Analyzing Photoreceptor Degeneration and Preservation in a Retinitis Pigmentosa Murine Model

Retinopathies affect hundreds of millions of people worldwide and are significant causes of visual impairment and blindness. Among these diseases, retinitis pigmentosa (RP) is a hereditary ocular disorder characterized by progressive retinal degeneration, affecting approximately 1.5 to 2 million people worldwide. Proof of concept studies in animal models of hereditary retinal dystrophies form an important basis of evidence for studies in pathophysiological mechanisms of the disease, treatment effectiveness and safety. Intravitreal injection in mice and cryostat sectioning are widely utilized techniques for investigating drug effects in RP models, as they enable a precise delivery of substances into vitreous humor and preparation of high-quality histological samples for detailed analysis of retinal alterations. Also, cell counting through immunofluorescence using antibodies against recoverin, a calcium-dependent protein expressed in retinal photoreceptors, has been recently employed to study cellular changes associated with retinal degeneration in RP models, because this approach facilitates evaluation of photoreceptor loss and potential cellular preservation following therapeutic interventions. The intravitreal injection has been optimized to ensure ocular integrity and reliable results, utilizing a fine needle to administer the solution into the vitreous chamber. After a predefined period to assess drug effects, histological processing is performed, with samples sectioned at 10 μm thickness using a cryostat, followed by immunofluorescence labeling with recoverin antibodies. Finally, cell counting is performed to assess whether the treatment with drugs exerted a protective effect, as evidenced by preservation of photoreceptors. Although these techniques have been extensively applied to generate consistent data in retinopathy research, challenges persist in achieving precise tissue handling and processing quality. This protocol provides a standardized approach to optimize each step, from intravitreal injection to the preparation of histological sections, ensuring reproducible and high-quality results.