Similar and different effects of capsaicin and resiniferatoxin on substance P release and transient receptor potential vanilloid type 1 expression of cultured rat dorsal root ganglion neurons.

The purpose of this study was to investigate the effects of capsaicin (CAP) and resiniferatoxin (RTX) on substance P (SP) release and transient receptor potential vanilloid type 1 (TRPV1) expression of cultured rat dorsal root ganglion (DRG) neurons. Dissociated DRG cells of embryonic 15-day-old Wistar rat were cultured for 3 days and then exposed to CAP (1 micromol/L, 10 micromol/L) or RTX (10 nmol/L, 100 nmol/L) for 10 min. At 3 days of culture growth, SP release increased significantly after 10 min of stimulation with CAP or RTX as compared with controls. Six days after acute exposure to CAP or RTX, SP release and SP expression of cultured rat DRG neurons decreased significantly in both CAP- and RTX-treated cultures as compared with controls. Preprotachykinin (PPT) mRNA, TRPV1 mRNA and TRPV1 protein expression decreased in CAP-treated cultures and RTX cultures treated with the higher concentration, whereas RTX cultures treated with the lower concentration were not affected. The results indicate that CAP and high concentrations of RTX are more neurotoxic to cultured rat DRG neurons while the inability of the neurons to express SP or TRPV1 after acute exposure to the lower concentration of RTX could be partially reversed after a period of incubation. The efficacy and therapeutic potential of the reversible action of RTX are more applicable as strategies for pain or neurogenic inflammation therapy.