Responses were amplified 5000X, high-pass filtered with a 10-Hz cutoff frequency, and low-pass filtered at 300 Hz using an amplifier. The ERG voltage and stimulusmonitor signals were digitalized with hardware and software from Ocuscience. Data were recorded at either 0.2 or 0.5 ms/pt. A stimulus set consisted of 3 to 20 responses at the same Hydrocortisone wavelength and intensity of light. The oscillatory Suplatast Tosylate potentials were isolated by a band-pass filtering the retinal response between 34 and 300 Hz. We chose 34 Hz as a cutoff frequency to avoid any loss of signal power, especially for the slower OPs of diabetic animals. OPs were isolated for a light stimulus of 3000 mcd.s/m22. The amplitude and implicit time of the ERG a-and b-waves were measured at the maximum negative and positive peaks of the recordings with respect to the baseline before stimulation. A significant increase in TUNEL-positive inmuno fluorescence was observed in diabetic mice in comparison with retinas from non diabetic mice at 8, 16 weeks and 24 weeks. Since the TUNEL-positive cells were mainly localized in the GCL, we also counted the percentage of apoptotic cells in this layer, and a significant increase was found in diabetic mice in comparison with non-diabetic mice at 8, 16 and 24 weeks. In addition, activated caspase-3 was found significantly higher in the retina of db/db mice in comparison with non-diabetic mice at 8, 16 and 24 weeks. Since in the ERG measurements we found a-wave abnormalities, which mainly indicate photoreceptor impairment, we wanted to examine whether apoptosis was also present in photoreceptors. For this purpose transmision electron microsocopy was used and striking DNA fragmentation was found in photoreceptors from db/db mice in comparison with non-diabetic mice. As expected, in non-diabetic mice GFAP expression was confined to the retinal GCL. In contrast, in diabetic mice we observed the ����reactive���� diabetic phenotype characterized by upregulation of GFAP in Muller cells.To unravel the molecular mechanisms involved in early retinal neurodegeneration besides glutamate and its metabolic pathways, we performed a genome-wide expression profiling analysis on total RNA isolated from retinas of 8-week old diabetic and control littermate mice.