Name: stereological estimation of dopaminergic neuron number in the mouse substantia nigra using the optical fractionator and standard microscopy equipment
Uploaded: 2017-09-01T14:00:00
Description: Watch this Scientific Journal Video about Stereological Estimation of Dopaminergic Neuron Number in the Mouse Substantia Nigra Using the Optical Fractionator and Standard Microscopy Equipment at JoVE.

The authors are grateful to Keali R&#246;hm, Louisa Frie&#223;, and Heike Menzel for their expert technical assistance; to Helga Br&#252;nner for the animal care; and to Chistopher S. Ward for the generation and distribution of the optical disector grid plugin for the ImageJ software.

All applicable international, national, and/or institutional guidelines for the care and use of animals were followed. The protocol was approved by local authorities at the Regierung von Unterfranken, Wuerzburg, Germany.
1. Tissue Processing and Immunohistochemistry
<ol>
	<li>Euthanize mice with CO2 or any other approved method.</li>
	<li>Perfuse six 12-week-old C56Bl/6N male mice transcardially with 10 mL of 0.1 M phosphate-buffered saline (PBS) using a 25-G needle and an infusio...

<ol>
	<li>Ip, C. W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=AAV1/2-induced+overexpression+of+A53T-alpha-synuclein+in+the+substantia+nigra+results+in+degeneration+of+the+nigrostriatal+system+with+Lewy-like+pathology+and+motor+impairment:+a+new+mouse+model+for+Parkinson's+disease.">AAV1/2-induced overexpression of A53T-alpha-synuclein in the substantia nigra results in degeneration of the nigrostriatal system with Lewy-like pathology and motor impairment: a new mouse model for Parkinson's disease.</a> Acta Neuropathol Commun. 5 (1), 11 (2017).</li><li>Ip, C. W., Beck, S. K., Volkmann, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lymphocytes+reduce+nigrostriatal+deficits+in+the+6-hydroxydopamine+mouse+model+of+Parkinson's+disease.">Lymphocytes reduce nigrostriatal deficits in the 6-hydroxydopamine mouse model of Parkinson's disease.</a> J Neural Transm (Vienna). 122 (12), 1633-1643 (2015).</li><li>West, M. J., Slomianka, L., Gundersen, H. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Unbiased+stereological+estimation+of+the+total+number+of+neurons+in+thesubdivisions+of+the+rat+hippocampus+using+the+optical+fractionator.">Unbiased stereological estimation of the total number of neurons in thesubdivisions of the rat hippocampus using the optical fractionator.</a> Anat Rec. 231 (4), 482-497 (1991).</li><li>Schmitz, C., Hof, P. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Design-based+stereology+in+neuroscience.">Design-based stereology in neuroscience.</a> Neuroscience. 130 (4), 813-831 (2005).</li><li>Tieu, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+guide+to+neurotoxic+animal+models+of+Parkinson's+disease.">A guide to neurotoxic animal models of Parkinson's disease.</a> Cold Spring Harb Perspect Med. 1 (1), e009316 (2011).</li><li>Abercrombie, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Estimation+of+nuclear+population+from+microtome+sections.">Estimation of nuclear population from microtome sections.</a> Anat Rec. 94, 239-247 (1946).</li><li>Rose, R. D., Rohrlich, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Counting+sectioned+cells+via+mathematical+reconstruction.">Counting sectioned cells via mathematical reconstruction.</a> J Comp Neurol. 263 (3), 365-386 (1987).</li><li>Weibel, E. R., Gomez, D. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+principle+for+counting+tissue+structures+on+random+sections.">A principle for counting tissue structures on random sections.</a> J Appl Physiol. 17, 343-348 (1962).</li><li>West, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Design-based+stereological+methods+for+counting+neurons.">Design-based stereological methods for counting neurons.</a> Prog Brain Res. 135, 43-51 (2002).</li><li>Keuker, J. I., Vollmann-Honsdorf, G. K., Fuchs, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=How+to+use+the+optical+fractionator:+an+example+based+on+the+estimation+of+neurons+in+the+hippocampal+CA1+and+CA3+regions+of+tree+shrews.">How to use the optical fractionator: an example based on the estimation of neurons in the hippocampal CA1 and CA3 regions of tree shrews.</a> Brain Res Brain Res Protoc. 7 (3), 211-221 (2001).</li><li>Mouton, P. R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+effects+of+age+and+lipopolysaccharide+(LPS)-mediated+peripheral+inflammation+on+numbers+of+central+catecholaminergic+neurons.">The effects of age and lipopolysaccharide (LPS)-mediated peripheral inflammation on numbers of central catecholaminergic neurons.</a> Neurobiol Aging. 33 (2), e427-e436 (2012).</li><li>Barreto, G. E., Sun, X., Xu, L., Giffard, R. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Astrocyte+proliferation+following+stroke+in+the+mouse+depends+on+distance+from+the+infarct.">Astrocyte proliferation following stroke in the mouse depends on distance from the infarct.</a> PLoS One. 6 (11), e27881 (2011).</li><li>Robinson, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microstructural+and+microglial+changes+after+repetitive+mild+traumatic+brain+injury+in+mice.">Microstructural and microglial changes after repetitive mild traumatic brain injury in mice.</a> J Neurosci Res. 95 (4), 1025-1035 (2017).</li><li>Paxinos, G., Franklin, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> The mouse brain in stereotaxic coordinates. , (2001).</li><li>. Grid_Overlay.java Available from: <a target="_blank" href="https://imagej.nih.gov/ij/plugins/graphic-overlay.html">https://imagej.nih.gov/ij/plugins/graphic-overlay.html</a> (2010)</li><li>. cell_counter.jar Available from: <a target="_blank" href="https://imagej.nih.gov/ij/plugins/cell-counter.html">https://imagej.nih.gov/ij/plugins/cell-counter.html</a> (2010)</li><li>Baquet, Z. C., Williams, D., Brody, J., Smeyne, R. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+comparison+of+model-based+(2D)+and+design-based+(3D)+stereological+methods+for+estimating+cell+number+in+the+substantia+nigra+pars+compacta+(SNpc)+of+the+C57BL/6J+mouse.">A comparison of model-based (2D) and design-based (3D) stereological methods for estimating cell number in the substantia nigra pars compacta (SNpc) of the C57BL/6J mouse.</a> Neuroscience. 161 (4), 1082-1090 (2009).</li><li>Fu, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+cytoarchitectonic+and+chemoarchitectonic+analysis+of+the+dopamine+cell+groups+in+the+substantia+nigra,+ventral+tegmental+area,+and+retrorubral+field+in+the+mouse.">A cytoarchitectonic and chemoarchitectonic analysis of the dopamine cell groups in the substantia nigra, ventral tegmental area, and retrorubral field in the mouse.</a> Brain Struct Funct. 217 (2), 591-612 (2012).</li><li>German, D. C., Manaye, K. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Midbrain+dopaminergic+neurons+(nuclei+A8,+A9,+and+A10):+three-dimensional+reconstruction+in+the+rat.">Midbrain dopaminergic neurons (nuclei A8, A9, and A10): three-dimensional reconstruction in the rat.</a> J Comp Neurol. 331 (3), 297-309 (1993).</li><li>Smeyne, R. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Assessment+of+the+Effects+of+MPTP+and+Paraquat+on+Dopaminergic+Neurons+and+Microglia+in+the+Substantia+Nigra+Pars+Compacta+of+C57BL/6+Mice.">Assessment of the Effects of MPTP and Paraquat on Dopaminergic Neurons and Microglia in the Substantia Nigra Pars Compacta of C57BL/6 Mice.</a> PLoS One. 11 (10), e0164094 (2016).</li></ol>

Stereology starts with tissue processing. The serial cutting of SN tissue must be performed carefully to prevent the loss of sections during stereological analysis. Additionally, one essential step is to mark one hemisphere in order to distinguish the right from the left SN when performing stereology. Placing a tiny hole at the upper part of the brainstem generated the best results in the presented study. Moreover, since working with the optical fractionator method demands that the tissue is cut in thick sections of abou...

The quantification of neuronal cell number is pivotal in pre-clinical Parkinson&#39;s disease research to determine the level of neurodegeneration within the substantia nigra (SN)1,2. The unbiased stereological estimation of cell number in a region of interest is considered the gold standard3,4,5.
Before the advent of unbiased stereology, the number of neurons in sections was assessed by manipulating counted cell profiles to correct for the variable probabilities that neurons come into sight in a section. One of the most commonly used methods was the correction of quantified cell counts described by Abercrombie6. This method attempted to take into account that cells can be quantified more than once if fragments of the same cell are found in adjacent thin sections. Therefore, Abercrombie and other authors generated equations that required assumptions about the shape, size, and orientation of the counted cells7,8. However, these assumptions were usually not realized and therefore led to systematic errors and divergence from the actual cell number (i.e., bias). Moreover, the bias could not be reduced by additional sampling3.
For the stereological estimation of cell numbers using the optical fractionator, mathematical principles are applied to directly estimate the cell numbers directly in a defined, 3-dimensional volume. The advantage of this method is that it does not involve assumptions about the shape, size, and orientation of the cells being counted. Thus, the estimated cell numbers are closer to the true values and get closer as the sample size increases (i.e., unbiased)3. Because many rules must be followed when using stereology to keep the method unbiased, ready-to-use commercial stereology systems have been developed (for review, see Schmitz and Hof, 20054). Specialized stereology systems implement design-based stereological methods with a priori defined probes and sampling schemes for stereological assessments that lead to independence from shape, size, spatial distribution, and orientation of the cells to be analyzed4,9. However, commercially available stereology systems are expensive; this may limit implementation in new research.
The aim of this study was to develop a usable technique for the design-based stereological estimation of dopaminergic cell counts in the mouse SN, employing the optical fractionator method and using standard microscopy equipment (i.e., light microscope, standard microscope software, and a motorized x, y, z stage). For this, a step-by-step guide on how to process mouse brain tissue and how to estimate SN cell numbers using design-based unbiased stereology is presented. Moreover, templates for the calculation of the estimated cell numbers and coefficients of error (CE) are provided.
The method described here is not limited to the analysis of the SN, but can be adapted for use in other anatomically defined regions of the mouse or rat brain. For instance, unbiased stereology has been used to estimate neuronal cell numbers in the hippocampus10 and the locus coeruleus11. Additionally, cell types other than neurons, such as astrocytes12 and microglia13, can be assessed as well. Therefore, this method can be useful to scientists who intend to implement unbiased stereology in their research but are not willing to spend a lot of money to purchase a stereology system.

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			<td height="25" style="height:25px;width:216px;">Paxinos mouse atlas</td>
			<td style="width:217px;"></td>
			<td style="width:119px;"></td>
			<td style="width:467px;">The Mouse Brain George Paxinos Keith B.J.FranklinCopyright @2001 by Academic Press CD Rom designet &#38; created by Paul Halasz</td>
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			<td height="21" style="height:21px;width:216px;">brain matrix slicer mouse</td>
			<td style="width:217px;">Zivic Instruments&#160;</td>
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			<td height="21" style="height:21px;width:216px;">paraformaldehyde</td>
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			<td style="width:119px;">1040051000</td>
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			<td height="21" style="height:21px;width:216px;">sucrose /D(+) Saccharose&#160;</td>
			<td style="width:217px;">Roth</td>
			<td style="width:119px;">4621.1</td>
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			<td height="21" style="height:21px;width:216px;">isopentane</td>
			<td style="width:217px;">Roth</td>
			<td style="width:119px;">3927.1</td>
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			<td height="21" style="height:21px;width:216px;">glycerol</td>
			<td style="width:217px;">Merck</td>
			<td style="width:119px;">1040931000</td>
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			<td height="21" style="height:21px;width:216px;">Ethanol</td>
			<td style="width:217px;">Sigma Aldrich</td>
			<td style="width:119px;">32205-1L</td>
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			<td height="21" style="height:21px;width:216px;">Name</td>
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			<td style="width:217px;">Sigma Aldrich</td>
			<td style="width:119px;">31434-1KG-R</td>
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			<td height="42" style="height:42px;width:216px;">potassium dihydrogen phosphate</td>
			<td style="width:217px;">Merck</td>
			<td style="width:119px;">1048731000</td>
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			<td height="42" style="height:42px;width:216px;">di-sodium hydrogen phosphate dihydrate</td>
			<td style="width:217px;">Merck</td>
			<td style="width:119px;">1065801000</td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:216px;">potassium chloride</td>
			<td style="width:217px;">Merck</td>
			<td style="width:119px;">1049360500</td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:216px;">normal goat serum</td>
			<td style="width:217px;">Dako</td>
			<td style="width:119px;">X0907</td>
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			<td height="21" style="height:21px;width:216px;">bovine serum albumin</td>
			<td style="width:217px;">Sigma&#160;</td>
			<td style="width:119px;">A4503-100G</td>
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			<td height="21" style="height:21px;width:216px;">Triton X-100</td>
			<td style="width:217px;">Sigma Aldrich</td>
			<td style="width:119px;">X100-100ml</td>
			<td>detergent</td>
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			<td height="63" style="height:63px;width:216px;">3,3-Diaminobenzidine-tetrahydrochlorid/DAB tablets 10mg pH 7.0</td>
			<td style="width:217px;">Kem En Tec</td>
			<td style="width:119px;">4170</td>
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			<td height="26" style="height:26px;width:216px;">H2O2/ Hydrogen peroxide 30%</td>
			<td style="width:217px;">Merck</td>
			<td style="width:119px;">1072090250</td>
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		<tr height="21">
			<td height="21" style="height:21px;width:216px;">avidin/biotin reagent</td>
			<td style="width:217px;">Thermo Scientific</td>
			<td style="width:119px;">32050</td>
			<td>Standard Ultra Sensitive ABC Staining Kit, 1:100</td>
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		<tr height="42">
			<td height="42" style="height:42px;width:216px;">rabbit anti mouse tyrosine hydroxylase antibody</td>
			<td style="width:217px;">abcam</td>
			<td style="width:119px;">Ab112</td>
			<td>1:1000</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">biotinylated goat-anti-rabbit IgG H+L</td>
			<td style="width:217px;">vector laboratories</td>
			<td style="width:119px;">BA-1000</td>
			<td>1:100</td>
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		<tr height="42">
			<td height="42" style="height:42px;width:216px;">StereoInvestigator version 11.07</td>
			<td style="width:217px;">MBF</td>
			<td style="width:119px;"></td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:216px;">BX53 microscope</td>
			<td style="width:217px;">Olympus</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Visiview</td>
			<td style="width:217px;">Visitron Systems GmbH</td>
			<td style="width:119px;">3.3.0.2</td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Axiophot2</td>
			<td style="width:217px;">Zeiss</td>
			<td style="width:119px;"></td>
			<td></td>
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			<td height="21" style="height:21px;width:216px;">ImageJ software</td>
			<td style="width:217px;">NIH</td>
			<td style="width:119px;">Version 4.7</td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Tissue-TEK OCT</td>
			<td style="width:217px;">Sakura</td>
			<td style="width:119px;">4583</td>
			<td></td>
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			<td height="21" style="height:21px;width:216px;">dry ice</td>
			<td style="width:217px;"></td>
			<td style="width:119px;"></td>
			<td></td>
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			<td height="21" style="height:21px;width:216px;">grid overlay plugin</td>
			<td style="width:217px;">Wayne Rasband</td>
			<td style="width:119px;"></td>
			<td>https://imagej.nih.gov/ij/plugins/graphic-overlay.html</td>
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		<tr height="21">
			<td height="21" style="height:21px;width:216px;">cell counter plugin</td>
			<td style="width:217px;">Kurt de Vos</td>
			<td style="width:119px;"></td>
			<td>https://imagej.nih.gov/ij/plugins/cell-counter.html).&#160;</td>
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		<tr height="21">
			<td height="21" style="height:21px;width:216px;">optical disector macro</td>
			<td style="width:217px;">Christopher Ward</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">C57Bl/6N male mice</td>
			<td style="width:217px;">Charles River, Germany</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">SuperFrost Plus coated object slides</td>
			<td style="width:217px;">Langenbrinck, Germany</td>
			<td style="width:119px;"></td>
			<td></td>
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			<td height="21" style="height:21px;width:216px;">25G needle Microlance 3</td>
			<td style="width:217px;">BD&#160;</td>
			<td align="right" style="width:119px;">300400</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">REGLO Analog Infusion pump</td>
			<td style="width:217px;">Ismatec</td>
			<td style="width:119px;">ISM 829</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">StereoInvestigator system</td>
			<td style="width:217px;"></td>
			<td style="width:119px;"></td>
			<td style="width:467px;">StereoInvestigator version 11.07</td>
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		<tr height="21">
			<td height="21" style="height:21px;width:216px;">BX53 microscope</td>
			<td style="width:217px;"></td>
			<td style="width:119px;"></td>
			<td style="width:467px;">BX53 microscope</td>
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		<tr height="21">
			<td height="21" style="height:21px;width:216px;">self-assorted stereology</td>
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			<td style="width:119px;"></td>
			<td style="width:467px;">Visiview</td>
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			<td height="21" style="height:21px;width:216px;">Axiophot2</td>
			<td style="width:217px;"></td>
			<td style="width:119px;"></td>
			<td style="width:467px;">Axiophot2</td>
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stereological estimation of dopaminergic neuron number in the mouse substantia nigra using the optical fractionator and standard microscopy equipment

In pre-clinical Parkinson&#39;s disease research, analysis of the nigrostriatal tract, including quantification of dopaminergic neuron loss within the substantia nigra, is essential. To estimate the total dopaminergic neuron number, unbiased stereology using the optical fractionator method is currently considered the gold standard. Because the theory behind the optical fractionator method is complex and because stereology is difficult to achieve without specialized equipment, several commercially available complete stereology systems that include the necessary software do exist, purely for cell counting reasons. Since purchasing a specialized stereology setup is not always feasible, for many reasons, this report describes a method for the stereological estimation of dopaminergic neuronal cell counts using standard microscopy equipment, including a light microscope, a motorized object table (x, y, z plane) with imaging software, and a computer for analysis. A step-by-step explanation is given on how to perform stereological quantification using the optical fractionator method, and pre-programmed files for the calculation of estimated cell counts are provided. To assess the accuracy of this method, a comparison to data obtained from a commercially available stereology apparatus was performed. Comparable cell numbers were found using this protocol and the stereology device, thus demonstrating the precision of this protocol for unbiased stereology.

Using the presented method, the estimated number of TH+ dopaminergic neurons in the right SN ranged between 7,363 and 7,987 cells and, in the left SN, between 7,446 and 7,904 cells. Thus, the mean number of dopaminergic neurons (&#177; SEM) was 7,647 &#177; 83 cells for the right SN and 7,675 &#177; 66 for the left SN. The calculated CE for each animal was lower than 0.08 (range: 0.073-0.079) (Figure 7). To ascertain the comparability of this method with comm...

Watch this Scientific Journal Video about Stereological Estimation of Dopaminergic Neuron Number in the Mouse Substantia Nigra Using the Optical Fractionator and Standard Microscopy Equipment at JoVE.

Stereological Estimation of Dopaminergic Neuron Number in the Mouse Substantia Nigra Using the Optical Fractionator and Standard Microscopy Equipment

This work presents a step-by-step protocol for the unbiased stereological estimation of dopaminergic neuronal cell numbers in the mouse substantia nigra using standard microscopy equipment (i.e., a light microscope, a motorized object table (x, y, z plane), and public domain software for digital image analysis.

In pre-clinical Parkinson&#39;s disease research, analysis of the nigrostriatal tract, including quantification of dopaminergic neuron loss within the ...

The overall goal of this protocol is to describe the design-based stereological estimation of dopaminergic cell number in the mouse SN using standard microscopy equipment. This method is useful to estimate the number of dopaminergic neurons in the mouse substantia nigra for preclinical Parkinson's disease research using design-based unbiased stereology. The main advantage of this technique is that it can be accomplished with standard microscopy equipment without need for a commercially available complete stereology setup.Demonstrating the procedure will be Louisa Friez, a technician from my laboratory. Begin by placing a paraformaldehyde fixed mouse brain into a brain matrix and making a cut plus 0.74 millimeters from bregma. Transfer the caudal part of the brain including the SN into 4%PFA in 0.1 molar and fix overnight at four degrees Celsius.The next day, exchange the PFA for 30%sucrose in 0.1 molar PBS and incubate for another two days at four degrees Celsius to cryo protect the sample. After two days when the brain has sunk in the sucrose, place the tissue into a Cryomold filled with optimal cutting temperature compound and slowly freeze the tissue in liquid dry ice cooled isopentane. Use a cryostat to serially cut 30 micron cryo sections in the coronal plane.Mark the right hemisphere by puncturing a small hole into the upper region of the brain stem. Collect four series of sections starting at minus 2.46 millimeters from bregma and ending at 4.04 millimeters from bregma. Transfer each series of sections into a tube filled with cryoprotectant and store at minus 20 degrees Celsius.Capture digital images of tyrosine hydroxylase immunohistochemically stained SN sections using imaging software coupled to a microscope. Start by determining the actual mount and thickness of the sections at three randomly selected counting sites per section. First click on view top offset to define the top of the section.Then click on stop view top. Thereafter, click on view bottom offset and then click on stop view bottom. Write down the thickness of the section.Calculate the guard zone by subtracting three microns from the top offset and type the result into the top offset box. Then subtract the 13 micron height of the optical dissector from the top offset number and type the result into the bottom offset box. Select the following parameters, steps 14, size 1.00.Select the directory to save the file. Click on sequence to start the acquisition. After the images have been acquired, click on processing and select the following parameters, all planes from sequence, montage and the fast and stitching boxes with an image overlap of 10%Start to stitch the images by clicking on start.This will generate stack images for analysis. To begin, open the image by clicking on file and open. Set the image scale by using the analyze and set scale command.From this step, change the defined size from pixels to microns. Select the plugins then grid then grid type lines command to randomly insert a grid. Check the random offset box.Define the size of one square within the grid as 130 microns by 130 microns to equal 16, 900 square microns. Change image type from 16-bit to RGB color by clicking on image then type then RGB color. Locate the substantia nigra pars compacta.Encircle the region with the paintbrush tool using a brush width of 11. Undo the set scale command by clicking on analyze then set scale then click to remove scale to calculate in pixels rather than microns. Take a screenshot, save the image file and open the new file with ImageJ.Select brush and a brush width of 25. Mark every grid square that contacts the SN for placement of an optical dissector. Select one grid square that includes parts of the SN.Measure the upper left corner of the square with the cursor in ImageJ to define the starting x and y coordinates.Select the spreadsheet template entitled optical dissector position and calculate the optical dissector position. Then estimate the cell number using the calculation of cell count spreadsheet as described in the written portion of the protocol. This low power image shows a section of mouse brain after TH staining for dopaminergic neurons.Higher magnification depicts TH positive dopaminergic neurons. The inset shows the boxed region at increased magnification. This image shows one series of TH stained SN sections covering the whole mouse SN from rostral to caudal.Each section is separated from the consecutive section by 120 microns. The number of TH positive neurons in the right and left mouse SN were estimated using the method shown in this video and using a commercially available stereology system. As seen here, both methods resulted in comparable cell counts and there were no significant differences between data sets.Don't forget that working with paraformaldehyde can be extremely hazardous and precautions such as wearing of personal protection equipment like protective gloves should always be taken while performing this procedure. After watching this video, you should have a good understanding of how to perform unbiased stereological estimation of dopaminergic neuron number in the mouse substantia nigra using the optical fraction method and standard microscopy equipment.

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Research

JoVE Journal

Neuroscience

In vivo Imaging of the Mouse Spinal Cord Using Two-photon Microscopy

In vivo imaging using two-photon microscopy 1 in mice that have been genetically engineered to express fluorescent proteins in specific cell types 2-3 has significantly broadened our knowledge of physiological and pathological processes in numerous tissues in vivo 4-7. In studies of the central nervous system (CNS), there has been a broad application of in vivo imaging in the brain, which has produced a plethora of novel and often unexpected findings about the behavior of cells such as neurons, astrocytes, microglia, under physiological or pathological conditions 8-17. However, mostly technical complications have limited the implementation of in vivo imaging in studies of the living mouse spinal cord. In particular, the anatomical proximity of the spinal cord to the lungs and heart generates significant movement artifact that makes imaging the living spinal cord a challenging task.
We developed a novel method that overcomes the inherent limitations of spinal cord imaging by stabilizing the spinal column, reducing respiratory-induced movements and thereby facilitating the use of two-photon microscopy to image the mouse spinal cord in vivo. This is achieved by combining a customized spinal stabilization device with a method of deep anesthesia, resulting in a significant reduction of respiratory-induced movements. This video protocol shows how to expose a small area of the living spinal cord that can be maintained under stable physiological conditions over extended periods of time by keeping tissue injury and bleeding to a minimum. Representative raw images acquired in vivo detail in high resolution the close relationship between microglia and the vasculature. A timelapse sequence shows the dynamic behavior of microglial processes in the living mouse spinal cord. Moreover, a continuous scan of the same z-frame demonstrates the outstanding stability that this method can achieve to generate stacks of images and/or timelapse movies that do not require image alignment post-acquisition. Finally, we show how this method can be used to revisit and reimage the same area of the spinal cord at later timepoints, allowing for longitudinal studies of ongoing physiological or pathological processes in vivo.

In vivo Imaging of the Mouse Spinal Cord Using Two-photon Microscopy

A minimally invasive protocol to stabilize the mouse spinal column and perform repetitive in vivo spinal cord imaging using two-photon microscopy is described. This method combines a spinal stabilization device and an anesthetic regimen to minimize respiratory-induced movements and produce raw imaging data that require no alignment or other post-processing.

In vivo imaging using two-photon microscopy 1 in mice that have been genetically engineered to express fluorescent proteins in specific cell types 2-3 has ...

Imaging Odor-Evoked Activities in the Mouse Olfactory Bulb using Optical Reflectance and Autofluorescence Signals

In the brain, sensory stimulation activates distributed populations of neurons among functional modules which participate to the coding of the stimulus. Functional optical imaging techniques are advantageous to visualize the activation of these modules in sensory cortices with high spatial resolution. In this context, endogenous optical signals that arise from molecular mechanisms linked to neuroenergetics are valuable sources of contrast to record spatial maps of sensory stimuli over wide fields in the rodent brain.
Here, we present two techniques based on changes of endogenous optical properties of the brain tissue during activation. First the intrinsic optical signals (IOS) are produced by a local alteration in red light reflectance due to: (i) absorption by changes in blood oxygenation level and blood volume (ii) photon scattering. The use of in vivo IOS to record spatial maps started in the mid 1980's with the observation of optical maps of whisker barrels in the rat and the orientation columns in the cat visual cortex1. IOS imaging of the surface of the rodent main olfactory bulb (OB) in response to odorants was later demonstrated by Larry Katz's group2. The second approach relies on flavoprotein autofluorescence signals (FAS) due to changes in the redox state of these mitochondrial metabolic intermediates. More precisely, the technique is based on the green fluorescence due to oxidized state of flavoproteins when the tissue is excited with blue light. Although such signals were probably among the first fluorescent molecules recorded for the study of brain activity by the pioneer studies of Britton Chances and colleagues3, it was not until recently that they have been used for mapping of brain activation in vivo. FAS imaging was first applied to the somatosensory cortex in rodents in response to hindpaw stimulation by Katsuei Shibuki's group4.
The olfactory system is of central importance for the survival of the vast majority of living species because it allows efficient detection and identification of chemical substances in the environment (food, predators). The OB is the first relay of olfactory information processing in the brain. It receives afferent projections from the olfactory primary sensory neurons that detect volatile odorant molecules. Each sensory neuron expresses only one type of odorant receptor and neurons carrying the same type of receptor send their nerve processes to the same well-defined microregions of &tilde;100&mu;m3 constituted of discrete neuropil, the olfactory glomerulus (Fig. 1). In the last decade, IOS imaging has fostered the functional exploration of the OB5, 6, 7 which has become one of the most studied sensory structures. The mapping of OB activity with FAS imaging has not been performed yet.
Here, we show the successive steps of an efficient protocol for IOS and FAS imaging to map odor-evoked activities in the mouse OB.

This article presents the protocols of intrinsic optical signals and flavoproteins autofluorescence signals imaging to map odor-evoked activities at the surface of the olfactory bulb in mice.

In the brain, sensory stimulation activates distributed populations of neurons among functional modules which participate to the coding of the stimulus. ...

In ovo Electroporation in Chick Midbrain for Studying Gene Function in Dopaminergic Neuron Development

Dopaminergic neurons located in the ventral midbrain control movement, emotional behavior, and reward mechanisms1-3. The dysfunction of ventral midbrain dopaminergic neurons is implicated in Parkinson's disease, Schizophrenia, depression, and dementia1-5. Thus, studying the regulation of midbrain dopaminergic neuron differentiation could not only provide important insight into mechanisms regulating midbrain development and neural progenitor fate specification, but also help develop new therapeutic strategies for treating a variety of human neurological disorders.
Dopaminergic neurons differentiate from neural progenitors lining the ventricular zone of embryonic ventral midbrain. The development of neural progenitors is controlled by gene expression programs6,7. Here we report techniques utilizing electroporation to express genes specifically in the midbrain of Hamburger Hamilton (HH) stage 11 (thirteen somites, 42 hours) chick embryos8,9. The external development of chick embryos allows for convenient experimental manipulations at specific embryonic stages, with the effects determined at later developmental time points10-13. Chick embryonic neural tubes earlier than HH stage 13 (nineteen somites, 48 hours) consist of multipotent neural progenitors that are capable of differentiating into distinct cell types of the nervous system. The pCAG vector, which contains both a CMV promoter and a chick &beta;-actin enhancer, allows for robust expression of Flag or other epitope-tagged constructs in embryonic chick neural tubes14. In this report, we emphasize special measures to achieve regionally restricted gene expression in embryonic midbrain dopaminergic neuron progenitors, including how to inject DNA constructs specifically into the embryonic midbrain region and how to pinpoint electroporation with small custom-made electrodes. Analyzing chick midbrain at later stages provides an excellent in vivo system for plasmid vector-mediated gain-of-function and loss-of-function studies of midbrain development. Modification of the experimental system may extend the assay to other parts of the nervous system for performing fate mapping analysis and for investigating the regulation of gene expression.

In ovo Electroporation in Chick Midbrain for Studying Gene Function in Dopaminergic Neuron Development

To assess the function and the regulation of genes during the development of midbrain dopaminergic neurons, we describe a method that involves in ovo electroporation of plasmid DNA constructs into embryonic chick ventral midbrain dopaminergic neuron progenitors. This technique can be used to achieve efficient expression of genes of interest to study different aspects of midbrain development and dopaminergic neuron differentiation.

Dopaminergic neurons located in the ventral midbrain control movement, emotional behavior, and reward mechanisms1-3. The dysfunction of ventral midbrain ...

Comprehensive Profiling of Dopamine Regulation in Substantia Nigra and Ventral Tegmental Area

Dopamine is a vigorously studied neurotransmitter in the CNS. Indeed, its involvement in locomotor activity and reward-related behaviour has fostered five decades of inquiry into the molecular deficiencies associated with dopamine regulation. The majority of these inquiries of dopamine regulation in the brain focus upon the molecular basis for its regulation in the terminal field regions of the nigrostriatal and mesoaccumbens pathways; striatum and nucleus accumbens. Furthermore, such studies have concentrated on analysis of dopamine tissue content with normalization to only wet tissue weight. Investigation of the proteins that regulate dopamine, such as tyrosine hydroxylase (TH) protein, TH phosphorylation, dopamine transporter (DAT), and vesicular monoamine transporter 2 (VMAT2) protein often do not include analysis of dopamine tissue content in the same sample. The ability to analyze both dopamine tissue content and its regulating proteins (including post-translational modifications) not only gives inherent power to interpreting the relationship of dopamine with the protein level and function of TH, DAT, or VMAT2, but also extends sample economy. This translates into less cost, and yet produces insights into the molecular regulation of dopamine in virtually any paradigm of the investigators' choice.
We focus the analyses in the midbrain. Although the SN and VTA are typically neglected in most studies of dopamine regulation, these nuclei are easily dissected with practice. A comprehensive readout of dopamine tissue content and TH, DAT, or VMAT2 can be conducted. There is burgeoning literature on the impact of dopamine function in the SN and VTA on behavior, and the impingements of exogenous substances or disease processes therein 1-5. Furthermore, compounds such as growth factors have a profound effect on dopamine and dopamine-regulating proteins, to a comparatively greater extent in the SN or VTA 6-8. Therefore, this methodology is presented for reference to laboratories that want to extend their inquiries on how specific treatments modulate behaviour and dopamine regulation. Here, a multi-step method is presented for the analyses of dopamine tissue content, the protein levels of TH, DAT, or VMAT2, and TH phosphorylation from the substantia nigra and VTA from rodent midbrain. The analysis of TH phosphorylation can yield significant insights into not only how TH activity is regulated, but also the signaling cascades affected in the somatodendritic nuclei in a given paradigm.
We will illustrate the dissection technique to segregate these two nuclei and the sample processing of dissected tissue that produces a profile revealing molecular mechanisms of dopamine regulation in vivo, specific for each nuclei (Figure 1).

Dopamine is distinctly regulated in the midbrain nuclei, which contain the cell bodies and dendrites of the dopamine neurons. Here we describe a dissection and sample-handling approach to maximize results, and thus conclusions and insights, on dopamine regulation in the midbrain nuclei of the substantia nigra (SN) and ventral tegmental area (VTA) in rodents.

Dopamine is a vigorously studied neurotransmitter in the CNS. Indeed, its involvement in locomotor activity and reward-related behaviour has fostered five ...

Directed Dopaminergic Neuron Differentiation from Human Pluripotent Stem Cells

Dopaminergic (DA) neurons in the substantia nigra pars compacta (also known as A9 DA neurons) are the specific cell type that is lost in Parkinson&#8217;s disease (PD). There is great interest in deriving A9 DA neurons from human pluripotent stem cells (hPSCs) for regenerative cell replacement therapy for PD. During neural development, A9 DA neurons originate from the floor plate (FP) precursors located at the ventral midline of the central nervous system. Here, we optimized the culture conditions for the stepwise differentiation of hPSCs to A9 DA neurons, which mimics embryonic DA neuron development. In our protocol, we first describe the efficient generation of FP precursor cells from hPSCs using a small molecule method, and then convert the FP cells to A9 DA neurons, which could be maintained in vitro for several months. This efficient, repeatable and controllable protocol works well in human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs) from normal persons and PD patients, in which one could derive A9 DA neurons to perform in vitro disease modeling and drug screening and in vivo cell transplantation therapy for PD.

We, based on knowledge from developmental biology and published research, developed an optimized protocol to efficiently generate A9 midbrain dopaminergic neurons from both human embryonic stem cells and human induced pluripotent stem cells, which would be useful for disease modeling and cell replacement therapy for Parkinson&#8217;s disease.

Dopaminergic (DA) neurons in the substantia nigra pars compacta  (also known as A9 DA neurons) are the specific cell type that is lost in ...

The Neuromuscular Junction: Measuring Synapse Size, Fragmentation and Changes in Synaptic Protein Density Using Confocal Fluorescence Microscopy

The neuromuscular junction (NMJ) is the large, cholinergic relay synapse through which mammalian motor neurons control voluntary muscle contraction. Structural changes at the NMJ can result in neurotransmission failure, resulting in weakness, atrophy and even death of the muscle fiber. Many studies have investigated how genetic modifications or disease can alter the structure of the mouse NMJ. Unfortunately, it can be difficult to directly compare findings from these studies because they often employed different parameters and analytical methods. Three protocols are described here. The first uses maximum intensity projection confocal images to measure the area of acetylcholine receptor (AChR)-rich postsynaptic membrane domains at the endplate and the area of synaptic vesicle staining in the overlying presynaptic nerve terminal. The second protocol compares the relative intensities of immunostaining for synaptic proteins in the postsynaptic membrane. The third protocol uses Fluorescence Resonance Energy Transfer (FRET) to detect changes in the packing of postsynaptic AChRs at the endplate. The protocols have been developed and refined over a series of studies. Factors that influence the quality and consistency of results are discussed and normative data are provided for NMJs in healthy young adult mice.

The neuromuscular junction (NMJ) is altered in a variety of conditions that can sometimes culminate in synaptic failure. This report describes fluorescence microscope-based methods to quantify such structural changes.

The neuromuscular junction (NMJ) is the large, cholinergic relay synapse through which mammalian motor neurons control voluntary muscle contraction. ...

Optical Control of a Neuronal Protein Using a Genetically Encoded Unnatural Amino Acid in Neurons

Photostimulation is a noninvasive way to control biological events with excellent spatial and temporal resolution. New methods are desired to photo-regulate endogenous proteins expressed in their native environment. Here, we present an approach to optically control the function of a neuronal protein directly in neurons using a genetically encoded unnatural amino acid (Uaa). By using an orthogonal tRNA/aminoacyl-tRNA synthetase pair to suppress the amber codon, a photo-reactive Uaa 4,5-dimethoxy-2-nitrobenzyl-cysteine (Cmn) is site-specifically incorporated in the pore of a neuronal protein Kir2.1, an inwardly rectifying potassium channel. The bulky Cmn physically blocks the channel pore, rendering Kir2.1 non-conducting. Light illumination instantaneously converts Cmn into a smaller natural amino acid Cys, activating Kir2.1 channel function. We express these photo-inducible inwardly rectifying potassium (PIRK) channels in rat hippocampal primary neurons, and demonstrate that light-activation of PIRK ceases the neuronal firing due to the outflux of K+ current through the activated Kir2.1 channels. Using in utero electroporation, we also express PIRK in the embryonic mouse neocortex in vivo, showing the light-activation of PIRK in neocortical neurons. Genetically encoding Uaa imposes no restrictions on target protein type or cellular location, and a family of photoreactive Uaas is available for modulating different natural amino acid residues. This technique thus has the potential to be generally applied to many neuronal proteins to achieve optical regulation of different processes in brains. The current protocol presents an accessible procedure for intricate Uaa incorporation in neurons in vitro and in vivo to achieve photo control of neuronal protein activity on the molecular level.

Here, a procedure to selectively activate a neuronal protein with a short pulse of light by genetically encoding a photo-reactive unnatural amino acid into a target neuronal protein expressed in neurons in culture or in vivo is presented.

Photostimulation is a noninvasive way to control biological events with excellent spatial and temporal resolution. New methods are desired to ...

The Optical Fractionator Technique to Estimate Cell Numbers in a Rat Model of Electroconvulsive Therapy

Stereological methods are designed to describe quantitative parameters without making assumptions about size, shape, orientation and distribution of cells or structures. These methods have been revolutionary for quantitative analysis of the mammalian brain, in which volumetric cell populations are too high to count manually, and stereology is now the technique of choice whenever estimates of three-dimensional quantities need to be extracted from measurements on two-dimensional sections. All stereological methods are in principle unbiased; however, they rely on proper knowledge about the structure of interest and the characteristics of the tissue. Stereology is based on Systematic Uniformly Random Sampling (SURS), with adjustment of sampling to the most efficient level in respect to precision, providing reliable, quantitative information about the whole structure of interest. Here we present the optical fractionator in conjunction with BrdU immunohistochemistry to estimate the production and survival of newly-formed neurons in the granule cell layer (including the sub-granular zone) of the rat hippocampus following electroconvulsive stimulation, which is among the most potent stimulators of neurogenesis. The optical fractionator technique is designed to provide estimates of the total number of cells from thick sections sampled from the full structure. Thick sections provide the opportunity to observe cells in their full 3-D extent and thus, allow for easy and robust cell classification based on morphological criteria. When correctly implemented, the sensitivity and efficiency of the optical fractionator provides accurate estimates with a fixed and predetermined precision.

Here, we present a stereological method, the optical fractionator, used to quantify the formation of new neurons, and their survival, in the rat hippocampus following electroconvulsive stimulation. When correctly implemented, the sensitivity and efficiency of stereological methods ensures accurate estimates with a fixed and predetermined precision.

Stereological methods are designed to describe quantitative parameters without making assumptions about size, shape, orientation and distribution of cells ...

Live Images of GLUT4 Protein Trafficking in Mouse Primary Hypothalamic Neurons Using Deconvolution Microscopy

Type 2 diabetes mellitus (T2DM) is a global health crisis which is characterized by insulin signaling impairment and chronic inflammation in peripheral tissues. The hypothalamus in the central nervous system (CNS) is the control center for energy and insulin signal response regulation. Chronic inflammation in peripheral tissues and imbalances of certain chemokines (such as CCL5, TNF&#945;, and IL-6) contribute to diabetes and obesity. However, the functional mechanism(s) connecting chemokines and hypothalamic insulin signal regulation still remain unclear.
In vitro primary neuron culture models are convenient and simple models which can be used to investigate insulin signal regulation in hypothalamic neurons. In this study, we introduced exogeneous GLUT4 protein conjugated with GFP (GFP-GLUT4) into primary hypothalamic neurons to track GLUT4 membrane translocation upon insulin stimulation. Time-lapse images of GFP-GLUT4 protein trafficking were recorded by deconvolution microscopy, which allowed users to generate high-speed, high-resolution images without damaging the neurons significantly while conducting the experiment. The contribution of CCR5 in insulin regulated GLUT4 translocation was observed in CCR5 deficient hypothalamic neurons, which were isolated and cultured from CCR5 knockout mice. Our results demonstrated that the GLUT4 membrane translocation efficiency was reduced in CCR5 deficient hypothalamic neurons after insulin stimulation.

This protocol describes a technique for observation of real-time Green Fluorescence Protein (GFP) tagged Glucose Transporter 4 (GLUT4) protein trafficking upon insulin stimulation and characterization of the biological role of CCR5 in the insulin&#8211;GLUT4 signaling pathway with Deconvolution Microscopy.

Type 2 diabetes mellitus (T2DM) is a global health crisis which is characterized by insulin signaling impairment and chronic inflammation in peripheral ...

A Microbiomechanical System for Studying Varicosity Formation and Recovery in Central Neuron Axons

Axonal varicosities are enlarged structures along the shafts of axons with a high degree of heterogeneity. They are present not only in brains with neurodegenerative diseases or injuries, but also in the normal brain. Here, we describe a newly-established micromechanical system to rapidly, reliably, and reversibly induce axonal varicosities, allowing us to understand the mechanisms governing varicosity formation and heterogeneous protein composition. This system represents a novel means to evaluate the effects of compression and shear stress on different subcellular compartments of neurons, different from other in vitro systems that mainly focus on the effect of stretching. Importantly, owing to the unique features of our system, we recently made a novel discovery showing that the application of pressurized fluid can rapidly and reversibly induce axonal varicosities through the activation of a transient receptor potential channel. Our biomechanical system can be utilized conveniently in combination with drug perfusion, live cell imaging, calcium imaging, and patch clamp recording. Therefore, this method can be adopted for studying mechanosensitive ion channels, axonal transport regulation, axonal cytoskeleton dynamics, calcium signaling, and morphological changes related to traumatic brain injury.

This protocol describes a physiologically relevant, pressurized fluid approach for rapid and reversible induction of varicosities in neurons.

Axonal varicosities are enlarged structures along the shafts of axons with a high degree of heterogeneity. They are present not only in brains with ...