Descending Command Neurons in the Brainstem that Halt Locomotion

Abstract

SUMMARY The episodic nature of locomotion is thought to be controlled by descending inputs from the brainstem. Most studies have largely attributed this control to initiating excitatory signals, but little is known about putative commands that may specifically determine locomotor offset. To link identifiable brainstem populations to a potential locomotor stop signal, we used developmental genetics and considered a discrete neuronal population in the reticular formation: the V2a neurons. We find that those neurons constitute a major excitatory pathway to locomotor areas of the ventral spinal cord. Selective activation of V2a neurons of the rostral medulla stops ongoing locomotor activity, owing to an inhibition of premotor locomotor networks in the spinal cord. Moreover, inactivation of such neurons decreases spontaneous stopping in vivo. Therefore, the V2a “stop neurons” represent a glutamatergic descending pathway that favors immobility and may thus help control the episodic nature of locomotion.

Generalized CNS arousal: An elementary force within the vertebrate nervous system

“…Importantly, elevated firing rates precede movement indicating that NGC provides the basis for sensory responsivity. Lastly, recent studies (Bretzner and Brownstone, 2013; Bouvier et al, 2015) showed that medullary reticular glutamatergic neurons are centrally involved in the activation of movement. Thus, these functional and anatomical features suggest that NGC is a strategic location for promoting arousal.…”

Locomotion Control: Brainstem Circuits Satisfy the Need for Speed

“…Thus, future quests probing the molecular heterogeneity of the mesencephalic locomotor region and medulla nuclei might unravel more dedicated pathways recruited in a context-dependent manner. Finally, another more restricted glutamatergic subpopulation (Chx10 + ) in the medulla has been described as necessary to halt locomotion [14], and understanding if and how this subpopulation is recruited by the mesencephalic locomotor region–lateral paragigantocellular nucleus pathway and whether it acts in conjunction with the pedunculopontine nucleus to promote a stop and explore behavior would shed further light on the logic of descending motor control.…”

Development of Electrophysiological Properties of Nucleus Gigantocellularis Neurons Correlated with Increased CNS Arousal

“…The marker is non-specific for NGC neurons; it also labels neurons elsewhere. More importantly, Chx10 labeled (V2a) brainstem neurons exert inhibitory influence on locomotion [67], a function opposite of that expected of neurons involved in arousal. Since we intended to study large NGC neurons that may regulate arousal, neurons with Chx10 marker are of little use.…”