Activation of Akt/FKHR in the medulla oblongata contributes to spontaneous respiratory recovery after incomplete spinal cord injury in adult rats

International audience; After incomplete spinal cord injury (SCI), patients and animals may ă exhibit some spontaneous functional recovery which can be partly ă attributed to remodeling of injured neural circuitry. This post-lesion ă plasticity implies spinal remodeling but increasing evidences suggest ă that supraspinal structures contribute also to the functional recovery. ă Here we tested the hypothesis that partial SCI may activate ă cell-signaling pathway(s) at the supraspinal level and that this ă molecular response may contribute to spontaneous recovery. With this ă aim, we used a rat model of partial cervical hemisection which injures ă the bulbospinal respiratory tract originating from the medulla oblongata ă of the brainstem but leads to a time-dependent spontaneous functional ă recovery of the paralyzed hemidiaphragm. We first demonstrate that after ă SCI the PI3K/Akt signaling pathway is activated in the medulla oblongata ă of the brainstem, resulting in an inactivation of its pro-apoptotic ă downstream target, forkhead transcription factor (FKHR/FOXO1A). ă Retrograde labeling of medullary premotoneurons including respiratory ă ones which project to phrenic motoneurons reveals an increased FKHR ă phosphorylation in their cell bodies together with an unchanged cell ă number. Medulla infusion of the PI3K inhibitor, LY294002, prevents the ă SCI-induced Akt and FKHR phosphorylations and activates one of its ă death-promoting downstream targets, Fas ligand. Quantitative EMG ă analyses of diaphragmatic contractility demonstrate that the inhibition ă of medulla PI3K/Akt signaling prevents spontaneous respiratory recovery ă normally observed after partial cervical SCI. Such inhibition does not ă however affect either baseline contractile frequency or the ventilatory ă reactivity under acute respiratory challenge. Together, these findings ă provide novel evidence of supraspinal cellular contribution to the ă spontaneous respiratory recovery after partial SCI. (C) 2014 Elsevier ă Inc All rights reserved.