Early inner retinal dysfunction in streptozotocin-induced diabetic rats

PURPOSE. Diabetes is known to alter retinal function, as measured with the electroretinogram (ERG), which shows a propensity toward inner retinal oscillatory potential (OPs) abnormalities. However, the effect that diabetes has on other ganglion cell-related responses is not known. This study was a systematic evaluation of streptozotocin (STZ) diabetes-related ERG changes in rats for the first 11 weeks after diabetogenesis. METHODS. Thirty Sprague-Dawley rats were randomly assigned to treated (50 mg/kg STZ (n = 16) and control groups (1 mL/kg citrate buffer, n = 14) at 6 weeks of age. Two control animals and four STZ animals were excluded because of blood glucose criteria or systemic complications. Diabetic animals were given daily SC injections of 1 to 2 units of long-acting insulin. ERGs were measured at 4, 8, and 11 weeks after treatment. The a-wave was used as an index of outer retinal function, whereas the b-wave, OPs, and the scotopic threshold response (STR) were used as indices of inner retinal function. RESULTS. Photoreceptoral (a-wave) and bipolar cell (b-wave) responses were not significantly reduced by STZ treatment. OPs were significantly reduced by 8 weeks (-25% +/- 7%, P < 0.05). The most severely affected component was the ganglion cell-dominated positive STR, which was significantly decreased from the first time point (-51% +/- 11% at 4 weeks, P < 0.05), but the negative component was unaffected over the 11-week period. CONCLUSIONS. The ganglion cell dominated pSTR showed large losses in STZ treated rats.