[An electrophysiological method for detecting diabetic retinopathy in rats]

The present study was undertaken to devise an electrophysiological method for detecting diabetic retinopathy in rats. The electroretinogram (ERG) and visual evoked potential (VEP) were recorded from unanesthetized and unrestrained rats rendered diabetic with a single i.v. injection of streptozotocin (STZ) at 35 or 40 mg/kg. The STZ-treated rats showed signs of diabetes: hyperglycemia, glucosuria, hypoinsulinemia, polyuria and increased water intake. Amplitudes of the ERG a- and b-waves and oscillatory potentials (OPs) on the b-wave were decreased and latencies of these waves were prolonged gradually after STZ was administered. Especially, latencies of the OPs became significantly different from the pre-treatment values. Latency of the VEP N1 wave showed a slight prolongation, which might be secondary to the depression of retinal function. Histological examination showed swelling and proliferation of the lens epithelium and swelling and vacuolization of the lens fiber were observed in the eyeball 9 weeks after STZ-treatment. Moreover, thinning of each retinal layer was observed in a few rats. Daily s.c. injection of insulin at 10 units/rat/day started from the 4th week. The ERG values returned to the control values after 2-3 weeks of insulin therapy. These results indicate that the ERG and VEP recording procedure used in the present study is useful for early detection of the diabetic retinopathy in rats and that the OP of the ERG appears to be vulnerable to diabetes in the rat as it is in the human.