Conduction velocity of the spinothalamic tract following CO2 laser stimulation of C-fibers in humans.
Pain-related somatosensory-evoked potential following CO(2) laser stimulation (laser-evoked potential (LEP)) is now used not only for research objectives, but also for clinical applications. Estimating the conduction velocity (CV) of the spinothalamic tract (STT) by analyzing LEP following activation of Adelta-fibers (Adelta-CVSTT) by CO(2) laser stimulation has been performed previously, but estimating the CV of STT following activation of C-fibers (C-CVSTT) has not. This is the first report to estimate the C-CVSTT in humans; by using the novel method of CO(2) laser stimulation applied to tiny skin areas. The calculation method was based on that of Kakigi and Shibasaki (Electroenceph clin Neurophysiol 80 (1991) 39) who measured Adelta-CVSTT by conventional CO(2) laser stimulation. The C-CVSTT ranged between 1.4 and 4.0 m/s, and its mean+/-SD was 2.9+/-0.8 m/s. This C-CVSTT was significantly slower than the Adelta-CVSTT, which ranged approximately from 10 to 21 m/s. The nociceptive signal of the C-fibers in STT is probably conveyed by unmyelinated axons of projection neurons to reach the thalamus. Our findings provide the first physiological evidence of the signals ascending through unmyelinated axons in the spinal cord in humans. In addition, estimating C-CVSTT and Adelta-CVSTT combined with conventional methods to measure the CV of the posterior column using electrical stimulation should be useful and have important clinical applications, particularly in patients with spinal cord lesions showing various kinds of sensory disturbances.
Tran
Tuan Diep
TD
Department of Integrative Physiology, National Institute for Physiological Sciences, Myodaiji, Okazaki, 444-8585 Japan. dieptuan@nips.ac.jp
Inui
Koji
K
Hoshiyama
Minoru
M
Lam
Khanh
K
Kakigi
Ryusuke
R
D000328:Adult; D002245:Carbon Dioxide; D005071:Evoked Potentials / Q000502:physiology; D005260:Female; D006801:Humans; D007834:Lasers; D008297:Male; D009412:Nerve Fibers / Q000502:physiology*; D009431:Neural Conduction / Q000502:physiology*; D013133:Spinothalamic Tracts / Q000502:physiology*; D018709:Statistics, Nonparametric
D002245:Carbon Dioxide