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

ABSTRACTPurpose: 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/m2. 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 includi...