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Stephen L. Mills, Ye Long, Hongyan Li; Properties of the G5 Ganglion Cell in the Rabbit Retina. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):3248.
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© ARVO (1962-2015); The Authors (2016-present)
Rockhill et al. (2002) described 13 basic types of rabbit ganglion cell, a few of which remain poorly characterized 13 years later. One such type, the G5, ramified just distal to the Off cholinergic band and had numerous dendritic spines. Roska et al. (2006) proposed that a ganglion cell type they recorded from and called type 4/OFF parasol corresponded to the G5. Its basic response type was Off brisk transient, but the detailed properties of the G5 are still poorly known. We have recorded and stained putative G5 cells to describe their morphology and physiology. The understanding of different ganglion cell type responses will help explain mechanisms of visual transmission.
Using Azure B or acridine orange vital staining, medium-sized somas whose border between cytoplasm and nuclei bisect the cell were recorded from via loose patch. Light responses were evoked by distinctive stimuli to investigate the cell response properties. Neurobiotin was injected after recording and visualized with streptavidin-Cy3 to display cell morphology. Cholineacetyltransferase (ChAT) antibody was used to accurately determine the stratification depth.
Cells with the basic appearance of the G5 were reliably OFF transient and ramified just distal to slightly within the Off cholinergic band. These cells were never selective for direction or orientation. Temporal responsiveness was modest, rarely responding about 5 Hz. G5 cells were well-coupled to amacrine cells which resemble the WF2 type (MacNeil & Masland 1998). Spiking was suppressed by moving gratings, light stimulation in the surround and white noise. Spike-triggered averages were measured with sparse white noise and were biphasic. The mGluR6 agonist L-AP4 produced a modest increase in spiking. GABA antagonists strongly increased firing. Strychnine produced a smaller increase in firing and reduced the increase in spiking produced by GABA antagonism, suggesting a polysynaptic inhibitory circuit. The kainate antagonist ACET abolished firing, suggesting input from kainate receptor-only bipolar cells.
The G5 ganglion cell in rabbit retina is an OFF transient ganglion cell whose responsivity was easily suppressed by activity in the near and distal surround. It contributes spatial sensitivity in the intermediate range, but only moderate temporal sensitivity. Its more specific contributions to visual processing remain unknown at present.
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