Amniotes Wave and Amphibians Look: Retinal Activity and the Wiring of Visual Circuits

Joint Biology, Physics and Neuroscience Seminar

 Jay Demas, Ph.D.
Physics Department, St. Olaf College

There are two major subdivisions of tetrapods: amphibians and amniotes. Unlike
amniotes, developing amphibians need vision to avoid predators and locate food long
before visual system circuits have fully matured. In all amniote species studied to date,
waves of spontaneous activity arising in the retina dominate early visual systems.
Furthermore, the patterns of activity imparted by retinal waves are thought to help refine the patterns of connectivity in the developing visual system. This raises two interesting questions: 1) Do amphibians have retinal waves, which might occlude critical sensory information? 2) Can visually evoked activity patterns inform visual system refinement? Here we develop an ex vivo preparation of the Xenopus laevis tadpole retina and use highdensity multi-electrode arrays to record simultaneously from ensembles of retinal ganglion cells (RGCs). We find that RGCs are spontaneously active at all stages of tadpole development, but their population activity never coalesces into waves. In addition, even at the earliest stages recorded, visual stimulation dominates over spontaneous activity and can generate patterns of RGC population activity similar to those observed spontaneously in amniotes. Taken together our findings suggest that the developing retinal circuits in the two major subdivisions of tetrapods evolved different strategies to supply similarly patterned activity to support circuit refinement in downstream visual targets, supporting early vision in amphibians and overcoming sensory deprivation in amniotes.