CHARACTERIZATION OF MEIBOMIAN GLAND INNERVATION IN THE CYNOMOLGUS MONKEY (MACACA-FASCICULARIS)

To characterize the innervation of the cynomolgus monkey (Macaca fasci cularis) Meibomian (tarsal) glands, upper lids of six cynomolgus monke ys were investigated with electronmicroscopical and double-labeling im munocytochemical methods. Antibodies against calcitonin gene-related p eptide (CGRP), dopamine-beta-hydroxylase (DBH), neuropeptide Y (NPY), nitric oxide synthase (NOS), protein gene product 9.5 (PGP 9.5), subst ance P (SP), tyrosine hydroxylase (TH), and vasoactive intestinal pept ide (VIP) were used. In addition, sections were processed for NADPH-di aphorase (NADPH-d) histochemistry. Staining for PGP 9.5 and electron m icroscopy showed that Meibomian gland acini were surrounded by a netwo rk of unmyelinated nerves and terminal varicose axons. The terminals c ontained small agranular (30-60 nm) and large granular vesicles (65-11 0 nm), and were observed in close contact with the basal lamina of the acini, but never internally to the basal lamina. Meibomian axons show ed like-immunoreactivity (LI) for the neuropeptides SP, CGRP, NPY, and VIP. In addition, the axons stained for TH, DBH, NOS, and NADPH-d. VI P-LI, NOS- and NADPH-d-positive axons appeared to be more numerous, TH - and DBH-positive axons more rare than others. Most SP-LI axons were double-labelled for CGRP-LI, some for VIP-LI or NPY-LI. In addition, s ome VIP-LI axons were double-labeled for NPY-LI. NPY/VIP-LI and NPY/SP -LI axons were only observed close to the Meibomian acini. Conversely, NPY-LI colocalized with TH-IR or DBH-IR predominated in perivascular nerves of Meibomian gland vasculature. The close association of varico se axons with the acini of Meibomian glands indicates that nervous sig nals modulate meibomian secretion. Meibomian gland nerve fibers in the cynomolgus monkey appear to utilize various neuropeptides, catecholam ines and nitric oxide as transmitter substances, and seem to derive fr om the pterygopalatine, superior cervical and trigeminal ganglion resp ectively.