Retinal dysfunction parallels morphologic alterations and precede clinically detectable vascular alterations in Meriones shawi, a model of type 2 diabetes.

Diabetic retinopathy is a major cause of reduced visual acuity and acquired blindness. The aim of this work was to analyze functional and vascular changes in diabetic Meriones shawi (M.sh) an animal model of metabolic syndrome and type 2 diabetes. The animals were divided into four groups. Two groups were fed a high fat diet (HFD) for 3 and 7 months, two other groups served as age-matched controls. Retinal function was assessed using full field electroretinogram (Ff-ERG). Retinal thickness and vasculature were examined by optical coherence tomography, eye fundus and fluorescein angiography. Immunohistochemistry was used to examine key proteins of glutamate metabolism and synaptic transmission. Diabetic animals exhibited significantly delayed scotopic and photopic ERG responses and decreases in scotopic and photopic a- and b-wave amplitudes at both time points. Furthermore, a decrease of the amplitude of the flicker response and variable changes in the scotopic and photopic oscillatory potentials was reported. A significant decrease in retinal thickness was observed. No evident change in the visual streak area and no sign of vascular abnormality was present; however, some exudates in the periphery were visible in 7 months diabetic animals. Imunohistochemistry detected a decrease in the expression of glutamate synthetase, vesicular glutamate transporter 1 and synaptophysin proteins. Results indicate that a significant retinal dysfunction was present in the HFD induced diabetes involving both rod and cone pathways and this dysfunction correlate well with the morphological abnormalities reported previously. Furthermore, neurodegeneration and abnormalities in retinal function occur before vascular alterations would be detectable in diabetic M.sh.

Characterizing the Retinal Function of Psammomys obesus: A Diurnal Rodent Model to Study Human Retinal Function.

PURPOSE: To compare the retinal function of a diurnal murid rodent, Psammomys obesus, with that of Wistar albino rat and human subjects. MATERIALS AND METHODS: Adult Psammomys obesus were captured and transferred to the animal facilities where they were maintained at 25°C with standard light/dark cycles and natural halophilic plants, rich in water and mineral salts. Standard full-field photopic and scotopic electroretinograms were obtained. RESULTS: The right eye of all animals displayed well detectable and reproducible scotopic and photopic electroretinogram (ERG) responses. Results were compared with those obtained from human subjects and Wistar rats. ERG measurement showed that the amplitudes of scotopic responses in Psammomys obesus are quite similar to those of human subjects. The amplitude of the photopic a-wave was comparable to that of humans and six times higher than that of the albino rat. The amplitudes of photopic b-wave, photopic oscillatory potentials (OPs), and 30 Hz flicker were all markedly larger in Psammomys obesus compared to those obtained from human subjects and Wistar rats. Furthermore, like the human photopic ERG, the photopic ERG of Psammomys obesus also includes prominent post b-wave components (i.e. i- and d-waves) while the ERG of Wistar rats does not. CONCLUSIONS: Our results suggest that the retinal function of Psammomys obesus, especially the cone-mediated function, shares several features with that of human subjects. We believe that Psammomys obesus represents an interesting alternative to study the structure and function of the normal and diseased retina in a human-like rodent model of retinal function.