Immunohistochemical Characterization of Neurotransmitters in the Episcleral Circulation in Rats

Episcleral venous pressure (EVP) greatly influences steady-state IOP and recent evidence suggests a neuronal influence on EVP. Yet little is known about the innervation of the episcleral circulation and, more specifically, the neurotransmitters involved. We identify possible neurotransmitter candida...

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Bibliographic Details
Published in:Investigative ophthalmology & visual science 2019-07, Vol.60 (8), p.3215-3220
Main Authors: Ladek, Anja Maria, Trost, Andrea, Bruckner, Daniela, Schroedl, Falk, Kaser-Eichberger, Alexandra, Lenzhofer, Markus, Reitsamer, Herbert Anton, Strohmaier, Clemens A
Format: Article
Language:English
Subjects:
Animals
Immunohistochemistry - methods
Models, Animal
Neurons - metabolism
Neurotransmitter Agents - blood
Rats
Rats, Sprague-Dawley
Sclera - blood supply
Venous Pressure - physiology
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Summary:Episcleral venous pressure (EVP) greatly influences steady-state IOP and recent evidence suggests a neuronal influence on EVP. Yet little is known about the innervation of the episcleral circulation and, more specifically, the neurotransmitters involved. We identify possible neurotransmitter candidates in the episcleral circulation of rats. Eight immersion-fixated rat eyes taken from four animals were cut into serial sections, followed by standard immunohistochemistry. Antibodies against choline acetyltransferase, dopamine-β-hydroxylase, synaptophysine, PGP 9.5, VIP, neuronal nitric oxide synthase (nNOS), substance P, CGRP, and galanin were used. Additionally, colocalization experiments with smooth muscle actin and neurofilament (200 kDa) were performed. In all specimens, the episcleral vessels showed immunoreactivity for smooth muscle actin and were reached by neurofilament (200 kDa)-positive structures. Furthermore, these structures colocalized with immunoreactivity for PGP 9.5, synaptophysine, choline acetyl transferase (ChAT), dopamine-β-hydroxylase, VIP, CGRP, nNOS, substance P and galanin. These findings indicate that there is neuronal input to the episcleral circulation. ChAT and VIP as well as dopamine-β-hydroxylase suggest parasympathetic and sympathetic innervation. Further studies are needed on whether the positively-stained structures are of functional significance for the regulation of the episcleral venous pressure and thereby IOP.
ISSN:1552-5783
1552-5783
DOI:10.1167/iovs.19-27109