Abstract
Purpose :
The choroid vasculature, constituted by a network of arteries and capillaries, is essential to answer the metabolic needs of the outer retina. To avoid hypo or hyper-perfusion, which can lead either to ischemia or oedema, the choroidal blood flow is finely regulated by a very dense nervous system. This choroidal nervous system is known to be constituted by extrinsic components (autonomous and sensory) and by an intrinsic component (intrinsic choroidal neurons). While the choroidal vasculature has been thoroughly studied, the anatomy and the role of the choroidal nervous system and its implication in the etiology of pathologies is still poorly understood.
Methods :
To better characterize the choroidal nervous system, choroids of mouse and rat, as well as human choroids, have been fixed and studied by histological approaches on transverse sections and/or flat-mounted tissue. Anatomical and neurochemical properties have been revealed by immunohistochemistry (IHC) using different markers of the autonomous and sensory nervous system such as TUBB3, myelin basic protein (MBP), neuropeptide Y (NPY) and calcitonin gene related peptide (CGRP). Furthermore, Electron microscopy (EM) has been used to analyze the ultrastructure of the nerve fibers and the myelination.
Results :
The NPY-positive sympathetic fibers seem to be located close to the blood vessels, the labelling is almost exclusively concentrated around the vessels, probably at the synaptic level. There are very few CGRP-positive sensory fibers, the labelling is visible all along the fibers and these fibers are not preferably organized around the vessels, covering different zone of the choroid. EM analysis and IHC labelling on transverse sections showed both myelinated and unmyelinated nerves. Finally, IHC showed that a consequent quantity of fibers is located in the choriocapillaris, very close to the Bruch’s membrane.
Conclusions :
The choroidal nervous system is a very dense and heterologous network. The sympathetic innervation seems to target preferably blood vessels, consistently with its role in the blood flow regulation. On the other hand, sensory nervous system displays a very different organization suggesting a different role in the choroid physiology. Moreover, the nervous fibers proximity with the Bruch’s membrane/retinal pigment epithelium complex could suggest a role of the choroidal nervous system in the regulation of the molecule efflux between the choroid and the retina.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.