Abstract
Purpose: :
Many ganglion cells exhibit push–pull interactions whereby excitation increases as inhibition decreases in response to a flash. Our lab has found similar interactions in most cone bipolar cells and amacrine cells. Here we describe the common features of this interaction in all three cell–types and investigate its functional role.
Methods: :
Rabbit retinal neurons were whole–cell patch–clamped in sliced and flat–mounted retinas to record excitation, inhibition and voltage. Ganglion cells were also loose–patched for spike recordings. Stimuli included flashes of +/– 100% contrast, sinusoids, gratings and modulated sinusoids. Spatial stimuli were used only in flat–mount on ganglion cells. We perfused tissue with 10µM strychnine or 100µM picrotoxin in Ames’ medium.
Results: :
Most bipolar, amacrine and ganglion cell subtypes responded to a light flash with either increased excitation accompanied by a reinforcing decrease in inhibition or decreased excitation reinforced by increased inhibition. This reinforcement between excitation and inhibition was maintained for sinusoidal stimuli over a wide range of frequencies (0.3Hz–15Hz). Synaptic rectification at many synapses distorted excitatory and inhibitory inputs to retinal neurons. This distortion mixed the high– and low–frequency components of signals so that changes in contrast for rapidly changing signal were indistinguishable from changes in baseline brightness in both time and space. Push–pull interactions between excitation and inhibition suppressed this distortion, resulting in a response that more accurately represented the structure of complex stimuli.
Conclusions: :
Push–pull interactions appear in a majority of bipolar, amacrine and ganglion cells. This interaction compensates for distortion generated by the inherently nonlinear synapses at every stage of processing so as to maintain an accurate representation of the visual world.
Keywords: retinal connections, networks, circuitry • retina: proximal (bipolar, amacrine, and ganglion cells) • amacrine cells