Müller Glia Cell Activation in a Laser-induced Retinal Degeneration and Regeneration Model in Zebrafish

The overall goal of this video is to show how to monitor cellular changes in vivo following a focal, laser-induced retinal damage in Zebrafish. This model can help you answer key questions of retinal regeneration, such as morphological changes, kinetics, as well as cell types involved. The main advantage of this technique is that by inducing a focal injury, biological processes can be investigated directly at the site of injury.

Though this method can provide insight into regeneration of Zebrafish retina, it can also be applied to study the repair mechanism in different animal models. Prepare a stock solution of anesthetic by dissolving 400 milligrams of tricaine powder in 97.9 millimeters of tank water, and 2.1 millimeters of one molar TBS. Adjust to pH 7.0 with one molar tris at pH 9.

To make the working solution, dilute the tricaine stock solution 1 to 25 in tank water and transfer 50 milliliters to a Petri dish. Then, place the Zebrafish into the anesthetic solution for two to five minutes until they become immobile and do not respond to external stimuli. Transfer each fish by hand to a custom made silicone pin holder for laser treatment.

Appropriate anesthesia is critical for the well-being of the animal and the success of procedure. Therefore, freshly prepared tricaine solution is pivotal, and the time out of the water should not far exceed 10 minutes. Set up the output power of the 532 nanometer dialed laser to 70 milliwatts, the pulse duration to 100 milliseconds, and the aerial diameter to 50 microns.

Then, apply one to two drops of 2%hydroxypropyl methylcellulose to the eye. When apply methylcell to the eye, ensure that the viscous solution doesn't go in the gills. Next, use a 2 millimeter fundus laser lens to focus the laser aiming beam on the retina.

Place four laser spots around the optic nerve on the left eye, and use the right, untreated eye as internal control. Immediately after laser induction, place the still anesthetized Zebrafish on a custom made silicone pin holder in the imaging area. To obtain optimal images, cut a commercially available hydrogel contact lens to fit the Zebrafish eye by means of a hole punch.

Fill the concave surface of the lens with methylcellulose, then place it over the cornea. Equip the optical coherence tomography system with a 78D non-contact slit lamp lens. Focus the infrared image in IR plus OCT mode to visualize the fundus of the eye.

Then, take the IR pictures by clicking the acquire button to localize the laser spots on the retina. Then, visualize a three dimensional section of the retinal layers in IR plus OCT mode, and take the pictures by clicking the acquire button. Observe the severity of injury in the outer nuclear layer in these images.

To reverse anesthesia after treatment and imaging, place the zebrafish in a container containing tank water. To support recovery, create a flow of fresh tank water over the gills by moving the zebrafish back and forth in the water. Immediately after laser treatment, a diffuse hyper-reflective signal was localized to the outer retina.

It extended from the retinal pigmented epithelium to the outer plexiform layer. The diffuse hyper-reflective signal is absent in the retina from the control un-lesioned eye. A similar diffuse hyper-reflective signal detected on day one after injury.

After day three, this diffuse signal became more organized and dense. It was consistently seen in the outer nuclear layer, extending into the photoreceptor layer. Following the first week, there was a significant decrease in average lesion size, and only a small hyper-reflective signal was detected.

Starting from day 14 until the latest time point investigated, the laser spots were no longer visible in IR and OCT images, and the morphology of the retina is comparable to the control side, seen here. H&E staining was employed to investigate the extent and kinetics of retinal degeneration and regeneration. This image shows the control section.

This image shows H&E staining three days after injury, when maximum photoreceptor loss is apparent. Immunohistochemistry to visualize the glial cell markers, glutamine synthetase, in red, and glial fibrillary acidic protein, in green, was performed. This image shows a control retina where there is very little green fluorescence, which is indicative of GFAP.

The GFAP signal was up-regulated at day three post injury, whereas the red glutamine synthetase signal remained unchanged. Following this procedure, other methods like two photon microscopy as well as cellular and molecular analysis can be performed in order to study the involvement of molecular cells in endogenous repair mechanisms. After watching this video, you should have a good understanding how to induce focal damage to the zebrafish retina and to monitor in vivo the following degenerative and regenerative processes.