The Participation of Neuropeptide F in the Innervation of Flatworm Musculate

Free-living flatworms, planarians, are often used as a biological model to study the morphogenesis and regeneration processes, as well as structure and function of their muscle system. In this study, the spatial relationships between musculature and the nervous system were examined in planarians Girardia tigrina (Turbellaria, Platyhelminthes) using confocal laser scanning microscopy, histochemical staining of filamentous actin with fluorescently labelled phalloidin, and immunocytochemical staining of the nervous system with parasitic worm neuropeptide F antibodies. The body wall musculature contains three layers: an outer circular layer, an inner longitudinal layer, and a layer of rare diagonal muscle fibers in-between running in two perpendicular directions. The results showed that the body wall musculature was intensively supplied with NPF-immunopositive (-IP) nerve fibers. Thus, NPF-IP nerve fibers were localized in the body wall muscle layer of worms including the tail region musculature. Such identification of NPF-IP neurons and its endings near the somatic muscle fibers of the body wall may indicate the potential neuropeptide F participation in the muscle contractility regulation in flatworms.