Characterization of Meibomian gland innervation in the cynomolgus monkey (Macaca fascicularis)

Abstract

To characterize the innervation of the cynomolgus monkey (Macaca fascicularis) Meibomian (tarsal) glands, upper lids of six cynomolgus monkeys were investigated with electronmicroscopical and double-labeling immunocytochemical methods. Antibodies against calcitonin gene-related peptide (CGRP), dopamine-beta-hydroxylase (DBH), neuropeptide Y (NPY), nitric oxide synthase (NOS), protein gene product 9.5 (PGP 9.5), substance P (SP), tyrosine hydroxylase (TH), and vasoactive intestinal peptide (VIP) were used. In addition, sections were processed for NADPH-diaphorase (NADPH-d) histochemistry. Staining for PGP 9.5 and electron microscopy showed that Meibomian gland acini were surrounded by a network of unmyelinated nerves and terminal varicose axons. The terminals contained small agranular (30-60 nm) and large granular vesicles (65-110 nm), and were observed in close contact with the basal lamina of the acini, but never internally to the basal lamina. Meibomian axons showed like-immunoreactivity (LI) for the neuropeptides SP, CGRP, NPY, and VIP. In addition, the axons stained for TH, DBH, NOS, and NADPH-d. VIP-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, some 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 varicose axons with the acini of Meibomian glands indicates that nervous signals modulate meibomian secretion. Meibomian gland nerve fibers in the cynomolgus monkey appear to utilize various neuropeptides, catecholamines and nitric oxide as transmitter substances, and seem to derive from the pterygopalatine, superior cervical and trigeminal ganglion respectively.

Vasoactive Intestinal Polypeptide (VIP) Innervation of the Human Eyelid Glands

“…In earlier studies we were able to visualize the neuropeptide SP and calcitonin gene-related peptide (CGRP) in human meibomian glands , but not VIP. With a modified technique we have now also succeeded in demonstrating VIP, which had previously been found only in species other than man (Gibbins, 1990 ;Fan and Smith, 1993 ;Simons and Smith, 1993 ;Chung et al, 1996 ;Kirch et al, 1996 ;. It is conceivable that the VIP-immunoreactive fibres are of a parasympathetic nature, as demonstrated experimentally on VIP-positive fibres of facial nerve origin in the orbital tissue, including the lids and main lacrimal glands of rabbits (Butler et al, 1984).…”

“…Bar 1 µm. Uno (1977), and VIP immunoreactive nerve-like structures have been demonstrated in meibomian glands (Gibbins, 1990 ;Fan and Smith, 1993 ;Simons and Smith, 1994 ;Chung et al, 1996 ;Kirch et al, 1996 ; and other sebaceous glands (Ebara et al, 1992) of non-human mammals, as well as in the sweat glands of rats, cats and humans (Landis and Fredieu, 1986 ;Lindh et al, 1988 ;AbdelRahman et al, 1992). Peptidergic nerve-like structures associated with Zeis glands have been found to be VIP-immunonegative in monkeys .…”

In vivo detection of clinically non-apparent ocular surface inflammation in patients with meibomian gland dysfunction-associated refractory dry eye symptoms: a pilot study

“…These nerves not only release neurotransmitters and neuropeptides but also express cognate receptors, 45,46 providing a channel for direct modulation of meibomian gland function and sensations of dryness, pain, and cooling. Some of these sensory neuropeptide receptors are also found on the neurovascular complex associated with meibomian gland acini, 45,47 allowing circulating neuropeptides and cytokines to indirectly regulate both sensory stimuli and meibomian gland function. Given the propensity for autonomic-immune interactions following cytokine release by immune cells, 48 it seems plausible that the presence of immune cells in the vicinity of palpebral conjunctival epithelium, substantia propria, and meibomian glands, as seen on IVCM, may stimulate these sensory nerves to trigger sensations of eye dryness and discomfort as reported by the patients presented in this paper.…”

Objective Metrics of Ocular Surface Disease in Contact Lens Wearers: Meibography

“…Another intriguing feature described by Hwang et al was the presence of an extensive mesh-like network between parallel meibomian glands, which cannot be attributed to ductal or glandular collaterals [45]. They speculated that this dense network around meibomian glands may represent a neuronal or vascular complex [62][63][64][65]. The next decade will be an exciting period of advancement in OCT meibography as metrics and indices of MG assessment develop, which may then be applied in larger studies, possibly even clinical trials.…”