Retinal Damage Induced by N-Methyl-N-Nitrosourea in Rats

Abstract

N-Methyl-N-Nitrosourea (MNU), a potent carcinogen, has been known to have retinotoxic action in rats. MNU was intraperitonealy administered once to rats at doses of 0, 40 and 60 mg/Kg. The rats were examined before and at 1, 2, 3, 7, 28, and 35 days after administration of MNU. Generally changes in electroretinography preceded those in morphology. Initial histochemical changes were detected in the retinal photoreceptor cells. The nuclei of photoreceptor cells showed disorder 3 days after treatment with 40 mg/Kg and piknosis 1 day after 60 mg/Kg. In the 40 mg/Kg group, photoreceptor cells showed a normal arrangement at 35 days, though the photoreceptor layer and outer nuclear layer were extensively disrupted 7 days after treatment with 60 mg/Kg. ERG revealed lowered amplitude in the a-wave and b-wave 1 day after the 40 and 60 mg/Kg treatment. In fundoscopy, narrowed retinal veins, increased fundal reflection and clear optic disks were observed 21 days after treatment with 40 mg/Kg and 7 days after 60 mg/Kg. In the 40 mg/Kg group, the damaged part of the retina disappeared and normal structure was restored by 35 days. The retinal lesion around the optic nerve head was severer than in the other retinal regions.