Noninvasive recording and response characteristics of the rat dc-electroretinogram

Abstract

In response to light, the retinal pigment epithelium (RPE) generates a series of potentials that can be recorded using the dc-electroretinogram (dc-ERG). As these potentials can be related to specific cellular events, they provide information about RPE function and how that may be altered by disease or experimental manipulation. The purposes of the present study were to define a noninvasive means for recording the rat dc-ERG, to use this to define the stimulus–response properties of the major components, and to relate these results to measures of the rat electrooculogram (EOG). Parallel studies were conducted in two strains of rats (Long-Evans, LE; Sprague-Dawley, SD) that are commonly used in vision research. Rats were sedated with ketamine/xylazine and placed on a heating pad. Ag/AgCl wire electrodes were bridged with capillary tubes filled with Hanks balanced salt solution. The active electrode was placed in contact with the corneal surface and referenced to a second electrode placed within the orbit. The dc-ERG signal was amplified (dc-100 Hz), digitized, and stored offline. The duration of full-field flash stimuli was controlled using a mechanical shutter and flash luminance was controlled with neutral density filters. EOGs were recorded using subdermal platinum needle electrodes placed near the eye. In response to a 5-min light exposure, the dc-ERG of LE and SD rats included a distinct b-wave, after potential, c-wave, fast oscillation, and a slow potential of positive polarity the characteristics of which are consistent with a light peak.