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H.–A. Hsueh, A.C. Molnar, F.S. Werblin; Rabbit Amacrine Cells: Many Morphologies but Only a Few Excitation/Inhibition Relationships . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2276.
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© ARVO (1962-2015); The Authors (2016-present)
The functional role of most amacrine cell types remains unknown. In an effort to gain insight about their functional properties, we measured the light response of a wide variety of amacrine cells, and correlated their responses with their morphology.
We patch clamped amacrine cells in the rabbit retinal slice, and measured excitation, inhibition, and voltage responses to bright vs. dark flashes, and sinusoids. Alexa Fluor 488 was added to the intracellular medium via the patch pipette so that we could examine morphology.
Each of the three major classes of ON, OFF, and ON/OFF amacrine cells, has a characteristic form of interaction between excitation and inhibition. Cells that received OFF excitation received only ON inhibition and stratified predominantly in the OFF sublamina. Cells that received ON/OFF excitation did not appear to receive any inhibition and stratified in the middle of the IPL. Cells that received ON excitation received two forms of inhibition: OFF inhibition and ON/OFF inhibition. ON/OFF inhibited cells received comparatively weak excitation and therefore only hyperpolarized. These cells had processes that extended in both ON and OFF sublaminae but had more processes in the ON sublamina. Although there are four dominant physiological groups, there are variations within each of these interactions, suggesting that there are multiple amacrine cell types in each group. Therefore, it appears that these four interactions between excitation and inhibition represent general signal processing forms in the inner retina.
Curiously, some wide–field amacrine cells did not generate action potentials, while some narrow–field amacrine cells did.
Despite many morphological classes of amacrine cells, the relationship between their excitatory and inhibitory inputs can be grouped into four forms. These interactions are comparable to those observed in bipolar and ganglion cells (other work in our lab). From these groupings, we propose some simple circuits by correlating stratification and temporal properties of amacrine cells with inhibition measured in bipolar and ganglion cells.
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