Ultrastructure and lectin cytochemistry of secretory cells in lingual glands of the Japanese quail (Coturnix coturnix japonica)

In the present study, as continuation of our previous research, Japanese quail (Coturnix coturnix japonica) lingual glands were investigated by means of transmission electron microscopy (TEM) to understand the cytoarchitecture and the subcellular sugar distribution within the different secretory structures. Indeed, glycosidic residues were visualized by applying an indirect technique of binding and the terminal sialoglycoconjugate sequences were characterized by employing sialidase digestion combined with lectin affinity. The ultrastructural analysis revealed an unusual cytoarchitecture of the caudal portion of anterior lingual gland that was composed of both secretory cells, filled with granules, and non-secretory cells, filled with mitochondria. Conversely, the posterior lingual gland was composed of secretory units of lingual glands only containing mucous cells filled with secretory granules with a variable morphology, including bipartite features characterized by an electron-lucent matrix and one or more electron-dense areas. Actual findings further supported that the quail lingual glands produce sialoglycoconjugates characterized by a heterogeneous composition. In conclusion, the cytological characteristics and the carbohydrate composition of quail lingual glands suggest that, analogously to mammal salivary glands, avian lingual glands could also be involved in several functions that can be correlated with the occurrence of sialic acids.