BSCLS — Brainstem-spinal circuits for control of locomotor steering.

The goal of this proposal is to understand the neuronal basis of turning maneuvers during locomotion. Due to the essential nature of locomotion, the underlying neuronal circuits have been long explored for (mostly hind-) limb movements that support straight-trajectory forward walking. In stark contrast, information on the motor substrates for turning is extremely sparse. We have recently uncovered, in the mouse, a population of reticulospinal neurons in the gigantocellular reticular nucleus (Gi) of the brainstem that is defined by expression of the transcription factor Chx10 (V2a neurons) and projects to all segments of the spinal cord. Experimentally activating the V2a Gi population induces the expression of multiple motor actions linked to orientation and results in robust turning movements. We, therefore, suggest that these cells represent a main orchestrator of orienting motor actions, including locomotor turning maneuvers. Importantly, our preliminary results also indicate that these neurons may control turning maneuvers due to their asymmetric control of motor circuits of the neck, upper trunk, and forelimb muscles. We will address here the underlying mechanisms for the generation and control of turning movements using a highly interdisciplinary approach and close interactive collaboration between two groups of investigators with complementary expertise in experimental (Julien Bouvier, CNRS/University Paris-Saclay) and computational (Jessica Ausborn and Ilya Rybak, Drexel University) studies of the neural control of movements. The proposed studies will utilize state-of-the-art electrophysiological, genetic, and viral-based tools in vitro and in vivo and combine them with the development of a neuro-biomechanical model to provide mechanistic explanations and generate predictions that will be tested within the project.