Glial Cell Line-derived Neurotrophic Factor in Myoepithelial Cells of Major and Minor Salivary Glands of Mice

Glial cell line-derived neurotrophic factor (GDNF) acts to promote the development, survival, and maintenance of central and peripheral neurons. Using RT-PCR analysis and immunohistochemical observations by both light and electron microscopy, we examined whether the myoepithelial cells in the major and minor salivary glands of normal mice expressed GDNF RT-PCR analysis revealed the existence of mRNAs of GDNF and its receptor, GFRal, in the submandibular glands. The immunoelectron microscopic observations showed that the GDNF-immunoreactive cells were located between the acinar secretory cells and the basement membrane, with their slender cytoplasmic processes containing bundles of filaments extending along the basement membrane, thus revealing them to be myoepithelial cells. Double immunostaining with anti-GDNF and anti-actin by confocal laser scanning microscopy in each gland revealed that most of these GDNF-immunoreactive cells were also actin-immunopositive. Numerous PGP9.5-immunoreactive nerve fibers were distributed in the serous glands of the parotid, submandibular, and Ebner glands (glands of von Ebner), which had less developed myoepithelial cells ; although Ebner glands had relatively more developing myoepithelial cells than the other two glands. On the other hand, the mucous glands of the sublingual gland and tongue mucous glands had sparse nerve fibers but highly developed myoepithelial cells. Thus, the degree of myoepithelial cell development was almost in inverse proportion to the degree of innervation.