Cataract in senescence accelerated mouse (SAM). 2. Development of a new strain of mouse with late-appearing cataract

A new strain of mouse with late-appearing hereditary cataract was developed in the Senescence Accelerated Mouse (SAM-R/3). At the beginning of the selection of the new strain (generation 4), 5% of mice which lived over 20 weeks had cataract, at least unilaterally. During selection and brother-sister inbreeding, the incidence increased and reached 68% of 78 mice whose lifespan exceeded 20 weeks, in the 12th generation. In recent populations, (generations 9-14), the cataract began to appear around 10 weeks of age and about 81% of 64 females and 49% of 47 males had cataract after 32 weeks of age. Inflammatory lesions of the cornea and eyelids began to occur later in life and the incidence was lower than that of cataract. This observation suggested to us that the cataract of this new strain was not congenital in origin but rather was age-related and did not occur consequently after the onset of inflammatory lesions around the lens tissue. Stereomicroscopic examination of the lens revealed that many of these cataracts occurred initially at the posterior area and that the mature cataract showed a characteristic protrusion at the posterior pole and nuclear dislocation. Histology of the mature cataract also revealed protrusion of the posterior pole and showed degeneration and liquefaction of lens cortex, nuclear dislocation and destruction of posterior lens capsule. The wet weight, water and protein contents showed that the lens of this strain developed normally and that the untoward events were the result but not the cause of cataract. The SAM-R/3 strain should prove to be a suitable murine model for investigation of age-related changes in the lens, and cataractogenesis.