Electrophysiologic and Histologic Analysis of Acute Retinal Changes From MNU–Induced Retinal Degeneration

Abstract

Abstract: : Purpose: To evaluate the early findings of electroretinogram (ERG) and morphological changes from the rat model of MNU–induced retinal degeneration. Methods: Eighteen 6–week–old male Sprague–Dawley rat were injected intraperitoneally with 60 mg/kg N–methyl–N–nitrosourea (MNU). Electroretinogram (ERGs) were recorded before injection and 6, 12, 24, 48 hours, and 1 week after MNU injection. The rats were sacrificed immediately after ERG recording and perfused with 4% paraformaldehyde. Eyes were enucleated and embeded for cryosectioning. Histologic sections were analyzed with Tdt–mediated dUTP–digoxigenin nick end labeling (TUNEL) method and Haematoxylin and Eosin (H&E) stain. Results: The decreases of the scotopic b–wave amplitude were detected 6 hours after MNU injection. Reduced precent of mean scotopic b–wave resulted in 8.60%(p<0.05), 28.98%, 51.80%, 75.91%, 96.24% in each times compared with baseline amplitude. The intensity gradient patterns of sccotopic amplitude were correlated with time dependent manner. Photoreceptor cell deaths were observed with TUNEL method 12 hours after injection, but the height change of outer nuclear layer were confirmed with H&E stain at 48 hours after injection. Conclusions: According to the ERG findings, functional changes of the retina may precede the apoptotic cell death confirmed with TUNEL method or routine histologic procedure.

Keywords: electrophysiology: non-clinical • cell death/apoptosis • photoreceptors