title: Epidural motor cortex stimulation suppresses somatosensory evoked potentials in the primary somatosensory cortex of the rat.
abstract: Motor cortex stimulation (MCS) is a promising clinical procedure to help alleviate chronic pain. Animal models demonstrated that MCS is effective in lessening nocifensive behaviors. The present study explored the effects of MCS on cortical somatosensory evoked potentials (SEPs) recorded at the primary somatosensory cortex (SI) of the rat. SEPs were evoked by electrical stimulation applied to the contralateral forepaws. Effects of different intensities, frequencies, and durations of MCS were tested. MCS at ≥2V suppressed SEPs of the ipsilateral SI. Suppression lasted 120 min at an intensity of 5 V. The optimal frequency was 50 Hz, and the duration was 30s. In contrast, MCS did not affect SEPs recorded on the contralateral SI. Cortical stimulation out of the motor cortex did not induce a decrease in the ipsilateral SEPs. We also investigated involvement of the endogenous opioid system in this inhibition of SEPs induced by MCS. The opioid antagonist, naloxone (0.5 mg/kg), was administered 30 min before MCS. Application of naloxone completely prevented the inhibitory effect of MCS on ipsilateral SEPs. These results demonstrate that MCS blocked the transmission of somatosensory information to the primary somatosensory cortex, and this interference was mediated by the endogenous opioid system. This inhibitory effect on sensory transmission induced by MCS may reflect its antinociceptive effect.
authors.affiliation: Department of Anatomy, School of Medicine, College of Medicine, Taipei Medical University, 250 Wu-Hsing Street, Taipei City 10031, Taiwan.
authors.forename: Ruei-Jen
authors.initials: RJ
authors.lastname: Chiou
authors.forename: Hsiao-Yun
authors.initials: HY
authors.lastname: Lee
authors.forename: Chen-Wei
authors.initials: CW
authors.lastname: Chang
authors.forename: Kuan-Hung
authors.initials: KH
authors.lastname: Lin
authors.forename: Chung-Chih
authors.initials: CC
authors.lastname: Kuo
mesh_terms: D000818:Animals; D015536:Down-Regulation / Q000502:physiology; D004558:Electric Stimulation / Q000379:methods; D004824:Epidural Space / Q000502:physiology; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology*; D051381:Rats; D020318:Rats, Long-Evans; D013003:Somatosensory Cortex / Q000502:physiology*