Dendritic Relationship Between Starburst Amacrine Cells And Direction–selective Ganglion Cells In The Rabbit Retina

Abstract

Abstract: : Purpose: To investigate the dendritic relationship between starburst amacrine cells (SAs) and morphologically and physiologically characterized ON– and ON–OFF direction–selective ganglion cells (DSGCs) in the rabbit retina. Methods: Animals were overdosed, eyes enucleated and hemisected. The retinas carefully isolated and maintained in Ames medium saturated with 95% O₂ and 5% CO₂. A small piece of retina was then transferred to a recording chamber and superfused at 2.5–3.5 ml/min with oxygenated Ames medium at 33–35°C. A micropipette (impedance ∼150 MΩ) containing 1% Lucifer Yellow (Sigma) and 4% Neurobiotin was used to impale the selected cells and fill the cell with tracers (1 nA, 1–3 min). For physiological identification, light responses to a bar (100×500 µm) drifting in 12 directions were recorded in whole–cell attached mode. The pipette contained 0.4% Neurobiotin. SAs on either the preferred side or the null side were injected using sharp micropipette containing 4% Lucifer Yellow after the recorded DSGCs were characterized. Retinas were fixed with 4% paraformaldehyde, cholinergic plexus was light up using an antibody against vesicular acetylcholine transporter. Single SAs on the preferred or null side were injected with 4% Lucifer Yellow, reacted with a rabbit anti–Lucifer Yellow. Negative controls were carried out by omitting the primary antibodies. Only overlapping and touching pixels were analysed using MetaMorph 5.0. Results: ON– and ON–OFF DSGCs were found to exhibit tight dendritic cofasciculation with the SA plexus, visualized by immuno–labeling of the vesicular acetylcholine transporter. The degree of cofasciculation of both types of DSGC dendrites and SA plexus was found to be significant, unlike the relationship between non–DS cells and the SA plexus that was close to chance distribution. No difference in the degree of cofasciculation in different regions of DS dendritic field was observed. Individual SAs intracellularly injected both on the preferred– and null–side of the DSGCs showed same degree of cofasciculation with the DSGCs. Conclusions: The computation of motion direction is unlikely to result from apparent asymmetry in geometric connections between SAs and DSGCs. Highly selective connections between SAs and DSGCs are necessary.

Keywords: retinal connections, networks, circuitry • amacrine cells • ganglion cells