The Journal of Neuroscience, June 1, 2002, 22(11):4693-4701
Segregation and Integration of Visual Channels: Layer-by-Layer
Computation of ON-OFF Signals by Amacrine Cell Dendrites
Ji-Jie
Pang,
Fan
Gao, and
Samuel M.
Wu
Cullen Eye Institute, Baylor College of Medicine, Houston, Texas
77030
The visual system analyzes images through parallel channels, and
our data suggest that the first set of parallel representations of the
visual world is embodied in the inner plexiform layer (IPL) of the
retina, in which light-evoked excitatory inputs of the ON and OFF
bipolar cells to amacrine cells (ACs) are organized in a layer-by-layer
manner. Approximately 30% of ACs have narrowly monostratified
dendrites in 1 of the 10 strata of the IPL, and they receive segregated
bipolar cell inputs: the light-evoked excitatory cation current,
IC, in strata 1, 2, and 4 is OFF
(predominantly mediated by the OFF bipolar cells), the current in
strata 3 and 7-10 is ON (predominantly mediated by ON bipolar cells),
and the current in strata 5 and 6 is ON-OFF (mediated by both ON and
OFF bipolar cells). The remaining 70% of ACs have 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
ICs that are sums of
ICs of individual strata. The
light-evoked inhibitory chloride current, ICl, in strata 1, 2, and 4-6 is
ON-OFF (mediated predominantly by ON-OFF ACs or ON ACs plus OFF ACs),
and the ICl in strata 3 and 7-10 is ON
(mediated predominantly by ON ACs). This indicates that the
amacrine-amacrine inhibitory synaptic circuitry in the IPL is
asymmetrical in favor of the ON channels.
Key words:
retina; amacrine cells; bipolar cells; inner plexiform
layer; dendritic stratification; ON and OFF visual channels; layer-by-layer signal computation; signal segregation and
integration
Copyright © 2002 Society for Neuroscience 0270-6474/02/22114693-09$05.00/0
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