Evidence for the coexistence of serotonin and calcitonin gene-related peptide at the subcellular level in neuroepithelial bodies in the lung of a marsupial, Isoodon macrourus.

The coexistence of serotonin and calcitonin gene-related peptide (CGRP) in neuroepithelial bodies of the bandicoot, Isoodon macrourus, has been examined using immunocytochemistry at the light- and electron-microscope levels. The avidin-biotin technique of antigen localisation was used initially to identify serotonin-like and CGRP-like immunoreactivity (-LI). Serotonin-LI and CGRP-LI were found in neuroepithelial cells in the lungs of 30-day-old bandicoots. CGRP-LI could also be demonstrated in nerve fibres associated with some neuroepithelial bodies. The protein A-gold technique of antigen localisation was used to label neuroepithelial cells and nerve fibres at the subcellular level. Serotonin-LI and CGRP-LI were observed in the same dense-cored vesicles of most neuroepithelial cells; however, some neuroepithelial cells were shown to possess serotonin-LI without CGRP-LI. Nerve fibres immediately adjacent to neuroepithelial bodies exhibited mainly CGRP-LI. These results show that serotonin-LI and CGRP-LI are present in neuroepithelial cells of the bandicoot in the same secretory vesicles. This pattern of co-localisation may reflect co-ordinated or synergistic actions of these two neuroactive substances.