Tectal activity underlying phototactic preferences in the Xenopus laevis tadpole
thesisposted on 13.05.2019, 00:00 by Jasper Hunt
The Xenopus laevis tadpole has long been known to exhibit phototactic preferences, i.e. preferences to swim towards or away from visual stimuli. Of particular interest is the tendency for stage 48 Xenopus tadpoles to prefer green light but for older tadpoles to prefer blue light. Recent work has begun to characterize the timeline of development for Xenopus rod and cone cells with different light specificities, relating this developmental timeline to the shift in color-guided phototactic preferences. Yet still little is known about the neural processing of color in the developing brain. The present study’s first experiment extends previous behavioral data, demonstrating that stage 48 Xenopus tadpoles’ phototactic preference for green light persists over extended testing periods and outside of forced-choice procedures. To further investigate the neural mechanisms underlying color processing in the developing brain, a second experiment used in vivo electrophysiology to examine neural activity in the optic tectum during the processing of color. To our knowledge, this is the first study comparing tectal activity in response to different colors of light. No differences in response to color were observed at the single-cell level, suggesting that the color of visual stimuli is likely encoded at the circuit level or higher. Finally, two distinct populations of neurons were identified based on the pattern of synaptic inputs they received during visual stimulation. Future studies will investigate the roles of these two neuronal types in the processing of visual stimuli.