The Retinal Connectome: Networks in the Amacrine Cell Layer

Abstract

Purpose: : Defining the retinal connectome is a grand challenge in neuroscience. We sought to build such a connectome by serial section Transmission Electron Microscopy (ssTEM) and computational molecular phenotyping (CMP).

Methods: : Anesthetized rabbits received intravitreal injections of agmatine (AGB) to map the activity of retinal neurons stimulated by light. After fixation and embedding, 400+ horizontal 70 nm sections were cut from the inner nuclear (INL) to ganglion cell layers (GCL). CMP was performed on bounding and every 20-30 sections. For every slice, a 0.25 mm diameter field of over 1000 tiles was captured with a JEOL JEM-1400 TEM and GATAN Ultrascan 4000 camera. Tiles were mosaicked and slices registered using our ir-tools package, and rendered / annotated with our Viking viewer .

Results: : We have built a canonical volume of rabbit retina containing multiple copies of every cell class. and are assembling its complete retinal network. Our first analyses focused on the amacrine cell layer and we have already discovered novel axosomatic amacrine > amacrine cell circuits.

Conclusions: : It is now feasible to recover the connectome of any major neural structure. We have already discovered new networks not predicted by physiology.

Keywords: retina • retinal connections, networks, circuitry • imaging/image analysis: non-clinical