title: Quantitative estimation of the effects of capsaicin on the mouse primary sensory neurons.
abstract: Studies were made on the quantitative effects of capsaicin on the L4 dorsal roots and their ganglia (DRG) in mice. Capsaicin at a dose of 50 mg/kg was injected s.c. 1-3 times into neonatal mice, while other mice received only vehicle as controls. After capsaicin treatment unmyelinated fibers decreased by 41.3-75.3% compared to controls. After 2 or 3 capsaicin injections there was a greater decrease in unmyelinated fibers than after a single treatment. Capsaicin had most effect on Schwann cell subunit size of more than 13 axons. Reduction of myelinated fibers ranged from 6.1 to 11.6% (mean: 7.9) in 4 mice. A beta and A delta fibers of 4-5 microns diameter were significantly reduced, whereas A delta fibers of less than 2.0 microns diameter were slightly increased. Small DRG neurons (50-500 microns 2 area) decreased by 50.6-77.4% (mean: 69.6) compared to controls. In addition, capsaicin caused a decrease of 14.2-51.6% (mean: 35.2, n = 4) in large-sized neurons (500-1950 microns 2 area). Thus, capsaicin widely affects small and certain types of large neurons as well as unmyelinated and certain myelinated fibers.
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002211:Capsaicin / Q000494:pharmacology*; D005260:Female; D005727:Ganglia, Spinal / Q000187:drug effects*; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D009413:Nerve Fibers, Myelinated / Q000187:drug effects; D009475:Neurons, Afferent / Q000187:drug effects; D013126:Spinal Nerve Roots / Q000187:drug effects*
chemical_list: D002211:Capsaicin