Age-dependent attenuation of the decrease of C fibers by capsaicin and its effects on responses to nociceptive stimuli.
The effects of subcutaneous treatment of mice 10, 15, or 20 days (young) or 30 or 60 days (adult) of age with capsaicin on development of unmyelinated (C) fibers in the L4 dorsal roots were examined. The responses of the mice 2-4 months later to thermal (hot plate; 55 degrees C) and neurogenic plasma extravasative (chemogenic nociception) stimuli were evaluated. Capsaicin treatment 10 days after birth affected development of myelinated fibers significantly (7.9% reduction). Capsaicin treatment 10, 15, 20, and 30 days after birth reduced the number of C fibers 11.0-51.7% and even treatment 60 days after birth caused a significant decrease (10.0%) in the mean number of C fibers. The destruction of C fibers by capsaicin was attenuated during development, but individual differences in the reduction of C fibers were observed on and after 15 days of life and seemed to become more marked over time. Neurogenic plasma extravasation related to primary sensory neurons was decreased by capsaicin, irrespective of the time of treatment. In parallel with reduction of C fibers, hot-plate latency was increased significantly by treatment of young animals with capsaicin. These results suggest that the effect of capsaicin on thermal nociception is age-dependent and is correlated with decrease of C fibers. However, a marked increase in hot-plate latency did not always correspond to a marked decrease of C fibers. In contrast, the reduction of plasma extravasation was not age-dependent: Reduced extravasation of dye persisted during development.(ABSTRACT TRUNCATED AT 250 WORDS)
Hiura
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A
Department of Oral Anatomy, School of Dentistry, Tokushima University, Japan.
López Villalobos
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E
Ishizuka
H
H
D000375:Aging / Q000187:drug effects*; D000818:Animals; D002211:Capsaicin / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005727:Ganglia, Spinal / Q000187:drug effects*; D051379:Mice; D008815:Mice, Inbred Strains; D009410:Nerve Degeneration / Q000187:drug effects*; D009412:Nerve Fibers / Q000187:drug effects*; D009619:Nociceptors / Q000187:drug effects*; D011930:Reaction Time / Q000187:drug effects; D012684:Sensory Thresholds / Q000187:drug effects; D009435:Synaptic Transmission / Q000187:drug effects*; D013697:Thermosensing / Q000187:drug effects
D002211:Capsaicin