Retinal synaptic pathways underlying the response of the rabbit local edge detector.
We studied the circuitry that underlies the behavior of the local edge detector (LED) retinal ganglion cell in rabbit by measuring the spatial and temporal properties of excitatory and inhibitory currents under whole cell voltage clamp. Previous work showed that LED excitation is suppressed by activity in the surround. However, the contributions of outer and inner retina to this characteristic and the neurotransmitters used are currently unknown. Blockage of retinal inhibitory pathways (GABA(A), GABA(C), and glycine) eliminated edge selectivity. Inverting gratings in the surround with 50-microm stripe sizes did not stimulate horizontal cells, but suppressed on and off excitation by roughly 60%, indicating inhibition of bipolar terminals (feedback inhibition). On pharmacologic blockage, we showed that feedback inhibition used both GABA(A) and GABA(C) receptors, but not glycine. Glycinergic inhibition suppressed GABAergic feedback inhibition in the center, enabling larger excitatory currents in response to luminance changes. Excitation, feedback inhibition, and direct (feedforward) inhibition responded to luminance-neutral flipping gratings of 20- to 50-microm widths, showing they are driven by independent subunits within their receptive fields, which confers sensitivity to borders between areas of texture and nontexture. Feedforward inhibition was glycinergic, its rise time was faster than decay time, and did not function to delay spiking at the onset of a stimulus. Both the on and off phases could be triggered by luminance shifts as short in duration as 33 ms and could be triggered during scenes that already produced a high baseline level of feedforward inhibition. Our results show how LED circuitry can use subreceptive field sensitivity to detect visual edges via the interaction between excitation and feedback inhibition and also respond to rapid luminance shifts within a rapidly changing scene by producing feedforward inhibition.
Russell
Thomas L
TL
Division of Neurobiology, Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720-3200, USA.
Werblin
Frank S
FS
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D025461:Feedback, Physiological / Q000187:drug effects; D058787:GABA-A Receptor Antagonists; D066298:In Vitro Techniques; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D009434:Neural Pathways / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D010775:Photic Stimulation; D011817:Rabbits; D018079:Receptors, GABA / Q000378:metabolism*; D011963:Receptors, GABA-A / Q000378:metabolism*; D018009:Receptors, Glycine / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012160:Retina / Q000187:drug effects / Q000502:physiology*; D051245:Retinal Bipolar Cells / Q000187:drug effects / Q000502:physiology; D051248:Retinal Horizontal Cells / Q000187:drug effects / Q000502:physiology; D013569:Synapses / Q000187:drug effects / Q000502:physiology*; D013997:Time Factors; D014785:Vision, Ocular / Q000187:drug effects / Q000502:physiology*
D058787:GABA-A Receptor Antagonists; C087200:GABA-C receptor; D018079:Receptors, GABA; D011963:Receptors, GABA-A; D018009:Receptors, Glycine
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