The mathematical model of retinal neurons based on ionic currents and calcium mechanisms

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In the neuroinformatics study of the retina, each retinal cell has been mathematically modeled based on their ionic current mechanisms. In order to reconstruct full model of the retina by integrating individual cell models, it is essential to introduce the synaptic transmission model. Because intracellular calcium ions is involved closely in the synaptic transmission mechanisms, a model of the synaptic transmission including calcium mechanisms has to be constructed. In the present study, a quantitative model for horizontal cell and bipolar cell which are secondary order neurons, and ganglion cell which is the output neuron of retina, and their synaptic mechanisms including calcium mechanisms have been developed.A retinal horizontal cell of rabbit was modeled based on the ionic current and the generating mechanisms of repetitive spikes was analyzed by using the model. The results suggest that the spikes are generated by a calcium current and a delayed rectifier potassium current in the horizontal cell. We constructed the model of a ganglion cell based on recent physiological evidence. The model included seven nonlinear ionic currents and one linear leakage current. The model could well reproduce responses under voltage champ and current clamp condition and spikes with blocked KィイD1+ィエD1 currents.Models of transmitter induced currents and synaptic terminal including calcium system in retinal ON-center bipolar cell were constructed. By integrating these models, an ON-center bipolar cell where spatial distribution of ionic channels is not uniform were modeled. Coupling coefficients between the soma and the synaptic terminal and light responses were analyzed using the model. The results suggested that the bipolar have easy to conduct signal to both direction and that dynamics of the light responses was strongly affected by ionic current of synaptic terminal.