Use a dip net to capture tadpoles from their tanks and transfer them into a 50 milliliter solution of 0.005%benzocaine. Allow them to remain in the solution until they no longer respond to stimuli. Use a spoon to gently pick up a tadpole and place it with its dorsal side facing up into a small Petri dish containing a damp tissue.
Then position the specimen under the stereo microscope. To begin, take a sharpened capillary, use a micro loader tip to load 10 microliters of cobalt chloride solution. Afterward, place the filled capillary into the micro injector handler to break off the capillary tip to adjust the ejection volume at about 30 nanoliters.
Using the micro injector and a stereo microscope, insert the capillary filled with cobalt chloride over the lens into the eye. Upon reaching the inside of the eye with the capillary tip, eject two drops of about 30 nanoliters per eye. After the right eye has been injected, turn the Petri dish to a 180 degree angle to inject the left eye.
Transfer the Petri dish containing the injected tadpole to a large tank containing one liter of rearing water. Keep observing the tadpoles until they have fully awakened. Injection of 10 millimolar cobalt chloride led to specific cell death of cone photoreceptors, while 25 millimolar led to broad retinal cell death.
Immuno staining revealed the absence of cones in 10 millimolar cobalt chloride injected retinas while rods were largely preserved. After injections of 25 millimolar cobalt chloride, both photoreceptors and bipolar cells were severely affected.
