An Immunohistochemical Analysis of Hypoxia in Multi-layer Avascular Retina and Vascular Pecten Oculi of the Developing Chicken

Abstract

The retina lines the internal surface of the back of the eye. In order to function, the retina requires a supply of oxygen. Retinal hypoxia often precedes proliferative diabetic retinopathy in human. In vertebrate eyes, there is a blood supply between retina and choroid, which supports the outer retinal layers. In humans, additional blood vessels enter the retina from the vitreal side and ramify in the plexiform layers. However, in chicks, such plexiform blood vessels are absent. The spatial oxidative state distribution in multi-layer avascular chick retina was studied using the oxygen-sensing reagent EF5. As development of the chick retina proceeds, different oxidation states in different layers were found.

            The hypoxic staining was almost evenly distributed throughout the tissues for E(mbryonic day) 5 chick retina. For E7 chick retina, the hypoxic stain was concentrated in a subset of ganglion cells. The inner portion of the inner nuclear layer and ganglion cell layer were hypotic for E11 chick retina,. For E14 chick retina, hypoxia was observed at the ganglion cell layer, but additional reaction was seen in the inner portion of the inner nuclear layer and the outer plexiform layer.  There was also some reaction in the region of budding photoreceptors. The Ganglion cell layer, and the Inner Nuclear Layer were more hypoxic for E19 chick retina,.  In most cases, the regions of hypoxia did not colocalize with the positions that have high mitochondrial density.

            Pecten oculi is a corrugated flap of tissue that extends along the back of the eye and is embedded in the vitreous body of the avian eye. It also contains a highly efficient glucose transporter. Hypoxia upregulates glucose transport activity. We found that pecten oculi is much less hypoxic than retina tissue nearby. There are more mitochondrial densities in pecten oculi than in retina.