Sigulinsky, Crystal; Anderson, James; Emrich, Daniel; Rapp, Christopher; Dahal, Jeebika; Pfeiffer, Rebecca; Rapp, Kevin; Yang, Jia-Hui; Watt, Carl; Marc, Robert; Jones, Bryan (University of Utah)
Faculty Advisor: Jones, Bryan (University of Utah, Ophthalmology/Visual Sciences)
Purpose: Mouse retina differs structurally from rabbit retina, as it is thicker and vascular, while rabbit retina is thinner and avascular. The implications of these differences on neuronal morphology and connectivity is unclear. We compare the morphology and connectivity of the Aii amacrine cell (AC) at ultrastructural precision in connectomes of mouse (RC2) and rabbit (RC1) retina.
Methods: RC1 and RC2 are 0.25 mm diameter volumes built by automated transmission electron microscopy at 2 nm/pixel resolution. RC1 is from a 13 month old, female Dutch Belted rabbit. RC2 is from a 5 month old female C57BL/6J mouse. The Viking application was used to annotate Aii ACs.
Results: Mouse Aii ACs are elongated with a prominent neck region. Lobular appendages in both species extend from the soma, neck and proximal arboreal dendrites in the OFF sublamina, forming reciprocal synapses with OFF cone bipolar cells (BCs). In rabbits, multiple arboreal dendrites emerge from the base of the neck, branch and travel obliquely through the ON sublamina, forming gap junctions with ON cone BCs, neighboring Aii ACs, and itself. They extend laterally at the base of the IPL, collecting ribbon input from rod BCs. In contrast, mouse arboreal dendrites branch from a single primary dendrite, travel vertically through the IPL with limited self-interaction, and terminate at variable depths that align with the more broadly ramified axon terminals of mouse rod BCs. Synaptology reveals greater output in the OFF vs ON layer in mouse versus rabbit. Uniquely, descending axons of mouse ON cone BCs form gap junctions with Aii AC somas.
Conclusions: Lateral expansion of rabbit Aii ACs may be attributable to eccentricity. However, morphological differences correlate with connectivity differences. Comparative anatomy connectomics is essential for understanding implications of retinal structure on neuronal morphology and connectivity underlying network differences between the mouse and rabbit.