This study was supported by the project of National Key R&#38;D Program of China (Project Code no. 2019YFC1709103; no. 2018YFC1707804) and National Natural Science Foundation of China (Project Code no. 81774211; no. 81774432; no. 81801561).

This study was approved by the Ethics Committee of the Institute of Acupuncture and Moxibustion, China Academy of Chinese Medical Sciences (reference number D2018-09-29-1). All procedures were conducted in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals (National Academy Press, Washington, D.C., 1996). Twelve adult Sprague-Dawley male rats (weight 220 &#177; 20 g) were used in this study. Animals [license number SCXK (JING) 2017-0005] were provided by the National Institutes for Food and Drug Control.
1. Innervation of rat cranial dura mater
<ol>
	<li>Perfusions
	<ol>
		<li>Intraperitoneally inject an overdose of tribromoethanol solution (250 mg/kg) to the rat to induce euthanasia.</li>
		<li>Once the breath stops, transcardially perfuse with 100 mL of 0.9% normal saline followed by 250-300 mL of 4% paraformaldehyde in 0.1 M phosphate buffer (PB, pH 7.4).</li>
		<li>After perfusion, remove the head skin and open the skull to expose the dura mater and dorsal side of the brain. Then dissect out the cranial dura mater along the brainstem to the olfactory bulb in the whole-mount pattern (Figure 1). Perform post-fixation in 4% paraformaldehyde for 2 h, and then cryoprotect in 25% sucrose in 0.1 M PB for more than 24 h at 4 &#176;C.</li>
	</ol>
	</li>
	<li>Fluorescence immunohistochemistry for CGRP and phalloidin labeling 
	NOTE: A combination of fluorescent staining of CGRP and phalloidin was applied to reveal the spatial correlation of dural nerve fibers and blood vessels in the rat cranial dura mater in the whole-mount pattern.
	<ol>
		<li>Rinse the cranial dura mater in 0.1 M PB for about 1 min.</li>
		<li>Incubate the dura mater in a blocking solution containing 3% normal donkey serum and 0.5% Triton X-100 in 0.1 M PB for 30 min.</li>
		<li>Transfer the dura mater into mouse anti-CGRP antibody (1:1000) in 0.1 M PB containing 1% normal donkey serum and 0.5% Triton X-100 overnight at 4 &#176;C11.</li>
		<li>Wash the dura mater three times in 0.1 M PB the following day.</li>
		<li>Incubate the dura mater in a mixed solution of donkey anti-mouse Alexa Fluor 488 secondary antibody (1:500) and phalloidin 568 (1:1000) in 0.1 M PB containing 1% normal donkey serum and 0.5% Triton X-100 for 1.5 h at room temperature (26 &#176;C).</li>
		<li>Wash the dura mater three times in 0.1 M PB.</li>
		<li>Trim the edges and mount it on microscope slides (see Table of Materials).</li>
		<li>Put on coverslips with 50% glycerin before observation.</li>
	</ol>
	</li>
	<li>Observation and recording
	<ol>
		<li>Observe the fluorescent samples under a fluorescent microscope or a confocal imaging system.</li>
		<li>Take the images of the whole-mount dura mater by a fluorescent microscope equipped with a digital camera (4x, NA: 0.13), and use an exposure time of 500 ms. The image mosaics of the dura mater were completed with a software of fluorescent microscope (see Table of Materials).</li>
		<li>Take images of the CGRP-immunoreactive nerve fibers and phalloidin-labeled blood vessels in the dura mater using a confocal microscope. The excitation and emission wavelengths were 488 nm (green) and 594 nm (red). The confocal pinhole is 110 (20x) and 105 &#181;m (40x). The resolution of image capture is 640 x 640 pixels.</li>
		<li>Capture 20 images in 2 &#181;m frames of from each 40 &#181;m thick section and perform single in-focus image integration with a confocal image processing associated software system for 3D analysis as follows: Set Start Focal Plane | Set End focal plane | Set step size | Choose Depth Pattern | Image Capture | Z series.</li>
		<li>Use a photo editing software to adjust the brightness and contrast of images to optimize the visualization. Pay attention to not remove any data from the images.</li>
	</ol>
	</li>
</ol>
2. Retrograde tracing study with FG
<ol>
	<li>Surgical procedures
	<ol>
		<li>Determine the coordinate area of interest in rat cranial dura mater.</li>
		<li>Prepare a 10 &#181;L micro-syringe and test it with liquid paraffin.</li>
		<li>Anesthetize the rats with tribromoethanol solution (150 mg/kg) via intraperitoneal injection. Check for the depth in anesthesia by the lack of response to toe pinch.</li>
		<li>Shave the rat&#39;s head with an electric razor.</li>
		<li>Put blunt ear bars to the rat and place it on the stereotaxic device. Then put the mouth holder and apply ophthalmic ointment on the eyes.</li>
		<li>Clean the surgical site of the head skin using 10% povidone iodine followed by 75% ethanol.</li>
		<li>Make an incision along the midline of the scalp.</li>
		<li>Bluntly remove the periosteum and muscle tissues away from the skull using sterile cotton-tipped applicators (Figure 1A).</li>
		<li>Drill a small hole (~5-7 mm) using a burr drill with a round-tip bit (#106) on the left parietal and temporal bones above the MMA12, and make sure that the cranial dura mater was kept intact (Figure 1B).</li>
		<li>Build a bank around the hole with dental silicate cement to limit the spread of the tracer (Figure 1C).</li>
		<li>Add 2 &#181;L of 2% FG into the hole around MMA with a 10 &#181;L micro-syringe (Figure 1D).</li>
		<li>Cover the hole with a small piece of hemostatic sponge.</li>
		<li>Put a piece of paraffin film on the hole and seal the edges with bone wax to prevent the leakage of tracer and to avoid contaminating to the surrounding tissues.</li>
		<li>Suture the wound with sterile thread.</li>
		<li>Keep the rats in a warm area until they have fully recovered.</li>
		<li>Return the rats back to their cages and add an antibiotic and analgesic into the drinking water.</li>
	</ol>
	</li>
	<li>Perfusions and sections
	<ol>
		<li>After 7 survival days, perfuse these rats as mentioned above in the procedures in section 1.1.</li>
		<li>Dissect out the TG and C1-4 DRGs, then post-fix and cryoprotect them as above mentioned in section 1.1.3 (Figure 1F).</li>
		<li>Cut the TG and DRGs at the thickness of 30 &#181;m on a cryostat microtome system in the sagittal direction and mounted on silane-coated glass slides.</li>
	</ol>
	</li>
	<li>Double immunofluorescences for FG- and CGRP-labeling in the TG and DRGs 
	NOTE: Although the FG-labeling can be directly observed with UV illumination under mercury lamp without additional staining13,14,15,16, the labeled neurons with FG were further examined in TG and cervical DRGs using double immunofluorescences with FG and CGRP for revealing the origins of dural CGRP-immunoreactive nerve fibers in the TG and DRGs.
	<ol>
		<li>Circle the sections with the histochemical pen.</li>
		<li>Incubate the sections for 30 min in a blocking solution containing 3% normal donkey serum and 0.5% Triton X-100 in 0.1 M PB.</li>
		<li>Transfer the samples into the solution of rabbit anti-fluorogold (1:1000) and mouse anti-CGRP antibody (1:1000) in 0.1 M PB containing 1% normal donkey serum and 0.5% Triton X-100 overnight at 4 &#176;C.</li>
		<li>Wash the sections three times in 0.1 M PB the following day.</li>
		<li>Incubate in a mixed solution of donkey anti-rabbit Alexa Fluor 594 (1:500) and donkey anti-mouse Alexa Fluor 488 (1:500) secondary antibody in 0.1 M PB containing 1% normal donkey serum and 0.5% Triton X-100 for 1.5 h at room temperature.</li>
		<li>Wash and apply coverslips to the sections as the procedures in steps 1.2.6 and 1.2.8.</li>
	</ol>
	</li>
	<li>Observation and recording
	<ol>
		<li>Take images of the FG-labeled neurons in TG and DRGs under UV illumination by fluorescent microscope equipped with a digital camera.</li>
		<li>Capture images of the FG- and CGRP-labeled neurons in TG and DRGs under a fluorescent microscope equipped with a digital camera.</li>
		<li>Use the editing software to adjust the brightness and contrast of images and to add labels in the pictures.</li>
	</ol>
	</li>
</ol>

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The authors have nothing to disclose.

In this study, we have successfully demonstrated the distribution and the origin of CGRP-immunoreactive nerve fibers in the cranial dura mater using immunofluorescence, 3D reconstruction and neural tracing approaches with CGRP antibody and FG neural tracer, providing the histological and chemical evidences to better understand the dural neurovascular network.
As it was known, CGRP plays a critical role in the pathogenesis of migraine4,17</su...

The cranial dura mater is the outermost layer of meninges to protect the brain and contains plentiful blood vessels and different kinds of nerve fibers1,2. Many studies have shown that sensitized cranial dura mater may be the key factor leading to the occurrence of headaches, involving the abnormal vasodilation and innervation3,4,5. Thus, the knowledge of neurovascular structure in the cranial dura mater is important for understanding the pathogenesis of headaches, especially for migraine.
Although the dura innervation has been previously studied with the conventional immunohistochemistry, the spatial correlation of nerve fibers and blood vessels in the cranial dura mater were less studied6,7,8,9. In order to reveal the dural neurovascular structure in more detail, calcitonin gene-related peptide (CGRP) and phalloidin were selected as the markers for respectively staining the dural nerve fibers and blood vessels in the whole-mount cranial dura mater with immunofluorescence and fluorescent histochemistry10. It may be an optimal choice to obtain a three-dimensional (3D) view of neurovascular structure. Additionally, fluorogold (FG) was applied on the area around middle meningeal artery (MMA) in the cranial dura mater to determine the origin of CGRP-immunoreactive nerve fibers, and traced to the trigeminal ganglion (TG) and cervical (C) dorsal root ganglia (DRGs), while the FG-labeled neurons were further examined together with CGRP using immunofluorescence.
The aim of this study was to provide an effective tool for investigating the neurovascular structure in the cranial dura mater for the CGRP-immunoreactive innervation and its origin. By taking the advantage of the transparent whole-mount dura mater and combining the immunofluorescence, retrograde tracing, confocal techniques, and 3D reconstruction, we expected to present a novel 3D view of the neurovascular structure in the cranial dura mater. These methodological approaches may be further served for exploring the pathogenesis of different headaches.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Alexa Fluor 488 donkey anti-mouse IgG (H+L)</td>
			<td>Invitrogen by Thermo Fisher Scientific</td>
			<td>A21202</td>
			<td>Protect from light; RRID: AB_141607</td>
		</tr>
		<tr>
			<td>Brain stereotaxis instrument</td>
			<td>Narishige</td>
			<td>SR-50</td>
			<td></td>
		</tr>
		<tr>
			<td>CellSens Dimension</td>
			<td>Olympus</td>
			<td>Version 1.1</td>
			<td>Software of fluorescent microscope</td>
		</tr>
		<tr>
			<td>Confocal imaging system</td>
			<td>Olympus</td>
			<td>FV1200</td>
			<td></td>
		</tr>
		<tr>
			<td>Fluorogold (FG)</td>
			<td>Fluorochrome</td>
			<td>52-9400</td>
			<td>Protect from light</td>
		</tr>
		<tr>
			<td>Fluorescent imaging system</td>
			<td>Olympus</td>
			<td>BX53</td>
			<td></td>
		</tr>
		<tr>
			<td>Freezing microtome</td>
			<td>Thermo</td>
			<td>Microm International&#160;GmbH</td>
			<td></td>
		</tr>
		<tr>
			<td>Olympus FV10-ASW 4.2a</td>
			<td>Olympus</td>
			<td>Version 4.2</td>
			<td>Confocal image processing software system</td>
		</tr>
		<tr>
			<td>Micro Drill</td>
			<td>Saeyang Microtech</td>
			<td>Marathon-N7</td>
			<td></td>
		</tr>
		<tr>
			<td>Mouse anti-CGRP</td>
			<td>Abcam</td>
			<td>ab81887</td>
			<td>RRID: AB_1658411</td>
		</tr>
		<tr>
			<td>Normal donkey serum</td>
			<td>Jackson ImmunoResearch</td>
			<td>017-000-121</td>
			<td></td>
		</tr>
		<tr>
			<td>Phalloidin 568</td>
			<td>Molecular&#160;Probes</td>
			<td>A12380</td>
			<td>Protect from light</td>
		</tr>
		<tr>
			<td>Photoshop and&#160; Illustration</td>
			<td>Adobe</td>
			<td>CS6</td>
			<td>Photo editing software</td>
		</tr>
		<tr>
			<td>Rabbit anti- Fluorogold</td>
			<td>Abcam</td>
			<td>ab153</td>
			<td>RRID: AB_90738</td>
		</tr>
		<tr>
			<td>Sprague Dawley</td>
			<td>National Institutes for Food and Drug Control</td>
			<td>SCXK (JING) 2014-0013</td>
			<td></td>
		</tr>
		<tr>
			<td>Superfrost plus microscope slides</td>
			<td>Thermo</td>
			<td>#4951PLUS-001</td>
			<td>25x75x1mm</td>
		</tr>
	</tbody>
</table>

visualizing the calcitonin gene-related peptide immunoreactive innervation of the rat cranial dura mater with immunofluorescence and neural tracing

The aim of this study was to examine the distribution and origin of the calcitonin gene-related peptide (CGRP)-immunoreactive sensory nerve fibers of the cranial dura mater using immunofluorescence, three-dimensional (3D) reconstruction and retrograde tracing technique. Here, the nerve fibers and blood vessels were stained using immunofluorescence and histochemistry techniques with CGRP and fluorescent phalloidin, respectively. The spatial correlation of dural CGRP-immuoreactive nerve fibers and blood vessels were demonstrated by 3D reconstruction. Meanwhile, the origin of the CGRP-immunoreactive nerve fibers were detected by neural tracing technique with fluorogold (FG) from the area around middle meningeal artery (MMA) in the cranial dura mater to the trigeminal ganglion (TG) and cervical (C) dorsal root ganglia (DRGs). In addition, the chemical characteristics of FG-labeled neurons in the TG and DRGs were also examined together with CGRP using double immunofluorescences. Taking advantage of the transparent whole-mount sample and 3D reconstruction, it was shown that CGRP-immunoreactive nerve fibers and phalloidin-labeled arterioles run together or separately forming a dural neurovascular network in a 3D view, while the FG-labeled neurons were found in the ophthalmic, maxillary, and mandibular branches of TG, as well as the C2-3 DRGs ipsilateral to the side of tracer application in which some of FG-labeled neurons presented with CGRP-immunoreactive expression. With these approaches, we demonstrated the distributional characteristics of CGRP-immunoreactive nerve fibers around the blood vessels in the cranial dura mater, as well as the origin of these nerve fibers from TG and DRGs. From the perspective of methodology, it may provide a valuable reference for understanding the complicated neurovascular structure of the cranial dura mater under the physiological or pathological condition.

Neurovascular structure of the cranial dura mater 
After immunofluorescent and fluorescent histochemical staining with CGRP and phalloidin, CGRP-immunoreactive nerve fibers and phalloidin-labeled dural arterioles and connective tissues were clearly demonstrated throughout the whole-mount cranial dura mater in a 3D pattern (Figure 2C,D,E,F). It was shown that both thick and thin CGRP-immunoreactive nerve fibers run in par...

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Visualizing the Calcitonin Gene-Related Peptide Immunoreactive Innervation of the Rat Cranial Dura Mater with Immunofluorescence and Neural Tracing

Here we present a protocol to visualize spatial correlation of calcitonin gene-related peptide (CGRP)-immunoreactive nerve fibers and blood vessels in the cranial dura mater using immunofluorescence and fluorescent histochemistry with CGRP and phalloidin, respectively. In addition, the origin of these nerve fibers was retrograde traced with a fluorescent neural tracer.

The aim of this study was to examine the distribution and origin of the calcitonin gene-related peptide (CGRP)-immunoreactive sensory nerve fibers of the ...

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Research

JoVE Journal

Neuroscience

3.9K Views.  China Academy of Chinese Medical Sciences. Here we present a protocol to visualize spatial correlation of calcitonin gene-related peptide (CGRP)-immunoreactive nerve fibers and blood vessels in the cranial dura mater using immunofluorescence and fluorescent histochemistry with CGRP and phalloidin, respectively. In addition, the origin of these nerve fibers was retrograde traced with a fluorescent neural tracer.

Video: Visualizing the Calcitonin Gene-Related Peptide Immunoreactive Innervation of the Rat Cranial Dura Mater with Immunofluorescence and Neural Tracing

Organotypic Cerebellar Cultures: Apoptotic Challenges and Detection

Organotypic cultures of neuronal tissue were first introduced by Hogue in 1947 1,2 and have constituted a major breakthrough in the field of neuroscience. Since then, the technique was developed further and currently there are many different ways to prepare organotypic cultures. The method presented here was adapted from the one described by Stoppini et al. for the preparation of the slices and from Gogolla et al. for the staining procedure 3,4.
A unique feature of this technique is that it allows you to study different parts of the brain such as hippocampus or cerebellum in their original structure, providing a big advantage over dissociated cultures in which all the cellular organization and neuronal networks are disrupted. In the case of the cerebellum it is even more advantageous because it allows the study of Purkinje cells, extremely difficult to obtain as dissociated primary culture. This method can be used to study certain developmental features of the cerebellum in vitro, as well as for electrophysiological and pharmacological experiments in both wild type and mutant mice.
The method described here was designed to study the effect of apoptotic stimuli such as Fas ligand in the developing cerebellum, using TUNEL staining to measure apoptotic cell death. If TUNEL staining is combined with cell type specific markers, such as Calbindin for Purkinje cells, it is possible to evaluate cell death in a cell population specific manner. The Calbindin staining also serves the purpose of evaluating the quality of the cerebellar cultures.

This method describes the generation of organotypic cerebellar cultures and the effect of certain apoptotic stimuli on the viability of different cerebellar cell types.

Organotypic cultures of neuronal tissue were first introduced by Hogue in 1947 1,2 and have constituted a major breakthrough in the field of neuroscience. ...

Investigating the Neural Mechanisms of Aware and Unaware Fear Memory with fMRI

Pavlovian fear conditioning is often used in combination with functional magnetic resonance imaging (fMRI) in humans to investigate the neural substrates of associative learning 1-5. In these studies, it is important to provide behavioral evidence of conditioning to verify that differences in brain activity are learning-related and correlated with human behavior. 
Fear conditioning studies often monitor autonomic responses (e.g. skin conductance response; SCR) as an index of learning and memory 6-8. In addition, other behavioral measures can provide valuable information about the learning process and/or other cognitive functions that influence conditioning. For example, the impact unconditioned stimulus (UCS) expectancies have on the expression of the conditioned response (CR) and unconditioned response (UCR) has been a topic of interest in several recent studies 9-14. SCR and UCS expectancy measures have recently been used in conjunction with fMRI to investigate the neural substrates of aware and unaware fear learning and memory processes 15. Although these cognitive processes can be evaluated to some degree following the conditioning session, post-conditioning assessments cannot measure expectations on a trial-to-trial basis and are susceptible to interference and forgetting, as well as other factors that may distort results 16,17 .
Monitoring autonomic and behavioral responses simultaneously with fMRI provides a mechanism by which the neural substrates that mediate complex relationships between cognitive processes and behavioral/autonomic responses can be assessed. However, monitoring autonomic and behavioral responses in the MRI environment poses a number of practical problems. Specifically, 1) standard behavioral and physiological monitoring equipment is constructed of ferrous material that cannot be safely used near the MRI scanner, 2) when this equipment is placed outside of the MRI scanning chamber, the cables projecting to the subject can carry RF noise that produces artifacts in brain images, 3) artifacts can be produced within the skin conductance signal by switching gradients during scanning, 4) the fMRI signal produced by the motor demands of behavioral responses may need to be distinguished from activity related to the cognitive processes of interest. Each of these issues can be resolved with modifications to the setup of physiological monitoring equipment and additional data analysis procedures. Here we present a methodology to simultaneously monitor autonomic and behavioral responses during fMRI, and demonstrate the use of these methods to investigate aware and unaware memory processes during fear conditioning.

A methodology to investigate the neural mechanisms that support aware and unaware memory processes during fear conditioning is described. This method monitors blood oxygen level dependent (BOLD) functional magnetic resonance imaging, skin conductance response, and unconditioned stimulus expectancy during Pavlovian fear conditioning to assess the neural correlates of distinct memory processes.

Pavlovian fear conditioning is often used in combination with functional magnetic resonance imaging (fMRI) in humans to investigate the neural substrates ...

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 ...

Viral Tracing of Genetically Defined Neural Circuitry

Classical methods for studying neuronal circuits are fairly low throughput. Transsynaptic viruses, particularly the pseudorabies (PRV) and rabies virus (RABV), and more recently vesicular stomatitis virus (VSV), for studying circuitry, is becoming increasingly popular. These higher throughput methods use viruses that transmit between neurons in either the anterograde or retrograde direction.
Recently, a modified RABV for monosynaptic retrograde tracing was developed. (Figure 1A). In this method, the glycoprotein (G) gene is deleted from the viral genome, and resupplied only in targeted neurons. Infection specificity is achieved by substituting a chimeric G, composed of the extracellular domain of the ASLV-A glycoprotein and the cytoplasmic domain of the RABV-G (A/RG), for the normal RABV-G1. This chimeric G specifically infects cells expressing the TVA receptor1. The gene encoding TVA can been delivered by various methods2-8. Following RABV-G infection of a TVA-expressing neuron, the RABV can transmit to other, synaptically connected neurons in a retrograde direction by nature of its own G which was co-delivered with the TVA receptor. This technique labels a relatively large number of inputs (5-10%)2 onto a defined cell type, providing a sampling of all of the inputs onto a defined starter cell type.
We recently modified this technique to use VSV as a transsynaptic tracer9. VSV has several advantages, including the rapidity of gene expression. Here we detail a new viral tracing system using VSV useful for probing microcircuitry with increased resolution. While the original published strategies by Wickersham et al.4 and Beier et al.9 permit labeling of any neurons that project onto initially-infected TVA-expressing-cells, here VSV was engineered to transmit only to TVA-expressing cells (Figure 1B). The virus is first pseudotyped with RABV-G to permit infection of neurons downstream of TVA-expressing neurons. After infecting this first population of cells, the virus released can only infect TVA-expressing cells. Because the transsynaptic viral spread is limited to TVA-expressing cells, presence of absence of connectivity from defined cell types can be explored with high resolution. An experimental flow chart of these experiments is shown in Figure 2. Here we show a model circuit, that of direction-selectivity in the mouse retina. We examine the connectivity of starburst amacrine cells (SACs) to retinal ganglion cells (RGCs).

A method of tracing synaptically connected neurons is described. We use TVA specificity of an upstream cell to probe whether a cell population of interest receives synaptic input from genetically defined cell types.

Classical methods for studying neuronal circuits are fairly low throughput. Transsynaptic viruses, particularly the pseudorabies (PRV) and rabies virus ...

Optogenetic Perturbation of Neural Activity with Laser Illumination in Semi-intact Drosophila Larvae in Motion

Drosophila larval locomotion is a splendid model system in developmental and physiological neuroscience, by virtue of the genetic accessibility of the underlying neuronal components in the circuits1-6. Application of optogenetics7,8 in the larval neural circuit allows us to manipulate neuronal activity in spatially and temporally patterned ways9-13. Typically, specimens are broadly illuminated with a mercury lamp or LED, so specificity of the target neurons is controlled by binary gene expression systems such as the Gal4-UAS system14,15. In this work, to improve the spatial resolution to "sub-genetic resolution", we locally illuminated a subset of neurons in the ventral nerve cord using lasers implemented in a conventional confocal microscope. While monitoring the motion of the body wall of the semi-intact larvae, we interactively activated or inhibited neural activity with channelrhodopsin16,17 or halorhodopsin18-20, respectively. By spatially and temporally restricted illumination of the neural tissue, we can manipulate the activity of specific neurons in the circuit at a specific phase of behavior. This method is useful for studying the relationship between the activities of a local neural assembly in the ventral nerve cord and the spatiotemporal pattern of motor output.

Optogenetic Perturbation of Neural Activity with Laser Illumination in Semi-intact Drosophila Larvae in Motion

Here we describe a protocol for optogenetic manipulation of motoneuronal activity while monitoring changes in motor output (muscle contraction) in semi-intact Drosophila larvae using lasers within a conventional confocal microscope. This technique enables researchers to achieve local perturbation of neural activity in a few neuromeres to elucidate the dynamics of motor circuits.

Drosophila larval locomotion is a splendid model system in developmental and physiological neuroscience, by virtue of the genetic accessibility of the ...

Conditional Genetic Transsynaptic Tracing in the Embryonic Mouse Brain

Anatomical path tracing is of pivotal importance to decipher the relationship between brain and behavior. Unraveling the formation of neural circuits during embryonic maturation of the brain however is technically challenging because most transsynaptic tracing methods developed to date depend on stereotaxic tracer injection. To overcome this problem, we developed a binary genetic strategy for conditional genetic transsynaptic tracing in the mouse brain. Towards this end we generated two complementary knock-in mouse strains to selectively express the bidirectional transsynaptic tracer barley lectin (BL) and the retrograde transsynaptic tracer Tetanus Toxin fragment C from the ROSA26 locus after Cre-mediated recombination. Cell-specific tracer production in these mice is genetically encoded and does not depend on mechanical tracer injection. Therefore our experimental approach is suitable to study neural circuit formation in the embryonic murine brain. Furthermore, because tracer transfer across synapses depends on synaptic activity, these mouse strains can be used to analyze the communication between genetically defined neuronal populations during brain development at a single cell resolution. Here we provide a detailed protocol for transsynaptic tracing in mouse embryos using the novel recombinant ROSA26 alleles. We have utilized this experimental technique in order to delineate the neural circuitry underlying maturation of the reproductive axis in the developing female mouse brain.

Capitalizing on a binary genetic strategy we provide a detailed protocol for neural circuit tracing in mice that express complementary transsynaptic tracers after Cre-mediated recombination. Because cell-specific tracer production is genetically encoded, our experimental approach is suitable to study the formation and maturation of neural circuitry during murine embryonic brain development at a single cell resolution.

Anatomical path tracing is of pivotal importance to decipher the relationship between brain and behavior. Unraveling the formation of neural circuits ...

Time-dependent Increase in the Network Response to the Stimulation of Neuronal Cell Cultures on Micro-electrode Arrays

Micro-electrode arrays (MEAs) can be used to investigate drug toxicity, design paradigms for next-generation personalized medicine, and study network dynamics in neuronal cultures. In contrast with more traditional methods, such as patch-clamping, which can only record activity from a single cell, MEAs can record simultaneously from multiple sites in a network, without requiring the arduous task of placing each electrode individually. Moreover, numerous control and stimulation configurations can be easily applied within the same experimental setup, allowing for a broad range of dynamics to be explored. One of the key dynamics of interest in these in vitro studies has been the extent to which cultured networks display properties indicative of learning. Mouse neuronal cells cultured on MEAs display an increase in response following training induced by electrical stimulation. This protocol demonstrates how to culture neuronal cells on MEAs; successfully record from over 95% of the plated dishes; establish a protocol to train the networks to respond to patterns of stimulation; and sort, plot, and interpret the results from such experiments. The use of a proprietary system for stimulating and recording neuronal cultures is demonstrated. Software packages are also used to sort neuronal units. A custom-designed graphical user interface is used to visualize post-stimulus time histograms, inter-burst intervals, and burst duration, as well as to compare the cellular response to stimulation before and after a training protocol. Finally, representative results and future directions of this research effort are discussed.

Mouse neuronal cells cultured on multi-electrode arrays display an increase in response following electrical stimulation. This protocol demonstrates how to culture neurons, how to record activity, and how to establish a protocol to train the networks to respond to patterns of stimulation.

Micro-electrode arrays (MEAs) can be used to investigate drug toxicity, design paradigms for next-generation personalized medicine, and study network ...

Improving the Application of High Molecular Weight Biotinylated Dextran Amine for Thalamocortical Projection Tracing in the Rat

High molecular weight biotinylated dextran amine (BDA) has been used as a highly sensitive neuroanatomical tracer for many decades. Since the quality of its labeling was affected by various factors, here, we provide a refined protocol for the application of high molecular weight BDA for studying optimal neural labeling in the central nervous system. After stereotactic injection of BDA into the ventral posteromedial nucleus (VPM) of the thalamus in the rat through a delicate glass pipette, BDA was stained with fluorescent streptavidin-Alexa (AF) 594 and counterstained with fluorescent Nissl stain AF500/525. On the background of green Nissl staining, the red BDA labeling, including neuronal cell bodies and axonal terminals, was more distinctly demonstrated in the somatosensory cortex. Furthermore, double fluorescent staining for BDA and the calcium-binding protein parvalbumin (PV) was carried out to observe the correlation of BDA labeling and PV-positive interneurons in the cortical target, providing the opportunity to study the local neural circuits and their chemical characteristics. Thus, this refined method is not only suitable for visualizing high quality neural labeling with the high molecular weight BDA through reciprocal neural pathways between the thalamus and cerebral cortex, but also will permit the simultaneous demonstration of other neural markers with fluorescent histochemistry or immunochemistry.

Here, we present a refined protocol to effectively reveal biotinylated dextran amine (BDA) labeling with a fluorescent staining method through a reciprocal neural pathway. It is suitable for analyzing the fine structure of BDA labeling and distinguishing it from other neural elements under a confocal laser scanning microscope.

High molecular weight biotinylated dextran amine (BDA) has been used as a highly sensitive neuroanatomical tracer for many decades. Since the quality of ...

Simultaneous Recordings of Cortical Local Field Potentials, Electrocardiogram, Electromyogram, and Breathing Rhythm from a Freely Moving Rat

Monitoring the physiological dynamics of the brain and peripheral tissues is necessary for addressing a number of questions about how the brain controls body functions and internal organ rhythms when animals are exposed to emotional challenges and changes in their living environments. In general experiments, signals from different organs, such as the brain and the heart, are recorded by independent recording systems that require multiple recording devices and different procedures for processing the data files. This study describes a new method that can simultaneously monitor electrical biosignals, including tens of local field potentials in multiple brain regions, electrocardiograms that represent the cardiac rhythm, electromyograms that represent awake/sleep-related muscle contraction, and breathing signals, in a freely moving rat. The recording configuration of this method is based on a conventional micro-drive array for cortical local field potential recordings in which tens of electrodes are accommodated, and the signals obtained from these electrodes are integrated into a single electrical board mounted on the animal's head. Here, this recording system was improved so that signals from the peripheral organs are also transferred to an electrical interface board. In a single surgery, electrodes are first separately implanted into the appropriate body parts and the target brain areas. The open ends of all of these electrodes are then soldered to individual channels of the electrical board above the animal's head so that all of the signals can be integrated into the single electrical board. Connecting this board to a recording device allows for the collection of all of the signals into a single device, which reduces experimental costs and simplifies data processing, because all data can be handled in the same data file. This technique will aid the understanding of the neurophysiological correlates of the associations between central and peripheral organs.

This study introduces a method for the simultaneous recording of local field potentials in the brain, electrocardiograms, electromyograms, and breathing signals of a freely moving rat. This technique, which reduces experimental costs and simplifies data analysis, will contribute to the understanding of the interactions between the brain and peripheral organs.

Monitoring the physiological dynamics of the brain and peripheral tissues is necessary for addressing a number of questions about how the brain controls ...

Visualizing Shifts on Neuron-Glia Circuit with the Calcium Imaging Technique

Here, we report on selective in vitro models of circuits based on glia (astrocytes, oligodendrocytes, and microglia) and/or neurons from peripheral (dorsal root ganglia) and central tissues (cortex, subventricular zone, organoid) that are dynamically studied in terms of calcium shifts. The model chosen to illustrate the results is the retina, a simple tissue with complex cellular interactions. Calcium is a universal messenger involved in most of the important cellular roles. We explain in a step-by-step protocol how retinal neuron-glial cells in culture can be prepared and evaluated, envisioning calcium shifts. In this model, we differentiate neurons from glia based on their selective response to KCl and ATP. Calcium permeable receptors and channels are selectively expressed in different compartments. To analyze calcium responses, we use ratiometric fluorescent dies such as Fura-2. This probe quantifies free Ca2+ concentration based on Ca2+-free and Ca2+-bound forms, presenting two different peaks, founded on the fluorescence intensity perceived on two wavelengths.

Cell calcium imaging is a versatile methodology to study dynamic signaling of individual cells, on mixed populations in culture or even on awakened animals, based on the expression of calcium-permeable channels/receptors that gives unique functional signatures.

Here, we report on selective in vitro models of circuits based on glia (astrocytes, oligodendrocytes, and microglia) and/or neurons from peripheral ...