[Abstract Title]. - Society for Neuroscience

Topic: D.08.j. Pain models
Support: NIH Grant R44NS046951
Title: Conduction velocity and thermal threshold of c vs a nociceptors activated by diode laser
Authors: N. MANERING 1,2 , J. M. CUELLAR 1,2 , *M. I. NEMENOV 1,3,2 , M. KLYUKINOV 1,2 ,
D. C. YEOMANS 1,2 ;
1 Anesthesia, 2 Pain Res. Ctr., Stanford Univ., Stanford, CA; 3 R&d, LASMED LLC, Mountain
View, CA
Abstract: Methods: Infrared diode laser stimulation provides relatively uniform heating of skin,
allowing a margin of laser power amplitude and duration between stimulation of pricking pain
and burning pain and providing a margin of safety over CO2 and Thulium lasers. Laser pulses
were applied to trigeminal innervated (facial) skin of rats. Two types of stimuli were used: 1)
brief (200 ms, 6.3mm2), relatively high power pulses, which produce clear pricking pain in
humans or 2) long (15 s, 15.4mm2), relatively low power pulses, which produce burning pain in
humans. Laser evoked skin temperatures were also measured using a high-speed thermal camera.
In some animals, the trigeminal nerve was dissected to determine actual conduction distances.
Results: C fiber nociceptors predominantly responded only to long pulse stimuli at an average
skin temperature of approximately 46 (we have recording with 49 C so better: 47 +/- 2 )+/- 1 o C
with an average CV of 0.5 m/s. Some A fibers responded only to the short pulses at an average
skin temperature of approximately 48 +/- 3 o C at an average CV of 2.7 m/s. Some intermediate
fibers responded to both long and short pulse stimuli, responding to long pulses at an average 5.8
o C below their responses to short pulses at an average CV of 1.33 m/s.
Conclusions: These results provide presumptive evidence that C fiber thermonociceptors are
selectively activated by long, low heating rate pulses whereas some A fibers are activated solely
by high rate brief stimuli; other fibers are activated by either. The relatively slow CV and the
threshold temperature range observed suggests that the A fibers were likely AMH type II, and
that all nociceptors recorded likely made use of TrpV1 heat transduction. The developed
trigeminal protocol could be used for quantitative evaluation of the effects of novel analgesic or
local anesthetic agents on these distinct nociceptor types.
Acknowledgements: NIH Grant R44NS046951
Reference: Jiang N et al., Proc. SPIE (2007) Vol. 6428, 642809, Tzabazis A. et al., Brain Res.,
1037 (2005):148-56, Nemenov MI et al., Patent Application (2003) # 20050027336.
Disclosures: N. Manering, None; J.M. Cuellar, None; M.I. Nemenov , LASMED LLC,
MOuntain View, CA, A. Employment (full or part-time); PI, B. Research Grant (principal
investigator, collaborator or consultant and pending grants as well as grants already received);
LASMED LLC, E. Ownership Interest (stock, stock options, patent or other intellectual
property); M. Klyukinov, None; D.C. Yeomans, None.
Poster