Name: an antibody feeding approach to study glutamate receptor trafficking in dissociated primary hippocampal cultures
Uploaded: 2019-08-02T15:00:00
Description: Watch this Scientific Journal Video about An Antibody Feeding Approach to Study Glutamate Receptor Trafficking in Dissociated Primary Hippocampal Cultures at JoVE.com

We thank the Northwestern Center for Advanced Microscopy for the use of the Nikon A1 Confocal microscope and their assistance in planning and analyzing the experiments. This research was supported by NIGMS (T32GM008061) (A. M. C.), and NIA (R00AG041225) and a NARSAD Young Investigator Grant from the Brain &#38; Behavior Research Foundation (#24133) (A. S. -C.).

Work pertaining to hippocampal primary culture preparation was reviewed and approved by the Northwestern University Animal Care and Use Committee (protocol #IS00001151).
1. Preparation Before Labeling
<ol>
	<li>Preparation and maintenance of primary hippocampal cultures
	<ol>
		<li>Prepare primary hippocampal cultures at a density of 150,000 cells plated on poly-D-lysine-coated (0.1 mg/mL) 18 mm cover glasses. Excellent guides for dissociated neuronal culture preparation are...

<ol>
	<li>Enns, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Overview+of+protein+trafficking+in+the+secretory+and+endocytic+pathways.">Overview of protein trafficking in the secretory and endocytic pathways.</a> Current Protocols in Cell Biology. , (2001).</li><li>Bedford, F. K., Binder, M. D., Hirokawa, N., Windhorst, U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Encyclopedia of Neuroscience. , 3385-3389 (2009).</li><li>Diering, G. H., Huganir, R. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+AMPA+Receptor+Code+of+Synaptic+Plasticity.">The AMPA Receptor Code of Synaptic Plasticity.</a> Neuron. 100 (2), 314-329 (2018).</li><li>Lussier, M. P., Sanz-Clemente, A., Roche, K. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dynamic+Regulation+of+N-Methyl-d-aspartate+(NMDA)+and+alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic+Acid+(AMPA)+Receptors+by+Posttranslational+Modifications.">Dynamic Regulation of N-Methyl-d-aspartate (NMDA) and alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid (AMPA) Receptors by Posttranslational Modifications.</a> The Journal of Biological Chemistry. 290 (48), 28596-28603 (2015).</li><li>Traynelis, S. F., 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=Glutamate+receptor+ion+channels:+structure,+regulation,+and+function.">Glutamate receptor ion channels: structure, regulation, and function.</a> Pharmacological Reviews. 62 (3), 405-496 (2010).</li><li>Molnar, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Long-term+potentiation+in+cultured+hippocampal+neurons.">Long-term potentiation in cultured hippocampal neurons.</a> Seminars in Cell &amp; Developmental Biology. 22 (5), 506-513 (2011).</li><li>Seibenhener, M. L., Wooten, M. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isolation+and+culture+of+hippocampal+neurons+from+prenatal+mice.">Isolation and culture of hippocampal neurons from prenatal mice.</a> Journal of Visualized Experiments. (65), (2012).</li><li>Nunez, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Primary+Culture+of+Hippocampal+Neurons+from+P0+Newborn+Rats.">Primary Culture of Hippocampal Neurons from P0 Newborn Rats.</a> Journal of Visualized Experiments. (19), (2008).</li><li>Lu, 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=Activation+of+synaptic+NMDA+receptors+induces+membrane+insertion+of+new+AMPA+receptors+and+LTP+in+cultured+hippocampal+neurons.">Activation of synaptic NMDA receptors induces membrane insertion of new AMPA receptors and LTP in cultured hippocampal neurons.</a> Neuron. 29 (1), 243-254 (2001).</li><li>Sanz-Clemente, A., Nicoll, R. A., Roche, K. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Diversity+in+NMDA+Receptor+Composition:+Many+Regulators,+Many+Consequences.">Diversity in NMDA Receptor Composition: Many Regulators, Many Consequences.</a> The Neuroscientist: A Review Journal Bringing Neurobiology, Neurology and Psychiatry. 19 (1), 62-75 (2013).</li><li>Tham, D. K. L., Moukhles, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determining+Cell-surface+Expression+and+Endocytic+Rate+of+Proteins+in+Primary+Astrocyte+Cultures+Using+Biotinylation.">Determining Cell-surface Expression and Endocytic Rate of Proteins in Primary Astrocyte Cultures Using Biotinylation.</a> Journal of Visualized Experiments. (125), (2017).</li><li>Bermejo, M. K., Milenkovic, M., Salahpour, A., Ramsey, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preparation+of+Synaptic+Plasma+Membrane+and+Postsynaptic+Density+Proteins+Using+a+Discontinuous+Sucrose+Gradient.">Preparation of Synaptic Plasma Membrane and Postsynaptic Density Proteins Using a Discontinuous Sucrose Gradient.</a> Journal of Visualized Experiments. (91), e51896 (2014).</li><li>Makino, H., Malinow, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=AMPA+receptor+incorporation+into+synapses+during+LTP:+the+role+of+lateral+movement+and+exocytosis.">AMPA receptor incorporation into synapses during LTP: the role of lateral movement and exocytosis.</a> Neuron. 64 (3), 381-390 (2009).</li><li>Bailey, D. M., Kovtun, O., Rosenthal, S. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Antibody-Conjugated+Single+Quantum+Dot+Tracking+of+Membrane+Neurotransmitter+Transporters+in+Primary+Neuronal+Cultures.">Antibody-Conjugated Single Quantum Dot Tracking of Membrane Neurotransmitter Transporters in Primary Neuronal Cultures.</a> Methods in Molecular Biology. 1570, 165-177 (2017).</li><li>Trussell, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Recording+and+analyzing+synaptic+currents+and+synaptic+potentials.">Recording and analyzing synaptic currents and synaptic potentials.</a> Current Protocols in Neuroscience. Chapter 6, Unit. , (2001).</li><li>Barreto-Chang, O. L., Dolmetsch, R. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Calcium+Imaging+of+Cortical+Neurons+using+Fura-2+AM.">Calcium Imaging of Cortical Neurons using Fura-2 AM.</a> Journal of Visualized Experiments. (23), e1067 (2009).</li></ol>

The interaction between a cell and its environment (e.g., communication with other cells, response to different stimuli, etc.), heavily relies on the correct expression of receptors at the cell surface. The rapid and fine-tuned regulation in surface-expressed receptor content enables proper cellular response to a constantly changing environment. In the particular case of neurons, alterations in the number, localization, and subunit composition of synaptically expressed receptors heavily influences synaptic communication,...

Cells utilize the active process of trafficking to mobilize proteins to specific subcellular localizations and exert strict spatiotemporal regulation over their function1. This process is especially important for transmembrane receptors, as cellular responses to different environmental stimuli rely on intracellular cascades triggered by receptor activation. Cells are able to modify these responses by altering the density, localization, and subunit composition of receptors expressed at the cell surface via receptor subcellular trafficking regulation2. Insertion of newly synthetized receptors into the plasma membrane, along with endocytosis and recycling of existing receptors are examples of trafficking processes that determine the net pool of surface-expressed receptors2. Many molecular mechanisms cooperate to regulate protein trafficking, including protein-protein interactions and posttranslational modifications such as phosphorylation, ubiquitination, or palmitoylation2.
Regulation of receptor trafficking is particularly required in strongly polarized cells with highly specialized structures. The paradigmatic example is the control of neuronal function by regulated trafficking of glutamate receptors (GluRs)3,4. Glutamate, the main excitatory neurotransmitter, binds and activates surface-expressed GluRs to control fundamental physiological neuronal functions such as synaptic neurotransmission and synaptic plasticity. The fact that altered GluR trafficking has been observed in a broad spectrum of neuropathies, ranging from neurodevelopmental disorders to neurodegenerative diseases, highlights the importance of this process5. Thus, understanding the molecular events that control GluR trafficking is of interest in many areas of research.
In this protocol, an antibody-feeding based method is used to quantify the level of surface-expressed GluRs in primary hippocampal neurons as well as evaluate how changes in internalization and recycling result in the observed net surface expression. The use of pharmacology and/or overexpression of exogenous receptors harboring specific mutations makes this protocol a particularly powerful approach for studying molecular mechanisms underlying neuronal adaptation to different environmental stimuli. A final example of the utility of this protocol is studying how multifactorial changes in the environment (such as in a disease models) affects GluR trafficking through the examination of surface expression in such models.
Using specific examples, it is initially demonstrated how a pharmacologic manipulation mimicking physiological synaptic stimulation [chemical LTP (cLTP)] increases the surface expression of the endogenous GluA1 subunit of the AMPA-type of GluRs (AMPARs)6. The trafficking of an overexpressed phospho-mimetic form of the GluN2B subunit of NMDA-type of GluRs (NMDARs) is also analyzed to exemplify how this protocol can be used to study the regulation of GluR trafficking by specific posttranslational modifications. Though these specific examples are used, this protocol can easily be applied to other GluRs and other receptors and proteins that possess antigenic extracellular domains. In the case that there are no antibodies available for extracellular domains, overexpression of extracellular epitope-tagged (e.g., Flag-, Myc-, GFP-tagged, etc.) proteins can assist in protein labeling.
The current protocol provides instructions for quantifying specific GluR subtype density and trafficking using specific antibodies. This protocol can be utilized to study 1) total GluR surface expression, 2) GluR internalization, and 3) GluR recycling. To study each process individually, it is advised to begin with sections 1 and 2 and continue with either section 3, 4, or 5. In all cases, finish with sections 6 and 8 (Figure 1).

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>18 mm dia. #1.5 thick coverglasses</td>
			<td>Neuvitro</td>
			<td>GG181.5</td>
			<td></td>
		</tr>
		<tr>
			<td>Alexa 555-conjugated goat anti-mouse secondary</td>
			<td>Life Technologies</td>
			<td>A21424</td>
			<td></td>
		</tr>
		<tr>
			<td>Alexa 555-conjugated goat anti-rabbit secondary</td>
			<td>Life Technologies</td>
			<td>A21429</td>
			<td></td>
		</tr>
		<tr>
			<td>Alexa 647-conjugated goat anti-mouse secondary</td>
			<td>Life Technologies</td>
			<td>A21236</td>
			<td></td>
		</tr>
		<tr>
			<td>Alexa 647-conjugated goat anti-rabbit secondary</td>
			<td>Life Technologies</td>
			<td>A21245</td>
			<td></td>
		</tr>
		<tr>
			<td>B27</td>
			<td>Gibco</td>
			<td>17504044</td>
			<td></td>
		</tr>
		<tr>
			<td>CaCl2</td>
			<td>Sigma</td>
			<td>C7902</td>
			<td></td>
		</tr>
		<tr>
			<td>Corning Costar Flat Bottom Cell Culture Plates</td>
			<td>Corning</td>
			<td>3513</td>
			<td></td>
		</tr>
		<tr>
			<td>Dynasore</td>
			<td>Tocris</td>
			<td>2897</td>
			<td></td>
		</tr>
		<tr>
			<td>Glucose</td>
			<td>Sigma</td>
			<td>G8270</td>
			<td></td>
		</tr>
		<tr>
			<td>Glycine</td>
			<td>Tocris</td>
			<td>0219</td>
			<td></td>
		</tr>
		<tr>
			<td>Goat anti-rabbit Fab fragments</td>
			<td>Sigma</td>
			<td>SAB3700970</td>
			<td></td>
		</tr>
		<tr>
			<td>HEPES</td>
			<td>Sigma</td>
			<td>H7006</td>
			<td></td>
		</tr>
		<tr>
			<td>KCl</td>
			<td>Sigma</td>
			<td>P9541</td>
			<td></td>
		</tr>
		<tr>
			<td>L-Glutamine</td>
			<td>Sigma</td>
			<td>G7513</td>
			<td></td>
		</tr>
		<tr>
			<td>Lipofectamine 2000</td>
			<td>Invitrogen</td>
			<td>11668019</td>
			<td></td>
		</tr>
		<tr>
			<td>Mouse anti-GluA1 antibody</td>
			<td>Millipore</td>
			<td>MAB2263</td>
			<td></td>
		</tr>
		<tr>
			<td>NaCl</td>
			<td>Sigma</td>
			<td>S6546</td>
			<td></td>
		</tr>
		<tr>
			<td>Neurobasal Media</td>
			<td>Gibco</td>
			<td>21103049</td>
			<td></td>
		</tr>
		<tr>
			<td>NGS</td>
			<td>Abcam</td>
			<td>Ab7481</td>
			<td></td>
		</tr>
		<tr>
			<td>Parafilm</td>
			<td>Bemis</td>
			<td>PM999</td>
			<td></td>
		</tr>
		<tr>
			<td>PBS</td>
			<td>Gibco</td>
			<td>10010023</td>
			<td></td>
		</tr>
		<tr>
			<td>Pelco BioWave</td>
			<td>Ted Pella</td>
			<td>36500</td>
			<td></td>
		</tr>
		<tr>
			<td>PFA</td>
			<td>Alfa Aesar</td>
			<td>43368</td>
			<td></td>
		</tr>
		<tr>
			<td>Picrotoxin</td>
			<td>Tocris</td>
			<td>1128</td>
			<td></td>
		</tr>
		<tr>
			<td>Poly-D-lysine hydrobromide</td>
			<td>Sigma</td>
			<td>P7280</td>
			<td></td>
		</tr>
		<tr>
			<td>ProLong Gold Antifade Mountant</td>
			<td>Life Technologies</td>
			<td>P36934</td>
			<td></td>
		</tr>
		<tr>
			<td>Rabbit anti-GFP antibody</td>
			<td>Invitrogen</td>
			<td>A11122</td>
			<td></td>
		</tr>
		<tr>
			<td>Rabbit anti-PSD-95 antibody</td>
			<td>Cell Signaling</td>
			<td>2507</td>
			<td></td>
		</tr>
		<tr>
			<td>Strychnine</td>
			<td>Tocris</td>
			<td>2785</td>
			<td></td>
		</tr>
		<tr>
			<td>Sucrose</td>
			<td>Sigma</td>
			<td>S0389</td>
			<td></td>
		</tr>
		<tr>
			<td>Superfrost plus microscope slides</td>
			<td>Fisher</td>
			<td>12-550-15</td>
			<td></td>
		</tr>
		<tr>
			<td>Triton X-100</td>
			<td>Sigma</td>
			<td>X100</td>
			<td></td>
		</tr>
		<tr>
			<td>TTX</td>
			<td>Tocris</td>
			<td>1078</td>
			<td></td>
		</tr>
	</tbody>
</table>

an antibody feeding approach to study glutamate receptor trafficking in dissociated primary hippocampal cultures

Cellular responses to external stimuli heavily rely on the set of receptors expressed at the cell surface at a given moment. Accordingly, the population of surface-expressed receptors is constantly adapting and subject to strict mechanisms of regulation. The paradigmatic example and one of the most studied trafficking events in biology is the regulated control of the synaptic expression of glutamate receptors (GluRs). GluRs mediate the vast majority of excitatory neurotransmission in the central nervous system and control physiological activity-dependent functional and structural changes at the synaptic and neuronal levels (e.g., synaptic plasticity). Modifications in the number, location, and subunit composition of surface expressed GluRs deeply affect neuronal function and, in fact, alterations in these factors are associated with different neuropathies. Presented here is a method to study GluR trafficking in dissociated hippocampal primary neurons. An &#34;antibody-feeding&#34; approach is used to differentially visualize GluR populations expressed at the surface and internal membranes. By labeling surface receptors on live cells and fixing them at different times to allow for receptors endocytosis and/or recycling, these trafficking processes can be evaluated and selectively studied. This is a versatile protocol that can be used in combination with pharmacological approaches or overexpression of altered receptors to gain valuable information about stimuli and molecular mechanisms affecting GluR trafficking. Similarly, it can be easily adapted to study other receptors or surface expressed proteins.

This protocol to study glutamate receptor trafficking is based on differential labeling of receptors expressed at the cell surface and those expressed in internal membranes. Segregation is achieved by the labeling the receptors before and after membrane permeabilization, using the same primary antibody but a secondary antibody conjugated to a different fluorophore. As outlined by the optional steps included the protocol, this is a very versatile method for interrogating different receptor...

Watch this Scientific Journal Video about An Antibody Feeding Approach to Study Glutamate Receptor Trafficking in Dissociated Primary Hippocampal Cultures at JoVE.com

An Antibody Feeding Approach to Study Glutamate Receptor Trafficking in Dissociated Primary Hippocampal Cultures

This article presents a method to study glutamate receptor (GluR) trafficking in dissociated primary hippocampal cultures. Using an antibody-feeding approach to label endogenous or overexpressed receptors in combination with pharmacological approaches, this method allows for the identification of molecular mechanisms regulating GluR surface expression by modulating internalization or recycling processes.

Cellular responses to external stimuli heavily rely on the set of receptors expressed at the cell surface at a given moment. Accordingly, the population ...

Cellular responses to external stimuli heavily rely on the set of proteins that are expressed on the cell surface in a given moment. Accordingly, the number, the sub-cellular localization, and subunit composition of these proteins are dynamically controlled. Here, we will use an antibody feeding approach to quantify the level of surface expressed receptors in cell cultures, as long as the internalization and recycling resume.This is a very versatile protocol, that provides mechanistic information of the regulation of surface expressed proteins. In our example, we will study glutamine receptors in primary hippocampal neurons. This protocol can be adapted to any protein possessing an anagenic extracellular epitope, if antibodies aren't available, transvection of tagged constructs can be useful for both labeling and studying specific mutations.In our examples, we use antibodies against endogenous GluA1, and tagged Glu12 B.To begin this procedure, transfer the cover slips cell side up to a paraffin film covered tray, to save reagents, and facilitate manipulation. Save and maintain conditioned media at 37 degrees Celsius for incubation and washing steps. Incubate the cells with primary antibodies diluted in conditioned media, at room temperature, for 15 minutes.After this, use a vacuum pipette to carefully aspirate off the antibody containing media, and wash the cells three times with conditioned media. If studying surface versus intracellular receptor expression fix the cells with paraformaldehyde after this step, as outlined in the text protocol. Maintain the cells in conditioned media without antibodies, and return them to the incubator at 37 degrees Celsius to allow for internalization.If studying internalization process, fix the cells with paraformaldehyde after this step, as outlined in the text protocol. To block the epitopes on the primary antibody attached to the surface expressed receptors that have not been internalized, incubate cells with unconjugated Fab anti-IgG antibody fragments diluted in conditioned media, for 20 minutes at room temperature. After this, wash the cells three times with conditioned media.Incubate the washed wells with conditioned media containing 80 micromolar Dynasore, at 37 degrees Celsius, to allow for recycling of internalized receptors. After finishing the modifications on live cells, wash the cells once with PBS plus. Add a solution of 4%paraformaldehyde and 4%sucrose in PBS to the cells, and incubate in a fume hood at room temperature for seven to eight minutes, to fix the cells.Then wash the cells three times with regular PBS. Add a solution of 10%Normal Goat Serum in PBS to the cells, and incubate at room temperature for 30 minutes, to block non-specific binding sites. Next, incubate the cells with fluorescently tagged secondary antibody diluted in 3%NGS in PBS at room temperature for one hour, to label primary antibody label receptors.After this, wash the cells three times with PBS. To begin labeling the intracellular receptors, add a solution of 0.25%TritonX in PBS, and incubate at room temperature for five to 10 minutes, to permeabilize the cells. Then block with 10%NGS at room temperature for 30 minutes.If studying surface versus total, incubate the cells with the same primary antibody used previously, diluted with 3%NGS in PBS, at room temperature for one hour, to label the intracellular receptors. Next, wash the cells three times with PBS. Label with second fluorescently tagged secondary antibody, diluted in 3%NGS in PBS, at room temperature for one hour.After this wash the cells three times with PBS. First gently place the cover slips, cell side down, on 12 to 15 microliters of the appropriate mounting media to mount the cells. Then image the cells on the appropriate confocal microscope, and analyze the cells as outlined in the text protocol.This protocol to study glutamate receptor trafficking is based on differential labeling of receptors, expressed at the cell surface, and those expressed in internal membranes. After acquiring confocal images, the fluorescent signal can be easily quantified to show an increase in surface expression, relative to intracellular population, following chemical LTP. No signal for PSD-95 can be obtained in non-permeabilized cells, demonstrating the integrity of the plasma membrane.This indicates that the signal obtained for surface GluA1 indeed corresponds to surface expressed receptors. Importantly, a minimal signal for internalized GluA1 can be observed under non-permeabilization conditions, showing that all surface epitopes are occupied by the initial round of antibody labeling. Receptors that have been internalized are then identified.This exampled highlights that GluN2B phosphorylation at S1480 promotes receptor internalization. As the phosphomimetic mutant S1480E displayed a much higher internalization ratio compared to wild-type receptors. As expected, no signal is obtained for internalized receptors in the control.Next, recycled receptors and internalized receptors are identified. The generated recycling ratio shows that GluN2B S1480E has no effect on NMDAR recycling. In the control, a strong signal can be observed for surface expressed GluN2B in the absence of Fab blocking.This signal disappears in Fab-treated cultures, demonstrating that the blocking protocol is sufficient to completely block the surface expressed epitopes, and that the surface signals observed after recycling indeed correspond to receptors trafficked back to the plasma membrane. The current protocol is just one of the methods available for studying the regulation of surface expressed proteins. Other approaches can be taken to expand or verify the data obtained here.Those include biochemical methods, as biotinylation, life imaging techniques, or functional approaches, like electrophysiology or calcium imaging. We use PFA to freeze the localization of receptors, however PFA is a known carcinogen, so it's crucial to perform steps using PFA under a fume hood, while wearing appropriate PPE.

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Research

JoVE Journal

Neuroscience

Organotypic Hippocampal Slice Cultures

The hippocampus, a component of the limbic system, plays important roles in long-term memory and spatial navigation 1. Hippocampal neurons can modify the strength of their connections after brief periods of strong activation. This phenomenon, known as long-term potentiation (LTP) can last for hours or days and has become the best candidate mechanism for learning and memory 2. In addition, the well defined anatomy and connectivity of the hippocampus 3 has made it a classical model system to study synaptic transmission and synaptic plasticity4.
As our understanding of the physiology of hippocampal synapses grew and molecular players became identified, a need to manipulate synaptic proteins became imperative. Organotypic hippocampal cultures offer the possibility for easy gene manipulation and precise pharmacological intervention but maintain synaptic organization that is critical to understanding synapse function in a more naturalistic context than routine culture dissociated neurons methods.
Here we present a method to prepare and culture hippocampal slices that can be easily adapted to other brain regions. This method allows easy access to the slices for genetic manipulation using different approaches like viral infection 5,6 or biolistics 7. In addition, slices can be easily recovered for biochemical assays 8, or transferred to microscopes for imaging 9 or electrophysiological experiments 10.

We describe a method to prepare organotypic hippocampal slices that can be easily adapted to other brain regions. Brain slices are laid on porous membranes and culture media is allowed to form an interface. This method preserves the gross architecture of the hippocampus for up to 2 weeks in culture.

The hippocampus, a component of the limbic system, plays important roles in long-term memory and spatial navigation 1. Hippocampal neurons can modify the ...

Post-embedding Immunogold Labeling of Synaptic Proteins in Hippocampal Slice Cultures

Immunoelectron microscopy is a powerful tool to study biological molecules at the subcellular level. Antibodies coupled to electron-dense markers such as colloidal gold can reveal the localization and distribution of specific antigens in various tissues1. The two most widely used techniques are pre-embedding and post-embedding techniques. In pre-embedding immunogold-electron microscopy (EM) techniques, the tissue must be permeabilized to allow antibody penetration before it is embedded. These techniques are ideal for preserving structures but poor penetration of the antibody (often only the first few micrometers) is a considerable drawback2. The post-embedding labeling methods can avoid this problem because labeling takes place on sections of fixed tissues where antigens are more easily accessible. Over the years, a number of modifications have improved the post-embedding methods to enhance immunoreactivity and to preserve ultrastructure3-5.
Tissue fixation is a crucial part of EM studies. Fixatives chemically crosslink the macromolecules to lock the tissue structures in place. The choice of fixative affects not only structural preservation but also antigenicity and contrast. Osmium tetroxide (OsO4), formaldehyde, and glutaraldehyde have been the standard fixatives for decades, including for central nervous system (CNS) tissues that are especially prone to structural damage during chemical and physical processing. Unfortunately, OsO4 is highly reactive and has been shown to mask antigens6, resulting in poor and insufficient labeling. Alternative approaches to avoid chemical fixation include freezing the tissues. But these techniques are difficult to perform and require expensive instrumentation. To address some of these problems and to improve CNS tissue labeling, Phend et al. replaced OsO4 with uranyl acetate (UA) and tannic acid (TA), and successfully introduced additional modifications to improve the sensitivity of antigen detection and structural preservation in brain and spinal cord tissues7. We have adopted this osmium-free post-embedding method to rat brain tissue and optimized the immunogold labeling technique to detect and study synaptic proteins.
We present here a method to determine the ultrastructural localization of synaptic proteins in rat hippocampal CA1 pyramidal neurons. We use organotypic hippocampal cultured slices. These slices maintain the trisynaptic circuitry of the hippocampus, and thus are especially useful for studying synaptic plasticity, a mechanism widely thought to underlie learning and memory. Organotypic hippocampal slices from postnatal day 5 and 6 mouse/rat pups can be prepared as described previously8, and are especially useful to acutely knockdown or overexpress exogenous proteins. We have previously used this protocol to characterize neurogranin (Ng), a neuron-specific protein with a critical role in regulating synaptic function8,9 . We have also used it to characterize the ultrastructural localization of calmodulin (CaM) and Ca2+/CaM-dependent protein kinase II (CaMKII)10. As illustrated in the results, this protocol allows good ultrastructural preservation of dendritic spines and efficient labeling of Ng to help characterize its distribution in the spine8. Furthermore, the procedure described here can have wide applicability in studying many other proteins involved in neuronal functions.

The localization and distribution of proteins provide important information for understanding their cellular functions. The superior spatial resolution of electron microscopy (EM) can be used to determine the subcellular localization of a given antigen following immunohistochemistry. For tissues of the central nervous system (CNS), preserving structural integrity while maintaining antigenicity has been especially difficult in EM studies. Here, we adopt a procedure that has been used to preserve structures and antigens in the CNS to study and characterize synaptic proteins in rat hippocampal CA1 pyramidal neurons.

Immunoelectron microscopy is a powerful tool to study biological molecules at the subcellular level. Antibodies coupled to electron-dense markers such as ...

Calcium Phosphate Transfection of Primary Hippocampal Neurons

Calcium phosphate precipitation is a convenient and economical method for transfection of cultured cells. With optimization, it is possible to use this method on hard-to-transfect cells like primary neurons. Here we describe our detailed protocol for calcium phosphate transfection of hippocampal neurons cocultured with astroglial cells.

Calcium phosphate precipitation is a convenient and economical method for transfection of cultured cells. With optimization, it is possible to use this ...

Membrane Potential Dye Imaging of Ventromedial Hypothalamus Neurons From Adult Mice to Study Glucose Sensing

Studies of neuronal activity are often performed using neurons from rodents less than 2 months of age due to the technical difficulties associated with increasing connective tissue and decreased neuronal viability that occur with age. Here, we describe a methodology for the dissociation of healthy hypothalamic neurons from adult-aged mice. The ability to study neurons from adult-aged mice allows the use of disease models that manifest at a later age and might be more developmentally accurate for certain studies. Fluorescence imaging of dissociated neurons can be used to study the activity of a population of neurons, as opposed to using electrophysiology to study a single neuron. This is particularly useful when studying a heterogeneous neuronal population in which the desired neuronal type is rare such as for hypothalamic glucose sensing neurons. We utilized membrane potential dye imaging of adult ventromedial hypothalamic neurons to study their responses to changes in extracellular glucose. Glucose sensing neurons are believed to play a role in central regulation of energy balance. The ability to study glucose sensing in adult rodents is particularly useful since the predominance of diseases related to dysfunctional energy balance (e.g.&#160;obesity) increase with age.

The activity of single neurons from adult-aged mice can be studied by dissociating neurons from specific brain regions and using fluorescent membrane potential dye imaging. By testing responses to changes in glucose, this technique can be used to study the glucose sensitivity of adult ventromedial hypothalamic neurons.

Studies of neuronal activity are often performed using neurons from rodents less than 2 months of age due to the technical difficulties associated with ...

Brain Slice Biotinylation: An Ex Vivo Approach to Measure Region-specific Plasma Membrane Protein Trafficking in Adult Neurons

Regulated endocytic trafficking is the central mechanism facilitating a variety of neuromodulatory events, by dynamically controlling receptor, ion channel, and transporter cell surface presentation on a minutes time scale.&#160;There is a broad diversity of mechanisms that control endocytic trafficking of individual proteins. Studies investigating the molecular underpinnings of trafficking have primarily relied upon surface biotinylation to quantitatively measure changes in membrane protein surface expression in response to exogenous stimuli and gene manipulation.&#160;However, this approach has been mainly limited to cultured cells, which may not faithfully reflect the physiologically relevant mechanisms at play in adult neurons.&#160;Moreover, cultured cell approaches may underestimate region-specific differences in trafficking mechanisms.&#160;Here, we describe an approach that extends cell surface biotinylation to the acute brain slice preparation.&#160;We demonstrate that this method provides a high-fidelity approach to measure rapid changes in membrane protein surface levels in adult neurons.&#160;This approach is likely to have broad utility in the field of neuronal endocytic trafficking.

Brain Slice Biotinylation: An Ex Vivo Approach to Measure Region-specific Plasma Membrane Protein Trafficking in Adult Neurons

Neuronal membrane trafficking dynamically controls plasma membrane protein availability and significantly impacts neurotransmission.&#160;To date, it has been challenging to measure neuronal endocytic trafficking in adult neurons.&#160;Here, we describe a highly effective, quantitative method to measure rapid changes in surface protein expression ex vivo in acute brain slices.

Regulated endocytic trafficking is the central mechanism facilitating a variety of neuromodulatory events, by dynamically controlling receptor, ion ...

Using an &#945;-Bungarotoxin Binding Site Tag to Study GABA A Receptor Membrane Localization and Trafficking

It is increasingly evident that neurotransmitter receptors, including ionotropic GABA A receptors (GABAAR), exhibit highly dynamic trafficking and cell surface mobility1-7. To study receptor cell surface localization and endocytosis, the technique described here combines the use of fluorescent &#945;-bungarotoxin with cells expressing constructs containing an &#945;-bungarotoxin (Bgt) binding site (BBS). The BBS (WRYYESSLEPYPD) is based on the &#945; subunit of the muscle nicotinic acetylcholine receptor, which binds Bgt with high affinity8,9. Incorporation of the BBS site allows surface localization and measurements of receptor insertion or removal with application of exogenous fluorescent Bgt, as previously described in the tracking of GABAA and metabotropic GABAB receptors2,10. In addition to the BBS site, we inserted a pH-sensitive GFP (pHGFP11) between amino acids 4 and 5 of the mature GABAAR subunit by standard molecular biology and PCR cloning strategies (see Figure 1)12. The BBS is 3&#39; of the pH-sensitive GFP reporter, separated by a 13-amino acid alanine/proline linker. For trafficking studies described in this publication that are based on fixed samples, the pHGFP serves as a reporter of total tagged GABAAR subunit protein levels, allowing normalization of the Bgt labeled receptor population to total receptor population. This minimizes cell to cell Bgt staining signal variability resulting from higher or lower baseline expression of the tagged GABAAR subunits. Furthermore the pHGFP tag enables easy identification of construct expressing cells for live or fixed imaging experiments.

Here we demonstrate the use of fluorescent Alexa dye coupled to &#945;-bungarotoxin to measure GABA A receptor surface localization and endocytosis in hippocampal neurons. Through the use of constructs bearing a short extracellular tag that binds &#945;-bungarotoxin, analysis of plasma membrane protein endocytic trafficking can be achieved.

It is increasingly evident that neurotransmitter receptors, including ionotropic GABA A receptors (GABAAR), exhibit highly dynamic trafficking and cell ...

The Analysis of Neurovascular Remodeling in Entorhino-hippocampal Organotypic Slice Cultures

Ischemic brain injury is among the most common and devastating conditions compromising proper brain function and often leads to persisting functional deficits in the affected patients. Despite intensive research efforts, there is still no effective treatment option available that reduces neuronal injury and protects neurons in the ischemic areas from delayed secondary death. Research in this area typically involves the use of elaborate and problematic animal models. Entorhino-hippocampal organotypic slice cultures challenged with oxygen and glucose deprivation (OGD) are established in&#160;vitro models which mimic cerebral ischemia. The novel aspect of this study is that changes of the brain blood vessels are studied in addition to neuronal changes and the reaction of both the neuronal compartment and the vascular compartment can be compared and correlated. The methods presented in this protocol substantially broaden the potential applications of the organotypic slice culture approach. The induction of OGD or hypoxia alone can be applied by rather simple means in organotypic slice cultures and leads to reliable and reproducible damage in the neural tissue. This is in stark contrast to the complicated and problematic animal experiments inducing stroke and ischemia in vivo. By broadening the analysis to include the study of the reaction of the vasculature could provide new ways on how to preserve and restore brain functions. The slice culture approach presented here might develop into an attractive and important tool for the study of ischemic brain injury and might be useful for testing potential therapeutic measures aimed at neuroprotection.

A protocol for entorhino-hippocampal organotypic slice cultures, which allows reproducing many aspects of ischemic brain injury, is presented. By studying changes of the neurovasculature in addition to changes in the neurons, this protocol is a versatile tool to study plastic changes in neural tissue after injury.

Ischemic brain injury is among the most common and devastating conditions compromising proper brain function and often leads to persisting functional ...

Stripe Assay to Study the Attractive or Repulsive Activity of a Protein Substrate Using Dissociated Hippocampal Neurons

Growing axons develop a highly motile structure at their tip, termed the growth cone. The growth cone contacts extracellular environmental cues to navigate axonal growth. Netrin, slit, semaphorin, and ephrins are known guidance molecules that can attract or repel axons upon binding to receptors and co-receptors on the axon. The activated receptors initiate various signaling molecules in the growth cone that alter the structure and movement of the neuron. Here, we describe the detailed protocol for a stripe assay to assess the ability of a guidance molecule to attract or repel neurons. In this method, dissociated hippocampal neurons from E15.5 mice are cultured on laminin-coated dishes processed with alternating stripes of ectodomain of fibronectin and leucine-rich transmembrane protein-2 (FLRT2) and control immunoglobulin G (IgG) fragment crystallizable region (Fc) protein. Both axons and cell bodies were strongly repelled from the FLRT2-coated stripe regions after 24 h of culture. Immunostaining with tau1 showed that ~90% of the neurons were distributed on the Fc-coated stripes compared to the FLRT2-Fc-coated stripes (~10%). This result indicates that FLRT2 has a strong repulsive effect on these neurons. This powerful method is applicable not only for primary cultured neurons but also for a variety of other cells, such as neuroblasts.

Axon guidance molecules regulate neuronal migration and targeted growth-cone navigation. We present a powerful method, the stripe assay, to assess the ability of guidance molecules to attract or repulse neurons. In this protocol, we demonstrate the stripe assay by showing FLRT2's ability to repel cultured hippocampal neurons.

Growing axons develop a highly motile structure at their tip, termed the growth cone. The growth cone contacts extracellular environmental cues to ...

Low-Density Primary Hippocampal Neuron Culture

The ability to probe the structure and physiology of individual nerve cells in culture is crucial to the study of neurobiology, and allows for flexibility in genetic and chemical manipulation of individual cells or defined networks. Such ease of manipulation is simpler in the reduced culture system when compared to the intact brain tissue. While many methods for the isolation and growth of these primary neurons exist, each has its own limitations. This protocol describes a method for culturing low-density and high-purity rodent embryonic hippocampal neurons on glass coverslips, which are then suspended over a monolayer of glial cells. This &#39;sandwich culture&#39; allows for exclusive long-term growth of a population of neurons while allowing for trophic support from the underlying glial monolayer. When neurons are of sufficient age or maturity level, the neuron coverslips can be flipped-out of the glial dish and used in imaging or functional assays. Neurons grown by this method typically survive for several weeks and develop extensive arbors, synaptic connections, and network properties.

This article describes the protocol for culturing low-density primary hippocampal neurons growing on glass coverslips inverted over a glial monolayer. The neuron and glial layers are separated by paraffin wax beads. The neurons grown by this method are suitable for high-resolution optical imaging and functional assays.

The ability to probe the structure and physiology of individual nerve cells in culture is crucial to the study of neurobiology, and allows for flexibility ...

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. ...