The distribution of neuropeptide Y-like immunoreactivity in the ascidian Styela plicata.

The occurrence of neuropeptide Y-like substances has been verified in the nervous system and alimentary tract of the ascidian Styela plicata. Neuropeptide Y-like immunoreactivity is present in a few small neurons and in a network of beaded nerve fibres of the cerebral ganglion. Neuropeptide Y-like immunoreactive material can be also localized in the endostyle and in a few cell bodies of the branchial walls. Moreover, immunofluorescent endocrine-like cells of the "open" type occur in the gastric folds. Finally, some possible functions of the ascidian neuropeptide Y are discussed.