Immunocytochemical and ultrastructural evaluation of the distribution of nervous tissue and neuropeptides in the meibomian gland

The ultrastructure of the meibomian gland, of its innervation and the localization of neuropeptides in the glandular tissue of the guinea pig and humans are incompletely known. Therefore they have been investigated in the present study. The ultrastructure of the tissue was examined using standard transmission electron microscopic techniques. Additional scanning electron microscopy was carried out on rabbit tissue. Antisera against the neuronal marker protein gene product were used to demonstrate the distribution pattern of the nerve fibers. The neuropeptides substance P (SP) and neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP) and calcitonin gene-related peptide (CGRP) and the neuronal enzyme tyrosine hydroxylase (TH) were identified by their specific antisera. The glands were found to be composed of arrays of alveoli. The outer cells of the alveoli form a germinal layer. Toward the inside of the alveolus the cells are laden with a secretory substance. The cells disintegrate as they approach the excretory duct. Nerve fibers form a plexus around the alveoli. These nerve fibers form synapses à distance to the basal alveolar cells and enter the basal lamina of the capillaries. In guinea pigs many nerve fibers were positive for the neuropeptides SP and NPY and for VIP, and fewer for CGRP and TH; in humans only SP and CGRP were demonstrated. Both the density of nerve fibers and the presence of various neuropeptides suggest that the stimulation of the meibomian gland is subject to nervous control.