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A. C. Molnar, F. Werblin; The Midline Amacrine Cell. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1416.
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© ARVO (1962-2015); The Authors (2016-present)
We observed amacrine soma embedded in the midst of the IPL, rather than in the INL or GCL that we call "midline cells." We sought to characterize their physiology and morphology, and to determine if they represent a single cell type or are simply a random assortment of partially displaced amacrine cells
Slices of rabbit retina were stimulated with light in the photopic range. Midline cells were recorded under cell attached and whole-cell patch-clamp. Spikes, excitatory and inhibitory currents and voltage responses were recorded. Light stimuli included narrow- and wide-field flashes and gratings of various spatial frequencies. Cells were filled and imaged with Alexa 488 and in some cases were further stained with neurobiotin to show dye coupling.
Of the 15 midline cells recorded, 9 showed a common morphology and physiology, while the remaining 6 were extremely varied in both physiology and morphology. The common type reliably had its cell body at the midline of the IPL, half way between INL and GCL. These cells extended very wide field (>400um) processes along the midline, such that the cell body was directly in-plane with its processes. Most strikingly, these cells were dye coupled (with both Alexa and neurobiotin) to other cell bodies which were also located at the midline of the IPL, revealing a broad network of cells confined specifically to the midline of the IPL.These midline amacrine cells had common physiological properties: They generated fast spikes that were blocked by the introduction of QX314. They showed a transient ON-OFF response to wide, narrow, and purely peripheral light flashes. In addition, the cells showed clear responses to flipping gratings with stripes of width 100um and 200um. Under whole cell voltage clamp, light elicited inward currents reversed close to 0mV, implying that the cells received excitatory but not inhibitory inputs, and that despite their wide ranging processes and dye coupling, the cells were reasonably well space clamped.
We have characterized a new class of amacrine cell that forms wide-field, electrically coupled networks, whose cell bodies and processes are entirely confined to the midline of the IPL. These cells show properties similar to those described previously in polyaxonal amacrine cells, and have ideal properties for carrying retina-wide, motion elicited signals such is those required for saccadic suppression.
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