Name: preparation of neuronal co-cultures with single cell precision
Uploaded: 2014-05-20T13:00:00
Description: Watch this Scientific Journal Video about Preparation of Neuronal Co-cultures with Single Cell Precision at JoVE.com

The authors are grateful to Ulrich Marggraf (ISAS) for SU-8 fabrication and Maria Becker (ISAS) for SEM imaging. The research was financially supported by the Deutsche Forschungsgemeinschaft (DFG WE3737/3-1), a Bundesministerium f&#252;r Bildung und Forschung grant (BMBF 0101-31P6541) and by the Ministerium f&#252;r Innovation, Wissenschaft und Forschung des Landes Nordrhein-Westfalen. Heike Hardelauf thanks the International Leibniz Graduate School "Systems Biology Lab-on-a-Chip" for financial support.

The protocols are intended for neuroscientists, and are summarized in Figure 2. As such it is recommend that microfabrication of the SU-8 masters used for PDMS replication is outsourced to commercial or institutional facilities. The two layer mask designs are freely available as supplementary information (ZIP) on the Royal Society of Chemistry website12. Importantly, the first SU-8 layer should be fabricated to a depth of 2.5-3.0 &#956;m, and the second to a depth of 25-30 &#956;m. These are k...

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The microfluidic arraying technique is the first of its kind that enables precision single neuron handling for establishing minimalistic cultures. Coupled with the in situ biomaterial patterning method, a powerful approach to align cell patterns with microfluidic structures, these minimalistic cultures have high intercompartment connectivity levels with reduced local entanglement. These features can be used for the efficient study of inter-compartment transmission, and with simple design modifications have the p...

Neuronal tissue is highly complex; a heterogeneous cellular mixture that is spatially ordered within defined layers and compartments and with plastic connectivity via cell contacts and especially via axon and dendrite outgrowths. New techniques are required to confer greater experimental freedom to gain deeper insights and unravel mechanisms central to disease, development, and healthy function. The Campenot chamber1,2 and more recently microfabricated embodiments3,4 can be used for the ex vivo preparation of networked neuronal co-cultures with the ability to selectively perturb the different somatic populations and also their neurite outgrowths. These microfluidic devices have for example been used to study axon degeneration and regeneration following chemical5,6 or laser axotomy6-8, tauopathy9, viral dissemination10,11, and mRNA localization in axons4.

To extend the reach of the neurobiologists, technological developments are required to prepare minimalistic neuronal co-cultures. This enables disentanglement of the neuronal network for the investigation of the system with single cell and sub-cellular precision. The requirement for minimal cell numbers opens the possibility to analyze rare cell types, including dopaminergic substantia nigra cells relevant to Parkinson&#39;s disease, spiral ganglia from the ear, peripheral neurons, and stem cells. Beyond this, cellular economy is relevant to the 3Rs initiative. Using these microfluidic platforms, large-scale toxicity screens or other high throughput, data rich experimental series requiring animal neurons can now be considered.

In this paper protocols for the fabrication and use of a microfluidic device are described. Microfluidic arraying in combination with an in situ biomaterial patterning method can be used for the registration of highly interconnected neuronal co-cultures using minimal cell numbers. Microfluidic arraying is based on a differential flow approach12&#8211;15, whereby microstructured traps are positioned within a fluidic circuit (illustrated along with SEM images in Figure 1). The path 0 &#8594; 1 has the lower fluidic resistance (R2 &#62; R1) for transporting neurons to a linear array of microstructured apertures &#8211; the inlets to the neurite outgrowth channels. Occupancy of the trap by a single cell locally impedes the flow to divert the streamlines for trapping subsequent cells in neighboring traps. Complete occupancy of the traps in the array switches the fluidic ratio (R1 &#62; R2) to divert the streamlines into the serpentine path (0 &#8594; 2) to produce a bypass mode of operation for the removal of excess neurons.
<img alt="Figure 1" fo:content-width="5in" src="/files/ftp_upload/51389/51389fig1highres.jpg" width="500" /> 
Figure 1. Microfluidic Circuit. A) The differential resistance fluidic circuit for single neuron arraying, with flanking culture chambers interconnected by neurite outgrowth channels. B,C) SEM images of the bilayer compartmentalized neuron co-culture array with meniscus pinning micropillars. With this design, trident-shaped neuron trapping structures were used to promote fasciculation of the neurite outgrowths. Figure and legend reproduced with permission of the Royal Society of Chemistry (RSC)12. <a href="https://www.jove.com/files/ftp_upload/51389/51389fig1highres.jpg" target="_blank">Click here to view larger image.</a>
The preparation of micropatterned neuronal networks on planar substrates can readily be achieved (for examples from our group, see Frimat et al.16 and Heike et al.17). However, encapsulating bioactive material patterns within PDMS devices and with the requirement of micrometer-scale alignment of these to the microfluidic channels poses a major technical challenge. In section 3.1 a protocol for the in-chip, or in situ, preparation of biomaterial patterns is presented. These patterns enable neuron registration during lengthy culture timescales and promote outgrowths between compartments. Meniscus-pinning microstructures are used to align a so-called water mask with the neuron arraying sites and neurite outgrowth channels. The water mask protects adhesion molecule coatings during plasma treatment, whereas exposed surfaces are disintegrated to define the biomaterial pattern. In addition, protocols are provided for cell culture and for fluidic isolation necessary for the selective treatment of the different co-culture compartments.
The protocols are designed to leverage the user-friendly principles of soft lithography for the replication of poly(dimethylsiloxane) (PDMS) microfluidic devices18. Similarly, in situ biomaterial patterning is straightforward, exploiting evaporation and surface tension phenomena, and only requiring an inexpensive hand-held plasma source. The microfluidic circuit effectively programs cell loading and compartment specific treatments making these operations simply a matter of dispensing materials into the correct bottom port and aspirating from above. In this manner, it is intended to give the neurobiologists the freedom to prepare and use microfluidic devices in their own laboratories.

<table border="0" cellpadding="0" cellspacing="0" width="857">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:235px;">PDMS Sylgard 184</td>
			<td style="width:163px;">Dow Corning</td>
			<td style="width:143px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">PDMS Elastosil RT 601</td>
			<td style="width:163px;">Wacker</td>
			<td style="width:143px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:235px;">Coverslips</td>
			<td style="width:163px;">VWR</td>
			<td>630-1590</td>
			<td>130-160 mm thick</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:235px;">3 mm Biopsy Punches</td>
			<td style="width:163px;">Kai Medical</td>
			<td style="width:143px;"></td>
			<td>Handle with care - extremely sharp</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Tygon Tubing</td>
			<td style="width:163px;">Fisher Scientific</td>
			<td style="width:143px;">S-50-HL</td>
			<td>1.65 mm ID; 3.35 mm OD</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">1 mL Syringe (Inkjekt and Omnifix)</td>
			<td style="width:163px;">Braun</td>
			<td style="width:143px;">6064204</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:235px;">4-Way Tubing Connector</td>
			<td style="width:163px;">VWR or Fisher Scientific</td>
			<td style="width:143px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:235px;">Flow Regulator</td>
			<td style="width:163px;">Harvard Apparatus</td>
			<td style="width:143px;">722645</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:235px;">0.5 mm Pins</td>
			<td style="width:163px;">Dressmaking Departments</td>
			<td style="width:143px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:235px;">PLL-g-PEG</td>
			<td style="width:163px;">SuSoS</td>
			<td style="width:143px;">PLL(20)-g[3.5]-PEG(5)</td>
			<td>Stability in storage can be an issue</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:235px;">poly-D-lysine</td>
			<td style="width:163px;">Sigma-Aldrich</td>
			<td style="width:143px;">P6407</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:235px;">poly-lysine-FITC</td>
			<td style="width:163px;">Sigma-Aldrich</td>
			<td style="width:143px;">P3069</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:235px;">poly-ornithine</td>
			<td style="width:163px;">Sigma-Aldrich</td>
			<td style="width:143px;">P4957</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:235px;">fibronectin</td>
			<td style="width:163px;">Sigma-Aldrich</td>
			<td style="width:143px;">F2006</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:235px;">laminin</td>
			<td style="width:163px;">Sigma-Aldrich</td>
			<td style="width:143px;">L2020</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:235px;">PBS</td>
			<td style="width:163px;">Sigma-Aldrich</td>
			<td style="width:143px;">P4417</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:235px;">Inverted Fluorescent Microscope</td>
			<td style="width:163px;"></td>
			<td style="width:143px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:235px;">Example Aspiration Pump</td>
			<td style="width:163px;">KNF Neuberger, Laboport</td>
			<td style="width:143px;">N811KVP</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:235px;">Hand Held Corona Discharge Device</td>
			<td style="width:163px;">Leybold-Heraeus, USA</td>
			<td style="width:143px;">VP23</td>
			<td>May not comply with your country&#39;s safety standards</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:235px;">Femto Plasma Oven</td>
			<td style="width:163px;">Diener Electronic</td>
			<td style="width:143px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:235px;">Vacuum Dessicator or Centrifuge</td>
			<td style="width:163px;"></td>
			<td style="width:143px;"></td>
			<td></td>
		</tr>
	</tbody>
</table>

preparation of neuronal co-cultures with single cell precision

Microfluidic embodiments of the Campenot chamber have attracted great interest from the neuroscience community. These interconnected co-culture platforms can be used to investigate a variety of questions, spanning developmental and functional neurobiology to infection and disease propagation. However, conventional systems require significant cellular inputs (many thousands per compartment), inadequate for studying low abundance cells, such as primary dopaminergic substantia nigra, spiral ganglia, and Drosophilia melanogaster neurons, and impractical for high throughput experimentation. The dense cultures are also highly locally entangled, with few outgrowths (&#60;10%) interconnecting the two cultures. In this paper straightforward microfluidic and patterning protocols are described which address these challenges: (i) a microfluidic single neuron arraying method, and (ii) a water masking method for plasma patterning biomaterial coatings to register neurons and promote outgrowth between compartments. Minimalistic neuronal co-cultures were prepared with high-level (&#62;85%) intercompartment connectivity and can be used for high throughput neurobiology experiments with single cell precision.

Water masking exploits surface tension. The pressure tolerance at the air-liquid interface scales inversely with the radius of curvature [<img fo:content-width="1in" src="/files/ftp_upload/51389/51389eq1.jpg" width="113" />, producing highly stable interfaces at microfluidic dimensions. The micropillars effectively anchor the water mask in place. Water mask formation is driven by evaporation from the microfluidic ports, with the rate increased by heating. Using the heat from low magnification (4X - 10X) microscopy illumi...

Watch this Scientific Journal Video about Preparation of Neuronal Co-cultures with Single Cell Precision at JoVE.com

Preparation of Neuronal Co-cultures with Single Cell Precision

Protocols for single neuron microfluidic arraying and water masking for the in-chip plasma patterning of biomaterial coatings are described. Highly interconnected co-cultures can be prepared using minimal cell inputs.

Microfluidic embodiments of the Campenot chamber have attracted great interest from the neuroscience community. These interconnected co-culture platforms ...

preparation-of-neuronal-co-cultures-with-single-cell-precision

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Neuroscience

Derivation of Enriched Oligodendrocyte Cultures and Oligodendrocyte/Neuron Myelinating Co-cultures from Post-natal Murine Tissues

Identifying the molecular mechanisms underlying OL development is not only critical to furthering our knowledge of OL biology, but also has implications for understanding the pathogenesis of demyelinating diseases such as Multiple Sclerosis (MS). Cellular development is commonly studied with primary cell culture models. Primary cell culture facilitates the evaluation of a given cell type by providing a controlled environment, free of the extraneous variables that are present in vivo. While OL cultures derived from rats have provided a vast amount of insight into OL biology, similar efforts at establishing OL cultures from mice has been met with major obstacles. Developing methods to culture murine primary OLs is imperative in order to take advantage of the available transgenic mouse lines. 
Multiple methods for extraction of OPCs from rodent tissue have been described, ranging from neurosphere derivation, differential adhesion purification and immunopurification 1-3. While many methods offer success, most require extensive culture times and/or costly equipment/reagents. To circumvent this, purifying OPCs from murine tissue with an adaptation of the method originally described by McCarthy &amp; 
de Vellis 2 is preferred. This method involves physically separating OPCs from a mixed glial culture derived from neonatal rodent cortices. The result is a purified OPC population that can be differentiated into an OL-enriched culture. This approach is appealing due to its relatively short culture time and the unnecessary requirement for growth factors or immunopanning antibodies. 
While exploring the mechanisms of OL development in a purified culture is informative, it does not provide the most physiologically relevant environment for assessing myelin sheath formation. Co-culturing OLs with neurons would lend insight into the molecular underpinnings regulating OL-mediated myelination of axons. For many OL/neuron co-culture studies, dorsal root ganglion neurons (DRGNs) have proven to be the neuron type of choice. They are ideal for co-culture with OLs due to their ease of extraction, minimal amount of contaminating cells, and formation of dense neurite beds. While studies using rat/mouse myelinating xenocultures have been published 4-6, a method for the derivation of such OL/DRGN myelinating co-cultures from post-natal murine tissue has not been described. Here we present detailed methods on how to effectively produce such cultures, along with examples of expected results. These methods are useful for addressing questions relevant to OL development/myelinating function, and are useful tools in the field of neuroscience.

This article describes methods to derive enriched populations of murine oligodendrocyte precursor cells (OPCs) in primary culture, which differentiate to produce mature oligodendrocytes (OLs). In addition, this report describes techniques to produce murine myelinating co-cultures by seeding mouse OPCs onto a neurite bed of mouse dorsal root ganglion neurons (DRGNs).

Identifying the molecular mechanisms underlying OL development is not only critical to furthering our knowledge of OL biology, but also has implications ...

Single Cell Measurement of Dopamine Release with Simultaneous Voltage-clamp and Amperometry

After its release into the synaptic cleft, dopamine exerts its biological properties via its pre- and post-synaptic targets1. The dopamine signal is terminated by diffusion2-3, extracellular enzymes4, and membrane transporters5. The dopamine transporter, located in the peri-synaptic cleft of dopamine neurons clears the released amines through an inward dopamine flux (uptake). The dopamine transporter can also work in reverse direction to release amines from inside to outside in a process called outward transport or efflux of dopamine5. More than 20 years ago Sulzer et al. reported the dopamine transporter can operate in two modes of activity: forward (uptake) and reverse (efflux)5. The neurotransmitter released via efflux through the transporter can move a large amount of dopamine to the extracellular space, and has been shown to play a major regulatory role in extracellular dopamine homeostasis6. Here we describe how simultaneous patch clamp and amperometry recording can be used to measure released dopamine via the efflux mechanism with millisecond time resolution when the membrane potential is controlled. For this, whole-cell current and oxidative (amperometric) signals are measured simultaneously using an Axopatch 200B amplifier (Molecular Devices, with a low-pass Bessel filter set at 1,000 Hz for whole-cell current recording). For amperometry recording a carbon fiber electrode is connected to a second amplifier (Axopatch 200B) and is placed adjacent to the plasma membrane and held at +700 mV. The whole-cell and oxidative (amperometric) currents can be recorded and the current-voltage relationship can be generated using a voltage step protocol. Unlike the usual amperometric calibration, which requires conversion to concentration, the current is reported directly without considering the effective volume7. Thus, the resulting data represent a lower limit to dopamine efflux because some transmitter is lost to the bulk solution.

The amperometric technique measures dopamine release from a single cell by detecting the oxidative current produced by spontaneous dopamine oxidization. Simultaneous voltage clamp and amperometry methodology reveal the mechanistic relationship between the overall "activity" of dopamine transporter and the regulatory role of this activity on the reverse transport of dopamine.

After its release into the synaptic cleft, dopamine exerts its biological properties via its pre- and post-synaptic targets1. The dopamine signal is ...

Optical Recording of Suprathreshold Neural Activity with Single-cell and Single-spike Resolution

Signaling of information in the vertebrate central nervous system is often carried by populations of neurons rather than individual neurons. Also propagation of suprathreshold spiking activity involves populations of neurons. Empirical studies addressing cortical function directly thus require recordings from populations of neurons with high resolution. Here we describe an optical method and a deconvolution algorithm to record neural activity from up to 100 neurons with single-cell and single-spike resolution. This method relies on detection of the transient increases in intracellular somatic calcium concentration associated with suprathreshold electrical spikes (action potentials) in cortical neurons. High temporal resolution of the optical recordings is achieved by a fast random-access scanning technique using acousto-optical deflectors (AODs)1. Two-photon excitation of the calcium-sensitive dye results in high spatial resolution in opaque brain tissue2. Reconstruction of spikes from the fluorescence calcium recordings is achieved by a maximum-likelihood method. Simultaneous electrophysiological and optical recordings indicate that our method reliably detects spikes (&gt;97% spike detection efficiency), has a low rate of false positive spike detection (&lt; 0.003 spikes/sec), and a high temporal precision (about 3 msec) 3. This optical method of spike detection can be used to record neural activity in vitro and in anesthetized animals in vivo3,4.

Understanding the function of the vertebrate central nervous system requires recordings from many neurons because cortical function arises on the level of populations of neurons. Here we describe an optical method to record suprathreshold neural activity with single-cell and single-spike resolution, dithered random-access scanning. This method records somatic fluorescence calcium signals from up to 100 neurons with high temporal resolution. A maximum-likelihood algorithm deconvolves the underlying suprathreshold neural activity from the somatic fluorescence calcium signals. This method reliably detects spikes with high detection efficiency and a low rate of false positives and can be used to study neural populations in vitro and in vivo.

Signaling of information in the vertebrate central nervous system is often carried by populations of neurons rather than individual neurons. Also ...

Simultaneous Pre- and Post-synaptic Electrophysiological Recording from Xenopus Nerve-muscle Co-cultures

Much information about the coupling of presynaptic ionic currents with the release of neurotransmitter has been obtained from invertebrate preparations, most notably the squid giant synapse1. However, except for the preparation described here, few vertebrate preparations exist in which it is possible to make simultaneous measurements of neurotransmitter release and presynaptic ionic currents. Embryonic Xenopus motoneurons and muscle cells can be grown together in simple culture medium at room temperature; they will form functional synapses within twelve to twenty-four hours, and can be used to study nerve and muscle cell development and synaptic interactions for several days (until overgrowth occurs). Some advantages of these co-cultures over other vertebrate preparations include the simplicity of preparation, the ability to maintain the cultures and work at room temperature, and the ready accessibility of the synapses formed2-4. The preparation has been used widely to study the biophysical properties of presynaptic ion channels and the regulation of transmitter release5-8. In addition, the preparation has lent itself to other uses including the study of neurite outgrowth and synaptogenesis9-12, molecular mechanisms of neurotransmitter release13-15, the role of diffusible messengers in neuromodulation16,17, and in vitro synaptic plasticity18-19.

Simultaneous Pre- and Post-synaptic Electrophysiological Recording from Xenopus Nerve-muscle Co-cultures

This video demonstrates the procedures used to grow primary cultures of embryonic Xenopus nerve and muscle cells and the usefulness of this preparation for making simultaneous pre- and post-synaptic patch clamp recordings.

Much information about the coupling of  presynaptic ionic currents with the release of neurotransmitter has been obtained  from invertebrate preparations, ...

A Procedure for Implanting Organized Arrays of Microwires for Single-unit Recordings in Awake, Behaving Animals

In vivo electrophysiological recordings in the awake, behaving animal provide a powerful method for understanding neural signaling at the single-cell level. The technique allows experimenters to examine temporally and regionally specific firing patterns in order to correlate recorded action potentials with ongoing behavior. Moreover, single-unit recordings can be combined with a plethora of other techniques in order to produce comprehensive explanations of neural function. In this article, we describe the anesthesia and preparation for microwire implantation. Subsequently, we enumerate the necessary equipment and surgical steps to accurately insert a microwire array into a target structure. Lastly, we briefly describe the equipment used to record from each individual electrode in the array. The fixed microwire arrays described are well-suited for chronic implantation and allow for longitudinal recordings of neural data in almost any behavioral preparation. We discuss tracing electrode tracks to triangulate microwire positions as well as ways to combine microwire implantation with immunohistochemical techniques in order to increase the anatomical specificity of recorded results.

Implanting organized arrays of microwires for use in single-unit electrophysiological recordings presents a number of technical challenges.&#160;Methods for performing this technique and the equipment necessary are described.&#160;Also, the beneficial use of organized microwire arrays to record from distinct neural subregions with high spatial selectivity is discussed.

In vivo electrophysiological recordings in the awake, behaving animal provide a powerful method for understanding neural signaling at the single-cell ...

Inducing Plasticity of Astrocytic Receptors by Manipulation of Neuronal Firing Rates

Close to two decades of research has established that astrocytes in situ and in vivo express numerous G protein-coupled receptors (GPCRs) that can be stimulated by neuronally-released transmitter. However, the ability of astrocytic receptors to exhibit plasticity in response to changes in neuronal activity has received little attention. Here we describe a model system that can be used to globally scale up or down astrocytic group I metabotropic glutamate receptors (mGluRs) in acute brain slices. Included are methods on how to prepare parasagittal hippocampal slices, construct chambers suitable for long-term slice incubation, bidirectionally manipulate neuronal action potential frequency, load astrocytes and astrocyte processes with fluorescent Ca2+ indicator, and measure changes in astrocytic Gq GPCR activity by recording spontaneous and evoked astrocyte Ca2+ events using confocal microscopy. In essence, a &#8220;calcium roadmap&#8221; is provided for how to measure plasticity of astrocytic Gq GPCRs. Applications of the technique for study of astrocytes are discussed. Having an understanding of how astrocytic receptor signaling is affected by changes in neuronal activity has important implications for both normal synaptic function as well as processes underlying neurological disorders and neurodegenerative disease.

Here we describe an adaptation of protocols used to induce homeostatic plasticity in neurons for the study of plasticity of astrocytic G protein-coupled receptors. Recently used to examine changes in astrocytic group I mGluRs in juvenile mice, the method can be applied to measure scaling of various astrocytic GPCRs, in tissue from adult mice in situ and in vivo, and to gain a better appreciation of the sensitivity of astrocytic receptors to changes in neuronal activity.

Close to two decades of research has established that astrocytes in situ and in vivo express numerous G protein-coupled receptors (GPCRs) that can be ...

Investigating Functional Regeneration in Organotypic Spinal Cord Co-cultures Grown on Multi-electrode Arrays

Adult higher vertebrates have a limited potential to recover from spinal cord injury. Recently, evidence emerged that propriospinal connections are a promising target for intervention to improve functional regeneration. So far, no in vitro model exists that grants the possibility to examine functional recovery of propriospinal fibers. Therefore, a representative model that is based on two organotypic spinal cord sections of embryonic rat, cultured next to each other on multi-electrode arrays (MEAs) was developed. These slices grow and, within a few days in vitro, fuse along the sides facing each other. The design of the used MEAs permits the performance of lesions with a scalpel blade through this fusion site without inflicting damage on the MEAs. The slices show spontaneous activity, usually organized in network activity bursts, and spatial and temporal activity parameters such as the location of burst origins, speed and direction of their propagation and latencies between bursts can be characterized. Using these features, it is also possible to assess functional connection of the slices by calculating the amount of synchronized bursts between the two sides. Furthermore, the slices can be morphologically analyzed by performing immunohistochemical stainings after the recordings. 
Several advantages of the used techniques are combined in this model: the slices largely preserve the original tissue architecture with intact local synaptic circuitry, the tissue is easily and repeatedly accessible and neuronal activity can be detected simultaneously and non-invasively in a large number of spots at high temporal resolution. These features allow the investigation of functional regeneration of intraspinal connections in isolation in vitro in a sophisticated and efficient way.

Here we present a protocol that is based on spinal cord slices cultured on multi-electrode arrays to study functional regeneration of propriospinal connections in vitro.

Adult higher vertebrates have a limited potential to recover from spinal cord injury. Recently, evidence emerged that propriospinal connections are a ...

Extracellular Recording of Neuronal Activity Combined with Microiontophoretic Application of Neuroactive Substances in Awake Mice

Differences in the activity of neurotransmitters and neuromodulators, and consequently different neural responses, can be found between anesthetized and awake animals. Therefore, methods allowing the manipulation of synaptic systems in awake animals are required in order to determine the contribution of synaptic inputs to neuronal processing unaffected by anesthetics. Here, we present methodology for the construction of electrodes to simultaneously record extracellular neural activity and release multiple neuroactive substances at the vicinity of the recording sites in awake mice. By combining these procedures, we performed microiontophoretic injections of gabazine to selectively block GABAA receptors in neurons of the inferior colliculus of head-restrained mice. Gabazine successfully modified neural response properties such as the frequency response area and stimulus-specific adaptation. Thus, we demonstrate that our methods are suitable for recording single-unit activity and for dissecting the role of specific neurotransmitter receptors in auditory processing.
The main limitation of the described procedure is the relatively short recording time (~3 hr), which is determined by the level of habituation of the animal to the recording sessions. On the other hand, multiple recording sessions can be performed in the same animal. The advantage of this technique over other experimental procedures used to manipulate the level of neurotransmission or neuromodulation (such as systemic injections or the use of optogenetic models), is that the drug effect is confined to the local synaptic inputs to the target neuron. In addition, the custom-manufacture of electrodes allows adjustment of specific parameters according to the neural structure and type of neuron of interest (such as the tip resistance for improving the signal-to-noise ratio of the recordings).

We present methods for the construction of electrodes to simultaneously record extracellular neural activity and release multiple neuroactive substances at the vicinity of the recording sites in awake mice. This technique allows the detailed analysis of putative local synaptic inputs to the neuron of interest.

Differences in the activity of neurotransmitters and neuromodulators, and consequently different neural responses, can be found between anesthetized and ...

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, ...

Neuron-Macrophage Co-cultures to Activate Macrophages Secreting Molecular Factors with Neurite Outgrowth Activity

There is strong evidence that macrophages can participate in the regeneration or repair of injured nervous system. Here, we describe a protocol in which macrophages are induced to produce conditioned medium (CM) that promotes neurite outgrowth. Adult dorsal root ganglion (DRG) neurons are acutely dissociated and plated. After the neurons are stably attached, peritoneal macrophages are co-cultured on a cell culture insert overlaid on the same well. Dibutyryl cyclic AMP (db-cAMP) is applied to the co-cultures for 24 h, after which the cell culture insert containing the macrophages is moved to another well to collect CM for 72 h. The CM from the co-cultures treated with db-cAMP, when applied to a separate adult DRG neuron culture, exhibits robust neurite outgrowth activity. The CM obtained from the db-cAMP-treated cultures consisting of single cell type alone, either DRG neuron or peritoneal macrophage, did not exhibit neurite outgrowth activity. This indicates that the interaction between neurons and macrophages is indispensable for the activation of macrophages secreting molecular factors with neurite outgrowth activity into CM. Thus, our co-culture paradigm will also be useful to study intercellular signaling in the neuron-macrophage interaction to stimulate the macrophages to be endowed with a pro-regenerative phenotype.

The current protocol presents experimental procedures to stimulate cultured macrophages to be endowed with capacity to release molecular factors that promote neurite outgrowth. Treatment of cAMP to the neuron-macrophage co-cultures induces the macrophages to produce conditioned medium that possesses strong neurite outgrowth activity.

There is strong evidence that macrophages can participate in the regeneration or repair of injured nervous system. Here, we describe a protocol in which ...