Arteriovenous anastomoses of the episcleral vasculature in the rabbit and rat eye.
OBJECTIVE
To obtain more information about the functional significance of arteriovenous anastomoses as regulatory elements, the authors investigated the topography and innervation of episcleral anastomoses in the rat and rabbit.


METHODS
The topography of arteriovenous anastomoses in the limbal and episcleral vasculature of the rat and rabbit eye was studied by scanning electron microscopy of vascular resin casts. The perivascular distribution of the following neuropeptides was investigated by fluorescence immunohistochemistry: neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP), substance P (SP), and calcitonin gene-related peptide (CGRP).


RESULTS
The episcleral arteriovenous anastomoses connect arterioles directly with the episcleral venous plexus which also drains the aqueous humor. The nerve fiber plexus around the episcleral arteriovenous anastomoses is far more dense than around arteriovenous connections at the limbal arcades. NPY-, VIP-, SP-, and CGRP-immunoreactive fibers concentrate at the arteriolar segment of the episcleral arteriovenous anastomoses and are reduced at the venular segment. Still, numerous VIP-IR fibers are on the venous side of the rabbit episcleral anastomoses.


CONCLUSIONS
We conclude that the elaborated innervation of the episcleral anastomoses is a prerequisite for a subtle modulation of the blood flow and possibly of the aqueous humor outflow dynamics.
Selbach
J M
JM
Institut für Anatomie, TU Dresden, Germany.
Schönfelder
U
U
Funk
R H
RH
D000818:Animals; D001163:Arteriovenous Anastomosis / Q000294:innervation / Q000378:metabolism / Q000648:ultrastructure; D001808:Blood Vessels / Q000000981:diagnostic imaging / Q000294:innervation / Q000378:metabolism; D016319:Corrosion Casting; D005260:Female; D019084:Fluorescent Antibody Technique, Indirect; D016850:Limbus Corneae / Q000098:blood supply*; D008297:Male; D008855:Microscopy, Electron, Scanning; D009479:Neuropeptides / Q000378:metabolism; D011817:Rabbits; D051381:Rats; D017208:Rats, Wistar; D012590:Sclera / Q000098:blood supply*; D014463:Ultrasonography
D009479:Neuropeptides