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.