Discovery of specific tryptophan hydroxylase in the brain of the beetle Harmonia axyridis

Rabbit anti-serotonin and mouse monoclonal anti-tryptophan hydroxylase antisera were applied on the brain sections of the beetle Harmonia axyridis, butterfly Childrena zenobia, moth Antheraea pernyi and ant Camponotus japonicus, using the Streptavidin–Peroxidase immunohistochemical method and Colophony–Paraffin embedded section technique. Results revealed that all the experimental insects showed notable serotonin-like immunoreactivity in the brain. However, only the brain sections of the beetle H. axyridis were strongly labeled by mouse monoclonal anti-tryptophan hydroxylase antiserum, with the distribution pattern matching that of serotonin. These results demonstrate that specific tryptophan hydroxylase may exist in the brain of the beetle and likely reflect the diversity of serotonin synthetic mechanisms as well as the evolution of aromatic amino acid hydroxylase genes.