Developmental changes in the blood-ocular barriers in chicken embryos
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The developing chicken eye becomes impermeable to proteins by E19. Leakage from uveal tract vessels initially allows proteins into ocular chambers, but developing meninges and lamina cribosa structures later restrict this influx.
Area of Science:
- Ophthalmology
- Developmental Biology
- Vascular Biology
Background:
- The developing eye's vascular system undergoes significant changes.
- Understanding ocular vascular permeability is crucial for development and disease.
- Previous studies have not fully characterized the ontogeny of ocular barrier formation.
Purpose of the Study:
- To investigate the developmental changes in ocular vascular permeability in chicken embryos.
- To identify the specific ocular structures and time points associated with barrier formation.
Main Methods:
- Intravascular injection of horseradish peroxidase (HRP) in chicken embryos (E9-P1).
- Light and electron microscopy to detect HRP-RP accumulation.
- Examination of HRP distribution in anterior and posterior segments, optic nerve, and associated structures.
Main Results:
- Focal HRP accumulation occurred in the anterior chamber angle up to E15, diffusing into chambers by 5 min.
- No leakage was observed in embryos E19 and older.
- Optic nerve permeability was initially high but reduced by meningeal development after E12.
- Choroidal vessels remained leaky, while iris, optic nerve, and pecten vessels were impermeable.
Conclusions:
- Vascular proteins access intraocular chambers before E19 via uveal tract vessels near the anterior chamber angle.
- Optic nerve permeability is regulated by meningeal development and lamina cribosa.
- Developing ocular blood vessels exhibit permeability characteristics similar to mature vessels.
Abstract:
Changes in the permeability characteristics of the developing chicken eye were studied using light and electron microscopy. Chicken embryos from 6-19 days of gestation (E9-E19) and within 1 day of hatching (P1) were injected intravascularly with horseradish peroxidase (HRP) and examined 1 and 5 min after injection. Within 1 min of injection there was focal accumulation of horseradish peroxidase reaction product (HRP-RP) at the angle of the anterior chamber in embryos up to E15. By 5 min post-injection the HRP diffused into the anterior and posterior chambers and vitreous body; and extended posteriorly into the developing uveal tract. No leakage was detected in the E19 or older animals. In the posterior segment of the eye prior to E12, HRP from the adjacent connective tissues diffused into zone III of the optic nerve. After E12 the developing meninges prevented the influx of the HRP. At the level of the lamina cribosa HRP permeated zone II up to E19 after which only 25% of the animals examined showed HRP-RP in this area. In zone I in all ages examined no HRP-RP was detected 5 min after injection. Developing blood vessels in the deep iris stroma, optic nerve and pecten remained impermeable even as they grew, while the choroidal vessels were consistently leaky. This study suggests: (1) that proteins from the vascular system reach the intraocular chambers before E19; (2) that the leakage occurs from vessels located in the uveal tract adjacent to the angle; (3) that the permeability of the optic nerve depends on the development of the meninges and the border tissues associated with the lamina cribosa; and (4) that the growing blood vessels in the developing eye have permeability characteristics similar to those found in mature vessels.