Serotonin immunoreactivity in the carotid body of adult humans

The distribution of serotonin immunoreactivity (-IR) was studied in adult human carotid bodies, obtained at post-mortem, using both the peroxidase-antiperoxidase method on paraffin sections and a double-labelling immunofluorescence on frozen sections. Antibodies against synaptophysin and protein gene product (PGP) 9.5 were used for identification of serotonin-IR cells. Serotonin-IR was demonstrable in the carotid bodies of adult humans and it was coexpressed mostly with synaptophysin or PGP 9.5 in type I cells. Some serotonin immunopositive type I cells were located in close proximity to capillaries. Serotonin-IR was also observed in a few endothelial cells.