Effect of capsaicin pretreatment on substance P binding to synaptic vesicles

Newborn or adult rats were pretreated with 50 mg kg-1 capsaicin. At the age of 2 to 4 months, binding of 125I-labelled Tyr8-substance P to synaptic vesicles prepared from different regions of the nervous system was examined. In both groups, capsaicin pretreatment led to a significant decrease in the number of binding sites in dorsal roots and spinal cord without having an effect on affinity. This decrease parallels the depletion of the substance P content (Gamse et al., 1980) and can be explained by degeneration of primary sensory neurons in newborn treated rats and by depletion of vesicles in adult treated rats.