The work presented in the paper was supported by the National Science Foundation, Emerging Frontiers in Research and Innovation (NSF-EFRI) program grant number 0938072. The contents of this paper are solely the responsibility of the authors and do not necessarily represent the official views of the NSF. The authors also wish to thank Dr. Samsoon Inayat for his work designing and testing the initial experimental setup for chemical stimulation and Mr. Ashwin Raghunathan for his work designing, fabricating, and evaluating the multiport microfluidic device used in this study.

<ol>
	<li>Pascolini, D., Mariotti, S. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Global+estimates+of+visual+impairment:+2010.">Global estimates of visual impairment: 2010.</a> Br J Ophthalmol. , (2011).</li><li>Fritsche, L. G., Fariss, R. N., Stambolian, D., Abecasis, G. R., Curcio, C. A., Swaroop, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Age-Related+Macular+Degeneration:+Genetics+and+Biology+Coming+Together.">Age-Related Macular Degeneration: Genetics and Biology Coming Together.</a> Annu Rev Genomics Hum Genet. 15, 151-171 (2014).</li><li>Marc, R. E., 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=Neural+reprogramming+in+retinal+degeneration.">Neural reprogramming in retinal degeneration.</a> Invest Ophthalmol Vis Sci. 48, 3364-3371 (2007).</li><li>Jones, B. W., Kondo, M., Terasaki, H., Lin, Y., McCall, M., Marc, 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=Retinal+remodeling.">Retinal remodeling.</a> Jpn J Ophthalmol. 56, 289-306 (2012).</li><li>Soto, F., Kerschensteiner, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synaptic+remodeling+of+neuronal+circuits+in+early+retinal+degeneration.">Synaptic remodeling of neuronal circuits in early retinal degeneration.</a> Front Cell Neurosci. 9, (2015).</li><li>Trenholm, S., Awatramani, G. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Origins+of+spontaneous+activity+in+the+degenerating+retina.">Origins of spontaneous activity in the degenerating retina.</a> Front Cell Neurosci. 9, (2015).</li><li>Euler, T., Schubert, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multiple+Independent+Oscillatory+Networks+in+the+Degenerating+Retina.">Multiple Independent Oscillatory Networks in the Degenerating Retina.</a> Front Cell Neurosci. 9, (2015).</li><li>Boye, S. E., Boye, S. L., Lewin, A. S., Hauswirth, W. 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S., de Juan, E., Dagnelie, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Bionic+Eye:+A+Quarter+Century+of+Retinal+Prosthesis+Research+and+Development.">The Bionic Eye: A Quarter Century of Retinal Prosthesis Research and Development.</a> Ophthalmol. 123, S89-S97 (2016).</li><li>Cruz, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Argus+II+epiretinal+prosthesis+system+allows+letter+and+word+reading+and+long-term+function+in+patients+with+profound+vision+loss.">The Argus II epiretinal prosthesis system allows letter and word reading and long-term function in patients with profound vision loss.</a> Br J Ophthalmol. 97, 632-636 (2013).</li><li>Zrenner, E., 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=Subretinal+electronic+chips+allow+blind+patients+to+read+letters+and+combine+them+to+words.">Subretinal electronic chips allow blind patients to read letters and combine them to words.</a> P R Soc B. 278, 1489-1497 (2011).</li><li>Stronks, H. 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B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Retinal+implants:+a+systematic+review.">Retinal implants: a systematic review.</a> Br J Ophthalmol. 98, 852-856 (2014).</li><li>Cai, C., Twyford, P., Fried, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+response+of+retinal+neurons+to+high-frequency+stimulation.">The response of retinal neurons to high-frequency stimulation.</a> J Neural Eng. 10, 036009 (2013).</li><li>Eiber, C. D., Lovell, N. H., Suaning, G. 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B., Humayun, M. S., Weiland, J. D., Suzuki, S., D'Anna, S. A., de Juan, 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+Histological+and+Electrophysiological+Results+of+an+Inactive+Epiretinal+Electrode+Array+Implantation+in+Dogs.">Long-Term Histological and Electrophysiological Results of an Inactive Epiretinal Electrode Array Implantation in Dogs.</a> Invest Ophthalmol Vis Sci. 40, 2073-2081 (1999).</li><li>Peterman, M. C., Noolandi, J., Blumenkranz, M. S., Fishman, H. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Localized+chemical+release+from+an+artificial+synapse+chip.">Localized chemical release from an artificial synapse chip.</a> PNAS. 101, 9951-9954 (2004).</li><li>Finlayson, P. 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The authors have nothing to disclose.

The method presented here demonstrates a unique neural stimulation paradigm, wherein retinal neurons are chemically stimulated by injecting native neurotransmitter chemicals into the subsurface of the retina in vitro. This chemical stimulation technique offers several benefits over the conventional electrical stimulation technique, including selectivity and high focal specificity of target neurons. The protocol above details how small volume pneumatic injections of the neurotransmitter glutamate delivered near t...

Photoreceptor degenerative diseases, such as retinitis pigmentosa and age-related macular degeneration, are leading inheritable causes of vision loss and are currently incurable1,2. Although these diseases arise from a variety of specific genetic mutations, photoreceptor degenerative diseases are characterized as a group by the progressive loss of the photoreceptor cells in the retina, which eventually causes blindness. The loss of photoreceptors triggers widespread remodeling throughout the retina but surviving retinal neurons, including the bipolar cells and RGCs, remain intact and relatively functional even in advanced stages of photoreceptor degeneration3,4,5,6,7.
The mechanisms and pathologies of these diseases have been well characterized3,4,5,6,7 but an effective treatment remains elusive. Over the past three decades, researchers worldwide have investigated a variety of therapeutic treatments for restoring vision to those affected with photoreceptor degenerative diseases including gene therapy8, stem cell treatment9, retinal transplantation10, and artificial stimulation11,12 of the surviving retinal neurons. Of these, the most clinically available are retinal prostheses, which are artificial neurostimulation devices that have traditionally utilized an array of electrodes to electrically stimulate either the bipolar cells or RGCs in specific patterns with the goal of creating artificial visual perceptions in patients11. Current generation electrical prostheses, such as the Argus II13 and Alpha-IMS14 devices, have achieved clinical approval and preliminary studies have indicated that they can improve the quality of life for patients by restoring a measure of vision using both epiretinal (front of the retina) and subretinal (back of the retina) implanted devices15,16. Research groups around the world are working on advancing retinal prostheses beyond the successes of these first-generation devices17,18,19,20 but have faced difficulties designing an electrical prosthesis capable of restoring high acuity vision below the legal blindness level to patients. Recent studies have shown that achieving higher spatial resolution than that enabled by the current generation electrical-based prostheses is challenging because of the charge injection limit, which necessitates the use of large electrodes to safely stimulate retinal neurons at the cost of spatial resolution, i.e. visual acuity11,21. Moreover, electrical stimulation is further limited because it typically stimulates all nearby cells and therefore elicits unnatural and confusing perceptions in patients, largely because it is an inherently unnatural stimulation paradigm21. Nevertheless, the early successes of electrical stimulation have demonstrated that artificial neurostimulation can be an effective treatment for photoreceptor degenerative diseases. This leads one to hypothesize that an even more effective treatment might be achievable by stimulating the retina with neurotransmitter chemicals, the natural agents of communication at chemical synapses. The purpose of the method presented in this paper is to explore the therapeutic feasibility of chemical stimulation, which seeks to mimic the natural system of synaptic communication between retinal neurons, as a biomimetic alternative to electrical stimulation for a retinal prosthesis.
Translation of the concept of therapeutic chemical stimulation to a chemical retinal prosthesis relies on chemically activating target retinal neurons with small quantities of native neurotransmitters, such as glutamate, released through a microfluidic device comprising a large array of microports in response to visual stimulation. In this way, a chemical retinal prosthesis would essentially be a biomimetic artificial photoreceptor layer that translates photons naturally reaching the retina to chemical signals. Since these chemical signals use the same neurotransmitters utilized in normal retinal signaling and stimulate the surviving retinal neurons of a degenerated retina through the same synaptic pathways used by normal vision pathways, the resulting visual perception achieved through a chemical retinal prosthesis could be more natural and comprehensible compared to one evoked through an electrical prosthesis. Moreover, since the microports through which neurotransmitters are released can be made extremely small and arrayed in high density, unlike the electrodes, a potential chemical prosthetic might be able to achieve more focal stimulation and higher spatial resolution than an electrical prosthesis. Thus, based on these potential advantages, a chemical retinal prosthesis offers a highly promising alternative to electrical prostheses.
Chemical stimulation of the retina, however, has been relatively little explored until recently. While electrical stimulation of the retina has been well characterized over decades of work through in vitro22,23, in vivo23,24, and clinical studies13,14, studies on chemical stimulation have been limited exclusively to a few in vitro works25,26,27,28. Iezzi and Finlayson26 and Inayat et al.27 demonstrated epiretinal chemical stimulation of the retina in vitro using a single electrode and a multielectrode array (MEA), respectively, to record the glutamate evoked responses of retinal neurons. More recently, Rountree et al.28 demonstrated the differential stimulation of the OFF and ON retinal pathways using glutamate from the subretinal side and an MEA to record the neuronal responses from multiple sites on the retina. Although these works have preliminarily established the feasibility of chemical stimulation, further studies are essential to investigate many aspects of this approach beyond those addressed so far25,26,27,28, and fine-tune the therapeutic stimulation parameters in both in vitro and in vivo animal models before translating this concept to a chemical retinal prosthesis as discussed above. However, currently there is no established methodology for accomplishing chemical stimulation of the retina in the literature and the methods used in the previous works have not been described in such detail as would be essential for replicative studies. Therefore, the rationale for this methods paper is to provide a well-defined framework for conducting in vitro chemical stimulation of the retina for those investigators interested in either replicating our previous studies27,28 or further advancing this nascent concept of chemical neurostimulation.
Here we demonstrate a method for conducting in vitro chemical stimulation of retinal neurons in wholemount retinas of wild-type rats and a photoreceptor degenerated rat model that closely mimics the progression of photoreceptor degenerative diseases in humans. The rationale behind developing this stimulation method in in vitro models is to evaluate the therapeutic ranges of various stimulation parameters and study neural response characteristics that would be impossible or difficult to observe in in vivo models, especially during the initial studies focused on evaluating the feasibility of this approach. In this procedure, we show both single-site and simultaneous multi-site chemical stimulations of retinas by delivering small quantities of 1 mM glutamate near target retinal neurons via commercially available single-port glass micropipettes and a custom micromachined multi-port microfluidic device, respectively. While both single-site and multi-site stimulations accomplish the basic objective of investigating the therapeutic feasibility of chemical neuromodulation, each serves a distinct purpose with a unique advantage. The single-site stimulation, which may be accomplished with commercially available pre-pulled glass micropipettes, can be used to inject chemicals directly into the subsurface of the retina at a single site and serves to investigate if observable RGC spike rate responses that are similar to visually evoked light responses can be elicited focally under the injection site. On the other hand, multi-site stimulation, which requires a specially fabricated multiport microfluidic device, can be used to inject chemicals spatially at multiple sites over the surface of the retina and serves to investigate how well glutamate-evoked RCG response patterns correspond to the glutamate injection patterns in pattern stimulation studies.

<table>
	<tbody>
		<tr>
			<td>Microelectrode array, perforated layout</td>
			<td>Multi Channel Systems, GmbH</td>
			<td>60pMEA200/30iR-Ti-pr</td>
			<td>http://www.multichannelsystems.com/products/microelectrode-arrays/60pmea20030ir-ti</td>
		</tr>
		<tr>
			<td>MEA amplifier</td>
			<td>Multi Channel Systems, GmbH</td>
			<td>MEA1060-Inv</td>
			<td>http://www.multichannelsystems.com/products/mea1060-inv</td>
		</tr>
		<tr>
			<td>Bottom perfusion groundplate for pMEA</td>
			<td>Multi Channel Systems, GmbH</td>
			<td>MEA1060-Inv-(BC)-PGP</td>
			<td>http://www.multichannelsystems.com/products/mea1060-inv-bc-pgp</td>
		</tr>
		<tr>
			<td>3-axis Motorized Micromanipulator</td>
			<td>Sutter Instruments, Novato, CA</td>
			<td>MP-285</td>
			<td>https://www.sutter.com/MICROMANIPULATION/mp285.html</td>
		</tr>
		<tr>
			<td>Micromanipulator Control System</td>
			<td>Sutter Instruments, Novato, CA</td>
			<td>MPC-200</td>
			<td>https://www.sutter.com/MICROMANIPULATION/mpc200.html</td>
		</tr>
		<tr>
			<td>Gantry style micromanipulator stand with linear slide</td>
			<td>Sutter Instruments, Novato, CA</td>
			<td>MT-75/LS</td>
			<td>https://www.sutter.com/STAGES/mt75.html</td>
		</tr>
		<tr>
			<td>8-channel Programmable Multichannel Pressure Injector</td>
			<td>OEM: MicroData Instrument, S. Plainfield, NJ 
			Vendor: Harvard Apparatus UK</td>
			<td>PM-8000 or PM-8</td>
			<td>OEM: http://www.microdatamdi.com/pm8000.htm 
			Vendor: https://www.harvardapparatus.co.uk/webapp/wcs/stores/servlet/product_11555_10001_39808_-1_HAUK_ProductDetail</td>
		</tr>
		<tr>
			<td>Axopatch 200A Integrating Patch Clamp Amplifier</td>
			<td>Molecular Devices, Sunnyvale, CA</td>
			<td>Axopatch 200A</td>
			<td>Axopatch 200A has been replaced with a newer model Axopatch 200B: 
			https://www.moleculardevices.com/systems/axon-conventional-patch-clamp/axopatch-200b-amplifier</td>
		</tr>
		<tr>
			<td>Patch clamp headstage</td>
			<td>Molecular Devices, Sunnyvale, CA</td>
			<td>CV 201A</td>
			<td>http://mdc.custhelp.com/app/answers/detail/a_id/16554/~/axopatch-200a%3A-selection-cv-headstage</td>
		</tr>
		<tr>
			<td>Vacuum waste kit</td>
			<td>ALA Scientific Instruments, Farmingdale, NY</td>
			<td>VMK</td>
			<td>http://alascience.com/product/vacuum-waste-kit/</td>
		</tr>
		<tr>
			<td>Pipette holder</td>
			<td>Warner Instruments, Hamden, CT</td>
			<td>QSW-A10P</td>
			<td>https://www.warneronline.com/product_info.cfm?id=915</td>
		</tr>
		<tr>
			<td>Pre-pulled 10 &#956;m tip diameter glass micropipettes</td>
			<td>World Precision Instruments, Sarasota, FL</td>
			<td>TIP10TW1</td>
			<td>https://www.wpiinc.com/products/laboratory-supplies/make-selection-pre-pulled-glass-pipettes-plain/</td>
		</tr>
		<tr>
			<td>Zoom stereomicroscope</td>
			<td>Nikon, Tokyo, Japan</td>
			<td>SMZ-745T</td>
			<td>https://www.nikoninstruments.com/Products/Stereomicroscopes-and-Macroscopes/Stereomicroscopes/SMZ745</td>
		</tr>
		<tr>
			<td>Microscope boom stand with dual linear ball bearing arm</td>
			<td>Old School Industries, Inc., Dacono, CO</td>
			<td>OS1010H-16BB</td>
			<td>http://www.osi-incorp.com/productdisplay/dual-linear-ball-bearing-arm</td>
		</tr>
		<tr>
			<td>Zoom Stereo Microscope with C-LEDS Hybrid LED Stand</td>
			<td>Nikon, Tokyo, Japan</td>
			<td>SMZ-445</td>
			<td>https://www.nikoninstruments.com/Products/Stereomicroscopes-and-Macroscopes/Stereomicroscopes/SMZ445</td>
		</tr>
		<tr>
			<td>Inverted microscope system</td>
			<td>Nikon, Tokyo, Japan</td>
			<td>Eclipse Ti-E</td>
			<td>https://www.nikoninstruments.com/Products/Inverted-Microscopes/Eclipse-Ti-E</td>
		</tr>
		<tr>
			<td>Ames medium</td>
			<td>Sigma-Aldrich, St. Louis, MO</td>
			<td>A1420</td>
			<td>http://www.sigmaaldrich.com/catalog/product/sigma/a1420</td>
		</tr>
		<tr>
			<td>L-Glutamic Acid (Glutamate)</td>
			<td>Sigma-Aldrich, St. Louis, MO</td>
			<td>G5667</td>
			<td>http://www.sigmaaldrich.com/catalog/product/mm/100291</td>
		</tr>
		<tr>
			<td>Sodium bicarbonate</td>
			<td>Sigma-Aldrich, St. Louis, MO</td>
			<td>S8761</td>
			<td>http://www.sigmaaldrich.com/catalog/product/sigma/s8761</td>
		</tr>
		<tr>
			<td>60 mm Petri dish (10 mm tall)</td>
			<td>Fischer Scientific, Waltham, MA</td>
			<td>FB0875713A</td>
			<td>60 mm clear petri dish; https://www.fishersci.com/shop/products/fisherbrand-petri-dishes-clear-lid-12/fb0875713a</td>
		</tr>
		<tr>
			<td>Jewelers #5 Forceps</td>
			<td>World Precision Instruments, Sarasota, FL</td>
			<td>555227F</td>
			<td>https://www.wpiinc.com/products/laboratory-supplies/555227f-jewelers-5-forceps-11cm-straight-titanium/</td>
		</tr>
		<tr>
			<td>Standard Scalpel Blad #24</td>
			<td>World Precision Instruments, Sarasota, FL</td>
			<td>500247</td>
			<td>https://www.wpiinc.com/products/laboratory-supplies/500247-standard-scalpel-blade-24/</td>
		</tr>
		<tr>
			<td>Scalpel Handle #4</td>
			<td>World Precision Instruments, Sarasota, FL</td>
			<td>500237</td>
			<td>https://www.wpiinc.com/products/laboratory-supplies/500237-scalpel-handle-4-14cm/</td>
		</tr>
		<tr>
			<td>Vannas Tubingen Dissection Scissors</td>
			<td>World Precision Instruments, Sarasota, FL</td>
			<td>503378</td>
			<td>https://www.wpiinc.com/products/laboratory-supplies/503378-vannas-tubingen-scissors-8cm-straight-german-steel/</td>
		</tr>
		<tr>
			<td>Nylon mesh kit</td>
			<td>Warner Instruments, Hamden, CT</td>
			<td>NYL/MESH</td>
			<td>https://www.warneronline.com/product_info.cfm?id=1173</td>
		</tr>
		<tr>
			<td>Harp slice grid</td>
			<td>ALA Scientific Instruments, Farmingdale, NY</td>
			<td>HSG-5AD</td>
			<td>http://alascience.com/product/standard-harp-slice-grids/</td>
		</tr>
		<tr>
			<td>Ag/AgCl reference electrode pellet</td>
			<td>Multi Channel Systems, GmbH</td>
			<td>P1060</td>
			<td>http://www.multichannelsystems.com/products/p1060</td>
		</tr>
		<tr>
			<td>4 Channel Valve Controlled Gravity Perfusion System</td>
			<td>ALA Scientific Instruments, Farmingdale, NY</td>
			<td>VC3-4xG</td>
			<td>http://alascience.com/product/4-channel-valve-controlled-gravity-perfusion-system/</td>
		</tr>
		<tr>
			<td>Zyla 5.5 sCMOS microscope camera</td>
			<td>Andor Technology, Belfast, UK</td>
			<td>Zyla 5.5 sCMOS</td>
			<td>http://www.andor.com/scientific-cameras/neo-and-zyla-scmos-cameras/zyla-55-scmos</td>
		</tr>
		<tr>
			<td>Silver wire (50 &#956;m diameter)</td>
			<td>Fischer Scientific, Waltham, MA</td>
			<td>AA44461G5</td>
			<td>https://www.fishersci.com/shop/products/silver-wire-0-05mm-0-002-in-dia-annealed-99-99-metals-basis-3/aa44461g5</td>
		</tr>
		<tr>
			<td>Tygon microbore tubing (1.6 mm diameter)</td>
			<td>Cole Parmer, Vernon Hills , IL</td>
			<td>EW-06419-01</td>
			<td>https://www.coleparmer.com/i/tygon-microbore-tubing-0-020-x-0-060-od-100-ft-roll/0641901</td>
		</tr>
		<tr>
			<td>Tilting Tool Holder with Steel Cannula</td>
			<td>ALA Scientific Instruments, Farmingdale, NY</td>
			<td>TILTPORT</td>
			<td>One each of these were utilized for top perfusion and suction; http://alascience.com/product/tilting-tool-holder-with-steel-cannula/</td>
		</tr>
		<tr>
			<td>Roscolux #26 Light Red Filter Sheet</td>
			<td>Rosco Laboratories Inc., 52 Harbor View, Stamford, CT</td>
			<td>R2611</td>
			<td>Manufacturer: http://us.rosco.com/en/products/catalog/roscolux 
			Vendor: https://www.bhphotovideo.com/c/product/43957-REG/Rosco_RS2611_26_Filter_Light.html</td>
		</tr>
		<tr>
			<td>Smith &#38; Wesson Galaxy Red Flashlight</td>
			<td>Smith &#38; Wesson, 2100 Roosevelt Avenue, Springfield, MA</td>
			<td>4588</td>
			<td>Manufacturer: https://www.smith-wesson.com/ 
			Vendor: http://www.mypilotstore.com/mypilotstore/sep/4588</td>
		</tr>
		<tr>
			<td>MC_Rack Software</td>
			<td>Multi Channel Systems, GmbH</td>
			<td>MC_Rack</td>
			<td>http://www.multichannelsystems.com/software/mc-rack</td>
		</tr>
		<tr>
			<td>Labview Software</td>
			<td>National Instruments, Austin, TX</td>
			<td>LabVIEW</td>
			<td>http://www.ni.com/labview/</td>
		</tr>
		<tr>
			<td>NIS-Elements: Basic Research Software</td>
			<td>Nikon, Tokyo, Japan</td>
			<td>NIS-Elements BR</td>
			<td>https://www.nikoninstruments.com/Products/Software/NIS-Elements-Basic-Research</td>
		</tr>
	</tbody>
</table>

methodology for biomimetic chemical neuromodulation of rat retinas with the neurotransmitter glutamate in vitro

Photoreceptor degenerative diseases cause irreparable blindness through the progressive loss of photoreceptor cells in the retina. Retinal prostheses are an emerging treatment for photoreceptor degenerative diseases that seek to restore vision by artificially stimulating the surviving retinal neurons in the hope of eliciting comprehensible visual perception in patients. Current retinal prostheses have demonstrated success in restoring limited vision to patients using an array of electrodes to electrically stimulate the retina but face substantial physical barriers in restoring high acuity, natural vision to patients. Chemical neurostimulation using native neurotransmitters is a biomimetic alternative to electrical stimulation and could bypass the fundamental limitations associated with retinal prostheses using electrical neurostimulation. Specifically, chemical neurostimulation has the potential to restore more natural vision with comparable or better visual acuities to patients by injecting very small quantities of neurotransmitters, the same natural agents of communication used by retinal chemical synapses, at much finer resolution than current electrical prostheses. However, as a relatively unexplored stimulation paradigm, there is no established protocol for achieving chemical stimulation of the retina in vitro. The purpose of this work is to provide a detailed framework for accomplishing chemical stimulation of the retina for investigators who wish to study the potential of chemical neuromodulation of the retina or similar neural tissues in vitro. In this work, we describe the experimental setup and methodology for eliciting retinal ganglion cell (RGC) spike responses similar to visual light responses in wild-type and photoreceptor-degenerated wholemount rat retinas by injecting controlled volumes of the neurotransmitter glutamate into the subretinal space using glass micropipettes and a custom multiport microfluidic device. This methodology and protocol are general enough to be adapted for neuromodulation using other neurotransmitters or even other neural tissues.

This protocol can be used to chemically stimulate both normal, wild-type retinas as well as photoreceptor degenerated retinas, despite the substantial cellular remodeling caused by the loss of the photoreceptors. Before beginning experiments with either photoreceptor degenerated or wild-type retinas, the recording and stimulation equipment (Figure 1 and Figure 2) need to be readied and the pMEA (Figure 5</str...

Watch this Scientific Journal Video about Methodology for Biomimetic Chemical Neuromodulation of Rat Retinas with the Neurotransmitter Glutamate In Vitro at JoVE.com

Methodology for Biomimetic Chemical Neuromodulation of Rat Retinas with the Neurotransmitter Glutamate In Vitro

This protocol describes a novel method for investigating a form of chemical neurostimulation of wholemount rat retinas in vitro with the neurotransmitter glutamate. Chemical neurostimulation is a promising alternative to the conventional electrical neurostimulation of retinal neurons for treating irreversible blindness caused by photoreceptor degenerative diseases.

Methodology for Biomimetic Chemical Neuromodulation of Rat Retinas with the Neurotransmitter Glutamate In Vitro

Photoreceptor degenerative diseases cause irreparable blindness through the progressive loss of photoreceptor cells in the retina. Retinal prostheses are ...

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Research

JoVE Journal

Bioengineering

7.7K Views.  University of Illinois at Chicago. This protocol describes a novel method for investigating a form of chemical neurostimulation of wholemount rat retinas in vitro with the neurotransmitter glutamate. Chemical neurostimulation is a promising alternative to the conventional electrical neurostimulation of retinal neurons for treating irreversible blindness caused by photoreceptor degenerative diseases.

Video: Methodology for Biomimetic Chemical Neuromodulation of Rat Retinas with the Neurotransmitter Glutamate In Vitro

Microfluidic Device for Recreating a Tumor Microenvironment in Vitro

We have developed a microfluidic device that mimics the delivery and systemic clearance of drugs to heterogeneous three-dimensional tumor tissues in vitro. Nutrients delivered by vasculature fail to reach all parts of tumors, giving rise to heterogeneous microenvironments consisting of viable, quiescent and necrotic cell types. Many cancer drugs fail to effectively penetrate and treat all types of cells because of this heterogeneity. Monolayers of cancer cells do not mimic this heterogeneity, making it difficult to test cancer drugs with a suitable in vitro model. Our microfluidic devices were fabricated out of PDMS using soft lithography. Multicellular tumor spheroids, formed by the hanging drop method, were inserted and constrained into rectangular chambers on the device and maintained with continuous medium perfusion on one side. The rectangular shape of chambers on the device created linear gradients within tissue. Fluorescent stains were used to quantify the variability in apoptosis within tissue. Tumors on the device were treated with the fluorescent chemotherapeutic drug doxorubicin, time-lapse microscopy was used to monitor its diffusion into tissue, and the effective diffusion coefficient was estimated. The hanging drop method allowed quick formation of uniform spheroids from several cancer cell lines. The device enabled growth of spheroids for up to 3 days. Cells in proximity of flowing medium were minimally apoptotic and those far from the channel were more apoptotic, thereby accurately mimicking regions in tumors adjacent to blood vessels. The estimated value of the doxorubicin diffusion coefficient agreed with a previously reported value in human breast cancer. Because the penetration and retention of drugs in solid tumors affects their efficacy, we believe that this device is an important tool in understanding the behavior of drugs, and developing new cancer therapeutics.

Microfluidic Device for Recreating a Tumor Microenvironment in Vitro

We present the procedure for fabrication and operation of a microfluidic device that recreates heterogeneous tumor microenvironments in vitro. The variability in apoptosis within tumor tissue was quantified using fluorescent stains and the effective diffusion coefficient of the chemotherapeutic drug doxorubicin into tumor tissue was evaluated.

We have developed a microfluidic device that mimics the delivery and systemic clearance of drugs to heterogeneous three-dimensional tumor tissues in ...

In vitro Cell Culture Model for Toxic Inhaled Chemical Testing

Cell cultures are indispensable to develop and study efficacy of therapeutic agents, prior to their use in animal models. We have the unique ability to model well differentiated human airway epithelium and heart muscle cells. This could be an invaluable tool to study the deleterious effects of toxic inhaled chemicals, such as chlorine, that can normally interact with the cell surfaces, and form various byproducts upon reacting with water, and limiting their effects in submerged cultures. Our model using well differentiated human airway epithelial cell cultures at air-liqiuid interface circumvents this limitation as well as provides an opportunity to evaluate critical mechanisms of toxicity of potential poisonous inhaled chemicals. We describe enhanced loss of membrane integrity, caspase release and death upon toxic inhaled chemical such as chlorine exposure. In this article, we propose methods to model chlorine exposure in mammalian heart and airway epithelial cells in culture and simple tests to evaluate its effect on these cell types.

In vitro Cell Culture Model for Toxic Inhaled Chemical Testing

This protocol is designed to demonstrate exposure method of cell cultures to inhaled toxic chemicals. Exposure of differentiated air-liquid&#160;interface (ALI) cultures of airway epithelial cells provides a unique model of airway exposure to toxic gases such as chlorine. In this manuscript we describe effect of chlorine exposure on air-liquid&#160;interface cultures of epithelial cells and submerged culture of cardiomyocytes. In vitro exposure systems allow important mechanistic studies to evaluate pathways that could then be utilized to develop novel therapeutic agents.

Cell cultures are indispensable to develop and study efficacy of therapeutic agents, prior to their use in animal models. We have the unique ability to ...

Eye Irritation Test (EIT) for Hazard Identification of Eye Irritating Chemicals using Reconstructed Human Cornea-like Epithelial (RhCE) Tissue Model

To comply with the Seventh Amendment to the EU Cosmetics Directive and EU REACH legislation, validated non-animal alternative methods for reliable and accurate assessment of ocular toxicity in man are needed. To address this need, we have developed an eye irritation test (EIT) which utilizes a three dimensional reconstructed human cornea-like epithelial (RhCE) tissue model that is based on normal human cells. The EIT is able to separate ocular&#160;irritants and corrosives (GHS Categories 1 and 2 combined) and those that do not require labeling (GHS No Category). The test utilizes two separate protocols, one designed for liquid chemicals and a second, similar protocol for solid test articles. The EIT prediction model uses a single exposure period (30 min for liquids, 6 hr for solids) and a single tissue viability cut-off (60.0% as determined by the MTT assay). Based on the results for 83 chemicals (44 liquids and 39 solids) EIT achieved 95.5/68.2/ and 81.8% sensitivity/specificity and accuracy (SS&#38;A) for liquids, 100.0/68.4/ and 84.6% SS&#38;A for solids, and 97.6/68.3/ and 83.1% for overall SS&#38;A. The EIT will contribute significantly to classifying the ocular irritation potential of a wide range of liquid and solid chemicals without the use of animals to meet regulatory testing requirements. The EpiOcular EIT method was implemented in 2015 into the OECD Test Guidelines as TG 492.

Eye Irritation Test EIT for Hazard Identification of Eye Irritating Chemicals using Reconstructed Human Cornea-like Epithelial RhCE Tissue Model

We have developed an eye irritation test which utilizes a three dimensional reconstructed human cornea-like epithelial (RhCE) tissue model. The test is able to discriminate between ocular irritant and corrosive materials (GHS Categories 1 and 2 combined) and those that do not require labeling (GHS No Category).

To comply with the Seventh Amendment to the EU Cosmetics Directive and EU REACH legislation, validated non-animal alternative methods for reliable and ...

Biomembrane Fabrication by the Solvent-assisted Lipid Bilayer (SALB) Method

In order to mimic cell membranes, the supported lipid bilayer (SLB) is an attractive platform which enables in vitro investigation of membrane-related processes while conferring biocompatibility and biofunctionality to solid substrates. The spontaneous adsorption and rupture of phospholipid vesicles is the most commonly used method to form SLBs. However, under physiological conditions, vesicle fusion (VF) is limited to only a subset of lipid compositions and solid supports. Here, we describe a one-step general procedure called the solvent-assisted lipid bilayer (SALB) formation method in order to form SLBs which does not require vesicles. The SALB method involves the deposition of lipid molecules onto a solid surface in the presence of water-miscible organic solvents (e.g., isopropanol) and subsequent solvent-exchange with aqueous buffer solution in order to trigger SLB formation. The continuous solvent exchange step enables application of the method in a flow-through configuration suitable for monitoring bilayer formation and subsequent alterations using a wide range of surface-sensitive biosensors. The SALB method can be used to fabricate SLBs on a wide range of hydrophilic solid surfaces, including those which are intractable to vesicle fusion. In addition, it enables fabrication of SLBs composed of lipid compositions which cannot be prepared using the vesicle fusion method. Herein, we compare results obtained with the SALB and conventional vesicle fusion methods on two illustrative hydrophilic surfaces, silicon dioxide and gold. To optimize the experimental conditions for preparation of high quality bilayers prepared via the SALB method, the effect of various parameters, including the type of organic solvent in the deposition step, the rate of solvent exchange, and the lipid concentration is discussed along with troubleshooting tips. Formation of supported membranes containing high fractions of cholesterol is also demonstrated with the SALB method, highlighting the technical capabilities of the SALB technique for a wide range of membrane configurations.

Biomembrane Fabrication by the Solvent-assisted Lipid Bilayer SALB Method

We present an experimental protocol to form a supported lipid bilayer on solid substrates without using lipid vesicles. We demonstrate a one-step method to form a lipid bilayer on silicon dioxide and gold as well as supported membranes with cholesterol-enriched domain for various biological applications.

In order to mimic cell membranes, the supported lipid bilayer (SLB) is an attractive platform which enables in vitro investigation of membrane-related ...

Three-dimensional Biomimetic Technology: Novel Biorubber Creates Defined Micro- and Macro-scale Architectures in Collagen Hydrogels

Tissue scaffolds play a crucial role in the tissue regeneration process. The ideal scaffold must fulfill several requirements such as having proper composition, targeted modulus, and well-defined architectural features. Biomaterials that recapitulate the intrinsic architecture of in vivo tissue are vital for studying diseases as well as to facilitate the regeneration of lost and malformed soft tissue. A novel biofabrication technique was developed which combines state of the art imaging, three-dimensional (3D) printing, and selective enzymatic activity to create a new generation of biomaterials for research and clinical application. The developed material, Bovine Serum Albumin rubber, is reaction injected into a mold that upholds specific geometrical features. This sacrificial material allows the adequate transfer of architectural features to a natural scaffold material. The prototype consists of a 3D collagen scaffold with 4 and 3 mm channels that represent a branched architecture. This paper emphasizes the use of this biofabrication technique for the generation of natural constructs. This protocol utilizes a computer-aided software (CAD) to manufacture a solid mold which will be reaction injected with BSA rubber followed by the enzymatic digestion of the rubber, leaving its architectural features within the scaffold material.

An innovative biofabrication technique was developed to engineer three-dimensional constructs that resemble the architectural features, components, and mechanical properties of in vivo tissue. This technique features a newly developed sacrificial material, BSA rubber, which transfers detailed spatial features, reproducing the in vivo architectures of a wide variety of tissues.

Tissue scaffolds play a crucial role in the tissue regeneration process. The ideal scaffold must fulfill several requirements such as having proper ...

Extraction of Plant-based Capsules for Microencapsulation Applications

Microcapsules derived from plant-based spores or pollen provide a robust platform for a diverse range of microencapsulation applications. Sporopollenin exine capsules (SECs) are obtained when spores or pollen are processed so as to remove the internal sporoplasmic contents. The resulting hollow microcapsules exhibit a high degree of micromeritic uniformity and retain intricate microstructural features related to the particular plant species. Herein, we demonstrate a streamlined process for the production of SECs from Lycopodium clavatum spores and for the loading of hydrophilic compounds into these SECs. The current SEC isolation procedure has been recently optimized to significantly reduce the processing requirements which are conventionally used in SEC isolation, and to ensure the production of intact microcapsules. Natural L. clavatum spores are defatted with acetone, treated with phosphoric acid, and extensively washed to remove sporoplasmic contents. After acetone defatting, a single processing step using 85% phosphoric acid has been shown to remove all sporoplasmic contents. By limiting the acid processing time to 30 hr, it is possible to isolate clean SECs and avoid SEC fracturing, which has been shown to occur with prolonged processing time. Extensive washing with water, dilute acids, dilute bases, and solvents ensures that all sporoplasmic material and chemical residues are adequately removed. The vacuum loading technique is utilized to load a model protein (Bovine Serum Albumin) as a representative hydrophilic compound. Vacuum loading provides a simple technique to load various compounds without the need for harsh solvents or undesirable chemicals which are often required in other microencapsulation protocols. Based on these isolation and loading protocols, SECs provide a promising material for use in a diverse range of microencapsulation applications, such as, therapeutics, foods, cosmetics, and personal care products.

This protocol/manuscript describes a streamlined process for the production of sporopollenin exine capsules (SECs) from Lycopodium clavatum spores and for the loading of hydrophilic compounds into these SECs.

Microcapsules derived from plant-based spores or pollen provide a robust platform for a diverse range of microencapsulation applications. Sporopollenin ...

Synthesis of Hydrogels with Antifouling Properties As Membranes for Water Purification

Hydrogels have been widely utilized to enhance the surface hydrophilicity of membranes for water purification, increasing the antifouling properties and thus achieving stable water permeability through membranes over time. Here, we report a facile method to prepare hydrogels based on zwitterions for membrane applications. Freestanding films can be prepared from sulfobetaine methacrylate (SBMA) with a crosslinker of poly(ethylene glycol) diacrylate (PEGDA) via photopolymerization. The hydrogels can also be prepared by impregnation into hydrophobic porous supports to enhance the mechanical strength. These films can be characterized by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) to determine the degree of conversion of the (meth)acrylate groups, using goniometers for hydrophilicity and differential scanning calorimetry (DSC) for polymer chain dynamics. We also report protocols to determine the water permeability in dead-end filtration systems and the effect of foulants (bovine serum albumin, BSA) on membrane performance.

This paper reports practical methods to prepare hydrogels in freestanding films and impregnated membranes and to characterize their physical properties, including water transport properties.

Hydrogels have been widely utilized to enhance the surface hydrophilicity of membranes for water purification, increasing the antifouling properties and ...

An In Vitro Organ Culture Model of the Murine Intervertebral Disc

Intervertebral disc (IVD) degeneration is a significant contributor to low back pain. The IVD is a fibrocartilaginous joint that serves to transmit and dampen loads in the spine. The IVD consists of a proteoglycan-rich nucleus pulposus (NP) and a collagen-rich annulus fibrosis (AF) sandwiched by cartilaginous end-plates. Together with the adjacent vertebrae, the vertebrae-IVD structure forms a functional spine unit (FSU). These microstructures contain unique cell types as well as unique extracellular matrices. Whole organ culture of the FSU preserves the native extracellular matrix, cell differentiation phenotypes, and cellular-matrix interactions. Thus, organ culture techniques are particularly useful for investigating the complex biological mechanisms of the IVD. Here, we describe a high-throughput approach for culturing whole lumbar mouse FSUs that provides an ideal platform for studying disease mechanisms and therapies for the IVD. Furthermore, we describe several applications that utilize this organ culture method to conduct further studies including contrast-enhanced microCT imaging and three-dimensional high-resolution finite element modeling of the IVD.

An In Vitro Organ Culture Model of the Murine Intervertebral Disc

Whole organ culture of the intervertebral disc (IVD) preserves the native extracellular matrix, cell phenotypes, and cellular-matrix interactions. Here we describe an IVD culture system using mouse lumbar and caudal IVDs in their functional spinal units and several applications utilizing this system.

Intervertebral disc (IVD) degeneration is a significant contributor to low back pain. The IVD is a fibrocartilaginous joint that serves to transmit and ...

Improved 3D Hydrogel Cultures of Primary Glial Cells for In Vitro Modelling of Neuroinflammation

In the central nervous system, numerous acute injuries and neurodegenerative disorders, as well as implanted devices or biomaterials engineered to enhance function result in the same outcome: excess inflammation leads to gliosis, cytotoxicity, and/or formation of a glial scar that collectively exacerbate injury or prevent healthy recovery. With the intent of creating a system to model glial scar formation and study inflammatory processes, we have generated a 3D cell scaffold capable of housing primary cultured glial cells: microglia that regulate the foreign body response and initiate the inflammatory event, astrocytes that respond to form a fibrous scar, and oligodendrocytes that are typically vulnerable to inflammatory injury. The present work provides a detailed step-by-step method for the fabrication, culture, and microscopic characterization of a hyaluronic acid-based 3D hydrogel scaffold with encapsulated rat brain-derived glial cells. Further, protocols for characterization of cell encapsulation and the hydrogel scaffold by confocal immunofluorescence and scanning electron microscopy are demonstrated, as well as the capacity to modify the scaffold with bioactive substrates, with incorporation of a commercial basal lamina mixture to improved cell integration.

Improved 3D Hydrogel Cultures of Primary Glial Cells for In Vitro Modelling of Neuroinflammation

Herein, we present a protocol for the 3D culture of rat brain-derived glia cells, including astrocytes, microglia, and oligodendrocytes. We demonstrate primary cell culture, methacrylated hyaluronic acid (HAMA) hydrogel synthesis, HAMAphoto-polymerization and cell encapsulation, and sample processing for confocal and scanning electron microscopic imaging.

In the central nervous system, numerous acute injuries and neurodegenerative disorders, as well as implanted devices or biomaterials engineered to enhance ...

Repressing Gene Transcription by Redirecting Cellular Machinery with Chemical Epigenetic Modifiers

Regulation of chromatin compaction is an important process that governs gene expression in higher eukaryotes. Although chromatin compaction and gene expression regulation are commonly disrupted in many diseases, a locus-specific, endogenous, and reversible method to study and control these mechanisms of action has been lacking. To address this issue, we have developed and characterized novel gene-regulating bifunctional molecules. One component of the bifunctional molecule binds to a DNA-protein anchor so that it will be recruited to an allele-specific locus. The other component engages endogenous cellular chromatin-modifying machinery, recruiting these proteins to a gene of interest. These small molecules, called chemical epigenetic modifiers (CEMs), are capable of controlling gene expression and the chromatin environment in a dose-dependent and reversible manner. Here, we detail a CEM approach and its application to decrease gene expression and histone tail acetylation at a Green Fluorescent Protein (GFP) reporter located at the Oct4 locus in mouse embryonic stem cells (mESCs). We characterize the lead CEM (CEM23) using fluorescent microscopy, flow cytometry, and chromatin immunoprecipitation (ChIP), followed by a quantitative polymerase chain reaction (qPCR). While the power of this system is demonstrated at the Oct4 locus, conceptually, the CEM technology is modular and can be applied in other cell types and at other genomic loci.

Regulation of the chromatin environment is an essential process required for proper gene expression. Here, we describe a method for controlling gene expression through the recruitment of chromatin-modifying machinery in a gene-specific and reversible manner.

Regulation of chromatin compaction is an important process that governs gene expression in higher eukaryotes. Although chromatin compaction and gene ...

Methodology for Biomimetic Chemical Neuromodulation of Rat Retinas with the Neurotransmitter Glutamate In Vitro

Summary

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Chapters in this video

Microfluidic Device for Recreating a Tumor Microenvironment in Vitro

In vitro Cell Culture Model for Toxic Inhaled Chemical Testing

Eye Irritation Test (EIT) for Hazard Identification of Eye Irritating Chemicals using Reconstructed Human Cornea-like Epithelial (RhCE) Tissue Model

Biomembrane Fabrication by the Solvent-assisted Lipid Bilayer (SALB) Method

Three-dimensional Biomimetic Technology: Novel Biorubber Creates Defined Micro- and Macro-scale Architectures in Collagen Hydrogels

Extraction of Plant-based Capsules for Microencapsulation Applications

Synthesis of Hydrogels with Antifouling Properties As Membranes for Water Purification

An In Vitro Organ Culture Model of the Murine Intervertebral Disc

Improved 3D Hydrogel Cultures of Primary Glial Cells for In Vitro Modelling of Neuroinflammation

Repressing Gene Transcription by Redirecting Cellular Machinery with Chemical Epigenetic Modifiers