title: Clonidine effects on pain evoked SII activity in humans.
abstract: We investigated pain evoked activity in the human secondary sensory cortex (SII) following clonidine administration in six healthy volunteers using multi-channel magnetoencephalography (MEG). Pain was elicited by electrical shocks applied intracutaneously to the fingertip. Subjects rated pain intensity and perceptions of tiredness and passiveness by numerical ranking scales. Each subject underwent two investigations, one week apart from each other, with clonidine doses of 1.5 or 3.0microg/kg, administered intravenously in a random order and double-blinded. We applied a total number of seven blocks, each consisting of 60 painful stimuli, with one adaptation block, one pre-medication block, four post-medication blocks and one recovery block at the end of the session. MEG data were analysed by dipole reconstruction using CURRY(R) (Neuroscan, Hamburg) software package. Cortical activity in the contralateral SII cortex appeared with peak latencies of 118.5+/-10ms. This activity was significantly reduced by clonidine, in parallel with a reduction of pain intensity and enhancement of subjective tiredness and passiveness. There was, however, no significant correlation between MEG and subjective effects. Although both clonidine doses had similar effects, the higher dose induced longer changes. Results indicate that intravenous clonidine is able to relieve pain, but the exact mechanism of clonidine at the level of the SII cortex remains unclear. It is possible that clonidine interacts with the brainstem ascending system regulating vigilance and arousal which would explain the observed decrement of pain induced activity in SII. An additional more specific analgesic action at spinal level cannot be excluded.
authors.affiliation: Institute of Physiology and Pathophysiology, University of Hamburg, Martinistrasse 52, D-20246 Hamburg, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Hauck
authors.forename: Petra
authors.initials: P
authors.lastname: Bischoff
authors.forename: Gunther
authors.initials: G
authors.lastname: Schmidt
authors.forename: Roger
authors.initials: R
authors.lastname: Zimmermann
authors.forename: Juergen
authors.initials: J
authors.lastname: Lorenz
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Morrow
authors.forename: Burkhart
authors.initials: B
authors.lastname: Bromm
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000008:administration & dosage*; D000328:Adult; D003000:Clonidine / Q000008:administration & dosage*; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D004569:Electroencephalography; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007262:Infusions, Intravenous; D015225:Magnetoencephalography; D008297:Male; D010146:Pain / Q000503:physiopathology*; D013003:Somatosensory Cortex / Q000187:drug effects* / Q000503:physiopathology*
chemical_list: D000316:Adrenergic alpha-Agonists; D003000:Clonidine