Chapter 11 Synaptic growth in the rod terminals after partial photoreceptor cell loss

Cellular responses following retinal injuries and therapeutic approaches for neurodegenerative diseases

Retinal neurodegenerative diseases like age-related macular degeneration, glaucoma, diabetic retinopathy and retinitis pigmentosa each have a different etiology and pathogenesis. However, at the cellular and molecular level, the response to retinal injury is similar in all of them, and results in morphological and functional impairment of retinal cells. This retinal degeneration may be triggered by gene defects, increased intraocular pressure, high levels of blood glucose, other types of stress or aging, but they all frequently induce a set of cell signals that lead to well-established and similar morphological and functional changes, including controlled cell death and retinal remodeling. Interestingly, an inflammatory response, oxidative stress and activation of apoptotic pathways are common features in all these diseases. Furthermore, it is important to note the relevant role of glial cells, including astrocytes, Müller cells and microglia, because their response to injury is decisive for maintaining the health of the retina or its degeneration. Several therapeutic approaches have been developed to preserve retinal function or restore eyesight in pathological conditions. In this context, neuroprotective compounds, gene therapy, cell transplantation or artificial devices should be applied at the appropriate stage of retinal degeneration to obtain successful results. This review provides an overview of the common and distinctive features of retinal neurodegenerative diseases, including the molecular, anatomical and functional changes caused by the cellular response to damage, in order to establish appropriate treatments for these pathologies.

Solar pruning of retinal rods in albino rainbow trout

Morphology of the central retina and scotopic visual sensitivity were compared in juvenile albino and normally pigmented rainbow trout living under natural and reduced daylight. Outdoor albinos avoided exposing their eyes to direct sunlight, whereas normals were indifferent to it. After 4 months outdoors (approximately 10,000 lux in albinos, approximately 100,000 lux in normals), albinos had severely truncated or missing rod outer segments (ROS) and some missing rod ellipsoids, but normal numbers of photoreceptor nuclei and fully intact cones. Albino estimated ROS volume was only 7.1% of normal in July, but increased to 20% by the following February, mainly via an increase in numbers of ROS. However, in albinos moved indoors October 7 and exposed to 10-30 lux ambient daylight, both the number and length of ROS increased significantly, with estimated ROS volume reaching 95% of normal by 34 days. Albinos generally had more phagosomes (approximately 3 x normal) and more macrophages (approximately 2 x normal) in their outer retina. An optomotor reflex was used to define the effect of ROS volume on the ability to respond visually during dark adaptation. In July, albinos and normals from outdoor raceways (3 months) or indoor raceways (35 days) showed equal sensitivity after first being placed in darkness, but after 1 h in darkness, outdoor albinos with 6% of normal ROS volume were 2.0 log units less sensitive than indoor or outdoor normals, whereas indoor albinos with 53% of normal ROS volume were only 0.7 log units less sensitive. This verifies that most rod cell bodies of albino trout can persist without functional ROS in indirect sunlight, and can regrow functional outer segments in dim daylight. This finding is distinct from the extensive retinal light damage observed in albino rats exposed to more moderate cyclic light, in which entire rod cells degenerate early on.