Neuronal circuits in the brainstem and spinal cord involved in forelimb behaviors and locomotion

Complexity, stability as well as flexibility of human and animal behavior is dependent on highly organized and intricate neuronal networks throughout the nervous system, many of which are poorly understood. The motor system in particular is composed of widely distributed neuronal circuits controlling the variable, often complicated patterns of muscle activity seen during behavior. The brainstem and spinal cord are both structures that are of critical importance for motor actions. However, mechanistic understanding on the construction and interaction of distinct motor actions at the neuronal level is largely missing. This dissertation unravels organization and function of brainstem and spinal cord circuits important for locomotion and forelimb movements. Using intersectional genetic, viral, electrophysiological and behavioral tools allows the targeting, manipulation and read out of involved circuits at fine resolution. In the spinal cord, we employ molecular entry points to disentangle the identity and organization of long-distance projection neurons and show their role in the coordination of fore- and hindlimbs as well as speed during locomotion. In a second part, we investigate circuits in the lateral rostral medulla of the brainstem we demonstrate to be involved in forelimb movements. In particular, we reveal the existence of multiple intermingled, but cellularly segregated circuits implicated in different forelimb actions stretching from simple to complex paired with differential functional coding properties of single neurons into distinct cell ensembles. Together, we identify neuronal circuit elements important for dedicated aspects of whole body and fine skilled motor behavior and provide evidence for how selected actions are controlled and constructed by specific neurons embedded into highly organized circuits