This work was supported grants from NINDS (NS066071) and the NIAAA. (P50AA017823) to ECO. The authors thank Dr. Robert Quinn and the staff in the Department of Laboratory Animal Resources for animal care. We thank Judson Belmont for technical support, Nicole Belletier for assistance as a Summer Undergraduate Research Fellow (SURF). We also thank Dr. David Cameron for comments and edits on an earlier version of the manuscript.

1. Ex utero Electroporations with Green Fluorescent Protein Expression Plasmid
<ol>
	<li>Plasmid DNA injection solutions are prepared with CAG-eGFP DNA 27 diluted to the final working concentration of 0.33 mg/ml in ddH2O. Qiagen Endo-Free Maxi-Preps are used to purify the plasmid from transformed bacteria. Fast green dye at ~0.02% (w/v final) is added to the DNA solution as an injection tracer.</li>
	<li>To prepare the surgical area, spray down bench top and dissecting microscope stage with a 70% ethanol solution and wipe dry. Spray surgical scissors and forceps with 70% ethanol prior to dissection and wipe dry.</li>
	<li>Timed Pregnant Swiss/Webster dams are sacrificed on E13 by transfer into a chamber filled with CO2 from a pressurized cylinder and the dam is monitored until all motion has stopped for at least 1 min. After sacrifice by CO2 inhalation the embryos are removed from the uterus and placed in a 10 cm Petri dish containing ice cold Hanks balanced saline solution (HBSS).</li>
	<li>Carefully dissect each embryo from the surrounding extraembryonic membranes and keep in ice-cold HBSS.</li>
	<li>Transfer each embryo individually to a second 10 cm Petri dish containing cold HBSS. Use a Hamilton syringe to inject 2-3 &mu;l of the DNA fast green mixture into the ventricle of the left cerebral hemisphere, taking care to inject in a cortical area spatially separate from the cortical area for future analysis.</li>
	<li>To electroporate, hold the embryo gently with forceps and lightly place the positive paddle of the tweezer electrode on the dorsal midline of the head and lightly place the negative paddle underneath the embryo chin. Electroporations are achieved with a BTX830 electroporator programmed to deliver five 30 V pulses of 50 msec duration, separated by 950 msec intervals. These settings are for the BTX830 model. Other systems can be used according to manufacturer's instructions.</li>
</ol>
2. Whole Hemisphere Explant Preparation
<ol>
	<li>After electroporation the embryos are placed back into ice-cold HBSS. The brain is removed using two #5 jeweler forceps to remove the skin and cartilaginous skull from the embryo head. A forcep is then slid underneath the brain to remove the intact brain from the skull. The electroporated hemisphere (left) is then dissected away from the brain and attached mid-brain tissue is removed. Throughout the dissection procedure care is taken to not damage the meninges overlying the left cortical hemisphere.</li>
	<li>Once dissected each embryo is transferred in HBSS using a pipettor with a cut 1 ml pipette tip. The hemisphere is gently expelled onto a collagen coated culture insert. Up to six hemisphere explants are arranged medial side down on each 24 mm insert. Once arranged, excess HBSS is removed from the insert and the insert is then placed into one 35 mm well of a 6 well dish. The well contains exactly 2.7 ml of media: DMEM-F12 media containing Glutamax and supplemented with 2% B-27, 1% G5 and 1% Penicillin-Strep. A few drops of the media from the well can be pipetted on top of each explant, but do not add media in excess of the original 2.7 ml per well.</li>
	<li>Once the explants have been placed onto Collagen filters the 6 well dish containing the explants is placed into a Billups Rothenberg (BR) chamber (that also contains a humidifying dish of water). A 95%/5% Oxygen/CO2 gas mixture is infused into the chamber for at least 1 min before sealing the chamber shut and disconnecting the 95%/5% Oxygen/CO2 gas supply tube. The BR chamber is then placed into a 37 &deg;C tissue culture incubator for the remainder of the culture period, 1-2 DIV.</li>
</ol>
3. Fixation of Explant Tissue for Histology
<ol>
	<li>In a fume hood prepare the Pagano fixation solution by first solubilizing 8 g of paraformaldehyde in 100 ml of preheated (~80 &deg;C) ddH2O. Add 1-3 drops concentrated NaOH to promote solubilization and gently stir. Once solubilized mix the 8% paraformaldehyde solution 1:1 with a solution that is 500 mM sucrose, 100 mM Hepes, pH 7.4, 50 mM MgCl2, 5 mM KCl for a final concentration of 4% paraformaldehyde in 250 mM sucrose 50 mM Hepes, 25 mM MgCl2, 2.5 mM KCl, pH 7.4.</li>
	<li>To fix the explants warm the Pagano fix solution to 37 &deg;C. Quickly remove most of the DMEM/F12 media from each culture well and add 5 ml of Pagano Fix to each well of explants. Make sure to cover each explant completely in fix. Fix for 1 hr at RT. Do not remove explants from filter prior to 1 hr of fixation.</li>
	<li>After fixation remove the Pagano fix solution and replace with Pagano solution without fix (250 mM sucrose 50 mM Hepes, 25 mM MgCl2, 2.5 mM KCl, pH 7.4). Add a few drops of 10% sodium azide and store at 4 &deg;C until embedding.</li>
</ol>
4. Embedding and Sectioning for Histology
<ol>
	<li>Prepare a 10% calf skin gelatin solution by solubilizing 10 g of calf skin gelatin in 100 ml of warm water (55-60 &deg;C). Place gelatin solution on a hot plate set to 60 &deg;C and swirl periodically until solubilized.</li>
	<li>Pour approximately 10 ml of the 10% gelatin solution into the bottom of a 10 cm Petri dish and allow 30 min to solidify. This will form a "pad" for embedding the explants. These pads can be prepared days in advance and stored at 4 &deg;C. Use a ruler to draw a grid on the bottom of the Petri dish and transfer individual explants into each box of the grid. Remove residual Pagano solution and using a pipettor, cover each explant with warm 10% gelatin solution and allow to solidify. Resume slow addition of gelatin solution until each explant is completely surrounded by gelatin, taking care not to melt the pad by the addition of too much warm gelatin at once. Allow for the gelatin to harden for ~1 hr. Once hardened the individual explants can be cut out in small blocks of gelatin. The blocks are then post-fixed in Pagano fix for 24-48 hr prior to sectioning with a vibratome.</li>
	<li>Explants in gelatin blocks are positioned olfactory bulb up and sectioned in the coronal plane at 100 &mu;m thickness. The sections are collected and stored in PBS + 0.1% sodium azide at 4 &deg;C until immunohistochemical processing.</li>
	<li>Immunohistochemical detection is performed by transferring sections into a 24 well plate (2-3 sections per well). First block non-specific antibody binding by adding 0.5 ml PBST+B (PBS + 0.5% Triton X 100 and 2% BSA) to each well, incubate 1 hr with gentle shaking. The appropriate primary antibody is then diluted in PBST+B and 0.4 ml per well is added for overnight incubation at RT. The primary is washed out with 3X PBS washes for at least 10 min each. The secondary antibody and 2 &mu;g/ml Hoechst 33342 nuclear stain are then diluted in PBST+B and the samples are incubated for 2 hr at RT with gentle shaking. Three PBS washes (10 min each) are performed and then the sections are mounted on slides using a 90% glycerol 50 mM Tris, pH7.4, mounting media.</li>
</ol>

The authors declare that they have no competing financial interests.

We have improved and evaluated an experimental model - whole hemisphere explants - for the study of early cortical development (E13-E15). The model has proven useful for the analysis of migration and differentiation of the excitatory neuron lineage that constitutes layer 6 of the cerebral cortex 25,37 . The principle advantages of the system are 1) organotypic growth for 2 DIV, 2) simplicity of preparation, and 3) experimental access to the neurons for electroporation, pharmacological manipulation and imaging ...

The mammalian cerebral cortex forms through the concerted proliferation, migration and differentiation of successively generated neurons. Each neuron is born in the ventricular zone (VZ) and migrates from the VZ into the intermediate zone (IZ), forming the cortical plate (CP) 1. As they pass through different cortical domains, the migrating neurons display multiple modes of migration 2,3 that depend on the extracellular environment and other cellular elements (e.g. radial glia) within the developing tissue. Cortical neurons then arrest migration at the top of the forming cortical plate in the coincident processes of neuronal migration arrest and dendritogenesis 4.
Cortical development is initiated between embryonic days 11-13 (E11-13) 5 through establishment of the primordial plexiform layer 6 or preplate (PP), a layer of pioneer neurons that overlies the VZ. Prospective layer 6 cortical neurons (i.e. the first cortical neurons born in the VZ) then orient their somata in a stereotypical pattern and coalesce into a distinct layer within the PP 7. These events split the preplate into a superficial marginal (future cortical layer 1) and a deep zone, the latter composed of subplate cells (transient cortical layer 7). This process, termed preplate splitting, is a foundational event in the future growth of the cerebral cortex 8.
Many genetic mutations have been identified that disrupt various aspects of cortical development 9. Cortical development can also be negatively impacted by exposure to ingested toxins such as cocaine 10 and alcohol 11. Because cortical malformations that arise during development are likely contributors to neurological disorders (e.g. autism, schizophrenia), empirical investigations of perturbations to cortical development are inherently important. It is therefore of considerable importance to establish approaches to study cortical development that allow rapid assays of genetic or toxin effects but that also preserve the possible interactions between differentiating neurons, other cell types and extracellular matrix (ECM) during this early period of brain development 12.
Slice explants 13 have provided such a system and have been widely used to assay cortical neuron development 14-16. However, slice assays can suffer from the drawback that neuronal migration and lamination can be abnormal 17 possibly due to damage to the meningeal cells that surround the developing brain and anchor the radial glial scaffold. As radial glial fibers are an important substrate for cortical neuron migration 18 disruption of the basal lamina by slicing may locally disrupt radial glial architecture and lead to altered cortical migration. In addition the sliced surfaces of explants provides a region of dead cells that may alter the normal composition of the ECM in these areas.
More recent approaches have focused their analysis on cells located deep in the slice that are surrounded by appropriate healthy cell types and ECM. However, in some cases these newer approaches can require that the original thick cultured slice be cryo-sectioned or paraffin-sectioned after fixation so that the relatively normal interior of the slice is made available for analysis 19-21. Both the original vibratome sectioning to prepare the live slices for culture as well as the subsequent cryosectioning of fixed slices for analysis require care and effort for these assays to work.
To provide a simple, complementary approach for studies of early cortical development, we have modified an existing slice approaches 13 to facilitate studies of early cortical development. We have developed a whole hemisphere explant model similar to an existing E14 whole hemisphere model that involved shaking cultures at 65 rotations per minute and permitted organotypic growth for 16-18 hr 22,23 . In our approach, whole hemisphere explants are placed on semi-permeable membrane 13 with in a high oxygen culture atmosphere 21,24 to extend organotypic cortical growth for 48 hr. This approach also allows for consistent electroporation of developing cortical neurons. The embryos are removed from the uterus and electroporated to introduce plasmid DNA and the telencephalon is then dissected. Each hemisphere is isolated and placed medial side down on a collagen-coated filter. The explant is then cultured for a period of 48 hr, a period that encompasses preplate splitting 8. During the culture period, L6 neurons develop from precursor to differentiated neuron 25, correctly positioned within the cortical plate. Throughout this period the developing neuron is surrounded by the appropriate ECM and cell types that would confront the corresponding cell in vivo. This system has already proved valuable in deciphering the cellular events that underlie ethanol toxicity 26, layer 6 formation and preplate splitting 7,25 .

<table border="1">
	<tbody>
		<tr>
			<td>Name </td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments (optional)</td>
		</tr>
		<tr>
			<td>Reagents</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>DMEM/F12 + GlutaMAX</td>
			<td>GIBCO</td>
			<td>10565</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>G5 Supplement 100X</td>
			<td>Invitrogen</td>
			<td>17503-012</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>B27 Serum-Free Suppl. 50X</td>
			<td>Invitrogen</td>
			<td>1504-044</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Pen / Strep Liquid 100X</td>
			<td>Invitrogen</td>
			<td>15140-122</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>HBSS 500 ml</td>
			<td>GIBCO</td>
			<td>14025</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Culture insert collagen coated</td>
			<td>Costar</td>
			<td>3492</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Bovine skin gelatin</td>
			<td>Sigma</td>
			<td>G9382</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Hoechst 33342</td>
			<td>Invitrogen</td>
			<td>H1399</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Bovine Serum Albumin</td>
			<td>Sigma</td>
			<td>7906</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>EndoFree Plasmid Maxi Kit</td>
			<td>Qiagen</td>
			<td>12362</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Equipment</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>BTX 830 Electroporator</td>
			<td>Harvard Apparatus</td>
			<td>450052</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Tweezer electrodes 10mm</td>
			<td>Harvard Apparatus</td>
			<td>450166</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Incubator</td>
			<td>Billups Rothenberg</td>
			<td>MIC-101</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Hamilton syringe (5 uL)</td>
			<td>Hamilton</td>
			<td>87930</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Hamilton syringe needle</td>
			<td>Hamilton</td>
			<td>7803-04</td>
			<td>Specify 1" and style 4</td>
		</tr>
		<tr>
			<td>Dumont #5 Forceps</td>
			<td>FST</td>
			<td>11251-10</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Fine Scissors Tough Cut 9 cm</td>
			<td>FST</td>
			<td>14058-09</td>
			<td>&nbsp;</td>
		</tr>
	</tbody>
</table>

ex utero electroporation and whole hemisphere explants: a simple experimental method for studies of early cortical development

Cortical development involves complex interactions between neurons and non-neuronal elements including precursor cells, blood vessels, meninges and associated extracellular matrix. Because they provide a suitable organotypic environment, cortical slice explants are often used to investigate those interactions that control neuronal differentiation and development. Although beneficial, the slice explant model can suffer from drawbacks including aberrant cellular lamination and migration. Here we report a whole cerebral hemisphere explant system for studies of early cortical development that is easier to prepare than cortical slices and shows consistent organotypic migration and lamination. In this model system, early lamination and migration patterns proceed normally for a period of two days in vitro, including the period of preplate splitting, during which prospective cortical layer six forms. We then developed an ex utero electroporation (EUEP) approach that achieves ~80% success in targeting GFP expression to neurons developing in the dorsal medial cortex.
The whole hemisphere explant model makes early cortical development accessible for electroporation, pharmacological intervention and live imaging approaches. This method avoids the survival surgery required of in utero electroporation (IUEP) approaches while improving both transfection and areal targeting consistency. This method will facilitate experimental studies of neuronal proliferation, migration and differentiation.

The embryonic rodent cortex exhibits a transverse neurogenetic gradient throughout the developmental period, such that lateral neocortex is approximately 1 day more mature than dorsal medial neocortex 28. The bulk of layer 6 neurons are thus generated (i.e. exhibit their final S-phase) on E12 in lateral cortex (also called Field 405) and at E13 in the dorsal medial cortex (also called Field 15). Preplate splitting begins approximately 1 day after Layer 6 neuron generation and thu...

Watch this Scientific Journal Video about Ex utero Electroporation and Whole Hemisphere Explants: A Simple Experimental Method for Studies of Early Cortical Development at JoVE.com

Ex utero Electroporation and Whole Hemisphere Explants: A Simple Experimental Method for Studies of Early Cortical Development

This protocol describes an improved explant procedure that involves ex utero electroporation, dissection and culture of entire cerebral hemispheres from the embryonic mouse. The preparation facilitates pharmacological studies and assays of gene function during early cortical development.

Ex utero Electroporation and Whole Hemisphere Explants: A Simple Experimental Method for Studies of Early Cortical Development

Cortical development involves complex interactions between neurons and non-neuronal elements including precursor cells, blood vessels, meninges and ...

ex-utero-electroporation-whole-hemisphere-explants-simple

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JoVE Journal

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12.8K Views.  SUNY Upstate Medical University. This protocol describes an improved explant procedure that involves ex utero electroporation, dissection and culture of entire cerebral hemispheres from the embryonic mouse. The preparation facilitates pharmacological studies and assays of gene function during early cortical development.

Video: Ex utero Electroporation and Whole Hemisphere Explants: A Simple Experimental Method for Studies of Early Cortical Development

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 ...

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 ...

Visualization and Genetic Manipulation of Dendrites and Spines in the Mouse Cerebral Cortex and Hippocampus using In utero Electroporation

In utero electroporation (IUE) has become a powerful technique to study the development of different regions of the embryonic nervous system 1-5. To date this tool has been widely used to study the regulation of cellular proliferation, differentiation and neuronal migration especially in the developing cerebral cortex 6-8. Here we detail our protocol to electroporate in utero the cerebral cortex and the hippocampus and provide evidence that this approach can be used to study dendrites and spines in these two cerebral regions.
Visualization and manipulation of neurons in primary cultures have contributed to a better understanding of the processes involved in dendrite, spine and synapse development. However neurons growing in vitro are not exposed to all the physiological cues that can affect dendrite and/or spine formation and maintenance during normal development. Our knowledge of dendrite and spine structures in vivo in wild-type or mutant mice comes mostly from observations using the Golgi-Cox method 9. However, Golgi staining is considered to be unpredictable. Indeed, groups of nerve cells and fiber tracts are labeled randomly, with particular areas often appearing completely stained while adjacent areas are devoid of staining. Recent studies have shown that IUE of fluorescent constructs represents an attractive alternative method to study dendrites, spines as well as synapses in mutant / wild-type mice 10-11 (Figure 1A). Moreover in comparison to the generation of mouse knockouts, IUE represents a rapid approach to perform gain and loss of function studies in specific population of cells during a specific time window. In addition, IUE has been successfully used with inducible gene expression or inducible RNAi approaches to refine the temporal control over the expression of a gene or shRNA 12. These advantages of IUE have thus opened new dimensions to study the effect of gene expression/suppression on dendrites and spines not only in specific cerebral structures (Figure 1B) but also at a specific time point of development (Figure 1C).
Finally, IUE provides a useful tool to identify functional interactions between genes involved in dendrite, spine and/or synapse development. Indeed, in contrast to other gene transfer methods such as virus, it is straightforward to combine multiple RNAi or transgenes in the same population of cells. 
In summary, IUE is a powerful method that has already contributed to the characterization of molecular mechanisms underlying brain function and disease and it should also be useful in the study of dendrites and spines.

Visualization and Genetic Manipulation of Dendrites and Spines in the Mouse Cerebral Cortex and Hippocampus using In utero Electroporation

This article describes in detail a protocol to electroporate in utero the cerebral cortex and the hippocampus at E14.5 in mice. We also show that this is a valuable method to study dendrites and spines in these two cerebral regions.

In utero electroporation (IUE) has become a powerful technique to study the development of different regions of the embryonic nervous system 1-5. To date ...

Generation of Topically Transgenic Rats by In utero Electroporation and In vivo Bioluminescence Screening

In utero electroporation (IUE) is a technique which allows genetic modification of cells in the brain for investigating neuronal development. So far, the use of IUE for investigating behavior or neuropathology in the adult brain has been limited by insufficient methods for monitoring of IUE transfection success by non-invasive techniques in postnatal animals. 
 For the present study, E16 rats were used for IUE. After intraventricular injection of the nucleic acids into the embryos, positioning of the tweezer electrodes was critical for targeting either the developing cortex or the hippocampus. 
 Ventricular co-injection and electroporation of a luciferase gene allowed monitoring of the transfected cells postnatally after intraperitoneal luciferin injection in the anesthetized live P7 pup by in vivo bioluminescence, using an IVIS Spectrum device with 3D quantification software. 
 Area definition by bioluminescence could clearly differentiate between cortical and hippocampal electroporations and detect a signal longitudinally over time up to 5 weeks after birth. This imaging technique allowed us to select pups with a sufficient number of transfected cells assumed necessary for triggering biological effects and, subsequently, to perform behavioral investigations at 3 month of age. As an example, this study demonstrates that IUE with the human full length DISC1 gene into the rat cortex led to amphetamine hypersensitivity. Co-transfected GFP could be detected in neurons by post mortem fluorescence microscopy in cryosections indicating gene expression present at &ge;6 months after birth.
 We conclude that postnatal bioluminescence imaging allows evaluating the success of transient transfections with IUE in rats. Investigations on the influence of topical gene manipulations during neurodevelopment on the adult brain and its connectivity are greatly facilitated. For many scientific questions, this technique can supplement or even replace the use of transgenic rats and provide a novel technology for behavioral neuroscience.

Generation of Topically Transgenic Rats by In utero Electroporation and In vivo Bioluminescence Screening

Genes can be manipulated during development of the cortex or the hippocampus of the rat via in utero electroporation (IUE) at E16, to enable fast and targeted modifications in neuronal connectivity for later studies of behavior or neuropathology in adult animals. Postnatal in vivo imaging for control of IUE success is performed by bioluminescence of activating co-transfected luciferase.

 In utero electroporation (IUE) is a technique which allows genetic modification of cells in the brain for investigating neuronal development. So far, the ...

Isolation of Cerebrospinal Fluid from Rodent Embryos for use with Dissected Cerebral Cortical Explants

The CSF is a complex fluid with a dynamically varying proteome throughout development and in adulthood. During embryonic development, the nascent CSF differentiates from the amniotic fluid upon closure of the anterior neural tube. CSF volume then increases over subsequent days as the neuroepithelial progenitor cells lining the ventricles and the choroid plexus generate CSF. The embryonic CSF contacts the apical, ventricular surface of the neural stem cells of the developing brain and spinal cord. CSF provides crucial fluid pressure for the expansion of the developing brain and distributes important growth promoting factors to neural progenitor cells in a temporally-specific manner. To investigate the function of the CSF, it is important to isolate pure samples of embryonic CSF without contamination from blood or the developing telencephalic tissue. Here, we describe a technique to isolate relatively pure samples of ventricular embryonic CSF that can be used for a wide range of experimental assays including mass spectrometry, protein electrophoresis, and cell and primary explant culture. We demonstrate how to dissect and culture cortical explants on porous polycarbonate membranes in order to grow developing cortical tissue with reduced volumes of media or CSF. With this method, experiments can be performed using CSF from varying ages or conditions to investigate the biological activity of the CSF proteome on target cells.

The ventricular cerebrospinal fluid (CSF) bathes the neuroepithelial and cerebral cortical progenitor cells during early brain development in the embryo. Here we describe the method developed to isolate ventricular CSF from rodent embryos of different ages in order to investigate its biological function. In addition, we demonstrate our cerebral cortical explant dissection and culture technique that allows for explant growth with minimal volumes of culture medium or CSF.

The CSF is a complex fluid with a dynamically varying proteome throughout development and in adulthood. During embryonic development, the nascent CSF ...

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 ...

A Novel Strategy Combining Array-CGH, Whole-exome Sequencing and In Utero Electroporation in Rodents to Identify Causative Genes for Brain Malformations

Birth defects that involve the cerebral cortex &#8212; also known as malformations of cortical development (MCD) &#8212; are important causes of intellectual disability and account for 20-40% of drug-resistant epilepsy in childhood. High-resolution brain imaging has facilitated in vivo identification of a large group of MCD phenotypes. Despite the advances in brain imaging, genomic analysis and generation of animal models, a straightforward workflow to systematically prioritize candidate genes and to test functional effects of putative mutations is missing. To overcome this problem, an experimental strategy enabling the identification of novel causative genes for MCD was developed and validated. This strategy is based on identifying candidate genomic regions or genes via array-CGH or whole-exome sequencing and characterizing the effects of their inactivation or of overexpression of specific mutations in developing rodent brains via in utero electroporation. This approach led to the identification of the C6orf70 gene, encoding for a putative vesicular protein, to the pathogenesis of periventricular nodular heterotopia, a MCD caused by defective neuronal migration.

A Novel Strategy Combining Array-CGH, Whole-exome Sequencing and In Utero Electroporation in Rodents to Identify Causative Genes for Brain Malformations

Periventricular nodular heterotopia (PNH) is the most common form of malformation of cortical development (MCD) in adulthood but its genetic basis remains unknown in most sporadic cases. We have recently developed a strategy to identify novel candidate genes for MCDs and to directly confirm their causative role in vivo.

Birth defects that involve the cerebral cortex &#8212; also known as malformations of cortical development (MCD) &#8212; are important causes of ...

In Utero Electroporation Approaches to Study the Excitability of Neuronal Subpopulations and Single-cell Connectivity

The nervous system is composed of an enormous range of distinct neuronal types. These neuronal subpopulations are characterized by, among other features, their distinct dendritic morphologies, their specific patterns of axonal connectivity, and their selective firing responses. The molecular and cellular mechanisms responsible for these aspects of differentiation during development are still poorly understood.
Here, we describe combined protocols for labeling and characterizing the structural connectivity and excitability of cortical neurons. Modification of the in utero electroporation (IUE) protocol allows the labeling of a sparse population of neurons. This, in turn, enables the identification and tracking of the dendrites and axons of individual neurons, the precise characterization of the laminar location of axonal projections, and morphometric analysis. IUE can also be used to investigate changes in the excitability of wild-type (WT) or genetically modified neurons by combining it with whole-cell recording from acute slices of electroporated brains. These two techniques contribute to a better understanding of the coupling of structural and functional connectivity and of the molecular mechanisms controlling neuronal diversity during development. These developmental processes have important implications on axonal wiring, the functional diversity of neurons, and the biology of cognitive disorders.

In Utero Electroporation Approaches to Study the Excitability of Neuronal Subpopulations and Single-cell Connectivity

This manuscript provides protocols that use in utero electroporation (IUE) to describe the structural connectivity of neurons at the single-cell level and the excitability of fluorescently labeled neurons. Histology is used to characterize dendritic and axonal projections. Whole-cell recording in acute slices is used to investigate excitability.

The nervous system is composed of an enormous range of distinct neuronal types. These neuronal subpopulations are characterized by, among other features, ...

Electrophysiological Method for Whole-cell Voltage Clamp Recordings from Drosophila Photoreceptors

Whole-cell voltage clamp recordings from Drosophila melanogaster photoreceptors have revolutionized the field of invertebrate visual transduction, enabling the use of D. melanogaster molecular genetics to study inositol-lipid signaling and Transient Receptor Potential (TRP) channels at the single-molecule level. A handful of labs have mastered this powerful technique, which enables the analysis of the physiological responses to light under highly controlled conditions. This technique allows control over the intracellular and extracellular media; the membrane voltage; and the fast application of pharmacological compounds, such as a variety of ionic or pH indicators, to the intra- and extracellular media. With an exceptionally high signal-to-noise ratio, this method enables the measurement of dark spontaneous and light-induced unitary currents (i.e.&#160;spontaneous and quantum bumps) and macroscopic Light-induced Currents (LIC) from single D. melanogaster photoreceptors. This protocol outlines, in great detail, all the key steps necessary to perform this technique, which includes both electrophysiological and optical recordings. The fly retina dissection procedure for the attainment of intact and viable ex vivo isolated ommatidia in the bath chamber is described. The equipment needed to perform whole-cell and fluorescence imaging measurements are also detailed. Finally, the pitfalls in using this delicate preparation during extended experiments are explained.

Electrophysiological Method for Whole-cell Voltage Clamp Recordings from Drosophila Photoreceptors

Whole-cell recordings from Drosophila melanogaster photoreceptors enable the measurement of spontaneous dark bumps, quantum bumps, macroscopic responses to light, and current-voltage relationships under various conditions. In combination with D. melanogaster genetic manipulation tools, this method enables the study of the ubiquitous inositol-lipid signaling pathway and its target, the TRP channel.

Whole-cell voltage clamp recordings from Drosophila melanogaster photoreceptors have revolutionized the field of invertebrate visual transduction, ...

High-resolution Confocal Imaging of the Blood-brain Barrier: Imaging, 3D Reconstruction, and Quantification of Transcytosis

The blood-brain barrier (BBB) is a dynamic multicellular interface that regulates the transport of molecules between the circulation and the brain. Transcytosis across the BBB regulates the delivery of hormones, metabolites, and therapeutic antibodies to the brain parenchyma. Here, we present a protocol that combines immunofluorescence of free-floating sections with laser scanning confocal microscopy and image analysis to visualize subcellular organelles within endothelial cells at the BBB. Combining this data-set with 3D image analysis software allows for the semi-automated segmentation and quantification of capillary volume and surface area, as well as the number and intensity of intracellular organelles at the BBB. The detection of mouse endogenous immunoglobulin (IgG) within intracellular vesicles and their quantification at the BBB is used to illustrate the method. This protocol can potentially be applied to the investigation of the mechanisms controlling BBB transcytosis of different molecules in vivo.

Here we present a microscopy-based protocol for high-resolution imaging and a three-dimensional reconstruction of the mouse neurovascular unit and blood-brain barrier using brain free-floating sections. This method allows for the visualization, analysis, and quantification of intracellular organelles at the BBB.

The blood-brain barrier (BBB) is a dynamic multicellular interface that regulates the transport of molecules between the circulation and the brain. ...