Purchase this article with an account.
K. Setayesh, P.B. Cook; Sinusoidally Modulated Light Stimulus Evokes Sustained and Transient Inputs to Transient Ganglion Cells of Salamander Retina . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2232.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Background:Light responses in ganglion cells (GCs) are commonly divided into sustained ON and sustained OFF, and transient (ON–OFF). The origin of the transient response in GCs has been attributed to a special class of transient ON bipolar. These inputs to transient GCs have been tested with steps of illumination, but we do not know if the response–intensity functions for these inputs differ significantly for steady excitatory inputs.Purpose: The purpose of this study was to determine if the GC responses to sinusoidally modulated light stimuli could provide a better measure of the synaptic inputs to GCs and to determine if transient GCs receive input from multiple bipolar cell types. Methods: We prepared retinal slices (250 µm thick) in low light conditions and recorded whole–cell synaptic currents from GCs using standard patch clamp techniques. EPSCs were recorded by holding the membrane at ECl (–45mV) and IPSCs were recorded holding the cell at 0mV. Retinas were stimulated with a LED light source that was projected through the objective (40x water immersion) to stimulate a narrow region (200 um) of retina, effectively within the receptive field center of most GCs. Light could be stepped or sinusoidally modulated at various contrast depths (1–100%), temporal frequencies (.5–10Hz) and wavelengths (520 nm and 610 nm). Sinusoidal illumination was presented and 8 to 10 steady state responses (4 seconds after light onset) were averaged to obtain the cell’s response. Results: We compared the responses evoked by step functions with the sinusoidally modulated light stimulus. Light steps evoked large IPSCs and small, weak EPSCs, while the sinusoidal stimulus evoked relatively larger EPSCs and smaller IPSCs. In transient GCs, the largest EPSCs that were evoked by sinusoidal light stimulation were the result of synaptic inputs from three bipolar cell classes: steady OFF, steady ON and a large transient ON. There was also a small transient EPSC evoked during decrements in illumination. IPSCs evoked by sinusoidal light stimulation could be identified as steady OFF, steady ON and very small component of transient ON and transient OFF. Conclusions: Sinusoidal light stimulation effectively and rapidly reveals the synaptic input contributing to the GC light response. Transient GCs have excitatory input from all known classes of bipolars, and possibly from a transient OFF bipolar cell. The IPSCs, presumbably driven from amacrine cells , but the strength of the IPSCs is not proporational to th . The transient OFF EPSC may arise from a transient bipolar cell.
This PDF is available to Subscribers Only