Comparative studies of serotonin-like immunoreactive cells in the digestive tract of vertebrates

Abstract

The gastrointestinal tract of representatives of all the vertebrate classes was investigated for the occurrence of serotonin-like immunoreactive cells using both polyclonal and monoclonal antibodies. In the alimentary canal of all the gnathostomes, but not in cyclostomes (Agnatha), serotonin-like immunoreactive cells were detected. These cells showed a wide distribution and were found more or less throughout the gut of all the species, indicating that serotonin-like immunoreactive cells were established in the gut at the stage of vertebrate evolution.