Inner-retinal contributions to the photopic sinusoidal flicker electroretinogram of macaques. Macaque photopic sinusoidal flicker ERG.
The purpose of this study was to examine inner-retinal contributions to the photopic sinusoidal flicker ERG. ERGs were recorded from 5 anesthetized monkeys to sinusoidally modulated (100%, 0.5-120 Hz) red full field flicker at Lmean of 3.2 log phot td on a rod saturating blue background (3.7 log scot td; 3.0 log phot td) before and after intravitreal injections of tetrodotoxin (TTX) to block Na+-dependent spikes of retinal ganglion and amacrine cells, followed by N-methyl-D-aspartate (NMDLA) to suppress all activity of these cells. Recordings also were made after blocking bipolar (and horizontal) cell responses with L-2-amino-4-phosphonobutyric acid (APB) and 2-cis-piperidine-2,3-dicarboxylic acid (PDA) or 6-cyano-nitroquinoxaline-2,3-dione (CNQX). Control fundamental (F1) and second harmonic (F2) amplitudes were large and variable at temporal frequencies up to 2 Hz. At higher frequencies, Fl amplitude was minimal with a phase step at a frequency between 13 and 19 Hz and maximal at 27-33 Hz. F2 was minimal at 2-3 Hz and maximal at 6-8 Hz, again with a phase step near the minimum. TTX, or NMDLA, produced small changes in Fl that shifted the amplitude minimum to a lower and the maximum to a higher frequency. In contrast, F2 was more strongly affected; both the amplitude minimum (and phase step) and maximum were greatly attenuated, leaving a moderate response from 0.5 to 8 Hz, which then declined as frequency was increased to 30 HZ. After APB and PDA or CNQX, F1 decreased continuously with increasing frequency and F2 was generally much smaller. The nearly linear F1 phase plotwas consistent with the presence of a single mechanism (i.e. photoreceptors). Inner-retinal neurons contribute to the photopic sinusoidal flicker ERG. Whereas for F1, inner-retinal contributions are small relative to those from bipolar cells; for F2, they are equal or greater between 2and 16 Hz.
Viswanathan
Suresh
S
College of Optometry, University of Houston, Houston, TX 77204-2020, USA.
Frishman
Laura J
LJ
Robson
John G
JG
D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000613:Aminobutyrates / Q000494:pharmacology; D000818:Animals; D004596:Electroretinography; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005260:Female; D008027:Light; D008253:Macaca mulatta; D008297:Male; D016202:N-Methylaspartate / Q000494:pharmacology; D010775:Photic Stimulation / Q000379:methods; D010786:Photoreceptor Cells / Q000502:physiology; D010875:Pipecolic Acids / Q000494:pharmacology; D012160:Retina / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects*; D013779:Tetrodotoxin / Q000494:pharmacology
D000613:Aminobutyrates; D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; D010875:Pipecolic Acids; D013779:Tetrodotoxin; C029262:2,3-piperidinedicarboxylic acid; D016202:N-Methylaspartate; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; C012729:2-amino-4-phosphonobutyric acid