The blood-retinal barrier

Published on April 27, 2016   18 min
0:00
On this series of lectures on biology of the eye, I will review the blood-retinal barrier, which will go along with this structure, function, and also its relevance to retinal diseases.
0:17
Eye disclosures are next.
0:21
And then, after, we will go on to the initial experiment that has been done with trypan blue in the brain. And this was repeated by us later on in the retina and choroid. And you can see that trypan blue penetrates in to the lungs and colors the lungs and other tissues of the body like the heart, but does not stain the brain or stains with the retina that you can see on the fourth, down in the picture.
0:55
The next slide shows you that the relationship between what I will describe afterwards, as the inner blood-retinal barrier and outer blood-retinal barrier join the endothelial, the relationship between retina and the blood capillary in the capillaries of the retinal vessel and the retinal vessels and in the relationship with retinal pigment epithelium. And you will see that it communicates between these layers and this extracellular fluid within the retina.
1:28
We, at that time in initial studies, in first studies were done in '66, '67, we showed there was an efflux outflow of, by active transport from organic anions like fluorescein, out of the vitreous in to the retina, involving the retinal pigment epithelial and the retinal vessels.
1:52
We have therefore a structure that also is crucial, is the demonstration of the tight-junctions in the retinal vessels. We are able to show for the first time in the retina that even before it was shown in the brain and blood-brain barrier, that there were zonulae occludentes structures uniting the endothelial cells of retinal vessels. And this will restrict the passage of the fluid, of the molecules, proteins, between the cells.
2:25
The value of the endothelial membrane or blood-retinal barrier is shown very well by an experiment done on a nine year old rabbit. For instance, what you could see that the only endothelial layers are present in the retina vessel without any basement membrane associated yet at this stage of age. And still, there was a barrier for trypan blue. Therefore the, in the retinal vessels, the main barrier was clearly identified, being the endothelial membrane and the tight-junctions.
3:01
Therefore we have a new inner blood-retinal barrier located at retinal vessel. We have formed by endothelial cells joined by tight-junctions, forming an epithelia-like structure, which is conditioned by other surrounding cells.
3:17
The ways, the pathways for solute movement across the inner blood-retinal barrier can be here, seen here. On the left, you have the tight-junctions and the vesicular transport dominating the normal situation. And then you have on the right side, ways of showing how it is a breakdown of the blood-retinal barrier with opening of the channels, increased number of vesicles and junctional opening allowing passage of substances across the inner blood-retinal barrier.
3:51
The outer blood-retinal barrier is located mainly at retinal pigment epithelium. And retinal pigment epithelial cells are also joined by tight-junctions. And which are of course the septic pigment epithelial cells condition by the surrounding cells and the needs, metabolic needs of the cells.
4:12
There are at both levels, inner and outer blood-retinal barrier a variety of transport mechanisms. Here it shown in the endothelial cells, we have pinocytosis, the passage of vesicles, the junctions, all these different processes of passage of substances, restricted passage in the blood-retinal barrier.
4:35
The concept of cell polarity at the blood-retinal barrier is a very important concept. Because of the tight-junctions and the epithelial-like structure, you'll see the cells have only an apical side and the basal side, which means that there is transport. We need an external transports that will control the passage of molecules. Paracellular diffusion between the cells is highly restricted. And you have more predominance of transport systems.
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The blood-retinal barrier

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