Supported by grants from the American Parkinson Disease Association (APDA) and NIH R01NS115809-01 to RS. We thank the Texas A&#38;M Institute for Genomic Medicine (TIGM) for providing timed pregnant mice to generate primary dopaminergic cultures.

<ol>
	<li>Marras, C., 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=Prevalence+of+Parkinson's+disease+across+North+America.">Prevalence of Parkinson's disease across North America.</a> NPJ Parkinson's Disease. 4, 21 (2018).</li><li>Poewe, 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=Parkinson+disease.">Parkinson disease.</a> Nature Reviews Disease Primers. 3, 17013 (2017).</li><li>Mehta, A., Prabhakar, M., Kumar, P., Deshmukh, R., Sharma, P. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Excitotoxicity:+bridge+to+various+triggers+in+neurodegenerative+disorders.">Excitotoxicity: bridge to various triggers in neurodegenerative disorders.</a> European Journal of Pharmacology. 698 (1-3), 6-18 (2013).</li><li>Ambrosi, G., Cerri, S., Blandini, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+further+update+on+the+role+of+excitotoxicity+in+the+pathogenesis+of+Parkinson's+disease.">A further update on the role of excitotoxicity in the pathogenesis of Parkinson's disease.</a> Journal of Neural Transmission (Vienna). 121 (8), 849-859 (2014).</li><li>Dong, X. X., Wang, Y., Qin, Z. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+mechanisms+of+excitotoxicity+and+their+relevance+to+pathogenesis+of+neurodegenerative+diseases.">Molecular mechanisms of excitotoxicity and their relevance to pathogenesis of neurodegenerative diseases.</a> Acta Pharmaceutica Sinica B. 30 (4), 379-387 (2009).</li><li>Vieira, M., 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=Excitotoxicity+through+Ca2+-permeable+AMPA+receptors+requires+Ca2+-dependent+JNK+activation.">Excitotoxicity through Ca2+-permeable AMPA receptors requires Ca2+-dependent JNK activation.</a> Neurobiology of Disease. 40 (3), 645-655 (2010).</li><li>Sebe, J. 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=Ca(2+)-Permeable+AMPARs+Mediate+Glutamatergic+Transmission+and+Excitotoxic+Damage+at+the+Hair+Cell+Ribbon+Synapse.">Ca(2+)-Permeable AMPARs Mediate Glutamatergic Transmission and Excitotoxic Damage at the Hair Cell Ribbon Synapse.</a> Journal of Neuroscience. 37 (25), 6162-6175 (2017).</li><li>Brickley, S. G., Farrant, M., Swanson, G. T., Cull-Candy, S. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=CNQX+increases+GABA-mediated+synaptic+transmission+in+the+cerebellum+by+an+AMPA/kainate+receptor-independent+mechanism.">CNQX increases GABA-mediated synaptic transmission in the cerebellum by an AMPA/kainate receptor-independent mechanism.</a> Neuropharmacology. 41 (6), 730-736 (2001).</li><li>Srinivasan, 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=Smoking-Relevant+Nicotine+Concentration+Attenuates+the+Unfolded+Protein+Response+in+Dopaminergic+Neurons.">Smoking-Relevant Nicotine Concentration Attenuates the Unfolded Protein Response in Dopaminergic Neurons.</a> Journal of Neuroscience. 36 (1), 65-79 (2016).</li><li>Henley, B. M., 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=Reliable+Identification+of+Living+Dopaminergic+Neurons+in+Midbrain+Cultures+Using+RNA+Sequencing+and+TH-promoter-driven+eGFP+Expression.">Reliable Identification of Living Dopaminergic Neurons in Midbrain Cultures Using RNA Sequencing and TH-promoter-driven eGFP Expression.</a> Journal of Visualized Experiments. (120), e54981 (2017).</li><li>Douhou, A., Troadec, J. D., Ruberg, M., Raisman-Vozari, R., Michel, P. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Survival+promotion+of+mesencephalic+dopaminergic+neurons+by+depolarizing+concentrations+of+K++requires+concurrent+inactivation+of+NMDA+or+AMPA/kainate+receptors.">Survival promotion of mesencephalic dopaminergic neurons by depolarizing concentrations of K+ requires concurrent inactivation of NMDA or AMPA/kainate receptors.</a> Journal of Neurochemistry. 78 (1), 163-174 (2001).</li><li>Lavaur, 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=The+noble+gas+xenon+provides+protection+and+trophic+stimulation+to+midbrain+dopamine+neurons.">The noble gas xenon provides protection and trophic stimulation to midbrain dopamine neurons.</a> Journal of Neurochemistry. 142 (1), 14-28 (2017).</li><li>Kritis, A. A., Stamoula, E. G., Paniskaki, K. A., Vavilis, T. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Researching+glutamate+-+induced+cytotoxicity+in+different+cell+lines:+a+comparative/collective+analysis/study.">Researching glutamate - induced cytotoxicity in different cell lines: a comparative/collective analysis/study.</a> Frontiers in Cellular Neuroscience. 9, 91 (2015).</li><li>Gupta, K., Hardingham, G. E., Chandran, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=NMDA+receptor-dependent+glutamate+excitotoxicity+in+human+embryonic+stem+cell-derived+neurons.">NMDA receptor-dependent glutamate excitotoxicity in human embryonic stem cell-derived neurons.</a> Neuroscience Letters. 543, 95-100 (2013).</li><li>Surmeier, D. J., Obeso, J. A., Halliday, G. 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The authors have nothing to disclose.

We describe a long-term primary ventral mesencephalic (VM) cell culture system for high-content analysis of glutamate-mediated apoptosis in neurons. Studies have employed primary midbrain dopaminergic cultures to elucidate excitotoxic mechanisms in the context of PD models11,12. In this study, we employ a combinatorial approach using Genetically Encoded Calcium Indicators (GECIs) to measure Ca2+ activity and further associate this activity with downstream molecular changes, such as initiation of apoptotic signaling cascades4. The method has multiple advantages to other similar cell culture systems. As we have particular interest in excitotoxicity within the context of Parkinson&#8217;s disease, using primary VM cell cultures is ideal. By using different field relocation techniques, such as gridded coverslips or a motorized XY microscope stage combined with TH immunostaining, we can directly study the cell type specific effects of glutamate-mediated apoptosis in ventral midbrain neurons. Additionally, the 3-week cell culture model allows for neurons to develop their full, mature molecular profile, reflecting adult DA neurons9. Previous methods have mainly focused on molecular changes following glutamate-mediated excitotoxicity13,14. The model is unique in its ability to correlate acute changes in neuronal physiology with downstream molecular events in identified cell types. One limitation of the primary culture model is that the dissection technique captures the entire ventral midbrain, including DA and GABAergic neurons as well as neurons from the SNc and VTA. Evidence now suggests that DA neurons of the SNc have selective vulnerability to calcium and eventual cell death compared to DA neurons of the neighboring VTA15. Unfortunately, differentiating SNc from VTA neurons in embryonic cultures has proven difficult with few anatomical landmarks to define these structures in the embryonic brain.
We demonstrate that the primary culture technique allows for quantification of heterogenous spontaneous Ca2+ activity (Figure 1). Therefore, this is an ideal cell culture system model to study tonically active cells, such as pacemaking dopaminergic neurons of the midbrain, neocortical neurons, and GABAergic neurons of the suprachiasmatic nucleus (SCN)16,17. In most applications, Ca2+ imaging does not achieve the same temporal resolution as electrophysiology. Therefore, it is likely that a single Ca2+ event is analogous to a burst of neuronal action potentials. This can be interpreted to mean that Ca2+ imaging allows for relatively accurate measures of abnormal bursting activity in pacemaking cells and is therefore appropriate for a high content screen of Ca2+-mediated excitotoxic cell death.
To achieve and maintain spontaneous Ca2+ activity, it is important to address two key points in the protocol. First is the plating density of the cells following dissection. For primary VM neurons, previous studies have used around 100,000 cells/cm2 9,10. We have adapted the protocol to plate a density of 200,000 cells/cm2, which creates a heterogenous range of spontaneous activity and increases the number of dopaminergic VM neurons present on each coverslip. Since different pacemaking neurons have distinct firing properties16, the plating density needs to be customized to the cell type being studied and optimized in order to achieve ideal levels of spontaneous activity. Second is the incubation time following viral infection of AAVs. Like plating density, this will be dependent on the specific context of the research question and type of AAV being used. For the specific AAV used here, 5 days of incubation following viral infection is ideal to achieve the desired protein expression levels, which allows for dynamic changes in GCaMP fluorescence in order to record Ca2+ activity. Many factors determine how quickly and efficiently an AAV will express its cargo, much of which is outside the scope of this method, but briefly, it is important to consider promoter activity and the rate at which the cargo protein matures and folds.
Another advantage of the method is that it allows for considerable flexibility in format, expression vectors, use of imaging equipment, and the range of scientific questions that can be addressed. In addition, the method enables inquiry into a wide range of specific questions that surround glutamate-mediated excitotoxicity in PD, and other models of nervous system dysfunction. For example, glutamate-mediated excitotoxicity involves multiple receptors and signaling cascades5. By using the method, and as demonstrated with the AMPAR blocker, NBQX in Figure 1, it is possible to dissect out specific components of the excitotoxic glutamate response at a physiological and molecular level. Conceivably, a similar approach using inhibitors of second messenger systems could be used to determine their contribution to excitotoxicity. Additionally, the AAVs used here could be adapted to express GECIs&#160;with cell-specific promoters or AAV-expressed optogenetic sensors that could be used to measure other parameters such as neurotransmitter release.
Apart from primary embryonic dissections and confocal imaging, much of the protocol uses basic laboratory skills that do not require specialized training. Therefore, the limitations to the model include the difficulty of the embryonic dissection technique, the length of time the cells must be cultured to reach maturity, and access to a confocal microscope, or similar imaging apparatus. The many benefits and flexibility of the method outweighs these limitations, making this an ideal model to study the role glutamate-mediated excitotoxicity in nervous system disorders. Finally, this model could be an effective tool to screen novel compounds for anti-apoptotic effects and their ability to preserve DA neuron health.

Parkinson&#8217;s Disease (PD) is the second most common neurodegenerative disorder worldwide, with no known cure. Estimates suggest that PD prevalence will continue to increase and is projected to surpass 1 million diagnoses by the year 2030 in the United States alone1. With few effective treatments currently available to combat PD, there is a pressing need to develop more effective therapies. PD is characterized by a rapid and progressive loss of midbrain dopamine (DA) neurons2. The mechanisms that underlie neurodegeneration in PD are poorly understood. Evidence suggests a likely convergence of multiple mechanisms, such as oxidative stress and&#160;mitochondrial dysfunction, etc. that contribute to the initiation of apoptotic signaling cascades and eventual cell death3.
One such convergent mechanism, glutamate-mediated excitotoxicity has been implicated in multiple neurodegenerative diseases, including PD4. While glutamate-mediated excitotoxicity is thought to work mainly through stimulation of NMDA receptors via an excessive increase in intracellular Ca2+ concentration and eventual initiation of apoptosis, Ca2+-permeable AMPA receptors have also been implicated in the excitotoxic response5,6,7. Therefore, it is of interest to determine the contribution of AMPA receptors to glutamate-mediated apoptosis within a PD model. This can be achieved using NBQX, an AMPA and kainate blocker, which at micromolar concentrations is selective for AMPA&#160;receptors8. Glutamate-mediated excitotoxicity and apoptotic signaling cascades are an ideal downstream target to measure the extent of cell death, and a potential target for therapeutic intervention. Therefore, developing a high-content method for assessing glutamate-mediated modulation of calcium activity and associated downstream signaling in primary ventral mesencephalic (VM) neurons would be valuable for screening novel treatment methods on their ability to preserve neuronal health.
Here, we have developed a protocol in which we express the genetically encoded calcium indicator (GECI), GCaMP6f, using AAV2/5 with the human synapsin (hSyn) promotor to measure the Ca2+ activity of mouse VM primary neurons in response to glutamate application which can be measured at the physiological and molecular level. This high-content screening can be adapted for discovering pharmaceuticals or treatments that modulate Ca2+ activity to preserve the health of VM neurons. We propose that this primary culture model is an effective way to screen for novel PD interventions, based on their ability to preserve the health of VM neurons and mitigate the progression of PD.

<table>
	<tbody>
		<tr>
			<td>10% Formalin/PBS</td>
			<td>VWR</td>
			<td>100496-506</td>
			<td></td>
		</tr>
		<tr>
			<td>10X NA 0.3 water-immersion objective</td>
			<td>Olympus</td>
			<td>UMPLFLN10XW</td>
			<td></td>
		</tr>
		<tr>
			<td>12 mm circular cover glass No. 1</td>
			<td>Phenix Research Products</td>
			<td>MS20-121</td>
			<td></td>
		</tr>
		<tr>
			<td>20X NA 0.85 oil-immersion objective</td>
			<td>Olympus</td>
			<td>UPLSAPO20XO</td>
			<td></td>
		</tr>
		<tr>
			<td>35 mm uncoated plastic cell culture dishes</td>
			<td>VWR</td>
			<td>25382-348</td>
			<td></td>
		</tr>
		<tr>
			<td>40X NA 0.3 water-immersion objective</td>
			<td>Olympus</td>
			<td>LUMPLFLN40XW</td>
			<td></td>
		</tr>
		<tr>
			<td>60X NA 1.35 oil-immersion objective</td>
			<td>Olympus</td>
			<td>UPLSAPO60XO</td>
			<td></td>
		</tr>
		<tr>
			<td>Ampicillin (sodium)</td>
			<td>Gold Bio</td>
			<td>A-301-25</td>
			<td></td>
		</tr>
		<tr>
			<td>B-27 supplement</td>
			<td>ThermoFisher</td>
			<td>17504044</td>
			<td>50x stock</td>
		</tr>
		<tr>
			<td>Binolcular Microscope</td>
			<td>Kent Scientific</td>
			<td>KSCXTS-1121</td>
			<td></td>
		</tr>
		<tr>
			<td>Bovine serum albumin (BSA)</td>
			<td>Sigma-Aldrich</td>
			<td>A7030</td>
			<td></td>
		</tr>
		<tr>
			<td>Calcium Chloride (CaCl2), anhydrous</td>
			<td>Sigma-Aldrich</td>
			<td>746495</td>
			<td></td>
		</tr>
		<tr>
			<td>Chicken polyclonal anti-Tyrosine Hydroxylase</td>
			<td>Abcam</td>
			<td>ab76442</td>
			<td></td>
		</tr>
		<tr>
			<td>Deoxyribonuclease I (DNase)</td>
			<td>Sigma-Aldrich</td>
			<td>DN25</td>
			<td></td>
		</tr>
		<tr>
			<td>D-glucose, andydrous</td>
			<td>Sigma-Aldrich</td>
			<td>RDD016</td>
			<td></td>
		</tr>
		<tr>
			<td>DMEM + GlutaMAX medium</td>
			<td>ThermoFisher</td>
			<td>10569010</td>
			<td>500 mL</td>
		</tr>
		<tr>
			<td>Equine serum</td>
			<td>ThermoFisher</td>
			<td>26050088</td>
			<td>heat-inactivated</td>
		</tr>
		<tr>
			<td>Fiber Optic Illuminator, 100V</td>
			<td>Kent Scientific</td>
			<td>KSC5410</td>
			<td></td>
		</tr>
		<tr>
			<td>Filter System, PES 22UM 250ML</td>
			<td>VWR</td>
			<td>28199-764</td>
			<td></td>
		</tr>
		<tr>
			<td>Fluoview 1000 confocal microscope</td>
			<td>Olympus</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Fluoview 1200 confocal microscope</td>
			<td>Olympus</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>GlutaMAX supplement</td>
			<td>ThermoFisher</td>
			<td>35050061</td>
			<td></td>
		</tr>
		<tr>
			<td>Goat polyclonal anti-chicken Alexa Fluor 594</td>
			<td>Abcam</td>
			<td>ab150176</td>
			<td></td>
		</tr>
		<tr>
			<td>Goat polyclonal anti-rabbit Alexa Fluor 594</td>
			<td>Abcam</td>
			<td>ab150077</td>
			<td></td>
		</tr>
		<tr>
			<td>Hanks-balanced Salt Solution (HBSS) 1x</td>
			<td>ThermoFisher</td>
			<td>14175095</td>
			<td>500 mL</td>
		</tr>
		<tr>
			<td>HEPES</td>
			<td>VWR</td>
			<td>101170-478</td>
			<td></td>
		</tr>
		<tr>
			<td>HeraCell 150 CO2 incubator</td>
			<td>Heraeus (ThermoFisher)</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>ImageJ v1.52e</td>
			<td>NIH</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>IRIS-Fine Scissors (Round Type)-S/S Str/31*8mm/13cm</td>
			<td>RWD</td>
			<td>S12014-13</td>
			<td></td>
		</tr>
		<tr>
			<td>Kanamycin monosulfate</td>
			<td>Gold Bio</td>
			<td>K-120-25</td>
			<td></td>
		</tr>
		<tr>
			<td>Laminin</td>
			<td>Sigma-Aldrich</td>
			<td>L2020</td>
			<td></td>
		</tr>
		<tr>
			<td>L-Ascorbic acid</td>
			<td>Sigma-Aldrich</td>
			<td>A7506</td>
			<td></td>
		</tr>
		<tr>
			<td>L-glutamic acid</td>
			<td>VWR</td>
			<td>97061-634</td>
			<td></td>
		</tr>
		<tr>
			<td>Magnesium Chloride (MgCl2), andydrous</td>
			<td>Sigma-Aldrich</td>
			<td>M8266</td>
			<td></td>
		</tr>
		<tr>
			<td>MPII Mini-Peristaltic Pump, 115/230 VAC, 50/60 Hz</td>
			<td>Harvard Apparatus</td>
			<td>70-2027</td>
			<td></td>
		</tr>
		<tr>
			<td>MULLER Micro Forceps-Str, 0.15mm Tips, 11cm</td>
			<td>RWD</td>
			<td>F11014-11</td>
			<td></td>
		</tr>
		<tr>
			<td>NBQX</td>
			<td>Hello Bio</td>
			<td>HB0443</td>
			<td></td>
		</tr>
		<tr>
			<td>Neurobasal medium</td>
			<td>ThermoFisher</td>
			<td>21103049</td>
			<td>500 mL</td>
		</tr>
		<tr>
			<td>Normal goat serum (NGS)</td>
			<td>Abcam</td>
			<td>ab7481</td>
			<td></td>
		</tr>
		<tr>
			<td>Origin 2020</td>
			<td>OriginLab</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>pAAV.Syn.GCaMP6f.WPRE.SV40</td>
			<td>Addgene</td>
			<td>100837-AAV1</td>
			<td>Titer: 1.00E+13 gc/ml</td>
		</tr>
		<tr>
			<td>Papain</td>
			<td>Worthington Biomedical Corporation</td>
			<td>LS003126</td>
			<td></td>
		</tr>
		<tr>
			<td>Penicillin streptomycin</td>
			<td>ThermoFisher</td>
			<td>15140122</td>
			<td>10,000 U/mL</td>
		</tr>
		<tr>
			<td>Phosphate-buffered saline (PBS) 1x</td>
			<td>ThermoFisher</td>
			<td>10010049</td>
			<td>500 mL</td>
		</tr>
		<tr>
			<td>Poly-L-lysine</td>
			<td>Sigma-Aldrich</td>
			<td>P4832</td>
			<td></td>
		</tr>
		<tr>
			<td>Poly-L-ornithine</td>
			<td>Sigma-Aldrich</td>
			<td>P4957</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium Chloride (KCl), anhydrous</td>
			<td>Sigma-Aldrich</td>
			<td>746436</td>
			<td></td>
		</tr>
		<tr>
			<td>Pump Head Tubing Pieces For MPII</td>
			<td>Harvard Apparatus</td>
			<td>55-4148</td>
			<td></td>
		</tr>
		<tr>
			<td>Rabbit monoclonal anti-caspase-3</td>
			<td>Abcam</td>
			<td>ab32351</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Chloride (NaCl), anhydrous</td>
			<td>Sigma-Aldrich</td>
			<td>746398</td>
			<td></td>
		</tr>
		<tr>
			<td>Sucrose</td>
			<td>Sigma-Aldrich</td>
			<td>S7903</td>
			<td>BioXtra, &#8805;99.5% (GC)</td>
		</tr>
		<tr>
			<td>Time-pregnant female C57BL/6 mice</td>
			<td>Texas A&#38;M Institue for Genomic Medicine</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Triton X-100</td>
			<td>Sigma-Aldrich</td>
			<td>X100</td>
			<td>500 mL</td>
		</tr>
		<tr>
			<td>Wide-bore blue pipette tips P1000</td>
			<td>VWR</td>
			<td>83007-380</td>
			<td></td>
		</tr>
	</tbody>
</table>

quantifying spontaneous ca2+ fluxes and their downstream effects in primary mouse midbrain neurons

Parkinson&#8217;s disease (PD) is a devastating neurodegenerative disorder caused by the degeneration of dopaminergic (DA) neurons. Excessive Ca2+ influx due to the abnormal activation of glutamate receptors results in DA excitotoxicity and has been identified as an important mechanism for DA neuron loss. In this study, we isolate, dissociate, and culture midbrain neurons from the mouse ventral mesencephalon (VM) of ED14 mouse embryos. We then infect the long-term primary mouse midbrain cultures with an adeno-associated virus (AAV) expressing a genetically encoded calcium indicator, GCaMP6f under control of the human neuron-specific synapsin promoter, hSyn. Using live confocal imaging, we show that cultured mouse midbrain neurons display spontaneous Ca2+ fluxes detected by AAV-hSyn-GCaMP6f. Bath application of glutamate to midbrain cultures causes abnormal elevations in intracellular Ca2+ within neurons and this is accompanied by caspase-3 activation in DA neurons, as demonstrated by immunostaining. The techniques to identify glutamate-mediated apoptosis in primary mouse DA neurons have important applications for the high content screening of drugs that preserve DA neuron health.

Following initial culturing of cells, we treated VM culture dishes at 14 DIV with 1 &#181;L of AAV hSyn-GCaMP6f and allowed for 5 days of viral expression. On the day of imaging HEPES recording buffer was prepared fresh. We used two conditions; in one condition 20 &#181;M glutamate was applied for 10 min, while in the other condition 5 min of 10 &#181;M NBQX application preceded a 10 min co-application of 10 &#181;M NBQX + 20 &#181;M glutamate. In both conditions, we observed heterogenous and spontaneous changes in GCaMP6f fluorescence, which indicate spontaneous Ca2+ fluxes, as shown in the representative traces (Figure 1A,B, Supplemental Movie 1-2). Application of 20 &#181;M glutamate generated a robust and sustained Ca2+ response in both spontaneously active and quiescent neurons (Figure 1A, Supplemental Movie 1). Application of 10 &#181;M NBQX reduced spontaneous activity, and partially blocked the glutamate response (Figure 1B, Supplemental Movie 2). The extent to which glutamate application stimulated a Ca2+ response in each condition was quantified using area under the curve, peak amplitude, and latency to respond. Both area under the curve and peak amplitude were similar for both the glutamate and NBQX + glutamate treated conditions (Figure 1C), while latency to response was significantly increased in the NBQX + glutamate condition (Figure 2A,B). In addition to quantifying the Ca2+ response to glutamate treatment, we fixed and stained samples with an anti-caspase-3 antibody as a measure of glutamate-mediated apoptosis. We observed a range of caspase-3 activation across the conditions (Figure 3A,B). Caspase-3 activation was quantified by measuring area and mean caspase-3 intensity. When compared to untreated control cells, the average area of cells with caspase-3 activation under glutamate and NBQX + glutamate conditions trended towards significance (Figure 3B). Mean caspase-3 intensity was significantly higher in the glutamate and NBQX + glutamate conditions as compared to untreated controls (Figure 3B). Together, these results demonstrate a high-content framework in which apoptosis of neurons can be measured by quantifying Ca2+ responses to excitotoxic agents and followed up with an analysis of downstream apoptotic events such as caspase-3 activation in the same set of cultures.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/61481/61481fig01.jpg" /> 
Figure 1: Cultured ventral mesencephalic neurons display spontaneous Ca2+ activity and are robustly stimulated by glutamate application.&#160;(A) Representative traces of spontaneous Ca2+ activity in VM neurons and their response to 20 &#181;M Glutamate application. (B) Representative traces of spontaneous Ca2+ activity in VM neurons and their response to 10 &#181;M NBQX + 20 &#181;M Glutamate application. (C) Population data showing area under the curve and peak amplitude of Ca2+ traces. <a href="https://www.jove.com/files/ftp_upload/61481/61481fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/61481/61481fig02v3.jpg" /> 
Figure 2: AMPAR blockade with NBQX delays response to glutamate application in cultured ventral mesencephalic neurons.&#160;(A) Representative Ca2+ traces of glutamate (gray) and NBQX + glutamate (blue) evoked responses. Average Ca2+ traces of glutamate (black) and NBQX + glutamate (red) are shown overlaid. (B) Population data showing latency to response for glutamate and NBQX + glutamate evoked responses. Percent change between glutamate and NBQX + glutamate conditions is displayed in the right panel. <a href="https://www.jove.com/files/ftp_upload/61481/61481fig02v3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/61481/61481fig03v3.jpg" /> 
Figure 3: Glutamate application increases caspase-3 expression in tyrosine hydroxylase (TH) positive ventral mesencephalic neurons.&#160;(A) Representative confocal images of VM cultures immunostained for caspase-3 (green) and TH (red), scale bar = 10 &#181;m. (B) Population data showing DA neuron area and mean gray value of caspase-3 expression in each condition. <a href="https://www.jove.com/files/ftp_upload/61481/61481fig03v3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Supplementary Movie 1: Spontaneous Ca2+ activity and response to glutamate application. 
Spontaneous Ca2+ fluxes in the presence of HEPES recording buffer (0-300 s) followed by application of 20 &#181;M glutamate (301-600 s). Scale bar = 50 &#181;m. <a href="https://cloudflare.jove.com/files/ftp_upload/61481/Supplementary_Movie 1_glutamate_ver_2.avi" target="_blank">Please click here to download this video.</a>
Supplementary Movie 2: Spontaneous Ca2+ activity and response to NBQX + glutamate application. 
Spontaneous Ca2+ fluxes in the presence of HEPES recording buffer (0-300 s) followed by application of 10 &#181;M NBQX (301-600 s), and 10 &#181;M NBQX + 20 &#181;M glutamate (601-900 s). Scale bar = 50 &#181;m. <a href="https://cloudflare.jove.com/files/ftp_upload/61481/Supplementary_Movie_2_NBQX_glut.avi" target="_blank">Please click here to download this video.</a>

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Quantifying Spontaneous Ca2+ Fluxes and their Downstream Effects in Primary Mouse Midbrain Neurons

Here we present a protocol to measure in vitro Ca2+ fluxes in midbrain neurons and their downstream effects on caspase-3 using primary mouse midbrain cultures. This model can be employed to study pathophysiologic changes related to abnormal Ca2+ activity in midbrain neurons, and to screen novel therapeutics for anti-apoptotic properties.

Quantifying Spontaneous Ca2+ Fluxes and their Downstream Effects in Primary Mouse Midbrain Neurons

Parkinson&#8217;s disease (PD) is a devastating neurodegenerative disorder caused by the degeneration of dopaminergic (DA) neurons. Excessive Ca2+ influx ...

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Neuroscience

6.2K Views.  Texas A&M University Health Science Center, College of Medicine. Here we present a protocol to measure in vitro Ca2+ fluxes in midbrain neurons and their downstream effects on caspase-3 using primary mouse midbrain cultures. This model can be employed to study pathophysiologic changes related to abnormal Ca2+ activity in midbrain neurons, and to screen novel therapeutics for anti-apoptotic properties.

Video: Quantifying Spontaneous Ca2+ Fluxes and their Downstream Effects in Primary Mouse Midbrain Neurons

Nucleofection and Primary Culture of Embryonic Mouse Hippocampal and Cortical Neurons

Hippocampal and cortical neurons have been used extensively to study central nervous system (CNS) neuronal polarization, axon/dendrite outgrowth, and synapse formation and function. An advantage of culturing these neurons is that they readily polarize, forming distinctive axons and dendrites, on a two dimensional substrate at very low densities. This property has made them extremely useful for determining many aspects of neuronal development. Furthermore, by providing glial conditioning for these neurons they will continue to develop, forming functional synaptic connections and surviving for several months in culture. In this protocol we outline a technique to dissect, culture and transfect embryonic mouse hippocampal and cortical neurons. Transfection is accomplished by electroporating DNA into the neurons before plating via nucleofection. This protocol has the advantage of expressing fluorescently-tagged fusion proteins early in development (~4-8hrs after plating) to study the dynamics and function of proteins during polarization, axon outgrowth and branching. We have also discovered that this single transfection before plating maintains fluorescently-tagged fusion protein expression at levels appropriate for imaging throughout the lifetime of the neuron (&gt; 2 months in culture). Thus, this methodology is useful for studying protein localization and function throughout CNS development with little or no disruption of neuronal function.

This protocol outlines the steps required to dissect, transfect via electroporation and culture mouse hippocampal and cortical neurons. Short-term cultures may be used for studies of axon outgrowth and guidance, while long-term cultures can be used for studies of synaptogenesis and dendritic spine analysis.

Hippocampal and cortical neurons have been used extensively to study central nervous system (CNS) neuronal polarization, axon/dendrite outgrowth, and ...

Imaging pHluorin-tagged Receptor Insertion to the Plasma Membrane in Primary Cultured Mouse Neurons

A better understanding of the mechanisms governing receptor trafficking between the plasma membrane (PM) and intracellular compartments requires an experimental approach with excellent spatial and temporal resolutions. Moreover, such an approach must also have the ability to distinguish receptors localized on the PM from those in intracellular compartments. Most importantly, detecting receptors in a single vesicle requires outstanding detection sensitivity, since each vesicle carries only a small number of receptors. Standard approaches for examining receptor trafficking include surface biotinylation followed by biochemical detection, which lacks both the necessary spatial and temporal resolutions; and fluorescence microscopy examination of immunolabeled surface receptors, which requires chemical fixation of cells and therefore lacks sufficient temporal resolution1-6 . To overcome these limitations, we and others have developed and employed a new strategy that enables visualization of the dynamic insertion of receptors into the PM with excellent spatial and temporal resolutions 7-17 . The approach includes tagging of a pH-sensitive GFP, the superecliptic pHluorin 18, to the N-terminal extracellular domain of the receptors. Superecliptic pHluorin has the unique property of being fluorescent at neutral pH and non-fluorescent at acidic pH (pH &lt; 6.0). Therefore, the tagged receptors are non-fluorescent when within the acidic lumen of intracellular trafficking vesicles or endosomal compartments, and they become readily visualized only when exposed to the extracellular neutral pH environment, on the outer surface of the PM. Our strategy consequently allows us to distinguish PM surface receptors from those within intracellular trafficking vesicles. To attain sufficient spatial and temporal resolutions, as well as the sensitivity required to study dynamic trafficking of receptors, we employed total internal reflection fluorescent microscopy (TIRFM), which enabled us to achieve the optimal spatial resolution of optical imaging (~170 nm), the temporal resolution of video-rate microscopy (30 frames/sec), and the sensitivity to detect fluorescence of a single GFP molecule. By imaging pHluorin-tagged receptors under TIRFM, we were able to directly visualize individual receptor insertion events into the PM in cultured neurons. This imaging approach can potentially be applied to any membrane protein with an extracellular domain that could be labeled with superecliptic pHluorin, and will allow dissection of the key detailed mechanisms governing insertion of different membrane proteins (receptors, ion channels, transporters, etc.) to the PM.

By tagging the extracellular domains of membrane receptors with superecliptic pHluorin, and by imaging these fusion receptors in cultured mouse neurons, we can directly visualize individual vesicular insertion events of the receptors to the plasma membrane. This technique will be instrumental in elucidating the molecular mechanisms governing receptor insertion to the plasma membrane.

A better understanding of the mechanisms governing receptor trafficking between the plasma membrane (PM) and intracellular compartments requires an ...

Primary Culture of Mouse Dopaminergic Neurons

Dopaminergic neurons represent less than 1% of the total number of neurons in the brain. This low amount of neurons regulates important brain functions such as motor control, motivation, and working memory. Nigrostriatal dopaminergic neurons selectively degenerate in Parkinson&#39;s disease (PD). This progressive neuronal loss is unequivocally associated with the motors symptoms of the pathology (bradykinesia, resting tremor, and muscular rigidity). The main agent responsible of dopaminergic neuron degeneration is still unknown. However, these neurons appear to be extremely vulnerable in diverse conditions. Primary cultures constitute one of the most relevant models to investigate properties and characteristics of dopaminergic neurons. These cultures can be submitted to various stress agents that mimic PD pathology and to neuroprotective compounds in order to stop or slow down neuronal degeneration. The numerous transgenic mouse models of PD that have been generated during the last decade further increased the interest of researchers for dopaminergic neuron cultures. Here, the video protocol focuses on the delicate dissection of embryonic mouse brains. Precise excision of ventral mesencephalon is crucial to obtain neuronal cultures sufficiently rich in dopaminergic cells to allow subsequent studies. This protocol can be realized with embryonic transgenic mice and is suitable for immunofluorescence staining, quantitative PCR, second messenger quantification, or neuronal death/survival assessment.

Dopaminergic neurons play a vital regulatory role in the brain. Their loss is associated with Parkinson's disease. In this video, we show how to generate primary cultures of central dopaminergic neurons from embryonic mouse mesencephalon. Such cultures are useful to study the extreme vulnerability of these neurons to various stresses.

Dopaminergic neurons represent less than 1% of the total number of neurons in the brain. This low amount of neurons regulates important brain functions ...

Environmental Modulations of the Number of Midbrain Dopamine Neurons in Adult Mice

Long-lasting changes in the brain or &#8216;brain plasticity&#8217; underlie adaptive behavior and brain repair following disease or injury. Furthermore, interactions with our environment can induce brain plasticity. Increasingly, research is trying to identify which environments stimulate brain plasticity beneficial for treating brain and behavioral disorders. Two environmental manipulations are described which increase or decrease the number of tyrosine hydroxylase immunopositive (TH+, the rate-limiting enzyme in dopamine (DA) synthesis) neurons in the adult mouse midbrain. The first comprises pairing male and female mice together continuously for 1 week, which increases midbrain TH+ neurons by approximately 12% in males, but decreases midbrain TH+ neurons by approximately 12% in females. The second comprises housing mice continuously for 2 weeks in &#8216;enriched environments&#8217; (EE) containing running wheels, toys, ropes, nesting material, etc., which increases midbrain TH+ neurons by approximately 14% in males. Additionally, a protocol is described for concurrently infusing drugs directly into the midbrain during these environmental manipulations to help identify mechanisms underlying environmentally-induced brain plasticity. For example, EE-induction of more midbrain TH+ neurons is abolished by concurrent blockade of synaptic input onto midbrain neurons. Together, these data indicate that information about the environment is relayed via synaptic input to midbrain neurons to switch on or off expression of &#8216;DA&#8217; genes. Thus, appropriate environmental stimulation, or drug targeting of the underlying mechanisms, might be helpful for treating brain and behavioral disorders associated with imbalances in midbrain DA (e.g. Parkinson&#8217;s disease, attention deficit and hyperactivity disorder, schizophrenia, and drug addiction).

This protocol describes two different environmental manipulations and a concurrent brain infusion protocol to study environmentally-induced brain changes underlying adaptive behavior and brain repair in adult mice.

Long-lasting changes in the brain or &#8216;brain plasticity&#8217; underlie adaptive behavior and brain repair following disease or injury. Furthermore, ...

Fluorescence and Bioluminescence Imaging of Subcellular Ca2+ in Aged Hippocampal Neurons

Susceptibility to neuron cell death associated to neurodegeneration and ischemia are exceedingly increased in the aged brain but mechanisms responsible are badly known. Excitotoxicity, a process believed to contribute to neuron damage induced by both insults, is mediated by activation of glutamate receptors that promotes Ca2+ influx and mitochondrial Ca2+ overload. A substantial change in intracellular Ca2+ homeostasis or remodeling of intracellular Ca2+ homeostasis may favor neuron damage in old neurons. For investigating Ca2+ remodeling in aging we have used live cell imaging in long-term cultures of rat hippocampal neurons that resemble in some aspects aged neurons in vivo. For this end, hippocampal cells are, in first place, freshly dispersed from new born rat hippocampi and plated on poli-D-lysine coated, glass coverslips. Then cultures are kept in controlled media for several days or several weeks for investigating young and old neurons, respectively. Second, cultured neurons are loaded with fura2 and subjected to measurements of cytosolic Ca2+ concentration using digital fluorescence ratio imaging. Third, cultured neurons are transfected with plasmids expressing a tandem of low-affinity aequorin and GFP targeted to mitochondria. After 24 hr, aequorin inside cells is reconstituted with coelenterazine and neurons are subjected to bioluminescence imaging for monitoring of mitochondrial Ca2+ concentration. This three-step procedure allows the monitoring of cytosolic and mitochondrial Ca2+ responses to relevant stimuli as for example the glutamate receptor agonist NMDA and compare whether these and other responses are influenced by aging. This procedure may yield new insights as to how aging influence cytosolic and mitochondrial Ca2+ responses to selected stimuli as well as the testing of selected drugs aimed at preventing neuron cell death in age-related diseases.

Fluorescence and Bioluminescence Imaging of Subcellular Ca2+ in Aged Hippocampal Neurons

Intracellular Ca2+ remodeling in aging may contribute to excitotoxicity and neuron damage, processes mediated by Ca2+ overload. We aimed at investigating Ca2+ remodeling in the aging brain using fluorescence and bioluminescence imaging of cytosolic and mitochondrial Ca2+ in long-term cultures of rat hippocampal neurons, a model of neuronal aging.

Susceptibility to neuron cell death associated to neurodegeneration and ischemia are exceedingly increased in the aged brain but mechanisms responsible ...

Modeling Neuronal Death and Degeneration in Mouse Primary Cerebellar Granule Neurons

Cerebellar granule neurons (CGNs) are a commonly used neuronal model, forming an abundant homogeneous population in the cerebellum. In light of their post-natal development, abundance, and accessibility, CGNs are an ideal model to study neuronal processes, including neuronal development, neuronal migration, and physiological neuronal activity stimulation. In addition, CGN cultures provide an excellent model for studying different modes of cell death including excitotoxicity and apoptosis. Within a week in culture, CGNs express N-methyl-D-aspartate (NMDA) receptors, a specific ionotropic glutamate receptor with many critical functions in neuronal health and disease. The addition of low concentrations of NMDA in conjunction with membrane depolarization to rodent primary CGN cultures has been used to model physiological neuronal activity stimulation while the addition of high concentrations of NMDA can be employed to model excitotoxic neuronal injury. Here, a method of isolation and culturing of CGNs from 6 day old pups as well as genetic manipulation of CGNs by adenoviruses and lentiviruses are described. We also present optimized protocols on how to stimulate NMDA-induced excitotoxicity, low-potassium-induced apoptosis, oxidative stress and DNA damage following transduction of these neurons.

This protocol describes a simple method for isolating and culturing primary mouse cerebral granule neurons (CGNs) from 6-7 day old pups, efficient transduction of CGNs for loss and gain of function studies, and modelling NMDA-induced neuronal excitotoxicity, low-potassium-induced cell death, DNA-damage, and oxidative stress using the same culture model.

Cerebellar granule neurons (CGNs) are a commonly used neuronal model, forming an abundant homogeneous population in the cerebellum. In light of their ...

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 ...

Rapid and Specific Immunomagnetic Isolation of Mouse Primary Oligodendrocytes

The efficient and robust isolation and culture of primary oligodendrocytes (OLs) is a valuable tool for the in vitro study of the development of oligodendroglia as well as the biology of demyelinating diseases such as multiple sclerosis and Pelizaeus-Merzbacher-like disease (PMLD). Here, we present a simple and efficient selection method for the immunomagnetic isolation of stage three O4+ preoligodendrocytes cells from neonatal mice pups. Since immature OL constitute more than 80% of the rodent-brain white matter at postnatal day 7 (P7) this isolation method not only ensures high cellular yield, but also the specific isolation of OLs already committed to the oligodendroglial lineage, decreasing the possibility of isolating contaminating cells such as astrocytes and other cells from the mouse brain. This method is a modification of the techniques reported previously, and provides oligodendrocyte preparation purity above 80% in about 4 h.

We describe the immunomagnetic isolation of primary mouse oligodendrocytes, which allows the rapid and specific isolation of the cells for in vitro culture.

The efficient and robust isolation and culture of primary oligodendrocytes (OLs) is a valuable tool for the in vitro study of the development of ...

Visualizing Axonal Growth Cone Collapse and Early Amyloid &#946; Effects in Cultured Mouse Neurons

Amyloid-&#946; (A&#946;) causes memory impairments in Alzheimer's disease (AD). Although therapeutics have been shown to reduce A&#946; levels in the brains of AD patients, these do not improve memory functions. Since A&#946; aggregates in the brain before the appearance of memory impairments, targeting A&#946; may be inefficient for treating AD patients who already exhibit memory deficits. Therefore, downstream signaling due to A&#946; deposition should be blocked before AD development. A&#946; induces axonal degeneration, leading to the disruption of neuronal networks and memory impairments. Although there are many studies on the mechanisms of A&#946; toxicity, the source of A&#946; toxicity remains unknown. To help identify the source, we propose a novel protocol that uses microscopy, gene transfection, and live cell imaging to investigate early changes caused by A&#946; in axonal growth cones of cultured neurons. This protocol revealed that A&#946; induced clathrin-mediated endocytosis in axonal growth cones followed by growth cone collapse, demonstrating that inhibition of endocytosis prevents A&#946; toxicity. This protocol will be useful in studying the early effects of A&#946; and may lead to more efficient and preventative AD treatment.

Visualizing Axonal Growth Cone Collapse and Early Amyloid &amp;#946; Effects in Cultured Mouse Neurons

Here a protocol to investigate the early effects of amyloid-&#946; (A&#946;) in the brain is presented. This shows that A&#946; induces clathrin-mediated endocytosis and collapse of axonal growth cones. The protocol is useful in studying early effects of A&#946; on axonal growth cones and may facilitate prevention of Alzheimer's disease.

Amyloid-&#946; (A&#946;) causes memory impairments in Alzheimer's disease (AD). Although therapeutics have been shown to reduce A&#946; levels in the ...

Primary Culture of Neurons Isolated from Embryonic Mouse Cerebellum

The use of primary cell cultures has become one of the major tools to study the nervous system in vitro. The ultimate goal of using this simplified model system is to provide a controlled microenvironment and maintain the high survival rate and the natural features of dissociated neuronal and nonneuronal cells as much as possible under in vitro conditions. In this article, we demonstrate a method of isolating primary neurons from the developing mouse cerebellum, placing them in an in vitro environment, establishing their growth, and monitoring their viability and differentiation for several weeks. This method is applicable to embryonic neurons dissociated from cerebellum between embryonic days 12&ndash;18.

Conducting in vitro experiments to reflect in vivo conditions as adequately as possible is not an easy task. The use of primary cell cultures is an important step toward understanding cell biology in a whole organism. The provided protocol outlines how to successfully grow and culture embryonic mouse cerebellar neurons.

The use of primary cell cultures has become one of the major tools to study the nervous system in vitro. The ultimate goal of using this simplified model ...