Spinal dI2 interneurons regulate the stability of bipedal stepping

Abstract

Peripheral and intraspinal feedback is delivered to the cerebellum through the spinocerebellar tracts in order to shape and update the output of spinal networks that execute motor behavior. However, genetic inaccessibility of the tract neurons prevented further elucidation of the ascending circuits. We report that genetically targeted lumbar dI2 interneurons, form a part of the avian ventral spinocerebellar tract. Lumbar dI2s receive synaptic input from afferents and pre-motoneurons. They innervate contralateral dI2s and pre-motoneurons at lumbar cord and their ascending axons give off collaterals to innervate contralateral brachial dI2s and premotoneurons, enroute to the cerebellum. Collectively these findings suggest that dI2s deliver peripheral and intraspinal feedback to the cerebellum, that they also function as interneurons in local lumbar circuits and involved in lumbo-brachial coupling. Targeted silencing of dI2s leads to destabilized stepping in P8 hatchlings, suggesting that the activated dI2s may contribute to stabilization of the bipedal gait.

In vitro atlas of dorsal spinal interneurons reveals Wnt signaling as a critical regulator of progenitor expansion

“…Each dI population is specialized for distinct somatosensory modalities and forms microcircuits that span different layers of the dorsal horn Lai et al, 2016). For example, dI1s (proprioceptors) (Lai et al, 2011), dI2s, dI3s (both mechanosensors) (Bui et al, 2013;Haimson et al, 2020), and dI6 (gait) (Perry et al, 2019) are located in the deep layers of the dorsal horn, while dI4s and dI5s regulate pain, heat, and itch in the superficial layers of the dorsal horn (Koch et al, 2018). To replace damaged spinal tissue, it will be critical to derive a complete complement of dorsal sensory interneurons that molecularly and functionally phenocopy endogenous dIs.…”