Purpose. To localize and characterize nerves in primate meibomian glan
ds using immunohistochemical staining for neuropeptides and neuronal e
nzymes. Methods. Upper eyelids were obtained from seven rhesus monkeys
(Macaca mulatta) and one cynomolgous monkey (Macaca fascicularis). Th
e tissues were fixed either by immersion in Zamboni's fixative or by t
ranscardiac perfusion with paraformaldehyde and glutaraldehyde and wer
e 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 in
testinal polypeptide (VIP), calcitonin gene-related peptide (CGRP), an
d substance P (SP), followed by a fluorescence visualization system. R
esults. Used as a marker for the overall nerve distribution, NSE antib
odies revealed abundant smooth and varicose nerve fibers closely appos
ed to the basement membranes of acini of the meibomian glands. Numerou
s nerve fibers near the meibomian gland acini were immunoreactive for
NPY and VIP, but nerve fibers containing TH, CGRP, and SP were more sp
arse in the meibomian glands. Nerve fibers also were visualized in oth
er eyelid structures, including conjunctiva, epidermis, hair follicles
, and subconjunctival lymphoid follicles. Conclusions. The meibomian g
lands of rhesus and cynomolgous monkeys are richly innervated by diver
se nerve fiber types. The immunohistochemical staining suggests a larg
ely parasympathetic origin for this innervation, with relatively small
er contributions from sympathetic and sensory sources. These findings
also suggest that meibomian gland secretion is under the control of di
verse neurotransmitter-neuromodulator mechanisms.