The structure and function of the human choroid.

In this manuscript, the structure of the human choroid is reviewed with emphasis of the macro- and microscopic anatomy including Bruch's membrane, choriocapillaris, Sattler's and Haller's layer, and the suprachoroid. We here discuss the development of the choroid, as well as the question of choroidal lymphatics, and further the neuronal control of this tissue, as well as the pathologic angiogenesis. Wherever possible, functional aspects of the various structures are included and reviewed.

Human intrinsic choroidal neurons do not alter the expression of intrinsic markers in response to pressure.

BACKGROUND: The choroid is densely innervated by all parts of the autonomic nervous system and further harbours a network of local nerve cells, the intrinsic choroidal neurons (ICN). Their function in ocular control is currently unknown. While morphological data assume a role in intraocular pressure regulation, we here test if increased pressure on isolated choroids may activate ICN. METHODS: Donor tissue was transferred into a pressurisable tissue culture chamber, and nasal and temporal choroid halves incubated for 1 or 4 hours, with pressures set to 15 or 50 mm Hg, followed by qRT-PCR expression analysis of the ICN-specific markers VIP, UCN, NOS1, UCH-L1. POL2-normalised data in the different pressure settings, incubation times and localisations were statistically analysed. RESULTS: The presence of the ICN-specific markers VIP, UCN, NOS1, UCH-L1 was confirmed using immunohistochemistry, and mRNA of all markers was detected in all experimental conditions. Marker analysis revealed no significant changes of mRNA expression levels between 15 and 50 mm Hg in the different incubation times. When comparing all samples over all experimental conditions, a significant increase of VIP and NOS1 mRNA was detected in temporal versus nasal choroids. CONCLUSION: In this functional analysis of human ICN in vitro, higher amounts of VIP and NOS1 mRNA were detected in the temporal choroid, that is, the choroidal site with ICN accumulation. Further, our data indicate that elevated pressure is apparently not able to trigger ICN responses via the investigated markers. Alternative markers and stimuli need to be investigated in upcoming studies in order to unravel ICN function.

Urocortin-positive nerve fibres and cells are present in the human choroid.

BACKGROUND: Choroidal vascular regulation is mediated by the autonomic nervous system in order to gain proper blood flow control. While the mechanisms behind this control are unknown, neuroregulatory peptides are involved in this process. To better understand choroidal function, we investigate the presence of urocortin-1 (UCN), a neuroregulatory peptide with vascular effects, in the human choroid and its possible intrinsic and extrinsic origin. METHODS: Human choroid and eye-related cranial ganglia (superior cervical ganglion- SCG, ciliary ganglion-CIL, pterygopalatine ganglion-PPG, trigeminal ganglion-TRI) were prepared for immunohistochemistry against UCN, protein-gene product 9.5 (PGP9.5), substance P (SP), tyrosine hydroxylase (TH) and vesicular acetylcholine transporter (VAChT). For documentation, confocal laser scanning microscopy was used. RESULTS: In choroidal stroma, UCN-immunoreactivity was present in nerve fibres, small cells and intrinsic choroidal neurons (ICN). Some UCN+ nerve fibres colocalised for VAChT, while others were VAChT. A similar situation was found with SP: some UCN+ nerve fibres showed colocalisation for SP, while others lacked SP. Colocalisation for UCN and TH was not observed. In eye-related cranial ganglia, only few cells in the SCG, PPG and TRI were UCN+, while many cells of the CIL displayed weak UCN immunoreactivity. CONCLUSION: UCN is part of the choroidal innervation. UCN+/VAChT+ fibres could derive from the few cells of the PPG or cells of the CIL, if these indeed supply the choroid. UCN+/SP+ fibres might originate from ICN, or the few UCN+ cells detected in the TRI. Further studies are necessary to establish UCN function in the choroid and its implication for choroidal autonomic control.

Choroidal melanocytes: subpopulations of different origin?

BACKGROUND: The human choroid derives from the mesectoderm, except the melanocytes originating from the neuroectoderm. To date, it is unclear whether all choroidal melanocytes share the same origin or might have different origins. The purpose of this study was to screen immunohistochemically for mesenchymal elements in the adult healthy human choroid, in the malignant melanoma of the choroid, as well as in the developing human fetal choroid. METHODS: Human choroids were obtained from cornea donors and prepared as flat whole mounts for paraffin- and cryoembedding. Globes enucleated for choroidal melanoma and eyes from human fetuses between 11 and 20 weeks of gestation were also embedded in paraffin. Sections were processed for immunohistochemistry of the mesenchymal marker vimentin, the melanocyte marker Melan-A, and the macrophage marker CD68, followed by light-, fluorescence-, and confocal laser scanning-microscopy. RESULTS: The normal choroid contained 499 ± 139 vimentin, 384 ± 78 Melan-A, and 129 ± 57 CD68 immunoreactive cells/mm2. The vimentin immunopositive cell density was significantly higher than the density of Melan-A and CD68 immunopositive cells (p < 0.001, respectively). By confocal microscopy, 24 ± 8% of all choroidal melanocytes displayed vimentin immunoreactivity. In choroidal melanomas, numerous melanoma cells of the epithelioid and spindle cell type revealed immunopositivity for both vimentin and Melan-A. The intratumoral density of vimentin immunoreactive cells was 1758 ± 106 cells/mm2, significantly higher than the density of Melan-A and CD68 immunopositive cells (p < 0.001, respectively). Comparing to healthy choroidal tissue, the choroidal melanomas revealed significantly higher densities of vimentin, Melan-A, and CD68 immunoreactive cells (p < 0.001, respectively). In the developing human fetal choroid, numerous vimentin and Melan-A immunopositive cells were detected not before the 16th week of gestation, with some of them showing colocalization of vimentin and Melan-A. CONCLUSIONS: The adult healthy human choroid is endowed with a significant number of vimentin immunopositive mesenchymal structures, including a subpopulation of vimentin immunoreactive choroidal melanocytes. These vimentin immunopositive melanocytic cells are also present in choroidal melanomas as well as in the developing human fetal choroid. Therefore, different embryologic origins can be considered for choroidal melanocytes.

Absence of lymphatic vessels in non-functioning bleb capsules of glaucoma drainage devices.

PURPOSE: To evaluate the presence and appearance of blood and lymphatic vessels in non-functioning bleb capsules of glaucoma drainage devices (GDD). MATERIALS AND METHODS: Non-functioning (n=14) GDD-bleb capsules of 12 patients were analyzed by immunohistochemistry for blood vessels (CD31, vascular endothelium), lymphatic vessels (lymphatic vessel endothelial hyaluronan receptor-1 [LYVE-1] and podoplanin) and macrophages (CD68). RESULTS: CD31+++ blood vessels and CD68+ macrophages were detected in the outer layer of all specimens. LYVE-1 immunoreactivity was registered in single non-endothelial cells in 8 out of 14 (57%) bleb capsule specimens. Podoplanin-immunoreactivity was detected in all cases, located in cells and profiles of the collagen tissue network of the outer and/or the inner capsule layer. However, a colocalization of LYVE-1 and podoplanin as evidence for lymphatic vessels was not detected. CONCLUSIONS: We demonstrate the presence of blood-vessels but absence of lymphatic vessels in non-functioning bleb capsules after GDD-implantation. While the absence of lymphatic vessels might indicate a possible reason for drainage device failure, this needs to be confirmed in upcoming studies, including animal experiments.

Thermal experience during embryogenesis contributes to the induction of dwarfism in whitefish Coregonus lavaretus.

Ecotype pairs provide well-suited model systems for study of intraspecific phenotypical diversification of animals. However, little is still known about the processes that account for the development of different forms and sizes within a species, particularly in teleosts. Here, embryos of a normal-growing 'large' form and a dwarf form of whitefish Coregonus lavaretus were incubated at two temperatures that are usually experienced at their own spawning sites (2°C for the normal and 6°C for the dwarf form). All fish were subjected to similar thermal treatment after hatching. The present data demonstrate for the first time that different thermal experience in embryonic life has lasting effects on body and muscle growth of this ecotype pair and contributes to the development of the dwarf form. Thus, juvenile fish of the regular form are much smaller and have less muscle mass when pre-hatching thermal conditions were similar to those typical for the spawning sites of the dwarf form (6°C) than when subjected to conditions of their own spawning sites (2°C). Surprisingly, fish of the dwarf form exhibit a similar pattern of response to thermal history (2°-fish much larger than 6°-fish), indicating that in their case, normal spawning site temperature (6°C) is indeed likely to act as a growth limiting factor. Results also demonstrate that the hypertrophic and hyperplastic muscle growth modes are similarly affected by thermal history. Immunolabelling experiments for Pax7, H3P and Mef2 provide evidence that the cellular mechanisms behind the increased growth rates after cold incubation in both ecotypes are increased proliferation and reduced differentiation rates of muscle precursor cells. This is of major significance to aspects of ecological and developmental biology and from the evolutionary perspective.