Non-Invasive Vagus Nerve Stimulation Improves Brain Lesion Volume and Neurobehavioral Outcomes in a Rat Model of Traumatic Brain Injury.

Traumatic brain injury (TBI) continues to be a major cause of death and disability worldwide. This study assessed the effectiveness of non-invasive vagus nerve stimulation (nVNS) in reducing brain lesion volume and improving neurobehavioral performance in a rat model of TBI. Animals were randomized into 3 experimental groups: 1) TBI with sham stimulation treatment (Control), 2) TBI treated with five lower doses (2-minute) nVNS, and 3) TBI treated with five higher doses (2x2-minute) nVNS. We used the gammaCore nVNS device to deliver stimulations. Magnetic resonance imaging studies were performed 1 and 7 days post-injury to confirm lesion volume. We observed smaller brain lesion volume in the lower dose nVNS group compared with the Control group on days 1 and 7. The lesion volume for the higher dose nVNS group was significantly smaller compared with both the lower dose nVNS and the Control groups on days 1 and 7 post-injury. The apparent diffusion coefficient differences between the ipsilateral and contralateral hemispheres on day 1 were significantly smaller for the higher dose (2x2-min) nVNS group compared with the Control group. Voxel-based morphometry analysis revealed an increase in the ipsilateral cortical volume in the Control group due to tissue deformation and swelling. On day 1, these abnormal volume changes were 13% and 55% smaller in the lower dose and higher dose nVNS groups, respectively, compared with the Control group. By day 7, nVNS dampened cortical volume loss by 35% and 89% in the lower dose and higher dose nVNS groups, respectively, compared with the Control group. Rotarod, beam walking, and anxiety performances were significantly improved in the higher-dose nVNS group on day 1 compared to the Control group. The anxiety indices were also improved on day 7 post-injury compared with the Control and the lower-dose nVNS groups. In conclusion, the higher dose nVNS (five 2x2-minute stimulations) reduced brain lesion volume to a level that further refined the role of nVNS therapy for the acute treatment of TBI. Should nVNS proven effective in additional preclinical TBI models and later in clinical settings, it would have an enormous impact on the clinical practice of TBI in both civilian and military settings as it can easily be adopted into routine clinical practice.