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ilaria piano, Antonella Caputo, Elena Novelli, Luigi Cervetto, Claudia Gargini; Differential impairment of rod and cone pathways in streptozotocin-induced diabetic mice. Invest. Ophthalmol. Vis. Sci. 2013;54(15):4614.
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Chronic exposure to hyperglycemia triggers a chain of biochemical and functional events eventually leading to vascular damage in various organs and to a series of central and periphery neuropathies that also include diabetic retinopathy (DR). Recent evidence indicates that vascular changes are preceded by signs of damage whose immediate outcome is the functional impairment and loss of neural, non-vascular retinal cells. The objective of this study is to investigate the early changes that occur in the biochemistry, morphology and function of retinal neurones in mice with streptozotocin (STZ) induced diabetes.
Mice were defined diabetic when blood glucose reached values above 300 mg/dl, a condition that usually occurred 48 hours after injection of STZ. The experimental tests, included biochemical assays, immunohistochemistry, confocal microscopy and electroretinography (ERG) and were repeated at regular intervals for a period of 12 weeks. Results obtained from the group of STZ treated mice were compared with those of a pair aged control group with normal blood glucose.
Biochemical, morphological and functional changes occurs at an early phase of the disease, well before any vascular damage becomes detectable. These changes include reduction in the rod number paralleled by rhodopsin decrease with normal levels of cone-opsin, thinning of the retinal thickness and suppression of the scotopic ERG response with a nearly normal photopic ERG. In these conditions the apoptotic figures are rare and glia is not activated. By contrast the tests for autophagy are positive.
The present results show that diabetic mice undergo substantial damage in rods and inner retinal cells well before glial activation and vascular changes become evident. The early expression of autofagy possibly reveals a condition from which retinal cells may be rescued. The functional changes that can be monitored by the analysis of the ERG may be useful for an early diagnosis of the disease.
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