Myoepithelial Cells and Neuronal Nitric Oxide Synthase in the Rabbit Lacrimal Gland

Abstract

Purpose. Myoepithelial cells are one of the major components in the mammalian lacrimal gland. However, their role in lacrimal secretion is still unclear. The present study explores the presence of myoepithelial cells in the rabbit lacrimal gland and their relationship with the innervation, particularly the nitric oxide (NO) pathway. Methods. Lacrimal glands were fixed with 4% paraformaldehyde and cryosectioned serially at 8 m. Sections were incubated with antibodies against S100 protein, synaptophysin, and neuronal nitric oxide synthase (nNOS). Secondary antibodies were conjugated with FITC, or Rhodamine Red. Conventional and confocal immunofluorescence microscopy was employed for observation. Results. The rabbit lacrimal gland is rich in myoepithelial cells, and most, if not all, acini were surrounded by them. Three dimensional reconstructions of these cells indicate that they have an octopus-like appearance with long cytoplasmic projections. These cells ramify among acini and frequently surround more than one acinus. nNOS immunoreactivity (IR) was also detected in the gland, and confirmed our previous results that it is not homogeneously distributed across the gland. Although most acinar cells had punctate nNOS IR within their cytoplasm, some acini were particularly rich in nNOS IR, showing “cluster” appearance. Nerves that were stained for S100 protein also demonstrated nNOS IR, particularly prominent in the nerve bundles. Strong synaptophysin IR was detected in the gland and some colocalized with S100 and nNOS IR. Conclusions. Our data indicate that there are numerous myoepithelial cells in the rabbit lacrimal gland. These octopus-like cells surround and envelop the acini. The colocalization and/or close contact between S100 IR, synaptophysin IR, and nNOS IR suggest that some myoepithelial cells are directly innervated by neural systems, particularly the NO pathway, as NO can easily diffuse across the membrane/tissue and most acini are surrounded by myoepithelial cells. Therefore, myoepithelial cells may play a role in lacrimal secretion, particularly in neural-secretion coupling. Commercial Relationship(s): None; Support: Sjogren’s Syndrome Foundation (CD), EY10550 (JES), DK48522