title: Electrical stimulation of the vagus nerve dermatome in the external ear is protective in rat cerebral ischemia.
abstract: BACKGROUND
  Although cervical vagus nerve stimulation is effective for reducing infarct volume in rats, it is not feasible for acute human stroke as it requires surgical incision of the neck. We hypothesized that stimulation of the dermatome in the external ear innervated by the vagus nerve (auricular vagus nerve stimulation; aVNS) reduces infarct volume after transient focal ischemia in rats.
  
  
  METHODS
  Animals were randomized to active aVNS or sham stimulation. For aVNS, electrical stimulation of the left cavum concha (1 h duration) using percutaneous needles was initiated 30 min after induction of ischemia. Behavioral and tissue outcome were measured 24 h after induction of ischemia. In a separate experimental dataset, c-Fos immunohistochemistry was performed to identify the brain regions activated after the stimulation.
  
  
  RESULTS
  Stimulation of the left cavum concha resulted in bilateral c-Fos staining in the nuclei tractus solitarii and the loci coerulei in all animals. There was no c-Fos staining in any part of the brainstem in sham control animals. The mean infarct volume (SD) as calculated by indirect method was 44.20 ± 7.58% in controls and 31.65 ± 9.67% in treated animals (P < 0.0001). The effect of aVNS on tissue outcome was associated with better neurological scores at 24 h after ischemia (P < 0.0001).
  
  
  CONCLUSIONS
  Electric stimulation of the vagus nerve dermatome in the external ear activates brainstem afferent vagal nuclei and reduces infarct volume in rats. This finding has potential to facilitate the development of treatments that leverage the brain's endogenous neuroprotective pathways at the setting of acute ischemic stroke.
authors.affiliation: MGH/MIT/HMS Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital East, 149 13th Street, Charlestown, MA 02129, USA. Electronic address: iay@mgh.harvard.edu.
authors.forename: Ilknur
authors.initials: I
authors.lastname: Ay
authors.affiliation: MGH/MIT/HMS Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital East, 149 13th Street, Charlestown, MA 02129, USA; Department of Biomedical Engineering, Kyunghee University, Yongin, South Korea.
authors.forename: Vitaly
authors.initials: V
authors.lastname: Napadow
authors.affiliation: MGH/MIT/HMS Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital East, 149 13th Street, Charlestown, MA 02129, USA.
authors.forename: Hakan
authors.initials: H
authors.lastname: Ay
mesh_terms: D000818:Animals; D002545:Brain Ischemia / Q000150:complications / Q000473:pathology / Q000628:therapy*; D002544:Cerebral Infarction / Q000150:complications / Q000473:pathology / Q000628:therapy; D004431:Ear, External / Q000294:innervation / Q000502:physiology*; D008125:Locus Coeruleus / Q000502:physiology; D008297:Male; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D051381:Rats; D017552:Solitary Nucleus / Q000502:physiology; D055536:Vagus Nerve Stimulation / Q000379:methods
chemical_list: D016760:Proto-Oncogene Proteins c-fos
keywords: Arnold's nerve; Cerebral ischemia; Neuroprotection; Rat; Vagus nerve stimulation; c-Fos