This study was supported by the China Academy of Chinese Medical Sciences Innovation Fund (Project Code no. CI2021A03404) and the National Traditional Chinese Medicine Interdisciplinary innovation Fund (Project Code no. ZYYCXTD-D-202202).

The present study was approved by the Ethics Committee of the Institute of Acupuncture and Moxibustion, China Academy of Chinese Medical Sciences (reference number D2018-04-13-1). All procedures were conducted following the National Institutes of Health Guide for the Care and Use of Laboratory Animals (National Academy Press, Washington, D.C., 1996). Three adult male rats (Sprague-Dawley, weight 230 &#177; 15 g) were used in this study. All animals were housed in a 12 h light/dark cycle with controlled temperature and hu...

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The authors have nothing to disclose.

The present study provides a detailed demonstration of the cutaneous nerve fibers in the hairy and glabrous skin by using immunofluorescence on thicker tissue sections with clearing treatment and a 3D view to understand the skin innervation better. The antibody incubation time of up to 1-2 days and an overnight cleaning process are important. These two key steps directly affect the immunofluorescence staining effect of thick sections. A further problem was raised from the choice of antibodies, not all of which are suitab...

The skin, the largest organ in the body, serving as a key interface to the environment, is densely innervated by many nerve fibers1,2,3. Although skin innervation has been widely studied previously with various histological methods, such as staining on whole-mount skin and tissue sections4,5,6, the detailed effective demonstration of cutaneous nerve fibers is still a challenge7,8. Given this, the present protocol developed a unique technique to exhibit cutaneous nerve fibers more clearly in the thick tissue section.
Because of the limit by the thickness of sections, the observation of innervated skin nerve fibers is not precise enough to accurately depict the relationship between calcitonin gene-related peptide (CGRP) nerve fibers and local tissues and organs from the acquired image information. The emergence of 3D tissue clearing technology provides a feasible method to solve this problem9,10. The fast development of tissue-clearing approaches has offered many tools for studying tissue structures, entire organs, neuronal projections, and whole animals in recent times11. The transparent skin tissue could be imaged in a much thicker section by confocal microscopy to obtain the data to visualize cutaneous nerve fibers.
In the current study, the plantar and dorsal skin of a rat hindfoot was selected as the two target sites of hairy and glabrous skin3,4,7. To trace the cutaneous nerve fibers at a longer distance, the skin tissue was sliced at the thickness of 300 &#181;m for immunohistochemical and histochemical staining, followed by tissue clearing treatment. CGRP was used to label the sensory nerve fibers12,13. In addition, to highlight the cutaneous nerve fibers on the tissue background, phalloidin and lymphatic vessel endothelial hyaluronan receptor 1 (LYVE1) were further used to label the blood vessels and lymphatic vessels, respectively14,15.
These approaches provided a straightforward method that can be applied to demonstrate a high-resolution view of the cutaneous nerve fibers and also to visualize the spatial correlation among the nerve fibers, blood vessels, and lymphatic vessels in the skin, which may provide much more information to understand the homeostasis of the normal skin and the cutaneous alteration under the pathological conditions.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>1x phosphate-buffered saline</td>
			<td>Solarbio Life Sciences</td>
			<td>P1020</td>
			<td>pH 7.2-7.4, 0.01 Mol</td>
		</tr>
		<tr>
			<td>2,2,2-Tribromoethanol</td>
			<td>Sigma Life Science</td>
			<td>T48402-5G</td>
			<td></td>
		</tr>
		<tr>
			<td>Confocal fluorescence microscopy</td>
			<td>Olympus Corporation</td>
			<td>Fluoview FV1200</td>
			<td></td>
		</tr>
		<tr>
			<td>Donkey anti-mouse IgG H&#38;L Alexa-Flour488</td>
			<td>Abcam plc.</td>
			<td>ab150105</td>
			<td></td>
		</tr>
		<tr>
			<td>Donkey anti-sheep IgG H&#38;L Alexa-Flour405</td>
			<td>Abcam plc.</td>
			<td>ab175676</td>
			<td></td>
		</tr>
		<tr>
			<td>EP tube</td>
			<td>Wuxi NEST Biotechnology Co.</td>
			<td>615001</td>
			<td>1.5 mL</td>
		</tr>
		<tr>
			<td>Freezing stage sliding microtome system</td>
			<td>Leica Biosystems</td>
			<td>CM1860</td>
			<td></td>
		</tr>
		<tr>
			<td>Imaris Software</td>
			<td>Oxford Instruments</td>
			<td>v.9.0.1</td>
			<td></td>
		</tr>
		<tr>
			<td>IRIS standard scissor</td>
			<td>WPI (World Precision Instruments Inc.)</td>
			<td>503242</td>
			<td></td>
		</tr>
		<tr>
			<td>iSpacer</td>
			<td>SunJin Lab co.</td>
			<td>IS005</td>
			<td></td>
		</tr>
		<tr>
			<td>Micro forceps-Str</td>
			<td>RWD</td>
			<td>F11020-11</td>
			<td></td>
		</tr>
		<tr>
			<td>Mouse monoclonal anti-CGRP antibody</td>
			<td>Santa cruz biotechnology, Inc.</td>
			<td>sc-57053</td>
			<td></td>
		</tr>
		<tr>
			<td>Neutral buffered Formalin</td>
			<td>Solarbio Life Sciences</td>
			<td>G2161</td>
			<td>10%</td>
		</tr>
		<tr>
			<td>Normal donkey serum</td>
			<td>Jackson ImmunoResearch Laboratories</td>
			<td>017-000-12</td>
			<td>10 mL</td>
		</tr>
		<tr>
			<td>Peristaltic pump</td>
			<td>Longer Precision Pump Co., Ltd</td>
			<td>BT300-2J</td>
			<td></td>
		</tr>
		<tr>
			<td>Phalloidin Alexa-Fluor 594</td>
			<td>Thermo Fisher Scientific</td>
			<td>A12381</td>
			<td></td>
		</tr>
		<tr>
			<td>RapiClear 1.52 solution</td>
			<td>SunJin Lab co.</td>
			<td>RC152001</td>
			<td>10 mL</td>
		</tr>
		<tr>
			<td>Regular agarose</td>
			<td>Gene Company Limited</td>
			<td>G-10</td>
			<td></td>
		</tr>
		<tr>
			<td>SEMKEN 1 x 2 Teeth Tissue Forceps-Str</td>
			<td>RWD</td>
			<td>F13038-12</td>
			<td></td>
		</tr>
		<tr>
			<td>Sheep polyclonal anti-LYVE1 antibody</td>
			<td>R&#38;D Systems, Inc.</td>
			<td>AF7939</td>
			<td></td>
		</tr>
		<tr>
			<td>Six-well plate</td>
			<td>Corning Incorporated</td>
			<td>3335</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium azide</td>
			<td>Sigma Life Science</td>
			<td>S2002</td>
			<td>25 g</td>
		</tr>
		<tr>
			<td>Sucrose</td>
			<td>Sigma Life Science</td>
			<td>V900116</td>
			<td>500 g</td>
		</tr>
		<tr>
			<td>Super Glue</td>
			<td>Henkel AG &#38; Co.</td>
			<td>Pattex 502</td>
			<td></td>
		</tr>
		<tr>
			<td>Surgical Handles</td>
			<td>RWD</td>
			<td>S32003-12</td>
			<td></td>
		</tr>
		<tr>
			<td>Triton X-100</td>
			<td>Solarbio Life Sciences</td>
			<td>9002-93-1</td>
			<td>100 mL</td>
		</tr>
		<tr>
			<td>Urethane</td>
			<td>Sigma Life Science</td>
			<td>U2500</td>
			<td>500 g</td>
		</tr>
		<tr>
			<td>VANNAS spring scissors</td>
			<td>RWD</td>
			<td>S1014-12</td>
			<td></td>
		</tr>
		<tr>
			<td>Vibratory microtome</td>
			<td>Leica Biosystems</td>
			<td>VT1200S</td>
			<td></td>
		</tr>
	</tbody>
</table>

demonstrating hairy and glabrous skin innervation in a 3d pattern using multiple fluorescent staining and tissue clearing approaches

Skin innervation is an important part of the peripheral nervous system. Although the study of the cutaneous nerve fibers has progressed rapidly, most of the understanding of their distributional and chemical characteristics comes from conventional histochemical and immunohistochemical staining on thin tissue sections. With the development of the tissue clearing technique, it has become possible to view the cutaneous nerve fibers on thicker tissue sections. The present protocol describes multiple fluorescent staining on tissue sections at a thickness of 300 &#181;m from the plantar and dorsal skin of rat hindfoot, the two typical hairy and glabrous skin sites. Here, the calcitonin gene-related peptide labels the sensory nerve fibers, while phalloidin and lymphatic vessel endothelial hyaluronan receptor 1 label the blood and lymphatic vessels, respectively. Under a confocal microscope, the labeled sensory nerve fibers were followed completely at a longer distance, running in bundles in the deep cutaneous layer and freestyle in the superficial layer. These nerve fibers ran in parallel to or surrounded the blood vessels, and lymphatic vessels formed a three-dimensional (3D) network in the hairy and glabrous skin. The current protocol provides a more effective approach to studying skin innervation than the existing conventional methods from the methodology perspective.

After triple fluorescent staining, the nerve fibers, blood vessels, and lymphatic vessels were clearly labeled with CGRP, phalloidin, and LYVE1, respectively, in the hairy and glabrous skin (Figure 3,4). With the clearing treatment, the CGRP-positive nerve fibers, phalloidin-positive blood vessels, and LYVE1-positive lymphatic vessels can be imaged at a greater depth to acquire the complete structural information of the skin (Figure 3). When the...

Watch this Scientific Journal Video about Demonstrating Hairy and Glabrous Skin Innervation in a 3D Pattern Using Multiple Fluorescent Staining and Tissue Clearing Approaches at JoVE.com

Demonstrating Hairy and Glabrous Skin Innervation in a 3D Pattern Using Multiple Fluorescent Staining and Tissue Clearing Approaches

The thickness of tissue sections limited the morphological study of the skin innervation. The present protocol describes a unique tissue clearing technique to visualize cutaneous nerve fibers in thick 300 &#181;m tissue sections under confocal microscopy.

Skin innervation is an important part of the peripheral nervous system. Although the study of the cutaneous nerve fibers has progressed rapidly, most of ...

Our protocol provided a feasible method to observe the sync section using confocal microscope, which could ensure precision in the observation of the nerve fibers. Simple and easy tissue cleaning protocol is a main advantage of this technique. The tissue cleaning process is efficient and it takes about 30 minutes to one hour.Conduct perfusion on the euthanized rat as mentioned in the text manuscript. Use a scalpel to remove the skin of the dorsum and sole from the hind paw. For samples requiring a frozen section, post fix the tissues in 4%from aldehyde in 0.1 molar PB for two hours.After washing, embed the skin tissues into 2%agarose at 37 degrees Celsius and place them inside the ice box for cooling. Fix the mounted tissue on the vibratory microtone with ice water and slice them at a thickness of 500 micrometers in the transversal direction. After slicing, remove the agarose from the sections and store them in a six well plate with 1x PBS.Incubate the tissue sections in a solution of 2%triton X-100 in 1x PBS overnight at four degrees Celsius. Place the tissue sections into the blocking buffer and rotate at 72 rotations per minute on the shaker overnight at four degrees Celsius. Transfer the tissue sections into the solution containing the primary antibodies of mouse monoclonal anti-CGRP and sheep polyclonal anti-LYVE-1 antibody in dilution buffer in the micro centrifuge tube.Then rotate on the shaker for two days at four degrees Celsius. Wash the tissue sections twice with washing buffer at room temperature, then keep them on the shaker overnight at four degrees Celsius in the washing buffer. The next day, transfer the tissue sections into the mixed solution containing the secondary antibodies in a micro centrifuge tube and rotate at 72 rotations per minute on the shaker for five hours at four degrees Celsius.Wash the tissue sections in a six well plate with washing buffer twice for one hour at room temperature. Keep the tissue sections in washing buffer on the shaker overnight at four degrees Celsius. Transfer the tissue sections into the tissue clearing reagent and rotate at 60 rotations per minute on the shaker gently for one hour at room temperature.Mount the clear tissues on the slide then circle the tissues with a spacer and stick the gap with fresh tissue clearing reagent and cover slip. The 3D pattern demonstrated that the CGRP positive nerve fibers passed through the subcutaneous tissue and dermis to the epidermis. These nerve fibers ran in bundles in the subcutaneous tissue branched within the dermis and terminated in the epidermis.In contrast, phalloidin in positive blood vessels and LYVE-1 positive lymphatic vessels are distributed in the subcutaneous tissue and dermis. Generally the CGRP positive nerve fibers ran parallel to or surrounded the blood vessels and lymphatic vessels forming a 3D network in the hairy and glabrous skin. With the conventional approach, although the nerve fibers blood vessels and lymphatic vessels were clearly labeled with CGRP phalloidin and LYVE-1 in the thin sections, the observation of these structures was limited by the slice thickness and cannot be observed completely.In the section with a thickness of 30 micrometers, there was no difference between hairy skin and glabrous skin in the surface area of CGRP positive nerve fibers. In the 300 micrometers thick tissue sections, compared with hairy skin, the surface area of CGRP positive nerve fibers of glabrous skin was significantly increased. It's important to use the cleaning buffer with high osmotic pressure after antibody incubation.Several times, the cleaning time required for the immuno fluorescence staining is necessary. Following this procedure, we believe there is a possibility of staining and observation of other tissues and organs in six sections also exist. This technique could assist neuroscience researchers encountering the surface area and the state of neuro fibers.It also helps us to observe the innovation of tissues and organs.

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2.4K Views.  China Academy of Chinese Medical Sciences. Our protocol provided a feasible method to observe the sync section using confocal microscope, which could ensure precision in the observation of the nerve fibers. Simple and easy tissue cleaning protocol is a main advantage of this technique. The tissue cleaning process is efficient and it takes about 30 minutes to one hour.Conduct perfusion on the euthanized rat as mentioned in the text manuscript. Use a scalpel to remove the skin of the dorsum and sole from the hind paw. For samples...