Abstract
Abstract: :
Purpose: To determine the direct contribution to components of the multifocal ERG response (mfERG) from activity in Rod photoreceptors. Methods: Using both conventional and multifocal methods for stimulation and signal acquisition, simultaneous recordings of the trans-retinal voltage (ERG) and Rod photoreceptor membrane potential were made from isolated, flat mounted, and perfused bullfrog retinas (Rana Catesbeiana). Dim multifocal stimuli were imaged at the plane of the photoreceptor outer segments. Multifocal stimulation and signal acquisition was performed using VERIS software and hardware (EDI; San Mateo, CA). Conventional recordings of responses elicited by diffuse white flashes of 10 msec duration were obtained using a CED Micro 1401 acquisition board and Signal software (CED Ltd., UK). Recordings were made in normal Ringer's and also following switch to Ringer's containing a combination of 200 microM 2-amino-4-phosphonobutyric acid (APB) and 3 milliM cis-2,3-piperidinedicarboxylic acid (PDA). Results: The switch to Ringer's containing APB + PDA was associated with little effect on the amplitude or kinetics of Rod photoreceptor responses to either dim or bright diffuse flash stimuli. In the presence of APB + PDA, the ERG b-wave elicited by the same stimuli was completely blocked and the a-wave was converted to a slow monophasic negative component. These effects are consistent with a presumed action of this drug combination to block all transmission from photoreceptor cells to second order retinal cells. Similar effects of APB + PDA were observed for Rod and ERG responses obtained with multifocal stimulation. In the presence of these test agents, the normally biphasic mfERG response (N1P1) is converted to a monophasic negative response whose waveform now closely resembles that of the simultaneously recorded Rod photoreceptor response. Conclusions: Under normal conditions, ERG responses to the dim multifocal stimuli used in these recordings contains little or no contribution from cone activity. Peak N1 of these responses reflects little direct contribution from activity in photoreceptors.
Keywords: 555 retina: distal(photoreceptors, horizontal cells, bipolar cells) • 394 electrophysiology: non-clinical • 396 electroretinography: non-clinical