|Ph.D Student||Massarweh Amir|
|Subject||The Effect of Prolonged Darkness on the Susceptibility of|
the Albino Rat Retina to Light Damage
|Department||Department of Medicine||Supervisor||Professor Emeritus Ido Perlman|
Light-induced retinal damage in albino rats is an established model for studying cellular and molecular mechanisms leading to apoptosis of photoreceptors, therefore serves as an accepted model for photoreceptor apoptosis in inherited and in acquired retinal diseases. Dark rearing is known to exacerbate the extent of photoreceptor damage following exposure to bright light compared to albino rats kept in 12/12 light/dark cycle. However, most studies were qualitative in nature and did not address the causes of this effect.
The transcriptomic analysis leads us to suggest the following theory: The outer segments of the photoreceptors, a high energy consuming cells, due to the active extrusion of sodium ions and intrusion of potassium ions by the Na/ K ATPase exchanger elongate in prolonged darkness. Therefore, the inflow of sodium ions through the cyclic GMP dependent sodium/calcium channels in the outer segment and the outflow the potassium ions in the inner segment and cell body increase, demanding higher ATP consumption by the Na/K transporter. The decreased ATP balance leads to down regulation of ATP-consuming pathways and up-regulation of ATP producing pathways. The net effect is increasing the susceptibility of the photoreceptors to external or internal insults, such as exposure to bright light. We further suggest that the effects of prolonged darkness may mimic some aspects of aging, and thus this model has the potential to become a new, easy and reversible model, to study the increased susceptibility to insults during aging.