Pharmacological study of d–wave of the primate photopic ERG

Abstract

Abstract: : Purpose: To determine how the photoreceptors and the ON– and OFF–pathways contribute to the d–wave (OFF–response) of the primate photopic ERG using pharmacological agents. Methods: Five adult monkeys (Macaca mutata and M. fascicularis) were studied. The d–wave was elicited by slow, saw–tooth (rapid–off) stimuli using green LEDs ( λ_max525 nm; half–width, 50 nm) in a Ganzfeld dome. NMDA+TTX were used to suppress inner retinal activities, and APB and PDA to block postreceptoral ON– and OFF–pathway activities. The postsynaptic ON– and OFF–components were isolated by subtracting the post–drug ERGs from the pre–drug ERGs. Results: The amplitudes of the oscillatory components of the d–wave were significantly reduced after TTX and NMDA. The amplitude of d–wave was also reduced slightly after TTX and NMDA, but after APB,the amplitude of d–wave increased significantly. After APB+ PDA, the amplitude of the d–wave from the remaining photoreceptors was as large as that of the initial d–wave, but the implicit time of the d–wave was markedly delayed. The isolated postsynaptic ON– and OFF–components had sharp positive and negative deflections, respectively, and these two waveforms were "mirror images" of each other.The timing of OFF–component was slightly earlier than that of ON–component. Conclusions:1. The activity of inner retinal neurons contributes to the positive component of the d–wave. 2. The initial rapid phase of the d–wave results mainly from the activity of the OFF–pathway and the later slow phase by the cone photoreceptors. 3. The activities of the postsynaptic ON– and OFF pathway produce opposing potentials.

Keywords: electroretinography: non–clinical • neurotransmitters/neurotransmitter systems • pharmacology