title: High-frequency monopolar electrical stimulation of the rat cerebral cortex.
abstract: OBJECTIVE
  Intraoperative monitoring of the motor-evoked potential has been widely used in patients undergoing neurosurgery. Direct stimulation of the brain with high-frequency monopolar stimulation (HFMS) is one of the most common methods to produce motor-evoked potential. We studied the influence of HFMS on the rat cerebral cortex.
  
  
  METHODS
  We applied 1.5, 15, 30, 40, or 50 mA of HFMS to the rat sensorimotor cortex by a short sequence of five monopolar, monophasic, anodal rectangular 500-Hz pulses. We delivered one short five-pulse train 100 times every 5 seconds and examined pre- and post-stimulation electroencephalograms and histological changes at the stimulation site.
  
  
  RESULTS
  We observed no spike waves after HFMS in any of the rats. There was no change in the power spectrum or frequency content in any of the rats exposed to HFMS. Histologically, there was significant swelling of the dendrites in rats sacrificed immediately after exposure to 40- and 50-mA stimulation; the 50-mA stimulation group also exhibited slight swelling of the mitochondria. These findings were not obtained in any of the rats sacrificed 30 days after stimulation.
  
  
  CONCLUSIONS
  In rats exposed to a stimulation intensity of 30-mA or less, no morphological or electrophysiological changes were observed. However, the possibility that HFMS may affect neural tissue cannot be ruled out.
authors.affiliation: Department of Neurosurgery, Fukushima Medical University, Fukushima, Japan. oinuma-nsu@umin.ac.jp
authors.forename: Masahiro
authors.initials: M
authors.lastname: Oinuma
authors.forename: Kyouichi
authors.initials: K
authors.lastname: Suzuki
authors.forename: Takashi
authors.initials: T
authors.lastname: Honda
authors.forename: Masato
authors.initials: M
authors.lastname: Matsumoto
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Sasaki
authors.forename: Namio
authors.initials: N
authors.lastname: Kodama
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D002540:Cerebral Cortex / Q000502:physiology* / Q000648:ultrastructure; D004558:Electric Stimulation / Q000379:methods; D004566:Electrodes; D019054:Evoked Potentials, Motor / Q000502:physiology; D008297:Male; D051381:Rats; D017208:Rats, Wistar