Principal ocular glands in the desert rodent Gerbillus tarabuli: morpho-functional adaptive analysis

Abstract

Abstract Background Desert rodent, Gerbillus tarabuli, is a seed-eating animal and do not require drinking water. It depends upon metabolic water. Understanding the functional characteristics of ocular glands which produce a watery lacrimal fluid is of interest. In the present study, we described the macroscopic anatomy and microscopic structure of the paraorbital glands in tarabul’s gerbil. Results There are up to four distinct orbital glands: lacrimal (LG), Harderian (HG), Meibomian (MG), and conjunctival mucous glands. Each eye has three eyelids, the main upper and lower lids and a third lid hidden between them in the inner corner of the eye. The LG is bipartite, situated on the dorsolateral aspect of the eyeball. The HG is large and localized deep in the orbit. The MG is found in the dense connective tissue plate. Upon light microscopic examination, the LG is an acinar gland; its secretory cells have mucous and serous granular cytoplasm. The endpieces of HG consist of tubuloalveoli, with two cellular types: prismatic vacuolated cells and pyramidal basophilic cells. The MG acini are closely arranged one after another. Each acinus contains a basal layer of myoepithelial cells and a mass of rounded, vacuolated cells. The nictitating membrane is formed by a semilunar fold of conjunctiva, supported by a hyaline cartilage. Numerous goblet cell clusters are detected in the covering conjunctiva particularly in the bulbar conjunctiva. Mucin glycoproteins appear to be abundant in the precorneal tear film, probably acting against desiccation stress. Conclusions Based on the data from this study, it could be concluded that the orbital glands of gerbil are well-developed, similar to other mammals.