title: Preclinical model of transcorneal alternating current stimulation in freely moving rats.
abstract: OBJECTIVE
  Transcorneal alternating current stimulation (tACS) has become a promising tool to modulate brain functions and treat visual diseases. To understand the mechanisms of action a suitable animal model is required. However, because existing animal models employ narcosis, which interferes with brain oscillations and stimulation effects, we developed an experimental setup where current stimulation via the eye and flicker light stimulation can be applied while simultaneously recording local field potentials in awake rats.
  
  
  METHODS
  tACS was applied in freely-moving rats (N = 24) which had wires implanted under their upper eye lids. Field potential recordings were made in visual cortex and superior colliculus. To measure visual evoked responses, rats were exposed to flicker-light using LEDs positioned in headset spectacles.
  
  
  RESULTS
  Corneal electrodes and recording assemblies were reliably operating and well tolerated for at least 4 weeks. Transcorneal stimulation without narcosis did not induce any adverse reactions. Stable head stages allowed repetitive and long-lasting recordings of visual and electrically evoked potentials in freely moving animals. Shape and latencies of electrically evoked responses measured in the superior colliculus and visual cortex indicate that specific physiological responses could be recorded after tACS.
  
  
  CONCLUSIONS
  Our setup allows the stimulation of the visual system in unanaesthetised rodents with flicker light and transcorneally applied current travelling along the physiological signalling pathway. This methodology provides the experimental basis for further studies of recovery and restoration of vision.
authors: Institute of Medical Psychology, Medical Faculty, Otto-von-Guericke University Magdeburg, Magdeburg, Germany.
authors: Elena G
authors: EG
authors: Sergeeva
authors: Institute of Medical Psychology, Medical Faculty, Otto-von-Guericke University Magdeburg, Magdeburg, Germany.
authors: Petra
authors: P
authors: Henrich-Noack
authors: Institute of Psychology, Russian Academy of Science, Moscow, Russia.
authors: Alexander G
authors: AG
authors: Gorkin
authors: Institute of Medical Psychology, Medical Faculty, Otto-von-Guericke University Magdeburg, Magdeburg, Germany.
authors: Bernhard A
authors: BA
authors: Sabel
mesh_terms: D000818:Animals; D003315:Cornea / Q000502:physiology*; D004599:Electric Stimulation Therapy / Q000009:adverse effects / Q000295:instrumentation / Q000379:methods*; D005071:Evoked Potentials; D005143:Eyelids; D058542:Implantable Neurostimulators / Q000009:adverse effects; D023421:Models, Animal; D010775:Photic Stimulation; D051381:Rats; D013477:Superior Colliculi / Q000502:physiology; D014793:Visual Cortex / Q000502:physiology; D014795:Visual Pathways / Q000502:physiology; D014796:Visual Perception / Q000502:physiology
keywords: Noninvasive brain stimulation; animal model; electrically evoked response; freely-moving animal; vision restoration; visual evoked potential