The purpose of these studies was to correlate physiological changes in oxygen distribution and consumption to gene expression changes in the diabetic rat retina. First, techniques to measure PO2 in light- and dark-adapted normal rat retina were established. PO2 depth profiles were recorded from retinas of anesthetized Long-Evans rats using oxygen microelectrodes. The three-layer one-dimensional diffusion model previously used for cat retina was fitted to profiles to determine photoreceptor oxygen consumption per unit volume, Qav. Light adaptation reduced Qav to 60.2±4.1% of the dark-adapted value. Minimum PO2 in the outer retina occurred at photoreceptor inner segments in dark adaptation (17.4±3.0 mmHg), and light adaptation increased minimum PO2 (29.9±5.3 mmHg). As expected, light adaptation increased minimum PO2 and decreased Qav in rat retina, as compared to dark adaptation, by a similar magnitude as in cat retina. However, the dark-adapted minimum PO2 in the outer retina was higher in rat than in cat.
Techniques established in the first study were then applied to investigate PO2 and Qav in the rat retina at 4 and 12 weeks after induction of diabetes. After 4 weeks, diabetic rats had comparable choroidal PO2, Qav, and average inner retinal PO2 to control rats. The 12-week diabetic rats showed no significant change in choroidal PO2 or Qav compared to age-matched controls. However, at 12 weeks, average inner retinal PO2 was significantly lower in controls than in diabetic rats, which was opposite to what was expected. Intraretinal PO2 reflects a balance between oxygen supply and consumption, both of which may change in diabetes.
Finally, qRT-PCR was used to measure gene expression changes in 4- and 12-week diabetic rat retinas. After 12 weeks of diabetes, genes expressed by retinal ganglion cells, including ionotropic glutamate receptor subunits, had significantly reduced mRNA levels, suggesting these cells were lost. Ganglion cell loss may explain why PO2 in the inner retina was higher in diabetic rats. Diabetes did not affect VEGF mRNA expression in the retina at these time points, but diabetes did increase VEGF protein levels. In summary, these studies showed that diabetes affects neural retina, retinal microvasculature, and retinal oxygenation.
|Advisor:||Linsenmeier, Robert A.|
|Commitee:||Leonard, Joshua N., Miller, William M., Moskal, Joseph R.|
|Department:||Chemical and Biological Engineering|
|School Location:||United States -- Illinois|
|Source:||DAI-B 72/12, Dissertation Abstracts International|
|Subjects:||Ophthalmology, Biomedical engineering, Chemical engineering|
|Keywords:||Diabetic retinopathy, Ganglion cells, Glutamate receptors, Oxygen consumption, Photoreceptors, Retina|
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