Abstract
Purpose::
Bush et al. (IOVS, 1995) demonstrated that the scotopic threshold response was more preserved than the scotopic b-wave in the aged Royal College of Surgeons (RCS) rat despite progression of photoreceptor loss. In the present study, we investigated how the third-order neuronal response contributes to shaping the electroretinogram (ERG) in the RCS rat.
Methods::
Full-field scotopic ERGs were recorded from dystrophic RCS rats (n=30) at 4, 6, 8, 10, 12 or 14 weeks of age in response to different stimulus intensities (maximum intensity, 0.84 log cd-s/m2). N-methyl-DL-aspartic acid (NMDA, 5 mM) was injected into the vitreous cavity of the right eyes to eliminate the third-order neuronal response. The left eyes received vehicle as controls. The third-order neuronal response was isolated by digitally subtracting waveforms of the NMDA-injected eyes from those of the control eyes.
Results::
The scotopic ERG a- and b-waves deteriorated with age. The third-order neuronal response was preserved to a greater degree than the b-wave despite progression of photoreceptor degeneration. Intravitreal injection of NMDA attenuated the a-wave and enhanced the b-wave across the stimulus range from the low to mid intensities. This tendency became more pronounced with advancing age. In aged dystrophic RCS rats, this phenomenon was seen even at the maximum intensity. The difference between NMDA-injected and vehicle-injected eyes was larger for the threshold than for the maximum amplitude at each examined time point (P<0.001). Intravitreal injection of NMDA decreased implicit times of the a- and b-waves after 8 weeks of age (P<0.005 for the a-wave).
Conclusions::
With advancing photoreceptor degeneration, the third-order neuronal response had a greater contribution to shaping the a- and b-waves in dystrophic RCS rats. The threshold of the a- and b-waves was more affected than the maximum amplitude by the third-order neuronal response.
Keywords: retinal degenerations: hereditary • electroretinography: non-clinical • drug toxicity/drug effects