We thank Ekaterina Karelina for help with soundtrack recording for the video, Ivan Molotkov for 3D animation and Dr. Peter Blaesse for CAG-EGFP plasmid preparation.
The work was supported by grants from the Centre of International Mobility of Finland, Finnish Cultural Foundation and the Academy of Finland.

1. Introduction
Creation of transgenic animals is a powerful method of investigation of gene functions in living animals1 and for unraveling disease mechanism2,3 as well as for manipulating properties of cells4. However, the procedure is rather laborious, extremely time consuming and expensive, thus warranting the use of alternative gene delivery methods such as viral injection5, neonatal ventricular injection with electroporation6 and in utero electroporation7,8. The method of postnatal non-ventricular injection and electroporation has a unique set of advantages: use of non-viral genetic constructs; possibility to create a local expression pattern in the area of interest; in situ transfection of non-migratory cell types, e.g. cortical astrocytes.
In this video, we demonstrate the detailed procedure of postnatal gene delivery to the neonatal rat brain using a plasmid encoding for the enhanced green fluorescent protein under chicken beta actin promoter with CMV enhancer (pCAG-EGFP)9. We illustrate the preparation of the plasmid-containing injection solution, manufacturing of thin glass pipettes and assembling of the microinjector on a stereotactic instrument. Then we talk about anaesthetizing rat pups with isoflurane, about performing the surgery, about the injection procedure and about the electroporation using forceps electrodes and the in vivo porator. Finally, we briefly discuss the anticipated results, perspectives and difficulties that may arise during these experiments.
2. Plasmid Preparation for Electroporation
<ol>
 <li>We usually prepare 10 &mu;l of the plasmid injection solution in a 200 &mu;l thin wall tube. This solution is sufficient for several experiments.</li>
 <li>We mix 8 &mu;l of the plasmid solution (see Materials and equipment) with 1 &mu;l of the 10X PBS (see Materials and equipment) and 1 &mu;l of 0,1% Fast Green water solution (see Materials and equipment).</li>
 <li>The final concentration of the plasmid in the injection solution should be between 1 and 3 &mu;g/&mu;l. Lower concentrations of plasmid DNA will reduce the transfection efficiency, while the higher DNA concentration will be too viscous for injection through the thin tip of the glass capillary.</li>
</ol>
3. Glass Needle Preparation
<ol>
 <li>For the glass pipette preparation, we use borosilicate glass capillary with a filament (see Materials and equipment) and a vertical electrode glass puller (see Materials and equipment) on maximum pulling and heating parameters.</li>
 <li>We then break the tip of the pipette using a piece of paper to achieve a tip 10-20 &mu;m in diameter.</li>
 <li>We check the tip diameter and shape under the microscope objective.</li>
</ol>
4. Microinjector Assembling
<ol>
 <li>Using a thin polymer capillary (see Materials and equipment) we fill approximately 1/3 of the volume of a 10 &mu;l Hamilton syringe (see Materials and equipment) with mineral oil (see Materials and equipment). Avoid air bubbles!</li>
 <li>Then we fill the glass pipette with mineral oil and insert the pipette into the Hamilton syringe. Avoid air bubbles!</li>
 <li>The syringe with glass pipette is then fixed on the microinjector connected to a controller (see Materials and equipment).</li>
 <li>The microinjection setup fixed on a stereotactic instrument (see Materials and equipment) allows us to safely immerse the tip of the glass pipette into the tube with the plasmid injection solution.</li>
 <li>When the tip touches the surface of the solution, dip it further by 1 or 2 mm and fill the pipette with approximately 1 &mu;l of the injection mix using the micro injector controller.</li>
</ol>
5. Anaesthetizing animal
All the procedures presented here were performed according to the University of Helsinki regulations for animal experiments.
<ol>
 <li>For each experiment, we fill a gas-tight syringe (see Materials and equipment) with approximately 2 ml of isoflurane (see Materials and equipment).</li>
 <li>Than the syringe is fixed on the anesthesia unit (see Materials and equipment) connected to the air flow source, the animal box and the mask fixed on stereotactic setup.</li>
 <li>On the anesthesia unit, we adjust the airflow to approximately 250 ml/min and the isoflurane level to 4 %.</li>
 <li>We place the rat pup into the animal box for 2-5 minutes.</li>
 <li>When the pup stops moving, place it on the heating pad (see Materials and equipment) attached to the stereotactic setup.</li>
 <li>Place a rostral part of pup's head into the anaesthetizing mask.</li>
 <li>It takes 5 to 10 minutes for the pup to enter the deep anesthesia.</li>
 <li>Check anesthesia deepness with a tail pinch and decrease the isoflurane inflow to about 1.5 to 2.0 %.</li>
</ol>
6. Surgery, Microinjection and Electroporation
<ol>
 <li>Treat the skin on the pup's head with the 70% ethanol.</li>
 <li>Using small scissors (see Materials and equipment) and thin forceps (see Materials and equipment), cut the skin from a scruff of the pup to its forehead.</li>
 <li>Bend skin pieces sideways and pull ear bars slightly into aural orifices of the skull for head and skin fixation.</li>
 <li>Using a binocular microscope, we locate the bregma point on the skull.</li>
 <li>Identify the region of interest using the stereotactic coordinates.</li>
 <li>Position the injection pipette above this region and mark it by dropping 25-50 nl of the injection solution onto the skull surface.</li>
 <li>Drill the skull gently and carefully at the marked point using a high speed surgical drill (see Materials and equipment) under the microscope until liquid appears in the drilled area.</li>
 <li>Fix an electropotation forceps electrodes (see Materials and equipment) on the sides of the skull with current conductive gel (see Materials and equipment) to achieve better conductivity.</li>
 <li>Remove the liquid drop from the drilled hole using small tampon (see Materials and equipment) and dip the glass needle to the hole according to the coordinates of the injection site.</li>
 <li>Infuse 25 to 100 nl of the injection solution at the rate of 5 to 20 nl/sec.</li>
 <li>Quickly remove the pipette and electroporate immediately. Electroporation is done by applying five rectangle pulses with the duration of 50 ms and amplitude of 99 V at the frequency of 1 Hz.</li>
 <li>Remove electrodes and ear bars.</li>
 <li>Sew the cut skin using a combination of a dumb (see Materials and equipment) and sharp forceps and surgical threads (see Materials and equipment).</li>
 <li>Place the pup into the warm chamber for 15-30 minutes to aid its recovery after anaesthesia.</li>
 <li>Then put the pup back to its mother's cage.</li>
</ol>
7. Representative Results
The expression of the transgene in the successfully transfected cells will appear approximately 10 hours after the electroporation, and it will remain stable for several weeks.
We microinjected the plasmid either into deep cortical layers or striatum region of postnatal day 2 (P2) Wistar rat pups and performed in vivo electroporation as described above. Brain slices (400 &mu;m in thickness) were cut after 2 to 6 days (P4-P8) using a vibrotome in cold slicing medium (Hepes buffered Earle's Balanced Salt Solution)10. Image acquisition was performed using Zeiss Axioplan 2 LSM5 Pascal confocal microscope (Zeiss, Germany) in the slicing medium at room temperature.
The injection sites in deep cortical layers and striatum contained many transfected cells expressing EGFP that were located in a compact region of approximately 200-300 &mu;m in diameter (Figure 1A, B). Within transfected cells, the EGFP expression level is sufficiently high to allow imaging of thin cellular processes (Figure 1C) including dendrites with spines of different shapes (Figure 1D) and axon bundles (Figure 1E). The robust stability of EGFP as well as cell viability after electroporation allowed tracing distal parts of axons (up to 1.5-2 mm from cell bodies) such as cortical terminals (Figure 1F).
<img src="/files/ftp_upload/2244/2244fig1.jpg" alt="Figure 1" /> Figure 1. (A) Successfully transfected cells in the striatum region of P4 rat brain delineating the plasmid injection site. (B) Transfected cells in deep cortical layers (approximately 1000 &mu;m below cortical surface) of P5 rat brain. (C) A transfected cell in the striatum region of P8 rat brain. (D) Dendritic processes of a transfected cell in the striatum region of P8 rat brain; arrows indicate different types of dendritic spines and filopodia. (E) Axons of transfected cells within collateral pathway. (F) Axons terminating at the pial surface of P8 rat cortex (arrowhead). Scale bars are 100 &mu;m on A, B, E and F; 10 &mu;m on C and D.

<ol>
	<li>Gerlai, R., Clayton, N. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analyzing+hippocampal+function+in+transgenic+mice:+an+ethological+perspective.+Trends+Neurosci.">Analyzing hippocampal function in transgenic mice: an ethological perspective. Trends Neurosci.</a> 22, 47-51 (1999).</li><li>McGowan, E., Eriksen, J., Hutton, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+decade+of+modeling+Alzheimer's+disease+in+transgenic+mice.">A decade of modeling Alzheimer's disease in transgenic mice.</a> Trends Genet. 2, 281-289 (2006).</li><li>Cryan, J. F., Holmes, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+ascent+of+mouse:+advances+in+modeling+human+depression+and+anxiety.">The ascent of mouse: advances in modeling human depression and anxiety.</a> Nat. Rev. Drug Discov. 4, 775-790 (2005).</li><li>Wells, T., Carter, D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Genetic+engineering+of+neural+function+in+transgenic+rodents:+towards+a+comprehensive+strategy.">Genetic engineering of neural function in transgenic rodents: towards a comprehensive strategy.</a> J. Neurosci. Methods. 108, 111-130 (2001).</li><li>Pilpel, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=reproducible+transduction+of+select+forebrain+regions+by+targeted+recombinant+virus+injection+into+the+neonatal+mouse+brain.">reproducible transduction of select forebrain regions by targeted recombinant virus injection into the neonatal mouse brain.</a> J. Neurosci. Methods. 182, 55-63 (2009).</li><li>Boutin, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Efficient+in+vivo+electroporation+of+the+postnatal+rodent+forebrain.">Efficient in vivo electroporation of the postnatal rodent forebrain.</a> PLoS One. 3, e1883-e1883 (2008).</li><li>Saito, T., Nakatsuji, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Efficient+gene+transfer+into+the+embryonic+mouse+brain+using+in+vivo+electroporation.">Efficient gene transfer into the embryonic mouse brain using in vivo electroporation.</a> Dev. Biol. 240, 237-246 (2001).</li><li>Saito, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vivo+electroporation+in+the+embryonic+mouse+central+nervous+system.">In vivo electroporation in the embryonic mouse central nervous system.</a> Nat. Protoc. 1, 1552-1558 (2006).</li><li>Matsuda, T., Cepko, C. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electroporation+and+RNA+interference+in+the+rodent+retina+in+vivo+and+in+vitro.">Electroporation and RNA interference in the rodent retina in vivo and in vitro.</a> Proc. Natl. Acad. Sci. U S A. 101, 16-22 (2004).</li><li>De Simoni, A., Yu, L. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preparation+of+organotypic+hippocampal+slice+cultures:+interface+method.">Preparation of organotypic hippocampal slice cultures: interface method.</a> Nat. Protoc. 1, 1439-1445 (2006).</li><li>Walantus, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+utero+intraventricular+injection+and+electroporation+of+E15+mouse+embryos.">In utero intraventricular injection and electroporation of E15 mouse embryos.</a> J. Vis. Exp. , (2007).</li><li>Walantus, W., Elias, L., Kriegstein, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+utero+intraventricular+injection+and+electroporation+of+E16+rat+embryos.">In utero intraventricular injection and electroporation of E16 rat embryos.</a> J. Vis. Exp. , (2007).</li><li>Umeshima, H., Hirano, T., Kengaku, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microtubule-based+nuclear+movement+occurs+independently+of+centrosome+positioning+in+migrating+neurons.">Microtubule-based nuclear movement occurs independently of centrosome positioning in migrating neurons.</a> Proc. Natl. Acad. Sci. 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Methods of gene delivery into living rodent brain are well established for in utero electroporation7,8,11,12 and, more recently, for postnatal electroporation6. However, these methods are based on intraventricular injection of the plasmid DNA, which may be limiting for several applications. For example, these methods do not allow targeting cells in certain brain areas such as hippocampus, nor transfection of such non-migratory cell types as cortical astrocytes. Non-ventricular injection cou...

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		<div>
		<table border="1">
		<thead>
		<tr>
		<th>Material Name</th>
		<th>Type</th>
		<th>Company</th>
		<th>Catalogue Number</th>
		<th>Comment</th>
		</tr>
		</thead>
		<tbody>
		
<tr>
<td>2A-sa dumb Tweezers, 115mm</td>
<td>equipment</td>
<td>XYtronic</td>
<td>XY-2A-SA</td>
<td>Treat with 70% ethanol for disinfection before use in surgical manipulations</td>
</tr>
<tr>
<td>Biological Temperature Controller with stainless steel heating pad</td>
<td>equipment</td>
<td>Supertech</td>
<td>TMP-5b</td>
<td>&nbsp;</td>
<tr>
<td>Borosilicate tube with filament</td>
<td>material</td>
<td>Sutter Instruments</td>
<td>BF120-69-10</td>
<td>Glass needle</td>
</tr>
<tr>
<td>Disposable drills</td>
<td>material</td>
<td>Meisinger</td>
<td>HP 310 104 001 001 008</td>
<td>&nbsp;</td>
<tr>
<td>Dulbeco's PBS 10X</td>
<td>reagent</td>
<td>Sigma</td>
<td>D1408</td>
<td>&nbsp;</td>
<tr>
<td>Dumont #5 forceps, 110 mm</td>
<td>equipment</td>
<td>FST</td>
<td>91150-20</td>
<td>Treat with 70% ethanol for disinfection before use in surgical manipulations</td>
</tr>
<tr>
<td>Ealing microelectrode puller</td>
<td>equipment</td>
<td>Ealing</td>
<td>50-2013</td>
<td>Vertical electrode glass puller</td>
</tr>
<tr>
<td>Ethilon monofil polyamide 6-0 FS-3 16 mm 3/8c</td>
<td>material</td>
<td>Johnson &amp; Johnson Medical</td>
<td>EH7177H</td>
<td>Surgical threads</td>
</tr>
<tr>
<td>Exmire micro syringe 10.0 ml</td>
<td>equipment</td>
<td>Exmire</td>
<td>MS*GLLX00</td>
<td>Gas-tight syringe</td>
</tr>
<tr>
<td>Fast Green</td>
<td>reagent</td>
<td>Sigma</td>
<td>F7252</td>
<td>&nbsp;</td>
<tr>
<td>Forceps electrodes</td>
<td>equipment</td>
<td>BEX</td>
<td>LF650P3</td>
<td>Treat with 70% ethanol for disinfection prior to use</td>
</tr>
<tr>
<td>Foredom drill control</td>
<td>equipment</td>
<td>Foredom </td>
<td>FM3545</td>
<td>Surgical drill power supply and control. Currently available analogue is micromotor kit K.1070 (Foredom) </td>
</tr>
<tr>
<td>Foredom micro motor handpiece</td>
<td>equipment</td>
<td>Foredom</td>
<td>MH-145</td>
<td>Currently available analogue is micromotor kit K.1070 (Foredom)</td>
</tr>
<tr>
<td>Gas anesthesia platform for mice</td>
<td>equipment</td>
<td>Stoelting</td>
<td>50264</td>
<td>Assembled on stereotaxic instrument</td>
</tr>
<tr>
<td>Isoflurane</td>
<td>reagent</td>
<td>Baxter</td>
<td>FDG9623</td>
<td>&nbsp;</td>
<tr>
<td>Micro dressing forceps, 105 mm</td>
<td>equipment</td>
<td>Aesculap</td>
<td>BD302R</td>
<td>Treat with 70% ethanol for disinfection before use in surgical manipulations</td>
</tr>
<tr>
<td>Microfil</td>
<td>material</td>
<td>WPI</td>
<td>MF34G-5</td>
<td>Micro syringe filling capillaries</td>
</tr>
<tr>
<td>Mineral oil</td>
<td>reagent</td>
<td>Sigma</td>
<td>M8410</td>
<td>&nbsp;</td>
<tr>
<td>NanoFil Syringe 10 microliter</td>
<td>equipment</td>
<td>WPI</td>
<td>NANOFIL</td>
<td>Hamilton syringe</td>
</tr>
<tr>
<td>plasmid CAG-EGFP</td>
<td>reagent</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>Extracted and purified with EndoFree Plasmid Maxi Kit (Qiagen) and dissolved in nuclease free water to concentration 1.5 mg/ml</td>
</tr>
<tr>
<td>Pulse generator CUY21Vivo-SQ</td>
<td>equipment</td>
<td>BEX</td>
<td>CUY21Vivo-SQ</td>
<td>&nbsp;</td>
<tr>
<td>Schiller electrode gel</td>
<td>reagent</td>
<td>Schiller AG</td>
<td>2.158000</td>
<td>Conductive gel</td>
</tr>
<tr>
<td>Small animal stereotaxic instrument</td>
<td>equipment</td>
<td>David Kopf Instruments</td>
<td>900</td>
<td>&nbsp;</td>
<tr>
<td>Stoelting mouse and neonatal rat adaptor</td>
<td>equipment</td>
<td>Stoelting</td>
<td>51625</td>
<td>Assembled on stereotaxic instrument.
Treat earbars with 70% ethanol for disinfection before use in surgical manipulations</td>
</tr>
<tr>
<td>Student iris scissors, straight 11.5 cm</td>
<td>equipment</td>
<td>FST</td>
<td>91460-11</td>
<td>Treat with 70% ethanol for disinfection before use in surgical manipulations</td>
</tr>
<tr>
<td>Sugi absorbent swabs 17 x 8 mm</td>
<td>material</td>
<td>Kettenbach</td>
<td>31602</td>
<td>Surgical tampons</td>
</tr>
<tr>
<td>UMP3 microsyringe pump and Micro 4 microsyringe pump controller</td>
<td>equipment</td>
<td>WPI</td>
<td>UMP3-1</td>
<td>Microinjector and controller</td>
</tr>
<tr>
<td>Univentor 400 Anesthesia Unit</td>
<td>equipment</td>
<td>Univentor</td>
<td>8323001</td>
<td>&nbsp;</td>		</tbody>
		</table>
		</div>

gene delivery to postnatal rat brain by non-ventricular plasmid injection and electroporation

Creation of transgenic animals is a standard approach in studying functions of a gene of interest in vivo. However, many knockout or transgenic animals are not viable in those cases where the modified gene is expressed or deleted in the whole organism. Moreover, a variety of compensatory mechanisms often make it difficult to interpret the results. The compensatory effects can be alleviated by either timing the gene expression or limiting the amount of transfected cells.
The method of postnatal non-ventricular microinjection and in vivo electroporation allows targeted delivery of genes, siRNA or dye molecules directly to a small region of interest in the newborn rodent brain. In contrast to conventional ventricular injection technique, this method allows transfection of non-migratory cell types. Animals transfected by means of the method described here can be used, for example, for two-photon in vivo imaging or in electrophysiological experiments on acute brain slices.

Watch this Scientific Journal Video about Gene Delivery to Postnatal Rat Brain by Non-ventricular Plasmid Injection and Electroporation at JoVE.com

Gene Delivery to Postnatal Rat Brain by Non-ventricular Plasmid Injection and Electroporation

This protocol describes a non-viral method of delivery of genetic constructs to a certain area of living rodent brain. The method consists of plasmid preparation, micropipette fabrication, neonatal rat pup surgery, microinjection of the construct, and in vivo electroporation.

Creation of transgenic animals is a standard approach in studying functions of a gene of interest in vivo. However, many knockout or transgenic animals ...

gene-delivery-to-postnatal-rat-brain-non-ventricular-plasmid

Research

JoVE Journal

Neuroscience

15.0K Views.  University of Helsinki. This protocol describes a non-viral method of delivery of genetic constructs to a certain area of living rodent brain. The method consists of plasmid preparation, micropipette fabrication, neonatal rat pup surgery, microinjection of the construct, and in vivo electroporation.

Video: Gene Delivery to Postnatal Rat Brain by Non-ventricular Plasmid Injection and Electroporation

In utero Electroporation followed by Primary Neuronal Culture for Studying Gene Function in Subset of Cortical Neurons

In vitro study of primary neuronal cultures allows for quantitative analyses of neurite outgrowth. In order to study how genetic alterations affect neuronal process outgrowth, shRNA or cDNA constructs can be introduced into primary neurons via chemical transfection or viral transduction. However, with primary cortical cells, a heterogeneous pool of cell types (glutamatergic neurons from different layers, inhibitory neurons, glial cells) are transfected using these methods. The use of in utero electroporation to introduce DNA constructs in the embryonic rodent cortex allows for certain subsets of cells to be targeted: while electroporation of early embryonic cortex targets deep layers of the cortex, electroporation at late embryonic timepoints targets more superficial layers. Further, differential placement of electrodes across the heads of individual embryos results in the targeting of dorsal-medial versus ventral-lateral regions of the cortex. Following electroporation, transfected cells can be dissected out, dissociated, and plated in vitro for quantitative analysis of neurite outgrowth. Here, we provide a step-by-step method to quantitatively measure neuronal process outgrowth in subsets of cortical cells.
The basic protocol for in utero electroporation has been described in detail in two other JoVE articles from the Kriegstein lab 1, 2. We will provide an overview of our protocol for in utero electroporation, focusing on the most important details, followed by a description of our protocol that applies in utero electroporation to the study of gene function in neuronal process outgrowth.

In utero Electroporation followed by Primary Neuronal Culture for Studying Gene Function in Subset of Cortical Neurons

In utero electroporation is a valuable method for transfecting neuronal progenitor cells in vivo. Depending upon the placement of the electrodes and the developmental timepoint of electroporation, certain subsets of cortical cells can be targeted. Targeted cells can then be analyzed in vivo or in vitro for effects of genetic alteration.

In vitro study of primary neuronal cultures allows for quantitative analyses of neurite outgrowth. In order to study how genetic alterations affect ...

Mosaic Analysis of Gene Function in Postnatal Mouse Brain Development by Using Virus-based Cre Recombination

Normal brain function relies not only on embryonic development when major neuronal pathways are established, but also on postnatal 
development when neural circuits are matured and refined. Misregulation at this stage may lead to neurological and psychiatric disorders such as autism 
and schizophrenia1,2. Many genes have been studied in the prenatal brain and found crucial to many developmental processes3-5. However, their 
function in the postnatal brain is largely unknown, partly because their deletion in mice often leads to lethality during neonatal development, and partly because their requirement in early development hampers the postnatal analysis. To overcome these obstacles, floxed alleles of these genes are currently being generated in mice 6. When combined with transgenic alleles that express Cre recombinase in specific cell types, conditional deletion can be achieved to study gene function in the postnatal brain. However, this method requires additional alleles and extra time (3-6 months) to generate the mice with appropriate genotypes, thereby limiting the expansion of the genetic analysis to a large scale in the mouse brain.
Here we demonstrate a complementary approach that uses virally-expressed Cre to study these floxed alleles rapidly and 
systematically in postnatal brain development. By injecting recombinant adeno-associated viruses (rAAVs)7,8 encoding Cre into the neonatal brain, 
we are able to delete the gene of interest in different regions of the brain. By controlling the viral titer and coexpressing a fluorescent 
protein marker, we can simultaneously achieve mosaic gene inactivation and sparse neuronal labeling. This method bypasses the requirement of 
many genes in early development, and allows us to study their cell autonomous function in many critical processes in postnatal brain development,
 including axonal and dendritic growth, branching, and tiling, as well as synapse formation and refinement. This method has been used successfully 
in our own lab (unpublished results) and others8,9, and can be extended to other viruses, such as lentivirus 9, as well as to the expression of 
shRNA or dominant active proteins 10. Furthermore, by combining this technique with electrophysiology as well as recently-developed optical 
imaging tools 11, this method provides a new strategy to study how genetic pathways influence neural circuit development and function in mice 
and rats.

An in vivo method to test gene function in postnatal brain is described. Recombinant AAVs expressing Cre and/or a fluorescent protein are injected into neonatal mouse brain. Mosaic gene inactivation and sparse neuronal labeling are achieved, allowing rapid analysis of gene function in processes critical to neural circuit development.

Normal brain function relies not only on embryonic development when major neuronal pathways are established, but also on postnatal 
development when ...

Efficient Gene Delivery into Multiple CNS Territories Using In Utero Electroporation

The ability to manipulate gene expression is the cornerstone of modern day experimental embryology, leading to the elucidation of multiple developmental pathways. Several powerful and well established transgenic technologies are available to manipulate gene expression levels in mouse, allowing for the generation of both loss- and gain-of-function models. However, the generation of mouse transgenics is both costly and time consuming. Alternative methods of gene manipulation have therefore been widely sought. In utero electroporation is a method of gene delivery into live mouse embryos1,2 that we have successfully adapted3,4. It is largely based on the success of in ovo electroporation technologies that are commonly used in chick5. Briefly, DNA is injected into the open ventricles of the developing brain and the application of an electrical current causes the formation of transient pores in cell membranes, allowing for the uptake of DNA into the cell. In our hands, embryos can be efficiently electroporated as early as embryonic day (E) 11.5, while the targeting of younger embryos would require an ultrasound-guided microinjection protocol, as previously described6. Conversely, E15.5 is the latest stage we can easily electroporate, due to the onset of parietal and frontal bone differentiation, which hampers microinjection into the brain. In contrast, the retina is accessible through the end of embryogenesis. Embryos can be collected at any time point throughout the embryonic or early postnatal period. Injection of a reporter construct facilitates the identification of transfected cells.
To date, in utero electroporation has been most widely used for the analysis of neocortical development1,2,3,4. More recent studies have targeted the embryonic retina7,8,9 and thalamus10,11,12. Here, we present a modified in utero electroporation protocol that can be easily adapted to target different domains of the embryonic CNS. We provide evidence that by using this technique, we can target the embryonic telencephalon, diencephalon and retina. Representative results are presented, first showing the use of this technique to introduce DNA expression constructs into the lateral ventricles, allowing us to monitor progenitor maturation, differentiation and migration in the embryonic telencephalon. We also show that this technique can be used to target DNA to the diencephalic territories surrounding the 3rd ventricle, allowing the migratory routes of differentiating neurons into diencephalic nuclei to be monitored. Finally, we show that the use of micromanipulators allows us to accurately introduce DNA constructs into small target areas, including the subretinal space, allowing us to analyse the effects of manipulating gene expression on retinal development.

Efficient Gene Delivery into Multiple CNS Territories Using In Utero Electroporation

In utero electroporation allows for rapid gene delivery in a spatially- and temporally-controlled manner in the developing central nervous system (CNS). Here we describe a highly adaptable in utero electroporation protocol that can be used to deliver expression constructs into multiple embryonic CNS domains, including the telencephalon, diencephalon and retina.

The ability to manipulate gene expression is the cornerstone of modern day experimental embryology, leading to the elucidation of multiple developmental ...

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 ...

Gene Transfer to the Developing Mouse Inner Ear by In Vivo Electroporation

The mammalian inner ear has 6 distinct sensory epithelia: 3 cristae in the ampullae of the semicircular canals; maculae in the utricle and saccule; and the organ of Corti in the coiled cochlea. The cristae and maculae contain vestibular hair cells that transduce mechanical stimuli to subserve the special sense of balance, while auditory hair cells in the organ of Corti are the primary transducers for hearing 1. Cell fate specification in these sensory epithelia and morphogenesis of the semicircular canals and cochlea take place during the second week of gestation in the mouse and are largely completed before birth 2,3. Developmental studies of the mouse inner ear are routinely conducted by harvesting transgenic embryos at different embryonic or postnatal stages to gain insight into the molecular basis of cellular and/or morphological phenotypes 4,5. We hypothesize that gene transfer to the developing mouse inner ear in utero in the context of gain- and loss-of-function studies represents a complimentary approach to traditional mouse transgenesis for the interrogation of the genetic mechanisms underlying mammalian inner ear development6.
The experimental paradigm to conduct gene misexpression studies in the developing mouse inner ear demonstrated here resolves into three general steps: 1) ventral laparotomy; 2) transuterine microinjection; and 3) in vivo electroporation. Ventral laparotomy is a mouse survival surgical technique that permits externalization of the uterus to gain experimental access to the implanted embryos7. Transuterine microinjection is the use of beveled, glass capillary micropipettes to introduce expression plasmid into the lumen of the otic vesicle or otocyst. In vivo electroporation is the application of square wave, direct current pulses to drive expression plasmid into progenitor cells8-10. 
We previously described this electroporation-based gene transfer technique and included detailed notes on each step of the protocol11. Mouse experimental embryological techniques can be difficult to learn from prose and still images alone. In the present work, we demonstrate the 3 steps in the gene transfer procedure. Most critically, we deploy digital video microscopy to show precisely how to: 1) identify embryo orientation in utero; 2) reorient embryos for targeting injections to the otocyst; 3) microinject DNA mixed with tracer dye solution into the otocyst at embryonic days 11.5 and 12.5; 4) electroporate the injected otocyst; and 5) label electroporated embryos for postnatal selection at birth. We provide representative examples of successfully transfected inner ears; a pictorial guide to the most common causes of otocyst mistargeting; discuss how to avoid common methodological errors; and present guidelines for writing an in utero gene transfer animal care protocol.

Gene Transfer to the Developing Mouse Inner Ear by In Vivo Electroporation

The mouse inner ear is a placode-derived sensory organ whose developmental program is elaborated during gestation. We define an in utero gene transfer technique consisting of three steps: mouse ventral laparotomy, transuterine microinjection, and in vivo electroporation. We use digital video microscopy to demonstrate the critical experimental embryological techniques.

The mammalian inner ear has 6 distinct sensory epithelia: 3 cristae in the ampullae of the semicircular canals; maculae in the utricle and saccule; and ...

Expansion of Embryonic and Adult Neural Stem Cells by In Utero Electroporation or Viral Stereotaxic Injection

Somatic stem cells can divide to generate additional stem cells (expansion) or more differentiated cell types (differentiation), which is fundamental for tissue formation during embryonic development and tissue homeostasis during adulthood 1. Currently, great efforts are invested towards controlling the switch of somatic stem cells from expansion to differentiation because this is thought to be fundamental for developing novel strategies for regenerative medicine 1,2. However, a major challenge in the study and use of somatic stem cell is that their expansion has been proven very difficult to control.
Here we describe a system that allows the control of neural stem/progenitor cell (altogether referred to as NSC) expansion in the mouse embryonic cortex or the adult hippocampus by manipulating the expression of the cdk4/cyclinD1 complex, a major regulator of the G1 phase of the cell cycle and somatic stem cell differentiation 3,4. Specifically, two different approaches are described by which the cdk4/cyclinD1 complex is overexpressed in NSC in vivo. By the first approach, overexpression of the cell cycle regulators is obtained by injecting plasmids encoding for cdk4/cyclinD1 in the lumen of the mouse telencephalon followed by in utero electroporation to deliver them to NSC of the lateral cortex, thus, triggering episomal expression of the transgenes 5-8. By the second approach, highly concentrated HIV-derived viruses are stereotaxically injected in the dentate gyrus of the adult mouse hippocampus, thus, triggering constitutive expression of the cell cycle regulators after integration of the viral construct in the genome of infected cells 9. Both approaches, whose basic principles were already described by other video protocols 10-14, were here optimized to i) reduce tissue damage, ii) target wide portions of very specific brain regions, iii) obtain high numbers of manipulated cells within each region, and iv) trigger high expression levels of the transgenes within each cell. Transient overexpression of the transgenes using the two approaches is obtained by different means i.e. by natural dilution of the electroporated plasmids due to cell division or tamoxifen administration in Cre-expressing NSC infected with viruses carrying cdk4/cyclinD1 flanked by loxP sites, respectively 9,15.
These methods provide a very powerful platform to acutely and tissue-specifically manipulate the expression of any gene in the mouse brain. In particular, by manipulating the expression of the cdk4/cyclinD1 complex, our system allows the temporal control of NSC expansion and their switch to differentiation, thus, ultimately increasing the number of neurons generated in the mammalian brain. Our approach may be critically important for basic research and using somatic stem cells for therapy of the mammalian central nervous system while providing a better understanding of i) stem cell contribution to tissue formation during development, ii) tissue homeostasis during adulthood, iii) the role of adult neurogenesis in cognitive functions, and perhaps, iv) better using somatic stem cells in models of neurodegenerative diseases.

Expansion of Embryonic and Adult Neural Stem Cells by In Utero Electroporation or Viral Stereotaxic Injection

Controlling the expansion of somatic stem cells is a major factor hampering their study and use in therapy. Here we describe a system to temporally control neural stem cells expansion during development and adulthood, which can be used to increase the number of neurons generated in the mouse brain.

Somatic stem cells can divide to generate additional stem cells (expansion) or more differentiated cell types (differentiation), which is fundamental for ...

In vivo Postnatal Electroporation and Time-lapse Imaging of Neuroblast Migration in Mouse Acute Brain Slices

The subventricular zone (SVZ) is one of the main neurogenic niches in the postnatal brain. Here, neural progenitors proliferate and give rise to neuroblasts able to move along the rostral migratory stream (RMS) towards the olfactory bulb (OB). This long-distance migration is required for the subsequent maturation of newborn neurons in the OB, but the molecular mechanisms regulating this process are still unclear. Investigating the signaling pathways controlling neuroblast motility may not only help understand a fundamental step in neurogenesis, but also have therapeutic regenerative potential, given the ability of these neuroblasts to target brain sites affected by injury, stroke, or degeneration.
In this manuscript we describe a detailed protocol for in vivo postnatal electroporation and subsequent time-lapse imaging of neuroblast migration in the mouse RMS. Postnatal electroporation can efficiently transfect SVZ progenitor cells, which in turn generate neuroblasts migrating along the RMS. Using confocal spinning disk time-lapse microscopy on acute brain slice cultures, neuroblast migration can be monitored in an environment closely resembling the in vivo condition. Moreover, neuroblast motility can be tracked and quantitatively analyzed. As an example, we describe how to use in vivo postnatal electroporation of a GFP-expressing plasmid to label and visualize neuroblasts migrating along the RMS. Electroporation of shRNA or CRE recombinase-expressing plasmids in conditional knockout mice employing the LoxP system can also be used to target genes of interest. Pharmacological manipulation of acute brain slice cultures can be performed to investigate the role of different signaling molecules in neuroblast migration. By coupling in vivo electroporation with time-lapse imaging, we hope to understand the molecular mechanisms controlling neuroblast motility and contribute to the development of novel approaches to promote brain repair.

In vivo Postnatal Electroporation and Time-lapse Imaging of Neuroblast Migration in Mouse Acute Brain Slices

Neuroblast migration is a fundamental event in postnatal neurogenesis. We describe a protocol for efficient labeling of neuroblasts by in vivo postnatal electroporation and subsequent visualization of their migration using time-lapse imaging of acute brain slices. We include a description for the quantitative analysis of neuroblast dynamics by video tracking.

The subventricular zone (SVZ) is one of the main neurogenic niches in the postnatal brain. Here, neural progenitors proliferate and give rise to ...

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 ...

Analysis of Gene Expression Changes in the Rat Hippocampus After Deep Brain Stimulation of the Anterior Thalamic Nucleus

Deep brain stimulation (DBS) surgery, targeting various regions of the brain such as the basal ganglia, thalamus, and subthalamic regions, is an effective treatment for several movement disorders that have failed to respond to medication. Recent progress in the field of DBS surgery has begun to extend the application of this surgical technique to other conditions as diverse as morbid obesity, depression and obsessive compulsive disorder. Despite these expanding indications, little is known about the underlying physiological mechanisms that facilitate the beneficial effects of DBS surgery. One approach to this question is to perform gene expression analysis in neurons that receive the electrical stimulation. Previous studies have shown that neurogenesis in the rat dentate gyrus is elicited in DBS targeting of the anterior nucleus of the thalamus1. DBS surgery targeting the ATN is used widely for treatment refractory epilepsy. It is thus of much interest for us to explore the transcriptional changes induced by electrically stimulating the ATN. In this manuscript, we describe our methodologies for stereotactically-guided DBS surgery targeting the ATN in adult male Wistar rats. We also discuss the subsequent steps for tissue dissection, RNA isolation, cDNA preparation and quantitative RT-PCR for measuring gene expression changes. This method could be applied and modified for stimulating the basal ganglia and other regions of the brain commonly clinically targeted. The gene expression study described here assumes a candidate target gene approach for discovering molecular players that could be directing the mechanism for DBS.

The mechanism underlying the therapeutic effects of Deep Brain Stimulation (DBS) surgery needs investigation. The methods presented in this manuscript describe an experimental approach to examine the cellular events triggered by DBS by analyzing the gene expression profile of candidate genes that can facilitate neurogenesis post DBS surgery.

Deep brain stimulation (DBS) surgery, targeting various regions of the brain such as the basal ganglia, thalamus, and subthalamic regions, is an effective ...

Using Fluorescence Activated Cell Sorting to Examine Cell-Type-Specific Gene Expression in Rat Brain Tissue

The brain is comprised of four primary cell types including neurons, astrocytes, microglia and oligodendrocytes. Though they are not the most abundant cell type in the brain, neurons are the most widely studied of these cell types given their direct role in impacting behaviors. Other cell types in the brain also impact neuronal function and behavior via the signaling molecules they produce. Neuroscientists must understand the interactions between the cell types in the brain to better understand how these interactions impact neural function and disease. To date, the most common method of analyzing protein or gene expression utilizes the homogenization of whole tissue samples, usually with blood, and without regard for cell type. This approach is an informative approach for examining general changes in gene or protein expression that may influence neural function and behavior; however, this method of analysis does not lend itself to a greater understanding of cell-type-specific gene expression and the effect of cell-to-cell communication on neural function. Analysis of behavioral epigenetics has been an area of growing focus which examines how modifications of the deoxyribonucleic acid (DNA) structure impact long-term gene expression and behavior; however, this information may only be relevant if analyzed in a cell-type-specific manner given the differential lineage and thus epigenetic markers that may be present on certain genes of individual neural cell types. The Fluorescence Activated Cell Sorting (FACS) technique described below provides a simple and effective way to isolate individual neural cells for the subsequent analysis of gene expression, protein expression, or epigenetic modifications of DNA. This technique can also be modified to isolate more specific neural cell types in the brain for subsequent cell-type-specific analysis.

The goal of this protocol is to use the fluorescence activated cell sorting (FACS) technique to sort specific types of neural cells for subsequent analysis of cell-type-specific gene expression, epigenetic markers, and or protein expression.

The brain is comprised of four primary cell types including neurons, astrocytes, microglia and oligodendrocytes. Though they are not the most abundant ...