Practical pathology of aging mice

Pettan-Brewer, Christina; Treuting, Piper M.

The cornea of mice is relatively large compared to humans and is exposed to exogenous irritants such as bedding dust and ammonia levels, which can cause contact keratitis. Skin commensals may also contribute to keratitis, conjunctivitis, and blepharitis. With age, atrophy and chronic inflammation of the lacrimal glands is very common and may result in decreased tear production and secondary corneal lesions (keratoconjucntivits sicca). Regardless of the cause, cornea lesions present as opaque eyes with variable amount of discharge. In pigmented strains, corneal opacity is particularly easy to recognize due to the contrast with the dark globe (Fig. 3C) . Ulcerative keratitis may be diagnosed clinically via ophthalmic exams and fluorescein stain uptake into the ulcerated cornea. Treatment options may include antibiotics and or steroids and will vary by facility and experimental protocol. Frequently in aged mice, the bulk of the ulceration and active inflammation is resolved; histologically, the chronic corneal lesion is characterized by proliferation of the corneal epithelium with varying neovascularization and chronic inflammation (Fig. 3E,F) . Other eye lesions commonly reported include proptosis with or without bulopthalmia secondary to retrobulbar abscesses, Harderian gland, or intraorbital gland neoplasias (Fig. 3B,D) . Cataracts are also quite common in aged mice but are more challenging to diagnose clinically usually requiring slit lamp examination (32, 33) antemortem or postmortem histopathological assessment.