Name: a microbiomechanical system for studying varicosity formation and recovery in central neuron axons
Uploaded: 2018-04-30T13:00:00
Description: Watch this Scientific Journal Video about A Microbiomechanical System for Studying Varicosity Formation and Recovery in Central Neuron Axons at JoVE.com

All animal experiments have been conducted in accordance with the National Institutes of Health Animal Use Guidelines. This work was supported in part by grants from National Institutes of Health (R01NS093073 and R21AA024873) to C. Gu.

All methods described below have been approved by the Institutional Animal Care and Use Committee (IACUC) of the Ohio State University.
1. Coverslip Preparation
<ol>
	<li>Place one or more boxes of 12 mm or 25 mm coverslips into a glass beaker containing 70% nitric acid and incubate the coverslips at room temperature overnight. 
	NOTE: Do not wash the 25 mm coverslips in the same beaker as the 12 mm coverslips. It is better to wash them separately.</li>
	<li>Transfer all coverslips into...

<ol>
	<li>Niki&#263;, I., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+reversible+form+of+axon+damage+in+experimental+autoimmune+encephalomyelitis+and+multiple+sclerosis.">A reversible form of axon damage in experimental autoimmune encephalomyelitis and multiple sclerosis.</a> Nat. Med. 17, 495-499 (2011).</li><li>Yang, 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=Regulation+of+axon+degeneration+after+injury+and+in+development+by+the+endogenous+calpain+inhibitor+calpastatin.">Regulation of axon degeneration after injury and in development by the endogenous calpain inhibitor calpastatin.</a> Neuron. 80 (5), 1175-1189 (2013).</li><li>Debanne, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Information+processing+in+the+axon.">Information processing in the axon.</a> Nat. Rev. Neurosci. 5, 304-316 (2004).</li><li>Gu, Y., Jukkola, P., Wang, Q., Esparza, T., Zhao, Y., Brody, D., Gu, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Polarity+of+varicosity+initiation+in+central+neuron+mechanosensation.">Polarity of varicosity initiation in central neuron mechanosensation.</a> J Cell Biol. 216 (7), 2179-2199 (2017).</li><li>Chung, R. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mild+axonal+stretch+injury+in+vitro+induces+a+progressive+series+of+neurofilament+alterations+ultimately+leading+to+delayed+axotomy.">Mild axonal stretch injury in vitro induces a progressive series of neurofilament alterations ultimately leading to delayed axotomy.</a> J. Neurotrauma. 22 (10), 1081-1091 (2005).</li><li>Staal, J. A., Dickson, T. C., Chung, R. S., Vickers, J. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cyclosporin-A+treatment+attenuates+delayed+cytoskeletal+alterations+and+secondary+axotomy+following+mild+axonal+stretch+injury.">Cyclosporin-A treatment attenuates delayed cytoskeletal alterations and secondary axotomy following mild axonal stretch injury.</a> Dev. Neurobiol. 67 (14), 1831-1842 (2007).</li><li>Tang-Schomer, M. D., Johnson, V. E., Baas, P. W., Stewart, W., Smith, D. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Partial+interruption+of+axonal+transport+due+to+microtubule+breakage+accounts+for+the+formation+of+periodic+varicosities+after+traumatic+axonal+injury.">Partial interruption of axonal transport due to microtubule breakage accounts for the formation of periodic varicosities after traumatic axonal injury.</a> Exp. Neurol. 233 (1), 364-372 (2012).</li><li>Donkin, J. J., Vink, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanisms+of+cerebral+edema+in+traumatic+brain+injury:+therapeutic+developments.">Mechanisms of cerebral edema in traumatic brain injury: therapeutic developments.</a> Curr Opin Neurol. 23 (3), 293-299 (2010).</li><li>Gardner, A., Jukkola, P., Gu, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Myelination+of+rodent+hippocampal+neurons+in+culture.">Myelination of rodent hippocampal neurons in culture.</a> Nat Protoc. 7 (10), 1774-1782 (2012).</li><li>Wang, Q., Zhang, X., Zhao, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Micromechanical+stimulator+for+localized+cell+loading:+fabrication+and+strain+analysis.">Micromechanical stimulator for localized cell loading: fabrication and strain analysis.</a> J. Micromech. Microeng. 23, 015002 (2013).</li><li>Lu, Y. B., 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=Viscoelastic+properties+of+individual+glial+cells+and+neurons+in+the+CNS.">Viscoelastic properties of individual glial cells and neurons in the CNS.</a> Proc. Natl. Acad. Sci. USA. 103 (47), 17759-17764 (2006).</li><li>Elkin, B. S., Azeloglu, E. U., Costa, K. D., Morrison, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanical+heterogeneity+of+the+rat+hippocampus+measured+by+atomic+force+microscope+indentation.">Mechanical heterogeneity of the rat hippocampus measured by atomic force microscope indentation.</a> J. Neurotrauma. 24 (5), 812-822 (2007).</li><li>Franze, K., 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=Neurite+branch+retraction+is+caused+by+a+threshold-dependent+mechanical+impact.">Neurite branch retraction is caused by a threshold-dependent mechanical impact.</a> Biophys. J. 97 (7), 1883-1890 (2009).</li><li>Camp&#224;s, O., 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=Quantifying+cell-generated+mechanical+forces+within+living+embryonic+tissues.">Quantifying cell-generated mechanical forces within living embryonic tissues.</a> Nat. Methods. 11 (2), 183-189 (2014).</li></ol>

The procedure of this microbiomechanical assay is straight forward. It will produce reliable results, if all its steps are carefully carried out. There are several key steps that, if improperly performed, will hinder successful data collection. The critical steps begin upstream of the actual application of the puffing stimulus. Careful dissection, culturing, and care of the primary neuron culture are paramount. If the cultured neurons are not healthy, they will not react consistently, since they might have already been p...

Varicosity formation, or swelling/beading, along axons, is a prominent feature of neurodegeneration observed in many disorders or injuries of the central nervous system, including multiple sclerosis, Alzheimer&#39;s disease, Parkinson&#39;s disease, and traumatic brain injury1,2. Despite the significant physiological impacts of axonal varicosities on action potential propagation and synaptic transmission3, how the varicosities are generated remains unknown. Recently, using a newly-established microbiomechanical assay on cultured hippocampal neurons from rodents, we found that mechanical stimuli can induce varicosities in these neurons with highly intriguing features. First, varicosity induction is rapid (&#60;10 s) and this process is unexpectedly reversible. Second, varicosity initiation depends on the strength of puffing pressure: the higher the pressure, the faster the initiation. Third, varicosity initiation depends on neuronal age. The axons of younger neurons appear more responsive to mechanical stress, compared to those of older neurons. Fourth, the varicosities form along the axons of hippocampal neurons, while the dendrites and initial axon segments of these neurons display no change under the same puffing condition. Thus, our study revealed a novel feature of neuronal polarity. These findings with the in vitro system are physiologically relevant. Using an in vivo model for mild traumatic brain injury (mTBI), we showed that axonal varicosities developed in a multi-focal fashion in the somatosensory cortex of the mice immediately after close-skull impact, consistent with our in vitro results4. It is important to note that our staining and imaging of the mTBI mice only provide a snap shot of neuronal morphological changes, since performing in vivo time-lapse imaging of neuronal morphology during a mechanical impact is still not feasible.
This fluid-puffing system allowed us not only to capture unique features associated with mechanical stress-induced varicosity formation, but also to determine the underlying mechanism. By testing different extracellular solutions, the blockers and openers of different candidates of mechanosensitive ion channels, and cellular electrophysiology, we identified that the transient receptor potential cation channel subfamily V member 4 (TRPV4) channel that is permeable to Ca2+ and Na+ and activated by puffing is mainly responsible for detecting initial mechanical stress during axonal varicosity formation4. This was further confirmed with an siRNA knockout approach. Taken together, this new assay system we have developed with hippocampal neuron culture, is highly valuable for studying the micromechanical properties of central neurons, especially in combination with other techniques.
This micromechanical system we have established is unique and differs from the previously-existing systems in several major aspects. First, in this system, the neurons experience out-of-plane mechanical stress in the forms of compression and shearing. During the mechanical impact, neuronal processes remain attached to the coverslip surface and do not move. This differs from other experimental systems that mainly involved bending and in-plane stretching (or tension), for instance, the deflection of bundled axons like moving strings5,6 or stretching axons grown on micropatterned channels and stretchable membranes7,8. Moreover, although axonal varicosities can also be induced in these assays like in our fluid-puffing system, the process in these settings takes much more time (from 10 min to several hours6,7,8) and appears irreversible. Finally, our system using local fluid puffing allows the examination of the spatial features of varicosity formation (e.g., dendrites, dendritic spines, soma, axonal initial segments, axonal terminals), besides its temporal features. Using this system, we discovered several unexpected and unique features of axonal varicosity formation, especially rapid onset, slow reversibility, and axon-dendrite polarity.
The system that we discuss in this paper is compatible with many techniques of molecular and cell biology. For instance, to study the effects of mechanical stress on neuronal morphology and function, it can be used together with myelin coculture, time-lapse imaging of fluorescent resonance energy transfer (FRET) and total internal reflection fluorescence (TIRF), calcium imaging, and patch clamp recording. In this paper, we focus on the core components of the system. Hippocampal neuron culture, the fluid-puffing setup, high-resolution time-lapse imaging for axonal transport, and calcium imaging are illustrated step-by-step below.

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		<col />
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	<tbody>
		<tr height="40">
			<td height="40" style="height:40px;width:341px;">12 mm coverslips&#160;</td>
			<td style="width:139px;">Warner Instruments&#160;</td>
			<td style="width:119px;">64-0702</td>
			<td style="width:167px;">for 24-well plate&#160;</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">25 mm coverslips&#160;</td>
			<td>Fisher Scientific&#160;</td>
			<td>12-545-102&#160;</td>
			<td>for 6-well plate&#160;</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Acetic acid</td>
			<td>Fisher Scientific&#160;</td>
			<td>A38-212</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Poly-D-lysine</td>
			<td>Sigma&#160;</td>
			<td>P6407</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Rat tail collagen&#160;</td>
			<td>Roche&#160;</td>
			<td>11 179 179 001&#160;</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">10X PBS&#160;</td>
			<td>National Diagnostics&#160;</td>
			<td>CL-253</td>
			<td></td>
		</tr>
		<tr height="40">
			<td align="left" height="40" style="height:40px;">Na2SO4</td>
			<td>Fisher Scientific&#160;</td>
			<td>S373-500</td>
			<td></td>
		</tr>
		<tr height="40">
			<td align="left" height="40" style="height:40px;">K2SO4</td>
			<td>Fisher Scientific&#160;</td>
			<td>P304-500</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">HEPES&#160;</td>
			<td>Fisher Scientific&#160;</td>
			<td>BP410-500</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">D-glucose&#160;</td>
			<td>Fisher Scientific&#160;</td>
			<td>D16-500</td>
			<td></td>
		</tr>
		<tr height="40">
			<td align="left" height="40" style="height:40px;">MgCl2</td>
			<td>Fisher Scientific&#160;</td>
			<td>BP214-500</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">NaOH</td>
			<td>Fisher Scientific&#160;</td>
			<td>SS255-1</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Protease enzyme&#160;</td>
			<td>Sigma&#160;</td>
			<td>P4032</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">FBS</td>
			<td>Gibco&#160;</td>
			<td>26140</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Sodium pyruvate&#160;</td>
			<td>Gibco&#160;</td>
			<td>11360-070</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">L-glutamine&#160;</td>
			<td>Gibco&#160;</td>
			<td>25030081</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Penicillin/Streptomycin 100x (P/S)</td>
			<td>Gibco&#160;</td>
			<td style="width:119px;">15140122</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">MEM Earle&#39;s Salts&#160;</td>
			<td>Gibco&#160;</td>
			<td>11090</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">B27 supplement&#160;</td>
			<td>Gibco&#160;</td>
			<td>17504-044</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Neurobasal&#160;</td>
			<td>Gibco&#160;</td>
			<td>21103-049</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Arabinosylcytosine (Ara-C)</td>
			<td>Sigma&#160;</td>
			<td>147-94-4</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Opti-MEM media&#160;</td>
			<td>Gibco&#160;</td>
			<td>31985-070</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Lipofectamine 2000</td>
			<td>Invitrogen&#160;</td>
			<td>1854313</td>
			<td>transfection reagent&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Borosilicate rods&#160;</td>
			<td>World Precision Instruments Inc.&#160;</td>
			<td>PG52151-4</td>
			<td>for puffing pipette&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">rubber tubing&#160;</td>
			<td style="width:139px;">Fisher Scientific&#160;</td>
			<td style="width:119px;">14-169-1A</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">10cc plastic syringe and plunger</td>
			<td>Becton Dickinson&#160;</td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">micromanipulator&#160;</td>
			<td>Sutter Instruments&#160;</td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">NaCl&#160;</td>
			<td>Fisher Scientific&#160;</td>
			<td>S640-3</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">KCl&#160;</td>
			<td>Fisher Scientific&#160;</td>
			<td>BP366-500</td>
			<td></td>
		</tr>
		<tr height="21">
			<td align="left" height="21" style="height:21px;">CaCl2</td>
			<td>Fisher Scientific&#160;</td>
			<td>C70-500</td>
			<td></td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;width:341px;">Cell culture dish (35 mm x 10 mm)</td>
			<td style="width:139px;">Corning&#160;</td>
			<td style="width:119px;">3294</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:341px;">Fluo-4 AM</td>
			<td style="width:139px;">Molecular Probes</td>
			<td style="width:119px;">F14201</td>
			<td style="width:167px;">for calcium imaging&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:341px;">Mito-YFP construct&#160;</td>
			<td style="width:139px;">Takara Bio Inc.&#160;</td>
			<td style="width:119px;"></td>
			<td style="width:167px;">for cell transfection&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:341px;">YFP-N1 construct&#160;</td>
			<td style="width:139px;">Takara Bio Inc.&#160;</td>
			<td style="width:119px;"></td>
			<td style="width:167px;">for cell transfection&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:341px;">Model P-1000 Flaming/Brown Micropipette puller&#160;</td>
			<td style="width:139px;">Sutter Instruments&#160;</td>
			<td style="width:119px;"></td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:341px;">Eclipse TE2000-U Mcroscope&#160;</td>
			<td style="width:139px;">Nikon</td>
			<td style="width:119px;"></td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:341px;">Plan Fluor ELWD 20x lens&#160;&#160;</td>
			<td style="width:139px;">Nikon</td>
			<td style="width:119px;">062933</td>
			<td style="width:167px;">objective&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:341px;">Apo TIRF 100x/1.49 oil lens&#160;</td>
			<td style="width:139px;">Nikon</td>
			<td style="width:119px;">MRD01991</td>
			<td style="width:167px;">objective&#160;</td>
		</tr>
	</tbody>
</table>

a microbiomechanical system for studying varicosity formation and recovery in central neuron axons

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

Prior to puffing, axons normally show little varicosity formation. Following puffing with our standard pressure (190 mmH2O height), the axons start to develop many bead-like varicosities. The formation of varicosities is partially reversible, as shown by regions of the axon returning to their pre-puffed state following a 10 min recovery period (Figure 2A-B). After a longer period of recovery (&#62;20 min), some axons completely rec...

Watch this Scientific Journal Video about A Microbiomechanical System for Studying Varicosity Formation and Recovery in Central Neuron Axons at JoVE.com

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

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

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

The overall goal of this pressurized fluid setup is to produce repeatable and consistent swellings along the axons of cultured neurons. This method can help answer key questions in the brain injury field such as the mechanisms behind subcellular morphological changes in neurons following injury. The main advantage of this technique is that the method produces consistent and repeatable morphological changes that recover over time.This is very important technique we developed in the lab. This is because we can not only use the system to identify molecular mechanism governing mechanical-stress-induced axon morphology change as a new form of neuronal plasticity, but also use the system as a screening tool to identify new drugs and the treatment strategy for mild or traumatic brain injury. To begin this procedure, place one or more boxes of 12-millimeter or 25-millimeter coverslips into a glass beaker containing 70%nitric acid, and incubate the coverslips at room temperature overnight.The next day, transfer all coverslips into a four-liter beaker filled with 2.5 liters of double-distilled water. Shake the beaker containing the coverslips for one hour at 100 RPM, and don't forget to use rubber bands to hold the beaker during shaking. Subsequently, transfer the cleaned coverslips to a dry flask with the metal cover.Bake the coverslips in an oven at 225 degrees Celsius for six hours. Then, allow them to cool to room temperature and store them in a sterilized plastic container until usage. Now, place one coverslip into each well of a 24-well plate.Add 30 microliters of coverslip coating solution onto a 12-millimeter coverslip and swirl. Afterward, add one milliliter of sterile PBS to each well. The plate can be either used immediately or stored at four degrees Celsius in sterile PBS for up to one week.On the day of dissection, remove PBS from the plate. Air dry and place the plate under UV light for two to four hours. To dissociate the hippocampal neurons for culture, thaw the protease enzyme solution and pre-warm the plating medium at 37 degrees Celsius.Next, rinse the dissected hippocampus with SLDS. Then, remove it and add two milliliters of protease enzyme solution and incubate the sample at 37 degrees Celsius for 15 minutes. Afterward, wash the hippocampus explants with five to 10 milliliters of plating medium twice and add five milliliters of plating medium.Dissociate the hippocampal explants into single cells by generating a small vortex using a pipette with a one-milliliter plastic tip. Pipette up and down about 40 times avoiding the formation of oxygen bubbles until the solution becomes cloudy and no large pieces of explant remain. Next, centrifuge the cells at 1, 125 times gravity for three minutes.Remove the supernatant with the cells submerged in medium and re-suspend the cells in 145 milliliters of plating medium. Then, add one milliliter of the cell suspension per well to a 24-well plate. Incubate the cells in the plating medium at 37 degrees Celsius for two to four hours.Afterward, remove the plating medium and replace it with fresh maintenance medium. After two days, replace half of the medium with two micromolar RSC dissolved in maintenance medium to inhibit growth of fibroblast, endothelial and glial cells. Then, after exposing the cells to RSC for two days, replace the medium with fresh maintenance medium.To transfect for the visualization of cell morphology, dilute the construct from stock at one microgram per microliter in Opti-MEM medium and vortex. Then, dilute liposome-mediated transfection reagent in Opti-MEM media and vortex. Subsequently, prepare one construction dilution and one transfection dilution for each well.Next, prepare a one-to-one mixture of the construct and Opti-MEM medium and transfection reagent and Opti-MEM medium and vortex. Incubate the mixture at room temperature for 20 minutes. After 20 minutes, remove half of the medium from each well and transfer this medium into a clean conical tube.Keep the tube in the incubator, then add 100 microliters of the mixture prepared in the previous step to the remaining medium in the well. Allow the cells to incubate at 37 degrees Celsius for 20 to 30 minutes. During incubation, add one volume of fresh maintenance medium to the medium in the conical tube and place the mixture in the same incubator.Following incubation, remove the mediums containing the transfection solution from the wells and replace it with the one-to-one mixture of old and fresh maintenance medium in the conical tube. In this procedure, insert the pipette into the screw top of the micromanipulator to hold it into place. Screw the metal flat-top screw attached to the micromanipulator arm so that it holds the unpulled end of the pipette just above where the rubber tubing is attached.Angle the pipette at a 45 degree angle with the surface of the neuron containing coverslips. Turn on the florescence filter. Open the aperture, and ensure a fluorescent spot can be seen coming through the objective.Using the micromanipulator, move the pipette into a position that lines up the tip with the fluorescent spot and lower the pipette into a position just above the height of the cell culture dish. Once it is in position, turn on the transmitted light and turn off the florescence. Using tweezers, transfer one coverslip with the cells facing toward the pipette from the cell culture plate to the cell culture dish containing 2 milliliters of Hank's buffer at room temperature.Using the fine focus knob and 20 fold objective, focus on a plane about four full turns above the cells. Subsequently, use the micromanipulator to position the pipette tip so that it is focused and in the center left-hand side of the plane as seen through the eyepieces. Once the pipette is in position, focus the microscope on a plane that contains the region of interest.In the imaging of seven div, GFP transfected mouse hippocampal neurons showed an axon pre and post puffing, as well as a following 10 minute recovery period. Here is the Kymograph of time-lapse imaging of the same neuron. Red arrows indicate the varicosities that have formed to following 150 seconds of 190 milliliter H2O puffing, beginning at 30 seconds.Once mastered, this technique can be done in three hours if it is performed properly. Following this procedure, other methods like whole cell recording, time-lapse FRET and TIRF imaging, and calcium imaging can be performed in order to answer additional questions like the impacts of mechanical stress on neural and electrical and calcium signaling, protein trafficking and interactions. After its development, this technique paved the way for researchers in the photo traumatic brain injury to explain molecular mechanisms underlying axonal varicosity formation in living neurons.After watching this video, you should have a good understanding of how to perform the experiments to study mechanosensations of central neurons.

a-microbiomechanical-system-for-studying-varicosity-formation

Research

JoVE Journal

Neuroscience

Systemic and Local Drug Delivery for Treating Diseases of the Central Nervous System in Rodent Models

Thorough preclinical testing of central nervous system (CNS) therapeutics includes a consideration of routes of administration and agent biodistribution in assessing therapeutic efficacy. Between the two major classifications of administration, local vs. systemic, systemic delivery approaches are often preferred due to ease of administration. However, systemic delivery may result in suboptimal drug concentration being achieved in the CNS, and lead to erroneous conclusions regarding agent efficacy. Local drug delivery methods are more invasive, but may be necessary to achieve therapeutic CNS drug levels. Here, we demonstrate proper technique for three routes of systemic drug delivery: intravenous injection, intraperitoneal injection, and oral gavage. In addition, we show a method for local delivery to the brain: convection-enhanced delivery (CED). The use of fluorescently-labeled compounds is included for in vivo imaging and verification of proper drug administration. The methods are presented using murine models, but can easily be adapted for use in rats.

Thorough preclinical testing of drugs that act in the central nervous system often involves assessing and comparing drug biodistribution in association with specific routes of administration. Here, three commonly used methods of systemic delivery (intravenous, intraperitoneal, and oral) as well as a method for local delivery (convection-enhanced delivery) are demonstrated in mice.

Thorough preclinical testing of central nervous system (CNS) therapeutics includes a consideration of routes of administration and agent biodistribution ...

Optic Nerve Transection: A Model of Adult Neuron Apoptosis in the Central Nervous System

Retinal ganglion cells (RGCs) are CNS neurons that output visual information from the retina to the brain, via the optic nerve. 
The optic nerve can be accessed within the orbit of the eye and completely transected (axotomized), cutting the axons of the entire RGC population. Optic nerve 
transection is a reproducible model of apoptotic neuronal cell death in the adult CNS 1-4. This model is particularly attractive because the vitreous
 chamber of the eye acts as a capsule for drug delivery to the retina, permitting experimental manipulations via intraocular injections. The diffusion of chemicals 
through the vitreous fluid ensures that they act upon the entire RGC population. Moreover, RGCs can be selectively transfected by applying short interfering RNAs 
(siRNAs), plasmids, or viral vectors to the cut end of the optic nerve 5-7 or injecting vectors into their target, the superior colliculus 8. 
This allows researchers to study apoptotic mechanisms in the desired neuronal population without confounding effects on other bystander neurons or surrounding glia. 
An additional benefit is the ease and accuracy with which cell survival can be quantified after injury. The retina is a flat, layered tissue and RGCs are localized in 
the innermost layer, the ganglion cell layer. The survival of RGCs can be tracked over time by applying a fluorescent tracer (3% Fluorogold) to the cut end of the 
optic nerve at the time of axotomy, or by injecting the tracer into the superior colliculus (RGC target) one week prior to axotomy. The tracer is retrogradely transported, labeling 
the entire RGC population. Because the ganglion cell layer is a monolayer (one cell thick), RGC densities can be quantified in flat-mounted tissue, without the need 
for stereology. Optic nerve transection leads to the apoptotic death of 90% of injured RGCs within 14 days postaxotomy 9-11. RGC apoptosis has a 
characteristic time-course whereby cell death is delayed 3-4 days postaxotomy, after which the cells rapidly degenerate. This provides a time window for 
experimental manipulations directed against pathways involved in apoptosis.

Optic Nerve transection is a widely used model of adult CNS injury. Ninety percent of retinal ganglion cells (RGCs) whose axons are completely transected (axotomy) die within 14 days after axotomy. This model is easily amenable to experimental manipulations and highly reproducible.

Retinal ganglion cells (RGCs) are CNS neurons that output visual information from the retina to the brain, via the optic nerve. 
The optic nerve can be ...

Morphological Analysis of Drosophila Larval Peripheral Sensory Neuron Dendrites and Axons Using Genetic Mosaics

Nervous system development requires the correct specification of neuron position and identity, followed by accurate neuron class-specific dendritic development and axonal wiring. Recently the dendritic arborization (DA) sensory neurons of the Drosophila larval peripheral nervous system (PNS) have become powerful genetic models in which to elucidate both general and class-specific mechanisms of neuron differentiation.
There are four main DA neuron classes (I-IV)1. They are named in order of increasing dendrite arbor complexity, and have class-specific differences in the genetic control of their differentiation2-10. The DA sensory system is a practical model to investigate the molecular mechanisms behind the control of dendritic morphology11-13 because: 1) it can take advantage of the powerful genetic tools available in the fruit fly, 2) the DA neuron dendrite arbor spreads out in only 2 dimensions beneath an optically clear larval cuticle making it easy to visualize with high resolution in vivo, 3) the class-specific diversity in dendritic morphology facilitates a comparative analysis to find key elements controlling the formation of simple vs. highly branched dendritic trees, and 4) dendritic arbor stereotypical shapes of different DA neurons facilitate morphometric statistical analyses.
DA neuron activity modifies the output of a larval locomotion central pattern generator14-16. The different DA neuron classes have distinct sensory modalities, and their activation elicits different behavioral responses14,16-20. Furthermore different classes send axonal projections stereotypically into the Drosophila larval central nervous system in the ventral nerve cord (VNC)21. These projections terminate with topographic representations of both DA neuron sensory modality and the position in the body wall of the dendritic field7,22,23. Hence examination of DA axonal projections can be used to elucidate mechanisms underlying topographic mapping7,22,23, as well as the wiring of a simple circuit modulating larval locomotion14-17.
We present here a practical guide to generate and analyze genetic mosaics24 marking DA neurons via MARCM (Mosaic Analysis with a Repressible Cell Marker)1,10,25 and Flp-out22,26,27 techniques (summarized in Fig. 1).

Morphological Analysis of Drosophila Larval Peripheral Sensory Neuron Dendrites and Axons Using Genetic Mosaics

The dendritic arborization sensory neurons of the Drosophila larval peripheral nervous system are useful models to elucidate both general and neuron class-specific mechanisms of neuron differentiation. We present a practical guide to generate and analyze dendritic arborization neuron genetic mosaics.

Nervous system development requires the correct specification of neuron position and identity, followed by accurate neuron class-specific dendritic ...

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

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

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

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

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

A Lightweight, Headphones-based System for Manipulating Auditory Feedback in Songbirds

Experimental manipulations of sensory feedback during complex behavior have provided valuable insights into the computations underlying motor control and sensorimotor plasticity1. Consistent sensory perturbations result in compensatory changes in motor output, reflecting changes in feedforward motor control that reduce the experienced feedback error. By quantifying how different sensory feedback errors affect human behavior, prior studies have explored how visual signals are used to recalibrate arm movements2,3 and auditory feedback is used to modify speech production4-7. The strength of this approach rests on the ability to mimic naturalistic errors in behavior, allowing the experimenter to observe how experienced errors in production are used to recalibrate motor output.
Songbirds provide an excellent animal model for investigating the neural basis of sensorimotor control and plasticity8,9. The songbird brain provides a well-defined circuit in which the areas necessary for song learning are spatially separated from those required for song production, and neural recording and lesion studies have made significant advances in understanding how different brain areas contribute to vocal behavior9-12. However, the lack of a naturalistic error-correction paradigm - in which a known acoustic parameter is perturbed by the experimenter and then corrected by the songbird - has made it difficult to understand the computations underlying vocal learning or how different elements of the neural circuit contribute to the correction of vocal errors13.
The technique described here gives the experimenter precise control over auditory feedback errors in singing birds, allowing the introduction of arbitrary sensory errors that can be used to drive vocal learning. Online sound-processing equipment is used to introduce a known perturbation to the acoustics of song, and a miniaturized headphones apparatus is used to replace a songbird's natural auditory feedback with the perturbed signal in real time. We have used this paradigm to perturb the fundamental frequency (pitch) of auditory feedback in adult songbirds, providing the first demonstration that adult birds maintain vocal performance using error correction14. The present protocol can be used to implement a wide range of sensory feedback perturbations (including but not limited to pitch shifts) to investigate the computational and neurophysiological basis of vocal learning.

We describe the design and assembly of miniaturized headphones suitable for replacing a songbird&#x2019;s natural auditory feedback with a manipulated acoustic signal. Online sound processing hardware is used to manipulate song output, introduce real-time errors in auditory feedback via the headphones, and drive vocal motor learning.

Experimental manipulations of sensory feedback during complex behavior have provided valuable insights into the computations underlying motor control and ...

Direct Intraventricular Delivery of Drugs to the Rodent Central Nervous System

Due to an inability to cross the blood brain barrier, certain drugs need to be directly delivered into the central nervous system (CNS). Our lab focuses specifically on antisense oligonucleotides (ASOs), though the techniques shown in the video here can also be used to deliver a plethora of other drugs to the CNS. Antisense oligonucleotides (ASOs) have the capability to knockdown sequence-specific targets 1 as well as shift isoform ratios of specific genes 2. To achieve widespread gene knockdown or splicing in the CNS of mice, the ASOs can be delivered into the brain using two separate routes of administration, both of which we demonstrate in the video.
The first uses Alzet osmotic pumps, connected to a catheter that is surgically implanted into the lateral ventricle. This allows the ASOs to be continuously infused into the CNS for a designated period of time. The second involves a single bolus injection of a high concentration of ASO into the right lateral ventricle. Both methods use the mouse cerebral ventricular system to deliver the ASO to the entire brain and spinal cord, though depending on the needs of the study, one method may be preferred over the other.

We describe a method to target drugs to the central nervous system by either implanting a catheter or performing a bolus injection into the right lateral ventricle in mice. We focus specifically on the delivery of antisense oligonucleotides. This technique is readily adaptable to other drugs and to rats.

Due to an inability to cross the blood brain barrier, certain drugs need to be directly delivered into the central nervous system (CNS). Our lab focuses ...

Immunohistochemical Analysis in the Rat Central Nervous System and Peripheral Lymph Node Tissue Sections

Immunohistochemistry (IHC) provides highly specific, reliable and attractive protein visualization. Correct performance and interpretation of an IHC-based multicolor labeling is challenging, especially when utilized for assessing interrelations between target proteins in the tissue with a high fat content such as the central nervous system (CNS).
Our protocol represents a refinement of the standard immunolabeling technique particularly adjusted for detection of both structural and soluble proteins in the rat CNS and peripheral lymph nodes (LN) affected by neuroinflammation. Nonetheless, with or without further modifications, our protocol could likely be used for detection of other related protein targets, even in other organs and species than here presented.

We here present an optimized, detailed protocol for double immunostaining in formalin-fixed, paraffin-embedded rat central nervous system (CNS) and peripheral lymph node (LN) tissue sections.

Immunohistochemistry (IHC) provides highly specific, reliable and attractive protein visualization. Correct performance and interpretation of an IHC-based ...

Laser Nanosurgery of Cerebellar Axons In Vivo

Only a few neuronal populations in the central nervous system (CNS) of adult mammals show local regrowth upon dissection of their axon. In order to understand the mechanism that promotes neuronal regeneration, an in-depth analysis of the neuronal types that can remodel after injury is needed. Several studies showed that damaged climbing fibers are capable of regrowing also in adult animals1,2. The investigation of the time-lapse dynamics of degeneration and regeneration of these axons within their complex environment can be performed by time-lapse two-photon fluorescence (TPF) imaging in vivo3,4. This technique is here combined with laser surgery, which proved to be a highly selective tool to disrupt fluorescent structures in the intact mouse cortex5-9.
This protocol describes how to perform TPF time-lapse imaging and laser nanosurgery of single axonal branches in the cerebellum in vivo. Olivocerebellar neurons are labeled by anterograde tracing with a dextran-conjugated dye and then monitored by TPF imaging through a cranial window. The terminal portion of their axons are then dissected by irradiation with a Ti:Sapphire laser at high power. The degeneration and potential regrowth of the damaged neuron are monitored by TPF in vivo imaging during the days following the injury.

Laser Nanosurgery of Cerebellar Axons In Vivo

Two-photon imaging, coupled to laser nanodissection, are useful tools to study degenerative and regenerative processes in the central nervous system with subcellular resolution. This protocol shows how to label, image, and dissect single climbing fibers in the cerebellar cortex in vivo.

Only a few neuronal populations in the central nervous system (CNS) of adult mammals show local regrowth upon dissection of their axon. In order to ...

In vivo Optogenetic Stimulation of the Rodent Central Nervous System

The ability to probe defined neural circuits in awake, freely-moving animals with cell-type specificity, spatial precision, and high temporal resolution has been a long sought tool for neuroscientists in the systems-level search for the neural circuitry governing complex behavioral states. Optogenetics is a cutting-edge tool that is revolutionizing the field of neuroscience and represents one of the first systematic approaches to enable causal testing regarding the relation between neural signaling events and behavior. By combining optical and genetic approaches, neural signaling can be bi-directionally controlled through expression of light-sensitive ion channels (opsins) in mammalian cells. The current protocol describes delivery of specific wavelengths of light to opsin-expressing cells in deep brain structures of awake, freely-moving rodents for neural circuit modulation. Theoretical principles of light transmission as an experimental consideration are discussed in the context of performing in vivo optogenetic stimulation. The protocol details the design and construction of both simple and complex laser configurations and describes tethering strategies to permit simultaneous stimulation of multiple animals for high-throughput behavioral testing.

In vivo Optogenetic Stimulation of the Rodent Central Nervous System

Optogenetics has become a powerful tool for use in behavioral neuroscience experiments. This protocol offers a step-by-step guide to the design and set-up of laser systems, and provides a full protocol for carrying out multiple and simultaneous in vivo optogenetic stimulations compatible with most rodent behavioral testing paradigms.

The ability to probe defined neural circuits in awake, freely-moving animals with cell-type specificity, spatial precision, and high temporal resolution ...

Methods and Tips for Intravenous Administration of Adeno-associated Virus to Rats and Evaluation of Central Nervous System Transduction

Adeno-associated virus (AAV) vectors are a key reagent in the neurosciences for clustered regularly interspaced short palindromic repeats (CRISPR), optogenetics, cre-lox targeting, etc. The purpose of this manuscript is to aid the investigator attempting expansive central nervous system (CNS) gene transfer in the rat via tail vein injection of AAV. Wide-scale expression is relevant for conditions with widespread pathology, and a rat model is significant due to its greater size and physiologic similarities to humans compared to mice. In this example application, a wide-scale neuronal transduction is used to mimic a neurodegenerative disease that affects the entire spinal cord, amyotrophic lateral sclerosis (ALS). The efficient wide-scale CNS transduction can also be used to deliver therapeutic protein factors in pre-clinical studies. After a post-injection expression interval of several weeks, the effects of the transduction are evaluated. For a green fluorescent protein (GFP) control vector, the amount of GFP in the cerebellum is estimated quickly and reliably by a basic imaging program. For motor disease phenotypes that are induced by the ALS related protein transactive response DNA-binding protein of 43 kDa (TDP-43), the deficits are scored by escape reflex and rotarod. Beyond disease modeling and gene therapy, there are diverse potential applications for the wide-scale gene targeting described here. The expanded use of this method will aid in expediting hypothesis testing in the neurosciences and neurogenetics.

Methods for a wide-scale central nervous system gene delivery in the rat are covered. In this example, the purpose is to mimic a disease that affects the entire spinal cord. The widespread transduction can be used to deliver a therapeutic protein to the CNS from a one-time, peripheral administration.

Adeno-associated virus (AAV) vectors are a key reagent in the neurosciences for clustered regularly interspaced short palindromic repeats (CRISPR), ...