Deciphering the role of inhibitory networks in the vestibulospinal control of posture in mice and Xenopus

In vertebrates, the whole body postural control is mainly achieved by motor reflexes of vestibular source. The responsible excitatory vestibulospinal (VS) pathways have been described in a large variety of species and show striking anatomical and functional resemblances despite strong biomechanical dissimilarities. Here, we investigate in two phylogenetically distant species whether the inhibitory networks surrounding these VS pathways may orchestrate vestibular-originating reflexes to possibly match them to specific biomechanics. Combining various anatomical techniques, we demonstrate the existence of VS cells expressing inhibitory neuronal markers in Xenopus, whereas adult mice rather seem exempt of such. Furthermore, our observations suggest distinct inhibitory controls onto the various populations of VS neurons, notably depending on the spinal level these neurons are projecting to. In parallel, we show that removing inhibitions in either brainstem (around VS neuron somata) or spinal cord (around VS terminals) dramatically modifies the expression of vestibular-induced postural reflexes both at rest and during ongoing locomotion. Our results thus point to a fundamental role of inhibitions in shaping accurate vestibulospinal control of posture.