proceeding. All tools and reagents should be sterilized prior to use.
1. Preparation of Tools, Solutions, and DNA Mixture
<ol>
	<li>Insert 100-mm fire polished borosilicate glass capillary tubes into a micropipette puller. Set heating to allow for standard weighted pull to form pipette tip of approximately 17.5 mm. Cut tips with sharp surgical scissors at a distance approximately 8-9 mm from the beginning of the tip to create roughly a 100 &#181;m diameter opening.</li>
	<li>Make a stock 1% w/v fast green solution by mixing filtered nuclease-free water (utilizing a 20-&#956;m syringe filter) with dry fast green.</li>
	<li>Isolate purified endotoxin-free plasmid DNA that is highly concentrated (i.e. &#62; 3 &#956;g/&#956;l), diluted in Tris-EDTA (TE) buffer. Add desired amounts of plasmid to mixture diluted in TE buffer and add a 1:10 ratio of the 1% fast green solution (making a 0.1% w/v final concentration of fast green). Use a 0.5-2.0 &#181;g/&#181;l final concentration of plasmid for robust expression of transgenes.</li>
</ol>
2. Animal Anesthesia, Pipette Loading, and Pial Surface Plasmid Injection
<ol>
	<li>Induce hypothermia anesthesia on 1-2 day postnatal mice by placing them on a Petri dish that is placed on ice for 5-8 min&#160;(time dependent on pup age/weight). Once hypothermia is confirmed by lack of movement from toe-pinching and/or tail reflex, mice are ready to be injected.&#160;&#160;Place animals back on ice if pain reflexes are evident.&#160; The injection procedure and electroporation take less than 2-3 min in total so time the hypothermia, injection, and electroporation procedures accordingly to maintain appropriate anesthesia.</li>
	<li>During anesthesia, using a standard pipette, carefully pipette desired amount of plasmid mix to be injected (0.5-2 &#956;l) onto a piece of paraffin wax film for reference. Here, a total volume of 0.5 &#181;l of plasmid mix is injected. Next, using a micro injector, carefully insert assembled glass capillary pipette into tube containing plasmid mixture. Take extra precaution to prevent the tip from breaking by making sure it does not touch the edges of the tube. Aspirate the solution into the pipette by slowly dialing back the transfer dial. Once a sufficient volume has been loaded into the pipette, dial forward until the pressure returns to the neutral position of 0 hPa.</li>
	<li>Using 300-450 hPa pressure for injection to ensure appropriate pressure for even filling of the pial surface/meningeal space, place the tip nearby the pipetted paraffin wax film reference injection (from 2.2) and use the foot pedal from the micro injector to eject one volume onto the paraffin wax film. Adjust pressure accordingly until the amount ejected equals the previously pipetted reference volume.</li>
	<li>Once the tip has been equilibrated and anesthesia has been confirmed, pups are ready to be injected.</li>
	<li>The goal of the experiment is to inject the plasmid mix under the skull and above the pial surface to allow for DNA electroporation downwards into the pial surface progenitors (Figure 1A). For cortex injections, hold the pup down using the thumb and index finger of the less dominant hand. The cortical hemispheres and other superficial structures such as the superior colliculi are visible between P0 and P2, allowing for facile targeting of these structures (Figure 1B). Using the dominant hand and target desired region of cortex (i.e. motor, somatosensory, etc.), insert pipette past the skin and skull taking care to avoid cerebral arteries. Make sure to prevent any further penetration of the tip past the skull (which is indicated by the lack of further resistance just after piercing the skull).</li>
	<li>Inject plasmid solution using the foot pedal of the micro injector and make sure it disperses evenly across the tissue (Figure 2A). 
	Note: It is very important to empirically determine an approach that maximizes plasmid delivery while avoiding hematoma due to fluid pressure. This can be done by adjusting the duration of the injection, the angle, the volume, and the precise target site to avoid vascular disruption.</li>
	<li>Be sure to try and keep the tip from drying in between injections by placing the tip in test droplets from injections made previously on wax paper or plastic paraffin film. This is required to prevent tip accumulation of evaporated and crystalized DNA solution, which can result in the clogging of the tip and inconsistent delivery volumes.</li>
</ol>
3. Electroporation
<ol>
	<li>Set the Electroporator to 135-150 V for five pulses, lasting 50 msec, with 950 msec intervals in between each pulse. In order to increase conductance and prevent burning of the skin, cover 3-mm platinum tweezertrodes with electroporation gel.&#160;Check for toe-pinching and tail reflexes at this point to ensure anesthesia.&#160; If responsive, place on ice for several minutes to anesthetize.</li>
	<li>For cortex (and superior colliculus) injections, employ a 3-mm electrode (Figure 2B) to increase viability of pups (as compared with the 7- and 10-mm electrodes, which are used for ventricular zone electroporation). Place the negatively charged probe of the electrode over the injected area and the positively charged probe around the contralateral region below the eye such that the electrode orientation is at a 45-60&#176;&#160;angle relative to the midline (Figure 2C).</li>
	<li>Use the foot pedal of the electroporator to trigger current and hold tweezertrodes in place for 3-5 pulses, depending on pup age and weight, effectively targeting DNA into underlying pial surface cells when accounting for curvature of the hemispheres. 
	Note: The negative pole can be swept over the injection area in between pulses or a larger electrode can be employed to increase the electroporated area.</li>
	<li>Immediately after electroporation, carefully clean off gel from pups and place them under a heat lamp for approximately 5 min.</li>
	<li>Pups will acutely lose their natural reddish-pink hue in the minutes after electroporation due to cyanosis. Observe the pups for the recovery of natural color and the initiation of normal movement before returning them to their cages.</li>
	<li>Ensure re-socialization with the mother by observing whether she brings the pups back to the nest and begins grooming them. If she becomes aggressive, make sure pups don&#39;t have remnants of gel and incubate them with some of the bedding to transfer the smell to the pups.</li>
</ol>
4. Modifications for Targeting the Superior Colliculi
Targeting:
<ol>
	<li>Inject the superior colliculus in the same fashion as the cortex but note that the target region lies just posterior and lateral to lambda and roughly at the midline (Figures 3A and 3B). With successful injections, the plasmid mix naturally fills the contours of the superior colliculus. Once injections have been made successfully, animals are ready for electroporation.</li>
</ol>
Electroporation:
<ol>
	<li>In a very similar fashion, for superior colliculus injections, place the negatively charged probe of the electrode over the injected area and the positively charged probe around the eye, snout or chin, driving DNA into the superficial regions of the superior colliculus (Figure 3C). In this case, the electrode orientation is at a 25-40&#176;&#160;angle relative to the midline.</li>
</ol>

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H., Maekawa, K., Yanagawa, Y., Obata, K., Murakami, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multidirectional+and+multizonal+tangential+migration+of+GABAergic+interneurons+in+the+developing+cerebral+cortex.">Multidirectional and multizonal tangential migration of GABAergic interneurons in the developing cerebral cortex.</a> Development. 133 (11), 2167-2176 (2006).</li><li>Ang Jr, E. S., Haydar, T. F., Gluncic, V., Rakic, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Four-dimensional+migratory+coordinates+of+GABAergic+interneurons+in+the+developing+mouse+cortex.">Four-dimensional migratory coordinates of GABAergic interneurons in the developing mouse cortex.</a> J Neurosci. 23 (13), 5805-5815 (2003).</li><li>Tamamaki, N., Fujimori, K. 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The authors declare that they have no competing financial interests.

The most critical aspect for successful electroporation of pial surface progenitors are: 1) targeting of plasmid mix to the pial surface; 2) avoiding the generation of hematomas at the injection site; and 3) avoiding mortality associated with midbrain electroporation.
Appropriately targeting the pial surface is accomplished by measured and careful puncturing of the skull to avoid penetration of the pial surface. Improper targeting to the overlying skin or underlying ventricle or brain parenchy...

Neural stem and progenitor cells are present throughout the mammalian CNS1,2. Their nature and properties in embryonic and adult germinal zones surrounding the ventricular regions of the brain and spinal cord have been extensively documented in the past decade1-3. In large part, this has been due to the development of increasingly precise genetic tools, such as nervous system specific Cre recombination of floxed alleles or retroviral lineage tracing4. However, one progenitor region&#8212;the pial surface progenitor zone&#8212;has only recently been described in any detail5-7&#160;and awaits comprehensive examination.
The pial surface of the brain is defined as the interface between the surface of the brain and the surrounding meninges8. During development, neuroepithelial and, later, radial glial end feet attach to this surface9,10. Some of the first neurons in the human brain and many neuronal mitoses are observed in this region11. Later, during embryonic neurogenesis, cortical interneurons are known to traverse the pial region, in addition to their migratory routes in the intermediate zone and subventricular zone12-14. During this period, stem cells can be cultured from this zone and it appears to be an active site of neuro- and gliogenesis5. In the adult brain, it has been reported that interneurons can be born from pial surface progenitors following hypoxic challenge7. However, the contribution of this region to his to genensis during embryonic and postnatal development has remained obscure in part due to the difficulty of specifically investigating this region6. In the superior colliculus and in the cerebral cortex, superficial (or layer I in the cortex) interneurons may modulate the circuit output of underlying excitatory neuron populations and thus contribute significantly to the function of these structures. In particular, layer 1 interneurons are in prime position to regulate the firing of neurons throughout the upper layers of the cerebral cortex given their extensive connectivity to the superficial and deep layers of cortical columns15,16. In a similar manner, horizontal interneurons receive excitatory input from cortical and retinal fibers, project over a relatively wide area and are speculated to mediate inhibition of neuronal populations responding to remote visual stimuli17,18. Also, their morphology is well-suited to play a potential role in the patterned wave activity in the developing visual system19. Interestingly, interneuron development and maturation happens to a large degree postnatally. Further, this maturation process has been found to be regulated by neuronal activity and is therefore a substrate of developmental plasticity with lifelong consequences on circuit function20,21. Notably, no promoters are described which can specifically target these cells transgenically. Dividing progenitors can be targeted with retrovirus7&#160;but virus production is time consuming and requires skill to yield the high titers needed for cell transduction.
Electroporation has led to a renaissance in the study of neurodevelopment as it allows for rapid and efficient genetic interrogation of signaling pathways in neural progenitors4,22,23. Electroporation involves the injection of plasmid DNA, followed by the delivery of electric pulses to the outside of the head, to unidirectionally drive the DNA into the proliferating progenitors surrounding the ventricles4,22,23. Electroporation appears to require transit of cells through M phase of the cell cycle for expression of plasmid transgenes24. Specifically, it has been found that only cells passing through M phase within 8 hr&#160;of electroporation of plasmids will express transgenes despite their effective delivery to all cells within ~160 &#181;m of the ventricular wall24. It is speculated that this is due to the need for nuclear envelope breakdown in allowing for nuclear access of the episomal plasmids, as chemicals causing nuclear permeabilization can induce expression of plasmids in post mitotic cells25. Originally employed in the embryo22, electroporation was adapted for use in the postnatal brain much later26,27. Recently, we have adapted electroporation for use in the genetic manipulation of pial surface progenitors6. Further, using this approach we have shown that there are apparently two distinct lineages of progenitors in this region&#8212;interneuronal and astrocytic6. This protocol details a simple, rapid, and powerful way to target these cells for the interrogation of the mechanisms regulating development of these cells.

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	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:248px;">Item Name</td>
			<td style="width:269px;">Vendor</td>
			<td style="width:177px;">Catalog Number</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Fire Polished Borosilicate Tubing</td>
			<td>World Precision Instruments, Inc.</td>
			<td>1B100F-4</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Micropipette Puller</td>
			<td>Sutter Instruments Company</td>
			<td>P-30</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Fast Green FCF</td>
			<td>Sigma Aldrich, Inc.</td>
			<td>F7528</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">XenoWorks Digital Microinjector</td>
			<td>Sutter Instruments Company</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">ECM 830 Generator</td>
			<td><a name="RANGE!B6">Harvard Apparatus, BTX Instrument Div</a></td>
			<td>45-0052</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">3mm Platinum Tweezertrodes</td>
			<td>Harvard Apparatus, BTX Instrument Div</td>
			<td>45-0487</td>
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			<td height="21" style="height:21px;">SignaGel Electrode Gel</td>
			<td>Cardinal Health</td>
			<td>70315-025</td>
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		<tr height="22">
			<td height="22" style="height:22px;">Tris-EDTA Buffer, pH 8.0</td>
			<td>Integrated DNA Technologies, Inc.</td>
			<td>11-01-02-05</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Infrared Heat Lamp</td>
			<td>VWR</td>
			<td>36547-009</td>
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			<td height="21" style="height:21px;">Fine Scissors Sharp</td>
			<td>Fine Science Tools</td>
			<td>14060-09</td>
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	</tbody>
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neonatal pial surface electroporation

Over the past several years the pial surface has been identified as a germinal niche of importance during embryonic, perinatal and adult neuro- and gliogenesis, including after injury. However, methods for genetically interrogating these progenitor populations and tracking their lineages had been limited owing to a lack of specificity or time consuming production of viruses. Thus, progress in this region has been relatively slow with only a handful of investigations of this location. Electroporation has been used for over a decade to study neural stem cell properties in the embryo, and more recently in the postnatal brain. Here we describe an efficient, rapid, and simple technique for the genetic manipulation of pial surface progenitors based on an adapted electroporation approach. Pial surface electroporation allows for facile genetic labeling and manipulation of these progenitors, thus representing a time-saving and economical approach for studying these cells.

Pial surface electroporation results in the expression of plasmid DNA in cells&#8212;mostly progenitors&#8212;at or near the pial surface6. More specifically, the orientation of the electrodes is critical in dictating the direction of plasmid movement and subsequent expression. Thus, in dual electrode configurations, the plasmid is directed in roughly a straight vector between the negative and positive electrode. Therefore, if the negative pole is placed over the injection site and the positive pole is ventral...

Watch this Scientific Journal Video about Neonatal Pial Surface Electroporation at JoVE.com

Neonatal Pial Surface Electroporation

The pial surface is a unique progenitor zone in the CNS that is receiving increasing attention. Herein, we detail a method for rapid genetic manipulation of this progenitor zone using a modified electroporation method. This procedure can be used for cellular and molecular investigations of cell lineages and signaling pathways involved in cell differentiation and to elucidate the fate and properties of daughter cells.

Over the past several years the pial surface has been identified as a germinal niche of importance during embryonic, perinatal and adult neuro- and ...

Research

JoVE Journal

Neuroscience

13.8K Views.  Cedars-Sinai Medical Center. The pial surface is a unique progenitor zone in the CNS that is receiving increasing attention. Herein, we detail a method for rapid genetic manipulation of this progenitor zone using a modified electroporation method. This procedure can be used for cellular and molecular investigations of cell lineages and signaling pathways involved in cell differentiation and to elucidate the fate and properties of daughter cells.

Video: Neonatal Pial Surface Electroporation

Transfection of Mouse Retinal Ganglion Cells by in vivo Electroporation

The targeting and refinement of RGC projections to the midbrain is a popular and powerful model system for studying how precise patterns of neural connectivity form during development. In mice, retinofugal projections are arranged in a topographic manner and form eye-specific layers in the Lateral Geniculate Nucleus (dLGN) of the thalamus and the Superior Colliculus (SC). The development of these precise patterns of retinofugal projections has typically been studied by labeling populations of RGCs with fluorescent dyes and tracers, such as horseradish peroxidase1-4. However, these methods are too coarse to provide insight into developmental changes in individual RGC axonal arbor morphology that are the basis of retinotopic map formation. They also do not allow for the genetic manipulation of RGCs.
Recently, electroporation has become an effective method for providing precise spatial and temporal control for delivery of charged molecules into the retina5-11. Current retinal electroporation protocols do not allow for genetic manipulation and tracing of retinofugal projections of a single or small cluster of RGCs in postnatal mice. It has been argued that postnatal in vivo electroporation is not a viable method for transfecting RGCs since the labeling efficiency is extremely low and hence requires targeting at embryonic ages when RGC progenitors are undergoing differentiation and proliferation6. 
In this video we describe an in vivo electroporation protocol for targeted delivery of genes, shRNA, and fluorescent dextrans to murine RGCs postnatally. This technique provides a cost effective, fast and relatively easy platform for efficient screening of candidate genes involved in several aspects of neural development including axon retraction, branching, lamination, regeneration and synapse formation at various stages of circuit development. In summary we describe here a valuable tool which will provide further insights into the molecular mechanisms underlying sensory map development.

Transfection of Mouse Retinal Ganglion Cells by in vivo Electroporation

We demonstrate an in vivo electroporation protocol for transfecting single or small clusters of retinal ganglion cells (RGCs) and other retinal cell types in postnatal mice over a wide range of ages. The ability to label and genetically manipulate postnatal RGCs in vivo is a powerful tool for developmental studies.

The targeting and refinement of RGC projections to the midbrain is a popular and powerful model system for studying how precise patterns of neural ...

In vivo Electroporation of Developing Mouse Retina

The functional characterization of genes expressed during mammalian retinal development remains a significant challenge. Gene targeting to generate constitutive or conditional loss of function knockouts remains cost and labor intensive, as well as time consuming. Adding to these challenges, retina expressed genes may have essential roles outside the retina leading to unintended confounds when using a knockout approach. Furthermore, the ability to ectopically express a gene in a gain of function experiment can be extremely valuable when attempting to identify a role in cell fate specification and/or terminal differentiation.
We present a method for the rapid and efficient incorporation of DNA plasmids into the neonatal mouse retina by electroporation. The application of short electrical impulses above a certain field strength results in a transient increase in plasma membrane permeability, facilitating the transfer of material across the membrane 1,2,3,4. Groundbreaking work demonstrated that electroporation could be utilized as a method of gene transfer into mammalian cells by inducing the formation of hydrophilic plasma membrane pores allowing the passage of highly charged DNA through the lipid bilayer 5. Continuous technical development has resulted in the viability of electroporation as a method for in vivo gene transfer in multiple mouse tissues including the retina, the method for which is described herein 6, 7, 8, 9, 10. 
DNA solution is injected into the subretinal space so that DNA is placed between the retinal pigmented epithelium and retina of the neonatal (P0) mouse and electrical pulses are applied using a tweezer electrode. The lateral placement of the eyes in the mouse allows for the easy orientation of the tweezer electrode to the necessary negative pole-DNA-retina-positive pole alignment. Extensive incorporation and expression of transferred genes can be identified by postnatal day 2 (P2). Due to the lack of significant lateral migration of cells in the retina, electroporated and non-electroporated regions are generated. Non-electroporated regions may serve as internal histological controls where appropriate. 
Retinal electroporation can be used to express a gene under a ubiquitous promoter, such as CAG, or to disrupt gene function using shRNA constructs or Cre-recombinase. More targeted expression can be achieved by designing constructs with cell specific gene promoters. Visualization of electroporated cells is achieved using bicistronic constructs expressing GFP or by co-electroporating a GFP expression construct. Furthermore, multiple constructs may be electroporated for the study of combinatorial gene effects or simultaneous gain and loss of function of different genes. Retinal electroporation may also be utilized for the analysis of genomic cis-regulatory elements by generating appropriate expression constructs and deletion mutants. Such experiments can be used to identify cis-regulatory regions sufficient or required for cell specific gene expression 11. Potential experiments are limited only by construct availability.

In vivo Electroporation of Developing Mouse Retina

A method for the incorporation of plasmid DNA into murine retinal cells for the purpose of performing either gain- or loss of function studies in vivo is presented. This method capitalizes on the transient increase in permeability of cell plasma membranes induced by the application of an external electrical field.

The functional characterization of genes expressed during mammalian retinal development remains a significant challenge.  Gene targeting to generate ...

Mouse in Utero Electroporation: Controlled Spatiotemporal Gene Transfection

In order to understand the function of genes expressed in specific region of the developing brain, including signaling molecules and axon guidance molecules, local gene transfer or knock- out is required. Gene targeting knock-in or knock-out into local regions is possible to perform with combination with a specific CRE line, which is laborious, costly, and time consuming. Therefore, a simple transfection method, an in utero electroporation technique, which can be performed with short time, will be handy to test the possible function of candidate genes prior to the generation of transgenic animals 1,2. In addition to this, in utero electroporation targets areas of the brain where no specific CRE line exists, and will limit embryonic lethality 3,4. Here, we present a method of in utero electroporation combining two different types of electrodes for simple and convenient gene transfer into target areas of the developing brain. First, a unique holding method of embryos using an optic fiber optic light cable will make small embryos (from E9.5) visible for targeted DNA solution injection into ventricles and needle type electrodes insertion to the targeted brain area 5,6. The patterning of the brain such as cortical area occur at early embryonic stage, therefore, these early electroporation from E9.5 make a big contribution to understand entire area patterning event. Second, the precise shape of a capillary prevents uterine damage by making holes by insertion of the capillary. Furthermore, the precise shape of the needle electrodes are created with tungsten and platinum wire and sharpened using sand paper and insulated with nail polish 7, a method which is described in great detail in this protocol. This unique technique allows transfection of plasmid DNA into restricted areas of the brain and will enable small embryos to be electroporated. This will help to, open a new window for many scientists who are working on cell differentiation, cell migration, axon guidance in very early embryonic stage. Moreover, this technique will allow scientists to transfect plasmid DNA into deep parts of the developing brain such as thalamus and hypothalamus, where not many region-specific CRE lines exist for gain of function (GOF) or loss of function (LOF) analyses.

Mouse in Utero Electroporation: Controlled Spatiotemporal Gene Transfection

A gene transfer method into the developing mouse brain is described by using a unique surgical method and special shape of electrodes. This unique technique allows transfection of plasmid DNA temporally and spatially, which will aid many neuroscientists in studying brain development.

In order to understand the function of genes expressed in specific region of the developing brain, including signaling molecules and axon guidance ...

Neonatal Subventricular Zone Electroporation

Neural stem cells (NSCs) line the postnatal lateral ventricles and give rise to multiple cell types which include neurons, astrocytes, and ependymal cells1. Understanding the molecular pathways responsible for NSC self-renewal, commitment, and differentiation is critical for harnessing their unique potential to repair the brain and better understand central nervous system disorders. Previous methods for the manipulation of mammalian systems required the time consuming and expensive endeavor of genetic engineering at the whole animal level2. Thus, the vast majority of studies have explored the functions of NSC molecules in vitro or in invertebrates.
Here, we demonstrate the simple and rapid technique to manipulate neonatal NPCs that is referred to as neonatal subventricular zone (SVZ) electroporation. Similar techniques were developed a decade ago to study embryonic NSCs and have aided studies on cortical development3,4 . More recently this was applied to study the postnatal rodent forebrain5-7. This technique results in robust labeling of SVZ NSCs and their progeny. Thus, postnatal SVZ electroporation provides a cost and time effective alternative for mammalian NSC genetic engineering.

We demonstrate a minimally invasive technique referred to as neonatal subventricular zone electroporation. The technique consists of injecting plasmid DNA into the lateral ventricles of neonatal pups and applying electrical current to deliver and genetically manipulate neural stem cells

Neural stem cells (NSCs) line the postnatal lateral ventricles and give rise to multiple cell types which include neurons, astrocytes, and ependymal ...

Subtype-selective Electroporation of Cortical Interneurons

The study of central nervous system (CNS) maturation relies on genetic targeting of neuronal populations. However, the task of restricting the expression of genes of interest to specific neuronal subtypes has proven remarkably challenging due to the relative scarcity of specific promoter elements. GABAergic interneurons constitute a neuronal population with extensive genetic and morphological diversity. Indeed, more than 11 different subtypes of GABAergic interneurons have been characterized in the mouse cortex1. Here we present an adapted protocol for selective targeting of GABAergic populations. We achieved subtype selective targeting of GABAergic interneurons by using the enhancer element of the homeobox transcription factors Dlx5 and Dlx6, homologues of the Drosophila distal-less (Dll) gene2,3, to drive the expression of specific genes through in utero electroporation.

This procedure shows how to target interneurons in the developing mouse forebrain by means of in utero electroporation. This technique was particularly efficient to achieve selective gene expression in interneuron subtypes destined to the superficial layers of the cortex.

The study of central nervous system (CNS) maturation relies on genetic targeting of neuronal populations. However, the task of restricting the expression ...

Recording EEG in Freely Moving Neonatal Rats Using a Novel Method

EEG is a useful method to detect electrical activity in the brain. Moreover, it is a widely used diagnostic tool for various neurological conditions, such as epilepsy and neurodegenerative disorders. However, it is technically difficult to obtain EEG recordings in neonates as it requires specialized handling and great care. Here, we present a novel method to record EEG in neonatal rat pups (P8-P15). We designed a simple and reliable electrode using computer pin loci; it can be easily implanted into the skull of a rat pup to record high-quality EEG signals in the normal and epileptic brain. Pups were given an intraperitoneal (i.p.) injection of the neurotoxin kainic acid (KA) to induce epileptic seizures. The surgical implantation performed in this procedure is less expensive than other EEG procedures for neonates. This method allows one to record high-quality and stable EEG signals for more than 1 week. Furthermore, this procedure can also be applied to adult rats and mice to study epilepsy or other neurological disorders.

Here, we introduce a novel technique designed to record electroencephalography (EEG) in freely moving neonatal epileptic pups and describe its procedures, features, and applications. This method allows one to record EEG for more than 1 week.

EEG is a useful method to detect electrical activity in the brain. Moreover, it is a widely used diagnostic tool for various neurological conditions, such ...

Spinal Cord Neurons Isolation and Culture from Neonatal Mice

We present a protocol for the isolation and culture of spinal cord neurons. The neurons are obtained from neonatal C57BL/6 mice and are isolated on postnatal day 1-3. A mouse litter, usually 4-10 pups born from one breeding pair, is gathered for one experiment, and spinal cords are collected individually from each mouse after euthanasia with isoflurane. The spinal column is dissected out and then the spinal cord is released from the column. The spinal cords are then minced to increase the surface area of delivery for an enzymatic protease that allows for the neurons and other cells to be released from the tissue. Trituration is then used to release the cells into solution. This solution is subsequently fractionated in a density gradient to separate the various cells in solution, allowing for neurons to be isolated. Approximately 1-2.5 x 106 neurons can be isolated from one litter group. The neurons are then seeded onto wells coated with adhesive factors that allow for proper growth and maturation. The neurons take approximately 7 days to reach maturity in the growth and culture medium and can be used thereafter for treatment and analysis.

This study presents a technique for the isolation of neurons from WT neonatal mice. It requires the careful dissection of the spinal cord from the neonatal mouse, followed by the separation of neurons from the spinal cord tissue through mechanical and enzymatic cleavage.

We present a protocol for the isolation and culture of spinal cord neurons. The neurons are obtained from neonatal C57BL/6 mice and are isolated on ...

Stereotaxic Surgery for Genetic Manipulation in Striatal Cells of Neonatal Mouse Brains

Many genes are expressed in embryonic brains, and some of them are continuously expressed in the brain after birth. For such persistently expressed genes, they may function to regulate the developmental process and/or physiological function in neonatal brains. To investigate neurobiological functions of specific genes in the brain, it is essential to inactivate genes in the brain. Here, we describe a simple stereotaxic method to inactivate gene expression in the striatum of transgenic mice at neonatal time windows. AAV-eGFP-Cre viruses were microinjected into the striatum of Ai14 reporter gene mice at postnatal day (P) 2 by stereotaxic brain surgery. The tdTomato reporter gene expression was detected in P14 striatum, suggesting a successful Cre-loxP mediated DNA recombination in AAV-transduced striatal cells. We further validated this technique by microinjecting AAV-eGFP-Cre viruses into P2Foxp2fl/fl mice. Double labeling of GFP and Foxp2 showed that GFP-positive cells lacked Foxp2 immunoreactivity in P9 striatum, suggesting the loss of Foxp2 protein in AAV-eGFP-Cre transduced striatal cells. Taken together, these results demonstrate an effective genetic deletion by stereotaxically microinjected AAV-eGFP-Cre viruses in specific neuronal populations in the neonatal brains of floxed transgenic mice. In conclusion, our stereotaxic technique provides an easy and simple platform for genetic manipulation in neonatal mouse brains. The technique can not only be used to delete genes in specific regions of neonatal brains, but it also can be used to inject pharmacological drugs, neuronal tracers, genetically modified optogenetics and chemogenetics proteins, neuronal activity indicators and other reagents into the striatum of neonatal mouse brains.

We describe a protocol of stereotaxic surgery with a homemade head-fixed device for microinjecting reagents into the striatum of neonatal mouse brains. This technique allows genetic manipulation in neuronal cells of specific regions of neonatal mouse brains.

Many genes are expressed in embryonic brains, and some of them are continuously expressed in the brain after birth. For such persistently expressed genes, ...

In Vivo Two-photon Imaging of Cortical Neurons in Neonatal Mice

Two-photon imaging is a powerful tool for the in vivo analysis of neuronal circuits in the mammalian brain. However, a limited number of in vivo imaging methods exist for examining the brain tissue of live newborn mammals. Herein we summarize a protocol for imaging individual cortical neurons in living neonatal mice. This protocol includes the following two methodologies: (1) the Supernova system for sparse and bright labeling of cortical neurons in the developing brain, and (2) a surgical procedure for the fragile neonatal skull. This protocol allows the observation of temporal changes of individual cortical neurites during neonatal stages with a high signal-to-noise ratio. Labeled cell-specific gene silencing and knockout can also be achieved by combining the Supernova with RNA interference and CRISPR/Cas9 gene editing systems. This protocol can, thus, be used for analyzing the developmental dynamics of cortical neurons, molecular mechanisms that control the neuronal dynamics, and changes in neuronal dynamics in disease models.

In Vivo Two-photon Imaging of Cortical Neurons in Neonatal Mice

We present an in vivo two-photon imaging protocol for imaging the cerebral cortex of neonatal mice. This method is suitable for analyzing the developmental dynamics of cortical neurons, the molecular mechanisms that control the neuronal dynamics, and the changes in neuronal dynamics in disease models.

Two-photon imaging is a powerful tool for the in vivo analysis of neuronal circuits in the mammalian brain. However, a limited number of in vivo imaging ...

Cochlear Surface Preparation in the Adult Mouse

Auditory processing in the cochlea depends on the integrity of the mechanosensory hair cells. Over a lifetime, hearing loss can be acquired from numerous etiologies such as exposure to excessive noise, the use of ototoxic medications, bacterial or viral ear infections, head injuries, and the aging process. Loss of sensory hair cells is a common pathological feature of the varieties of acquired hearing loss. Additionally, the inner hair cell synapse can be damaged by mild insults. Therefore, surface preparations of cochlear epithelia, in combination with immunolabeling techniques and confocal imagery, are a very useful tool for the investigation of cochlear pathologies, including losses of ribbon synapses and sensory hair cells, changes in protein levels in hair cells and supporting cells, hair cell regeneration, and determination of report gene expression (i.e., GFP) for verification of successful transduction and identification of transduced cell types. The cochlea, a bony spiral-shaped structure in the inner ear, holds the auditory sensory end organ, the organ of Corti (OC). Sensory hair cells and surrounding supporting cells in the OC are contained in the cochlear duct and rest on the basilar membrane, organized in a tonotopic fashion with high-frequency detection occurring in the base and low-frequency in the apex. With the availability of molecular and genetic information and the ability to manipulate genes by knockout and knock-in techniques, mice have been widely used in biological research, including in hearing science. However, the adult mouse cochlea is miniscule, and the cochlear epithelium is encapsulated in a bony labyrinth, making microdissection difficult. Although dissection techniques have been developed and used in many laboratories, this modified microdissection method using cell and tissue adhesive is easier and more convenient. It can be used in all types of adult mouse cochleae following decalcification.

This article presents a modified cochlear surface preparation method that requires decalcification and use of a cell and tissue adhesive to adhere the pieces of cochlear epithelia to 10 mm round cover slips for immunohistochemistry in adult mouse cochleae.

Auditory processing in the cochlea depends on the integrity of the mechanosensory hair cells. Over a lifetime, hearing loss can be acquired from numerous ...