Spinal dI2 interneurons regulate the stability of bipedal stepping

Peripheral and intraspinal feedback is required to shape and update the output of spinal networks that execute motor behavior. We report that lumbar dI2 spinal interneurons of the chick receive synaptic input from afferents and pre-motoneurons. They innervate contralateral premotor networks in the lumbar and brachial spinal cord and their ascending projections innervate the cerebellum. These findings suggest that dI2 neurons function as interneurons in local lumbar circuits and involved in lumbo-brachial coupling and that part of them deliver peripheral and intraspinal feedback to the cerebellum. Silencing of dI2 neurons leads to destabilized stepping in P8 hatchlings with occasional collapses, variable step-profiles and wide-base walking, suggesting that the dI2 neurons may contribute to stabilization of the bipedal gait.