Age-Dependent Attenuation of the Decrease of C Fibers by Capsaicin and Its Effects on Responses to Nociceptive Stimuli

Abstract

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)

Transient expression of vanilloid receptor subtype 1 in rat cardiomyocytes during development

“…In particular, functional studies provided evidence for the existence of at least one vanilloid receptor subtype in the rat heart (Gomez Alvis et al 1998;Milesi et al 2001;Yamato et al 1996). Rats exposed to an overdose of capsaicin die due to cardiorespiratory distress, and susceptibility to capsaicin changes during early postnatal life (Hiura et al 1992;Jancsó and Király 1981). This prompted us to hypothesise that cells of the rat cardiovascular system express VR1, and that this expression changes during perinatal development.…”

Effects of Capsaicin‐Induced Sensory Denervation on Osteoclastic Resorption in Adult Rats

“…Despite this half the capsaicintreated animals died during the procedure or recovery period from respiratory distress. This appears to be a frequent event after capsaicin treatment (Hiura et al 1992). This protocol was adapted from Biggs & Ladenius (1990).…”

Roles of Glia, Immune Cells and the Thermo-TRP Channels, TRPV1, TRPA1 and TRPM8, in Pathological Pain

“…Similarly, mice pretreated with capsaicin as neonates behaved normally when exposed to acute noxious heat [75][76][77]. Therefore, an acute noxious heat sensor other than TRPV1 was speculated to exist in primary afferent neurons [78,79].…”

“…Despite the profound loss of L4 DRG small neurons and dorsal root unmyelinated fibers in mice treated with capsaicin as neonates (2 and 5 days of life), the animals behaved normally in response to noxious heat (hot plate: 55℃, radiant heat) [75,76], suggesting the presence of an unknown sensor beside capsaicin-sensitive, TRPV1-expressing DRG neurons in mice [77][78][79]. In this regard, recently it was reported that TRPV2 knockout or TRPV1/TRPV2 double knockout mice behaved normally to a broad range of noxious heat (48-58 ℃) even though in the peripheral inflammatory conditions [118].…”