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JJ Pang, F Gao, SM Wu; Layer-by-layer Segregation and Integration of Visual Signals in the Inner Plexiform Layer of the Dark-adapted Tiger Salamander Retina . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3787.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The objective of this project is to study how bipolar cell signals segregated in various strata in the inner plexiform layer (IPL) are integrated and computed by amacrine cells (ACs). Methods: Light-evoked currents of bipolar cells and amacrine cells were recorded from dark-adapted tiger salamander retinal slices under voltage clamp conditions, and the cell morphology was revealed by Lucifer yellow fluorescence with confocal microscopy. Results: A previous study suggests that various attributes of visual signals are segregated by stratification of bipolar cell axon terminals in the IPL. Confocal microscopic analysis reveals that axon terminals of about 70% of bipolar cells are monostratified in the IPL, 11% are bistratified, 1% are tristratified, and 18% have pyramidal axon terminals. About 30 % of ACs have narrowly monostratified dendrites in one of the ten strata of the IPL, and they receive segregated bipolar cell inputs: the light-evoked excitatory cation current, Δ;IC, in strata 1, 2 and 4 are OFF (predominately mediated by the OFF bipolar cells), in strata 3, 7, 8, 9 and 10 are ON (predominately mediated by ON bipolar cells), and in strata 5 and 6 are ON-OFF (mediated by both ON and OFF bipolar cells). The remaining 70% of ACs have either broadly monostratified, multistratified or diffuse dendrites, and they integrate bipolar cell signals through layer-by-layer summation: ACs with dendrites ramified in multiple strata exhibit Δ;IC that are sums of Δ;ICs of individual strata. The light-evoked inhibitory chloride current, Δ;ICl, in strata 1, 2, 4, 5 and 6 are ON-OFF (mediated predominately by ON-OFF ACs or ON ACs plus OFF ACs), and Δ;ICl in strata 3, 7, 8, 9 and 10 are ON (mediated predominately by ON ACs). Conclusions: ACs process bipolar cells in two ways: Narrowly monostratified cells carry segregated bipolar cell signals constituting the segregated inhibitory pathway in the inner retina, whereas broadly monostratified and multistratified cells integrate bipolar cell signals through layer-by-layer summation. Additionally, AC-AC inhibitory synaptic circuitry in the IPL is asymmetrical in favor of the ON channels. CR: None. Supported by NIH EY04446, EY07001, the Retina Research Foundation (Houston), and Research to Prevent Blindness, Inc.
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