Photoreceptor plasticity in the albino rat retina following unilateral optic nerve section.

Rhodopsin content of the retina increased when an albino rat was moved to a lower intensity cyclic light, and decreased when moved to a higher intensity. Unilateral optic nerve section was employed to test if intact optic nerves are necessary to maintain regulation of rhodopsin when albino rats are switched between two intensities, 3 lx and 600 lx (12 hr/12 hr, cyclic light). The ability to regulate rhodopsin content was altered but not lost in the eye which had the optic nerve transected. This alteration was in the direction of incomplete up-regulation when the intensity change was from high to low, and was in the direction of excessive down-regulation when the intensity change was from low to high. This indicates that efferent fibers from the brain to the retina may be involved in the regulation of rhodopsin content. Using histological techniques, cell number and rod outer segment (ROS) length were measured: surgery alone had no effect on ROS length or outer nuclear layer thickness and in all cases ROS lengths were inversely related to habitat illuminance.