Peptidergic innervation of the primate meibomian gland

To localize and characterize nerves in primate meibomian glands using immunohistochemical staining for neuropeptides and neuronal enzymes.

Upper eyelids were obtained from seven rhesus monkeys (Macaca mulatta) and one cynomolgous monkey (Macaca fascicularis). The tissues were fixed either by immersion in Zamboni's fixative or by transcardiac perfusion with paraformaldehyde and glutaraldehyde and were then postfixed. Cryostat tissue sections of the lids were stained by immunohistochemistry using rabbit antisera to neuron-specific enolase (NSE), tyrosine hydroxylase (TH), neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP), calcitonin gene-related peptide (CGRP), and substance P (SP), followed by a fluorescence visualization system.

Used as a marker for the overall nerve distribution, NSE antibodies revealed abundant smooth and varicose nerve fibers closely apposed to the basement membranes of acini of the meibomian glands. Numerous nerve fibers near the meibomian gland acini were immunoreactive for NPY and VIP, but nerve fibers containing TH, CGRP, and SP were more sparse in the meibomian glands. Nerve fibers also were visualized in other eyelid structures, including conjunctiva, epidermis, hair follicles, and subconjunctival lymphoid follicles.

The meibomian glands of rhesus and cynomolgous monkeys are richly innervated by diverse nerve fiber types. The immunohistochemical staining suggests a largely parasympathetic origin for this innervation, with relatively smaller contributions from sympathetic and sensory sources. These findings also suggest that meibomian gland secretion is under the control of diverse neurotransmitter-neuromodulator mechanisms.