Response Characteristics and Retinal Origin of the Photopic Negative Response of the Electroretinogram in Dogs.

Purpose: To investigate the response characteristics and retinal origin of the photopic negative response (PhNR) of the electroretinograms (ERGs) in dogs. Methods: Photopic ERGs were elicited by white flash stimuli of different intensities under a steady white background illumination in four anesthetized dogs. These ERGs were also recorded in the same manner after intravitreal injection of tetrodotoxin (TTX). Additionally, retinal localization of voltage-gated sodium channel Nav 1.6 was assessed by immunohistochemistry. Results: The amplitude of the a-wave and the PhNR was increased as the stimulus intensity was raised, while the amplitude of the b-wave was peaked at the moderate stimulus intensity of 3.09 cd.s/m(2). TTX greatly attenuated the PhNR, while the reduction in the b-waves and a-wave was mild or insignificant. Nav 1.6-expression was specifically detected on the retinal ganglion cells (RGCs). Conclusions: Our results are consistent with the PhNR primarily derived from the inner retina including RGCs in dogs, suggesting that the PhNR can be used to monitor function of these retinal components in dogs.