Financial support for the experiments presented in the study was provided by the Marie Heim-V&#246;gtlin program of the Swiss National Science Foundation.
We thank Ms. Johanna Nyffeler for developing a set of modified MATLAB programs for screening for statistically significant differences in real-time cell analyzer&#8217;s data and Dr. Yama Abassi for helpful discussion.

1. Preparation
<ol>
	<li>Place the real-time cell analyzer&#8217;s station in a tissue culture incubator set at 37 &#176;C and with 5% CO2. Carry out all cell culture handling and pharmacological treatments in a tissue culture hood under sterile conditions.</li>
	<li>NOTE: Neuronal cell lines requiring different temperature settings compared to standard conditions for culture, should be adjusted accordingly. For weakly adherent cell lines, use coating agents to facilitate the interaction of cells with the gold microelectrodes in the bottom of the wells of the E-Plate 96.</li>
	<li>Prepare 1,000X stock solutions of the pharmacological compounds for cell culture treatment (neuroprotective agents or second messenger pathways inhibitors in the appropriate solvent &#8211; dimethylsulfoxide or sterile water) and store them at -20 &#176;C. Use the solvent as vehicle in the following treatments.</li>
	<li>Culture human neuroblastoma SK-N-SH cells in DMEM/F12 medium supplemented with 10% fetal bovine serum (FBS) (proliferation medium) in cell culture flasks with 175 cm2 surface to density of about 75%. Keep cell passage number within a range (of about 10 passages) to ascertain consistency between experiments in terms of rate of cell proliferation and response to cytotoxicity. Lower passage numbers are preferred.</li>
	<li>Wash the adherent SK-N-SH cell layer with PBS, and trypsinize with 0.05% trypsin-EDTA solution for 5 min at 37 &#730;C. Centrifuge the cells at 170 &#215; g for 5 min to remove trypsin. Resuspend the cells in 10 ml proliferation medium. Count the cells with Scepter cell counter and adjust cell number to 300,000 cells/ml by diluting cells with proliferation medium.</li>
</ol>
2. Plating and Proliferation of SK-N-SH Cells
<ol>
	<li>Add 100 &#181;l proliferation medium to each well of the E-Plate 96 and leave it for 30 min in the tissue culture hood at RT to equilibrate. Insert the E-Plate 96 in the real-time cell analyzer station in the CO2 incubator at 37 &#176;C.</li>
	<li>Start the real-time cell analyzer software. On the Layout page select the wells included in the experiment and enter in the edit boxes the information about cell type, cell number, names and concentrations of chemical compounds used for cell treatment. 
	NOTE: For the purposes of this protocol at least 4 replicates are recommended for each treatment.</li>
	<li>On the Schedule software page determine &#8220;Steps&#8221; included in the experiment, by selecting the number of sweeps measuring Cell Index and the interval between sweeps for each step. Since Step 1 is predetermined for background measurement, select &#8220;Add a step&#8221; and set Step 2 to measure the Cell Index every 15 min for 96 hr. 
	NOTE: For treatments, in which effects with fast kinetics are expected, set sweeps at shorter intervals.</li>
	<li>Click Start to initiate the automatically predetermined Step 1 and measure the background impedance of the media. This value is automatically subtracted by the software at each data point once the cells are added to the wells.</li>
	<li>Use the previously prepared in step 1.5) cell suspension of 300,000 cells/ml in proliferation medium. 30,000 cells/well for cell toxicity/neuroprotection studies and 15,000 cells/well for cell proliferation studies. Take out the E-Plate and add 100 &#181;l cell suspension per well for cell toxicity/neuroprotection studies and add 50 &#181;l cell suspension and 50 &#181;l proliferation medium per well for cell proliferation studies. The number of cells plated per well needs to be optimized for each cell line empirically.</li>
	<li>Gently swirl the E-Plate 96 for even plating of the cells. Leave the E-Plate 96 for 30 min in the tissue culture hood at RT to allow the cells settle evenly to the bottom of the wells.</li>
	<li>Insert the E-Plate 96 in the real-time cell analyzer station and start Step 2 on the Schedule page. Monitor Cell Index values throughout the experiment by viewing the cell curves on the Plot page and the raw Cell Index data on the Cell Index page of the software.</li>
</ol>
3. Serum Deprivation
<ol>
	<li>24 hr after plating the cells, pause the experiment, and remove the E-Plate 96 from the real-time cell analyzer station. Dilute second messenger inhibitors from 1,000X stocks with DMEM/F12 serum-free medium &#8211; to 200&#215; the final concentration. Treat cells with 1 &#956;l inhibitors of second messenger pathways to be tested for their involvement in neurotoxicity/neuroprotection 30 min before initiating cytotoxicity, to inhibit the respective pathways. Return the E-Plate 96 to the station and resume experimental Cell Index measurements.</li>
	<li>After 30 min pause the experiment again. Carefully remove proliferation medium fully from the E-Plate 96 wells with a pipette (or multi-channel pipette), taking care not to disrupt the adherent cell layer by directing the edge of the pipette tip to the corner of the well. Add 200 &#181;l/well of serum-free DMEM/F12 medium (serum deprivation medium). Ensure rapid exchange of cell culture medium to minimize mechanical agitation of the cells.</li>
	<li>Dilute compounds to be tested for their neuroprotective effects from 1,000X stock with serum-free DMEM/F12 medium to 200&#215; the final concentration. Add 1 &#956;l compounds to be tested for their neuroprotective effects and 1 &#956;l inhibitors of second messenger pathways in the individual wells according to the experimental plan.</li>
	<li>In cells for proliferation studies do not change medium. Dilute compounds to be tested from 1,000X stock to 200&#215; the final concentration in proliferation medium, treat with 1 &#956;l per well and continue to culture in proliferation medium.</li>
	<li>Resume the experiment to continue with Cell Index measurements every 15 min for 96 hr as previously set.</li>
</ol>
4. Data Analysis
<ol>
	<li>For neurotoxicity/neuroprotection data normalize Cell Index to the last time point before pharmacological treatment or medium change to reduce variation between experiments by selecting &#8220;normalized Cell Index&#8221; and &#8220;normalize Time&#8221; on the Plot page.</li>
	<li>Highlight the wells on the Plot page for the experimental conditions of interest and click &#8220;Add&#8221; to plot the normalized Cell Index curves. Observe the kinetics of the neurotoxic/neuroprotective effect, or of second messengers inhibition as normalized Cell Index curves as a function of time.</li>
	<li>Observe the Cell Index curves for the tested drug treatments in proliferation medium as a function of time to assess whether an effect on proliferation is involved in the neuroprotective/neurotoxic effect.</li>
	<li>Export the experimental info for all Cell Index time points from the Cell Index software page into an Excel file to initiate statistical evaluation of the results 
	NOTE: As an initial step in the statistical analysis a set of modified MATLAB programs that use the Welch&#39;s t-test, with the p-value plotted semilogarithmically, utilize inverted axis against the time scale (provided as supplementary code files). These programs allow detection of p-values over the time-course of an entire real-time cell analyzer experiment, and thus aid the selection of time points for more detailed statistical analysis. See the supplementary material for detailed information on the programs.</li>
	<li>For statistical analysis of differences in Cell Index values under different treatment conditions at specific time points, select Cell Index values at respective time points from the exported Excel file. Analyze the Cell Index values for the selected time points with one-way or two-way analysis of variance (ANOVA) followed by a post-hoc test using statistical software.</li>
</ol>

<ol>
	<li>Cavallucci, V., D'Amelio, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Matter+of+life+and+death:+the+pharmacological+approaches+targeting+apoptosis+in+brain+diseases.">Matter of life and death: the pharmacological approaches targeting apoptosis in brain diseases.</a> Curr. Pharm. Des. 17 (3), 215-229 (2011).</li><li>Bull, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=HPA+CHaPD+001:+Review+of+Environmental+Chemicals+and+Neurotoxicity.">HPA CHaPD 001: Review of Environmental Chemicals and Neurotoxicity.</a> Focus on Neurological Diseases. , (2007).</li><li>Ke, N., Wang, X., Xu, X., Abassi, Y. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+xCELLigence+system+for+real-time+and+label-free+monitoring+of+cell+viability.">The xCELLigence system for real-time and label-free monitoring of cell viability.</a> Methods Mol. Biol. 740, 33-43 (2011).</li><li>Limame, 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=Comparative+analysis+of+dynamic+cell+viability,+migration+and+invasion+assessments+by+novel+real-time+technology+and+classic+endpoint+assays.">Comparative analysis of dynamic cell viability, migration and invasion assessments by novel real-time technology and classic endpoint assays.</a> PLoS One. 7 (10), e46536 (2012).</li><li>Diemert, 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=Impedance+measurement+for+real-time+detection+of+neuronal+cell+death.">Impedance measurement for real-time detection of neuronal cell death.</a> J. Neurosci. Methods. 203 (1), 69-77 (2012).</li><li>Kustermann, 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=A+label-free,+impedance-based+real+time+assay+to+identify+drug-induced+toxicities+and+differentiate+cytostatic+from+cytotoxic+effects.">A label-free, impedance-based real time assay to identify drug-induced toxicities and differentiate cytostatic from cytotoxic effects.</a> Toxicol In Vitro. 27 (5), 1589-1595 (2013).</li><li>Marinova, Z., Walitza, S., Gr&#252;nblatt, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=5-HT2A+serotonin+receptor+agonist+DOI+alleviates+cytotoxicity+in+neuroblastoma+cells:+role+of+the+ERK+pathway.">5-HT2A serotonin receptor agonist DOI alleviates cytotoxicity in neuroblastoma cells: role of the ERK pathway.</a> Prog. Neuropsychopharmacol. Biol. Psychiatry. 44, 64-72 (2013).</li><li>Gonz&#225;lez-Maeso, 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=Hallucinogens+recruit+specific+cortical+5-HT(2A)+receptor-mediated+signaling+pathways+to+affect+behavior.">Hallucinogens recruit specific cortical 5-HT(2A) receptor-mediated signaling pathways to affect behavior.</a> Neuron. 53 (3), 439-452 (2007).</li><li>Tsuchioka, M., Takebayashi, M., Hisaoka, K., Maeda, N., Nakata, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Serotonin+(5-HT)+induces+glial+cell+line-derived+neurotrophic+factor+(GDNF)+mRNA+expression+via+the+transactivation+of+fibroblast+growth+factor+receptor+2+(FGFR2)+in+rat+C6+glioma+cells.">Serotonin (5-HT) induces glial cell line-derived neurotrophic factor (GDNF) mRNA expression via the transactivation of fibroblast growth factor receptor 2 (FGFR2) in rat C6 glioma cells.</a> J. Neurochem. 106 (1), 244-257 (2008).</li><li>Galante, D., 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=Differential+toxicity,+conformation+and+morphology+of+typical+initial+aggregation+states+of+A&#946;1-42+and+A&#946;py3-42+beta-amyloids.">Differential toxicity, conformation and morphology of typical initial aggregation states of A&#946;1-42 and A&#946;py3-42 beta-amyloids.</a> Int. J. Biochem. Cell. Biol. 44 (11), 2085-2093 (2012).</li><li>Sheline, C. T., Cai, A. L., Zhu, J., Shi, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Serum+or+target+deprivation-induced+neuronal+death+causes+oxidative+neuronal+accumulation+of+Zn2+and+loss+of+NAD.">Serum or target deprivation-induced neuronal death causes oxidative neuronal accumulation of Zn2+and loss of NAD.</a> Eur. J. Neurosci. 32, 894-904 (2010).</li></ol>

Publication costs for the current video-article were sponsored by &#8220;ACEA Biosciences&#8221;.

The current protocol presents the utility of a real-time cell analyzer to assess continuously and under label-free conditions the neuroprotective/neurotoxic effects of compounds in neuronal cell lines and to gain insight into the second messenger pathways involved in the effect.
Even though the real-time cell analyzer&#8217;s utility to study cytotoxicity and effects of drugs on cell proliferation is generally recognized, only a few studies have used it in neuronal related cell types. We have ...

Neuronal cell death plays a critical role in the pathophysiology of many brain-related disorders1. The availability of reliable and high-throughput in vitro toxicity assays is critical to gain better insight into the mechanisms of neurotoxicity and to help select neuroprotective molecules as therapeutic candidates in drug development2. However, there are many limitations to most widely used in vitro neurotoxicity assays.They assess neurotoxicity/neuroprotection at a single time-point not allowing kinetic resolution; often use label or probe which can interfere with the signaling pathways and limit additional studies in the same cell population, and are often labor-intensive, and in many cases do not provide mechanistic insight. In the present study we demonstrate the utility of a real-time impedance-based cell analyzer to determine neurotoxicity and neuroprotection in a neuronal cell line in real-time and under label-free conditions and to provide insight into downstream mechanisms through analysis of second messenger pathways involved in the effect.
Previous studies have confirmed the validity of the real-time cell analyzer to determine cytotoxicity as well as effects on cell proliferation in cell lines in comparison with standard techniques3,4,5,6. For example, a good correlation was observed between readouts of the standard cell viability WST-1 assay and Cell Index values at several time points under basal proliferation conditions and after two different toxic paradigms in HeLa cells3. In A549 and MDA-MB-231 cells proliferation and cytotoxicity provoked with the microtubule stabilizer paclitaxel showed very similar values when assessed by Cell Index measurements and the standardly used sulforhodamine B (SRB) assay4. In the neuronal cell line of immortalized hippocampal neurons HT-22 Cell Index measurements were validated for their ability to detect cell proliferation, glutamate cytotoxicity and cytoprotection against the widely used 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyltetrazolium-bromide (MTT) assay5. In the same study the MTT assay results and Cell Index measurements also correlated well in measuring neuronal progenitor cells proliferation, cytotoxicity after growth factors deprivation and rescue of cytotoxicity by the pan-caspase inhibitor QVD5. Cytotoxicity induced in NIH 3T3 cells by Vandetanib (vascular endothelial growth factor receptor and epidermal growth factor receptor inhibitor) showed similar results measured with Cell Index values or neutral red uptake assay6.
We have recently used the real-time cell analyzer system to assess neuroprotective effects of the serotonin 2A (5-HT2A) receptor agonist (&#177;)-2,5-dimethoxy-4-iodoamphetamine hydrochloride (DOI) in a neuronal cell line (SK-N-SH cells) and screened for the involvement of second messenger pathways through monitoring the effect of their chemical inhibition on the observed neuroprotection7. Interestingly, the 5-HT2A receptor has both hallucinogenic and nonhallucinogenic agonists (like DOI and lisuride, respectively), which may activate both common and distinct second messenger pathways8.
The advantages of the presented technique are that it allows to collect real-time information on cell survival in the course of days, to delineate second-messenger pathways involved, to assess the possible contribution of proliferation effects to neuroprotection, and to select an optimal time for additional end-point studies on the same cell population. A schematic diagram of the workflow in the current protocol is presented in Figure 1.

<table border="0" cellpadding="0" cellspacing="0" width="1015">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:279px;">Name of Material/ Equipment</td>
			<td style="width:161px;">Company</td>
			<td style="width:119px;">Catalog Number</td>
			<td style="width:457px;">Comments/Description</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:279px;">xCELLigence&#160; RTCA SP system bundle</td>
			<td style="width:161px;">ACEA Biosciences</td>
			<td style="width:119px;">No: 00380601030</td>
			<td>consists of RTCA Analyzer, RTCA SP Station and RTCA Control Unit</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:279px;">E-plate 96</td>
			<td style="width:161px;">ACEA Biosciences</td>
			<td style="width:119px;">No: 05232368001</td>
			<td>for culturing the cells, inserted in the RTCA SP Station</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:279px;">SK-N-SH cells</td>
			<td style="width:161px;">ATCC - (in partnership with LGC Standards)</td>
			<td style="width:119px;">HTB-11</td>
			<td>can be replaced by another adherent neuronal cell line of interest</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:279px;">DMEM/F12&#160;</td>
			<td style="width:161px;">Sigma-Aldrich</td>
			<td style="width:119px;">D8437</td>
			<td>cell culture medium</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:279px;">fetal bovine serum</td>
			<td style="width:161px;">Life Technologies</td>
			<td style="width:119px;">16140-063</td>
			<td>supplements proliferation, but not serum deprivation medium</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:279px;">tisue culture flask T175</td>
			<td style="width:161px;">Sarstedt</td>
			<td style="width:119px;">83.1812.302&#160;</td>
			<td>for culturing cells, which will be later plated on the E-Plate 96</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:279px;">0.05% Trypsin-EDTA</td>
			<td style="width:161px;">Life Technologies</td>
			<td style="width:119px;">25300-054</td>
			<td>for trypsinization of cells cultured in tissue culture flasks</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:279px;">Scepter 2.0 cell counter</td>
			<td style="width:161px;">Merck Millipore</td>
			<td style="width:119px;">PHCC20060</td>
			<td>automated cell counter</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:279px;">phosphate-buffered saline</td>
			<td style="width:161px;">Life Technologies</td>
			<td style="width:119px;">10010-015</td>
			<td>for washing the cells</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:279px;">(&#177;)-DOI hydrochloride</td>
			<td style="width:161px;">Sigma-Aldrich</td>
			<td style="width:119px;">D101</td>
			<td>5-HT2A agonist for cell culture treatment</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:279px;">LY-294,002 hydrochloride</td>
			<td style="width:161px;">Sigma-Aldrich</td>
			<td style="width:119px;">L9908</td>
			<td>PI3-K inhibitor for cell culture treatment&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:279px;">lisuride maleate</td>
			<td style="width:161px;">Tocris Bioscience</td>
			<td align="right" style="width:119px;">4052</td>
			<td>compound with 5-HT2A agonistic activity for cell culture treatment</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:279px;">dimethyl sulfoxide</td>
			<td style="width:161px;">Sigma-Aldrich</td>
			<td style="width:119px;">D4540</td>
			<td>for dissolving LY-294,002 and lisuride maleate</td>
		</tr>
	</tbody>
</table>

real-time impedance-based cell analyzer as a tool to delineate molecular pathways involved in neurotoxicity and neuroprotection in a neuronal cell line

Many brain-related disorders have neuronal cell death involved in their pathophysiology. Improved in vitro models to study neuroprotective or neurotoxic effects of drugs and downstream pathways involved would help gain insight into the molecular mechanisms of neuroprotection/neurotoxicity and could potentially facilitate drug development. However, many existing in vitro toxicity assays have major limitations &#8211; most assess neurotoxicity and neuroprotection at a single time point, not allowing to observe the time-course and kinetics of the effect. Furthermore, the opportunity to collect information about downstream signaling pathways involved in neuroprotection in real-time would be of great importance. In the current protocol we describe the use of a real-time impedance-based cell analyzer to determine neuroprotective effects of serotonin 2A (5-HT2A) receptor agonists in a neuronal cell line under label-free and real-time conditions using impedance measurements. Furthermore, we demonstrate that inhibitors of second messenger pathways can be used to delineate downstream molecules involved in the neuroprotective effect. We also describe the utility of this technique to determine whether an effect on cell proliferation contributes to an observed neuroprotective effect. The system utilizes special microelectronic plates referred to as E-Plates which contain alternating gold microelectrode arrays on the bottom surface of the wells, serving as cell sensors. The impedance readout is modified by the number of adherent cells, cell viability, morphology, and adhesion. A dimensionless parameter called Cell Index is derived from the electrical impedance measurements and is used to represent the cell status. Overall, the real-time impedance-based cell analyzer allows for real-time, label-free assessment of neuroprotection and neurotoxicity, and the evaluation of second messenger pathways involvement, contributing to more detailed and high-throughput assessment of potential neuroprotective compounds in vitro, for selecting therapeutic candidates.

Serum deprivation leads to decrease in Cell Index values, which can be monitored continuously with the real-time cell analyzer
Neurotoxic stimuli to the cells lead to a decrease in Cell Index values, which can be monitored in real-time with the presented technique and the dynamics of which is dependent on the specific neurotoxic stimulus and the cell type studied. Figure 2 demonstrates the increase in Cell Index when SK-N-SH cells are grown in proliferation me...

Watch this Scientific Journal Video about Real-Time Impedance-based Cell Analyzer as a Tool to Delineate Molecular Pathways Involved in Neurotoxicity and Neuroprotection in a Neuronal Cell Line at JoV

Real-Time Impedance-based Cell Analyzer as a Tool to Delineate Molecular Pathways Involved in Neurotoxicity and Neuroprotection in a Neuronal Cell Line

Improved in vitro neurotoxicity assays would aid the identification of new neuroprotective compounds. The utility of a real-time impedance-based cell analyzer to determine cytotoxicity and cytoprotection in neuronal cell lines and to delineate the involvement of second messenger pathways, thus gaining insight in the mechanism of neuroprotection is presented.

Many brain-related disorders have neuronal cell death involved in their pathophysiology. Improved in vitro models to study neuroprotective or neurotoxic ...

real-time-impedance-based-cell-analyzer-as-tool-to-delineate

Research

JoVE Journal

Neuroscience

11.4K Views.  University of Zürich. Improved in vitro neurotoxicity assays would aid the identification of new neuroprotective compounds. The utility of a real-time impedance-based cell analyzer to determine cytotoxicity and cytoprotection in neuronal cell lines and to delineate the involvement of second messenger pathways, thus gaining insight in the mechanism of neuroprotection is presented.

Video: Real-Time Impedance-based Cell Analyzer as a Tool to Delineate Molecular Pathways Involved in Neurotoxicity and Neuroprotection in a Neuronal Cell Line

Automated Sholl Analysis of Digitized Neuronal Morphology at Multiple Scales

Neuronal morphology plays a significant role in determining how neurons function and communicate1-3. Specifically, it affects the ability of neurons to receive inputs from other cells2 and contributes to the propagation of action potentials4,5. The morphology of the neurites also affects how information is processed. The diversity of dendrite morphologies facilitate local and long range signaling and allow individual neurons or groups of neurons to carry out specialized functions within the neuronal network6,7. Alterations in dendrite morphology, including fragmentation of dendrites and changes in branching patterns, have been observed in a number of disease states, including Alzheimer's disease8, schizophrenia9,10, and mental retardation11. The ability to both understand the factors that shape dendrite morphologies and to identify changes in dendrite morphologies is essential in the understanding of nervous system function and dysfunction.
Neurite morphology is often analyzed by Sholl analysis and by counting the number of neurites and the number of branch tips. This analysis is generally applied to dendrites, but it can also be applied to axons. Performing this analysis by hand is both time consuming and inevitably introduces variability due to experimenter bias and inconsistency. The Bonfire program is a semi-automated approach to the analysis of dendrite and axon morphology that builds upon available open-source morphological analysis tools. Our program enables the detection of local changes in dendrite and axon branching behaviors by performing Sholl analysis on subregions of the neuritic arbor. For example, Sholl analysis is performed on both the neuron as a whole as well as on each subset of processes (primary, secondary, terminal, root, etc.) Dendrite and axon patterning is influenced by a number of intracellular and extracellular factors, many acting locally. Thus, the resulting arbor morphology is a result of specific processes acting on specific neurites, making it necessary to perform morphological analysis on a smaller scale in order to observe these local variations12.
The Bonfire program requires the use of two open-source analysis tools, the NeuronJ plugin to ImageJ and NeuronStudio. Neurons are traced in ImageJ, and NeuronStudio is used to define the connectivity between neurites. Bonfire contains a number of custom scripts written in MATLAB (MathWorks) that are used to convert the data into the appropriate format for further analysis, check for user errors, and ultimately perform Sholl analysis. Finally, data are exported into Excel for statistical analysis. A flow chart of the Bonfire program is shown in Figure 1.

We have developed a computer program to analyze neuronal morphology. In combination with two existing open source analysis tools, our program performs Sholl analysis and determines the number of neurites, branch points, and neurite tips. The analyses are performed so that local changes in neurite morphology can be observed.

Neuronal morphology plays a significant role in determining how neurons function and communicate1-3.  Specifically, it affects the ability of neurons to ...

Efficient Derivation of Human Neuronal Progenitors and Neurons from Pluripotent Human Embryonic Stem Cells with Small Molecule Induction

There is a large unfulfilled need for a clinically-suitable human neuronal cell source for repair or regeneration of the damaged central nervous system (CNS) structure and circuitry in today's healthcare industry. Cell-based therapies hold great promise to restore the lost nerve tissue and function for CNS disorders. However, cell therapies based on CNS-derived neural stem cells have encountered supply restriction and difficulty to use in the clinical setting due to their limited expansion ability in culture and failing plasticity after extensive passaging1-3. Despite some beneficial outcomes, the CNS-derived human neural stem cells (hNSCs) appear to exert their therapeutic effects primarily by their non-neuronal progenies through producing trophic and neuroprotective molecules to rescue the endogenous cells1-3. Alternatively, pluripotent human embryonic stem cells (hESCs) proffer cures for a wide range of neurological disorders by supplying the diversity of human neuronal cell types in the developing CNS for regeneration1,4-7. However, how to channel the wide differentiation potential of pluripotent hESCs efficiently and predictably to a desired phenotype has been a major challenge for both developmental study and clinical translation. Conventional approaches rely on multi-lineage inclination of pluripotent cells through spontaneous germ layer differentiation, resulting in inefficient and uncontrollable lineage-commitment that is often followed by phenotypic heterogeneity and instability, hence, a high risk of tumorigenicity7-10. In addition, undefined foreign/animal biological supplements and/or feeders that have typically been used for the isolation, expansion, and differentiation of hESCs may make direct use of such cell-specialized grafts in patients problematic11-13. To overcome these obstacles, we have resolved the elements of a defined culture system necessary and sufficient for sustaining the epiblast pluripotence of hESCs, serving as a platform for de novo derivation of clinically-suitable hESCs and effectively directing such hESCs uniformly towards clinically-relevant lineages by small molecules14 (please see a schematic in Fig. 1). Retinoic acid (RA) does not induce neuronal differentiation of undifferentiated hESCs maintained on feeders1, 14. And unlike mouse ESCs, treating hESC-differentiated embryoid bodies (EBs) only slightly increases the low yield of neurons1, 14, 15. However, after screening a variety of small molecules and growth factors, we found that such defined conditions rendered retinoic acid (RA) sufficient to induce the specification of neuroectoderm direct from pluripotent hESCs that further progressed to neuroblasts that generated human neuronal progenitors and neurons in the developing CNS with high efficiency (Fig. 2). We defined conditions for induction of neuroblasts direct from pluripotent hESCs without an intervening multi-lineage embryoid body stage, enabling well-controlled efficient derivation of a large supply of human neuronal cells across the spectrum of developmental stages for cell-based therapeutics.

We have established a protocol for induction of neuroblasts direct from pluripotent human embryonic stem cells maintained under defined conditions with small molecules, which enables derivation of a large supply of human neuronal progenitors and neuronal cell types in the developing CNS for neural repair.

There is a large unfulfilled need for a clinically-suitable human neuronal cell source for repair or regeneration of the damaged central nervous system ...

Simultaneous Electroencephalography, Real-time Measurement of Lactate Concentration and Optogenetic Manipulation of Neuronal Activity in the Rodent Cerebral Cortex

Although the brain represents less than 5% of the body by mass, it utilizes approximately one quarter of the glucose used by the body at rest1. The function of non rapid eye movement sleep (NREMS), the largest portion of sleep by time, is uncertain. However, one salient feature of NREMS is a significant reduction in the rate of cerebral glucose utilization relative to wakefulness2-4. This and other findings have led to the widely held belief that sleep serves a function related to cerebral metabolism. Yet, the mechanisms underlying the reduction in cerebral glucose metabolism during NREMS remain to be elucidated.
	One phenomenon associated with NREMS that might impact cerebral metabolic rate is the occurrence of slow waves, oscillations at frequencies less than 4 Hz, in the electroencephalogram5,6. These slow waves detected at the level of the skull or cerebral cortical surface reflect the oscillations of underlying neurons between a depolarized/up state and a hyperpolarized/down state7. During the down state, cells do not undergo action potentials for intervals of up to several hundred milliseconds. Restoration of ionic concentration gradients subsequent to action potentials represents a significant metabolic load on the cell8; absence of action potentials during down states associated with NREMS may contribute to reduced metabolism relative to wake.
	Two technical challenges had to be addressed in order for this hypothetical relationship to be tested. First, it was necessary to measure cerebral glycolytic metabolism with a temporal resolution reflective of the dynamics of the cerebral EEG (that is, over seconds rather than minutes). To do so, we measured the concentration of lactate, the product of aerobic glycolysis, and therefore a readout of the rate of glucose metabolism in the brains of mice. Lactate was measured using a lactate oxidase based real time sensor embedded in the frontal cortex. The sensing mechanism consists of a platinum-iridium electrode surrounded by a layer of lactate oxidase molecules. Metabolism of lactate by lactate oxidase produces hydrogen peroxide, which produces a current in the platinum-iridium electrode. So a ramping up of cerebral glycolysis provides an increase in the concentration of substrate for lactate oxidase, which then is reflected in increased current at the sensing electrode. It was additionally necessary to measure these variables while manipulating the excitability of the cerebral cortex, in order to isolate this variable from other facets of NREMS.
	We devised an experimental system for simultaneous measurement of neuronal activity via the elecetroencephalogram, measurement of glycolytic flux via a lactate biosensor, and manipulation of cerebral cortical neuronal activity via optogenetic activation of pyramidal neurons. We have utilized this system to document the relationship between sleep-related electroencephalographic waveforms and the moment-to-moment dynamics of lactate concentration in the cerebral cortex. The protocol may be useful for any individual interested in studying, in freely behaving rodents, the relationship between neuronal activity measured at the electroencephalographic level and cellular energetics within the brain.

A procedure is described for manipulating the activity of cerebral cortical pyramidal neurons optogenetically while the electroencephalogram, electromyogram, and cerebral lactate concentration are monitored. Experimental recordings are performed on cable-tethered mice while they undergo spontaneous sleep/wake cycles. Optogenetic equipment is assembled in our laboratory; recording equipment is commercially available.

Although the brain represents less than 5% of the body  by mass, it utilizes approximately one quarter of the glucose used by the body  at rest1. The ...

Fast Micro-iontophoresis of Glutamate and GABA: A Useful Tool to Investigate Synaptic Integration

One of the fundamental interests in neuroscience is to understand the integration of excitatory and inhibitory inputs along the very complex structure of the dendritic tree, which eventually leads to neuronal output of action potentials at the axon. The influence of diverse spatial and temporal parameters of specific synaptic input on neuronal output is currently under investigation, e.g. the distance-dependent attenuation of dendritic inputs, the location-dependent interaction of spatially segregated inputs, the influence of GABAergig inhibition on excitatory integration, linear and non-linear integration modes, and many more.
With fast micro-iontophoresis of glutamate and GABA it is possible to precisely investigate the spatial and temporal integration of glutamatergic excitation and GABAergic inhibition. Critical technical requirements are either a triggered fluorescent lamp, light-emitting diode (LED), or a two-photon scanning microscope to visualize dendritic branches without introducing significant photo-damage of the tissue. Furthermore, it is very important to have a micro-iontophoresis amplifier that allows for fast capacitance compensation of high resistance pipettes. Another crucial point is that no transmitter is involuntarily released by the pipette during the experiment.
Once established, this technique will give reliable and reproducible signals with a high neurotransmitter and location specificity. Compared to glutamate and GABA uncaging, fast iontophoresis allows using both transmitters at the same time but at very distant locations without limitation to the field of view. There are also advantages compared to focal electrical stimulation of axons: with micro-iontophoresis the location of the input site is definitely known and it is sure that only the neurotransmitter of interest is released. However it has to be considered that with micro-iontophoresis only the postsynapse is activated and presynaptic aspects of neurotransmitter release are not resolved. In this article we demonstrate how to set up micro-iontophoresis in brain slice experiments.

In this article we introduce fast micro-iontophoresis of neurotransmitters as a technique to investigate integration of postsynaptic signals with high spatial and temporal precision.

One of the fundamental interests in neuroscience is to understand the integration of excitatory and inhibitory inputs along the very complex structure of ...

Sex Stratified Neuronal Cultures to Study Ischemic Cell Death Pathways

Sex differences in neuronal susceptibility to ischemic injury and neurodegenerative disease have long been observed, but the signaling mechanisms responsible for those differences remain unclear. Primary disassociated embryonic neuronal culture provides a simplified experimental model with which to investigate the neuronal cell signaling involved in cell death as a result of ischemia or disease; however, most neuronal cultures used in research today are mixed sex. Researchers can and do test the effects of sex steroid treatment in mixed sex neuronal cultures in models of neuronal injury and disease, but accumulating evidence suggests that the female brain responds to androgens, estrogens, and progesterone differently than the male brain. Furthermore, neonate male and female rodents respond differently to ischemic injury, with males experiencing greater injury following cerebral ischemia than females. Thus, mixed sex neuronal cultures might obscure and confound the experimental results; important information might be missed. For this reason, the Herson Lab at the University of Colorado School of Medicine routinely prepares sex-stratified primary disassociated embryonic neuronal cultures from both hippocampus and cortex. Embryos are sexed before harvesting of brain tissue and male and female tissue are disassociated separately, plated separately, and maintained separately. Using this method, the Herson Lab has demonstrated a male-specific role for the ion channel TRPM2 in ischemic cell death. In this manuscript, we share and discuss our protocol for sexing embryonic mice and preparing sex-stratified hippocampal primary disassociated neuron cultures. This method can be adapted to prepare sex-stratified cortical cultures and the method for embryo sexing can be used in conjunction with other protocols for any study in which sex is thought to be an important determinant of outcome.

Primary disassociated embryonic hippocampal neuronal cultures are useful for investigating the signaling mechanisms involved in neuron death. Sexing the embryos before the isolation and dissociation of the hippocampus allows the preparation of separate male and female cultures, which enables the researcher to identify and investigate sex-specific cell signaling.

Sex differences in neuronal susceptibility to ischemic injury and neurodegenerative disease have long been observed, but the signaling mechanisms ...

Inducing Plasticity of Astrocytic Receptors by Manipulation of Neuronal Firing Rates

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

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

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

Utilizing Combined Methodologies to Define the Role of Plasma Membrane Delivery During Axon Branching and Neuronal Morphogenesis

During neural development, growing axons extend to multiple synaptic partners by elaborating axonal branches. Axon branching is promoted by extracellular guidance cues like netrin-1 and results in dramatic increases to the surface area of the axonal plasma membrane. Netrin-1-dependent axon branching likely involves temporal and spatial control of plasma membrane expansion, the components of which are supplied through exocytic vesicle fusion. These fusion events are preceded by formation of SNARE complexes, comprising a v-SNARE, such as VAMP2 (vesicle-associated membrane protein 2), and plasma membrane t-SNAREs, syntaxin-1 and SNAP25 (synaptosomal-associated protein 25). Detailed herein isa multi-pronged approach used to examine the role of SNARE mediated exocytosis in axon branching. The strength of the combined approach is data acquisition at a range of spatial and temporal resolutions, spanning from the dynamics of single vesicle fusion events in individual neurons to SNARE complex formation and axon branching in populations of cultured neurons. This protocol takes advantage of established biochemical approaches to assay levels of endogenous SNARE complexes and Total Internal Reflection Fluorescence (TIRF) microscopy of cortical neurons expressing VAMP2 tagged with a pH-sensitive GFP (VAMP2-pHlourin) to identify netrin-1 dependent changes in exocytic activity in individual neurons. To elucidate the timing of netrin-1-dependent branching, time-lapse differential interference contrast (DIC) microscopy of single neurons over the order of hours is utilized. Fixed cell immunofluorescence paired with botulinum neurotoxins that cleave SNARE machinery and block exocytosis demonstrates that netrin-1 dependent axon branching requires SNARE-mediated exocytic activity.

Light microscopy techniques coupled with biochemical assays elucidate the involvement of SNARE-mediated exocytosis in netrin-dependent axon branching. This combination of techniques permits identification of molecular mechanisms controlling axon branching and cell shape change.

During neural development, growing axons extend to multiple synaptic partners by elaborating axonal branches. Axon branching is promoted by extracellular ...

Microglia as a Surrogate Biosensor to Determine Nanoparticle Neurotoxicity

Nanoparticles found in air pollutants can alter neurotransmitter profiles, increase neuroinflammation, and alter brain function. Therefore, the assay described here will aid in elucidating the role of microglia in neuroinflammation and neurodegenerative diseases. The use of microglia, resident immune cells of the brain, as a surrogate biosensor provides novel insight into how inflammatory responses mediate neuronal insults. Here, we utilize an immortalized murine microglial cell line, designated BV2, and describe a method for nanoparticle exposure using silver nanoparticles (AgNPs) as a standard. We describe how to expose microglia to nanoparticles, how to remove nanoparticles from supernatant, and how to use supernatant from activated microglia to determine toxicity, using hypothalamic cell survival as a measure. Following AgNP exposure, BV2 microglial activation was validated using a tumor necrosis factor alpha (TNF-&#945;) enzyme linked immunosorbent assay (ELISA). The supernatant was filtered to remove the AgNP and to allow cytokines and other secreted factors to remain in the conditioned media. Hypothalamic cells were then exposed to supernatant from AgNP activated microglia and survival of neurons was determined using a resazurin-based fluorescent assay. This technique is useful for utilizing microglia as a surrogate biomarker of neuroinflammation and determining the effect of neuroinflammation on other cell types.

Microglia (immune cells of the brain), are used as a surrogate biosensor to determine how nanoparticles influence neurotoxicity. We describe a series of experiments designed to assay microglial response to nanoparticles and exposure of hypothalamic neurons to supernatant from activated microglia to determine neurotoxicity.

Nanoparticles found in air pollutants can alter neurotransmitter profiles, increase neuroinflammation, and alter brain function. Therefore, the assay ...

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

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

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

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

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

Organotypic Hippocampal Slice Cultures As a Model to Study Neuroprotection and Invasiveness of Tumor Cells

In organotypic hippocampal slice cultures (OHSC), the morphological and functional characteristics of both neurons and glial cells are well preserved. This model is suitable for addressing different research questions that involve studies on neuroprotection, electrophysiological experiments on neurons, neuronal networks or tumor invasion. The hippocampal architecture and neuronal activity in multisynaptic circuits are well conserved in OHSC, even though the slicing procedure itself initially lesions and leads to formation of a glial scar. The scar formation alters presumably the mechanical properties and diffusive behavior of small molecules, etc. Slices allow the monitoring of time dependent processes after brain injury without animal surgery, and studies on interactions between various brain-derived cell types, namely astrocytes, microglia and neurons under both physiological and pathological conditions. An ambivalent aspect of this model is the absence of blood flow and immune blood cells. During the progression of the neuronal injury, migrating immune cells from the blood play an important role. As those cells are missing in slices, the intrinsic processes in the culture may be observed without external interference. Moreover, in OHSC the composition of the medium-external environment is precisely controlled. A further advantage of this method is the lower number of sacrificed animals compared to standard preparations. Several OHSC can be obtained from one animal making simultaneous studies with multiple treatments in one animal possible. For these reasons, OHSC are well suited to analyze the effects of new protective therapeutics after tissue damage or during tumor invasion. 
The protocol presented here describes a preparation method of OHSC that allows generating highly reproducible, well preserved slices that can be used for a variety of experimental research, like neuroprotection or tumor invasion studies.

Organotypic hippocampal slice cultures (OHSC) represent an in vitro model that simulates the in vivo situation very well. Here we describe a vibratome-based improved slicing protocol to obtain high quality slices for use in assessing the neuroprotective potential of novel substances or the biological behavior of tumor cells.

In organotypic hippocampal slice cultures (OHSC), the morphological and functional characteristics of both neurons and glial cells are well preserved. ...