[Age-related changes in the rat lacrimal gland: specific morphology and unknown nature]

The rat lacrimal apparatus includes several glands; among them, the exorbital gland plays the central role. Its parenchyma and stroma undergo prominent morphologic changes with age. The parenchymal transformation includes metaplasia of some of its acini and their turning into Harderian gland-like structures (harderization), accumulation of gland ducts ("ductularization"), and morphologic dysplasia-cytomegaly, karyomegaly, and'cell and nuclearpolymorphism in the other part of acini. All these transformations are hormone-dependent andsex-specific: theyoften appear in males. On the final stages of age-related transformations, the lacrimal gland tissue is morphologically similar to the neoplasm and has neoplastic morphology but no other features of a tumor. Therefore, the rat lacrimal gland is an interesting object to study tissue and cell atypia. In the rat glandular stroma, lymphocytic infiltration and fibrosis appear with age; these changes are similar to processes taking place in human lacrimal apparatus involved in the pathogenesis of senile dry eye syndrome. The spontaneous changes in the rat lacrimal gland, predominantly in male rats, can be used as a model of the human lacrimal apparatus disorders.