Supported by NEI grant EY014850.

1.	Preparation of Sylgard-covered dishes, experimental chambers, and razor blades
<ol>
<li>35 mm Falcon Petri dishes coated with Sylgard elastomer are needed for the proper chopping of an isolated retina to obtain single photoreceptor cells. The elastomer is prepared according to the supplier's instructions and a small amount is poured into each dish to cover its bottom with a layer. Replace the dish covers after coating and store them. In a few days' time the elastomer hardens and the dishes are ready.</li>
<li>Isolated photoreceptors need to stick to the bottom of the experimental chamber so that they are immobilized during the course of an imaging experiment. This is achieved by coating the bottoms of the chambers with poly-L-lysine or poly-L-ornithine. Add 200 &mu;L of 0.01% solution of either one per chamber, and cover the chambers with a paper towel to protect them from dust. After the solution has dried, wash the chambers with distilled water and store in a closed box. Use within 2 weeks.</li>
<li>To clean the chambers at the end of an experiment, wash them with 100% ethanol to remove any oil from the oil-immersion lens and cell debris. To remove the cell debris, use cotton-tipped applicators and carefully scrub the bottom of the chamber. Afterwards, wash with distilled water and let the chambers dry before re-coating.</li>
<li>Cut double-edged razor blades into small pieces (8 from one blade) with a metal cutter.</li>
</ol>
2.	Preparation of solutions
<ol>
<li>The composition of solutions depends on the species. For amphibians, the Ringer's has (in mmol/L): 110 NaCl, 2.5 KCl, 1.6 MgCl2, 1 CaCl2, 5 HEPES, pH = 7.55. The pH should be adjusted to the final value with NaOH. For mammals, the Ringer's has (in mmol/L): 130 NaCl, 5 KCl, 0.5 MgCl2, 2 CaCl2, 25 hemisodium-HEPES, pH = 7.40. The Ringer's solution can be kept well-sealed at room temperature for a few months.</li>
<li>Stock glucose solution, 1 mol/L, kept at -20 &deg;C to avoid bacterial growth.</li>
<li>On the day of the experiment, add glucose to the Ringer's solution to a final concentration of 5 mmol/L. At the end of the day, discard the Ringer's that contains glucose because it might grow bacteria.</li>
</ol>
3.	Isolation of retinas
<ol>
<li>For the proper excision of a retina it is important that the animal be dark-adapted for at least 2-3 hours before sacrifice. Animals should be dark-adapted in a suitable ventilated container in the dark-room.</li>
<li>Fill two 35 mm Petri dishes half-way with Ringer's solution.</li>
<li>Sacrifice the animal under dim red light and remove the eyes. Subsequently, all procedures are carried out under infrared light using a dissecting microscope or a camera with a video monitor.</li>
<li>Remove any leftover tissue from the outside surface of the eye. Cut and remove the anterior part, then transfer the eyecup into one of the Petri dishes filled with Ringer's.</li>
<li>Remove the vitreous and carefully separate the retina from the rest of the eyecup by pinching off or cutting any attachments. Gently lift the retina and separate it fully from the eyecup.</li>
<li>Transfer the retina to the second Petri dish with a plastic transfer pipette. Keep the dish containing the retina in a light-tight box.</li>
</ol>
4.	Isolation of single photoreceptor cells
<ol>
<li>All procedures are carried out under infrared light. Cut a small piece of retina and transfer it with a plastic pipette to a Sylgard-covered dish. The volume of the solution containing the retina piece should be about 250 &mu;L.</li>
<li>Grab a small piece of razor blade with the blade holder -- the edge of the blade should be at approximately 45&deg; angle to the holder. Flatten the piece of retina on the Sylgard layer and using the blade chop the piece of retina finely while keeping it stuck to the Sylgard layer.</li>
<li>Transfer 200 &mu;L of the solution containing the cells to an experimental chamber &#x2013; leave any remaining piece of retina in the Sylgard-covered dish. Keep the chamber with the isolated cells in a light-tight box.</li>
<li>Wait for 10 min for the cells to settle, then add 2-3 mL of Ringer's. At this stage, the isolated cells can be loaded with a particular fluorescent dye (for example Fura-2) according to the dye loading protocol.</li>
<li>The cells can now be taken to the microscope stage for experiments.</li>
</ol>
5.	Fluorescence imaging
<ol>
<li>Transfer the chamber to the stage of the epifluorescence microscope. Adjust solution perfusion, temperature probes, infrared illumination, etc.</li>
<li>Close the curtains and begin experiment. Turn on the infrared light inside the microscope cage, focus on the bottom of the experimental chamber, and move the stage looking for cells.</li>
</ol>
6. Representative Results:
Fig. 1 shows the morphology of healthy isolated rod and cone photoreceptors obtained with this protocol from a salamander (Ambystoma tigrinum) retina. Salamander cells have been used extensively for single cell fluorescence imaging studies because of their large size and their ability to survive for several hours after isolation from the retina. In addition, from a salamander retina one can regularly obtain both rod and cone photoreceptors.
One important criterion for the health of the cells is the presence of an intact ellipsoid (Fig. 1), the part of the cell where the mitochondria are concentrated. When the cells are viewed under DAPI optics, this concentration of mitochondria gives a strong fluorescence signal (Fig. 2) due to the presence of NADH. Lack of an intact ellipsoid is a sign of a damaged cell, generally unfit for experiment. Fig. 3 shows a damaged salamander rod photoreceptor, with a swollen cell body and a condensed nucleus. Such cells display much lower fluorescence under DAPI optics, but viewed under FITC optics show a strong FAD signal in the ellipsoid region (originating from oxidized flavin nucleotides and flavoproteins). Another criterion for the health of isolated photoreceptors is their ability to generate all-trans retinol (vitamin A) in their outer segments upon stimulation by light. The generation of vitamin A requires substantial amounts of NADPH, which depends on an intact metabolic machinery. Figures 4 and 5 show the formation of vitamin A in the outer segments of intact frog and mouse rod photoreceptors respectively.
<img src="/files/ftp_upload/2789/2789fig1.jpg" alt="Figure 1"/> 
Figure 1. Healthy single rod and cone photoreceptors. The cells were isolated from a tiger salamander retina. Phototransduction takes place in the outer segment and the ellipsoid is densely packed with mitochondria. Rods are responsible for dim light vision, cones for bright light vision.
<img src="/files/ftp_upload/2789/2789fig2.jpg" alt="Figure 2"/> 
Figure 2. Fluorescence of living salamander rod and cone. These are dark-adapted cells, showing strong NADH fluorescence in their respective ellipsoids and no significant vitamin A fluorescence in their outer segments. The capture of the fluorescence image represents their first exposure to visible light after the period of dark-adaptation.
<img src="/files/ftp_upload/2789/2789fig3.jpg" alt="Figure 3"/> 
Figure 3. Damaged salamander rod photoreceptor. The swollen cell body and the condensed nucleus are indicative of damage. The cell is oxidized and there is minimal NADH signal (DAPI optics), but much stronger FAD signal (FITC optics).
<img src="/files/ftp_upload/2789/2789fig4.jpg" alt="Figure 4"/> 
Figure 4. Frog rod with NADH and retinol. This is a healthy frog rod photoreceptor showing strong NADH fluorescence in the ellipsoid region. Before light exposure there is minimal fluorescence in the outer segment. Following light exposure, there is a significant increase in the outer segment fluorescence due to the formation of vitamin A.
<img src="/files/ftp_upload/2789/2789fig5.jpg" alt="Figure 5"/> 
Figure 5. Mouse rod with retinol. This is a healthy mouse rod photoreceptor showing significant outer segment fluorescence after light exposure due to the formation of vitamin A. The ellipsoid regions of mouse rod photoreceptors do not show a strong fluorescence signal.

<ol>
	<li>Burns, M. E., Arshavsky, V. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Beyond+Counting+Photons:+Trials+and+Trends+in+Vertebrate+Visual+Transduction.">Beyond Counting Photons: Trials and Trends in Vertebrate Visual Transduction.</a> Neuron. 48, 387-401 (2005).</li><li>Ebrey, T., Koutalos, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vertebrate+Photoreceptors.">Vertebrate Photoreceptors.</a> Prog Retin Eye Res. 20, 49-94 (2001).</li><li>Fain, G. L., Matthews, H. R., Cornwall, M. C., Koutalos, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adaptation+in+Vertebrate+Photoreceptors.">Adaptation in Vertebrate Photoreceptors.</a> Physiol Rev. 81, 117-151 (2001).</li><li>Palczewski, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=G+Protein-Coupled+Receptor+Rhodopsin.">G Protein-Coupled Receptor Rhodopsin.</a> Annu Rev Biochem. 75, 743-767 (2006).</li><li>Saari, 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=Biochemistry+of+Visual+Pigment+Regeneration:+The+Friedenwald+Lecture.">Biochemistry of Visual Pigment Regeneration: The Friedenwald Lecture.</a> Invest Ophthalmol Vis Sci. 41, 337-348 (2000).</li><li>Lamb, T. D., Pugh, E. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dark+Adaptation+and+the+Retinoid+Cycle+of+Vision.">Dark Adaptation and the Retinoid Cycle of Vision.</a> Prog Retin Eye Res. 23, 307-380 (2004).</li><li>Imanishi, Y., Lodowski, K. H., Koutalos, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Two-Photon+Microscopy:+Shedding+Light+on+the+Chemistry+of+Vision.">Two-Photon Microscopy: Shedding Light on the Chemistry of Vision.</a> Biochemistry. 46, 9674-9684 (2007).</li><li>Sampath, A. P., Matthews, H. R., Cornwall, M. C., Fain, G. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bleached+Pigment+Produces+a+Maintained+Decrease+in+Outer+Segment+Ca2++in+Salamander+Rods.">Bleached Pigment Produces a Maintained Decrease in Outer Segment Ca2+ in Salamander Rods.</a> J Gen Physiol. 111, 53-64 (1998).</li><li>Sampath, A. P., Matthews, H. R., Cornwall, M. C., Bandarchi, J., Fain, G. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Light-Dependent+Changes+in+Outer+Segment+Free-Ca2++Concentration+in+Salamander+Cone+Photoreceptors.">Light-Dependent Changes in Outer Segment Free-Ca2+ Concentration in Salamander Cone Photoreceptors.</a> J Gen Physiol. 113, 267-277 (1999).</li><li>Woodruff, M. L., Sampath, A. P., Matthews, H. R., Krasnoperova, N. V., Lem, J., Fain, G. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measurement+of+Cytoplasmic+Calcium+Concentration+in+the+Rods+of+Wild-Type+and+Transducin+Knock-out+Mice.">Measurement of Cytoplasmic Calcium Concentration in the Rods of Wild-Type and Transducin Knock-out Mice.</a> J Physiol. 542, 843-854 (2002).</li><li>Leung, Y. T., Fain, G. L., Matthews, H. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simultaneous+Measurement+of+Current+and+Calcium+in+the+Ultraviolet-Sensitive+Cones+of+Zebrafish.">Simultaneous Measurement of Current and Calcium in the Ultraviolet-Sensitive Cones of Zebrafish.</a> J Physiol. 579, 15-27 (2007).</li><li>Matthews, H. R., Fain, G. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Laser+Spot+Confocal+Technique+to+Measure+Cytoplasmic+Calcium+Concentration+in+Photoreceptors.">Laser Spot Confocal Technique to Measure Cytoplasmic Calcium Concentration in Photoreceptors.</a> Methods Enzymol. 316, 146-163 (2000).</li><li>Szikra, T., Cusato, K., Thoreson, W. B., Barabas, P., Bartoletti, T. M., Krizaj, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Depletion+of+Calcium+Stores+Regulates+Calcium+Influx+and+Signal+Transmission+in+Rod+Photoreceptors.">Depletion of Calcium Stores Regulates Calcium Influx and Signal Transmission in Rod Photoreceptors.</a> J Physiol. 586, 4859-4875 (2008).</li><li>Krizaj, D., Copenhagen, D. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Compartmentalization+of+Calcium+Extrusion+Mechanisms+in+the+Outer+and+Inner+Segments+of+Photoreceptors.">Compartmentalization of Calcium Extrusion Mechanisms in the Outer and Inner Segments of Photoreceptors.</a> Neuron. 21, 249-256 (1998).</li><li>Chen, C., Nakatani, K., Koutalos, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Free+Magnesium+Concentration+in+Salamander+Photoreceptor+Outer+Segments.">Free Magnesium Concentration in Salamander Photoreceptor Outer Segments.</a> J Physiol. 553, 125-135 (2003).</li><li>Chen, C., Jiang, Y., Koutalos, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dynamic+Behavior+of+Rod+Photoreceptor+Disks.">Dynamic Behavior of Rod Photoreceptor Disks.</a> Biophys J. 83, 1403-1412 (2002).</li><li>Tsina, E., Chen, C., Koutalos, Y., Ala-Laurila, P., Tsacopoulos, M., Wiggert, B., Crouch, R. K., Cornwall, M. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Physiological+and+Microfluorometric+Studies+of+Reduction+and+Clearance+of+Retinal+in+Bleached+Rod+Photoreceptors.">Physiological and Microfluorometric Studies of Reduction and Clearance of Retinal in Bleached Rod Photoreceptors.</a> J Gen Physiol. 124, 429-443 (2004).</li><li>Ala-Laurila, P., Kolesnikov, A. V., Crouch, R. K., Tsina, E., Shukolyukov, S. A., Govardovskii, V. I., Koutalos, Y., Wiggert, B., Estevez, M. E., Cornwall, M. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Visual+Cycle:+Dependence+of+Retinol+Production+and+Removal+on+Photoproduct+Decay+and+Cell+Morphology.">Visual Cycle: Dependence of Retinol Production and Removal on Photoproduct Decay and Cell Morphology.</a> J Gen Physiol. 128, 153-169 (2006).</li><li>Koutalos, Y., Cornwall, M. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microfluorometric+Measurement+of+the+Formation+of+All-Trans-Retinol+in+the+Outer+Segments+of+Single+Isolated+Vertebrate+Photoreceptors.">Microfluorometric Measurement of the Formation of All-Trans-Retinol in the Outer Segments of Single Isolated Vertebrate Photoreceptors.</a> Methods Mol Biol. 652, 129-147 (2010).</li><li>Wu, Q., Blakeley, L. R., Cornwall, M. C., Crouch, R. K., Wiggert, B. N., Koutalos, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Interphotoreceptor+Retinoid-Binding+Protein+Is+the+Physiologically+Relevant+Carrier+That+Removes+Retinol+from+Rod+Photoreceptor+Outer+Segments.">Interphotoreceptor Retinoid-Binding Protein Is the Physiologically Relevant Carrier That Removes Retinol from Rod Photoreceptor Outer Segments.</a> Biochemistry. 46, 8669-8679 (2007).</li><li>Kolesnikov, A. V., Ala-Laurila, P., Shukolyukov, S. A., Crouch, R. K., Wiggert, B., Estevez, M. E., Govardovskii, V. I., Cornwall, M. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Visual+Cycle+and+Its+Metabolic+Support+in+Gecko+Photoreceptors.">Visual Cycle and Its Metabolic Support in Gecko Photoreceptors.</a> Vision Res. 47, 363-374 (2007).</li><li>Chen, C., Blakeley, L. R., Koutalos, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Formation+of+All-Trans+Retinol+after+Visual+Pigment+Bleaching+in+Mouse+Photoreceptors.">Formation of All-Trans Retinol after Visual Pigment Bleaching in Mouse Photoreceptors.</a> Invest Ophthalmol Vis Sci. 50, 3589-3595 (2009).</li></ol>

No conflicts of interest declared.

If healthy isolated cells are not obtained, the problem lies either with the isolation or health of the retina or with its chopping. Typically, after removing the front of the eye and the vitreous, the retina readily lifts off the pigment epithelium. If it does not, try to peel it off starting from the periphery of the eyecup. If it is still difficult to separate, a likely possibility is that the animal has not been dark-adapted for an adequate period of time, or the red light is too bright. Ensure proper dark-adapta...

<table border="1">
 <tbody>
 <tr>
 <th>Name</th>
 <th>Company</th>
 <th>Catalogue number</th>
 <th>Comments</th>
 </tr>
 <tr>
 <td>Dark room (100-150 ft2)</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Red lights19</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 <td>Online stores</td>
 </tr>

 <tr>
 <td>Infrared light sources and
infrared image viewers
</td>
 <td>FJW Optical Systems, Inc.</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 </tr>

 <tr>
 <td>Dissecting microscope19</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 <td>Outfitted with infrared viewers</td>
 </tr>

 <tr>
 <td>Epifluorescence microscope enclosed in a light-tight cage19</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 </tr>

 <tr>
 <td>Dissecting tools
(scissors, forceps, blade holder) 
</td>
 <td>Roboz or
Fine Science Tools
</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 </tr>

 <tr>
 <td>Sylgard elastomer</td>
 <td>Essex (Charlotte, NC)</td>
 <td>Sylgard 184 elastomer kit</td>
 <td>&nbsp;</td>
 </tr>

 <tr>
 <td>Poly-L-ornithine (0.01%)</td>
 <td>Sigma-Aldrich</td>
 <td>P4957</td>
 <td>&nbsp;</td>
 </tr>

 <tr>
 <td>Poly-L-lysine (0.1%)</td>
 <td>Sigma-Aldrich</td>
 <td>P8920</td>
 <td>Dilute to 0.01%</td>
 </tr>

 <tr>
 <td>Experimental chambers</td>
 <td>Warner Instruments (Hamden, CT)</td>
 <td>D3512P</td>
 <td>&nbsp;</td>
 </tr>

 <tr>
 <td>Petri dishes, plastic pipettes</td>
 <td>Fisher Scientific</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 </tr> 
 </tbody>
</table>

preparation of living isolated vertebrate photoreceptor cells for fluorescence imaging

In the vertebrate retina, phototransduction, the conversion of light to an electrical signal, is carried out by the rod and cone photoreceptor cells1-4. Rod photoreceptors are responsible for vision in dim light, cones in bright light. Phototransduction takes place in the outer segment of the photoreceptor cell, a specialized compartment that contains a high concentration of visual pigment, the primary light detector. The visual pigment is composed of a chromophore, 11-cis retinal, attached to a protein, opsin. A photon absorbed by the visual pigment isomerizes the chromophore from 11-cis to all-trans. This photoisomerization brings about a conformational change in the visual pigment that 
initiates a cascade of reactions culminating in a change in membrane potential, and bringing about the transduction of the light stimulus to an electrical signal. The 
recovery of the cell from light stimulation involves the deactivation of the intermediates activated by light, and the reestablishment of the membrane potential. Ca2+ modulates the activity of several of the enzymes involved in phototransduction, and its concentration is reduced upon light stimulation. In this way, Ca2+ plays an important role in the recovery of the cell from light stimulation and its adaptation to background light.
Another essential part of the recovery process is the regeneration of the visual pigment that has been destroyed during light-detection by the 
photoisomerization of its 11-cis chromophore to all-trans5-7. This regeneration begins with the release of all-trans retinal by 
the photoactivated pigment, leaving behind the apo-protein opsin. The released all-trans retinal is rapidly reduced in a reaction utilizing NADPH to all-
trans retinol, and opsin combines with fresh 11-cis retinal brought into the outer segment to reform the visual pigment. All-trans retinol is 
then transferred out of the outer segment and into neighboring cells by the specialized carrier Interphotoreceptor Retinoid Binding Protein (IRBP).
Fluorescence imaging of single photoreceptor cells can be used to study their physiology and cell biology. Ca2+-sensitive fluorescent dyes can be used to examine in detail the interplay between outer 
segment Ca2+ changes and response to light8-12 as well as the role of inner segment Ca2+ stores in Ca2+ homeostasis13,14. 
Fluorescent dyes can also be used for measuring Mg2+ concentration15, pH, and as tracers of aqueous and membrane compartments16. 
Finally, the intrinsic fluorescence of all-trans retinol (vitamin A) can be used to monitor the kinetics of its formation and removal in single 
photoreceptor cells17-19.

Watch this Scientific Journal Video about Preparation of Living Isolated Vertebrate Photoreceptor Cells for Fluorescence Imaging at JoVE.com

Preparation of Living Isolated Vertebrate Photoreceptor Cells for Fluorescence Imaging

A method is described for the preparation of single living photoreceptor cells from different vertebrate species for fluorescence imaging. The method can be used to image the fluorescence of endogenous fluorophores, such as NADH or vitamin A, or that of exogenously added fluorescent dyes sensitive to Ca2+ or other factors.

In the vertebrate retina, phototransduction, the conversion of light to an electrical signal, is carried out by the rod and cone photoreceptor cells1-4.  ...

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12.2K Views.  Medical University of South Carolina. A method is described for the preparation of single living photoreceptor cells from different vertebrate species for fluorescence imaging. The method can be used to image the fluorescence of endogenous fluorophores, such as NADH or vitamin A, or that of exogenously added fluorescent dyes sensitive to Ca2+ or other factors.

Video: Preparation of Living Isolated Vertebrate Photoreceptor Cells for Fluorescence Imaging

An Isolated Retinal Preparation to Record Light Response from Genetically Labeled Retinal Ganglion Cells

The first steps in vertebrate vision take place when light stimulates the rod and cone photoreceptors of the retina 1. This information is then segregated into what are known as the ON and OFF pathways. The photoreceptors signal light information to the bipolar cells (BCs), which depolarize in response to increases (On BCs) or decreases (Off BCs) in light intensity. This segregation of light information is maintained at the level of the retinal ganglion cells (RGCs), which have dendrites stratifying in either the Off sublamina of the inner plexiform layer (IPL), where they receive direct excitatory input from Off BCs, or stratifying in the On sublamina of the IPL, where they receive direct excitatory input from On BCs. This segregation of information regarding increases or decreases in illumination (the On and Off pathways) is conserved and signaled to the brain in parallel.
The RGCs are the output cells of the retina, and are thus an important cell to study in order to understand how light information is signaled to visual nuclei in the brain. Advances in mouse genetics over recent decades have resulted in a variety of fluorescent reporter mouse lines where specific RGC populations are labeled with a fluorescent protein to allow for identification of RGC subtypes 2 3 4 and specific targeting for electrophysiological recording. Here, we present a method for recording light responses from fluorescently labeled ganglion cells in an intact, isolated retinal preparation. This isolated retinal preparation allows for recordings from RGCs where the dendritic arbor is intact and the inputs across the entire RGC dendritic arbor are preserved. This method is applicable across a variety of ganglion cell subtypes and is amenable to a wide variety of single-cell physiological techniques.

This article provides a description of how to dissect and record from the isolated retinal preparation in mouse. In particular, we describe how to record light responses from a fluorescently labeled ganglion cell population and subsequently identify and analyze its morphology.

The first steps in vertebrate vision take place when light stimulates the rod and cone photoreceptors of the retina 1.  This information is then ...

Live-cell Imaging of Sensory Organ Precursor Cells in Intact Drosophila Pupae

Since the discovery of Green Fluorescent Protein (GFP), there has been a revolutionary change in the use of live-cell imaging as a tool for understanding fundamental biological mechanisms. Striking progress has been particularly evident in Drosophila, whose extensive toolkit of mutants and transgenic lines provides a convenient model to study evolutionarily-conserved developmental and cell biological mechanisms. We are interested in understanding the mechanisms that control cell fate specification in the adult peripheral nervous system (PNS) in Drosophila. Bristles that cover the head, thorax, abdomen, legs and wings of the adult fly are individual mechanosensory organs, and have been studied as a model system for understanding mechanisms of Notch-dependent cell fate decisions. Sensory organ precursor (SOP) cells of the microchaetes (or small bristles), are distributed throughout the epithelium of the pupal thorax, and are specified during the first 12 hours after the onset of pupariation. After specification, the SOP cells begin to divide, segregating the cell fate determinant Numb to one daughter cell during mitosis. Numb functions as a cell-autonomous inhibitor of the Notch signaling pathway.
Here, we show a method to follow protein dynamics in SOP cell and its progeny within the intact pupal thorax using a combination of tissue-specific Gal4 drivers and GFP-tagged fusion proteins 1,2.This technique has the advantage over fixed tissue or cultured explants because it allows us to follow the entire development of an organ from specification of the neural precursor to growth and terminal differentiation of the organ. We can therefore directly correlate changes in cell behavior to changes in terminal differentiation. Moreover, we can combine the live imaging technique with mosaic analysis with a repressible cell marker (MARCM) system to assess the dynamics of tagged proteins in mitotic SOPs under mutant or wildtype conditions. Using this technique, we and others have revealed novel insights into regulation of asymmetric cell division and the control of Notch signaling activation in SOP cells (examples include references 1-6,7 ,8).

Live-cell Imaging of Sensory Organ Precursor Cells in Intact Drosophila Pupae

In this video, we describe a method for live cell imaging of asymmetrically dividing sensory organ progenitor cells and epidermal cells in intact Drosophila pupae

Since the discovery of Green Fluorescent Protein (GFP), there has been a revolutionary change in the use of live-cell imaging as a tool for understanding ...

Detection of Microregional Hypoxia in Mouse Cerebral Cortex by Two-photon Imaging of Endogenous NADH Fluorescence

The brain's ability to function at high levels of metabolic demand depends on continuous oxygen supply through blood flow and tissue oxygen diffusion. Here we present a visualized experimental and methodological protocol to directly visualize microregional tissue hypoxia and to infer perivascular oxygen gradients in the mouse cortex. It is based on the non-linear relationship between nicotinamide adenine dinucleotide (NADH) endogenous fluorescence intensity and oxygen partial pressure in the tissue, where observed tissue NADH fluorescence abruptly increases at tissue oxygen levels below 10 mmHg1. We use two-photon excitation at 740 nm which allows for concurrent excitation of intrinsic NADH tissue fluorescence and blood plasma contrasted with Texas-Red dextran. The advantages of this method over existing approaches include the following: it takes advantage of an intrinsic tissue signal and can be performed using standard two-photon in vivo imaging equipment; it permits continuous monitoring in the whole field of view with a depth resolution of ~50 &mu;m. We demonstrate that brain tissue areas furthest from cerebral blood vessels correspond to vulnerable watershed areas which are the first to become functionally hypoxic following a decline in vascular oxygen supply. This method allows one to image microregional cortical oxygenation and is therefore useful for examining the role of inadequate or restricted tissue oxygen supply in neurovascular diseases and stroke.

Here we describe a method to directly visualize microregional tissue hypoxia in the mouse cortex in vivo. It is based on concurrent two-photon imaging of nicotinamide adenine dinucleotide (NADH) and the cortical microcirculation. This method is useful for high resolution analysis of tissue oxygen supply.

The brain's ability to function at high levels of metabolic demand depends on continuous oxygen supply through blood flow and tissue oxygen diffusion. ...

Preparation of Acute Subventricular Zone Slices for Calcium Imaging

The subventricular zone (SVZ) is one of the two neurogenic zones in the postnatal brain. The SVZ contains densely packed cells, including neural progenitor cells with astrocytic features (called SVZ astrocytes), neuroblasts, and intermediate progenitor cells. Neuroblasts born in the SVZ tangentially migrate a great distance to the olfactory bulb, where they differentiate into interneurons. Intercellular signaling through adhesion molecules and diffusible signals play important roles in controlling neurogenesis. Many of these signals trigger intercellular calcium activity that transmits information inside and between cells. Calcium activity is thus reflective of the activity of extracellular signals and is an optimal way to understand functional intercellular signaling among SVZ cells.
Calcium activity has been studied in many other regions and cell types, including mature astrocytes and neurons. However, the traditional method to load cells with calcium indicator dye (i.e. bath loading) was not efficient at loading all SVZ cell types. Indeed, the cellular density in the SVZ precludes dye diffusion inside the tissue. In addition, preparing sagittal slices will better preserve the three-dimensional arrangement of SVZ cells, particularly the stream of neuroblast migration on the rostral-caudal axis.
Here, we describe methods to prepare sagittal sections containing the SVZ, the loading of SVZ cells with calcium indicator dye, and the acquisition of calcium activity with time-lapse movies. We used Fluo-4 AM dye for loading SVZ astrocytes using pressure application inside the tissue. Calcium activity was recorded using a scanning confocal microscope allowing a precise resolution for distinguishing individual cells. Our approach is applicable to other neurogenic zones including the adult hippocampal subgranular zone and embryonic neurogenic zones. In addition, other types of dyes can be applied using the described method.

A method to load subventricular zone (SVZ) cells with calcium indicator dyes for recording calcium activity is described. The postnatal SVZ contains tightly packed cells including neural progenitor cells and neuroblasts. Rather than using bath loading we injected the dye by pressure inside the tissue allowing better dye diffusion.

The subventricular zone (SVZ) is one of the two neurogenic zones in the postnatal brain. The SVZ contains densely packed cells, including neural ...

Visualization of Endosome Dynamics in Living Nerve Terminals with Four-dimensional Fluorescence Imaging

Four-dimensional (4D) light imaging has been used to study behavior of small structures within motor nerve terminals of the thin transversus abdominis muscle of the garter snake. Raw data comprises time-lapse sequences of 3D z-stacks. Each stack contains 4-20 images acquired with epifluorescence optics at focal planes separated by 400-1,500 nm. Steps in the acquisition of image stacks, such as adjustment of focus, switching of excitation wavelengths, and operation of the digital camera, are automated as much as possible to maximize image rate and minimize tissue damage from light exposure. After acquisition, a set of image stacks is deconvolved to improve spatial resolution, converted to the desired 3D format, and used to create a 4D "movie" that is suitable for variety of computer-based analyses, depending upon the experimental data sought. One application is study of the dynamic behavior of two classes of endosomes found in nerve terminals-macroendosomes (MEs) and acidic endosomes (AEs)-whose sizes (200-800 nm for both types) are at or near the diffraction limit. Access to 3D information at each time point provides several advantages over conventional time-lapse imaging. In particular, size and velocity of movement of structures can be quantified over time without loss of sharp focus. Examples of data from 4D imaging reveal that MEs approach the plasma membrane and disappear, suggesting that they are exocytosed rather than simply moving vertically away from a single plane of focus. Also revealed is putative fusion of MEs and AEs, by visualization of overlap between the two dye-containing structures as viewed in each three orthogonal projections.

Four-dimensional (4D) imaging is utilized to study the behavior and interactions among two types of endosomes in living vertebrate nerve terminals. Movement of these small structures is characterized in three dimensions, permitting confirmation of events such as endosome fusion and exocytosis.

Four-dimensional (4D) light imaging has been used to study behavior of small structures within motor nerve terminals of the thin transversus abdominis ...

Vibratome Sectioning Mouse Retina to Prepare Photoreceptor Cultures

The retina is a part of the central nervous system that has organized architecture, with neurons in layers from the photoreceptors, both rods and cones in contact with the retinal pigmented epithelium in the most distant part on the retina considering the direction of light, and the ganglion cells in the most proximal distance. This architecture allows the isolation of the photoreceptor layer by vibratome sectioning. The dissected neural retina of a mouse aged 8 days is flat-embedded in 4% gelatin on top of a slice of 20% gelatin photoreceptor layer facing down. Using a vibratome and a double edged razor blade, the 100 &#181;m thick inner retina is sectioned. This section contains the ganglion cells and the inner layer with notably the bipolar cells. An intermediary section of 15 &#181;m is discarded before 200 &#181;m of the outer retina containing the photoreceptors is recovered. The gelatin is removed by heating at 37 &#176;C. Pieces of outer layer are incubated in 500 &#181;l of Ringer&#39;s solution with 2 units of activated papain for 20 min at 37 &#176;C. The reaction is stopped by adding 500 &#181;l 10% fetal calf serum (FCS) in Dulbecco&#39;s Modified Eagle Medium (DMEM), then 25 units of DNAse I is added before centrifugation at RT, washed several times to remove serum and the cells are resuspended in 500 &#181;l of DMEM and seeded at 1 x 105 cells/cm2. The cells are grown to 5 days in vitro and their viability scored using live/dead assay. The purity of the culture is first determined by microscopic observation during the experiment. The purity is then validated by seeding and fixing cells on a histological slide and analyzing using a rabbit polyclonal anti-SAG, a photoreceptor marker and mouse monoclonal anti-RHO, a rod photoreceptor specific marker. Alternatively, the photoreceptor layer (97% rods) can be used for gene or protein expression analysis and for transplantation.

Neural retina of a mouse aged 8 days is on top of a 4% gelatin block. After isolation of the photoreceptor layer (200 &#181;m) by vibratome, the photoreceptors are seeded after mechanical and enzymatic dissociation for culture. The photoreceptor layer can be used for molecular, biochemical analyses or transplantation.

The retina is a part of the central nervous system that has organized architecture, with neurons in layers from the photoreceptors, both rods and cones in ...

Imaging Ca2+ Dynamics in Cone Photoreceptor Axon Terminals of the Mouse Retina

Retinal cone photoreceptors (cones) serve daylight vision and are the basis of color discrimination. They are subject to degeneration, often leading to blindness in many retinal diseases. Calcium (Ca2+), a key second messenger in photoreceptor signaling and metabolism, has been proposed to be indirectly linked with photoreceptor degeneration in various animal models. Systematically studying these aspects of cone physiology and pathophysiology has been hampered by the difficulties of electrically recording from these small cells, in particular in the mouse where the retina is dominated by rod photoreceptors. To circumvent this issue, we established a two-photon Ca2+ imaging protocol using a transgenic mouse line that expresses the genetically encoded Ca2+ biosensor TN-XL exclusively in cones and can be crossbred with mouse models for photoreceptor degeneration. The protocol described here involves preparing vertical sections (&#8220;slices&#8221;) of retinas from mice and optical imaging of light stimulus-evoked changes in cone Ca2+ level. The protocol also allows &#8220;in-slice measurement&#8221; of absolute Ca2+ concentrations; as the recordings can be followed by calibration. This protocol enables studies into functional cone properties and is expected to contribute to the understanding of cone Ca2+ signaling as well as the potential involvement of Ca2+ in photoreceptor death and retinal degeneration.

Imaging Ca2+ Dynamics in Cone Photoreceptor Axon Terminals of the Mouse Retina

We describe a protocol to monitor Ca2+ dynamics in the axon terminals of cone photoreceptors using an ex-vivo&#160;slice preparation of the mouse retina. This protocol allows comprehensive studies of cone Ca2+ signaling in an important mammalian model system, the mouse.

Retinal cone photoreceptors (cones) serve daylight vision and are the basis of color discrimination. They are subject to degeneration, often leading to ...

Assay Development for High Content Quantification of Sod1 Mutant Protein Aggregate Formation in Living Cells

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease that can be caused by inherited mutations in the gene encoding copper-zinc superoxide dismutase 1 (SOD1). The structural instability of SOD1 and the detection of SOD1-positive inclusions in familial-ALS patients supports a potential causal role for misfolded and/or aggregated SOD1 in ALS pathology. In this study, we describe the development of a cell-based assay designed to quantify the dynamics of SOD1 aggregation in living cells by high content screening approaches. Using lentiviral vectors, we generated stable cell lines expressing wild-type and mutant A4V SOD1 tagged with yellow fluorescent protein and found that both proteins were expressed in the cytosol without any sign of aggregation. Interestingly, only SOD1 A4V stably expressed in HEK-293, but not in U2OS or SH-SY5Y cell lines, formed aggregates upon proteasome inhibitor treatment. We show that it is possible to quantify aggregation based on dose-response analysis of various proteasome inhibitors, and to track aggregate-formation kinetics by time-lapse microscopy. Our approach introduces the possibility of quantifying the effect of ALS mutations on the role of SOD1 in aggregate formation as well as screening for small molecules that prevent SOD1 A4V aggregation.

We describe a method to quantify the aggregation of misfolded proteins. Our protocol details lentiviral induced stable cell line generation, automated confocal imaging, and image analysis of protein aggregates. As an illustrative application, we studied the effect of small molecules in promoting SOD1 aggregation in a time- and dose-dependent manner.

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease that can be caused by inherited mutations in the gene encoding copper-zinc ...

Reliable Isolation of Central Nervous System Microvessels Across Five Vertebrate Groups

Isolation of microvessels from the central nervous system (CNS) is commonly performed by combining cortical tissue from multiple animals, most often rodents. This approach limits the interrogation of blood-brain barrier (BBB) properties to the cortex and does not allow for individual comparison. This project focuses on the development of an isolation method that allows for the comparison of the neurovascular unit (NVU) from multiple CNS regions: cortex, cerebellum, optic lobe, hypothalamus, pituitary, brainstem, and spinal cord. Moreover, this protocol, originally developed for murine samples, was successfully adapted for use on CNS tissues from small and large vertebrate species from which we are also able to isolate microvessels from brain hemisphere white matter. This method, when paired with immunolabeling, allows for quantitation of protein expression and statistical comparison between individuals, tissue type, or treatment. We proved this applicability by evaluating changes in protein expression during experimental autoimmune encephalomyelitis (EAE), a murine model of a neuroinflammatory disease, multiple sclerosis. Additionally, microvessels isolated by this method could be used for downstream applications like qPCR, RNA-seq, and Western blot, among others. Even though this is not the first attempt to isolate CNS microvessels without the use of ultracentrifugation or enzymatic dissociation, it is unique in its adeptness for the comparison of single individuals and multiple CNS regions. Therefore, it allows for investigation of a range of differences that may otherwise remain obscure: CNS portions (cortex, cerebellum, optic lobe, brainstem, hypothalamus, pituitary, and spinal cord), CNS tissue type (gray or white matter), individuals, experimental treatment groups, and species.

The goal of this protocol is to isolate microvessels from multiple regions of the central nervous system of lissencephalic and gyrencephalic vertebrates.

Isolation of microvessels from the central nervous system (CNS) is commonly performed by combining cortical tissue from multiple animals, most often ...

Millisecond Hydrogen/Deuterium-Exchange Mass Spectrometry for the Study of Alpha-Synuclein Structural Dynamics Under Physiological Conditions

Alpha-synuclein (aSyn) is an intrinsically disordered protein whose fibrillar aggregates are abundant in Lewy bodies and neurites, which are the hallmarks of Parkinson's disease. Yet, much of its biological activity, as well as its aggregation, centrally involves the soluble monomer form of the protein. Elucidation of the molecular mechanisms of aSyn biology and pathophysiology requires structurally highly resolved methods and is sensitive to biological conditions. Its natively unfolded, meta-stable structures make monomeric aSyn intractable to many structural biology techniques. Here, the application of one such approach is described: hydrogen/deuterium-exchange mass spectrometry (HDX-MS) on the millisecond timescale for the study of proteins with low thermodynamic stability and weak protection factors, such as aSyn. At the millisecond timescale, HDX-MS data contain information on the solvent accessibility and hydrogen-bonded structure of aSyn, which are lost at longer labeling times, ultimately yielding structural resolution up to the amino acid level. Therefore, HDX-MS can provide information at high structural and temporal resolutions on conformational dynamics and thermodynamics, intra- and inter-molecular interactions, and the structural impact of mutations or alterations to environmental conditions. While broadly applicable, it is demonstrated how to acquire, analyze, and interpret millisecond HDX-MS measurements in monomeric aSyn.

The structural ensemble of monomeric alpha-synuclein affects its physiological function and physicochemical properties. The present protocol describes how to perform millisecond hydrogen/deuterium-exchange mass spectrometry and subsequent data analyses to determine conformational information on the monomer of this intrinsically disordered protein under physiological conditions.

Alpha-synuclein (aSyn) is an intrinsically disordered protein whose fibrillar aggregates are abundant in Lewy bodies and neurites, which are the hallmarks ...