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F. Gao, J.J. Pang, S.M. Wu; Integration and Computation of Visual Signals in the Inner Plexiform Layer by Retinal Ganglion Cells . Invest. Ophthalmol. Vis. Sci. 2003;44(13):5187.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The objective of this project is to study how bipolar cell (BC) and amacrine cell (AC) signals in various strata of the inner plexiform layer (IPL) are integrated and computed by retinal ganglion cells (RGCs). Methods: Light-evoked currents of RGCs were recorded from dark-adapted tiger salamander retinal slices or flat-mounted retinas under voltage clamp conditions, and the cell morphology was revealed by Lucifer yellow fluorescence with confocal microscopy. Results: Previous studies suggest that various attributes of visual signals are segregated in different strata of the IPL by BC axon terminals and AC dendrites. Confocal microscopic analysis reveals that axon terminals of about 37% of BCs are narrowly monostratified in one of the ten strata of the IPL, and the rest are either broadly monostratified, multistratified, or have pyramidal axon terminals. Dendrites of 30 % of ACs are narrowly monostratified, the rest are either broadly monostratified, multistratified, or diffuse in the IPL. In contrast, only 9% of RGCs have narrowly monostratified dendrites, suggesting that relatively few RGCs in the salamander retina receive segregated BC and AC inputs. The remaining RGCs have either broadly monostratified (11%), bistratified (24%), multistratified (23%) or diffuse (33%) dendrites, and they integrate BC and AC signals in a layer-by-layer fashion. Integration of bipolar cell signals in some RGCs appears linear whereas in others it is nonlinear, and integration of AC signals are often highly nonlinear. Studies of AC neurotransmitter actions on RGC light responses provided important clues for the nonlinear integration carried out on RGCs. Conclusions: RGCs process BC and AC signals in two ways. Less than 10% are narrowly monostratified cells and they process segregated BC and AC signals and carry them to the brain. Other RGCs are broadly monostratified, multistratified or diffuse and they integrate BC and AC signals by complex rules that involve linear and nonlinear signal summation, AC-AC synaptic interactions, and AC feedback and feedforward synapses in the IPL.
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