NERVE-CELLS IN THE HUMAN CILIARY MUSCLE - ULTRASTRUCTURAL AND IMMUNOCYTOCHEMICAL CHARACTERIZATION

Purpose. Intrinsic nerve cells in the human ciliary muscle were identi fied and characterized by immunohistochemical and ultrastructural meth ods. Methods. Serial sections through the ciliary muscle of 10 human d onors (age range, 53 to 91 years) were investigated by electron micros copy, NADPH-diaphorase (NADPH-d) staining, and immunohistochemistry. A ntibodies against nitric oxide synthase (NOS), protein gene product 9. 5 (PGP 9.5), neurofilament proteins, tyrosine hydroxylase (TH), neurop eptide Y (NPY), vasoactive intestinal peptide (VIP), substance P (SP) and calcitonin gene-related peptide (CGRP) were used. Nerve cell densi ty per millimeter of circumferential width was analyzed in three eyes, and in one eye the total number of neurons in the entire ciliary musc le was evaluated. Results. Small (70% of the total; longitudinal diame ter 10 to 14 mu m) and large (longitudinal diameter 20 to 30 mu m) gan glion cells were identified in the inner parts of the muscles' reticul ar and circular portions. No nerve cells were observed in the anterior longitudinal portion. The cells were in contact with unmyelinated axo ns and synaptic boutons containing small agranular and large granular vesicles. Axe-somatic and axo-dendritic synapses were observed. Histoc hemically and ultrahistochemically, the neurons stained intensely for NADPHI-d. Both cell types were multipolar and expressed long filamento us processes. Axonal processes with periodic swellings suggesting vari cosities ran close and parallel to neighboring muscle bundles. Some ne rve cells were connected with each other by axonal processes. No periv ascular NADPH-d-positive nerves were seen around ciliary muscle vessel s, but they were present in the wall of the major arterial circle of t he iris. A small number of ganglion cells contributed to this perivasc ular network. NADPH-d-positive neurons stained for PGP 9.5 and NOS. No TH, NPY, or VIP-positive ciliary muscle neurons were observed. In dou ble labeling experiments, 70% of the nerve cells were in contact with nerve endings expressing SP-like and CGRP-like immunoreactivity. Seven teen to 32 NADPH-d-positive neurons were counted per millimeter of cil iary muscle circumferential width, with 923 in the entire ciliary musc le of one donor eye. Conclusions. The presence of intrinsic NOS-positi ve nerve cells concentrated in the inner parts of the ciliary muscle m ight indicate a physiological role of nitric oxide for disaccommodatio n or fluctuations during accommodation. Invest Ophthalmol Vis Sci. 199 5;36:414-426.