Mechanisms of photoreceptor death and survival in mammalian retina
Section snippets
Durability and fragility
It is easy to be impressed by both the durability and the fragility of mammalian photoreceptors. In phylogenetic terms their design—each is a neurone of the central nervous system in which the cilium is specialised to bear photosensitive pigments and signal their breakdown—is considered to have been conserved throughout the evolution of vertebrates, thus over hundreds of millions of years. In ontogenetic terms the photoreceptor shares the ability of all central nervous system neurones to
Developmental death of photoreceptors
The generation of photoreceptors and other retinal neurones has been reviewed elsewhere (Stone, 1987; Robinson, 1991; Rapaport and Vietri, 1991; LaVail et al., 1991). Emphasis is given here to a period of death among photoreceptors which appears to be a normal part of their development. During this period (we suggest) the population of photoreceptors is culled from an initial excess to a level appropriate for adult life. Evidence of a cull is reviewed here because regulation of the cull is a
Adaptability of energy sourcing
“The…retina has three unusual properties: it converts glucose to lactic acid with prodigious speed; it consumes oxygen more readily than other tissues; and the formation of lactic acid is rapid even in the presence of oxygen….” Cohen and Noell (1965)
Mechanisms of adult instability: dearth of energy and excess of oxygen
What mechanisms make the adult retina unstable, despite the natural longevity of mammalian CNS neurones and the self-protective mechanisms the retina has evolved? We review here three distinct forms of retinal destabilisation.
A two stage model of retinal dystrophies
The ideas and data presented in Section 4lead to the following model of photoreceptor dystrophies (other than the dystrophy which follows detachment).
Retinal detachment: oxygen supplementation will improve outcomes
The retina's response to detachment is the degeneration of some photoreceptors, degenerative changes in the survivors and a glial proliferation (Section 4.1). From the evidence set out in Section 4.1.2we predict that oxygen supplementation between diagnosis and surgery will be of benefit in corresponding ways: it will rescue photoreceptors in the detached portion of retina, preserve the structure of surviving photoreceptors and reduce the proliferation of glial cells. The clinical outcome
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