Pharmacological effect of capsaicin on rat avoidance behaviours elicited by sine-wave electrical stimulation of different frequencies by Neurometer.
The Neurometer is a diagnostic device for measuring the perception and threshold of transcutaneous stimulation. It has been used in patients to selectively activate Abeta-, Adelta- and C-fibres in the primary afferents at different stimulus frequencies (2000, 250 and 5 Hz, respectively). In this study, we investigated use of the Neurometer to selectively activate nerves in conscious rats. The behavioural endpoint of paw withdrawal was used to measure the current threshold (CT). This behaviour was elicited by a lower stimulus current than other behaviours evoked by Neurometer stimulation and caused only mild stress in rats. Repeated topical application of capsaicin (four doses of 100 microg) or systemic administration of the capsaicin analogue resiniferatoxin (30 or 300 microg kg(-1)) increased the CT value for this behaviour at 5 Hz stimulation but not at 2000 Hz or 250 Hz. This change in CT at 5 Hz is probably due to C-fibre desensitization by the pharmacological treatments. The combination of 5 Hz sine-wave stimulation with a Neurometer and the observation of paw withdrawal behaviour make it possible to perform preclinical studies of C-fibres in animals as an alternative to the use of high- and low-rate heating of the paw.
Fujiuchi
Akiyoshi
A
Discovery Biology Research, Nagoya Laboratories, Pfizer Global Research and Development, Pfizer Japan Inc., 5-2 Taketoyo, Aichi, 470-2393, Japan.
Toga
Tetsuo
T
D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects*; D001522:Behavior, Animal / Q000187:drug effects*; D002211:Capsaicin / Q000494:pharmacology*; D004224:Diterpenes / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation / Q000295:instrumentation; D007279:Injections, Subcutaneous; D008297:Male; D009412:Nerve Fibers / Q000502:physiology; D017288:Pain Threshold; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time / Q000187:drug effects; D004561:Transcutaneous Electric Nerve Stimulation / Q000295:instrumentation
D004224:Diterpenes; C024353:resiniferatoxin; D002211:Capsaicin