INNERVATION OF MYOFIBROBLAST-LIKE SCLERAL SPUR CELLS IN HUMAN AND MONKEY EYES

Purpose. To study the innervation of the presumably contractile, myofi broblast-like scleral spur cells in human and cynomolgus monkey eyes. Methods. Serial tangential sections of the scleral spur region of the eyes of 16 human donors and 6 cynomolgus monkeys were investigated wit h immunocytochemical methods. Antibodies against acetylcholinesterase, synaptophysin, alpha-smooth muscle actin, calcitonin gene-related pep tide (CGRP), neuropeptide Y (NPY), nitric oxide synthase (NOS), substa nce P (SP), tyrosine hydroxylase (TH), and vasoactive intestinal pepti de (VIP) were used. In addition, sections were processed for glyoxylic acid-induced catecholamine fluorescence (CF) and for NADPH-diaphorase (NADPH-d). Results. In the eyes of both species, circumferentially or iented varicose axons were observed in the scleral spur region of all quadrants. Double labeling showed that most of these scleral spur axon s were in close contact with the cu-smooth muscle actin-positive, myof ibroblast-like scleral spur cells. In human eyes, the axons showed lik e-immunoreactivity (LI) for SP, CGRP, NPY, VIP, and NOS. In addition, numerous scleral spur axons stained for NADPH-d. Most SP-LI scleral sp ur axons were double-labeled for CGRP-LI, and none for VIP-LI. All NPY -LI scleral spur axons were double labeled for VIP-LI but lacked immun oreactivity to TH. Some VIP-LI axons were not labeled for NPY-LI. Nerv e fibers immunoreactive (IR) for TH or positively stained for CF were not observed in association with scleral spur cells. In contrast, in c ynomolgus monkey eyes, circumferentially oriented TH-IR and CF-positiv e Varicose axons were observed frequently in the scleral spur region. In addition, SP-LI, CGRP-LI, and NPY-LI/TH-IR axons were present in th e chamber angle of monkey eyes, whereas VIP-LI, VIP-LI/NPY-LI, NOS-pos itive, or NADPH-d-positive nerve fibers were absent. In both species, positive staining for acetylcholinesterase was seen only in the ciliar y muscle, not in the scleral spur region. Conclusions. The close assoc iation of varicose axons with the myofibroblast-like scleral spur cell s indicates that nervous signals modulate scleral spur cell tone. A sy mpathetic scleral spur cell innervation is present only in cynomolgus monkeys but seems to be absent in humans. Conversely, scleral spur axo ns of presumably parasympathetic origin (NOS-IR or NADPH-d-positive, V IP-LI, and VIP-LI/NPY-LI) are absent in the cynomolgus monkey but pres ent in humans. In both species, a cholinergic innervation of the scler al spur cells seems to be rare or absent.