An electrophysiological method for detecting diabetic retinopathy in rats

Abstract

No abnormality in the retinal vessels of diabetic rats can be detected, even by an electron microscopic examination(von Sallmann,L.& Grimes,P., Amer.J.Ophthalmol.71,312,1971), within 2 months after streptozotocin(STZ) injection. However, depressed oscillatory potential s(OP) of the electro-retinogram(ERG) can be recorded at an early stage of diabetes in man (Yonemura.D.et al., Arch.Ophthal.Chicago 68,19,1962). The present study was undertaken to devise an electrophysiological method for detecting diabetic retinopathy in STZ-treated rats. STZ(35 or 40 mg/kg) was injected i.v. into male Wistar rats(15-20 weeks of age). The ERG and visual evoked potential(VEP) were recorded from unanesthetized and unrestrained rats using a method previously reported(Sato,et al., Japan.J.Pharmacol.32,489, 1982). All the rats receiving STZ showed signs of diabetes such as marked elevation of serum and urine glucose levels and increase of water intake and urine volume. Three weeks after injection of STZ, the peak latency of Op in the OP was prolonged significantly compared with the pre-drug value. At week 6, 01 and 03 latencies of the OP were also prolonged. Thereafter, wavelet index and amplitudes of a- and b-waves in the ERG and the VEP N, latency were depressed. At 4 weeks after a single i.v. of STZ, it was of interest to study the effect of insulin on the depressed ERG. For this purpose, insulin was injected s.c.(10 units/rat/day) for 4 weeks. The above-mentioned changes were recovered during the insulin-treatment period. These findings indicate that diabetic retinopathy in rats can be detected at an early stage by the ERG recordings, and the OP of the ERG in diabetic rats appears to be vulnerable as it is in man.