Beta-Amyloid in the Optic Nerves of Young Mouse Models of Alzheimer's Disease without Clinical Symptoms

Purpose: This study investigated the presence of beta-amyloid in the retina and optic nerve of 2-month-old mouse models of Alzheimer's disease (AD) prior to the onset of clinical symptoms and compared the findings to those of age-matched controls. Methods: Visual acuity and contrast sensitivity were measured using an OptoDrum (R) in 2-month-old mouse models (5xFAD) and 2-month-old normal mice (C57BL/6). The retina and optic nerve of the experimental and control groups were stained fluorescently using an amyloid-beta antibody, and the level of amyloid-beta expression in the two groups was compared and analyzed histologically. Results: The 2-month-old mouse models (5xFAD) are at a stage prior to the characteristic spatial learning and cognitive impairments associated with AD. Visual acuity and contrast sensitivity did not differ between the experimental and control groups. Beta-amyloid was not observed in the retina or optic nerve of the control group or in the retina of the experimental group. In contrast to normal mice of the same age, beta-amyloid accumulated in the optic nerve in the experimental group, with a tendency for increased beta-amyloid accumulation in the optic nerve closer to the brain. Conclusions: In young AD mouse models prior to the onset of clinical symptoms, there were no differences in visual acuity, contrast sensitivity, or histological changes in the retina compared to controls. However, pathological changes in the accumulation of beta-amyloid in the optic nerve in the experimental group preceded other changes. These findings should aid the early diagnosis of AD in the future.