ELSC Seminar Series

Bipedal locomotion, the habitual use of striding bipedal gaits in walking and running, and flight are traits that evolved from quadrupedal stepping vertebrates. Walking, swimming and flying require coordination between the left and right limbs. Refinement of locomotion, adjusting locomotion to predicted and unexpected events in the environment, requires a feedback system that reports the degree of motorneuron activation to the cerebellum.

Using a “toolbox” that we developed for targeting, tracking, and manipulating neuronal circuits in the chick nervous system, we studied stepping and flying in birds. 1) we targeted a specific subtype of lumbar spinal interneurons – dI2, that deliver peripheral and intraspinal feedback to the contralateral spinal cord and the cerebellum. Silencing of dI2 neurons leads to destabilized stepping, suggesting that dI2 neurons stabilize the bipedal gait. 2) In mammals, the axonal guidance molecule ephrin-B3 is expressed in the spinal cord midline and is required for forming spinal circuits that instruct alternate stepping. We found that birds lack a functional ephrin-B3 and that this loss is linked to the evolution of synchrony-mediating circuitry at spinal wing levels in birds.