Abstract
Purpose:
Vision functions over a large range of light intensities. It is not known how the ambient light level might influence response properties of retinal ganglion cells to an otherwise identical stimulus. We characterized retinal output over scotopic, mesopic, and photopic light levels.
Methods:
We used multi-electrode arrays to record from ganglion cells of whole-mount mouse retinas. We characterized their responses to 2s full-field steps of positive and negative contrast. The polarity of the cells (ON, OFF) was determined based on their linear filters, obtained from responses to Gaussian white noise. We tested the responses of ganglion cells at 8 different light levels separated by 1 log unit each, ranging from scotopic to high photopic level.
Results:
Cells robustly increased spiking activity to full-field steps of their preferred contrast (light decrements for OFF cells). Background luminance affected only amplitude and duration of these responses. Surprisingly, all OFF ganglion cells also had excitatory ON responses (to light increments) at least at one light level. The overall ON response pattern in OFF cells was very diverse: short-latency suppression, as well as short- and long-latency excitatory responses (peaking at ~170ms and ~680ms, respectively). The long-latency ON response could be preceded by either suppression or the short-latency ON response. Interestingly, the pattern was robust for each cell at a given light level, but could qualitatively change at different luminance. APB (an agonist of mGluR6 receptors that prevents synaptic activation of ON bipolar cells) blocked some, but not all ON responses in OFF cells, and even revealed some ON responses that were absent without APB. Robust luminance-induced changes of the response pattern were also observed for a naturalistic movie stimulus.
Conclusions:
Our results suggest that retinal output strongly depends on ambient luminance. Responses change not only quantitatively, but qualitatively for many ganglion cells. The source of the ON response in OFF cells appears to be diverse in different cell types, and at different luminance levels within a cell type.
Keywords: 691 retina: proximal (bipolar, amacrine, and ganglion cells) •
693 retinal connections, networks, circuitry •
531 ganglion cells