Abstract
Purpose: :
We studied the space-time interactions between excitation and inhibition that lead to the special response properties of the local edge detector retinal ganglion cell (LED).
Methods: :
We measured the patterns of excitation and inhibition that were generated by the LEDs response to a dark edge. Currents were measured with whole-cell patch-clamp in the light-adapted rabbit retina. We assessed the contributions of individual inhibitory neurotransmitter systems by using combinations of SR95531, TPMPA, and strychnine to block GABAa, GABAc and glycine.
Results: :
When all inhibition was blocked, the excitatory pattern of the LED behaved like an OFF bipolar cell, responding to luminance changes in areas distant from the edge. Allowing either GABAa and GABAc inhibition generated an edge-detection pattern: sustained excitatory currents remained selectively at the edge.
Conclusions: :
Excitatory input is modified by a combination of GABAa and GABAc inhibition acting presynaptic to the LED to generate the edge detection properties of the LED. Suppression of excitation is greatest at areas distant from the edge, and smallest near the edge. Either system can perform this function, thus the inhibition is acting redundantly.
Keywords: retinal connections, networks, circuitry • inhibitory neurotransmitters • retina: proximal (bipolar, amacrine, and ganglion cells)