Immunohistochemical localization of bioactive substances in the epidermis of the earthworm, Lumbricus terrestris (Annelida, oligochaeta).

Serotonin (5HT), endothelin-big (ET-big) and neuron-specific enolase (NSE) are present in some epithelial paraneuronal cells of vertebrates. In the invertebrates, we show for the first time, by immunofluorescence and immunoperoxidase methods, the immunoreactions to antibodies raised to ET, 5-HT and NSE in the epidermis of the Lumbricus terrestris. It is assumed that the reactive cells are small granular cells that may have a paracrine action in the mechanisms of cell proliferation and secretory processes. The function of these bioactive substances in the epidermis of the earthworm awaits investigation. Phylogenetically it is very interesting that paraneuronal-like type of cells appear in such an ancient species of invertebrate which uses the epidermis for various functional activities.