Density and Spatial Mapping of OFF-Bipolar Cells in the Mouse Retina

Abstract

Purpose : Regional heterogeneity of neuron distribution is a well-recognized feature of retinal organization, yet there is knowledge gap concerning regional and spatial distribution of OFF bipolar cells (BPCs) in the mouse, the most common animal model for vision science. In this study we investigated OFF-BPC distribution throughout regions (dorsal, ventral, nasal and temporal) of the retina and comparing male and female mice. Because OFF bipolar cells have discreate functions between cell types, we hypothesize that density and spatial heterogeneity varies between sub-populations and occurs in a regional dependent fashion.

Methods : OFF BPC number density in C57BI/J6 mice (N=12 male; N=12 female), labeled with antibodies or the Thy1-mitoCFP-P transgene. Antibodies labling blue cone opsin were used to orient the dorsal and ventral planes of the retina. 0.15 mm² fields were captured representing all regions of the retina. Density maps were generated using OriginPro 2020. Local spatial heterogeneity was measured by performing Voronoi domain analysis using the coefficient of variation. One Way ANOVA, Kruskal-Wallis with post-hocs and student t tests were used to determine significance.

Results : Both dorsal and ventral regions of the retina show a significant (p=0.00296) change in density in all 6 populations of OFF-BPCs whereas nasal and temporal show no difference (p=0.428), with a higher density in the ventral retina compared to the dorsal retina. Type 4 BPCs had the steepest gradient in the dorsal region nearing almost 6-fold between highest and lowest densities. Type 3b BPCs had the flattest distribution with a reduction of 2-fold in the dorsal. No difference was observed between male and female (p=0.86). Spatial heterogeneity varies between sub-populations (p<0.0001). Type 1b had the highest coefficient of variation (~0.65.) and 3b had the lowest (~0.39).

Conclusions : In this study we found both density and spatial heterogeneity of OFF-BPC populations is dependent on cell type and region which is consistent with our hypothesis. We also we found that field distance from the optic nerve is a positive predictor of homotypic cellular spatial heterogeneity, whereas higher density is a negative predictor. Further examination will be needed to understand both development and physiological relevance of these differences.

This is a 2020 ARVO Annual Meeting abstract.

 

A) Retina extraction. B) Field sampling. C) Cell-specific immunoflourecence. D) Density and spatial mapping.