Morphologic indication for proprioception in the human ciliary muscle.
OBJECTIVE
To search for proprioceptive nerve terminals in human ciliary muscle.


METHODS
In 48 human donor eyes, histologic and ultrathin sections cut in different planes and wholemounts of the ciliary muscle were studied. Immunohistochemical staining with antibodies against pan-neuronal antigens and antigens reported as markers for sensory terminals in other organs was performed.


RESULTS
Among the markers for proprioceptive terminals, only calretinin was present in the ciliary body. Calretinin-immunoreactive (IR) nerve terminals surrounded the posterior and reticular ciliary muscle tips and their elastic tendons. Terminals in that region contained mitochondria and neurofilaments. At the anterior tips larger terminals with numerous membrane-filled vesicles were located between the muscle fibers. The most elaborate network of calretinin-IR nerve fibers was present in the ground plate covering the circular muscle portion. Here calretinin-IR neurons with morphologic features of mechanoreception were present. Within the circular muscle portion numerous calretinin-IR ganglion cells were found. Their processes were connected to the calretinin-IR network but also surrounded ciliary muscle cells and NADPH-diaphorase-positive ganglion cells.


CONCLUSIONS
These morphologic findings indicate that there are proprioreceptors in the ciliary muscle that morphologically and presumably functionally differ at different locations. At the posterior muscle tips, the receptors could measure stretch of the tendons, whereas the large receptor organs located at the anterior muscle tips morphologically resemble mechanoreceptors measuring shear stress. The presence of the numerous intrinsic nerve cells indicates that contraction of the circular muscle portion can be modulated locally via a self-contained reflex arc.
Flügel-Koch
Cassandra
C
Institute of Anatomy II, University of Erlangen-Nürnberg, Universitätsstrasse 19, 91054 Erlangen, Germany. cassandra.fluegel-koch@anatomie2.med.uni-erlangen.de
Neuhuber
Winfried L
WL
Kaufman
Paul L
PL
Lütjen-Drecoll
Elke
E
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers / Q000378:metabolism; D064032:Calbindin 2; D002924:Ciliary Body / Q000502:physiology* / Q000648:ultrastructure; D019084:Fluorescent Antibody Technique, Indirect; D006801:Humans; D018613:Microscopy, Confocal; D008875:Middle Aged; D009130:Muscle, Smooth / Q000294:innervation* / Q000378:metabolism / Q000648:ultrastructure; D009252:NADPH Dehydrogenase / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009802:Oculomotor Nerve / Q000033:anatomy & histology* / Q000378:metabolism / Q000648:ultrastructure; D010275:Parasympathetic Nervous System / Q000033:anatomy & histology / Q000378:metabolism; D011434:Proprioception / Q000502:physiology*; D064030:S100 Calcium Binding Protein G / Q000378:metabolism; D011984:Sensory Receptor Cells / Q000502:physiology*
D015415:Biomarkers; C576764:CALB2 protein, human; D064032:Calbindin 2; D009419:Nerve Tissue Proteins; D064030:S100 Calcium Binding Protein G; D009252:NADPH Dehydrogenase