A mechanistic model of the spatial interaction between blue cones and blue cone bipolar cells in macaque retina

The spatial positions of blue cones (BC) and blue cone bipolars (BCBP) are positively correlated in macaque retina (Kouyama & Marshak, 1997): BCs, located in the outer nuclear layer (ONL), and BCBPs, located in the inner nuclear layer (INL), tend to be located close to each other in the lateral dimension. They also form separate homotypic mosaics and, finally, most BCBPs contact only a single BC pedicle. We present a mechanistic model of the BC-BCBP interaction to account for the development of these two mosaics and their connections. It assumes that BCs are immobile and that BCBPs can migrate within the INL due to a compromise between a dendritic string force and an intrinsic INL friction force. Model parameters were selected to optimise the fit with observed fields (Kouyama & Marshak, 1997). Simulated density recovery profiles (DRPs) closely mimic the observed DRPs. In particular, for each of the five retinal fields studied, the simulated DRP for the interaction between BCs and BCBPs has a peak at distances less than around 20 m and a small dip at distances up to the maximal lateral dendritic length ([~] 44 m), matching the profiles of the real data. We conclude that our mechanistic model is a candidate for the unknown mechanism that drives the observed interaction between BCs and BCBPs in macaque retina.