Purpose. Animal models for human disease are an important resource for experimental exploration of disease processes. There are currently several models for age-related retinal degeneration in the monkey, rat, pigeon and quail. We report here that the aquatic-phase tiger salamander (Ambystoma tigrinum), with a life span of about 11-12 years, also exhibits age-related retinal degeneration. Methods. Salamanders 11 inches or more in length, approximately 10 years old, were designated as "old" and compared with salamanders, 6-9 inches in length, or approximately 2-7 years old and designated as "young." Vision was assessed by analysis of the optomotor reflex at three light levels; retinal morphology was examined with conventional light and electron microscopy. Twenty-six salamanders, collected in both summer and winter seasons, were used. Results. The greatest disparity in visually stimulated performance occurred under low light conditions (5nW): old animals responded correctly an average of 47% of the time, i.e., almost randomly; in contrast, young animals responded appropriately 77% of the time. With increased light, both old and young animals had improved performance. However, old animals still responded appropriately only 66-78%, whereas young animals responded correctly 93-95%, of the time. Microscopic examination of visually tested animals demonstrated that reduced visual responsiveness correlated with abnormal retinal histology. Aging retinas showed various types of degeneration. Abnormal photoreceptors whose outer segments were either truncated, misaligned, or missing, were present and both hyperplasia and absence of the retinal pigmented epithelium occurred. Aging retinas also contained pyknotic cells (∼2/mm retina) which were not found in younger retinas. Since rod and cone cell density is decreased in old retinas, it is possible that photoreceptors are lost with age. Conclusions. Old salamanders can show retinal pathology. Moreover, performance in the optomotor test can be used to select animals with degenerate retinas. This predictive tool, in addition to the available data on normal retinal physiology and anatomy, should make the tiger salamander a useful model for age-related retinal disease.
|Original language||English (US)|
|Journal||Investigative Ophthalmology and Visual Science|
|State||Published - Feb 15 1996|
All Science Journal Classification (ASJC) codes
- Sensory Systems
- Cellular and Molecular Neuroscience