Capsaicin depletes CCK-like immunoreactivity detected by immunohistochemistry, but not that measured by radioimmunoassay in rat dorsal spinal cord.

In rats treated neonatally with capsaicin there were significant reductions in substance P measured by radioimmunoassay in dorsal spinal cord, spinal ganglia, and coeliac ganglia, but concentrations of cholecystokinin octapeptide (CCK8) measured by radioimmunoassay were not decreased. However, immunohistochemical studies using antisera to both substance P and CCK8, respectively, demonstrated decreased immunoreactive material in the dorsal horn of the spinal cord. The nature of the material localized by CCK8 antiserum in immunohistochemistry remains to be resolved.