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Akito Ishihara; A simulation study of information transmission in OFF cone bipolar cell pathway. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1873.
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© ARVO (1962-2015); The Authors (2016-present)
Several subtypes of OFF bipolar cells (OFF-BCs) in mammal retina have been identified by morphology and temporal responses of ionotropic glutamate receptor (iGluR), and convey distinct temporal visual information to higher order neurons in parallel. In order to elucidate role of the OFF-BC pathways to visual information processing in detail, it is necessary to analyze light responses of the OFF-BCs under various light conditions. We computationally analyzed how neural mechanisms of OFF-BCs contribute to the light responses.
We constructed a mathematical model for analysis of temporal information processing in neural network of cone-OFF-BCs with computer simulation. The OFF-BC was described by Hodgkin-Huxley type equations. Synaptic inputs from cone to OFF-BC were mediated by iGluR which was described by kinetic scheme model. Light responses of cone photoreceptor were calculated using the already known model. Parameters of the model were estimated from electrophysiological evidence of mammalian retina. Numerical solutions and computer simulations using the developed model were obtained and run using MATLAB.
In order to clarify the difference in retinal transmission from cone to OFF-BCs by iGluR subtype, we analyzed relationship of model's parameters and temporal frequency responses of OFF-BC at different mean illumination to sinusoidal stimulus and square wave stimulus. The OFF-BC with transient iGluR such as AMPA receptors responded band-pass temporal frequency responses to sinusoidal stimulus and the low frequency responses decreased with increasing in mean illumination. Whereas the temporal frequency responses to square wave stimulus had low-pass filtering characteristics and low frequency responses were emphasized with increasing in mean illumination. Our simulation analysis showed the responses depend on desensitization of ionotropic type glutamate receptors, time constant of cell membrane, and intrinsic ionic current of bipolar cells.
The results show the temporal frequency responses depend on kinetics of iGluR's desensitization and its characteristics are nonlinearly modulated by mean illumination. The model predicted that the OFF-BCs plays a role of transmitting visual information adjusted by mean light intensities in wider dynamic range to higher order neurons.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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