title: Spatiotemporal changes of optical signals in the somatosensory cortex of neuropathic rats after electroacupuncture stimulation.
abstract: BACKGROUND
  Peripheral nerve injury causes physiological changes in primary afferent neurons. Neuropathic pain associated with peripheral nerve injuries may reflect changes in the excitability of the nervous system, including the spinothalamic tract. Current alternative medical research indicates that acupuncture stimulation has analgesic effects in various pain symptoms. However, activation changes in the somatosensory cortex of the brain by acupuncture stimulation remain poorly understood. The present study was conducted to monitor the changes in cortical excitability, using optical imaging with voltage-sensitive dye (VSD) in neuropathic rats after electroacupuncture (EA) stimulation.
  
  
  METHODS
  Male Sprague-Dawley rats were divided into three groups: control (intact), sham injury, and neuropathic pain rats. Under pentobarbital anesthesia, rats were subjected to nerve injury with tight ligation and incision of the tibial and sural nerves in the left hind paw. For optical imaging, the rats were re-anesthetized with urethane, and followed by craniotomy. The exposed primary somatosensory cortex (S1) was stained with VSD for one hour. Optical signals were recorded from the S1 cortex, before and after EA stimulation on Zusanli (ST36) and Yinlingquan (SP9).
  
  
  RESULTS
  After peripheral stimulation, control and sham injury rats did not show significant signal changes in the S1 cortex. However, inflamed and amplified neural activities were observed in the S1 cortex of nerve-injured rats. Furthermore, the optical signals and region of activation in the S1 cortex were reduced substantially after EA stimulation, and recovered in a time-dependent manner. The peak fluorescence intensity was significantly reduced until 90 min after EA stimulation (Pre-EA: 0.25 ± 0.04 and Post-EA 0 min: 0.01 ± 0.01), and maximum activated area was also significantly attenuated until 60 min after EA stimulation (Pre-EA: 37.2 ± 1.79 and Post-EA 0 min: 0.01 ± 0.10).
  
  
  CONCLUSIONS
  Our results indicate that EA stimulation has inhibitory effects on excitatory neuronal signaling in the S1 cortex, caused by noxious stimulation in neuropathic pain. These findings suggest that EA stimulation warrants further study as a potential adjuvant modulation of neuropathic pain.
authors.affiliation: Department of Physiology, Yonsei University College of Medicine, C.P.O. Box 8044, Seoul, 03722, Republic of Korea.
authors.forename: Myeounghoon
authors.initials: M
authors.lastname: Cha
authors.affiliation: Acupuncture and Meridian Science Research Center, College of Korean Medicine, Kyung Hee University, Seoul, 02447, Republic of Korea.
authors.forename: Younbyoung
authors.initials: Y
authors.lastname: Chae
authors.affiliation: Department of Anesthesiology and Pain medicine, Yonsei University College of Medicine, Seoul, 03722, Republic of Korea.
authors.forename: Sun Joon
authors.initials: SJ
authors.lastname: Bai
authors.affiliation: Department of Physiology, Yonsei University College of Medicine, C.P.O. Box 8044, Seoul, 03722, Republic of Korea. bhlee@yuhs.ac.|Brain Korea PLUS Project for Medical Science, Brain Research Institute, Epilepsy Research Institute, Yonsei University College of Medicine, Seoul, 03722, Republic of Korea. bhlee@yuhs.ac.
authors.forename: Bae Hwan
authors.identifier: http://orcid.org/0000-0003-4719-9021
authors.initials: BH
authors.lastname: Lee
mesh_terms: D000818:Animals; D015671:Electroacupuncture; D006801:Humans; D008027:Light; D008297:Male; D009437:Neuralgia / Q000503:physiopathology / Q000628:therapy*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013003:Somatosensory Cortex / Q000503:physiopathology* / Q000528:radiation effects
keywords: Electroacupuncture (EA); Neuropathic pain; Optical signal; Primary somatosensory cortex (S1); Spatiotemporal change