ON- and OFF-inputs to transient amacrine cells and the effects of light modulation depth: An experimental and theoretical study in catfish retina.
Item
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Title
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ON- and OFF-inputs to transient amacrine cells and the effects of light modulation depth: An experimental and theoretical study in catfish retina.
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Identifier
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AAI9405565
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identifier
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9405565
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Creator
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Naylor, David Earl.
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Contributor
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Advisers: Daniel Tranchina | Michael Lacker
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Date
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1993
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Language
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English
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Publisher
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City University of New York.
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Subject
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Biology, Neuroscience | Biology, Animal Physiology | Engineering, Biomedical
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Abstract
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A L{dollar}\sb1{dollar}-N-L{dollar}\sb2{dollar} model involving convergence of parallel ON- and OFF-bipolar inputs onto a transient amacrine C cell enabled the prediction of analytic forms for 1{dollar}\sp{lcub}\rm st{rcub}{dollar} and 2{dollar}\sp{lcub}\rm nd{rcub}{dollar} order Wiener kernels which incorporate the bipolar {dollar}\rm (L\sb1\sp{lcub}on{rcub},\ L\sb1\sp{lcub}off{rcub}){dollar} and amacrine (L{dollar}\sb2){dollar} filter parameters. These parameters were adjusted to fit simultaneously the 1{dollar}\sp{lcub}\rm st{rcub}{dollar} order kernel and diagonal of the 2{dollar}\sp{lcub}\rm nd{rcub}{dollar} order kernels of 22 transient amacrines. Fits of amacrine responses then characterized the synaptic ON- and OFF-static-nonlinearities (N{dollar}\sb1,{dollar} N{dollar}\sb2).{dollar} Several conclusions emerged. First, shape variation of the 1{dollar}\sp{lcub}\rm st{rcub}{dollar} order kernels suggested cancellation between ON- and OFF-pathways and required the parallel model. This linear cancellation explains the strong 2{dollar}\sp{lcub}\rm nd{rcub}{dollar} order kernels of C cells. Also, the model predicted slower kinetics for ON- as opposed to OFF-pathways. In addition, the ON-nonlinearity was not as monotonic as the OFF-suggesting pathway differences at the amacrine synapse, possibly due to different receptor subtypes. C cell responses to decreasing modulation depths of light were recorded. The Wiener kernels showed an increase in sensitivity at lower modulations, with a greater scaling occurring in the 2{dollar}\sp{lcub}\rm nd{rcub}{dollar} order kernel relative to 1{dollar}\sp{lcub}\rm st{rcub}{dollar} order kernel. Shape changes indicated an increased dominance of the OFF-pathway at lower modulations. New features, such as oscillations, emerged at lower modulation levels and occurred later along the time axis of kernels. Their time course was inconsistent with an origin solely from centripetal bipolar inputs, but was compatible with a proposed circuitry containing ganglion cell feedbacks. The feedback is postulated to be more linear than bipolar inputs and, consequently, becomes prominent at lower modulations. The parallel L{dollar}\sb1{dollar}-N-L{dollar}\sb2{dollar} model, which does not account for feedback, performed less well at lower modulations due to the late features. Three cells without strong late features were analysed with the present model and showed a slowing in ON- and OFF-pathways at low modulations. The nonlinearities did not change significantly with decreasing modulation levels. A scaling increase of bipolar inputs to transient amacrines at the presynapse, probably via feedback from the inner retina, is consistent with the results and can explain the increased sensitivity of C cells at low modulation levels.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
