Nocifensive behaviors components evoked by brief laser pulses are mediated by C fibers.
Nocifensive behavior involves several response elements that have been used to assess neuropharmacological effects in different animal models of pain. Our previous analysis of laser-evoked nocifensive behaviors suggested that hierarchically organized responses in the nocifensive motor system are recruited in varying degrees by noxious stimuli of different intensities. Nocifensive behaviors can be differentially elicited and mediated by different classes of nociceptors. Thus, the aim of this study was to test the hypothesis that nocifensive behavioral elements elicited by brief laser pulse stimuli are mediated by C nociceptors. Laser-evoked cortical potentials and nocifensive behavior elements were recorded concurrently. As stimulus energy increased, rats exhibited a larger number of different responses and a greater frequency of each response element. Applying the neurotoxin, capsaicin, which selectively inhibits C fibers, to the sciatic nerves of rats, differentially blocked nocifensive behavioral components of flinch, withdrawal and licking but not non-nocifensive responses, namely movement and head turning. Based on these results we suggest that flinch, withdrawal and licking are mediated by C fibers, which are temporally associated with the nocifensive motor system as well as spinal and cortical evoked potentials. These results link hierarchically organized nocifensive responses and the afferent C fibers in the nocifensive motor system.
Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan, ROC.
Ruey-Jane
RJ
Fan
Jen-Chuang
JC
Kung
Bengt A
BA
Olausson
Bai-Chung
BC
Shyu
D000758:Anesthesia; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects / Q000502:physiology*; D002211:Capsaicin / Q000494:pharmacology; D002540:Cerebral Cortex / Q000187:drug effects / Q000502:physiology; D004567:Electrodes, Implanted; D004569:Electroencephalography / Q000187:drug effects; D004576:Electromyography; D004594:Electrophysiology; D005071:Evoked Potentials / Q000502:physiology; D054020:Lasers, Gas; D008297:Male; D036421:Nerve Fibers, Unmyelinated / Q000187:drug effects / Q000502:physiology*; D009431:Neural Conduction / Q000187:drug effects / Q000502:physiology; D009619:Nociceptors / Q000502:physiology*; D010146:Pain / Q000523:psychology*; D010812:Physical Stimulation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012584:Sciatic Nerve / Q000187:drug effects; D013116:Spinal Cord / Q000187:drug effects / Q000502:physiology
D002211:Capsaicin