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J. S. Pritchett, K. Thongkhao-on, S. A. Shippy; In vivo Sampling From the Rat Vitreoretinal Interface of Diabetic and Aged Models Using Low-Flow Push-Pull Perfusion. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4987.
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Chemical changes or dysfunction of signaling molecule systems at the retina have been implicated in retinal diseases that lead to blindness. In diabetic retinopathy there are a number of known and suspected chemical changes including nitric oxide, glutamate, peptides and proteases. Similarly, a cascade of chemical events in the retina occurs during the aging process which may also lead to visual deterioration. This study utilizes a sampling tool capable of monitoring changes in the chemical composition at the vitreoretinal interface (VRI) of diabetic and aged rat models.
Diabetes is induced in rats via a single i.p. injection of streptozotocin and normal animals are allowed to age beyond five months. Samples are collected from the VRI or vitreous at various time points using low-flow push-pull perfusion (LFPPP). Sampling probes are constructed from 90-micron outer- and 20-micron inner diameter fused silica capillary inserted into 170-micron outer and 100-micron inner diameter capillary. The probes are positioned in the in the vitreous cavity using a 29-gauge guide needle. Probe placement is confirmed by indirect ophthalmoscopy. Nanoliter sample collection occurs at a flow rate of 50 nL/min as physiological saline is infused and withdrawn through the probe concurrently. Nitric oxide (NO) metabolites (nitrate and nitrite), glutamate and other amino acids are monitored by capillary electrophoresis (CE) with absorbance or laser-induced fluorescence detection, respectively.
Animal models are suitable for in vivo sample collection from the vitreous cavity. Diabetes induction significantly elevates glutamate and NO metabolite levels at the VRI at 6 and 8 weeks respectively. Additionally, when compared to normal animals, aged animals display ~ 3 fold increase in nitrate production.
The data implicates both glutamate and NO involvement in diabetic retinopathy. NO, as the primary source of nitrate and nitrite, appears also to be involved with chemical changes occurring during the aging process. With LFPPP it is possible to characterize multiple types of chemical changes. By following the chemical changes relevant to differing disease hypotheses it will likely provide unique targets for potential treatments.
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