Secretin-like Immunoreactivity in the Neural Complex of a Protochordate

By means of immunocytochemical methods, a secretin-like immunoreactivity is demonstrated in the neural complex of the ascidian Styela plicata. Secretinergic neurons are localized in the cortex of the cerebral ganglion and numerous secretin-like immunoreactive cells are detected in some lobules of the neural gland. The possible functions of secretin-like substances in the ascidian neural complex are discussed.