Neurokinin a is a main constituent of sensory neurons innervating the anterior segment of the eye.
OBJECTIVE
To study the innervation pattern of the anterior segment of the eye by neurokinin (NK)-A-immunoreactive nerves and to determine their sensory origin.


METHODS
The presence and distribution of NKA was examined in human eyes by radioimmunoassay and immunofluorescence. The source of nerves was determined by measuring the concentration of NKA in the trigeminal ganglion (TG) in comparison with that of the classic sensory peptides substance P (SP) and calcitonin gene-related peptide (CGRP) and in eye tissues in capsaicin-pretreated rats versus control subjects. The NKA-like immunoreactivities were further characterized by reversed phase HPLC in the rat TG and the human iris-ciliary body complex. The presence of gamma-PPT-A mRNA was studied in the rat TG by in situ hybridization.


RESULTS
The levels of NKA in human eye tissues were approximately 10 times higher than those of SP but lower than those of CGRP. Nerve fibers were visualized in the cornea, the trabecular meshwork, the iridial stroma, and, prominently, in the sphincter muscle, the ciliary body stroma and muscle and processes, and the choroidal stroma and surrounding blood vessels. In the rat TG, the concentration of NKA was approximately five times higher than that of SP. Capsaicin led to a >60% decrease of the concentration of the peptide in the rat TG and rat eye tissues except for the retina. NKA-like immunoreactivities were present in a single peak corresponding to synthetic NKA, both in the rat TG and in the human iris-ciliary body complex, and numerous ganglion cells of small size were labeled by a gamma-PPT-A probe in the rat TG.


CONCLUSIONS
The present results clearly demonstrate that NKA is a main constituent of sensory neurons innervating the anterior segment of the eye. The presence of the peptide in C fibers in ocular tissues indicates a participation in sensory transmission and an involvement in the irritative response in the eye, a model for neurogenic inflammation in lower mammals.
Schmid
Eduard
E
Department of Ophthalmology, University Clinic of Psychiatry, Innsbruck Medical University, Austria.
Leierer
Johannes
J
Doblinger
Alfred
A
Laslop
Andrea
A
Fischer-Colbrie
Reiner
R
Humpel
Christian
C
Theodorsson
Elvar
E
Teuchner
Barbara
B
Lalehabbasi
Djavad
D
Dragosits
Ernst
E
Kunze
Christian
C
Philipp
Wolfgang
W
Göttinger
Wolfgang
W
Troger
Josef
J
D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D000831:Animals, Newborn; D000869:Anterior Eye Segment / Q000187:drug effects / Q000294:innervation*; D015740:Calcitonin Gene-Related Peptide / Q000378:metabolism; D002211:Capsaicin / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid; D005260:Female; D019084:Fluorescent Antibody Technique, Indirect; D006801:Humans; D017403:In Situ Hybridization; D008297:Male; D008875:Middle Aged; D015288:Neurokinin A / Q000378:metabolism*; D011498:Protein Precursors / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D011863:Radioimmunoassay; D051381:Rats; D017207:Rats, Sprague-Dawley; D013373:Substance P / Q000378:metabolism; D015320:Tachykinins / Q000235:genetics; D012668:Trigeminal Ganglion / Q000378:metabolism*
D011498:Protein Precursors; D012333:RNA, Messenger; D015320:Tachykinins; C044206:preprotachykinin; D013373:Substance P; D015288:Neurokinin A; D015740:Calcitonin Gene-Related Peptide; D002211:Capsaicin